Prostaglandin E2 enhances long-term repopulation but does not permanently alter inherent stem cell competitiveness

Abstract

Hematopoietic stem cell (HSC) transplantation is a lifesaving therapy for malignant and nonmalignant hematologic diseases and metabolic disorders. Although successful, hematopoietic transplantation can be hindered by inadequate stem cell number or poor engrafting efficiency. To overcome these deficits, we and others have previously reported the HSC-enhancing ability of a short-term exposure of prostaglandin E2 (PGE2); this strategy has now progressed to phase 1 clinical trials in double cord blood transplantation. To further analyze the short- and long-term effects of HSC exposure to PGE2, we followed the repopulation kinetics of PGE2-treated hematopoietic grafts through 5 serial transplantations and compared inherent long-term competitiveness in a HSC head-to-head secondary transplantation model. Treatment with PGE2 did not result in a long-term increase in HSC competitiveness, lineage bias, or enhanced proliferative potential, demonstrating that pulse exposure to PGE2 results in transient increases in HSC homing and engraftment potential.

Figure 1

dmPGE₂ pulsed grafts maintain repopulating ability through serial transplantations. (A) Increased chimerism of dmPGE₂-treated cells vs vehicle is shown for primary transplant at 20 weeks (time of secondary transplant) and in a subcohort at 32 weeks (time of 12-week analysis of secondary transplant); for secondary transplant at 12 weeks and 24 weeks; and for tertiary, quaternary, and quinary at 12 weeks. Data for 20-week primary transplant were from 2 pooled experiments, n = 5 mice per group, per experiment, each assayed individually. Data for secondary, tertiary, quaternary, and quinary transplants were from n = 5 mice per group, each assayed individually. Data are expressed as mean ± SEM; *P < .05. (B) Relative contribution to lineages of myeloid and B- and T-lymphoid. Multilineage analysis for primary transplant (32 weeks) and at 12 weeks posttransplant in serially transplanted secondary, tertiary, and quaternary mice. n = 5-10 mice per group, each assayed individually. (C) Representative Wright’s Giemsa-stained cytospins from normal bone marrow, marrow from secondary bone marrow transplant 12 weeks after transplantation, and marrow from quinary transplanted mice 12 weeks after transplantation. Cytospins were photographed at ×200 (×20 objective) with a Leica DM2500 Microscope outfitted with Q-Imaging micropublisher camera (W. Nushbaum Inc., McHenry, IL). Bone marrow cytospins show normal cellularity. Both myeloid and precursors are present and show normal maturation as well as megakaryocytes. There was no evidence of myeloid hyperplasia, no noticeable increase in myeloid or erythroid blasts, and no obvious increase in immature granulocytic, monocytic cells, or evidence of lymphoblastic transformation.

Figure 2

dmPGE₂ pulsed HSCs do not have an inherent competitive advantage in secondary transplants. (A) Schematic representation of experimental design. WBM from CD45.1 mice and CD45.2 mice was treated with both vehicle and dmPGE₂ and then transplanted head to head into lethally irradiated (1100 cGy, split dose) CD45.1/CD45.2 hybrid mice as shown (2.5 × 10⁵ cells per group). Chimerism was analyzed at 12 weeks, and bone marrow from recipients was collected and stained with fluorescent antibodies for phenotypic markers, and cells were sorted for SLAM SKL. SLAM SKL cells were transplanted head to head into a second cohort of lethally irradiated CD45.1/CD45.2 mice along with 2.0 × 10⁵ WBM CD45.1/CD45.2 competitors, and chimerism analyzed 12 weeks later. (B) Chimerism in peripheral blood is shown for 12 weeks after the primary transplant and 12 weeks after the secondary transplant (mean ± SEM). n = 10 mice per group (total of 20 mice for primary and 20 mice for secondary); *P < .001.