
==== Front
Hum Vaccin Immunother
Hum Vaccin Immunother
Human Vaccines & Immunotherapeutics
2164-5515
2164-554X
Taylor & Francis

39286868
10.1080/21645515.2024.2394252
2394252
Version of Record
Review Article
Immunotherapy - Cancer
Immunotherapy and delivery systems for melanoma
H. LIU ET AL.
HUMAN VACCINES & IMMUNOTHERAPEUTICS
https://orcid.org/0009-0000-5568-4153
Liu Hui *
https://orcid.org/0009-0004-5609-9465
Gou Xi *
https://orcid.org/0000-0002-0512-9837
Tan Yuanfang
https://orcid.org/0009-0001-0985-6521
Fan Qiuying
https://orcid.org/0000-0002-6199-7807
Chen Juanjuan
Jiangxi Province Key Laboratory of Immunology and Inflammation, Department of Clinical Laboratory, The Second Affiliated Hospital, Jiangxi Medical College, Nanchang University , Nanchang, Jiangxi, China
CONTACT Juanjuan Chen ndefy11330@ncu.edu.cn Jiangxi Province Key Laboratory of Immunology and Inflammation, Department of Clinical Laboratory, The Second Affiliated Hospital, Jiangxi Medical College, Nanchang University, Nanchang, Jiangxi 330006, China.
* These authors contributed equally to this work.

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© 2024 The Author(s). Published with license by Taylor & Francis Group, LLC.
2024
The Author(s)
https://creativecommons.org/licenses/by-nc/4.0/ This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. The terms on which this article has been published allow the posting of the Accepted Manuscript in a repository by the author(s) or with their consent.

ABSTRACT

Melanoma is a highly malignant tumor of melanocyte origin that is prone to early metastasis and has a very poor prognosis. Early melanoma treatment modalities are mainly surgical, and treatment strategies for advanced or metastatic melanoma contain chemotherapy, radiotherapy, targeted therapy and immunotherapy. The efficacy of chemotherapy and radiotherapy has been unsatisfactory due to low sensitivity and strong toxic side effects. And targeted therapy is prone to drug resistance, so its clinical application is limited. Melanoma has always been the leader of immunotherapy for solid tumors, and how to maximize the role of immunotherapy and how to implement immunotherapy more accurately are still urgent to be explored. This review summarizes the common immunotherapies and applications for melanoma, illustrates the current research status of melanoma immunotherapy delivery systems, and discusses the advantages and disadvantages of each delivery system and its prospects for clinical application.

KEYWORDS

Melanoma
immunotherapy
delivery system
tumor vaccine
nanoparticles
National Natural Science Foundation of China 10.13039/501100001809 82160314 and 81960497 This work was supported by the National Natural Science Foundation of China, grants [82160314 and 81960497] to J.C. The funders had no role in the study design, data collection, and analysis, decision to publish, or preparation of the manuscript.
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pmcIntroduction

Melanoma is a malignant tumor derived from melanocytes, which are neural crest-derived cells that are widely colonized the skin, eyes, and to a lesser extent, other tissues throughout the body during development, and these melanocytes at different sites can give rise to phenotypically different types of melanoma1. Approximately 3% of these melanomas lack an identifiable primary site, also known as melanoma of unknown primary (MUP). Compared with classic melanomas of known primary (MKP), patients with MUP appear to have a better prognosis than patients with primary site-matched MKP, which may be attributed to higher immunogenicity as reflected by immune-mediated regression of the primary site.2 Although melanoma may appear on any superficial skin surface, it mostly tends to grow on preexisting skin moles.3

According to the melanoma staging system issued by the American Joint Committee on Cancer (AJJC), melanoma can be divided into five main stages: first, there is the T0 stage, in which the melanoma is located in the most superficial layer of the skin and spreads only over the surface of the skin because it is not invasive, also known as melanoma in situ. Then it is T1 stage, the tumor is within 1 mm, subdividing the T1 stage, the clinically relevant threshold is taken as 0.8 mm, at this time, it may or may not be accompanied by ulceration, it will extend along the basal layer to the dermis, so it has invasiveness. Immediately following stage T2, the tumor grows into the 1 and 2 mm thickness range and can be described as an intermediate or high-risk melanoma, with a high risk of spread, usually without lymph node spread. By stage T3, the tumor is beyond 2 mm but less than 4 mm thick, and melanoma cells can be detected to have spread to at least one lymph node or surrounding tissue by sentinel lymph node biopsy. Finally, in stage T4, the tumor grows to a thickness greater than 4 mm, which is an advanced tumor with cancer cells that have progressed to distant areas of the body, and the 5-year survival rate is less than 10%.4 Melanoma also metastasizes to other organs such as distant lungs, liver, brain, and bone by entering blood vessels or lymphatic vessels.3

The main risk factor for melanoma is long-term ultraviolet exposure. Melanoma is very common in fair-skinned individuals and much less common in dark-skinned individuals. A family history of melanoma likewise puts an individual at increased risk, including familial atypical multiple nevus melanoma syndrome. And other risk factors are severe blistering sunburns, living at high altitude, viruses, and mechanical or chemical irritation.5 The incidence of melanoma is increasing every year and is also increasing among young people. It poses a great challenge in tumor control because it is highly aggressive and metastatic, spreading rapidly to other parts of the body, including the lymph nodes, liver, lungs, and brain, and has a very poor prognosis.

As of now, the primary treatment for early stage melanoma is surgical resection, including extended resection of the primary lesion and biopsy of the sentinel lymph nodes or regional lymph node dissection, and most early stage melanomas can be cured. For patients with metastatic disease, surgery alone will not be curative and drug therapy is the next line of defense, and the only treatment option for patients with metastatic melanoma is chemotherapy.6 Prior to the era of immunotherapy, the only treatment option for inoperable melanoma was to receive chemotherapy based primarily on dacarbazine, temozolomide, or formustine.7 Radiation therapy can also be used to treat locally advanced melanoma that cannot be removed surgically or melanoma that has metastasized by targeting radiation to the tumor tissue to kill the cancer cells or slow the growth of the tumor.8 Similarly, a variety of targeted therapies are available to fight melanoma, using specific drugs to target specific molecules or signaling pathways in melanoma cells, the most promising of which include B-Raf proto-oncogene (BRAF) inhibitors vemurafenib and dabrafenib, approved for the treatment of metastatic and unresectable BRAF-mutant melanoma.9 There is also PTEN (phosphatase and tensin homologue) which typically inhibits the PI3K/AKT/mTOR growth-promoting signaling cascade seen in 38% of patients with primary melanoma and 58% of patients with metastatic disease. Changes in the PTEN and BRAF pathways are often concurrent, theoretically allowing for simultaneous dysregulation of the MAPK and PI3K pathways. Therefore, PI3K inhibitors may be of benefit to patients with PTEN and/or BRAF mutant melanoma.10 Melanomas are often highly radioresistant, chemotherapy-resistant7 and severe side effects, setting the stage for the need for innovative treatment strategies that go beyond traditional treatments such as surgery, chemotherapy, and radiation.

