Blood 2017 10 19() pii 10.1182/blood-2017-07-791608
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 anti-leukemic effects can be delivered by donor T cells specific for particular minor histocompatibility (H) antigens. Thus, T cell receptors (TCR) 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 four components: 1) a TCR specific for the hematopoietic-restricted, leukemia-associated minor H antigen, HA-1; 2) a CD8 co-receptor 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; naïve T cells are excluded to limit the potential for alloreactivity mediated by native TCR co-expressed 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.