Abstract
2508 Background: We hypothesize that the activity of vaccines based on DC loaded with tumor antigens will be enhanced by modifications that increase antigen expression and costimulatory activity of the DC. Methods: In an ongoing phase I study, we are administering 1, 2, or 3 cycles of 4 triweekly subcutaneous / intradermal injections of ex vivo generated DC (5 x 10E6 cells) modified with the recombinant fowlpox vector rF-CEA(6D)-TRICOM (2.5 x 10E7 pfu/5 x 10E7 DC). Results: Thus far, 14 patients have been enrolled into the first 2 cohorts. There were no grade 3/4 toxicities directly referable to the immunizations. One patient had a decrease in the CEA level from 46 to 6.8 and a minor regression in supraclavicular adenopathy that occurred several months after completion of the immunizations. Three other patients were stable through at least 1 cycle of immunization (3 months). Direct analysis of T cells in peripheral blood using the ELISpot assay demonstrated an increase in the frequency of T cells specific for the CEA-expressing vector in 10 of the 12 patients completing participation (range 10 to 541 CEA-specific cells/100,000 peripheral blood mononuclear cells (PBMC).) A greater CEA-specific response was observed for patients with either a minor response or stable disease following at least 1 cycle of therapy compared with those who progressed (mean of 241 vs 50 CEA-specific cells/100,000 PBMC, P=0.03). Cytokine flow cytometry demonstrated that the CEA-specific immune response occurred amongst both CD4 and CD8+ T cells in all responders. Changes in the frequency of CD4+CD25+ regulatory T cells were observed and, in some patients, were inversely correlated with the frequency of CEA-specific CD4+ T cells suggesting that regulatory mechanisms might impact the greatest magnitude of CEA-specific T cells that can be achieved. Conclusions: This immunization strategy is safe and feasible and activates potent CEA-specific immune responses. This study will continue into the third cohort. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Therion Biologics Corp.
Published Version
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