Quantitation of primitive and lineage-committed progenitors in mobilized peripheral blood for prediction of platelet recovery post autologous transplant

Leukapheresis collections obtained following one of four mobilization regim ens from 90 cancer patients were analyzed for their content of various prog enitor cell types including erythroid and granulopoietic colony-forming cel ls in methylcellulose (total CFC), CFC-megakaryocyte (CFC-Mk), CFC detected after 10, 35 and 56 days in long-term culture (LTC), and total CD34(+) cel ls. The number of each of these progenitor cell types collected from indivi dual patients varied over 1000-fold. Nevertheless, within an individual leu kapheresis, there was a significant correlation between the number of CD34( +) cells and each progenitor type (except day 56 LTC CFC) suggesting that a ll of them are mobilized by a common mechanism. Patients who had previously received extensive chemotherapy and/or radiotherapy mobilized fewer of all these cell types than those who had not. For the 65 patients who proceeded to autologous transplantation, the median times to an absolute neutrophil count (ANC) of greater than or equal to 0.5 x 10(9)/1 and the last platelet transfusion post transplant were 13 and 11 days, respectively, with 13 (22 %) of patients having platelet recovery delayed beyond day 21. There was no significant difference between patients who had or had not received extens ive chemo/radiotherapy or among the different mobilization regimens for tim e to neutrophil or platelet recovery or the number of platelet or red blood cell transfusions received post transplant. Threshold doses of the differe nt cell types transplanted (per kg of patient weight) which predicted rapid platelet recovery were 2 x 10(6) CD34(+) cells, 5 x 10(5) total CFC and 2. 5 x 10(4) CFC-Mk. Corresponding thresholds for progenitor activity measured in LTC could not be established. These results further support the view th at standard mobilization regimens yield progenitor numbers that are, in mos t cases, nonlimiting for generating neutrophil and platelet recoveries with in 2 to 3 weeks after myeloablative therapy. Assessment of the CD34(+) cell and/or CFC content of leukapheresis collections may identify patients in w hom platelet recovery is likely to be significantly delayed although CFC-Mk enumeration does not appear to offer any unique predictive advantage.