Development of T-cell immunotherapy for hematopoietic stem cell transplantation recipients at risk of leukemia relapse.

Leukemia relapse remains the major cause of allogeneic hematopoietic stem cell transplantation (HCT) failure, and the prognosis for patients with post-HCT relapse is poor. There is compelling evidence that potent selective antileukemic effects can be delivered by donor T cells specific for particular minor histocompatibility (H) antigens. Thus, T-cell receptors (TCRs) isolated from minor H antigen-specific T cells represent an untapped resource for developing targeted T-cell immunotherapy to manage post-HCT leukemic relapse. Recognizing that several elements may be crucial to the efficacy and safety of engineered T-cell immunotherapy, we developed a therapeutic transgene with 4 components: (1) a TCR specific for the hematopoietic-restricted, leukemia-associated minor H antigen, HA-1; (2) a CD8 coreceptor to promote function of the class I-restricted TCR in CD4+ T cells; (3) an inducible caspase 9 safety switch to enable elimination of the HA-1 TCR T cells in case of toxicity; and (4) a CD34-CD20 epitope to facilitate selection of the engineered cell product and tracking of transferred HA-1 TCR T cells. The T-cell product includes HA-1 TCR CD4+ T cells to augment the persistence and function of the HA-1 TCR CD8+ T cells and includes only memory T cells; naive T cells are excluded to limit the potential for alloreactivity mediated by native TCR coexpressed by HA-1 TCR T cells. We describe the development of this unique immunotherapy and demonstrate functional responses to primary leukemia by CD4+ and CD8+ T cells transduced with a lentiviral vector incorporating the HA-1 TCR transgene construct.