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T cell activity is governed by T cell receptor (TCR) signaling and constrained by immune checkpoint molecules, including programmed cell death protein 1 (PD-1), cytotoxic T lymphocyte–associated antigen 4 (CTLA-4), and lymphocyte activation gene 3 (LAG-3). The basis for how LAG-3 binds to human leukocyte antigen class II molecules (HLA-II) remains unknown. Here, we present the 3.4-angstrom crystal structure of a LAG-3–peptide–HLA-II complex and probe the energetics of the complex interface. Coincident with the HLA-II binding site of the ancestrally related, monomeric CD4 receptor, the LAG-3 homodimer laterally engages two HLA-II molecules via distal D1 domain surfaces, imposing a 38° angular offset. The LAG-3–HLA-II interface is discontinuous and lacks involvement of the D1 extra loop, a binding site for anti–LAG-3 therapeutic monoclonal antibodies. Upon HLA-II binding, intrinsically mobile loops of the LAG-3 molecule become ordered, with contact residues highly conserved across HLA-DR, DQ, and DP allomorphs. Our data provide a structural foundation for development of immunomodulatory approaches targeting LAG-3. Editor's summary: Lymphocyte activation gene 3 (LAG-3) is an important immune checkpoint receptor on T cells currently being targeted for cancer immunotherapy. LAG-3 is evolutionarily related to CD4 and shares with it the ability to recognize MHC-II (HLA-II in humans). Petersen et al. report a 3.4-Å crystal structure of a human LAG-3–peptide–HLA-II complex. The LAG-3 homodimer binds two separate HLA-II molecules via its D1 domain, suggesting that LAG-3 binding is sensitive to ligand density and orientation on antigen-presenting cells. Moreover, LAG-3's binding site overlaps with the CD4–HLA-II binding site but is more extensive, explaining its higher affinity. —Seth Thomas Scanlon [ABSTRACT FROM AUTHOR]

Immune checkpoint inhibitors (antibodies that block the T cell co‐inhibitory receptors PD‐1/PD‐L1 or CTLA‐4) have revolutionized the treatment of some forms of cancer. Importantly, combination approaches using drugs that target both pathways have been shown to boost the efficacy of such treatments. Subsequently, several other T cell inhibitory receptors have been identified for the development of novel immune checkpoint inhibitors. Included in this list is the co‐inhibitory receptor lymphocyte activation gene‐3 (LAG‐3), which is upregulated on T cells extracted from tumor sites that have suppressive or exhausted phenotypes. However, the molecular rules that govern the function of LAG‐3 are still not understood. Using surface plasmon resonance combined with a novel bead‐based assay (AlphaScreenTM), we demonstrate that LAG‐3 can directly and specifically interact with intact human leukocyte antigen class II (HLA‐II) heterodimers. Unlike the homologue CD4, which has an immeasurably weak affinity using these biophysical approaches, LAG‐3 binds with low micromolar affinity. We further validated the interaction at the cell surface by staining LAG‐3+ cells with pHLA‐II‐multimers. These data provide new insights into the mechanism by which LAG‐3 initiates T cell inhibition. [ABSTRACT FROM AUTHOR]

This report is a summary of 'New Cancer Immunotherapy Agents in Development' program, which took place in association with the 31st Annual Meeting of the Society for Immunotherapy of Cancer (SITC), on November 9, 2016 in National Harbor, Maryland. Presenters gave brief overviews of emerging clinical and pre-clinical immune-based agents and combinations, before participating in an extended panel discussion with multidisciplinary leaders, including members of the FDA, leading academic institutions and industrial drug developers, to consider topics relevant to the future of cancer immunotherapy. [ABSTRACT FROM AUTHOR]