In recent years, the emergence of immunotherapy as a breakthrough treatment has raised hopes and highlighted its potential to revolutionize the treatment paradigm, but maximizing the efficacy of immunotherapy through precise and targeted delivery remains a huge hurdle. The aim of this review is to introduce the current status of melanoma immunotherapy and assess its clinical applications, then summarize the relevant delivery systems that can be used to improve therapeutic efficacy and reduce side effects in recent years, and discuss the advantages and disadvantages of each delivery system and their prospects for clinical applications.

Immunotherapy for melanoma

Immunotherapy is the most widely studied treatment for melanoma. Immunotherapy can be divided into five main categories (Figure 1). The first category is based on vaccination strategies with peptides, whole proteins, viruses, DNA, or DC. The second category consists of immune checkpoint inhibitors, such as anti-CTLA-4 and anti-PD-1/PD-L1 antibodies, which mark a paradigm shift in melanoma treatment. The third category is based on over-the-counter cellular therapies, including the use of so-called lymphokine-activated killer (LAK) cells, tumor-infiltrating lymphocytes (TILs) and other specialized lymphocytes. And the fourth category includes biologic agents such as cytokines, interferons, and granulocyte-monocyte colony-stimulating factor. The last category is oncolytic virus, which is a relatively emerging treatment method. Figure 1. Different types of melanoma immunotherapy. They mainly consist of cancer vaccines, blockade of immune checkpoints (e.g. antibody), adoptive cell therapy, cytokine therapy, infection of oncolytic viruses.

1. Tumor vaccines

Tumor vaccines deliver tumor antigens into the patient’s body through different forms of peptides, proteins, cells and nucleic acids to activate the body’s immune response to exert anti-tumor effects. Tumor vaccines can be categorized into two main groups, preventive vaccines and therapeutic vaccines, according to their uses.

Preventive vaccines can be further divided into vaccines designed against tumor-inducing pathogens and vaccines against tumor antigens. Currently, mature preventive vaccines are mainly vaccines against virus-induced cancers, such as the well-known human papillomavirus vaccine to prevent cervical cancer and the hepatitis B vaccine to reduce the incidence of primary hepatocellular carcinoma11 and the hepatitis B vaccine, which reduces the incidence of primary hepatocellular carcinoma. Virus-induced cancers account for only 15% of human malignancies, and no vaccine has been successfully developed to prevent the remaining 85% of non-viral cancers, partly because of the diversity and complexity of tumor antigens, and partly because it will take a long time to prove its efficacy.12,13 There is no good treatment for advanced melanoma and the best option for these high-risk groups is prevention and early detection. Ashkan Safavia et al.14 prepared and purified a multi-epitope peptide vaccine containing immunodominant epitopes of SYCP1 and ACRBP and demonstrated its high immune system activation and tumor preventive effects in a mouse melanoma model. Helge Riemann et al.15 developed a prophylactic melanoma vaccine prepared from fully recombinant yeast expressing MART-1, and found that subcutaneous injection of recombinant yeast expressing MART-1 was protective against melanoma development in vivo in a transplantable mouse melanoma model. Most of the prophylactic vaccines against melanin are currently in preclinical studies, and more experimental and clinical trials are expected to demonstrate the feasibility of these prophylactic vaccines.

Therapeutic vaccines are mainly vaccines designed against tumor-associated antigens (TAA) and specific antigens (TSA). Depending on the source of the tumor vaccine, they can be further classified into tumor cell vaccines, dendritic cell vaccines, recombinant protein/peptide vaccines, nucleic acid vaccines, viral vector vaccines and personalized neoantigen vaccines. Tumor cell vaccines include autologous or allogeneic tumor whole cell vaccines, and tumor cell lysate vaccines. Whole tumor cells are not highly immunogenic, and there are usually two ways to increase the immunogenicity of tumor whole-cell vaccines; one way is to combine potent adjuvant semi-antigens to stimulate a strong inflammatory response, and the other is to genetically or chemically modify tumor cell.16 Talimogene Laherparepvec (T-VEC), an oncolytic herpes simplex virus, which was engineered to express granulocyte colony-stimulating factor. Recently, the results of the OPTiM trial, a phase 3 randomized control trial comparing T-VEC to GM-CSF alone, was presented at the American Society of Clinical Oncology. Unresectable Stage IIIB/C or Stage IV patients with injectable cutaneous, subcutaneous or nodal lesions were randomized to intralesional T-VEC or subcutaneous GM-CSF. The objective response rate (ORR) with T-VEC was 26% with 11% complete response (CR) compared to GM-CSF alone which had a 6% ORR and 1% CR. Durable response rate for T-VEC was 16% compared to 2% for GM-SCF. Interim overall survival analysis showed a trend in benefit toward T-VEC. Thus, T-VEC is the first such melanoma local immune therapy to show benefit in overall survival in a phase 3 randomized clinical trial in melanoma.17 Although cellular vaccines do not lead to a complete cure of the tumor, it may be possible to enhance the patient’s immune response and prolong survival through multiple injections of cellular vaccines after surgery, or by combining them with other immunotherapeutic modalities to achieve better results. Dendritic cells (DCs) are the most functional specialized antigen-presenting cells in the body, activating initial CD4 and CD8 T cells, which play a key role in promoting immune responses against antigens.18 Currently, the main strategies for constructing therapeutic tumor vaccines based on DCs are19: (i) conventional tumor therapeutic vaccines plus adjuvants that help DC maturation; (ii) tumor therapeutic vaccines targeting DCs in vivo; and (iii) tumor therapeutic vaccines in vitro DC relay. Several clinical trials of therapeutic DC vaccines for melanoma (Clinical Trial Numbers: NCI-V01-1646; NCT00436930; NCT00948480; NCT01690377) have demonstrated that DC vaccines have a better prognosis than tumor cell vaccines in melanoma patients. In addition, Jurjen Tel et al. demonstrated that natural human plasmacytoid dendritic cells can be safely used and induce antigen-specific CD4+ and CD8+ T-cell responses in melanoma patients,20 sometimes with some toxicity.21 Future studies on DC vaccines should focus on promoting DC maturation migration and combination therapy, and also explore the efficacy of different human DC subsets in cancer patients.

