Super Cross-Presentation of Tumor Antigens to Elicit Anti-Lymphoma Immunity By Synthetic Design of an Anti-Phosphatidylserine Bridge Protein

Cell loss by apoptosis is a common feature in tumors. Dying tumor cells induce immune tolerance within the tumor microenvironment largely through highly conserved homeostatic clearance programs that restore tissue immune homeostasis and contribute to the formation of an immunosuppressive niche. The translocation of phosphatidylserine (PS) on cellular membranes, during the initial phases of apoptosis, functions as a recognition and removal signal that limits the immunogenicity of cell death. We examined whether altering clearance of dying cancer cells to elicit inflammatory turnover potentiates immune responses against lymphoma cells. To remove inhibitory signals in the homeostatic clearance pathway we utilized a molecular bridge scaffold to engineer a modified phosphatidylserine bridge protein (FA58C2-hIgG1 or C2-hIgG1) that works as a bridge between apoptotic cells expressing aminophospholipids and phagocytes bearing Fc receptors. In vitro administration of C2-hIgG1 to murine bone marrow derived macrophages promotes engulfment of apoptotic murine lymphoma cells (38C13 cell line) and ablates the secretion of the anti-inflammatory cytokine interleukin-10 (IL-10) and suppression of pro-inflammatory cytokines tumor necrosis factor (TNF-α) and IL-12p40 to the presence of apoptotic cells. Similarly, uptake of C2-hIgG1 treated lymphoma cells triggers upregulation of the costimulatory markers CD80, CD86, and MHC class II on macrophages and promotes secretion of Th1-recruiting lymphocyte chemokines CXCL9, CXCL10, and CCL5. Accordingly, in vivo administration of C2-hIgG1 partially restores immune responses to dead lymphoma cells in antigen cross presentation assays and promotes recruitment and retention of tumor antigen specific CD8⁺ T cells, dendritic cells, and natural killer cells into tumors. These effects combine to elicit anti-lymphoma immunity, improve responses to immune checkpoint inhibitors, and enhance the effectiveness of adoptive T cell transfers using engineered T Cell Receptors (TCRs) but not CD19-directed chimeric antigen receptor engineered (CAR-T) T cells.