Hematopoietic stem cells in microgravity

Abstract

Abstract Engraftment and progenitor expansion was compared after microgravity or conventional culture. Rotating Wall Vessels (RWV) were compared with Teflon flask cultures. Two systems were used: 1) Male BALB/c whole bone marrow was cultured with varying cytokines, time intervals ranging from 24 hours to 7 days at 10–40 RPM. The cultured marrow was competed with an equal amount of fresh female marrow into lethally ablated female BALB/c mice. 2) Male B6.SJL (CD45.1) marrow was cultured with varying time intervals ranging from 24 hours to 14 days at 10 RPM with FLT-3 ligand, steel factor, and thrombopoietin. Fresh C57BL/6J (CD 45.2) marrow (3 × 10 6 cells) was competed with 3 × 10 6 cultured B6SJL male cells in lethally ablated male C57BL recipients. Engraftment was analyzed at 3–10 weeks. Progenitor expansion increased over controls by 24 hours with significantly greater expansion in the RWV cultures by 48 hours. The dominant theme was a fluctuation in engraftment phenotype, which transcended cytokine combination and murine strain. A nadir of engraftable stem cells occurred between 36–44 hours in Teflon flask cultures and 30–48 hours in RWV cultures. There was a consistent phase shift of engraftment between culturing conditions of 4–6 hours. The engraftable stem cells in RWV showed superior support of short-term engraftment in multiple experiments up to 32 hours in culture. Slower rational speed improved RWV engraftment and in-vitro progenitor number. Longer culturing time gave similar engraftment results. Surrogate progenitors from both culture conditions did not reflect engraftment data, with an overall increase in progenitors over time compared with dramatic engraftment fluctuation. Enhanced plating efficiency and increased number of progenitors seen in the RWV cultures when compared with the Teflon flask cultures persisting after 24 hours in culture. The fluctuating engraftment phenotype persists with different strains and cytokine combinations, signifying that this is a crucial physiologic phenomenon.