After nearly a decade of PD-1/PD-L1–targeting antibodies dominating the immune checkpoint inhibitor (ICI) landscape, the cancer immunotherapy field is branching out.

 In March 2022, the FDA approved the combination of nivolumab and relatlimab-rmbw (Opdualag) for the treatment of patients 12 years of age and older with unresectable or metastatic melanoma.

 Relatlimab is the first drug targeting the LAG-3 pathway to gain FDA approval.

 The fixed-dose regimen combines relatlimab, an anti–LAG-3 monoclonal antibody, with nivolumab (Opdivo), a PD-1 inhibitor approved for the treatment of 13 tumor types.

Although expanding the repertoire of ICIs has been a major research priority,

 the approval of relatlimab in the combination regimen represents just the third successfully targeted checkpoint to enter the oncology armamentarium. Of the 8 previously approved ICIs, 7 are directed at the PD-1/PD-L1 pathway and 1, ipilimumab (Yervoy), targets CTLA-4.

The regimen’s approval validates the concept of targeting LAG-3 for cancer therapeutics and is expected to generate interest in developing additional therapies directed at this checkpoint.

 More than 100 clinical trials evaluating 35 LAG-3–inhibitory drugs are ongoing.7 Although most novel agents are being evaluated in phase 1 studies, several therapies have moved into later stages of development in a range of cancer types (TABLE

LAG-3 is a type I transmembrane cell-surface protein that functions as an inhibitory coreceptor in the immune system, similar to PD-1 and CTLA-4.

 The gene that encodes LAG-3 was identified in 1990 by Frédéric Triebel, MD, PhD, and colleagues at Gustave Roussy in Villejuif, France, through analysis of complementary DNA clones expressed in an IL-2–dependent CD3-negative natural killer–cell line. They observed that the 

 gene encodes a membrane protein with 4 extracellular immunoglobulin superfamily domains.

Investigators have described the role that LAG-3 and other inhibitory immune checkpoints play in cancer in the context of T-cell exhaustion. When T cells undergo prolonged exposure to an antigen, such as neoantigens expressed on cancer cells, they become desensitized and less able to activate and multiply in the presence of the antigen, a state called T-cell exhaustion.

 Exhausted T cells may also downregulate production of tumor-killing cytokines.

 Increased expression of inhibitory receptors such as LAG-3 is also associated with T-cell exhaustion.

 LAG-3 limits activation of T cells, reducing their ability to attack and destroy tumor cells, whereas inhibition of LAG-3 restores T-cell functioning.

Research has shown that levels of LAG-3 expression and infiltration of LAG-3–positive cells in tumors correlate with unfavorable clinical outcomes, tumor progression, and poor prognosis in a range of cancer types, including colorectal cancer, renal cell carcinoma, lymphomas, breast cancer, non–small cell lung cancer (NSCLC), and head and neck squamous cell carcinoma (HNSCC).

 Investigators initially studied LAG-3 inhibition as monotherapy but found that a single-agent strategy had limited efficacy. Rather, targeting LAG-3 in combination therapy has proven more effective.

 Investigators showed in mouse models that dual blockade of LAG-3 and PD-1 receptors resulted in synergistic activity to decrease tumor growth and promote antitumor immunity.

 Although further research is needed to delineate the exact mechanism underlying this synergy, it may be due to differences in inhibitory mechanisms and/or expression profiles of LAG-3 and PD-1.

Since his discovery, Triebel has continued to explore the therapeutic potential of LAG-3 inhibition at Immutep SA, a biotechnology company that he founded.

, Triebel discussed the rationale behind dual checkpoint inhibition in melanoma. “The hope is to have more patients responding to anti–PD-1 therapy,” he said.

 Triebel now serves as chief medical officer and chief scientific officer at Immutep.

