Adjuvant Effect of Chaperone-Rich Cell Lysate: The Effects of CRCL on the Activation of Immune Cells

Abstract

Cancer immunotherapy aims to use and manipulate the host’s immune system to fight against cancer. The objective of this strategy is to induce specific and persistent immune responses leading to tumor eradication. Heat shock proteins (HSP) purified from cancer tissues have been identified as unique mediators of specific anti-tumor immunity. In our laboratory, we have developed an original vaccine, termed CRCL (Chaperone-Rich Cell Lysate) that consists of multiple HSP complexes enriched from tumor lysates. CRCL immunization leads to an efficient protection against a wide variety of murine cancers by inducing a strong, long-lasting, and specific T and NK-cell dependent immune responses against the tumor from which it has been generated. Tumor-derived CRCL has been shown to be more efficient in triggering DC activation than individual purified HSP or tumor lysates. The immunostimulatory effects of CRCL arise from its superior ability to provide a wide variety of tumor antigens to the immune system and by providing potent adjuvant effects. However, CD4⁺CD25⁺ regulatory T lymphocytes (Treg) critically contribute to the mechanisms of cancer-induced suppression. Data from independent groups including ours suggests they may also restrain the function of antigen presenting cells. The current study was designed to elucidate the molecular signaling events triggered by the tumor-derived CRCL vaccine in antigen presenting cells and evaluate whether CRCL may overcome the inhibitory effects of Treg modulation of DC and macrophage activation. Our results indicate CRCL activates DC and macrophages by inducing proinflammatory cytokine chemokine secretion. CRCL induces iNOS expression and NO production in macrophages. CRCL activation of DC and macrophages results in transcription factor NF-κB activation in vitro and in vivo, and this includes the activation of additional signaling molecules upstream of NF-κB. Following CRCL treatment the phenotypic maturation of DC, the production of DC and macrophage pro-inflammatory cytokines, and the activation of the transcription factor NF-κB are not affected by Treg. Additionally, CRCL induced activation of DC is not diminished by the immunosuppressive cytokine TGF-β 1. Our results indicate tumor-derived CRCL-treated DC and macrophages are refractory to Treg inhibition. These results are important for advancing CRCL-based vaccines in Phase I clinical trials.