Abstract A024: Identifying a T-cell receptor for immunotherapy against a leukemia-associated self-antigen in an allogeneic setting

Our aim was to identify a T-cell receptor (TCR) that recognizes a leukemia-associated self-antigen that is highly expressed in acute myeloid leukemia and that is restricted by HLA-A2 (expressed in approximately 50% of Caucasians) for future adoptive T-cell therapy. Tumor-associated self-antigens (self-TAA) make attractive targets for adoptive T-cell therapy in cancer. However, autologous T-cells are tolerant to self-TAA expressed on self-HLA if antigen expression is sufficiently high. In contrast, T-cells are not tolerant to self-antigens presented on non-self HLA. By identifying alloreactive T-cells reactive to self-peptide in complex with foreign HLA and subsequently cloning their TCR, it is possible to redirect patient T-cells against self-TAA. The advantage of targeting self-antigens is the potential application of TCR-engineered T-cells in all cancer patients with a certain cancer type and expressing the restricting HLA molecule. We identified a protein that is selectively expressed in normal myeloid cells and highly expressed by leukemic cells in patients with acute myeloid leukemia (AML). HLA-A2 negative CD8 T-cells from healthy donors were stimulated with HLA-A2 positive dendritic cells that were expressing the full-length target antigen. CD8 T-cells recognizing peptides from the target antigen in complex with HLA-A2 were subsequently identified and sorted using fluorescently labeled HLA-A2-peptide-multimers. T-cell clones obtained from sorted multimer-positive T-cells responded to HLA-A2 positive patient leukemia cells and cell lines expressing the antigen, whereas no response was seen to HLA-A2 positive antigen negative targeT-cells, unless loaded with the relevant peptide. Responses were measured as secretion of interferon gamma, expression of the T-cell activation marker CD137 or expression of the degranulation marker CD107. The TCR sequences were identified, and we next evaluated specificity and functionality of TCR-engineered cells. Indeed, TCR-transduced healthy donor T-cells were able to selectively kill HLA-A2 positive AML patient-derived leukemic cells as well as antigen positive cell lines in vitro. We also performed a comprehensive peptide scan to determine potential cross reactivity of the obtained TCR. For this scan, the amino acids (AA) in each position of the target peptide-epitope were individually replaced by every other natural amino acid (19 AA for each position x 9 postions = 171 peptides). In addition, potential responses to other variants of the 9mer target peptide based on the natural antigen protein sequence were evaluated (8mer, 10mers, 11mers and 12mers). Based on the results obtained with TCR-transduced T-cells (interferon gamma ELISA), candidate peptides naturally occurring in the proteome to which our TCR could cross-react were not identified. These data warrant further evaluation of the TCR for in vivo efficacy and specificity. Citation Format: Maxi-Lu Boschen, Weiwen Yang, Erlend Stronen, Johanna Olweus. Identifying a T-cell receptor for immunotherapy against a leukemia-associated self-antigen in an allogeneic setting [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A024.