Recombinant protein/peptide vaccines, these cancer vaccines are developed by focusing on epitopes on peptides that stimulate humoral and cellular immune responses against TAA or TSA. The ideal antigen is one that is specifically highly expressed only in tumor tissue cells and low or absent in normal tissue cells. Common melanoma vaccine targets include gp100, MAGE-A3, MART-1, BIRC5, and NY-ESO-1.22–24 Recombinant protein/peptide vaccines are early hotspots for tumor vaccine research, but have been slow to progress, for example, the failure of GSK1572932A (MAGE-A3 peptide vaccine), developed by GlaxoSmithKline Biologicals SA, in a phase III clinical trial terminated the development of MAGE-A3 immunotherapy for melanoma.25 The main reasons were defective vaccine design, lack of effective immune adjuvants and poor clinical trial design. Peptide-based cancer vaccines have struggled to achieve efficacy as monotherapies, but show great promise as a component of combination therapy strategies. In a multicenter phase III randomized trial, 185 patients with advanced melanoma were randomized, and the results showed that the treatment group receiving the gp100 peptide vaccine plus combination IL-2 was superior to the IL-2 alone group.26 Currently, the major thrust of recombinant protein/peptide vaccine development is the development of multivalent vaccines, preparations that contain multiple identified antigens common to many patients’ melanomas and that can be easily scaled up to large patient populations. For example, Seviprotimut-L, a melanoma multivalent vaccine developed by Polynoma UK, contains several melanoma antigens such as MAGE-A3, MelanA, gp100, etc. The results of the phase III clinical trial demonstrated that for patients with stage IIB/C melanoma and among melanoma patients under 60 years of age, the recurrence-free Survival (RFS) improved, and Seviprotimut-L was very well tolerated.27 On June 23, 2020, the U.S. Food and Drug Administration (FDA) granted Accelerated Approval Eligibility Designation for Polynoma’s melanoma vaccine, Seviprotimut-L, for use as adjuvant therapy in postoperative treatment of patients with Stage IIB/IIC melanoma in order to improve patients’ RFS.

The mRNA vaccine is a promising vaccine platform relative to conventional vaccines, which possesses the advantages of being easily modifiable, stable, and highly translatable.28 Compared to viral as well as DNA-based vaccines, the use of mRNA has several beneficial features: first, safety: since mRNA is a noninfectious, non-integrated platform, there is no potential risk of infection or insertion mutagenesis. In addition, mRNAs are degraded by normal cellular processes, and their in vivo half-life can be adjusted by using various modifications and delivery methods. mRNAs’ inherent immunogenicity can be down-regulated to further enhance safety. Second, efficacy: various modifications make mRNAs more stable and translatable. mRNAs can be formulated into carrier molecules that can be rapidly ingested and expressed in the cytoplasm for efficient in vivo delivery. mRNAs are the smallest genetic vectors, thus avoiding antiviral immunity, and mRNA vaccines can be repeatedly administered. Third, production: mRNA vaccines have the potential for rapid, inexpensive, and scalable production, largely due to the high yield of in vitro transcription reactions.28 BioNTech announced the realization of effective targeting of dendritic cells in vivo by RNA-lipid complexes (RNA-LPX) by means of intravenous injection. During treatment, LPX mediates the efficient uptake and expression of the transgene by RNA in APCs.29 Meanwhile, IVAC® mutant, an individualized RNA vaccine based on patient-specific mutations, induces anti-tumor activity in high-risk patients with advanced melanoma.30

Neoantigenic cancer vaccines may produce stronger anti-tumor immune responses than classical DC cancer vaccines loaded with TAA (tumor-associated antigen).31 The neoantigens are highly immunogenic and absent in normal tissues, bypassing central thymic tolerance and being completely specific for cancer cells, which would help overcome two major obstacles to effective cancer therapy: tumor heterogeneity and selective targeting of tumors relative to healthy tissues.30,32 These antigens have been reported to originate from viral proteins, post-translational modifications and somatic mutations.33 It has been demonstrated that personal neoantigenic long peptide vaccines in melanoma patients produce memory T-cell responses that exhibit cytolytic properties in vivo and persist in peripheral blood for several years.34 Among these, NeoVax, an individual neoantigenic long peptide vaccine formulated with the TLR-3 and MDA5 agonist poly-ICLC, is feasible, safe, and immunogenic in high-risk melanoma patients.32 In conclusion, neoantigenic cancer vaccines have shown promising results in early clinical trials.

2. Immune checkpoint inhibitors

Immune checkpoints are one of the body’s key mechanisms for maintaining self-tolerance and preventing autoimmune damage to normal tissues. Tumor cells can hijack this mechanism to resist immune attacks, especially from T cells.35 Currently there are two main immune checkpoints in melanoma, CTLA-4 and PD-1, and thus there are two corresponding immunotherapies targeting the immunosuppressive pathway: anti-CTLA-4 antibodies acting at the lymph node level, and drugs targeting the interaction between PD-1 and PDL-1 in lymphoid, peripheral and tumor tissues.36

CTLA-4 was the first immune checkpoint to be discovered and belongs to the CD28 superfamily, which has two specific ligands: B7–1 and B7–2.37 CTLA-4 is constitutively expressed on T cells and recognizes the B7–1/2 receptor on APCs.38 CTLA-4 competes with CD28 for binding to B7–1/2, with opposite responses: when CD28 binds to B7–1/2, the immune response is activated, while CTLA-4 inhibits the immune response when it binds to B7–1/2.6 Ipilimumab is a human monoclonal IgG1 antibody against CTLA-4, which effectively blocks CTLA-4,36 and is the first globally approved immune checkpoint inhibitor for metastatic melanoma.39 In a Phase III clinical trial, ipilimumab was the first drug to improve overall survival in patients with advanced melanoma. Many strategies that can block CTLA-4 have been evaluated in multiple clinical trials worldwide.

Another key immune checkpoint is PD-1, which induces apoptosis in mature T cells, allowing the immune system to self-regulate, while self-antigens in the lymph nodes are recognized by these T cells.6 PD-1 acts as a cell surface molecule with inhibitory properties, preventing apoptosis of regulatory T cells.40 PD-L1, a homologous ligand of PD-1, can be expressed on immune cells such as macrophages and monocytes, so tumor cells can use this mechanism to evade immune attack. Immunotherapies based on PD-1 blockade have shown promising results in melanoma, and a number of drugs targeting the PD-1/PD-L1 pathway are now approved for use in melanoma, such as Nivolumab, Pembrolizumab, and Atezolizumab. During the effector phase, PD-1/PD-L1 inhibitors are effective by blocking t-cell-tumor suppressor interactions at the tumor level.36 In September 2014, pembrolizumab was approved by the FDA for use in two classes of patients with severe melanoma: to treat advanced patients who have failed prior treatment and patients with unresectable tumors.35

