Novel therapeutic combination strategies for advanced melanoma

Introduction

Melanoma, a highly aggressive form of skin cancer, has seen significant advancements in treatment with the advent of immune checkpoint inhibitors (ICIs) targeting the programmed cell death protein 1 (PD-1) pathway. ¹ These agents such as pembrolizumab and nivolumab have demonstrated remarkable clinical responses and improved survival rates in a subset of patients with advanced melanoma. ²  Notably, for individuals with stage IV melanoma, median survival has increased from approximately six months to nearly six years, largely attributed to the success of immunotherapy. ³ However, a considerable proportion of patients either fail to respond initially or develop resistance over time, presenting a major obstacle in achieving effective and durable treatment outcomes. ³ This clinical reality underscores the urgent need for novel therapeutic approaches, particularly in the realm of combination strategies.

Combination strategies offer a promising avenue for enhancing melanoma treatment efficacy. By utilizing agents with distinct but complementary mechanisms of action, these approaches aim to produce synergistic anti-tumor effects to potentially overcome resistance mechanisms that limit the efficacy of monotherapies. ³ This review will explore recent advancements in combination therapies for advanced melanoma, particularly in the PD-1–refractory setting, and examine their potential use in the frontline setting to improve the effectiveness and durability of PD-1 blockade. The scope of this review will specifically focus on combination strategies involving immune checkpoint inhibitors (ICIs), oncolytic viruses, tumor-infiltrating lymphocytes (TILs), and therapeutic vaccines.

Defining PD-1 refractory melanoma

PD-1 refractory melanoma is characterized by disease progression despite anti-PD-1 therapy. ⁴  The Society for Immunotherapy of Cancer (SITC) has established guidelines to define resistance to ICIs, which help standardize clinical trials and inform treatment selection, enabling more precise identification of patients who may benefit from alternative therapies. ⁵ According to the SITC guidelines, primary resistance occurs when tumors fail to respond to initial therapy or progress within the first six months of treatment, and secondary resistance develops after an initial period of tumor control lasting six months or more, followed by disease progression. ⁶

In a recent Skin Cancer VJ Session, Omid Hamid, MD, The Angeles Clinic and Research Institute, Los Angeles, CA, emphasized the importance of clearly defining PD-1 resistance to advance treatment strategies:

“When we’re going to develop drugs, we all need to have the same language and contribute to the conversation on the same footing. The SITC has sent out a consensus guideline, which most of us agree to.”

Primary resistance may arise from several factors, including ineffective T-cell activation, defective antigen presentation that prevents tumor recognition, and impaired T-cell infiltration into the tumor. Tumors may also express inhibitory factors or possess intrinsic resistance to T-cell–mediated killing. ⁴ Secondary resistance can result from tumor cell changes such as genetic mutations or altered antigen presentation, making the cells less recognizable to the immune system. Upregulation of other inhibitory molecules or immune-suppressive factors can further dampen T-cell activity. Additionally, T-cell exhaustion, characterized by a state of dysfunction caused by chronic antigen exposure, and changes in the tumor microenvironment (TME) that enhance immunosuppression have also been implicated in acquired resistance.⁴

Resistance to anti-PD-1 therapy remains a significant clinical challenge, with primary resistance observed in 40% to 65% of patients and secondary resistance occurring in 25% to 30% of initial responders. ⁴ Given the complex and multifactorial nature of resistance, a variety of therapeutic combination strategies are currently under investigation to overcome these barriers and improve outcomes in patients with refractory melanoma.

Checkpoint inhibitor combinations: a key strategy

Combining ICIs has emerged as a pivotal strategy for patients with advanced melanoma who have progressed on prior anti–PD-1 or anti–PD-L1 therapies. One such approach involves the use of a cytotoxic T-lymphocyte–associated antigen 4 (CTLA-4) inhibitor, such as ipilimumab, in conjunction with continued PD-1 inhibition using nivolumab. ⁷

Inderjit Mehmi, MD, The Angeles Clinic and Research Institute, Los Angeles, CA, highlighted the importance of this approach:

“For single-agent PD-1 refractory cases, ipilimumab and nivolumab combinations, supported by the SWOG study, show around 30% response with some durability. It’s a reasonable option.”

