Activated CD4+ T Cells Dramatically Enhance Chemotherapeutic Tumor Responses In Vitro and In Vivo

Chemoimmunotherapy has been widely studied in melanoma, with various degrees of success. One of the most common approaches is the so-called biochemotherapy, which is associated with increased toxicities, but without overall survival benefit. Another conventional strategy is the use of chemotherapy as an immunomodulator to enhance the effect of cancer vaccines or adoptive cell transfer therapy. Based on this approach, recent studies using chemotherapy to prepare the host before the infusion of ex vivo-activated, melanoma Ag-specific tumor-infiltrating lymphocytes and high dose IL-2 resulted in an impressive response rate. However, the development of immunotherapy for the treatment of a broad range of cancer type is still lacking. In this study, we report the development of a simple yet universal approach termed chemocentric chemoimmunotherapy that has potential application in the treatment of all cancer types. This technique uses nonspecifically activated CD4(+) T cells as a chemosensitizer before the administration of chemotherapy. Dramatic enhancement of the cytotoxic effect of chemotherapeutic drugs, either active or nonactive as single agents, was observed both in in vitro and in vivo human tumor xenograft models. Soluble factors secreted from activated CD4(+) T cells, likely acting on the tumor and its microenvironment, were responsible for the observed effect. Although IFN-gamma played a major role in the therapeutic outcome, it was consistently found to be inferior to the use of activated CD4(+) T cells in tumor chemosensitization. Our model may provide a plausible mechanism to facilitate further understanding, design and development of improved chemoimmunotherapy in the treatment of cancer. The Journal of Immunology, 2009, 183: 6800-6807.