TCR-transgenic T cells were engineered to coexpress c-MPL. Activation of this receptor by thrombopoietin (TPO) or a small-molecule c-MPL agonist provides both costimulatory and cytokine signals to the T cells (T cell activation signals 2 and 3), which enhances their cytokine production, expansion, and antitumor function, improves immune synapse formation, enables sequential killing of tumor cells, leads to a persistent central memory phenotype, and improves survival in a human TPO-transgenic leukemia xenograft model.

Adoptively transferred T cell receptor (TCR)-engineered T-cells depend on host-derived co-stimulation and cytokine signals for their full and sustained activation. However, in cancer patients both signals are frequently impaired. Hence, we developed a novel strategy that combines both essential signals in one transgene by expressing the non-lymphoid hematopoietic growth factor receptor c-MPL (myeloproliferative leukemia), the receptor for thrombopoietin (TPO), in T-cells. C-MPL signaling activates pathways shared with conventional co-stimulatory and cytokine receptor signaling. Thus, we hypothesized that host-derived TPO, present in the tumor microenvironment, or FDA-approved pharmacological c-MPL agonists could deliver both signals to c-MPL engineered TCR-transgenic T-cells. We found that c-MPL+ polyclonal T cells expand and proliferate in response to TPO, and persist longer after adoptive transfer in immunodeficient human TPO-transgenic mice. In TCR-transgenic T-cells, c-MPL activation enhances anti-tumor function, T-cell expansion, and cytokine production and preserves a central memory phenotype. C-MPL signaling also enables sequential tumor cell killing, enhances the formation of effective immune synapses, and improves anti-leukemic activity in vivo in a leukemia xenograft model. We identify the type I interferon pathway as a molecular mechanism by which c-MPL mediates immune-stimulation in T cells. In conclusion, we present a novel immunotherapeutic strategy using c-MPL enhanced transgenic T cells responding to either endogenously produced TPO (a microenvironment factor in hematologic malignancies) or c-MPL-targeted pharmacological agents.

Author Info: (1) Center for Cell and Gene Therapy, Baylor College of Medicine, Houston Methodist Hospital and Texas Children's Hospital, United States. (2) Center for Human Immunobiology, Baylo

Author Info: (1) Center for Cell and Gene Therapy, Baylor College of Medicine, Houston Methodist Hospital and Texas Children's Hospital, United States. (2) Center for Human Immunobiology, Baylor College of Medicine, Houston, TX, United States. (3) Center for Human Immunobiology, Baylor College of Medicine, Houston, TX, United States. (4) Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States. (5) Center for Cell and Gene Therapy, Baylor College of Medicine, Houston Methodist Hospital and Texas Children's Hospital, United States. (6) Department of Biostatistics, Baylor College of Medicine, Houston, TX, United States. (7) Department of Biostatistics, Baylor College of Medicine, Houston, TX, United States. (8) Center for Cell and Gene Therapy, Baylor College of Medicine, Houston Methodist Hospital and Texas Children's Hospital, United States. (9) Department of Pediatrics, Baylor College of Medicine, Houston, TX, United States. (10) Department of Medicine, Baylor College of Medicine, Houston, TX, United States. (11) Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States. (12) Department of Medicine, Baylor College of Medicine, Houston, TX, United States caroline.arber@gmail.com.