The randomized Phase II SWOG S1616 trial (NCT03033576) evaluated this strategy by comparing ipilimumab alone versus ipilimumab plus nivolumab in patients with metastatic melanoma refractory to PD-1 or PD-L1 blockade. ⁷ The combination therapy demonstrated a statistically significant improvement in progression-free survival (PFS), with six-month PFS estimates of 34% compared to 13% for ipilimumab alone. Additionally, the objective response rate (ORR) was notably higher at 28% versus 9%, respectively. These findings suggest that continuing PD-1 blockade while adding CTLA-4 inhibition can help overcome primary resistance in a subset of patients. ⁷

Another approach involves targeting alternative immune checkpoints, such as lymphocyte-activation gene 3 (LAG-3), in combination with PD-1 inhibitors. ⁸ The Phase I/IIa RELATIVITY-020 trial (NCT01968109) assessed the efficacy and safety of nivolumab combined with relatlimab, an anti–LAG-3 antibody, in patients with advanced melanoma who had progressed during or within three months of receiving one or more prior anti–PD-(L)1–containing regimens.  The ORR, as assessed by blinded independent central review (BICR), was 12.0% in patients who had progressed on one prior anti–PD-1 regimen and 9.2% in those who had progressed on two or more. ⁸

Notably, the fixed-dose combination of nivolumab and relatlimab was approved by the FDA in March 2022 for previously untreated metastatic or unresectable melanoma, based on the results of the Phase III RELATIVITY-047 trial (NCT03470922). This trial demonstrated a statistically significant improvement in PFS, with a median PFS of 10.1 months for the combination therapy versus 4.6 months for nivolumab alone. ⁹ However, while this combination has demonstrated efficacy in the frontline setting, its effectiveness appears more limited in patients whose disease has already progressed on PD-1 inhibitors. Dr Mehmi remarked:

“For PD-1 refractory patients, LAG-3 combinations seem less effective. Trials by Regeneron and BMS show about 10–12% response rates with little durability. So PD-1/LAG-3 combinations might be considered when nothing else is left. Tumor-infiltrating lymphocytes (TIL) therapy may be more relevant.”

Tumor-infiltrating lymphocyte (TIL) therapy: a landmark advancement

TIL therapy has emerged as a significant advancement in treating advanced melanoma, especially for patients who have progressed after anti–PD-1 therapy. This personalized immunotherapy involves harvesting lymphocytes from a patient’s tumor, expanding them ex vivo, and reinfusing them following a lymphodepleting regimen to enhance their anti-tumor activity.

Allison Betof Warner, MD, Stanford Cancer Center, Stanford, CA, emphasized the transformative progress of this approach: “This was pioneered in the late 1980s by Dr Rosenberg at the National Cancer Institute. But over the last five years or so, we’ve seen real ability to centrally manufacture, ship these products, and develop this as a real commercial product that now has proven efficacy for PD-1 refractory melanoma.”

The efficacy of TIL therapy was demonstrated in the Phase II C-144-01 trial (NCT02360579), where lifileucel achieved an ORR of 31.5% in patients with unresectable or metastatic melanoma who had previously received anti–PD-1 therapy. The median duration of response (DOR) was not reached, suggesting durable benefit. ¹⁰ These promising results led to the FDA’s accelerated approval of lifileucel in February 2024, marking the first FDA-approved cell therapy for a solid tumor. ¹¹

In the Phase III M14TIL trial (NCT02278887) TIL therapy was directly compared with ipilimumab in patients with unresectable stage IIIC/IV melanoma refractory to PD-1 blockade. ¹² TIL therapy significantly improved outcomes, achieving a median PFS of 7.2 months vs. 3.1 months with ipilimumab, as well as higher ORR (48.8% vs. 21.4%) and complete response rate (CRR) (20.2% vs. 7.1%). A trend towards improved overall survival (OS) was also observed. While grade ≥3 adverse events were more frequent with TIL therapy (100% vs. 57%), most were chemotherapy-related and manageable.¹²

