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Cellular therapy, vaccines and resistance in melanoma

TL;DR — Tumour-infiltrating lymphocyte therapy is the first cellular therapy with randomised evidence in a solid tumour: in 168 patients with unresectable stage IIIC/IV melanoma (86% refractory to anti-PD-1), TIL therapy gave median progression-free survival 7.2 months (95% CI 4.2–13.1) versus 3.1 months (3.0–4.3) with ipilimumab (HR 0.50, 0.35–0.72, P < .001), objective response 49% versus 21%, and median overall survival 25.8 versus 18.9 months (Rohaan 2022, PMID 36477031). The commercial product lifileucel produced an objective response rate of 31.4% (24.1–39.4) in 153 heavily pretreated patients with a median 3 prior lines and 54.2% having raised LDH, with median duration of response not reached at 27.6 months (Chesney 2022, PMID 36600653). Individualised neoantigen mRNA therapy added to adjuvant pembrolizumab improved recurrence-free survival in KEYNOTE-942 (HR 0.561, 95% CI 0.309–1.017, two-sided P = .053 at 23–24 months; HR 0.510, 0.294–0.887 at a median 60.3 months, with DMFS HR 0.411, 0.200–0.843) (Weber 2024, PMID 38246194; Khattak 2026, PMID 42223134). Resistance to PD-1 blockade is now formally defined by SITC consensus, and applying those definitions to 55 studies gives primary resistance in roughly 35% of first-line and 42% of later-line anti-PD-1 monotherapy patients (Shui 2022, PMID 36223314).

Tumour-infiltrating lymphocyte therapy

Study Design Result
M14TIL (Rohaan 2022, PMID 36477031) Phase 3, multicentre, open-label; 168 patients with unresectable stage IIIC/IV melanoma randomised 1:1 to TIL (≥5×10⁹ cells after non-myeloablative cyclophosphamide–fludarabine lymphodepletion, followed by high-dose IL-2) or ipilimumab 3 mg/kg. 86% refractory to anti-PD-1 Median PFS 7.2 months (4.2–13.1) vs 3.1 (3.0–4.3), HR 0.50 (0.35–0.72), P < .001. Objective response 49% (38–60) vs 21% (13–32). Median OS 25.8 months (18.2–NR) vs 18.9 (13.8–32.6)
C-144-01 initial cohort (Sarnaik 2021, PMID 33979178) Phase 2, open-label, single-arm, multicentre; 66 patients previously treated with checkpoint inhibitors and BRAF ± MEK agents; 22-day centralised manufacture, lymphodepletion, single lifileucel infusion, up to six doses high-dose IL-2 Mean 3.3 prior therapies (100% anti-PD-(L)1, 80% anti-CTLA-4, 23% BRAF ± MEK). ORR 36% (25–49) with 2 complete and 22 partial responses; disease control 80% (69–89); median duration of response not reached at 18.7 months median follow-up. In the anti-PD-(L)1-primary-refractory subset, ORR 41% (26–57)
C-144-01 pooled cohorts (Chesney 2022, PMID 36600653) 153 patients treated; median 3.0 prior lines, 81.7% had both anti-PD-1 and anti-CTLA-4; median target-lesion sum of diameters 97.8 mm; LDH above upper limit of normal in 54.2% ORR 31.4% (24.1–39.4) by independent review, 8 complete and 40 partial responses; median duration of response not reached at 27.6 months median follow-up, with 41.7% of responses ongoing

TIL therapy's evidence base is unusual in two ways. It is randomised — rare for a cellular therapy in solid tumours — and its comparator, ipilimumab, is a real active drug rather than best supportive care. But the regimen requires tumour resection, three weeks of centralised manufacture, non-myeloablative lymphodepleting chemotherapy and high-dose IL-2, which restricts it to fit patients at specialist centres.

The IL-2 component carries its own history: in 270 patients treated with high-dose IL-2 across eight trials 1985–1993, the objective response rate was 16% (95% CI 12–21) with 6% complete and 10% partial responses, median response duration not reached for complete responders, and no patient responding beyond 30 months subsequently progressed (Atkins 1999, PMID 10561265). That durability signal in a small fraction is the direct ancestor of the checkpoint-blockade plateau described in immunotherapy in advanced disease.

What limits delivery

TIL therapy is a manufacturing process as much as a drug. A systematic review and meta-analysis searching PubMed, Scopus, CENTRAL and the WHO ICTRP from inception to 31 December 2025 restricted quantitative synthesis to clinically comparable cohorts — predominantly melanoma studies reporting objective response rate — and synthesised survival, safety, manufacturing success and resection-to-infusion time narratively because of clinical and methodological heterogeneity (Surendran 2026, PMID 42558559). Manufacturing success and time-to-infusion are the variables that determine whether a patient with progressing disease actually receives the therapy, and they are reported inconsistently across the trials in the table above. Lifileucel's 22-day centralised manufacturing process is stated explicitly in both C-144-01 reports (PMID 33979178; PMID 36600653), which is unusual and useful.

