Adoptive cell therapy (ACT) utilizes patient-derived CD8+ T cells to mount anti-tumour response, leading to tumour regression. Despite recent advances, ACT is limited by the presence of immunosuppressive regulatory T cells (Treg) within solid tumours. We are investigating the adoptive transfer of genetically modified CD8+ T cells to enhance anti-tumour immune response. Cbl-b is an E3 ubiquitin ligase that negatively regulates TCR signalling. Ablation of Cbl-b in CD8+ T cells have been shown to enhance proliferation and induce an inflammatory phenotype. The primary objective of this study was to investigate the mechanism of Cbl-b deficient CD8+ T cell resistance against Tregs. Cbl-b-/- CD8 T cells were characterized by surface marker expression and cytokine secretion profile. Furthermore, Treg suppression assays (TSA) were conducted with CD8+ T cells from either C57BL/6 or Cbl-b-/- mice to determine the role of Cbl-b dependent resistance against Tregs. We demonstrated that Cbl-b-/- CD8+ T cells had an increased expression of activation markers, hyper-secretion of pro-inflammatory cytokines, and were unresponsive to Treg immunosuppression. Exogenous introduction of IFN-γ was sufficient in inducing Treg resistance specifically in WT CD8+ T cells. Finally, TSA performed using CD8+ T cells or Tregs from IFN-γR1-/- mice demonstrated that IFN-γ confers Treg resistance in an autocrine-dependent manner. We report that ablation of Cbl-b results in IFN-γ dependent CD8+ T cell resistance against Treg cells. While IFN-γ has previously been shown to enhance anti-tumour immunity by enhancing T cell activation, this study is the first to demonstrate its role in resistance of immune suppression.
Princess Margaret Hospital
University Health Network (Princess Margaret Hospital)
Princess Margaret Cancer Centre