TIL therapy’s advantages include its personalized mechanism, potential for long-lasting remission, and effectiveness in PD-1-refractory disease. However, significant challenges remain, such as complex manufacturing, high costs, and the need to manage toxicity. To overcome these limitations, ongoing efforts are focused on optimizing lymphodepletion regimens to minimize toxicity and developing engineered TILs or T-cell receptor (TCR) therapies that target antigens like PRAME—which is expressed in over 90% of melanomas—with the goal of improving response rates and reducing cytokine-related toxicities. ¹³

Oncolytic virus therapy: RP1 and beyond

Oncolytic virus therapy represents a promising avenue for patients with advanced melanoma, particularly those who have progressed on prior anti–PD-1 or anti–CTLA-4 therapies. RP1 (vusolimogene oderparepvec), a genetically modified herpes simplex virus type 1, is engineered to selectively replicate within tumor cells, leading to direct oncolysis and the release of tumor-derived antigens, thereby enhancing systemic immune activation. ¹⁴

The Phase I/II IGNYTE trial (NCT03767348) evaluated RP1 in combination with nivolumab in patients with advanced melanoma. Among 140 participants, the confirmed ORR was 33.6%, with a CRR of 15%. ¹⁵ In patients with primary anti-PD-1 resistance, the ORR was 34.4%, and for those previously treated with both PD-1 and CTLA-4 inhibitors, the ORR was 26.2%. Treatment-related adverse events (TRAEs) were mostly low-grade, with 12.8% experiencing grade ≥3 TRAEs. Notably, responses were observed not only in lesions that were directly injected with the virus but also in distant, non-injected lesions, suggesting a systemic anti-tumor effect. This ability to induce responses beyond the local site of injection is a significant advantage, indicating a broader impact on tumor control. ¹⁶

Dr Mehmi noted “a lot of the time when we discuss these options with intralesional therapies, our mindset is, “is this just effective for that injected lesion?” However, RP1 data shows that that’s not true, that actually you can have responses, and they’ve shown that responses are possible in noninjected lesions as well. So I think that [RP1] is a really good option that’s going to be coming up, and hopefully it stands the test of a Phase III study.”

Building on the promising results IGNYTE trial, the confirmatory Phase III IGNYTE-3 trial (NCT06264180) is currently underway. ¹⁷ This randomized, controlled, multicenter study compares RP1 plus nivolumab versus physician’s choice of treatment in patients with advanced melanoma who have progressed on anti–PD-1 and anti–CTLA-4 therapies or are ineligible for anti–CTLA-4 treatment. The primary endpoint is OS, with key secondary endpoints including PFS and ORR. ¹⁷

Dr Betof-Warner underscored the potential of RP1 therapy:

“It’s important to note that [RP1] has gotten breakthrough designation by the FDA and the biologic license application (BLA) is now submitted for accelerated approval in 2025. So I do think that this becomes a strategy that we should absolutely be thinking about for our patients.”

Treatment sequencing and future considerations

Optimizing treatment sequencing remains one of the most pivotal challenges in melanoma management. For instance, the success of TIL therapy in later-line settings has sparked a debate surrounding its potential benefits when administered earlier in the treatment sequence. Indeed, retrospective analyses have suggested that prior treatment with anti-PD-1 therapy can diminish the efficacy of subsequent TIL therapy. ¹⁸ This has led to the hypothesis that administering TIL therapy earlier, before the tumor develops extensive resistance mechanisms or the patient’s immune system is significantly altered by prior treatments, might yield greater benefit. Dr Mehmi noted “We have had decades of understanding about early TIL being better. We know that in any type of T-cell therapy, less exposure to therapy gives you more vibrant cells.”

The Phase III M14TIL trial previously compared TIL therapy to the CTLA-4 inhibitor ipilimumab as a first- or second-line treatment in patients with advanced unresectable stage IIIC or IV melanoma, demonstrating improved PFS with TIL therapy. ¹² While this trial provides valuable comparative data, it is important to note that ipilimumab is now less commonly used as a first-line monotherapy for advanced melanoma, with PD-1 inhibitors or combination immunotherapy regimens being the more frequent initial treatment choices. ¹⁹ Therefore, the results of ongoing trials that compare TIL therapy to these current first-line standards will be crucial in determining its optimal placement in the treatment sequence.