Purpose: Eftilagimod alpha (efti), a soluble LAG3 protein, activates antigen-presenting cells (APC) and downstream T cells. TACTI-002 (part C) evaluated whether combining efti with pembrolizumab led to strong antitumor responses in patients with second-line recurrent or metastatic head and neck squamous cell carcinoma (R/M HNSCC) while demonstrating good tolerability., Patients and Methods: In this multinational phase II trial using Simon's two-stage design, patients who were PD-L(1)-naïve with R/M HNSCC who had failed first-line platinum-based therapy, unselected for PD-L1, received intravenous pembrolizumab (200 mg, once every 2 weeks) combined with subcutaneous efti (30 mg once every 2 weeks for 24 weeks and once every 3 weeks thereafter). The primary endpoint was objective response rate per RECIST 1.1 modified for immune-based therapy by investigator assessment. Additional endpoints included duration of response, progression-free survival, overall survival, and tolerability. Pharmacodynamic effects (absolute lymphocyte count) and Th1 cytokine biomarkers (IFNγ/CXCL10)] were evaluated in liquid biopsies., Results: Between March 2019 and January 2021, 39 patients were enrolled; 37 were evaluated for response. All patients received prior chemotherapy, and 40.5% were pretreated with cetuximab; 53.1% of patients had PD-L1 combined positive score <20. With a median follow-up of 38.8 months, the objective response rate was 29.7%, including 13.5% complete responders. The median duration of response was not reached. Rapid and sustained absolute lymphocyte count increase was observed in patients who had an objective response. Th1 biomarkers increased sustainably after first treatment. No unexpected safety signals were observed., Conclusions: Efti plus pembrolizumab was safe and showed encouraging antitumor activity and pharmacodynamic effects in patients with second-line head and neck squamous cell carcinoma (HNSCC), thus supporting further evaluation of this combination in earlier treatment lines., (©2024 American Association for Cancer Research.)

Purpose: Eftilagimod alpha (efti), a soluble lymphocyte activation gene (LAG-3) protein and MHC class II agonist, enhances innate and adaptive immunity. Active Immunotherapy PAClitaxel (AIPAC) evaluated safety and efficacy of efti plus paclitaxel in patients with predominantly endocrine-resistant, hormone receptor-positive, HER2-negative metastatic breast cancer (ET-resistant HR+ HER2- MBC)., Patients and Methods: Women with HR+ HER2- MBC were randomized 1:1 to weekly intravenous paclitaxel (80 mg/m2) and subcutaneous efti (30 mg) or placebo every 2 weeks for six 4-week cycles, then monthly subcutaneous efti (30 mg) or placebo maintenance. Primary endpoint was progression-free survival (PFS) by blinded independent central review. Secondary endpoints included overall survival (OS), safety/tolerability, pharmacokinetics/pharmacodynamics, and quality of life. Exploratory endpoints included cellular biomarkers., Results: 114 patients received efti and 112 patients received placebo. Median age was 60 years (91.6% visceral disease, 84.1% ET-resistant, 44.2% with previous CDK4/6 inhibitor treatment). Median PFS at 7.3 months was similar for efti and placebo. Median OS was not significantly improved for efti (20.4 vs. 17.5 months; HR, 0.88; P = 0.197) but became significant for predefined exploratory subgroups. EORTC QLQC30-B23 global health status was sustained for efti but deteriorated for placebo. Efti increased absolute lymphocyte, monocyte and secondary target cell (CD4, CD8) counts, plasma IFNγ and CXCL10 levels., Conclusions: Although the primary endpoint, PFS, was not met, AIPAC confirmed expected pharmacodynamic effects and demonstrated excellent safety profile for efti. OS was not significantly improved globally (2.9-month difference), but was significantly improved in exploratory biomarker subgroups, warranting further studies to clarify efti's role in patients with ET-resistant HER2- MBC., (©2023 The Authors; Published by the American Association for Cancer Research.)

This report is a summary of 'New Cancer Immunotherapy Agents in Development' program, which took place in association with the 31st Annual Meeting of the Society for Immunotherapy of Cancer (SITC), on November 9, 2016 in National Harbor, Maryland. Presenters gave brief overviews of emerging clinical and pre-clinical immune-based agents and combinations, before participating in an extended panel discussion with multidisciplinary leaders, including members of the FDA, leading academic institutions and industrial drug developers, to consider topics relevant to the future of cancer immunotherapy.