Abstract

Human Vα24+ Natural Killer T (NKT) cells are cytotoxic against a range of malignancies, including human lymphoma and myeloid leukaemia in vitro and in murine models in vivo. Human NKT cells are activated by α-galactosylceramide (KRN7000) when presented by the MHC Class I-like molecule, CD1d, expressed by antigen presenting cells, particularly dendritic cells (DCs). Successful activation of human NKT cell antitumor activity in a clinical setting, particularly if this also activates natural killer (NK) cells and enhances tumor-specific cytotoxic T lymphocyte (CTL) activity, has the potential to be more potent and effective than current strategies focusing entirely on activation of peptide antigen specific CTL. In order to evaluate this we initiated a clinical study aiming to determine whether all three cell types could be activated with a single therapy. Melanoma was evaluated because of the known responsiveness to DC based immune therapy and the availability of well-defined peptide tumor antigens amenable to evaluation in a large number of subjects. Subjects with stage IV metastatic melanoma who were HLA-A*0201 were randomized to receive multiple intradermal or intravenous treatments with autologous mature monocyte derived DC pulsed with KRN7000, 4 peptide antigens (Mart-1, gp100, tyrosinase and Mage 3) or both. Peripheral blood NKT cells, NK cells and CD8+ CTL specific for the four melanoma antigens were monitored before, during, and after the series of treatments using 5 color flow cytometry. Antigen specific CTL were monitored using tetramers obtained from Beckman Coulter. Our results were that DC pulsed with KRN7000 + peptide were able to activate NKT cells and NK cells as well as increase the number of tumour antigen specific CTL. Activation of NKT and NK cells was most marked after intravenous treatment. However increased tumor antigen specific CTL were observed after treatment by both routes. Minor disease responses and stabilization were noted in subjects with non-bulky disease. We conclude that activation of NKT, NK and antigen specific CTL is possible with a single modality of immune therapy and that this is associated with disease responses.

Disclosures: Administration of autologous dendritic cells pulsed with KRN7000.; None of the authors recieve salary from the company listed below.; Recieve research funding from Kirin Pharmaceutical Division.

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