Early results from Cohort 1A of the Phase II IOV-COM-202 trial (NCT03645928) evaluating lifileucel plus pembrolizumab demonstrated a high ORR of 65.2% in immune checkpoint inhibitor-naive unresectable or metastatic melanoma, including a 30.4% CRR. ²⁰ These results support the combinations further evaluation in the ongoing Phase III TILVANCE-301 trial (NCT04217473) comparing the efficacy of lifileucel in combination with pembrolizumab as a first-line treatment for unresectable or metastatic melanoma against pembrolizumab alone. ²¹ The results of this trial aim to establish whether TIL therapy combined with anti-PD1 can offer a superior first-line treatment option compared to the current standard of care.

Similarly, therapeutic cancer vaccines, such as IO102-IO103, are under investigation to enhance anti-PD1 in frontline melanoma therapy. IO102-IO103 is an investigational, off-the-shelf therapeutic cancer vaccine designed to target both tumor cells and immune-suppressive cells in the tumor microenvironment by stimulating the activation and expansion of T-cells against indoleamine 2,3-dioxygenase (IDO1) and/or PD-L1, both of which are overexpressed in melanoma, contributing to immune evasion. ²² By targeting these key immunosuppressive pathways within the tumor microenvironment, IO102-IO103 aims to create a more immunologically favorable environment that can enhance anti-tumor immune responses and potentially overcome resistance to checkpoint inhibitors in the frontline setting. ²²

A Phase I/II trial (NCT03047928) evaluating IO102-IO103 plus nivolumab in anti–PD-1 naïve metastatic melanoma demonstrated an 80% ORR, including a 47% CRR, with a favorable safety profile. ²³ The ongoing Phase III IOB-013/KN-D18 trial (NCT05155254) is investigating IO102-IO103 in combination with pembrolizumab in patients with previously untreated, unresectable, or metastatic melanoma. Data from this trial are anticipated in 2025, potentially expanding the evidence base for IO102-IO103’s efficacy in the frontline setting.​ ²⁴

These studies underscore the potential benefits of integrating TIL therapy and therapeutic cancer vaccines earlier in the treatment paradigm for advanced melanoma. Ongoing and future trials will be instrumental in defining the optimal sequencing and combination strategies to maximize patient outcomes.​

Conclusion

The therapeutic landscape for advanced melanoma is rapidly evolving, with innovative combination strategies offering renewed hope for patients in both frontline and PD-1 refractory settings. Personalized treatment plans, guided by patient-specific factors and emerging biomarkers, are essential to maximize efficacy and minimize adverse effects. Investigating the optimal sequencing of these novel therapies with existing treatment options, such as immune checkpoint inhibitors and targeted therapies, will be crucial for maximizing the clinical benefit for individual patients. The ongoing exploration of combination strategies involving immune checkpoint inhibitors, oncolytic viruses, TILs, and vaccines offers considerable promise for further improving patient outcomes and potentially achieving long-term control of advanced melanoma.​

Written by Ellie Jackson

Edited by Hannah Elkheir

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References:

