Priming and Activation of Human Ovarian and Breast Cancer-specific CD8+ T Cells by Polyvalent Listeria monocytogenes-based Vaccines

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Immunotherapeutic vaccine is potentially an effective strategy to combat cancer. Essential components of an effective vaccine must include antigens that are processed by the major histocompatibility complex class I pathway, presented by the tumor major histocompatibility complex molecules, and an effective antigen delivery platform that is capable of breaking self-tolerance. In this study, we characterized a set of ovarian cancer-specific T-cell epitopes delivered by live-attenuated recombinant Listeria monocytogenes (Lm ΔactAΔinlB) as a vaccine vector. We present data that peptide-specific T cells recognize the human monocytic cell line THP-1 infected with recombinant Lm ΔactAΔinlB encoding the epitopes. Furthermore, we demonstrate that recombinant L. monocytogenes (Lm)-infected antigen-presenting cells can prime and expand epitope-specific CD8+ T cells in vitro and such CD8+ T cells recognize not only peptide-loaded targets but also ovarian and breast tumor cells presenting endogenous epitopes. Finally, peptide-specific T cells generated using peripheral blood mononuclear cell from ovarian cancer patients recognize target cells infected with recombinant Lm ΔactAΔinlB encoding the epitopes. Our results demonstrate that live-attenuated recombinant Lm can be used effectively as a vehicle to deliver cancer peptide antigens singly or as a multiepitope construct. Thus, the use of recombinant live-attenuated Lm strains encoding endogenously processed and presented tumor epitopes/antigens represents an attractive strategy for active cancer immunotherapy in a clinical setting.

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