ACT is a form of precision immunotherapy in which a patient’s own immune cells are extracted, expanded or genetically modified in the laboratory to sharpen their tumor-killing capacity, and then reinfused into the body. The approach encompasses several distinct modalities: tumor-infiltrating lymphocyte therapy, chimeric antigen receptor T cell therapy, T cell receptor-engineered T cell therapy, and emerging strategies built on natural killer cells, dendritic cells, and gamma-delta T cells. The review arrives at a pivotal moment. Targeted therapies against BRAF and NRAS mutations and immune checkpoint inhibitors targeting PD-1 and CTLA-4 have already transformed advanced melanoma care, with pembrolizumab demonstrating an objective response rate of fifty-six percent after its 2014 approval. Yet nearly half of patients either resist these drugs from the start or acquire resistance during treatment, leaving an urgent need for more durable options.

The clearest success story belongs to TIL therapy, which harvests lymphocytes that have already infiltrated a patient’s tumor, expands them massively in culture, and returns them after a round of non-myeloablative lymphodepleting chemotherapy followed by several days of interleukin-2 support. Pioneered clinically by Steven Rosenberg in the 1980s, the approach exploits melanoma’s high mutational burden and dense immune infiltration. A systematic analysis of thirteen trials conducted between 1988 and 2016 found an overall response rate of forty-one percent, with fourteen percent of patients achieving complete responses, among 410 advanced melanoma patients treated with TILs plus interleukin-2. More recent data have been equally striking: a multicenter Phase II trial reported an objective response rate of 31.4 percent among 153 patients whose disease had resisted immunotherapy, with survival rates of 54 percent at one year and nearly 22 percent at four years.

Those results culminated in a historic milestone. On February 16, 2024, lifileucel, a TIL product developed by Iovance Biotherapeutics, became the first TIL-based therapy ever approved by the U.S. Food and Drug Administration, indicated for advanced melanoma refractory to PD-1 or PD-L1 checkpoint inhibitors. A Phase III trial further strengthened the case, showing that TIL therapy achieved a forty-nine percent objective response rate and outperformed the CTLA-4 inhibitor ipilimumab in patients whose tumors had progressed on PD-1 blockade, while also improving quality of life and physical function. Even in uveal melanoma, a rare subtype notoriously resistant to immunotherapy, TIL therapy produced responses in thirty-five percent of patients. The review notes that TILs carry inherent advantages: their broad T cell receptor diversity allows them to recognize many tumor antigens simultaneously, reducing off-target toxicity, and their natural origin within the tumor confers superior homing ability compared with engineered cells directed at a single antigen.

TIL therapy is not without weaknesses, however. Prolonged exposure to tumor antigens can drive functional exhaustion in the very cells that matter most, and tumors harbor large populations of bystander T cells that recognize nothing and contribute little cytotoxic activity. The manufacturing process is labor-intensive, technically demanding, and expensive, limiting broad accessibility. Metabolic reprogramming offers one route forward: studies show that overexpressing PGC-1alpha, a master regulator of mitochondrial biogenesis, restores metabolic fitness and expansion capacity in exhausted TILs, enhancing memory CD8-positive T cell formation and antitumor activity. Such interventions represent a growing toolkit for rejuvenating cells that would otherwise fade before finishing the job.

CAR-T therapy, by contrast, takes a fully engineered approach. T cells are modified to express a chimeric receptor combining an antibody-derived antigen-binding fragment with T cell signaling domains, allowing them to kill tumor cells independently of MHC presentation, thereby sidestepping a common immune-evasion trick. The technology has advanced through five generations, from a simple receptor coupled to CD3ζ signaling, through designs incorporating CD28 or 4-1BB costimulatory domains, to fourth-generation cells that secrete cytokines such as IL-12 or IL-15 to remodel the tumor microenvironment, and fifth-generation platforms that integrate CRISPR-Cas9 editing for scalable manufacturing. CAR-T has delivered dramatic results in blood cancers since tisagenlecleucel’s 2017 approval, but melanoma has proven far harder. The only published clinical trial, targeting VEGFR2 in twenty-four melanoma patients, produced no objective responses and was terminated early. Preclinical work continues against targets including GD2, c-Met, CD70, gp100, and NY-ESO-1, with one Phase I study testing vaccine-primed CAR-T cells to promote in vivo expansion in relapsed melanoma.