1. Mehta A, Motavaf M, Nebo I, et al. Advancements in Melanoma Treatment: A Review of PD-1 Inhibitors, T-VEC, mRNA Vaccines, and Tumor-Infiltrating Lymphocyte Therapy in an Evolving Landscape of Immunotherapy. Journal of Clinical Medicine. 2025; 14(4):1200. https://doi.org/10.3390/jcm14041200
2. Chang E, Pelosof L, Lemery S, Gong Y, et al. Systematic Review of PD-1/PD-L1 Inhibitors in Oncology: From Personalized Medicine to Public Health, The Oncologist, Volume 26, Issue 10, October 2021, Pages e1786–e1799, https://doi.org/10.1002/onco.13887
3. Zielińska MK, Ciążyńska M, Sulejczak D, Rutkowski P, Czarnecka AM. Mechanisms of Resistance to Anti-PD-1 Immunotherapy in Melanoma and Strategies to Overcome It. Biomolecules. 2025; 15(2):269. https://doi.org/10.3390/biom15020269
4. Knight A, Karapetyan L, Kirkwood JM. Immunotherapy in Melanoma: Recent Advances and Future Directions. Cancers (Basel). 2023 Feb 9;15(4):1106. doi: 10.3390/cancers15041106. PMID: 36831449; PMCID: PMC9954703.
5. Kluger HM, Barrett JC, Gainor J, Hamid O, Hurwitz M, LaVallee T, et al. Defining tumor resistance to PD-1 pathway blockade: recommendations from the first meeting of the SITC Immunotherapy Resistance Taskforce. J Immunother Cancer. 2020;8(1):e000398.
6. Kluger H, Barrett JC, Gainor JF, et al. Society for Immunotherapy of Cancer (SITC) consensus definitions for resistance to combinations of immune checkpoint inhibitors. J Immunother Cancer. 2023 Mar;11(3):e005921. doi: 10.1136/jitc-2022-005921. PMID: 36918224; PMCID: PMC10016305.
7. Hodi FS, Chesney J, Pavlick AC, Robert C, et al. Combined nivolumab and ipilimumab versus ipilimumab alone in patients with advanced melanoma: 2-year overall survival outcomes in a multicentre, randomised, controlled, phase 2 trial. Lancet Oncol. 2016 Nov;17(11):1558-1568. doi: 10.1016/S1470-2045(16)30366-7. Epub 2016 Sep 9. PMID: 27622997; PMCID: PMC5630525.
8. Ascierto PA, Lipson EJ, Dummer R, et al. Nivolumab and Relatlimab in Patients With Advanced Melanoma That Had Progressed on Anti-Programmed Death-1/Programmed Death Ligand 1 Therapy: Results From the Phase I/IIa RELATIVITY-020 Trial. J Clin Oncol. 2023 May 20;41(15):2724-2735. doi: 10.1200/JCO.22.02072. Epub 2023 Feb 13. PMID: 36780608; PMCID: PMC10431305.
9. U.S. Food and Drug Administration approves first LAG-3-blocking antibody combination, Opdualag™ (nivolumab and relatlimab-rmbw), as treatment for patients with unresectable or metastatic melanoma. News release. Bristol Myers Squibb. March 18, 2022.
10. Keam SJ. Lifileucel: First Approval. Mol Diagn Ther. 2024 May;28(3):339-344. doi: 10.1007/s40291-024-00708-y. Epub 2024 Apr 16. PMID: 38625642.
11. Long GV, Hodi FS, Lipson EJ, et al. Relatlimab and nivolumab versus nivolumab in previously untreated metastatic or unresectable melanoma: Overall survival and response rates from RELATIVITY-047 (CA224-047). Presented at: ASCO Plenary Series: March 2022 Session; March 15, 2022; virtual. Abstract 360385. https://bit.ly/3KNB9KM
12. Parums DV. Editorial: First Regulatory Approval for Adoptive Cell Therapy with Autologous Tumor-Infiltrating Lymphocytes (TILs) – Lifileucel (Amtagvi). Med Sci Monit. 2024 May 1;30:e944927. doi: 10.12659/MSM.944927. PMID: 38689550; PMCID: PMC11071689.
13. Haanen J, Los C, Phan GQ, Betof Warner A. Adoptive Cell Therapy for Solid Tumors: Current Status in Melanoma and Next-Generation Therapies. Am Soc Clin Oncol Educ Book. 2024 Jun;44(3):e431608. doi: 10.1200/EDBK_431608. PMID: 38776509.
14. Nassief G, Anaeme A, Moussa K, Mansour AN, Ansstas G. Recent Advancements in Cell-Based Therapies in Melanoma. International Journal of Molecular Sciences. 2024; 25(18):9848. https://doi.org/10.3390/ijms25189848
