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181 CIRCULATING HEMATOPOIETIC PROGENITOR CELLS IN PREMATURE INFANTS: THEIR IN-VITRO RESPONSE TO ERYTHROPOIETIN AMD INTERLEUKIN 3

Burst forming units (BFU-E) in peripheral blood of five premature infants (gestational age 28-32 wk) were studied over a period of 8 weeks. Mononuclear cells were isolated by Ficoll-Hypaque gradient sedimentation on day 3, 14, 28 and 56 of life. 5×104 cells were cultured in 1 ml semisolid medium of 0.9% methylcellulose containing 30% fetal calf serum, 5×105 M β-mercaptoethanol, 500 U granulocyte macrophage colony stimulating factor (GMCSF) and erythropoietin (EPO) in doses of 0.25-20 U (day 3) and of 1 U (day 14-56). All infants showed in vitro sensitivity to increasing doses of EPO on day 3. Maximum stimulatory response was achieved with 1 U EPO and resulted in 38±13 BFU-E/5×104 cells. This response was almost ten times higher than in normal children. Peripheral BFU-E remained high until day 28. On day 56 BFU-E fell to 20% of the day 3 values (7±2 BFU-E/5×104 cells). Additional in-vitro stimulation with interleukin 3 (IL3) resulted in a 40% increase in peripheral BFU-E on day 3 to 25. No response to IL3 was observed in preterm infants on day 56 and in children. This indicates that early BFU-E circulate until day 25. We conclude that peripheral blood in preterm infants contains high levels of EPO- and IL3-sonsitive BFU-E. The sharp decline in circulatory erythropoietic progenitor cells correlates with the onset of anemia of prematurity.