TCR-T therapy occupies a middle ground, engineering peripheral blood T cells to express receptors with known specificity for tumor antigens presented on MHC molecules, granting access to intracellular targets that antibodies cannot reach. Melanoma supplied the field’s founding antigens, MART-1 and gp100, and early trials showed promise: a 2006 study achieved remission in two of thirteen metastatic melanoma patients, while later work with high-affinity MART-1 receptors reached a thirty percent response rate and NY-ESO-1-targeted cells achieved forty-five percent in metastatic melanoma. The approach has since earned its first approval in synovial sarcoma with afamitresgene autoleucel, and TCR-T cells targeting the HPV oncoprotein E7 have shown fifty percent response rates in virus-driven cancers. Key limitations persist, however, including MHC restriction, tumor downregulation of MHC expression, off-tumor toxicity in normal tissues, and the difficulty of identifying receptors with ideal specificity and affinity.

The review’s forward-looking section maps five optimization frontiers. Enriching tumor-reactive T cells, whether through peptide-MHC multimer sorting, neoantigen-guided expansion informed by whole-exome and RNA sequencing, or selection of activation markers such as CD137, promises to strip away useless bystander cells and concentrate therapeutic firepower. Multi-target CAR designs, such as tandem receptors against CD70 and B7-H3, counter antigen escape, while bispecific chimeric TCRs and HLA-agnostic screening platforms bypass MHC restrictions. To improve infiltration and persistence, engineers are arming cells with chemokine receptors like CXCR2 to home in on CXCL1-producing melanoma cells, expressing heparanase to digest the dense extracellular matrix, knocking out PD-1 or AKT genes via CRISPR, and deploying armored CARs that secrete IL-12 or IL-18 to recruit supportive macrophages and suppress regulatory T cells. Safety innovations, including inducible caspase-9 suicide switches and controllable CAR platforms, aim to tame cytokine release syndrome and neurotoxicity.

Combination strategies may ultimately prove decisive. Oncolytic viruses delivered systemically can inflame tumors and dual-activate CAR-T cells through both engineered and natural antigen recognition, significantly prolonging survival in mouse models. Photothermal therapy using PLGA-ICG nanoparticles disrupts tumor stroma and boosts T cell infiltration, while pairing TIL therapy with PD-1 inhibitors or PD-1-knockout melanoma-specific T cells with alpha-particle-conjugated PD-L1 blockers has produced synergistic effects in preclinical studies. The authors conclude that while tumor heterogeneity, immunosuppressive microenvironments, manufacturing complexity, and toxicity remain formidable barriers, advances in genetic engineering, single-cell sequencing, and artificial intelligence-driven antigen discovery are converging to address them. If cost-effective manufacturing and validated combinations follow, adoptive cell therapy could evolve from a specialized achievement into a cornerstone of melanoma treatment and, eventually, of solid tumor medicine more broadly.

Subject of Research: Adoptive cell therapy strategies, including TIL, CAR-T, and TCR-T approaches, for treating advanced melanoma

Article Title: Application and Advances of Adoptive Cell Therapy for Melanoma

Article References: Wei, C., Xie, L., Wei, C., & Gu, J. (2025). Application and Advances of Adoptive Cell Therapy for Melanoma. Clinical Cancer Bulletin, 4(1), Article 17. https://doi.org/10.1007/s44272-025-00045-z

Image Credits: AI Generated

DOI: 10.1007/s44272-025-00045-z

Keywords: melanoma, adoptive cell therapy, TIL therapy, CAR-T, TCR-T, lifileucel, immunotherapy, tumor microenvironment, CRISPR, immune checkpoint inhibitors, oncolytic viruses, cancer immunotherapy

The clinical foundation of TIL therapy rests on a deceptively simple concept. Tumor-infiltrating lymphocytes, primarily cytotoxic CD8-positive T cells and helper CD4-positive T cells, migrate from peripheral blood into the tumor microenvironment, where they recognize and attack malignant cells through direct cytotoxicity. Adoptive cell therapy with autologous TILs amplifies this natural response: tumor-resident T cells are isolated from excised tumor tissue, expanded to billions in the laboratory, and returned to the patient after a non-myeloablative lymphodepleting chemotherapy regimen designed to clear immunosuppressive cells and cytokine sinks. The protocol that underpins most current regimens, including the FDA-approved product lifileucel, traces directly to the pioneering work of Steven Rosenberg’s laboratory at the U.S. National Cancer Institute, with only minor modifications accumulated over decades.

The clinical evidence base is now substantial. In 2024, the U.S. Food and Drug Administration approved lifileucel as the first autologous TIL product for patients with advanced cutaneous melanoma, a landmark moment for the field. A meta-analysis of 13 studies employing high-dose interleukin-2 in TIL therapy, encompassing 617 patients with advanced cutaneous melanoma including some with brain metastases, reported an objective response rate of 34 percent among patients previously treated with anti-PD-(L)1 agents and 44 percent among those without such prior treatment. Notably, the analysis found no statistically significant difference in objective response or complete response rates between the two groups, suggesting that interleukin-2’s immunomodulatory effects allow TIL therapy to retain benefit even after checkpoint inhibitor failure. Recent studies of patients refractory to immune checkpoint inhibitors or targeted therapies have shown objective response rates of 28 to 49 percent in melanoma resistant to standard treatments.