15. Wong MKK, Sacco JJ, Robert C, et al. Efficacy and safety of RP1 combined with nivolumab in patients with anti–PD-1–failed melanoma from the IGNYTE clinical trial. J Clin Oncol. 2024;42(suppl 16):9517. doi:10.1200/JCO.2024.42.16_suppl.9517
16. Replimune Presents Primary Analysis Data from IGNYTE Clinical Trial of RP1 Combined with Nivolumab in Anti-PD1 Failed Melanoma at European Society for Medical Oncology (ESMO) Congress 2024 | Replimune [Internet]. Replimune. 2024 [cited 2025 Jun 10]. Available from: https://ir.replimune.com/news-releases/news-release-details/replimune-presents-primary-analysis-data-ignyte-clinical-trial
17. IGNYTE-3 Trial: Harnessing the Power of Viruses to Activate the Immune System and Treat Advanced Melanoma – Melanoma Research Alliance [Internet]. Curemelanoma.org. 2024. Available from: https://www.curemelanoma.org/blog/ignyte-3-trial-harnessing-the-power-of-viruses-to-activate-the-immune-system-and-treat-advanced-melanoma
18. Smithy, JW, Schoenfeld, AJ and Warner, AB (2025). The Clinical TIL Experience in Melanoma: Past, Present, Future. Transplantation and Cellular Therapy, 31(3), pp.S626–S634. doi:https://doi.org/10.1016/j.jtct.2024.11.013.
19. Rohaan MW, Borch TH, van den Berg JH, Met Ö, et al. Tumor-Infiltrating Lymphocyte Therapy or Ipilimumab in Advanced Melanoma. N Engl J Med. 2022 Dec 8;387(23):2113-2125. doi: 10.1056/NEJMoa2210233. PMID: 36477031.
20. SS Thomas, Gogas H, Hong YK, et al. efficacy and safety of lifileucel, an autologous tumor-infiltrating lymphocyte cell therapy, and pembrolizumab in patients with immune checkpoint inhibitor-naive unresectable or metastatic melanoma: Updated results from IOV-COM-202 cohort 1A. Journal of Clinical Oncology. 9505-9505(2024). DOI:10.1200/JCO.2024.42.16_suppl.9505
21. Olson DJ, Larkin J, Hong Y, et al. 778 TILVANCE-301, a phase 3 study of lifileucel tumor-infiltrating lymphocyte (TIL) cell therapy combined with pembrolizumab (pembro) vs pembro alone in treatment-naïve unresectable or metastatic melanoma. Journal for ImmunoTherapy of Cancer 2023;11:doi: 10.1136/jitc-2023-SITC2023.0778
22. IO Biotech Completes Enrollment in Phase 2 Trial of its Investigational, Off-the-shelf Therapeutic Cancer Vaccine, IO102-IO103, as Neoadjuvant/Adjuvant Treatment for Patients with Resectable Melanoma or Head and Neck Cancer. Iobiotech.com. Available from: https://investors.iobiotech.com/news-events/news/news-details/2025/IO-Biotech-Completes-Enrollment-in-Phase-2-Trial-of-its-Investigational-Off-the-shelf-Therapeutic-Cancer-Vaccine-IO102-IO103-as-NeoadjuvantAdjuvant-Treatment-for-Patients-with-Resectable-Melanoma-or-Head-and-Neck-Cancer/default.aspx
23. Kjeldsen JW, Lorentzen CL, Martinenaite E, et al. A phase 1/2 trial of an immune-modulatory vaccine against IDO/PD-L1 in combination with nivolumab in metastatic melanoma. Nat Med. 2021 Dec;27(12):2212-2223. doi: 10.1038/s41591-021-01544-x. Epub 2021 Dec 9. Erratum in: Nat Med. 2022 Apr;28(4):871. doi: 10.1038/s41591-022-01771-w. PMID: 34887574; PMCID: PMC8904254.
24. O Biotech Updates on Pivotal Phase 3 Trial of IO102-IO103 in Combination with KEYTRUDA® (pembrolizumab) as a First-Line Treatment for Patients with Advanced Melanoma [Internet]. Iobiotech.com. 2023 [cited 2025 Jun 10]. Available from: https://investors.iobiotech.com/news-events/news/news-details/2024/IO-Biotech-Updates-on-Pivotal-Phase-3-Trial-of-IO102-IO103-in-Combination-with-KEYTRUDA-pembrolizumab-as-a-First-Line-Treatment-for-Patients-with-Advanced-Melanoma/default.aspx