498 Preclinical characterization of OR502, an anti-LILRB2 antibody that rescues innate and adaptive immune responses from LILRB2 mediated immune suppression

Abstract

<h3>Background</h3> The inhibitory receptor leukocyte immunoglobulin-like receptor subfamily B member 2 (LILRB2, ILT4) is expressed on immunosuppressive myeloid cells and expression correlates with poor survival in multiple cancers and contributes to anti-PD1 resistance. Interaction of LILRB2 with HLA class I ligands (e.g., HLA-G, HLA-A, etc.) mediates immune suppression by myeloid cells and promotes tumor immune evasion in the tumor microenvironment (TME). Blocking this interaction may enhance efficacy of T cell checkpoint inhibitors. Antibodies targeting LILRB2 are currently being evaluated in clinical trials for the treatment of cancer. <h3>Methods</h3> Anti-LILRB2 antibodies were cloned from B cells derived from rabbits immunized with human LILRB2 recombinant protein. Clones were humanized after selection based on activity in a panel of functional and phenotypic assays using primary human macrophages and T cells. Humanized variants were screened for their ability to rescue T cell activity (proliferation and IFN-γ) from M2c macrophage-mediated suppression and enhance LPS-induced IFN-γ production by PBMCs. The top variants were also evaluated for cytokine release in whole blood. The pharmacokinetic profiles of lead LILRB2 antibodies were determined in humanized FcRn mice. <h3>Results</h3> We have identified a panel of humanized anti-LILRB2 antibodies that specifically bind to human LILRB2-expressing cell lines and human myeloid cells without detectable binding to other LILRA or LILRB family members. These antibodies block LILRB2 interaction with HLA-G expressed on tumor cells. The lead antibody, OR502, enhanced LPS-induced IFN-γ production by PBMCs, and relieved M2c macrophage-mediated suppression of proliferation and IFN-γ secretion by anti-CD3-activated human CD8⁺ T cells in coculture assays. Furthermore, OR502 restored the ability of exhausted T cells to secrete IFN-γ in the presence of M2c macrophages and significantly enhanced the activity of pembrolizumab in combination studies. OR502-treatment did not trigger inflammatory cytokine release or activation of neutrophils in human whole blood. The pharmacokinetics of OR502 in humanized FcRn mice demonstrated a half-life of 6-10 days. <h3>Conclusions</h3> We have identified a novel humanized anti-LILRB2 antibody, OR502, that restores innate and adaptive immune responses by modulating immunosuppressive myeloid cells. These data provide a strong rationale for further development of OR502 for cancer treatment.