In addition to the two main immune checkpoints, CTLA-4 and PD-1, there are other immune checkpoints. CD137, a member of the TNF family, is capable of producing co-stimulatory molecular effects. Among the anti-cd137 monoclonal antibodies is one called BMS-663513, which can stimulate t-cells, leading to an increase in IFN-γ production, bringing about the most common drug-related toxicities such as fatigue, reversible transaminitis, and neutropenia.CTLA-4 and PD-1 are members of the CD28/CTLA-4 immunoglobulin superfamily, and other members of this family also may be important targets for new therapeutic approaches.41 Preclinical studies have shown that ICOS is a key player in the antitumor effects of CTLA-4 blockade. In mouse experiments, coadministration of a tumor cell vaccine expressing ICOS ligands at the time of CTLA-4 blockade significantly improved the rejection of established melanomas, suggesting enhanced anti-tumor responses to melanomas in mice.42 B and T lymphocyte attenuators were identified as a novel inhibitory receptor with structural and functional similarities to CTLA-4, capable of inhibiting human CD8+ cancer-specific T cell function and may be an important target for immunotherapy.43

Adoptive cell therapy

Adoptive cell therapy (ACT) is a highly personalized cancer therapy that involves the administration of a cancer-bearing host of immune cells with direct anticancer activity. It uses natural host cells with anti-tumor responsiveness or host cells genetically engineered with anti-tumor T-cell receptor (TCR) or chimeric antigen receptor (CAR).44 The three main types of over-the-counter T-cell therapies are tumor-infiltrating lymphocyte therapies, engineered TCR therapies, and chimeric antigen receptor (CAR) therapies, which differ slightly from each other but whose primary goal is to augment the cytotoxicity of cytotoxic T-cells and other immune cells, which are then infused back into the patient to induce tumor regression.6

Tumor-infiltrating lymphocyte therapy

Tumor infiltrating lymphocyte therapy is the basis for engineered TCR therapy and CAR therapy,45 which requires isolation of tumor infiltrating lymphocytes (TIL) from resected tumors. TIL therapy in patients with metastatic melanoma has shown significant remission rates of ≥ 50%, with 22% of patients demonstrating complete remission.46 The disadvantages of TIL therapy are that the tumor must be resectable, the resected tumor needs to have TIL that can be isolated and expanded, and the overall health of the patient.47 The high mutation rate in melanoma, the high number of TILs isolated from melanoma patients, and the reduced immunogenicity of tumor-associated antigens (TAAs) in other cancers make TIL therapy more effective in melanoma than in other solid cancers.48 Meanwhile, TIL cell therapy has emerged as a promising option for the treatment of advanced ICI-refractory solid tumors because of the polyclonal nature of the infusion product against different tumor antigens, which is thought to attenuate immune escape through loss of target antigen expression by tumor cells.49 Overall results showed that tumor-infiltrating lymphocytes (TIL) combined with low-dose IL-2 significantly reduced the level of toxicity and resulted in a longer-lasting response.50 Lifileucel (LN-144) is a one-time autologous TIL cell therapy that uses tumor tissue T cells capable of recognizing tumor antigens and expanding in vitro, while maintaining a heterogeneous pool of T cells using a centralized manufacturing process that generates billions of polyclonal patient-specific TILs from TILs recovered from patient tumor tissue in an intensive 22-day production process.51 TIL are a mixture of CD8+ and CD4+ T cells with a predominantly effector memory phenotype associated with cytotoxic functions.44 Following a single infusion of Lifileucel, TILs migrate to tumor sites throughout the body where they recognize and target a variety of individualized tumor-associated neoantigens and mediate tumor cell lysis.51 In conclusion, investigational lifileucel demonstrated clinically meaningful activity in heavily pretreated patients with advanced melanoma and high tumor burden.52

Genetically engineered TCR therapy

Genetically engineered TCR therapies have been developed to overcome the barriers to isolating TIL from tumors and the availability of tumor-specific T cells in patients,47 which utilizes T cells isolated from patients and genetically engineers these T cells to express tumor antigen-specific TCRs,44 this therapy requires high levels and uniform expression of the target antigen, in addition to MHC limitations, which often limit the number of patients eligible for treatment.53

Chimeric antigen receptor (CAR) therapy

Chimeric antigen receptors are constructed by attaching a variable region of an antibody as a single chain (scFv) to a T-cell signaling fragment consisting of CD3ζ and 1 or more co-stimulatory structural domains, the latter of which enable T cells to activate upon recognition of a target by the scFv and to function in an MHC-independent manner.53 Chimeric antigen receptors introduced into T cells are designed to recognize antigens specifically by fusing the structural domain of a monoclonal antibody, which is connected to components of the intracellular TCR through transmembrane structural domains, and to co-stimulatory molecules required for T cell activation,54 this fusion receptor enables T cells to recognize tumor antigens on the surface of the tumor independently of MHC binding, enabling CAR T cells to eliminate cancer cells regardless of MHC status.55 The disadvantages of CAR-T cell therapy are the time, cost, and toxicity required to develop CAR-T cells using the patient’s T cells.56

Cytokine therapy

Cytokines play a pivotal role in the regulation of innate and adaptive immunity. In certain tumor treatments involving key aspects of immunity, the release or intervention of cytokines is indispensable.

IFN-α is a cytokine that was the first drug used to treat metastatic melanoma. It has not become a standard treatment for metastatic disease because the response rates observed in phase II trials are rare (about 15%), usually transient, and usually limited to patients with small amounts of soft tissue metastases.35

One of the first cytokine immunotherapies developed for metastatic melanoma was interleukin 2 (IL2) therapy, which was approved for use in 1992.57 IL-2 is a pro-proliferative cytokine, secreted primarily by Th1 effector cells, that promotes the expansion of melanoma-specific T cells.6 As early as 40 years ago, IL-2 was shown to be beneficial in some patients with advanced melanoma. A review describing extended follow-up of 270 patients treated with high-dose IL-2 pills reported complete remission in 6% of patients and partial remission in another 10% of patients.35

Oncolytic viruses

The study of viruses killing cancer cells is not new, and lysosomal viruses are beginning to be gradually promoted in the treatment of melanoma. Although the mechanism of intercellular action has not been fully elucidated, it is widely believed in the industry that lysogenic viruses have two mechanisms to achieve anti-tumor effects: first, the virus enters the tumor cell, replicates selectively, manipulates aberrant signaling factors, and induces cell death, thereby lysing the tumor cell; second, the induction of systemic anti-tumor immunity, after the death of lysogenic cells, the tumor cell releases tumor-associated antigens, which can promote adaptive immune responses that mediate tumor regression at distant tumor sites not exposed to the virus.58 Many of the oncolytic viruses currently in the clinic have a natural tropism for cell surface proteins that are aberrantly expressed by cancer cells, e.g., HSV-1 uses the Herpesvirus Entry Medium (HVEM) and selected nectins to enter the cell, and these surface receptors are overexpressed on a number of cancer cells, including melanomas and a variety of cancers.59 Herpesviruses have been used as oncolytic viruses for cancer vaccination, and a promising strategy has been tested with GM-CSF as an adjuvant or APC growth factor for replication of herpesvirus vectors.60 Cowpox virus encoding the B7.1 T-cell costimulatory molecule (rV-B7.1) was tested in a phase I clinical trial in patients with advanced melanoma, where the virus was found to be safe, and the patients showed melanoma-specific T-cell responses, with evidence of tumor regression in 3 of 12 patients, including 1 complete remission.61 The cowpox virus encoding TRICOM (rV-TRICOM) was also evaluated in a phase I melanoma trial with a remission rate of 30.7%.62 In October 2015, the FDA approved the first drug of this kind, Talimogene laherparepvec (T-vec), for the treatment of melanoma in patients with inoperable tumors. T-vec is a genetically modified herpes simplex virus type 1 that infects host tumor cells via granulocyte macrophage colony-stimulating factor (GM-CSF) to enhance the host immune response.6

