EFFECT OF SPACEFLIGHT ON HUMAN STEM-CELL HEMATOPOIESIS - SUPPRESSION OF ERYTHROPOIESIS AND MYELOPOIESIS

Humans subjected to periods of microgravity develop anemia, thrombocyt openia, and abnormalities in red blood cell structure, The causes of t hese abnormalities are complex and unclear, The in vitro effects of sp aceflight on hematopoietic cell proliferation and differentiation were investigated during the space shuttle missions STS-63 (Discovery) and STS-69 (Endeavour). CD34(+) bone marrow progenitor cells were culture d in liquid suspension culture and on hematopoietic supportive stromal cells using hollow-fiber culture modules, One set of cultures was mai ntained at microgravity (flight cultures) for the last 8-10 days of cu lture and a second control was at full gravity (ground control), Over the 11- to 13-test-day period, ground control culture total cell numbe r increased 41.0- to 65.5-fold but flight culture total cell number in creased only 10.1- to 11.6-fold (51-84% decrease), Comparing ground co ntrol cultures and microgravity cultures, respectively, for progenitor cell content, myeloid progenitor cell numbers expanded 2.6- to 17.5-f old compared with 0.9- to 7.0-fold and erythroid progenitor cell numbe rs expanded 2.0- to 4.1-fold in ground control cultures but actually d eclined at microgravity (> 83% reduction), Moreover, microgravity cult ures demonstrated accelerated maturation/differentiation toward the ma crophage lineage, These data indicate that spaceflight has a direct ef fect on hematopoietic progenitor cell proliferation and differentiatio n and that specific aspects of in vitro hematopoiesis, particularly er ythropoiesis, involve gravity-sensitive components.