Active Immunotherapy with Pox Vector Modified DC

这个修订后的项目将测试用编码肿瘤抗原癌胚抗原（CEA）的痘载体修饰的树突状细胞（DC）是否会在结肠癌患者中诱导肿瘤抗原特异性T细胞的临床有效频率。抗原特异性T细胞的活化和增殖是临床有效免疫反应的必要条件。有希望的激活抗原特异性T细胞的方法包括使用抗原负载DC。在资助的最初阶段，我们给患有最小CEA的患者施用装载mRNA编码的DC

This revised project will test whether dendritic cells (DC) modified with pox vectors encoding the tumor antigen carcinoembryonic antigen (CEA) will induce a clinically-effective frequency of tumor antigen-specific T cells in patients with colon cancer. Antigen-specific T cell activation and proliferation are essential for clinically effective immune responses. Promising methods for activating antigen-specific T cells include the use of antigen loaded DC. During the initial period of funding, we administered DC loaded with mRNA encoding CEA to patients with minimal residual disease following resection of hepatic metastases of colon cancer. Although the DC were well-tolerated, we observed little augmentation of the CEA-specific immune response and no improvement in recurrence free survival. This can be explained partly by inadequate antigen expression and presentation within the DC, by poor T cell activation due to low levels of costimulatory molecules such as CD80 on the immature DC, and by limited immunogenicity of the native tumor antigen. To overcome these problems, we have modified DC with recombinant, replication-defective pox vectors (including vaccinia (rV) and fowlpox (rF)) that express a TRiad of COstimulatory Molecules (CD80, CD54, and CD58, designated TRICOM) as well as a modified tumor antigen CEA(6D), with an amino acid substitution that creates a more potent epitope. In a phase I study of patients with CEA-expressing malignancies who received ex vivo generated DC modified with rF-CEA(6D)-TRICOM, we detected antigen-specific T cell responses in the range of 0.1-0.5% of the peripheral blood mononuclear cells (PBMC). Clinical benefit was associated with the highest levels of immune response. Recently, it has been observed that greater levels of immune response to pox vector-encoded antigens occur with heterologous prime-boost immunizations. Priming with vaccinia encoding CEA followed by boosts with fowlpox encoding CEA has been suggested to improve survival in patients with advanced cancer. Nonetheless, the induced CEA-specific immune responses were 0.01% or less of the PBMC. We hypothesize that prime-boost strategies with pox vector-modified DC will achieve greater clinical benefit by increasing the level of CEA-specific T cell activity. Therefore, we propose a phase II study to choose between two immunization strategies, DC infected with rV-CEA(6D)-TRICOM followed by DC infected with rF-CEA(6D)-TRICOM or rV-CEA(6D)-TRICOM followed by rF-CEA(6D)-TRICOM, in terms of which is associated with a better rate of disease-free survival at 2 years following hepatic metastasis resection and adjuvant chemotherapy. We will also measure the rate and magnitude of the CEA-specific immune response by ELISPOT. IL-2 increases the magnitude of the CEA specific T cell responses to pox-vector immunizations. Therefore, we will subsequently explore the role of IL-2 in augmenting CEA-specific immunity when given with the optimal immunization strategy.