Lifileucel: FDA-approved T-cell therapy for melanoma

Abstract

This commentary reports on the history of tumor-infiltrating lymphocytes (TIL) for adoptive cell therapy and where TIL fits into the treatment options for metastatic melanoma.

The history and evolution of tumor-infiltrating lymphocytes for adoptive cell therapy

The availability of the T-cell growth factor, interleukin-2, was essential to the study of T-cell biology. It became available in recombinant form in 1984¹ and by 1985, it was being applied to the production of antitumor T cells for therapy in murine models. Simply placing enzymatically dispersed murine or human tumors into human IL-2 led to the rapid outgrowth of what have become known as tumor-infiltrating lymphocytes (TIL).² This outgrowth coincided with the rapid destruction of the cocultured tumor cells in vitro, leading to a pure preparation of expanding T lymphocytes. At first, these were empirically tested against tumors in murine models using adoptive cell transfer.³ Brief support with systemic IL-2 was also given with the TIL to enhance their survival in vivo. TIL proved to be highly effective against early micrometastases at lower doses than nonspecific antitumor cells such as lymphokine-activated killer cells (LAK). It was also noted that the addition of high-dose cyclophosphamide or whole-body radiation prior to TIL administration was able to cause the regression of much larger established tumors in mice. Early clinical trials with TIL in patients began in 1988.⁴ These showed that TIL and IL-2 alone had modest activity, but the addition of pretreatment with cyclophosphamide and the later addition of fludarabine to lymphodeplete the recipient could cause durable major regressions in patients with melanoma.⁵

A major advance in our understanding of the mechanism of TIL-induced tumor rejection was the discovery of the relevant tumor-associated antigens targeted by TIL from melanoma. Initially, the T-cell reactivity identified in melanoma TIL was against normal, unmutated melanocyte-specific proteins such as MART-1, tyrosinase, and gp100. Yet when patients were treated with T cells genetically engineered with T-cell receptors targeting these antigens, they suffered toxicity to normal melanocytes (eg. uveitis, hearing loss, and vitiligo), not typically seen after TIL therapy. This argued that the cogent antigens in melanoma TIL were not these normal tissue differentiation antigens. The discovery of neoantigens; non-self epitopes generated by tumor-specific mutations, recognized by clinically active TIL helped explain this apparent contradiction.⁶ This also clarified that TIL were patient-specific and would need to be generated for each patient because the tumor mutation profiles of cancers rarely overlapped. In addition, the few shared mutations such as the BRAF V600E mutation in melanoma also proved to be poorly immunogenic and TIL typically did not contain such reactivity. A year after the discovery of neoantigen reactivity in melanoma TIL, correlative population studies showed that the presence of larger numbers of potential neoantigens was also associated with more frequent clinical responses to checkpoint inhibitors, reinforcing their central importance in immunotherapy.

Laboratory studies also helped clarify the role of preparative host immunosuppression in TIL efficacy. In murine models, preirradiation had 3 mechanisms that improved TIL antitumor activity. First, it depleted host T-regulatory cells. Second, the depletion of the overall host lymphocyte count led to the elaboration of homeostatic cytokines such as IL-7 and IL-15 from nonlymphoid sources which serve to restore the lymphocyte count. TIL-treated mice genetically knocked out for IL-7 and IL-15 had reduced benefit from host immunosuppression. In addition, fewer bystander host lymphocytes led to more homeostatic cytokines available to the transferred TIL. Finally, radiation and chemotherapy led to damaged mucosal barriers and higher levels of ligands for toll-like receptors, especially lipopolysaccharide (LPS). These ligands serve to nonspecifically stimulate antigen-presenting cells and the effects of lymphodepletion were reduced in mice genetically unresponsive to LPS.

The role of systemic IL-2 in TIL therapy remains less resolved. In murine models, IL-2 clearly helps TIL. It has been presumed that it increases the in vivo expansion of transferred TIL, but its detrimental role as a simulator of regulatory T cells has become increasingly important. It also is a powerful inducer of IFN-gamma secretion, which upregulates MHC and antigen processing on tumors and other cells and mutations in the interferon signaling pathway in tumor cells have been associated with resistance to immunotherapy. A small unpublished experience in the Surgery Branch, NCI gave TIL after standard lymphodepletion without IL-2 to 17 patients with metastatic melanoma. Five patients had responses (29%), with 3 durable complete responses, compared to a contemporaneous experience that included IL-2 where the overall response rate was nearly twice as high. The patients responding in this trial predominantly had disease confined to skin and lymph nodes, a favorable disease pattern. Patients were also not randomized, but selected due to factors that elevated their risk from IL-2 (eg, age, prior brain metastases and comorbidities), so these data must be interpreted with caution.

Clinical trials supporting the use of TIL for metastatic melanoma

The Surgery Branch, NCI pursued a single institution experience with lymphodepletion, TIL, and IL-2 which involved, in aggregate, 194 patients with metastatic melanoma.^7,8 The overall objective response rate was 55% (23% CR, 32% PR) (Figure 1). Performed prior to the availability of anti-PD-1 antibodies, this trial showed that prior exposure to single-agent anti-CTLA had no detrimental impact on TIL responses. The Ella Institute in Tel Aviv, MD Anderson, and Moffitt Cancer Center all published studies where the overall response rates were 40%, 50%, and 38%, respectively, and durable complete responses were again achieved with a single transfer of TIL.^9-11

Figure 1.