The reach of TIL therapy now extends well beyond melanoma. In non-small cell lung cancer, the IOV-COM-202 trial tested lifileucel in two cohorts following the same nonmyeloablative lymphodepletion regimen of cyclophosphamide and fludarabine, a single TIL infusion, and up to six doses of high-dose interleukin-2. Cohort 3B, comprising 28 patients with immunosuppressant-resistant metastatic disease, achieved an objective response rate of 21.4 percent after a median follow-up of 16 months. Cohort 3A, in checkpoint inhibitor-naive patients receiving pembrolizumab before lymphodepletion, showed a striking 64.3 percent objective response rate in the EGFR-wildtype subgroup at a median follow-up of 25.6 months. In cervical cancer, a National Cancer Institute phase 2 trial of 18 patients with HPV16- or HPV18-positive disease reported a 28 percent response rate, including two durable complete responses lasting 67 and 53 months, while a multicenter study by Iovance Biotherapeutics in checkpoint-naive advanced cervical cancer achieved a 44 percent objective response rate among 27 patients. Meta-analytic estimates suggest objective response rates of up to 26.3 percent across gynecologic cancers, and early signals of activity have emerged in colorectal cancer, cholangiocarcinoma, breast cancer, head and neck squamous cell carcinoma, and pancreatic ductal adenocarcinoma.

Understanding why interleukin-2 is both indispensable and hazardous requires a look at its receptor biology. The interleukin-2 receptor is a heterotrimeric protein composed of alpha (CD25), beta (CD122) and gamma (CD132) subunits, whose variable expression across immune cell types produces the cytokine’s diverse functional effects. Preclinical work has established the beneficial face of interleukin-2 signaling. Trentin and colleagues, studying TILs from 16 patients with solid tumors, demonstrated that interleukin-2 signaling through CD122 and CD25 promotes TIL proliferation and functional activation, marked by increased activity in the JAK/STAT pathway. Interleukin-2 also enhances cytotoxic function by boosting secretion of interferon-gamma and tumor necrosis factor-alpha, cytokines that directly inhibit tumor growth. In one in vitro study, interleukin-2 exposure led to downregulation of PD-1 on CD8-positive tumor-specific TILs, hinting at a mechanism for potentiating anti-tumor activity. The historical arc began in 1986, when Rosenberg’s group showed in murine models that interleukin-2 supplementation improves TIL efficacy, and culminated in a 1988 clinical trial combining TIL therapy with high-dose interleukin-2 that achieved a 60 percent objective response rate in previously untreated advanced melanoma patients. The standard regimen that followed, delivering at least 720,000 international units per kilogram intravenously every eight hours until dose-limiting toxicity or tolerance, has anchored metastatic melanoma treatment for more than 30 years.

The adverse face of interleukin-2, however, is impossible to ignore. In a clinical study of 391 patients, 87 percent experienced hypotension and 73 percent developed vascular leak syndrome or edema after high-dose treatment. Activation of CD25 on endothelial cells appears to contribute to these effects. Vascular leak syndrome induces hypovolemia that cascades into multi-organ dysfunction affecting the heart, kidneys, gastrointestinal tract and brain, producing reduced perfusion, ischemia, oliguria and neurological symptoms including confusion. In the pulmonary vasculature it can cause congestion and dyspnea, with severity increasing under continuous interleukin-2 therapy. The black box warning for high-dose interleukin-2 mandates intensive care monitoring due to the risk of acute kidney injury from renal hypoperfusion and cytokine-mediated neurotoxicity. Lifileucel, despite its efficacy, carries a treatment-related mortality rate of 7.5 percent, and its label restricts administration to trained clinicians at specialized facilities. The trial record is sobering: Creelan and colleagues reported two early deaths in patients with anti-PD-1-resistant metastatic lung cancer linked to rapidly progressive disease combined with the physiological stress of lymphodepletion and interleukin-2, and the IOV-LUN-202 trial in advanced non-small cell lung cancer was halted by the FDA in December 2023 following a treatment-related death.

