A dendritic cell-based vaccine effects on T-cell responses compared with a viral vector vaccine when administered to patients following resection of colorectal metastases in a randomized phase II study.

Abstract

2533 Background: CD8+ T cell responses to colorectal cancer are associated with longer survival. This has led to the hypothesis that cancer vaccines, capable of activating T cell responses, may improve clinical outcome. Vaccines based on antigen-presenting cells/dendritic cells (DC) and viral vectors, potent stimulators of adaptive immunity, have been associated with enhanced survival in prostate cancer patients. We compared rates of tumor antigen-specific T cell and antibody responses between a DC and a poxvector vaccine. The clinical outcome data is reported elsewhere. Methods: 74 patients with no evidence of disease after colorectal cancer metastasectomy and completion of peri-operative chemotherapy were randomized 1:1 to receive injections of one of either: DC mixed with PANVAC-VF (poxvectors encoding CEA, MUC1, CD54, CD58, CD80) or PANVAC-VF along with local injections of GM-CSF. Peripheral blood was drawn before and after completing the immunizations for analysis of CEA and MUC-1 immune (T cell and antibody) responses by ELISPOT and ELISA. Results: T cell responses against CEA were significantly more frequent in the DC arm (69 versus 41%, p=0.02) although the magnitude of the T cell response among responders was similar. There was a trend for improved relapse-free survival among patients with CEA-specific T cell responses (log rank p = 0.10). The antibody response to CEA was more frequent with the PANVAC alone (100% versus 67%, (p= 0.018)) and the antibodies in serum from vaccinated patients could bind to CEA-expressing tumor cells and mediated ADCC. No antibody response was induced against MUC-1. The antibody response against CEA did not correlate with clinical benefit. Few deaths were observed limiting comparison of survival by immune response. Conclusions: A dendritic cell vaccine leads to a greater frequency of CEA-specific T cell responses which is associated with enhanced RFS. Ongoing studies are evaluating the role of additional immunostimulatory cytokines and modulation of regulatory cell populations and molecules in enhancing the adaptive immune response to the DC-based vaccine.