Development of immunotherapy targeting neoplastic lymphocyte-specific antigen (2D7) against hematological malignancies

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We first examined the expression of 2D7 antigen among hematological malignancies. Flow cytometric analysis showed. that 2D7 was highly expressed on myeloma cells and B-cell lymphoblastic cells. These cells expressed 2D7 at significantly higher levels than normal hematopoietic cells. Molecular cloning of 2D7 revealed that the epitope protein was a part of human histocompatibility leukocyte antigen (HLA) class I complex, HLA-A. We next investigated the biological function of 2D7 by using, 2D7 antibody. The 2D7 antibody induced cell death in neoplastic myeloma cells in the presence of secondary antibody in a dose-dependent manner. In contrast, 2D7 antibody did not affect cell viability of normal blood cells. To establish HLA class I-targeting therapy, we generated a recombinant single-chain Fv diabody (2D7 diabody). We found that 2D7 diabody induced myeloma cell death more efficiently than 2D7 antibody without any effector-mediated mechanisms. In a severe combined immunodeficiency mouse model of human myeloma, administration of 2D7 diabody significantly reduced M-protein level and prolonged survival of these mice. Next, we analyzed the mechanism of cell death induced by 2D7 diabody using several signal transduction inhibitors. 2D7 diabody-mediated cell death was completely inhibited by actin polymerization inhibitors such as cytochalasin D and latrunculin A, suggesting the involvement of actin network. In fact, 2D7 diabody induced actin aggregation and this type of cell death was different from classical apoptosis. These findings demonstrate that 2D7 diabody specifically and potently induces cell death of neoplastic lymphoid cells expressing high levels of HLA-A, and suggest that HLA-A is a potential target for immunotherapy in patients with lymphoid malignancies.