W138 - A Bispecific CD8-dependent Immunoconjugate to Crosslink and Eliminate Antigen-specific B Cells

Margaret Regan, B.S. – Research Associate, Medicine, Uniformed Services University of Health Sciences; John Weldon, PhD – Associate Professor, Biology, Towson University

Abstract Text: We previously used regulatory or cytotoxic T cells expressing an antigenic epitope to modulate or kill B cells producing adverse/inhibitory antibodies. We call these “BAR” T cells in analogy to chimeric antigen receptor (CAR) T cells. Herein, we describe an immunoconjugate that can target B cells by crosslinking a CD8 effector cells in a model of hemophilia A (HA). HA is an X-linked recessive bleeding disorder in which patients with mutations in the F8 gene lack pro-coagulant protein FVIII. Typically, HA patients are treated with intravenous infusion of Factor VIII prophylactically or on demand. Due to lack of tolerance to FVIII, approximately 30% of HA patients develop an adverse immune response leading to antibodies that neutralize FVIII, which are a major impediment to therapy. Inhibitors primarily bind to epitopes on the immunodominant C2 and A2 domains, both critical for FVIII activity. We have designed and produced a bispecific antibody that expresses the C2 domain of FVIII, as well as an anti-human CD8 arm, as an approach to eliminate inhibitors. The construct brings cytotoxic T cells in proximity to FVIII-specific B cells to initiate killing. Using FVIII-specific hybridomas as targets, we have demonstrated via ELISpot that this cytotoxic CD8 T-cell conjugate is capable of killing FVIII-specific B cell populations in the presence of human CD8+ T cells. These data support the use of bispecific CD8-dependent immunoconjugate to module adverse immune responses.
(Supported by NIH R21 HL152318.)