Broader clinical application of umbilical cord blood (UCB), as a source of hematopoietic stem/progenitor cells (HSPCs), is limited by low CD34+ and T-cell numbers, contributing to slow lymphohematopoietic recovery, infection, and relapse. Studies have evaluated the safety, feasibility, and expedited neutrophil recovery associated with the transplantation of CD34+ HSPCs from ex vivo expansion cultures using the aryl hydrocarbon receptor antagonist StemRegenin-1 (SR1). In a phase 1/2 study of 17 patients who received combined SR1-expanded and unexpanded UCB units, a considerable advantage for enhancing T-cell chimerism was not observed. We previously showed that progenitor T (proT) cells generated in vitro from HSPCs accelerated T-cell reconstitution and restored immunity after hematopoietic stem cell transplantation (HSCT). To expedite immune recovery, we hypothesized that SR1-expanded HSPCs together with proT cells could overcome the known T-cell immune deficiency that occurs post-HSCT. Here, we show that SR1-expanded UCB can induce >250-fold expansion of CD34+ HSPCs, which can generate large numbers of proT cells upon in vitro differentiation. When compared with nonexpanded naive proT cells, SR1 proT cells also showed effective thymus-seeding and peripheral T-cell functional capabilities in vivo despite having an altered phenotype. In a competitive transfer approach, both naive and SR1 proT cells showed comparable thymus-engrafting capacities. Single-cell RNA sequencing of peripheral CD3+ T cells from mice injected with either naive or SR1 proT cells revealed functional subsets of T cells with polyclonal T-cell receptor repertoires. Our findings support the use of SR1-expanded UCB grafts combined with proT-cell generation for decreasing T-cell immunodeficiency post-HSCT.
Bibliographical noteFunding Information:
This work was supported by grants from the Canadian Institutes of Health Research (FND154332), the Ontario Institute for Regenerative Medicine, the Krembil Foundation, Medicine by Design: a Canada First Research Excellence Fund Program at the University of Toronto, and an Innovation to Impact grant from the Canadian Cancer Society (#705960) (J.C.Z.-P.); from the National Cancer Institute, National Institutes of Health (2P01 CA142106) (B.R.B.); from the Children's Cancer Research Fund (H.E.S. and B.R.B.); and from the National Institute of Child Health and Human Development, National Institutes of Health (K12-HD068322), and St. Baldrick's Foundation (H.E.S.).
© 2019 by The American Society of Hematology.