The role of high fluorescent reticulocytes in monitoring the aplasia outcome and optimizing the timing of peripheral blood stem cell harvesting.

WE READ WITH INTEREST the Research Report “Automated immature reticulocyte counts are early markers of engraftment following autologous peripheral blood stem cell transplantation (PBSCT) in patients with lymphoma,” by George et al. (1). We would like to extend some claims, according to a 10-year experience of aplasia outcome monitoring using reticulocytes parameters as surrogate markers for the peripheral blood (PB) CD341 cell enumeration. The study (1) examined the reticulocyte parameters in an homogeneous group of 23 non-Hodgkin’s malignant lymphoma (NHL) patients, all treated with a single protocol (BEAM) before PB stem cell transplantation (SCT). Standard engraftment parameters—total white blood cell (WBC) count and absolute neutrophil count (ANC)— were measured together with reticulocytes. These last cells were determined using Methylene Blue and light scatter with an Abbott (Maidenhead, UK) automated counter, and divided into three fluorescence ratios with the high fluorescence reticulocytes (HFR) as the most immature cells. The recovery of the HFR to 2% of the total reticulocytes was significantly shorter when compared to the ANC at 0.5 3 109/L (median of 8 days vs. 10 days in 21 out 23 patients). The authors subsequently claimed that HFR measurement might be used as an early indicator of engraftment following PBSCT. Numerous studies have focused on reticulocyte assessment in hematological diseases. Nevertheless, reticulocyte studies dedicated to NHL patients are rare (2). Using the Sysmex R-1000 and 3000 devices (TOA Medical Electronics Ltd, Kobe, Japan), we also evaluated HFR counts in 10 patients affected by NHL and submitted to PBSCT after BEAM conditioning (3; unpublished data). During the leukopenic phase, only reticulocytes of low fluorescence ratio (LFR) at extremely low level (,10 3 109/L) were found. HFR counts declined to an undetectable level from days 11 to 13, and then became detectable and reached 5% of total reticulocyte count by day 10 (62). The ANC recovery achieved a value .0.5 3 109/L at day 111 (62). No correlation was found between HFR and PBSC yield; circulating CD341 cells were measured by flow cytometry, and colonyforming units granulocyte-macrophage (CFU-GM) measured by semisolid media assay. Hence, we agree that HFR gave advance notice of complete and stable hematopoietic engraftment as compared to traditional WBC and ANC counts. Immature reticulocytes succeeded in providing a realtime assessment of the functional state of erythropoiesis, and further to be a useful marker to predict hematopoietic recovery after treatment for severe aplastic anemia, chemotherapy for acute leukemias, and allogenic or autologous BMT (4). Moreover, HFR did not show transfusion support-related fluctuations. However, HFR is not widely used by the physicians for monitoring aplasia outcome after chemotherapy or SCT, or stem cell (SC) harvest timing. From this point of view, HFR failed to demonstrate its clinical value. In the BM transplant setting, there is no clear evidence that the use of this index results in improved care of the patients. First, a variety of analyzers are now available to determine the immature reticulocytes (using semior fully automated methods based on fluorescence or optical RNA amount detection). Although good agreement has been proven between these analyzers (5), low-level HFR measurement might change from one