Oncolytic and intralesional therapy

Talimogene laherparepvec (oncolytic HSV-1 expressing GM-CSF) is the only intralesional agent with a positive randomised phase 3 trial. In OPTiM's final analysis, 436 patients with unresectable stage III–IV melanoma were randomised 2:1; at median 49 months' follow-up median overall survival was 23.3 months (95% CI 19.5–29.6) versus 18.9 (16.0–23.7) for GM-CSF (unstratified HR 0.79, 0.62–1.00, P = .0494, descriptive). Durable response rate was 19.0% versus 1.4% (unadjusted OR 16.6, 4.0–69.2, P < .0001), objective response 31.5% versus 6.4%, and complete response in 50 patients (16.9%) versus 1 (0.7%) (Andtbacka 2019, PMID 31171039). Its role is largely in in-transit disease — see surgical management and margins. Other intralesional approaches (PV-10, IL-2, imiquimod, diphenylcyclopropenone) have data too sparse for meta-analysis (Read 2019, PMID 30734295).

The IL-2 component and its own history

High-dose interleukin-2 is a required component of the TIL regimen in both the randomised trial and the commercial protocol (PMID 36477031; PMID 33979178), and it carries a fifty-year record of its own. Across 270 assessable patients enrolled in eight clinical trials between 1985 and 1993, receiving 600,000 or 720,000 IU/kg by 15-minute intravenous infusion every 8 hours for up to 14 consecutive doses over 5 days with maximum support including pressors: the overall objective response rate was 16% (95% CI 12–21) with 17 complete (6%) and 26 partial responses (10%); median response duration was not reached for complete responders and was 5.9 months for partial responders; 12 of 43 responding patients (28%) including 10 of 17 complete responders (59%) remained progression-free; and no patient responding for more than 30 months subsequently progressed (Atkins 1999, PMID 10561265). Single-centre experience with high-dose IL-2 in the modern era, including in brain metastases, has been reported (PMID 28923120; PMID 19846971), as has durable complete response to intralesional IL-2 for in-transit disease (PMID 33529083).

That 16% response rate with a durable tail is the shape checkpoint blockade later reproduced at a higher level (PMID 25667295), and it is why the field expected a plateau before it had one.

Individualised neoantigen therapy

Analysis Design Result
KEYNOTE-942 primary (Weber 2024, PMID 38246194; NCT03897881) Open-label randomised phase 2b, adjuvant; 157 patients with completely resected stage IIIB–IV cutaneous melanoma assigned 2:1 to mRNA-4157 (max 9 intramuscular doses) plus pembrolizumab (max 18 doses) or pembrolizumab alone; USA and Australia Median follow-up 23 and 24 months. Recurrence-free survival HR 0.561 (95% CI 0.309–1.017), two-sided P = .053
KEYNOTE-942 5-year update (Khattak 2026, PMID 42223134) Same cohort, data cutoff December 2025, median planned follow-up 60.3 months (range 50.5–76.4); descriptive analyses RFS HR 0.510 (0.294–0.887); DMFS HR 0.411 (0.200–0.843)

The primary analysis did not meet conventional significance (P = .053) and the five-year analyses are explicitly descriptive; the agent (now intismeran autogene) is being tested in phase 3. Broader mRNA-vaccine strategy and adjuvant-vaccine comparisons have been reviewed (PMID 41002441; PMID 40573987).

Resistance: definitions first

The field's terminology was harmonised by SITC consensus, which supplies definitions for primary resistance, secondary resistance and resistance after stopping therapy, for both single-agent PD-(L)1 inhibitors and combinations (Kluger 2023, PMID 37487665). Applying those definitions systematically to 55 studies, and to the 37 that specified progression by best overall response, gives primary resistance in a median 35.50% (range 21.19–39.13%) of first-line and 41.54% (30.00–56.41%) of second-line-or-later anti-PD-1 monotherapy patients (Shui 2022, PMID 36223314). Roughly a third to a half of patients never respond, which is the size of the problem cellular therapy addresses.

Mechanisms of resistance

Programme Evidence
Loss of antigen expression Tumour-intrinsic IFN-γ signalling and melanoma dedifferentiation cause loss of wild-type differentiation antigens (Lim 2023, PMID 36934113)
Disrupted antigen presentation Multiple independent mechanisms affecting MHC expression (PMID 36934113); truncating B2M mutation abolishing surface MHC class I in an acquired-resistance biopsy (Zaretsky 2016, PMID 27433843)
Loss of IFN-γ responsiveness Loss-of-function JAK1 or JAK2 mutations with wild-type allele deletion, producing insensitivity to IFN-γ including its antiproliferative effects (PMID 27433843); conserved IFN-γ transcriptome response absent when the receptor is altered (Grasso 2020, PMID 32916126)
Immune exclusion PTEN loss reduces T-cell trafficking and infiltration, correlates with lower success of TIL expansion from resected tumours and inferior anti-PD-1 outcomes; PI3Kβ inhibition improved checkpoint efficacy in mice (Peng 2016, PMID 26645196; PMID 36934113)
Non-genetic phenotype switching MITF-high and MITF-low/AXL-high transcriptional states coexist in every tumour profiled at single-cell resolution, the latter carrying a drug-resistance programme (Tirosh 2016, PMID 27124452); MAFG–MITF and BRN2:MYC axes proposed as drivers (PMID 42168173; PMID 41405996)
Absent tertiary lymphoid structure T cells in TLS-negative tumours show a dysfunctional molecular phenotype (Cabrita 2020, PMID 31942071)
MAPK-pathway resistance (targeted therapy) BRAF splice variants, BRAF amplification, NRAS and MEK1/2 mutations reactivating MAPK; PD-L1 induction reverts the microenvironment to low immunogenicity (Proietti 2020, PMID 33003483; Rizos 2014, PMID 24463458)

