Re-Engineering γ δ T Cells by α β T Cell Receptor Gene Transfer Creates Potent Effector Cells with Anti-Leukemic Reactivity.

Retroviral transfer of T cell receptors (TCRs) to peripheral blood derived T cells generates large numbers of T cells with the same antigen specificity, which can potentially be used for adoptive immunotherapy. One drawback of this procedure is the formation of mixed α β TCR dimers with unknown specificities due to pairing of endogenous and introduced TCR chains. To completely prevent the formation of mixed TCR dimers by TCR gene transfer to α β T cells we investigated whether γ δ T cells can serve as alternative host T cells for α β TCR transfer, since the γ δ TCR is not capable of forming dimers with the α β TCR. Peripheral blood derived γ δT cells were isolated by immunomagnetic bead isolation and subsequent FACS sorting, resulting in >99% pure populations of γ δT cells. The isolated γ δT cells were retrovirally transduced with three different TCRs specific for the hematopoietic minor histocompatibility antigen (mHag) HA-2 in the context of HLA-A2, for CMV-pp65 in the context of HLA-B7, or for the HLA class II restricted mHag DBY. The TCR-transduced γ δT cells expressed both the introduced TCRs and the endogenous γ δTCR at their cell surface as determined by FACS analysis. When γ δT cells transduced with the HLA class I restricted HA-2-TCR or CMV-TCR were stained with tetramers, only the CMV-TCR expressing γ δT cells but not the HA-2-TCR expressing γ δT cells were capable of strong antigen specific tetramer binding. In contrast, functional analysis indicated that all TCR-transduced γ δT cells specifically recognized peptide pulsed target cells leading to target cell lysis and IFNγ and IL-4 production, indicating that while the avidity of the HA-2-TCR engineered γ δT cells was insufficient for strong antigen specific tetramer binding, the avidity was high enough for the specific recognition of peptide pulsed target cells. However, the functional reactivity of the TCR-transduced γ δT cells against target cells presenting endogenously processed antigens was low. FACS analysis indicated that most γ δT cells lacked the expression of the coreceptors CD4 and CD8. Therefore, we investigated whether introduction of the relevant coreceptor could enhance the functionality of the redirected γ δT cells. Co-transfer of the CD8α β coreceptor to the HA-2-TCR and CMV-TCR transferred γ δT cells turned them into effective, antigen specific tetramer binders. Furthermore, expression of CD8α β by the HA-2-TCR and CMV-TCR transduced γ δT cells and CD4 by the DBY-TCR transduced γ δT cells generated powerful effector cells exerting high levels of antigen specific lysis of both peptide pulsed target cells and target cells presenting endogenously processed antigen. In addition, coreceptor expressing TCR-engineered γ δT cells produced high amounts of IFNγ and IL-4 when stimulated with peptide pulsed target cells or endogenously processed antigen. To investigate the anti-leukemic reactivity of TCR-transferred γ δT cells, we determined the antigen specific cytotoxicity and cytokine production against primary CML and AML cells by γ δT cells equipped with the HA-2-TCR and CD8α β . We observed both antigen specific cytolytic activity and cytokine production against both CML and AML cells expressing the hematopoiesis specific mHag HA-2, while HLA-A2⁺ leukemic cells lacking expression of the HA-2 mHag were not recognized. These data demonstrate that transfer of α β TCRs to γ δT cells generated potent effector cells for immunotherapy of leukemia, without the expression of potentially hazardous mixed TCR dimers.