Lymphocyte activation gene 3 (LAG-3), also known as CD223, is an emerging immune checkpoint that follows PD-1 and CTLA-4. Several LAG-3 targeting inhibitors in clinical trials and the combination of relatlimab (anti-LAG-3) and nivolumab (anti-PD-1) have been approved for treating - unresectable or metastatic melanoma. Despite the encouraging clinical potential of LAG-3, the physiological function and mechanism of action in tumors are still not well understood. In this review, we systematically summarized the structure of LAG-3, ligands of LAG-3, cell-specific functions and signaling of LAG-3, and the current status of LAG-3 inhibitors under development.

OBJECTIVE: Colorectal cancer is the most common malignancy worldwide. A number of pathological and molecular genetic criteria are currently used as predictors of the disease. They include assessment of MMR deficiency or MSI/MSS status, which among others, determine the immunogenicity of the tumor. In this regard, the evaluation of PD-L1, CTLA-4, and LAG-3 immune checkpoint molecules in different tumor compartments according to MMR status deserves special attention.
METHODS: Multiplex immunohistochemistry was used to evaluate the expression of immune checkpoint molecules in the tumor core and at the invasive margin.
RESULTS: Data analysis showed the predominance of PD-L1 (p = 0.011), CTLA-4 (p = 0.004), and LAG-3 (p = 0.013) expression at the invasive margin of dMMR carcinomas compared to pMMR samples. Quantitative analysis of TILs population in the tumor core and at the invasive margin allowed establishment of the predominance of CD3+ and CD8+ lymphocytes at the invasive margin of dMMR carcinomas. Study of the CD163+ macrophages population in the same tumor compartments revealed the predominance of the studied TAMs in the core and at the invasive margin of dMMR carcinomas and the predominance of CD163+ macrophages with PD-L1-phenotype in the tumor stroma.
CONCLUSIONS: This study revealed a significant predominance of PD-L1, CTLA-4, LAG-3, and CD 3+ ,CD8+ lymphocytes in dMMR colorectal carcinomas. Further research on the immune landscape in different tumor compartments will likely have high prognostic value for CRC patients, as it might expand the criteria for prescribing immunotherapy.

Lymphocyte activation gene (Lag)-3 is an inhibitory co-receptor and target of immune checkpoint inhibitor (ICI) therapy for cancer. The dynamic behavior of Lag-3 was analyzed at the immune synapse upon T-cell activation to elucidate the Lag-3 inhibitory mechanism. Lag-3 formed clusters and co-localized with T-cell receptor microcluster (TCR-MC) upon T-cell activation similar to PD-1. Lag-3 blocking antibodies (Abs) inhibited the co-localization between Lag-3 and TCR-MC without inhibiting Lag-3 cluster formation. Lag-3 also inhibited MHC-II-independent stimulation and Lag-3 Ab, which did not block MHC-II binding could still block Lag-3\'s inhibitory function, suggesting that the Lag-3 Ab blocks the Lag-3 inhibitory signal by dissociating the co-assembly of TCR-MC and Lag-3 clusters. Consistent with the combination benefit of PD-1 and Lag-3 Abs to augment T-cell responses, bispecific Lag-3/PD-1 antagonists effectively inhibited both cluster formation and co-localization of PD-1 and Lag-3 with TCR-MC. Therefore, Lag-3 inhibits T-cell activation at TCR-MC, and the target of Lag-3 ICI is to dissociate the co-localization of Lag-3 with TCR-MC.