The recurring structural point is that the IFN-γ axis is simultaneously the mechanism of checkpoint response and, when genetically disrupted or chronically engaged, a route to resistance (PMID 32916126; PMID 27433843; PMID 36934113). Lim's three-programme taxonomy places compromised antigen production and presentation as the dominant mechanism and argues for salvage strategies aimed at restoring MHC expression, stimulating innate immunity and re-expressing wild-type differentiation antigens (PMID 36934113) — which is a mechanistic rationale for TIL therapy and for oncolytic agents rather than for further checkpoint blockade.

What to do after checkpoint failure

Option Evidence quality
TIL therapy Randomised phase 3 in an 86% anti-PD-1-refractory population (PMID 36477031); commercial product with pooled phase 2 data (PMID 36600653)
Rechallenge / retreatment Retrospective series and meta-analyses only (Nardin 2023, PMID 37509227; PMID 41202502; PMID 39726701)
Targeted therapy in BRAF-mutant disease DREAMseq arm C response rate 47.8% after immunotherapy (Atkins 2023, PMID 36166727)
Oncolytic therapy Positive randomised trial in unresectable stage III–IV disease with a descriptive primary analysis (PMID 31171039)
Anti-PD-1 plus tyrosine-kinase inhibitor Retrospective comparison against chemotherapy after PD-1/CTLA-4 failure (PMID 39435288)
Chemotherapy Historical comparator; no modern randomised support

What is being tested next

Trial Approach Status (verified 2026-09-01)
NCT05727904 Lifileucel regimen plus pembrolizumab versus pembrolizumab alone in untreated advanced melanoma — moving TIL therapy to first line Recruiting, n = 670, primary completion 2028-03-01
NCT06743126 (SUPRAME) ACTengine IMA203, a TCR-engineered T-cell product, versus investigator's choice in previously treated unresectable or metastatic cutaneous melanoma Recruiting, n = 360, primary completion 2028-01
NCT05933577 (V940-001) Intismeran autogene plus pembrolizumab versus pembrolizumab in high-risk resected melanoma — the phase 3 successor to KEYNOTE-942 Active, not recruiting, n = 1,089, primary completion 2029-10-26
NCT06264180 (IGNYTE-3) Oncolytic virus plus nivolumab versus physician's choice in melanoma progressing on anti-PD-1 and anti-CTLA-4 Recruiting, n = 400, primary completion 2030-09-30
NCT03897881 (KEYNOTE-942) The phase 2b trial reporting the 5-year update Active, not recruiting, n = 267

Two structural shifts are visible: cellular and vaccine approaches are moving from the post-checkpoint salvage setting into first line and into the adjuvant setting, and TCR-engineered products are entering phase 3 alongside autologous TIL. Full landscape in clinical trials landscape.

Interpretation rules for this page

  • State the prior-therapy burden. TIL results come from populations with a median 3 prior lines and 82–100% prior checkpoint exposure (PMID 33979178; PMID 36600653).
  • TIL therapy is a regimen, not a drug — resection, manufacture, lymphodepletion and high-dose IL-2 are all components, and toxicity attribution is correspondingly complex (PMID 36477031).
  • Duration of response "not reached" is not the same as durable cure; report median follow-up alongside it (PMID 36600653).
  • KEYNOTE-942's primary analysis was not statistically significant (P = .053) and its later analyses are descriptive (PMID 38246194; PMID 42223134).
  • Apply the SITC resistance definitions before comparing resistance rates between studies (PMID 37487665; PMID 36223314).
  • Genetic and non-genetic resistance coexist; sequencing a progressing biopsy detects only the former (PMID 27124452; PMID 24463458).

Open questions

  • Should TIL therapy move earlier in the treatment sequence, and can it be given without high-dose IL-2 (PMID 36477031; PMID 36600653)?
  • Does individualised neoantigen therapy improve overall survival, and will phase 3 confirm the phase 2b signal (PMID 42223134)?
  • Can restoring antigen presentation — the dominant resistance programme — be achieved pharmacologically (PMID 36934113)?
  • Which resistance mechanism should be assayed at progression, given that a single biopsy misses heterogeneity (PMID 24463458; PMID 32087194)?
  • Is there a role for oncolytic therapy in combination with checkpoint blockade in checkpoint-refractory disease (PMID 31171039)?
  • Can TIL manufacturing capacity and cost be reduced enough for the therapy to reach beyond specialist centres (PMID 36600653)?

References

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