REGULATION OF VACCINE-INDUCED ANTI-TUMOR IMMUNITY BY CD4+CD25+ T CELL HYBRIDOMAS.

2.3
#40-OR
REGULATION OF VACCINE-INDUCED ANTI-TUMOR IMMUNITY BY CD4+CD25+ T CELL HYBRIDOMAS.
David Lubaroff Ph.D. , Jeanne Howard MS , Mohamed Nasr MD and Elizabeth Field MD . Iowa City IA, VA Medical Center, 52240, Research Department ; Iowa City IA, University of Iowa, 52242, Department of Urology and Iowa City IA, University of Iowa, 52242, Department of Internal Medicine .

Vaccination of mice with a replication-deficient adenovirus recombinant for the prostate specific antigen (PSA) gene (Ad/PSA) induces strong anti-PSA immune responses that can be measured by enumeration of interferon-γ secreting T cells using intracellular cytokine staining (ICS) and cytotoxicity (CTL). CD4+CD25+ regulatory T cells down-regulate a variety of immune responses, including anti-tumor immunity. We previously described the generation of RD6+ CD4+CD25+ hybridomas that inhibit polyclonal and alloantigen triggered T cell responses in vitro. In this study we investigate whether RD6+ hybridomas suppress immune response to the anti-tumor Ad/PSA vaccine in vivo. BALB/c mice were injected intravenously with RD6+ or the BW5147 fusion-partner cell line and then vaccinated with either Ad/PSA or control Ad/lacZ 24 hours later. Two weeks after vaccination spleen cells were analyzed for the number of CD8+IFNγ+ cells by ICS and cytotoxic activity against PSA-secreting RM11/PSA or control RM11/neo target cells. BALB/c mice given RD6+ hybridomas showed a 35.7 percent decrease in cytotoxic activity and a 73.7 percent decrease in the number of CD8+IFNγ+ secreting cells compared to mice that received the vaccine alone. These data demonstrate that pre-treatment with CD4+CD25+ hybridoma can inhibit the development of vaccine-induced anti-PSA responses. Future studies will examine the translation of this inhibition to the ability of the hybridoma recipients to destroy tumors following the injection of PSA-secreting prostate tumor cells. These studies will allow us to examine the function of regulatory CD4+CD25+ cells in vaccine-induced active immunotherapies for cancer.