Although ICIs have improved outcomes in a broad range of tumor types, treatment resistance poses a significant challenge. Most patients do not respond to treatment with ICIs, exhibiting primary resistance, and many patients who initially respond eventually relapse due to acquired resistance.

 The need to improve responses with fewer adverse effects (AEs) is helping to fuel research efforts to develop therapies targeting novel immune coreceptors.

“We have to find new pathways, inhibitory pathways, and LAG-3 is certainly an immune checkpoint now validated through phase 3,” Triebel said in an interview with BioSpace in December 2021 in reference to nivolumab/ relatlimab data.

The FDA approval of the nivolumab-relatlimab combination therapy was based on findings from the phase 2/3 RELATIVITY-047 trial (NCT03470922).

 This global, double-blind trial compared the fixed-dose combination of relatlimab plus nivolumab against nivolumab alone in patients with previously untreated metastatic or unresectable melanoma. Eligible patients were at least aged 12 years with measurable stage III or IV melanoma per RECIST 1.1. LAG-3 and PD-L1 had to be evaluable in tumor tissue, and patients were stratified for each biomarker based on level of expression (≥ 1% or < 1%) as determined via immunohistochemistry.

From May 2018 through December 2020, 714 patients were randomly assigned to receive relatlimab-nivolumab (n = 355) or nivolumab alone (n = 359). Patients received relatlimab 160 mg and nivolumab 480 mg intravenously in a fixed-dose combination or 480 mg of nivolumab.

 The primary end point of the study was progression-free survival (PFS), and secondary end points included overall survival (OS) and objective response rate (ORR).

After a median follow-up of 13.2 months, the median PFS was 10.1 months (95% CI, 6.4-15.7) in the relatlimab-nivolumab group compared with 4.6 months (95% CI, 3.4-5.6) in the nivolumab-alone group (HR for progression or death, 0.75; 95% CI, 0.62-0.92; log-rank 

 = .006). The 12-month PFS rate was 47.7% (95% CI, 41.8%-53.2%) in the relatlimab-nivolumab group compared with 36.0% (95% CI, 30.5%-41.6%) in the nivolumab group.

The ORR was 43% (95% CI, 38%-48%) in the relatlimab-nivolumab arm vs 33% (95% CI, 28%-38%) with nivolumab alone. Median OS was not reached (NR; 95% CI, 34.2-NR) with the combination compared with 34.10 months (95% CI, 25.2-NR) for nivolumab alone. OS was numerically superior in the combination group (HR, 0.80; 95% CI, 0.64-1.01), but the difference did not achieve statistical significance at the trial’s alpha threshold of 

Data from exploratory analyses indicated that PFS favored combination therapy vs monotherapy in prespecified subgroups. Patients with traits commonly associated with worse prognosis, such as visceral metastases, high tumor burden, elevated lactate dehydrogenase levels, or mucosal or acral melanoma, had better outcomes with relatlimab-nivolumab than with nivolumab alone.

In terms of LAG-3, patients with expression of 1% or greater had longer median PFS in both treatment groups, and participants treated with the combination had better PFS regardless of LAG-3 expression level. At the same time, the median PFS with relatlimab-nivolumab was greater than with nivolumab monotherapy for those with LAG-3 of 1% or more (12.58 vs 4.76 months, respectively) than for patients with LAG-3 less than 1% (4.83 vs 2.79 months, respectively).

However, these trends were not seen in the PD-L1 data. Median PFS was similar in patients whose tumors had PD-L1 expression of 1% or greater for combination therapy compared with nivolumab alone (15.7 months vs 14.7 months, respectively). For participants with PD-L1 expression of less than 1%, median PFS was 6.4 months (95% CI, 4.6-11.8) with the combination and 2.9 months (95% CI, 2.8-4.5) for nivolumab alone (HR, 0.66; 95% CI, 0.51-0.84).