BACKGROUND: Worse survival persists for African-Americans (AA) with breast cancer compared to other race/ethnic groups despite recent improvements for all. Unstudied in outcomes disparities to date is soluble LAG-3 (sLAG-3), cleaved from the LAG-3 immune checkpoint receptor which is a proposed target for deactivation in emerging immunotherapies due to its prominent immunosuppressive function in the tumoral microenvironment. A prior study has found that lower sLAG-3 baseline level was associated with poor outcomes.
METHODS: In a cross-sectional study of 95 patients with primary breast cancer (n = 58 Caucasian, n = 37 AA), we measured sLAG-3 (ELISA pg/ml) in pre-treatment blood samples using the non-parametric Mann-Whitney u-Test for independent samples, and, calculated Pearson r correlation coefficients of sLAG-3 with circulating cytokines by race.
RESULTS: Mean sLAG-3 level was lower in AA compared to Caucasian patients (1377.6 vs 3690.3, P = .002), and in patients with triple-negative breast cancer (TNBC) compared to those with non-TNBC malignancies (P = .02). When patients with TNBC tumors were excluded from analyses, the difference in sLAG-3 level between AA (n = 21) and Caucasian patients (n = 40) substantially remained (1937.4 vs 4182.4, P = .06). Among Caucasian patients, sLAG-3 was correlated with IL-6, IL-8 and IL-10 (r = .69, P < .001; r = .70, P < .001; and, r = .46, P = .01; respectively). For AA patients, sLAG-3 was correlated only with IL-6 (r = .37, P = .03).
CONCLUSIONS: We present the first report that African-American breast cancer patients might have comparatively low pre-treatment sLAG-3 levels, independent of TNBC status, along with reduced co-expression with circulating cytokines. The mechanistic and prognostic role of cleaved LAG-3, particularly in disparate outcomes, remains to be elucidated.

Systemic lupus erythematosus (SLE) represents an autoimmune disorder that affects multiple systems. In the treatment of this condition, the focus primarily revolves around inflammation suppression and immunosuppression. Consequently, targeted therapy has emerged as a prevailing approach. Currently, the quest for highly sensitive and specifically effective targets has gained significant momentum in the context of SLE treatment. Lymphocyte activation gene-3 (LAG-3) stands out as a crucial inhibitory receptor that binds to pMHC-II, thereby effectively dampening autoimmune responses. Fibrinogen-like protein 1 (FGL1) serves as the principal immunosuppressive ligand for LAG-3, and their combined action demonstrates a potent immunosuppressive effect. This intricate mechanism paves the way for potential SLE treatment by targeting LAG-3 with FGL1. This work provides a comprehensive summary of LAG-3\'s role in the pathogenesis of SLE and elucidates the feasibility of leveraging FGL1 as a therapeutic approach for SLE management. It introduces a novel therapeutic target and opens up new avenues of therapeutic consideration in the clinical context of SLE treatment.

Blockade of immune checkpoint receptors has shown outstanding efficacy for tumor immunotherapy. Promising treatment with anti-lymphocyte-activation gene-3 (LAG-3) has already been recognized as the next efficacious treatment, but there is still limited understanding of the mechanism of LAG-3-mediated immune suppression. Here, utilizing high-resolution molecular imaging, we find a mechanism of CD4 T cell suppression via LAG-3, in which LAG-3-bound major histocompatibility complex (MHC) class II molecules on antigen-presenting cells (APCs) gather at the central region of an immunological synapse and are trans-endocytosed by T cell receptor-driven internalization motility toward CD4 and CD8 T cells expressing LAG-3. Downregulation of MHC class II molecules on APCs thus results in the attenuation of their antigen-presentation function and impairment of CD4 T cell activation. From these data, anti-LAG-3 treatment is suggested to have potency to directly block the inhibitory signaling via LAG-3 and simultaneously reduce MHC class II expression on APCs by LAG-3-mediated trans-endocytosis for recovery from T cell exhaustion.

Tumor immunotherapy has garnered considerable attention, emerging as a new standard of care in cancer treatment. The conventional targets, such as VEGF and EGFR, have been extended to others including BRAF and PD-1/PD-L1, which have shown significant potential in recent cancer treatments. This review aims to succinctly overview the impact and mechanisms of therapies that modulate PD-1/PD-L1 expression by targeting VEGF, EGFR, LAG-3, CTLA-4 and BRAF. We investigated how modulation of PD-1/PD-L1 expression impacts growth factor signaling, shedding light on the interplay between immunomodulatory pathways and growth factor networks within the tumor microenvironment. By elucidating these interactions, we aim to provide insights into novel potential synergistic therapeutic strategies for cancer immunotherapy.