Combination immunotherapy

Despite the success of immune checkpoint inhibitors, only a minority of patients have achieved a durable clinical response with monotherapy. In fact, the most successful outcomes of these drugs can be achieved in combination with other immune checkpoint blockers, chemotherapy, radiotherapy, or targeted molecular therapies.37 Currently, the NCCN recommends navumab/ipilimumab or pembrolizumab/ipilimumab combination therapy as an option for metastatic and unresectable disease. Indications associated with combination therapy compared to PD-1 monotherapy include patients’ willingness to risk immune-related adverse events (irAEs), lack of comorbidities that increase the risk of irAEs, social support, and expected adherence to toxicity management.36 Ipilimumab in combination with anti-CTLA-4 immunotherapy and nivolumab in combination with anti-PD-1 immunotherapy appear to be more effective than either drug alone, but at the cost of increased toxicity.63 Combination therapy with PD-1 and CTLA-4 inhibitors shows great promise in terms of efficacy, although combination therapy will come at the expense of increased toxicity.35 Low-dose ipilimumab Low-dose ipilimumab in combination with T-vec injections, and combination therapy with CTLA-4 and PD-1 immune checkpoint inhibition have shown the most promising response data to date. In September 2015, the FDA approved nivolumab in combination with ipilimumab for patients with unresectable or metastatic BRAF V600 WT melanoma. KEYNOTE-029 (NCT 02089685) Preliminary data from the expanded cohort evaluating pembrolizumab in combination with low-dose ipilimumab were presented at the 2016 American Society of Clinical Oncology meeting.6

Delivery systems for melanoma

As for the delivery system, it plays an equally important role in the immunotherapy of melanoma. Delivery systems ensure the efficient transportation and release of drugs in the body, thereby improving drug bioavailability and efficacy. Currently, various delivery systems are being researched and developed to optimize the effects of immunotherapy.

Nanoparticle-based delivery

Nanoparticles (NPs) are one-dimensional particles ranging from 1 to 100 nm. NPs have a wide range of applications in drug delivery for the treatment of melanoma. These NPs include liposomes, polymers, dendritic polymers, inorganic nanoparticles, and exosomes.64,65 Some examples are shown in graphic cartoons (Figure 2). Figure 2. Some representative formats of immunotherapy delivery systems. Nanoparticles (NPs) can be formed by different materials, including liposomes, polymers, dendritic polymers, inorganic nanoparticles, and exosomes.

Liposomes

Liposomes, consisting of a bilayer of phospholipids and cholesterol, are one of the most commonly used drug delivery systems and have applications in melanoma. Virofenib-resistant melanoma can be treated with protein kinase C inhibitor-anchored BRD4 PROTAC polyethylene glycolized nanoliposomes.66 Liu et al. tested a strategy to deliver cytokine mRNA to TME using novel lipid nanoparticles (LNP). The results showed that diaminolipid-derived nanoparticles (DAL4-LNP) could efficiently deliver mRNA for cytokine expression in vitro and in vivo, and intra-tumor delivery of dual IL-12 + IL-27 mRNA showed the most effective inhibition of melanoma growth.67

Polymers

Polymeric nanoparticles (PNPs) are widely used as controlled and slow-release drug carriers, and the key features of PNPs as drug carriers are that they can be surface functionalized to actively target tumor tissues or cells and stimulate reactivity and controlled drug release,68 a commonly used polymer in melanoma is polylactic glycolic acid (PLGA).64 PLGA has good biodegradability and compatibility, as well as easy-to-process mechanical properties, and the loaded drugs are able to effectively overcome the skin barrier and reach the malignant melanoma located deep in the skin, realizing the targeted delivery of drugs.69,70 An AD-3281 with superior inhibitory MetAp2 enzyme activity effectively inhibits cancer and endothelial cell proliferation and impairs endothelial cell tube formation in vitro. Biodegradable nanoparticles composed of PLGA were delivered to AD-3281, and nanoparticles transporting AD-3281 showed favorable cell availability and uptake and its anticancer activity.71

Dendritic polymers

Dendrimers are molecules with a central core and repeating branches. Anti-cancer drugs encapsulated in dendritic macromolecules have slower release, lower toxicity and higher accumulation rates in solid tumors compared to free drugs.72 Xia et al. developed a cationic polyamidoamine dendrimer (amino-terminal PAMAM) as a vehicle for the simultaneous delivery of doxorubicin (DOX) and immunoadjuvant cytosine-phosphate-guanine oligodeoxynucleotide (CpG ODN) for the treatment of metastatic melanoma.73 However, PAMAM dendrimers have several drawbacks, such as poor biocompatibility, high toxicity, and rapid clearance by the bloodstream due to a positively charged surface at biophysiological pH.74

Inorganic nanoparticles

Inorganic nanoparticles provide versatile platforms for a wide range of drug delivery, encompassing both metallic and nonmetallic particles.75 Gold nanoparticle (AuNP)-based drug delivery systems can selectively deliver drugs to melanoma cells, potentially improving drug delivery.76 MiR-21-3p is a novel iron death promoter targeting thioredoxin reductase 1, and systemic delivery of miR-21-3p by AuNP potently improves the efficacy of anti-PD-1 antibody, which has a significant therapeutic effect in melanoma.77 The low water solubility and limited bioavailability of mulberry protein, the encapsulation of mulberry protein hydrate (MH) by mesoporous silica nanoparticles (MSN) can improve the bioavailability of mulberry protein and increase the anti-tumor effect of melanoma cells.78 In addition, silver nanoparticles (AGNP) have been extensively studied as antimelanoma agents for drug delivery because of the excellent properties that make them favorable for drug delivery and genetic material to specific regions.79

