A ″Non-Fratricidal″ αβ-T Cell Receptor That Targets Survivin Expressed By Hematological Malignancies

Survivin is broadly expressed by hematological malignancies and may be a suitable target for T-cell immunotherapy. Previously, the utility of this approach has been challenged by the occurrence of “fratricide” when T cells expressing a high avidity survivin-specific T cell receptor (TCR) isolated from allogeneic cultures killed each other because survivin epitopes can be presented by T cells themselves (Leisegang M et al, J Clin Invest. 2010;120:3869). To overcome this obstacle, we used autologous cultures to isolate a new T-cell clone targeting the HLA-A*02-restricted survivin_95-104 epitope. This clone displayed nanomolar avidity and specific killing against survivin⁺HLA-A*02⁺ leukemia cells (BV173, 39±16% specific lysis, E:T 40:1) and multiple myeloma cells (U266, 20±7%) but not against HLA-A*02^– HL-60 cells (2±2%). Colony formation of primary myeloid leukemias was inhibited (>50% reduction) while that of healthy bone marrow (BM) was not. The TCR α- and β-chains were cloned in a retroviral vector and used to efficiently transduce CD8⁺ T cells (89±4%, n=6). As compared to non-transduced (NT) T cells, TCR⁺ T cells produced significant lysis of BV173 (46±14% vs 8±6%, E:T 20:1, n=12, p<0.001) and U266 (27±12% vs 14±6%, p=0.003) but not of HL-60 (14±7 vs 14±6 %, p=NS). TCR⁺ cells also inhibited colony formation (32-78% reduction, n=5) of primary myeloid leukemias while preserving normal clonogenic capacity of BM or CB (n=5). When tested in vivo in a xenograft mouse model of leukemia (FFLuc⁺BV173) with bioluminescent imaging, progression was significantly slower in mice treated with TCR⁺ versus NT T cells (8.1x10⁶ ± 9x10⁶ vs 195x10⁶ ± 85x10⁶ photons/sec) (day 40, p=0.003, n=10/group). Overall survival was improved (day 80, p<0.001) and 3/10 mice treated with TCR⁺ T cells completely cleared the leukemia. Crucially, the TCR cloned from our autologous culture system produced no fratricidal activity against HLA-A*02⁺ activated T cells (1±2%, E:T 20:1, n=7). To elucidate at the molecular level the selective antitumor activity of our “autologous” TCR as opposed to the fratricidal “allogeneic” TCRs, we modeled the structure of each TCR-peptide-HLA ternary complex. While the overall binding energies of TCR-peptide-HLA interfaces for both TCRs were similar, the “autologous” TCR showed a 48% higher binding energy contribution for the peptide as compared to the fratricidal TCR, whose interaction was primarily with the HLA molecule rather than with the survivin peptide in the HLA-binding groove. In conclusion, we have cloned a novel survivin-TCR with a highly epitope-specific binding mode that can be efficiently expressed in polyclonal T cells and provides antitumor activity in vitro and in vivo without affecting the survival of T cells or normal hematopoiesis. Our results indicate that maximal recognition of the peptide presented in the HLA groove is critical for TCR selectivity.