OS2.6 Identification of IDH1R132H-specific T cell receptors from a humanized mouse model and from glioma patients treated with an IDH1R132H-specific peptide vaccine

Abstract

AbstractCentral to clinically relevant immunotherapy of gliomas are the discovery of tumor-specific antigens and the development of therapeutic strategies that effectively exploit them. One such example is the mutation in the gene encoding for isocitrate dehydrogenase 1 (IDH1). The point mutation IDH1R132H is the most frequent one in grade II and grade III gliomas and secondary glioblastomas. We have previously shown that a peptide vaccine encoding the IDH1R132H epitope evokes an MHC II restricted CD4+ T Helper-1 cell (TH1) immune response and is therapeutic in an MHC-humanized A2.DR1 mouse tumor model.To determine the clonality in the T-cell receptor (TCR) repertoire of the IDH1R132H specific T-cells, a T-cell line was developed from splenocytes of vaccinated A2.DR1 mice by re-stimulations with autologous, naive irradiated and p132–142 (IDH1R132H)-loaded splenocytes. The cells were then sorted for IDH1R132H specificity by tetramer staining. Deep sequencing analyses of the variable V-J or V-D-J regions of the TRA and TRB genes, which code for the hyper-variable regions of the TCR-alpha and TCR-beta chains, respectively, revealed multiple dominant TRA and TRB sequences. Full length TCRs were constructed by pairing the two most dominant TRA and TRB sequences and cloned into expression vectors for functional validation.In addition to identifying the murine HLA-DR1-restricted TCR, we have analysed IDH1R132H-specific TCRs from a patient with a progressive IDH1R132H-mutated astrocytoma, who has been treated with an IDH1(R132H) vaccine on a compassionate use basis. Single T-cells from this patient, who had a high baseline mutation-specific T-cell response, specifically responding to IDH1(R132H), were expanded in vitro and subjected to single-cell-sorting and subsequent TCR sequencing. 11 different TCR sequences have been identified.The long-term goal is to develop an adoptive T-cell therapy using autologous IDH1R132H-specific T cells.