The RELATIVITY-047 investigators concluded that neither biomarker was clearly useful in selecting patients for ICI therapy. In terms of AEs, 18.9% of the patients in the relatlimab-nivolumab group experienced grade 3 or 4 treatment-related AEs (TRAEs) compared with 9.7% of the nivolumab-alone group. The most frequent grade 3 or 4 TRAEs in the relatlimab-nivolumab group included increased levels of lipase, alanine aminotransferase, and aspartate aminotransferase (1.7%, 1.4%, and 1.4% of patients, respectively), as well as fatigue (1.1%).

Furthermore, 14.6% of patients in the relatlimab-nivolumab group discontinued treatment due to TRAEs compared with 6.7% in the nivolumab group, but no new safety signals were identified with relatlimab-nivolumab treatment.

Three treatment-related deaths occurred in the combination-therapy group (0.8%) and 2 in the monotherapy group (0.6%).

Although OS data from RELATIVITY-047 are not yet mature, results so far suggest that the relatlimab-nivolumab combination could become the new frontline standard of care for patients with advanced melanoma.19 In this clinical setting, the median PFS associated with the relatlimab-nivolumab regimen has been similar to that seen with the combination of nivolumab plus ipilimumab, the current first-line standard, in the CheckMate 067 trial (NCT01844505), but with a lower incidence of grade 3 or 4 TRAEs (19% with relatlimab-nivolumab vs 59% with nivolumab-ipilimumab).

However, the long-term OS results with the nivolumab-ipilimumab combination have set the bar high. After a minimum follow-up of 6.5 years, the median OS reached an unprecedented 72.1 months (95% CI, 38.2-NR) in CheckMate 067.

The nivolumab-ipilimumab results represent the longest median OS reported in a phase 3 advanced melanoma study, CheckMate 067 investigators said. The milestone is “staggering” and sets a benchmark for judging whether relatlimab-nivolumab will be a new standard for previously untreated patients, according to a commentary in the 

Longer-term data also may clarify the role of LAG-3 expression as a biomarker in guiding therapy for patients.

 Although higher LAG-3 expression correlated with longer median PFS in the RELATIVITY-047 trial, a recent study in NSCLC described a negative association between LAG-3 expression and response to anti–PD-1 therapy. The study evaluated LAG-3, PD-1, and TIM-3 protein expression in NSCLC tissue specimens. Investigators found that patients whose tumor samples had elevated LAG-3 expression were less susceptible to PD-1 inhibitors (associated with a shorter PFS). More research is needed to fully delineate the association between expression of these biomarkers and treatment response in patients with cancer.

Investigators are exploring several novel strategies to target LAG-3 besides monoclonal antibodies, including bispecific antibodies directed at PD-1/PD-L1 in addition to LAG-3. Based on where antibodies bind to LAG-3, they can alter its interactions with its ligands in different ways.

One novel candidate, tebotelimab, is a PD-1/ LAG-3 bispecific antibody that inhibits both checkpoints on a single T cell.4 MacroGenics, Inc, the company developing the drug, plans to study tebotelimab in combination with a cell-killing antibody specific to tumor cells. However, in July 2022, the company closed a phase 2 study (NCT04634825) evaluating enoblituzumab, a B7-H3 mAb, plus tebotelimab or retifanlimab, a PD-1 inhibitor, in recurrent or metastatic HNSCC after 7 fatalities potentially associated with hemorrhagic events, including 1 possibly related to the study treatment, were reported among 62 participants.

Roche’s candidate, RG6139, is also a bispecific antibody that targets PD-1 and LAG-3. This agent has higher affinity for PD-1 than for LAG-3, causing it to preferentially target tumor-infiltrating activated T cells rather than regulatory T cells.

Merck is developing favezelimab (MK-4280), a humanized anti–LAG-3 monoclonal antibody, as combination therapy with pembrolizumab (Keytruda), a PD-1 inhibitor, to treat hematologic malignancies and solid tumors including NSCLC, small cell lung cancer, renal cell carcinoma, and colorectal cancer.

