Assessment of hematologic progenitor engraftment by complete reticulocyte maturation parameters after autologous and allogeneic hematopoietic stem cell transplantation

Background and Objectives. Hematopoietic restoration after marrow ablation is initiated by the erythroid compartment. However, the absolute microscope counts or corrected percentage of reticulocytes have proven to be poor mar kers of hematopoietic engraftment. Some reports have highlighted the useful ness of automatic flow cytometry methods to determine highly fluorescent re ticulocytes, or mean fluorescence index in this series of 60 hematopoietic stem cell transplants, we sought the normal kinetics throughout the post-tr ansplant period of the following reticulocyte maturing parameters: highly f luorescent reticulocytes (REM), immature reticulocyte fraction (IRF), mean fluorescence index (MR) and also mean reticulocyte volume (MRV). Design and Methods. Sixty consecutive patients undergoing allogeneic bone m arrow (30 cases) and autologous mobilized stem cell transplantation (30 cas es) were studied. Parameters of reticulocyte maturation were measured every other day from the beginning of the conditioning regimen until myeloid eng raftment. Results. Nadir values far the analyzed reticulocyte parameters were found b etween days +4 and +7 and thereafter, increases in these reticulocyte param eters appeared earlier than the rise in neutrophils. We considered erythroi d engraftment to have occurred an the day when RETH reached 3%, IRF 10%, MF I 10 and MRV 110 fL. These cut-offs were assigned considering the 25% quart ile for each parameter on the day that the myeloid engraftment occurred. Th e median engraftment days for RETH were +9 and +16, for IRF +9 and +13, for MFI +9 and +13 and for MRV +11 and +13 in autologous and allogeneic proced ures, respectively. When compared to standard neutrophil engraftment, IRF a nd MFI engraftment occurred significantly earlier in all patients. Remarkab ly, we found a statistical correlation between the day a reticulocyte param eter reached its cut-off and the subsequent day of absolute neutrophil coun t (ANC) recovery for MFI after allogeneic transplants and for MRV after aut ologous procedures (p < 0.001 and p= 0.02, respectively). Of all the clinic al parameters tested, only the number of infused CD34 cells showed a statis tical influence on erythroid engraftment in autologous transplant. Interpretation and Conclusions. Early reticulocytes appear sooner than neut rophils after both autologous and allogeneic transplants, and any determine d reticulocyte parameter can reliably measure this fraction. Nevertheless, our results show that MRV and MFI cut-offs are useful for determining subse quent myeloid engraftment. These findings could be relevant to decision-mak ing in those patients with primary graft failure heralded by an absence of increasing values of MFI and MRV, indicating very tow production of reticul ocytes from the graft, who could, therefore, benefit from earlier rescue th erapy. (C) 2001, Ferrata Storti Foundation.