Antigen-loaded antibodies
Project leader:
We are developing a novel strategy for targeting B cell lymphoma tumor cells by activating Epstein Barr virus (EBV)-specific T cells (Yu, Ilecka et al. Blood 2015). Here the tumor cells are used as antigen-presenting cells that present EBV antigens and are recognized by EBV-specific T cells (Figure 1). To this end, we have designed a panel of recombinant antibodies that target various B cell surface receptors (CD19, CD20, CD21 and CD22), and that are designed to contain immunodominant T cell epitopes from EBV (Figure 1). These are known as antigen-armed antibodies (AgAbs). Treatment with AgAbs results in direct binding to B cells. This is followed by uptake of the AgAbs by the tumor cells wherein they are processed into smaller peptides, which are then presented on the surface of the B cells to T cells in the context of MHC molecules. In this way, the EBV epitopes are also presented on the surface of the neoplastic cell, and this results in the activation of EBV-specific CD4-positive cytotoxic T cells (Figure 2). This strategy shows a high degree of efficacy with B cell lymphoma cell lines (Yu, Ilecka et al. Blood 2015).
We are currently evaluating the efficacy of this therapeutic approach in a mouse model of B cell lymphoma (A20) using antibodies that recognize murine B cell markers and that are loaded with antigens specific for mouse cytomegalovirus.
In parallel, we are currently conducting an ex vivo study with peripheral blood from patients with a chronic lymphocytic leukemia (CLL). EBV-specific T cells from these patients are expanded and their ability to mount an immune response against CLL cells exposed to antibodies loaded with EBV antigens is tested in cytokine release assays and killing assays.
Figure 1: Principle of AgAb-mediated tumor killing The rationale behind this strategy is to force tumor cells to act as an antigen-presenting cell. AgAb consist of antibodies specific to CD19, CD20, CD21 and CD22 that are fused to antigens from the Epstein-Barr virus. The antibodies bind to B cell lymphomas, are internalized, processed and the viral antigens are presented at the surface of the tumor cells. This leads to an immune reaction against the tumor cells mediated by T cells specific for the virus
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Figure 2: A20 killing assay A20 murine lymphoma cells internalize, process and present MHCII- restricted epitopes from murine cytomegalovirus (mCMV) delivered by an aCD22 antibody in a dose dependent manner. A20 cells were loaded with decreasing amount of AgAb, incubated for 6h and mixed with 14.13 CD4+ T cell hybridoma cells that recognizes one of the mCMV epitopes incorporated into the antibody. The hybridoma response was quantified by IL-2 release ELISA.
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