Patient with extensive liver metastases from melanoma, treated with lymphodepletion, one infusion of autologous TIL, and high-dose IL-2 in 2003. He remains in complete response at his last scan in 2015.

The advent of other effective treatments for melanoma altered the landscape for TIL therapy in melanoma. BRAF and MEK inhibitors showed high response rates for BRAF-mutated tumors, but limited durations. Checkpoint inhibitors (CPI), especially targeting PD-1/PDL-1, with high efficacy against metastatic melanoma entered the armamentarium for this disease. It would be logical to assume that patients with the most immunogenic tumors would respond to both CPI and TIL. Therefore, when given in succession, the response rate of the second treatment would likely be lower. The FDA approval of numerous CPI led to the relegation of TIL to a second-line role. This was despite the fact that TIL typically required only one administration with no maintenance, autoimmunity was very rare, overall and complete response rates were similar and complete responders to TIL rarely relapsed. Therefore, new trials were required to establish the benefit of TIL therapy in patients who had progressed after CPI and other approved therapies.

A pivotal randomized trial was conducted with TIL generated by multiple individual institutions in the European Union and Australia using harmonized TIL manufacturing procedures.¹² Of the 168 randomized patients, 86% had prior anti-PD-1 or anti-PDL-1 in the adjuvant or first-line metastatic setting. Patients were randomized to either ipilimumab or TIL with lymphodepletion and IL-2. The objective response rates were 21% (95% CI, 13-32) and 49% (95% CI, 38-60), respectively. Median progression-free survivals were 3.1 months versus 7.2 months (P < .001) and median overall survivals, 18.9 months versus 25.8 months.

The trial C-144-01 was a multicenter, prospective, single-arm phase 2 trial testing a standardized TIL product, lifileucel (Amtagvi, Iovance Biotherapeutics, Inc.) that enrolled 153 patients.¹³ This population was heavily pretreated with a median of 3 lines of prior therapies. All had anti-PD-1 or anti-PDL-1 therapy. The overall response rate was 31.4% (95% CI: 24.1%-39.4%) with 8 complete responses and 40 partial responses. The median duration of response was not reached at the median study follow-up of 27.6 months with 41.7% of responses maintained 18 months or longer. The median overall survival was 13.9 months. Progression-free survival was 4.1 months. The most common grade 3 or 4 treatment-related adverse events were thrombocytopenia (76.9%), anemia (50.0%), and febrile neutropenia (41.7%) which were related to the lymphodepleting regimen.

On February 16, 2024, TIL became an approved autologous cellular treatment for unresectable and metastatic melanoma when lifileucel was approved by the US FDA.¹⁴ The accelerated approval was granted based on the C-144-01 study of patients with advanced melanoma that progressed after immune checkpoint inhibitors and targeted therapy if BRAF mutated.

Where do TIL fit in the hierarchy of treatments for metastatic melanoma?

The array of choices for the treatment of metastatic melanoma has blossomed in the last 20 years. The current challenge is often how to use them and in what sequence. There has been a general consensus that potentially curative options (ie, immunotherapies) be tried first. In addition, when patients whose melanoma contained the BRAF V600E or V600K mutations were treated with TIL after BRAF or BRAF/MEK-targeted small-molecule therapy, an ORR of 21% and a median 9.3-month survival was seen, significantly lower than the historical rate for those never receiving these agents.¹⁵ The mechanism of decreased efficacy of TIL after BRAF inhibition is not known, however, in vitro analysis of vemurafenib (PLX4032) has demonstrated its negative impact on the peripheral blood T cell and treatment TIL viability and proliferation at therapeutic levels.¹⁶ These data support the use of TIL prior to BRAF or MEK inhibition in patients with the relevant mutations.

In one institutional experience, patients naïve to anti-PD-1 therapy showed an overall ORR of 56% (108/192) with a median melanoma-specific survival of 28.5 months with TIL therapy. Then sequential, nonrandomized data showed patients that had progressed after anti-PD-1 therapy and then gone on to TIL therapy had an ORR of 24% (8/34) and 11.6-month melanoma-specific survival.¹⁵ It is not clear whether this was due only to the patient editing or selection mentioned above or to some active immunological mechanism. There is currently a phase 3, multicenter, open-label, randomized trial of lifileucel (LN-144) with pembrolizumab compared to pembrolizumab alone for patients with untreated, unresectable, or metastatic melanoma in the first-line setting (NCT05727904). This trial allows crossover of the pembrolizumab monotherapy group after confirmed progressive disease to receive lifileucel monotherapy. Expected enrollment is 670 and may determine if autologous adoptive cellular transfer should be used in the first-line setting.

Finally, future efforts are attempting to extend TIL treatment to the common epithelial cancers that cause >80% of all cancer deaths and where checkpoint inhibition has had minimal impact. This has required that TIL be screened and selected for neoantigen recognition, which is less abundant than in melanoma TIL. With that, several early successes have illustrated the promise and potential of TIL for these diseases.^17,18

Funding

J.C.Y. research is supported by a CRADA between Iovance Biotherapeutics and the NCI.

Conflicts of interest

None declared.