Application of the immunoregulatory receptor LILRB1 as a crystallisation chaperone for human class I MHC complexes

LAG Time in the Era of Immunotherapy-New Molecular Insights Into the Immunosuppression Mechanism of Lymphocyte Activation Gene-3

The immune checkpoint receptor lymphocyte activation gene-3 (LAG3) inhibits T-cell activation and was recently validated as a target for cancer immunotherapy. Despite its emergence as a therapeutic target, a lack of molecular-level insight has obscured our understanding of the LAG3 immunosuppression mechanism. This review highlights a series of breakthroughs that have illuminated fundamental aspects of LAG3 molecular biology. Key discoveries include structural insights into LAG3 interactions with ligands and antibodies, mechanistic studies of LAG3 interference with T-cell receptor (TCR) signaling, and the development of novel therapeutics. A particular focus is placed on structure-function relationships for LAG3-targeting drugs, as it has become apparent that several distinct approaches to LAG3 antagonism are viable. In addition to LAG3 antagonists, agonistic LAG3 antibodies and immunostimulatory LAG3 extracellular domains (ECDs) are discussed in the context of current structural and mechanistic data. Collectively, these findings should provide an updated landscape for the design of optimal LAG3-based therapeutics for cancer and autoimmune diseases.

The Structural Basis for Recognition of Human Leukocyte Antigen Class I Molecules by the Pan-HLA Antibody W6/32

The central immunological role of HLA class I (HLA-I) in presenting peptide Ags to cellular components of the immune system has been the focus of intense study for >60 y. A confounding factor in the study of HLA-I has been the extreme polymorphism of these molecules. The mAb W6/32 has been a fundamental reagent bypassing the issue of polymorphism by recognizing an epitope that is conserved across diverse HLA-I allotypes. However, despite the widespread use of W6/32, the epitope of this Ab has not been definitively mapped. In this study, we present the crystal structure of the Fab fragment of W6/32 in complex with peptide-HLA-B*27:05. W6/32 bound to HLA-B*27:05 beneath the Ag-binding groove, recognizing a discontinuous epitope comprised of the α1, α2, and α3 domains of HLA-I and β2-microglobulin. The epitope comprises a region of low polymorphism reflecting the pan-HLA-I nature of the binding. Notably, the W6/32 epitope neither overlaps the HLA-I binding sites of either T cell Ag receptors or killer cell Ig-like receptors. However, it does coincide with the binding sites for leukocyte Ig-like receptors and CD8 coreceptors. Consistent with this, the use of W6/32 to block the interaction of NK cells with HLA-I only weakly impaired inhibition mediated by KIR3DL1, but impacted HLA-LILR recognition.

MHC1/LILRB1 axis as an innate immune checkpoint for cancer therapy

Immune checkpoint blockades (ICBs) have revolutionized cancer therapy through unleashing anti-tumor adaptive immunity. Despite that, they are usually effective only in a small subset of patients and relapse can occur in patients who initially respond to the treatment. Recent breakthroughs in this field have identified innate immune checkpoints harnessed by cancer cells to escape immunosurveillance from innate immunity. MHC1 appears to be such a molecule expressed on cancer cells which can transmit a negative signal to innate immune cells through interaction with leukocyte immunoglobulin like receptor B1 (LILRB1). The review aims to summarize the current understanding of MHC1/LILRB1 axis on mediating cancer immune evasion with an emphasis on the therapeutic potential to block this axis for cancer therapy. Nevertheless, one should note that this field is still in its infancy and more studies are warranted to further verify the effectiveness and safety in clinical as well as the potential to combine with existing immune checkpoints.

Leukocyte Immunoglobulin-Like Receptors in Regulating the Immune Response in Infectious Diseases: A Window of Opportunity to Pathogen Persistence and a Sound Target in Therapeutics

Immunoregulatory receptors are essential for orchestrating an immune response as well as appropriate inflammation in infectious and non-communicable diseases. Among them, leukocyte immunoglobulin-like receptors (LILRs) consist of activating and inhibitory receptors that play an important role in regulating immune responses modulating the course of disease progression. On the one hand, inhibitory LILRs constitute a safe-guard system that mitigates the inflammatory response, allowing a prompt return to immune homeostasis. On the other hand, because of their unique capacity to attenuate immune responses, pathogens use inhibitory LILRs to evade immune recognition, thus facilitating their persistence within the host. Conversely, the engagement of activating LILRs triggers immune responses and the production of inflammatory mediators to fight microbes. However, their heightened activation could lead to an exacerbated immune response and persistent inflammation with major consequences on disease outcome and autoimmune disorders. Here, we review the genetic organisation, structure and ligands of LILRs as well as their role in regulating the immune response and inflammation. We also discuss the LILR-based strategies that pathogens use to evade immune responses. A better understanding of the contribution of LILRs to host-pathogen interactions is essential to define appropriate treatments to counteract the severity and/or persistence of pathogens in acute and chronic infectious diseases lacking efficient treatments.