Perhaps the most provocative findings concern interleukin-2’s subtler immunological sabotage. Work by Liu and colleagues and recent single-cell analyses show that interleukin-2 drives exhaustion of tumor-reactive CD8-positive T cells. In the absence of CD3/CD28 co-stimulation, interleukin-2 alone does not impair cytokine production but increases expression of the inhibitory receptors PD-1, LAG-3 and TIM-3. Prolonged high-dose exposure causes sustained STAT5 activation, which increases tryptophan hydroxylase-1 activity and enhances inhibitory receptor signaling, progressively degrading cytokine and effector molecule production. Single-cell transcriptomic and epigenetic studies trace the full exhaustion trajectory: prolonged interleukin-2 signaling pushes T cells from progenitor-like to terminally exhausted subsets, sequentially activating exhaustion-associated transcriptional programs such as TOX and NR4A while eroding memory-related gene expression. The tumor microenvironment compounds the problem, as hypoxia, nutrient competition, and immunosuppressive factors like TGF-beta and prostaglandin E2 interact with interleukin-2 to reinforce exhaustion-associated epigenetic programs. High CD25 expression also gives regulatory T cells a competitive advantage in capturing interleukin-2, allowing them to outcompete cytotoxic T cells and suppress the anti-tumor response, which in turn necessitates intensive lymphodepletion with its own toxicities.

The search for interleukin-2-independent TIL therapy has therefore become the field’s most active frontier. The clearest clinical success to date is GC101, developed by Shanghai Juncell Therapeutics as the first reported TIL therapy that eliminates post-infusion interleukin-2 altogether. GC101 is cultured in a pre-rapid expansion protocol medium containing interleukin-2, interleukin-7 and interleukin-15, followed by expansion with low-dose interleukin-2 at 300 international units per milliliter, allowing the final product to function without exogenous interleukin-2 after transfer. It uses a three-day lymphodepletion regimen of cyclophosphamide with hydroxychloroquine, and in phase 1 trials involving 14 evaluable patients with advanced gynecologic cancers achieved a 36 percent objective response rate, including complete remission in a patient with recurrent cervical cancer. Critically, GC101 can be administered entirely in general wards rather than intensive care units, improving safety and reducing costs. It has now advanced to a pivotal phase 2 randomized controlled trial in melanoma. Genetic engineering offers a parallel route: GC203, engineered to constitutively express membrane-bound interleukin-7, showed no grade 3 or higher non-hematologic adverse events in the first 18 ovarian cancer patients treated, while OBX-115 from Obsidian Therapeutics, expressing regulated membrane-bound interleukin-15, demonstrated in preliminary data from 10 patients an improved safety profile with no grade 4 or higher and only limited grade 3 non-hematologic events. Earlier attempts carry cautionary lessons, however: TILs engineered to secrete interleukin-12 achieved a 63 percent response rate in a 2015 first-in-human study but the trial was terminated early after life-threatening hemodynamic instability from interleukin-12 toxicity. CRISPR-based approaches are also emerging, with KSQ Therapeutics knocking out SOCS1 and Regnase-1 to enhance T cell activation, now in ongoing clinical trials.

The review’s authors are careful to separate proof-of-concept promise from validated clinical reality. Current engineered TIL evidence rests on small patient numbers, lacks randomized controlled trials, and involves short follow-up, while personalized genetic modification imposes stringent quality control demands and high production costs that limit scalability. Potential risks of sustained cytokine expression and CRISPR off-target effects demand careful trial design and long-term monitoring. Still, the strategic direction is clear. In the near term, the authors argue for predictive biomarkers incorporating T-cell exhaustion signatures, stem-like progenitor frequency and tumor microenvironment features to guide patient selection, alongside comparative studies to refine lymphodepletion regimens. Looking ahead, they call for next-generation interleukin-2 analogs that selectively stimulate effector T cells while sparing regulatory T cells, electroporation-based engineering as a safer alternative to viral vectors, and combination strategies with checkpoint inhibitors, targeted therapies or oncolytic viruses. If the field succeeds on both fronts, biologically precise interleukin-2-independent engineering and scalable, cost-effective manufacturing, TIL therapy could establish itself as a cornerstone of precision oncology for treatment-refractory solid tumors, finally resolving the paradox that interleukin-2 has imposed on cancer immunotherapy for nearly forty years.

Subject of Research: The dual role of interleukin-2 in tumor-infiltrating lymphocyte therapy for solid tumors

Article Title: Dual role of interleukin-2 in tumor-infiltrating lymphocyte therapy

Article References: Dual role of interleukin-2 in tumor-infiltrating lymphocyte therapy. (n.d.). https://doi.org/10.1007/s44272-026-00059-1

Image Credits: AI Generated

DOI: 10.1007/s44272-026-00059-1

Keywords: tumor-infiltrating lymphocytes, interleukin-2, TIL therapy, immunotherapy, solid tumors, lifileucel, melanoma, vascular leak syndrome, T cell exhaustion, engineered TIL, GC101, cancer immunotherapy