Photodynamic therapy

In recent years, photodynamic therapy (PDT) has been proposed as a new therapeutic option for tumor ablation and necrosis to inactivate pathogens.PDT promotes the destruction of cancer cells through the accumulation of irradiation-activated photosensitizers (PS) in the target organ or cell, and the combination of intracellular molecular oxygen in the tissues and light generates reactive oxygen species (ROS).However, penetration and retention are the most important challenges in the conventional photodynamic therapies, and NP is capable of overcoming this challenge because of its small size and physical properties, it is well able to overcome this challenge.3,80,81 Internally metastasized melanoma is more difficult to treat with PDT because of the low penetration of laser light to these sites, whereas exosomes, as naturally occurring nanoparticles, can be reassembled with PS to improve the efficiency of cellular uptake and at the same time efficiently deliver more photosensitizers to the cells, with a high targeting capacity for effective photodynamic therapy. Zhao et al. have demonstrated this by using silica NPs as a carrier to encapsulate and delivering the photosensitizer phthalocyanine 4 (Pc4) to treat melanoma, showing higher permeability and lower cell survival than with free Pc4 molecules.82 In conclusion, NP increases the therapeutic efficacy of PDT by increasing PS solubility, enhancing drug delivery, improving tumor penetration, enhancing tumor accumulation, and providing controlled release and more efficient ROS generation. NP-based PDT has become a promising therapeutic strategy for melanoma treatment.83

Cell-based delivery

Melanoma is a poorly immunogenic cancer, and precise targeted delivery of antigens is essential for tumor therapy; cell-based delivery offers better biocompatibility and lower immunogenicity, and enables more precise delivery of antigens to tumor cells.84 Dendritic cells (DCs) have emerged as a natural mediator of antigen delivery in the treatment of melanoma, and DC-based antigen presentation is the most effective means of initiating T-cell immunity, which triggers a strong T-cell response. Over the past decade, dendritic cell-based immunotherapies have been vigorously attempted.85,86 Engineered cells are also an important cell delivery platform, and engineered platelets loaded with adriamycin (DOX) (DPG-PL@DOX) had the strongest antitumor effects in a mouse melanoma model and significantly enhanced antitumor effects in a tumor hemorrhage model.84 Engineered mesenchymal stem cells (MSCs) are rapidly developing in tumor therapy due to their low immunogenicity and natural tumor homing ability.87 MSCs are able to migrate toward the tumor site and penetrate cancer cells, and a MSC-based photomimetic delivery platform impregnated with submicron-sized composite capsules containing antitumor drugs has been developed to effectively improve the mortality of melanoma spheroids.88

Extracellular vesicles

Extracellular vesicles (EVs) are particles that are naturally released from cells, separated by lipid bilayers89 that contain different protein, lipid, and nucleic acid species of the source cell, but do not contain a functional nucleus. Based on size and biogenesis, EVs are identified as exosomes (30–150 nm in diameter), microvesicles (0.1–1 μm) and apoptotic vesicles (1–4 μm).90 Cancer-derived EVs have immunomodulatory potential, while melanoma-derived EVs can inhibit CD8+ T cell proliferation, function and viability along multiple mechanisms.91 Given EV’s ability to cross physical barriers, inherent targeting properties and high biocompatibility,92 EVs have emerged as promising delivery systems for melanoma therapy. For example, Lee et al. loaded the transforming growth factor-β receptor I kinase inhibitor (SD-208) and the TLR-7/8 agonist, sequinimod (R848), on EVs to effectively inhibit melanoma growth.93 Plant-derived EVs can mediate interspecies communication in mammalian cells.Cao et al. successfully isolated and purified extracellular vesicular nanoparticles derived from ginseng roots, termed ginseng-derived nanoparticles (GDNPs). In a mouse model of melanoma, GDNPs significantly promoted M2 to M1 phenotype polarization and accelerated the functional shift of tumor-associated macrophages to an M1-like phenotype. This ultimately led to the inhibition of tumor growth in vivo.94

Intratumor injection

Intratumoral injection is a collective term for therapeutic methods of injecting medication into the tumor using a syringe, which can lead to a rapid increase in local drug concentration within the tumor, and thus effectively inhibit the growth of the tumor in a targeted treatment modality. Melanoma lesions are usually cutaneous and have a tendency to spread subcutaneously, providing a unique opportunity for direct intratumor injection.95 A phase I/IIa clinical study demonstrated that intratumor injection of Japanese enveloped carrier hemagglutinin virus resulted in an increase in NK cell activity and IFN-γ levels, which led to the activation of systemic innate immunity and cytotoxic T cell-mediated immunity, and had an antitumor effect on advanced melanoma.96

Implantable stent

Implantable drug delivery systems originated in the 1960s as a way of delivering medications that could overcome the problems associated with taking specific therapies orally. Implantable stents can be inserted into specific body locations, and examples of such stents include intraocular, vaginal, and intrauterine inserts.97 One study developed an intraocularly implantable ab interno XEN gel scaffold for the delivery of mitomycin C, a broad-spectrum antitumor antibiotic isolated from Streptomyces cephalosporus cultures, which has anticancer effects against a variety of cancers and works by depolymerizing cellular DNA while blocking DNA replication, thereby inhibiting tumor cell division. Ab interno XEN gel scaffold delivery of mitomycin C may provide an effective method for intraoperative pressure control in patients with refractory intraoperative pressure after radiotherapy for uveal melanoma plaques.98

Microneedle-mediated drug delivery systems

MNs are an emerging method of transdermal drug delivery, typically consisting of arrays of micrometer-sized needles with heights of 10–2000 μm and widths of 10–50 μm.99 The active ingredients of anticancer drugs can reach the dermis layer of skin directly with the help of MNs, which can penetrate the dermis layer of skin directly and make the drugs have good permeability, which is very favorable to realize local targeted therapy. Currently, the MNs used in the treatment of melanoma include solubilized MNs, core-shell MNs, encapsulated MNs, hollow MNs, cryogenic MNs, and active MNs. MNs, as a new drug delivery system, have shown great potential in the treatment of melanoma, and the development of more therapeutic options has become very important.93 It is believed that MNs will become an important platform for the treatment of melanoma with future research.

Discussion

Melanoma is characterized by a poor prognosis and high mortality, especially in the metastatic stage. Some of these biomarkers are diagnostic or prognostic, and the use of lactate dehydrogenase (LDH) and S100 calcium-binding protein B in disease prognosis and monitoring is well documented. Other serum biomarkers, such as melanoma inhibitory activity (MIA) and vascular endothelial growth factor (VEGF), have been associated with advanced disease and poor prognosis, but their use has been limited by their low specificity. On the other hand, DNA markers (e.g., BRAF and NRAS) have established good associations with patient selection and predict response to targeted therapy. Circulating tumor DNA (ctDNA), microRNA (miRNA), and long-stranded noncoding RNA (IncRNA) provide useful insights into tumor genetics and contribute to the understanding of disease pathophysiology, with the great advantage of permitting continuous, noninvasive sampling for disease monitoring.10 Radical surgical resection of limited lesions provides the best therapeutic outcome; however, for disseminated processes, surgery has a limited role and systemic therapy is necessary. However, in conventional treatment, chemotherapy, radiotherapy, and targeted therapy for metastatic patients do not bring the expected results. Therefore, further research and improvement of therapeutic approaches are needed.