Despite the numerous studies on the clinical aspects of early-onset preeclampsia, our understanding of the immunological consequences of inadequate placenta development remains incomplete. The Th1-predominance characteristic of early-onset preeclampsia significantly impacts maternal immunotolerance, and the role of immune checkpoint molecules in these mechanisms is yet to be fully elucidated. Our study aims to fill these crucial knowledge gaps. A total of 34 pregnant women diagnosed with early-onset preeclampsia and 34 healthy pregnant women were enrolled in this study. A mononuclear cell fragment from the venous blood was separated and frozen. The CD8+ and CD8- NK cell subpopulations were identified and compared to their immune checkpoint molecule expressions using multicolor flow cytometry. The serum CD226 levels were measured by ELISA. Based on our measures, the frequency of the CD8- subpopulation was significantly higher than that of the CD8+ counterpart in both the NKdim and NKbright subsets. Significantly lower CD226 surface expressions were detected in the preeclamptic group compared to healthy women in all the investigated subpopulations. However, while no difference was observed in the level of the soluble CD226 molecule between the two groups, the CD112 and CD155 surface expressions were significantly different. Our study\'s findings underscore the significant role of the CD8+ and CD8- NK subpopulations in the Th1-dominated immune environment. This deepens our understanding of early-onset preeclampsia and suggests that each subpopulation could contribute to the compensation mechanisms and the restoration of the immunological balance in this condition, a crucial step toward developing effective interventions.

Relatlimab (rela; anti-LAG-3) plus nivolumab (nivo; anti-PD-1) is safe and effective for treatment of advanced melanoma. We designed a trial (NCT03743766) where advanced melanoma patients received rela, nivo, or rela+nivo to interrogate the immunologic mechanisms of rela+nivo. Analysis of biospecimens from this ongoing trial demonstrated that rela+nivo led to enhanced capacity for CD8+ T cell receptor signaling and altered CD8+ T cell differentiation, leading to heightened cytotoxicity despite the retention of an exhaustion profile. Co-expression of cytotoxic and exhaustion signatures was driven by PRDM1, BATF, ETV7, and TOX. Effector function was upregulated in clonally expanded CD8+ T cells that emerged after rela+nivo. A rela+nivo intratumoral CD8+ T cell signature was associated with a favorable prognosis. This intratumoral rela+nivo signature was validated in peripheral blood as an elevated frequency of CD38+TIM3+CD8+ T cells. Overall, we demonstrated that cytotoxicity can be enhanced despite the retention of exhaustion signatures, which will inform future therapeutic strategies.

Exhausted CD8 T (Tex) cells in chronic viral infection and cancer have sustained co-expression of inhibitory receptors (IRs). Tex cells can be reinvigorated by blocking IRs, such as PD-1, but synergistic reinvigoration and enhanced disease control can be achieved by co-targeting multiple IRs including PD-1 and LAG-3. To dissect the molecular changes intrinsic when these IR pathways are disrupted, we investigated the impact of loss of PD-1 and/or LAG-3 on Tex cells during chronic infection. These analyses revealed distinct roles of PD-1 and LAG-3 in regulating Tex cell proliferation and effector functions, respectively. Moreover, these studies identified an essential role for LAG-3 in sustaining TOX and Tex cell durability as well as a LAG-3-dependent circuit that generated a CD94/NKG2+ subset of Tex cells with enhanced cytotoxicity mediated by recognition of the stress ligand Qa-1b, with similar observations in humans. These analyses disentangle the non-redundant mechanisms of PD-1 and LAG-3 and their synergy in regulating Tex cells.