Development of a novel T-cell immunotherapy targeting HEATR1.

Abstract

149 Background: Allogeneic hematopoietic stem cell transplantation (HCT) often cures acute leukemia. However leukemic relapse remains a major cause of HCT failure, and patients with post-HCT relapse have a very poor prognosis. We are developing T cell immunotherapies targeting leukemia-associated minor histocompatibility (H) antigens to manage post-HCT relapse. Because the presentation of minor H antigens is HLA-restricted, a panel of hematopoietic-restricted, leukemia-associated minor H antigens is required to enable the development of broadly applicable minor H antigen targeted immunotherapy. We previously discovered a HLA- B*0801-restricted, leukemia-associated minor H antigen, HEATR1. We showed that HEATR1-specific T cells can specifically kill leukemic blasts and prevent engraftment in a murine model, implying that this minor H antigen is expressed in leukemic stem cells. We have now developed immunotherapy targeting HEATR1 using genetically modified T cells. Methods: We isolated a HEATR1-specific T cell clone from the peripheral blood of a normal donor and sequenced its T cell receptor (TCR). The TCR was codon-optimized and cysteine-modified to maximize expression in T cells and reduce the risk of mispairing with endogenous TCR chains, then cloned into a multicistronic lentiviral vector (LV). Primary CD8+T cells were transduced with the HEATR1 TCR LV and evaluated with a range of assays. Results: The HEATR1-specific T cell clone specifically killed B8+ HEATR1+ primary leukemia. Similarly, CD8+ HEATR1 TCR-transduced T cells killed target cells pulsed with HEATR1 peptide (ISKERAEAL), but not the allelic variant control peptide (ISKERAGAL), and specifically killed cell lines that endogenously present the HEATR1 minor H antigen. HEATR1-transduced T cells also secrete cytokines and proliferate in response to HEATR1+ but not HEATR1-cells. Conclusions: We have demonstrated that HEATR1-specific T cell clone and HEATR1 TCR-transduced T cells can kill HEATR1+ cells. If the safety and efficacy of HEATR1 TCR immunotherapy is confirmed in further preclinical studies, development of phase I clinical studies will be warranted and may ultimately provide a new option for management of relapse after HCT.