Checkpoint inhibitors in melanoma immunotherapy, such as anti-CTLA-4 and anti-PD-1/PD-L1 antibodies, mark a paradigm shift in melanoma treatment. Immune checkpoints prevent unwanted and deleterious self-directed activities that lead to autoimmunity, and therapies that overcome these mechanisms by blocking or inhibiting checkpoints allow for revitalization of the immune system’s ability to detect and produce anti-tumor activity, either alone or in concert with other therapies,100 which in turn improves patient prognosis and survival. Although immunotherapy is a targeted therapy that is better tolerated than regular chemotherapy and radiotherapy, its efficacy is not universal and either a proportion of patients do not respond or develop resistance. In addition, a new type of toxicity of immune abnormalities, called irAEs (immune-related adverse events), emerges, which poses a challenge to its widespread use.101 Advance cell therapy (ACT), including tumor-infiltrating lymphocyte (TIL) therapy, engineered TCR therapy, and chimeric antigen receptor (CAR) T-cell therapy, represents a personalized approach to cancer treatment. While showing promising results, ACT is limited by the complexity of cell manufacturing, the need for lymphocyte clearance prior to infusion, and the management of treatment-related toxicity.37 Cytokine therapy, utilizing agents such as interleukin-2 (IL-2) and interferon-alpha (IFN-α), plays a key role in modulating the immune response against melanoma. In many studies of IFN-adjuvant therapy for melanoma, recurrence-free survival appears to be the primary benefit of this treatment modality.102 Despite the potential of cytokines, their clinical benefits are often overshadowed by their toxicity and the transient nature of their response. Tumor vaccines are a promising therapeutic approach; tumor vaccines can stimulate the body’s immune system to attack melanoma cells and achieve therapeutic goals by directing the immune system to recognize and destroy tumor cells; they can also be personalized to the individual patient, as melanoma has a high level of genomic variation, and personalized treatment regimens are likely to be more effective; and compared to traditional treatments such as chemotherapy and radiation therapy Tumor vaccines typically have fewer side effects because they fight tumors primarily by stimulating the immune system, rather than directly poisoning or damaging normal cells60; at the same time, there may be a continuous production of immune memory, allowing the body to recognize and remove melanoma cells over time, reducing the risk of recurrence. However, tumor cells are often able to evade attack by the immune system, for example by changing surface antigens to avoid immune surveillance, which may affect the therapeutic efficacy of tumor vaccines. Vaccines are individually variable and may have different efficacy in different patients, some of whom may be insensitive or ineffective. The high cost of the vaccine, its high price, and the long treatment period are also reasons for the limitations. Overall, tumor vaccines, as a personalized immunotherapeutic approach, have certain advantages in melanoma treatment, but there are still some challenges and limitations that require further research and improvement.

Immunotherapy represents a cutting-edge approach to the treatment of melanoma, utilizing the body’s immune system to recognize and destroy cancer cells. While delivery systems play a key role in immunotherapy, the development of delivery systems aims to address the limitations of current immunotherapies by increasing targeting efficiency, reducing systemic toxicity and improving treatment outcomes (Table 1). Nanoparticles can be engineered to specifically target tumor cells, reducing off-target effects and enhancing therapeutic efficacy; at the same time, they can allow for controlled release of the drug, allowing for a continuous supply of the drug at the tumor site and reducing the need for frequent drug administration.103 The drug can also be released in a controlled manner, allowing for a continuous supply of drug at the tumor site and reducing the need for frequent administration. In addition, by coating specific targeting ligands (e.g. antibodies or peptides), these nanocarriers can be modified for more active molecular targeting and tumor imaging to improve the pharmacokinetic profile of the compounds and increase selectivity for cancer tissues.104 Of course, there are some disadvantages, such as biocompatibility issues: some nanoparticle compositions may cause immune reactions or toxicity, which could compromise patient safety. Designing nanoparticles for specific targeting requires sophisticated techniques and an understanding of tumor biology, which can be challenging and costly. There is also a risk of nanoparticles accumulating in non-target organs, which could lead to toxicity.65 Cell-based delivery systems are highly specific and designed to specifically target melanoma cells, which can reduce the impact on healthy tissues; they can potentially provide a sustained immune response against tumor cells and achieve long-lasting antitumor activity.86 At the same time, cells are capable of delivering a range of therapeutic agents directly into the tumor microenvironment. However, there are limitations to the clinical use of cells as delivery vehicles, related to the difficulty of obtaining such carrier cells under natural conditions, the need for complex and expensive cell manipulation and culture facilities, and the complexity of cell functionalization.88 There is a risk of immune rejection or adverse immune reactions, which in some cases may be life-threatening. Extracellular vesicles are naturally occurring and have the natural ability to carry biomolecules and can serve as effective carriers for therapeutic agents, potentially reducing the risk of adverse reactions, with high biocompatibility and low toxicity.91 Isolation and large-scale production of extracellular vesicles is technically challenging and costly, and they may have a limited capacity to carry large amounts of drugs or therapeutic agents. Melanoma lesions are usually cutaneous and have a tendency to spread dermally/subcutaneously, and intratumor injection permits delivery of therapeutic agents directly into the tumor, minimizing systemic exposure, potentially increasing local concentrations and efficacy, and reducing systemic toxicity.95 A major limitation to the use of intratumor injections is that they are limited to accessible tumors, are not applicable to the treatment of metastatic or inaccessible tumors, and require invasive procedures that may be associated with pain, infection, and other complications. In addition, the tumor microenvironment may vary considerably from organ to organ, and thus the efficacy of intratumor drug delivery may vary. Implantable stents provide a continuous supply of drugs directly to the tumor site, ensuring consistent therapeutic effects while reducing systemic exposure to drugs and minimizing side effects. However, they also face limitations such as surgical risks, potential complications, and the possibility that the stent may become clogged or run out of drug and need to be replaced or removed. Microneedle-mediated drug delivery systems offer a less invasive alternative to traditional injections, with the potential to improve patient compliance; avoid hepatic first-pass elimination effects, increase metabolic concentrations and bioavailability of drugs, and reduce gastrointestinal tract irritation and damage.105 It can realize local drug delivery, sustained release of drugs, prolong the blood circulation cycle, ensure that the drug is maintained at the level of therapeutic concentration for a long time, and has a better therapeutic effect.106 Avoid the hydrolysis of the drug in the gastrointestinal tract by the destruction of protease, and improve its bioavailability.107 However, its high mechanical strength requirements, skin barrier function limits the effectiveness of the drug, affecting the delivery efficiency of the drug; due to the size, stability or dosage requirements, not all drugs are suitable for drug delivery via microneedle.93Table 1. Advantages and disadvantages of delivery systems in immunotherapy.

