T Cell Receptor Gene Transfer to Produce MHC Class I-Restricted CD4 Helper T Cells: Implications for Immunotherapy of Leukaemia.

CD4 helper T cells play a critical role in the anti-tumour immune response. Cytokines secreted by CD4 T cells can have a direct effect on tumour cells and provide help for CTL priming and effector function. In this study we tested if it was possible to generate MHC class I-restricted helper T cells by retroviral TCR gene transfer into CD4 lymphocytes. Methods: We used a TCR (utilising V11) that recognises the influenza virus A nucleoprotein (NP366–379) peptide in the context of murine D^b MHC class I. Murine splenocytes were isolated from C57BL/6 mice (H2^b) and activated with conconavalin A and IL-7, and after 48 hours transduced with the pMX-TCR-IRES-TCR retroviral vector. The transduced splenocytes were then cultured in the presence of IL2 for a further 48 hours before staining with anti-murine CD4, CD8 and V11 antibodies and sorting into CD4+ V11+ and CD8+ V11+ populations. Sorted cells were expanded for a further 48–72 hours prior to functional assays. Functional Assays: Purified TCR-transduced (TCR-Td) CD8+ cells and purified TCR-Td CD4+ cells were tested for IFN secretion in response to dendritic cells (DCs) pulsed with NP peptide, an irrelevant peptide (pMDM100) or no peptide. Further experiments examined IFN secretion in response to peptide-loaded tumour cells (EL4 murine lymphoma cells) or transfected tumour cells expressing NP endogenously. Secretion of IFN was measured by ELISA. Results: (1) Antigen-specific IFN secretion was observed by both CD8+ (100% purity) and CD4+ cells (99.93% purity) expressing the class I-restricted TCR when incubated with peptide-loaded DCs. When tested with no peptide or irrelevant peptide, no IFN secretion was observed. The CD8+ cells were more sensitive, recognizing lower concentrations of peptide (10pM) than CD4+ cells (100pM). With peptide-coated EL4 tumour cells as stimulator cells, CD8+ cells showed a peptide-specific response. In contrast, the TCR-Td CD4+ cells were only able to elicit a weak peptide-specific response. Similarly, TCR-Td CD8+ cells were able to recognise NP transfected EL4 tumour cells (EL4NP68), whereas the CD4+ cells were unable to. However, the addition of syngeneic DCs restored the CD4+ cell response to NP transfected EL4 tumour cells to one equivalent to that seen with the TCR-Td CD8+ populations (Table 1). Summary: We have demonstrated that it is feasible to generate MHC class I-restricted CD4+ helper T cells, that are specific for peptide epitopes presented in the context of MHC class I. The CD4+ T cells can recognise antigen-expressing tumour cells in the presence of professional APC, such as DCs. The mechanism by which APC restore tumour recognition may involve trans-costimulation or cross presentation. The data suggest that class I-restricted CD4+ T cells may be able to contribute to enhanced anti-tumour immunity.

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γIFN Secretion (ng/ml) After Stimulation with DCs or Tumour Cells