 The combination, called MK-4280A, has advanced to the phase 3 MK-4280A-007 study (NCT05064059) in patients with previously treated, metastatic, PD-L1–positive colorectal cancer.

At the 2022 American Society of Clinical Oncology (ASCO) Annual Meeting, investigators reported data from a different MK-4280A trial, an ongoing phase 1/2 study (NCT03598608) evaluating the combination in hematologic malignancies. In a cohort of 29 patients with relapsed classical Hodgkin lymphoma refractory to anti–PD-1 therapy who received the recommended phase 2 dose of 800 mg favezelimab plus 200 mg pembrolizumab every 3 weeks, the ORR was 31% (95% CI, 15%-51%) at a median follow-up of 16.5 months. This included 2 compete responses and 7 partial responses.

Immutep Limited’s candidate, eftilagimod alpha, is a soluble LAG-3 fusion protein that binds major histocompatibility complex class II proteins on the surface of antigen-presenting cells (APCs) to modulate APCs and CD8 T cells.

 Unlike LAG-3 inhibitors, eftilagimod alpha does not bind to LAG-3 on the T cell; instead, the agent “pushes the accelerator on the immune response” by activating APCs and increasing the supply of activated T cells. Investigators theorize that enhanced T-cell activation may result in an improved response to PD-1/PD-L1 inhibitors.

Eftilagimod alpha was evaluated in HER2negative/hormone receptor–positive metastatic breast cancer previously treated with endocrine therapy in the phase 2b AIPAC study (NCT02614833). Patients received either eftilagimod plus paclitaxel or paclitaxel alone. The combination therapy led to a nonsignificant increase in OS in the overall population of 226 evaluable patients. The median OS was 20.4 months (95% CI, 14.3-25.1) in the eftilagimod-paclitaxel group vs 17.5 months (95% CI, 12.9-21.9) in the paclitaxel group (HR, 0.88; 95% CI, 0.64-1.19; 

 = .197). However, median OS was significantly improved with eftilagimod-paclitaxel therapy in 3 subgroups: patients who were younger than 65 years, had low baseline monocytes (< 250/µL), or had the more aggressive luminal B subtype, with HRs of 0.66, 0.44, and 0.67, and 

 values of .017, .008, and .049, respectively.

Eftilagimod alpha also is being studied in combination with pembrolizumab in patients with NSCLC and HNSCC. At the 2021 ASCO Annual Meeting, Immutep reported interim results from the phase 2 TACTI-002 trial (NCT03625323). The ORR was 41.7% for firstline treatment of 36 patients with NSCLC and 29.7% for second-line treatment of 37 patients with HNSCC. These results reflect an improvement compared with anti–PD-1 monotherapy for first-line NSCLC, investigators said.

The exciting results in first-line NSCLC prompted an expansion of this cohort, and updated findings were presented at the 2022 ASCO Annual Meeting. After a median follow-up of 11.2 months, the ORR by iRECIST criteria (modified RECIST 1.1 for immune-based therapeutics) was 38.6% (95% CI, 29.6%-48.2%) in 114 patients in the intention-to-treat population and 42.7% (95% CI, 33.0%-52.9%) in 103 participants evaluable for response (≥ 1 on-study tumor staging after baseline).

Patients were not selected for the study based on PD-L1 expression status, but results were stratified by 5 tumor proportion score (TPS) groups (< 1%, 1% to 49%, ≥ 50%, ≥ 1%, and < 50%). Approximately 70% of trial participants had a TPS of less than 50%. Responses were observed across all PD-L1 expression subgroups, with higher ORRs in patients with higher PD-L1 expression. The ORR was 52.6 % (95% CI, 28.9%75.6%) in 19 patients with a TPS of 50% or greater by central assessment and 51.6% (95% CI, 33.1%-69.9%) in 31 patients assessed for PD-L1 status both centrally and locally.

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