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CCL5-Mediated Endogenous Antitumor Immunity Elicited by Adoptively Transferred Lymphocytes and Dendritic Cell Depletion

Departments of ¹ Microbiology and Immunology and ² Medicine, Dartmouth Medical School, Lebanon, New Hampshire

Requests for reprints: Jose R. Conejo-Garcia, 640W Borwell, HB 7556, 1 Medical Center Drive, Lebanon, NH 03756. Phone: 603-650-6822; Fax: 603-650-6223; E-mail: Jose.R.Conejo-Garcia{at}Dartmouth.edu.

Key Words: adoptive T cells • immunotherapy • ovarian cancer

Adoptive transfer of antitumor T cells is a promisingly effective therapy for various cancers, but its effect on endogenous antitumor immune mechanisms remains largely unknown. Here, we show that the administration of naive T cells de novo primed for only 7 days against tumor antigens resulted in the durable rejection of otherwise lethal ovarian cancers when coupled with the depletion of tumor-associated immunosuppressive dendritic cells (DC). Therapeutic activity required tumor antigen specificity and perforin expression by the adoptively transferred T cells, but not IFN- production. Importantly, these shortly primed T cells secreted large amounts of CCL5, which was required for their therapeutic benefit. Accordingly, transferred T cells recruited CCR5⁺ DCs into the tumor, where they showed distinct immunostimulatory attributes. Activated CCR5⁺ host T cells with antitumor activity also accumulated at tumor locations, and endogenous tumor-specific memory T cells remained elevated after the disappearance of transferred lymphocytes. Therefore, persistent, long-lived antitumor immunity was triggered by the administration of ex vivo activated T cells, but was directly mediated by immune cells of host origin. Our data unveil a CCL5-dependent mechanism of awakening endogenous antitumor immunity triggered by ex vivo expanded T cells, which is augmented by tumor-specific targeting of the cancer microenvironment. [Cancer Res 2009;69(15):6331–8]