leukotoxin and Lymphoma--B-Cell

Leukotoxin (LtxA) is a protein secreted from the oral bacterium Aggregatibacter actinomycetemcomitans. LtxA binds to the β2 integrin lymphocyte-associated function antigen-1 (LFA-1) on human white blood cells (WBCs), resulting in cell death. LtxA is currently under investigation as a novel therapy (Leukothera(®)) for treating hematologic malignancies and autoimmune diseases. We show here that LtxA has potent in vivo anti-lymphoma activity in mice. LtxA caused complete regression of B-cell tumors and promoted long-term survival of mice. The mechanism of LtxA-mediated killing of malignant lymphocytes was further examined. We found that LtxA kills malignant lymphocytes by a novel mechanism requiring the death receptor Fas and caspase-8, but not Fas ligand (FasL) or caspase-9. We also determined that LFA-1 and Fas are closely associated on the cell surface and this proximity of LFA-1 and Fas could explain how signaling through an integrin can lead to cell death. In addition to LFA-1, this work reveals a second surface protein, Fas, that is critical for LtxA-mediated cell death. Knowledge of the mechanism of cell death induced by LtxA will facilitate the development and understanding of this potent experimental therapeutic agent.

Topics: Aggregatibacter actinomycetemcomitans; Animals; B-Lymphocytes; Bacterial Toxins; Caspase 8; Caspase 9; Drug Delivery Systems; Exotoxins; fas Receptor; Humans; Immunosuppressive Agents; Jurkat Cells; Lymphocyte Function-Associated Antigen-1; Lymphoma, B-Cell; Mice; Mice, Inbred NOD; Mice, SCID; Xenograft Model Antitumor Assays