Signal Regulatory Protein α Sets A Threshold For Dendritic Cell Activation And Abrogation Of Local Cancer Recurrence After Radiofrequency Ablation By Dendritic Cell-based Hyperthermic Tumor Vaccine In Mice

Part I Signal Regulatory ProteinαSets a Threshold for Dendritic Cell ActivationPurpose: Signal regulatory protein (SIRP)a, also known as SHPS-1 or SIRPα, is a transmembrane protein that binds to the protein tyrosine phosphatases SHP-1 and SHP-2 through its cytoplasmic region. Due to its high expression in dendritic cells and macrophages, SIRPαwas often thought to have an important role in the immune system. In innate immune responses, SIRPαhad been proved to play a critically negative role in macrophage activation. However, whether or how SIRPαregulate the adaptive immune response is not very clear. Here we firstly purposed to delineate potential regulations of SIRPαin DCs, and then discussed its potential functions in adaptive immunity against tumor.Experimental Design: To examine SIRPαregulation of the adaptive immune responses, lentiviral-mediated, microRNA-based RNA interference of SIRPαin DC was designed. After infected by lentivirus, in vitro and in vivo growth and survival of DCs were evaluated firstly. Secondly, maturation and cytokine production of DCs regulated by SIRPαwere detected. Thirdly, T cell responses and anti-tumor immune effects were evaluated. Finally, the molecular mechanisms.of SIRPαin regulation of DC function were discussed.Results: SIRPαwas found to suppress the survival, phenotypic and functional maturation of immature dendritic cells (DCs) and to inhibit cytokine production by mature DCs. Moreover, SIRPαsilenced-DCs showed potent antitumor effects by activation of antigen-specific cytotoxic T lymphocytes.Conclusions: This study indicates that SIRPαis a critical regulator of DC function, and inhibiting SIRPαis necessary to evoke potent adaptive immunity and induce effective antitumor responses in an antigen-specific manner. Part II Abrogation of Local Cancer Recurrence after Radiofrequency Ablation by Dendritic Cell-based Hyperthermic Tumor Vaccine in MicePurpose: Radiofrequency thermal ablation (RFA) has become a viable treatment option for small solid focal malignancies. However, aggressive local and distant recurrence indicate a need to combine it with other treatment modalities. Here we investigated whether proactive priming with tumor heat-shocked tumor lysate-pulsed dendritic cells (HT-DC), which mimics RFA effects in vivo, can prevent local cancer recurrence after RFA treatment.Experimental Design: Poorly immunogenic melanoma tumors were established in syngeneic mice and sequentially treated with DC cancer vaccines and RFA. Local cancer recurrence and survival were monitored. In vitro and in vivo induction of antitumor responses of RFA as single modality and in combination with DC pre-vaccination were evaluated by immunohistochemistry, IFN-γrelease, and CTL assay.Results: The combination treatment with HT-DC and RFA showed potent anti-tumor effects compared with either treatment modality alone, with >90% of tumor recurrence abrogated in the combination group. However, pre-vaccination with un-heated tumor lysate-pulsed DC failed to prevent late tumor recurrence, suggesting a need for hyperthermia-induced DC activation and cryptic antigen presentation. The spleens of mice treated with HT-DC plus RFA contained tumor-specific cytotoxic and IFN-γ-secreting T ells whereas the spleens of control groups did not. Moreover, adoptive transfer of splenocytes from successfully treated tumor-free mice protected naive animals from a tumor recurrence after RFA, and this was mediated mainly by CD8+ T cells.Conclusions: The optimal priming for the DC vaccination before RFA is important for boosting antigen-specific T cell responses and this combined modalities may provide a potent therapeutic strategy for cancer treatment.