INCREASED LEVELS OF MEGAKARYOCYTE PROGENITORS IN PERIPHERAL-BLOOD MOBILIZED BY CHEMOTHERAPY AND OR HEMATOPOIETIC GROWTH-FACTOR PROTOCOLS/

We have quantitated colony-forming unit megakaryocyte, (CFU-Mk), burst -forming unit megakaryocyte, (BFU-Mk), colony-forming unit granulocyte -macrophage (CFU-GM), and CD34(+) cells in 98 mobilised PB samples fro m 53 patients mobilised by one of six protocols, including myelosuppre ssive chemotherapy alone (n = 22), or in combination with recombinant haemopoietic growth factors (n = 32), and growth factors alone (n = 17 ) or in combination (n = 27). The frequency of megakaryocyte progenito rs (total Mk = CFU-Mk +BFU-Mk) in mobilised PB (mean 356, range 0-3240 /10(6)) was similar to that in steady-state BM (mean 429, range 0-3315 /10(6) n = 45). The levels of total Mk in mobilised PB (mean 1509, ran ge 0-36 099/ml) showed a mean 75-fold increase compared with steady st ate PB (mean 20, range 0-86/ml, n = 15). In mobilised PB the levels of CFU-Mk were significantly correlated with levels of BFU-Mk (r(s) = 0. 71, P < 0.0001) and the levels of megakaryocyte progenitors correlated significantly with those of myeloid progenitors (r(s) = 0.59, P < 0.0 001) and CD34(+) cells (r(s) = 0.69, P < 0.0001). The mobilisation of megakaryocyte progenitors into the circulation in response to high-dos e chemotherapy and/or haemopoietic growth factors contributes to an un derstanding of the rapid platelet recovery following PBSC transplantat ion and suggests that the measurement of megakaryocyte progenitors may be a useful indicator for platelet reconstitutive capacity.