Immunotherapy with IL-2 is accompanied by severe toxicity leading to development of vascular leak syndrome (VLS). Previous studies from our laboratory demonstrated that CD44 knockout mice exhibit marked decrease in IL-2 induced VLS, thereby suggesting a role for CD44 in VLS. In the current study we tested whether use of mAbs against CD44 or hyaluronic acid (HA), the ligand for CD44, can abrogate IL-2 induced VLS. Administration of IL-2 (75,000 U/mouse, three times a day for 4 days) into C57BL/6 mice triggered significant VLS in the lungs and liver. Interestingly, HA caused a marked increase in IL-2-induced VLS in the lungs and liver. In contrast, use of anti-CD44 mAbs reduced IL-2-induced VLS in the lungs and liver. The change in VLS seen following HA or anti-CD44 mAbs treatment was not due to any defect in lymphocyte migration or homing to various organs because histopathological studies in these mice demonstrated significant and often greater perivascular infiltration of lymphocytes when compared to mice treated with IL-2 alone. However, HA treatment exhibited a marked increase in IL-2-induced lymphokine-activated killer (LAK) cell activity while anti-CD44 mAbs treatment led to a significant decrease in IL-2-induced LAK cell activity. These studies demonstrate that HA or anti CD44 mAbs may serve as a useful tool to selectively alter the LAK activity as well as to prevent the toxicity induced by IL-2. Altering CD44-HA interactions in vivo may offer a novel therapeutic approach to prevent endothelial cell injury by cytotoxic lymphocytes in a variety of clinical diseases. / Master of Science

In addition to the antigen-specific receptors, the T and B cells also express a variety of adhesion molecules, which are known to participate in cell-cell interaction, migration, homing and signal transduction. CD44 is a widely distributed cell surface glycoprotein whose principal ligand has been identified as hyaluronic acid (HA), a major component of the extracellular matrix. In the current study, we investigated whether HA or mAbs against CD44 would induce a proliferative response in mouse lymphocytes. Spleen cells from normal and nude but not severe combined immunodeficient mice, exhibited strong proliferative responsiveness to stimulation with soluble HA or anti-CD44 mAbs. Furthermore, purified B cells but not T cells were found to respond to HA. These data demonstrated that interaction between HA and CD44 can regulate murine B cell effector functions and that such interactions may play a critical role during normal or autoimmune responsiveness of B cells. Endothelial cell injury resulting in vascular leak syndrome (VLS) is one of the most widely noted phenomenons in a variety of clinical diseases, however, the underlying reason for which remains unclear. We used interleukin-2 induced VLS as a model to investigate the role of cytolytic lymphocytes in the direct cytotoxicity of endothelial cells. BL/6 wild-type mice developed significant VLS in the lungs, liver and spleen following IL-2 administration. Interestingly, perforin-knockout mice exhibited marked decrease in VLS in all three organs tested. Also, FasL-defective (gld) mice and Fas-deficient (lpr) mice exhibited decreased VLS in the liver and spleen, but not in the lungs. These results demonstrated for the first time that perforin and FasL may actively participate in endothelial cell injury and induction of VLS in a variety of organs. Inasmuch as, CD44 also plays a major role in the lymphocyte adhesion to the endothelial cells, we used CD44-knockout mice and observed that such mice exhibited markedly diminished VLS following IL-2-treatment. Our data also suggested that blocking CD44 helps in reducing the IL-2-induced VLS and therefore such an approach may serve as a useful tool to prevent endothelial cell damage seen in a variety of clinical disorders. / Ph. D.