Delivery Systems for Immunotherapy	Advantages	Disadvantages	Ref.	
Nanoparticle-based delivery	Nanoparticles include small molecules, proteins, and nucleic acids, which can reduce acute toxicity, improve drug dissolution rate, and provide a wide range of therapeutic methods. They can be specifically designed for tumor cells to achieve more active molecular targeting and tumor imaging, thereby improving the pharmacokinetic characteristics of compounds, reducing off target effects, and enhancing therapeutic efficacy. Meanwhile, they can control the release of drugs, making them continuously available at the tumor site and reducing the need for frequent administration.	Nanoparticles pose a risk of accumulation in non target organs and are physiologically non degradable, potentially leading to toxicity. Some nanoparticle compositions may elicit immune responses or toxicity, impacting patient safety. Producing nanoparticles with consistent quality and characteristics can be challenging and costly.	65,103,104	
Cell-based delivery	Specially designed for melanoma cells, it can directly deliver a series of therapeutic agents into the tumor microenvironment, potentially providing a sustained immune response against tumor cells and reducing the impact on healthy tissues.	It may not be possible to effectively target or penetrate deep tumor tissue or metastatic sites, requiring complex and expensive cell manipulation and culture facilities. The risk of immune rejection or adverse immune reactions remains a significant challenge.	86,88	
Extracellular vesicles	Extracellular vesicles are naturally occurring ，with high biocompatibility and low toxicity, and can serve as efficient carriers for therapeutic agents, potentially reducing the risk of adverse reactions.	They might have limited capacity to carry a large amount of drugs or therapeutic agents. The isolation and large-scale production of extracellular vesicles can be technically challenging and costly.	91	
Intratumoral therapies	Allowing for direct delivery of therapeutic agents into the tumor, potentially increasing local concentration and efficacy. Minimizing systemic exposure, therefore the risk of systemic side effects.	Limited to accessible tumors and requiring invasive surgery related to pain, infection, and other complications.	95	
Implantable drug delivery systems	It can provide continuous drug supply directly to the tumor site, reduce systemic exposure of drugs, minimize side effects, and ensure consistent treatment outcomes.	Implantation involves surgical risks and potential complications, and the stent may clog or deplete the medication, requiring replacement or removal.	 	
Microneedles-mediated drug delivery system	Providing a minimally invasive alternative to traditional injection, which belongs to local administration, avoids liver first pass elimination, improves drug metabolic concentration and bioavailability, and can also be designed for targeted drug delivery and controlled release over time.	Not all drugs are suitable for delivery through microneedles due to size, stability, or dose requirements. Effectiveness can be limited by the skin’s barrier function, affecting drug delivery efficiency.	105–108	

In summary, various delivery systems have unique advantages and limitations in melanoma immunotherapy, and future research should be devoted to optimizing the design and performance of delivery systems to improve drug targeting, bioavailability, and therapeutic efficacy, as well as to reduce therapeutic risks and side effects for patients.

Conclusions

Immunotherapy and delivery systems for melanoma is a complex and evolving field. With further research and technological advances, it is believed that more and more effective treatment options will be available for melanoma patients in the future. Meanwhile, the continuous optimization and innovation of delivery systems will further promote the application and development of immunotherapy in melanoma.

Frontiers and prospects

The future of melanoma treatment lies in the relentless pursuit of innovation, both in the development of new immunotherapies and in the improvement of drug delivery systems. Combinations between immunotherapies hold the promise of designing highly precise, efficient, and patient-friendly treatments, such as combining immune checkpoint inhibitors with lysoviruses, therapeutic mRNA vaccines, and microbial transplants, which have revolutionized immunotherapy treatments and improved efficacy. Another promising strategy is the triple combination of anti-PD-1/PD-L1 immunotherapy and anti-BRAF plus anti-MEK targeted therapies, the rationale for which stems from the fact that immunotherapy and targeted therapies are complementary. Chemoprophylaxis is a reasonable and cost-effective approach, and despite the large amount of preclinical data suggesting that a variety of chemoprophylactic agents can prevent or delay melanoma, it is realized that there are insufficient clinical studies to evaluate their efficacy and long-term safety for human use. Improvements in delivery systems have also progressed, and PLGA is now widely used in photodynamic therapy and targeted therapies by modulating signaling proteins and drug-DNA interactions. In addition, the emergence of artificial intelligence and machine learning in oncology research provides unprecedented opportunities to predict treatment response and optimize treatment regimens. As we enter a new era of cancer treatment, interdisciplinary collaboration and patient-centered research will be paramount to overcoming existing challenges and unlocking the full potential of melanoma immunotherapy. In conclusion, while significant progress has been made in the fight against melanoma, the journey to a cure is far from over. Continued innovation in immunotherapy and delivery systems is critical to transforming the bleak outlook for advanced melanoma into a future of effective and sustainable treatments for all patients.

Hui Liu is a master’s degree candidate, researching in tumor immunology. She obtained her bachelor’s degree from Jiujiang College in 2022. In 2023, she began to study in the School of Public Health (Clinical Laboratory Diagnostics) of Nanchang University for training as a residency and researcher.

Xi Gou is a master’s degree candidate, researching in tumor immunology. She graduated from Clinical College of Hebei Medical University in 2021. In 2022, she began to study in the School of Public Health (Clinical Laboratory Diagnostics) of Nanchang University for training as a residency and researcher.

Yuanfang Tan was recommended for the master’s degree study to the School of Public Health of Nanchang University in 2021. Her research direction is tumor vaccines and tumor immunology. She obtained a master’s degree in clinical laboratory diagnosis from Nanchang University in 2024.

Qiuying Fan received her master’s degree in clinical laboratory diagnosis from Jiangxi Medical College, Nanchang University, China. Her research direction is tumor immunology. During the postgraduate period, she completed the standardized training of resident doctors and obtained the certificate of qualification of resident doctors.

Dr. Juanjuan Chen is an Associate Professor and Associate Director of Department of Clinical Laboratory, the Second Affiliated Hospital, Jiangxi Medical College, Nanchang University, China. Dr. Chen is the recipient of the third Prize of 2016 Jiangxi Provincial Science and Technology Progress Award and 2018 Outstanding Young Scholar Award of Jiangxi Immunological Society. She received her bachelor of clinical medicine degree from Tongji Medical College of Huazhong University of Science and Technology in 2006. She earned her Ph.D. in immunology from Peking University Health Science Center in 2011. She is a member of Youth Committee of the Chinese Society of Immunology and Youth Committee of the Laboratory Physicians Branch of the Chinese Medical Association.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

Conceptualization, J.C.; writing – original draft preparation, H.L. and X.G.; writing – review and editing, J.C., Y.T., Q.F. All authors have read and agreed to the published version of the manuscript.
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