Poor stem cell harvest may not always be related to poor mobilization: lessons gained from a mobilization study in patients with β‐thalassemia major

Abstract

BACKGROUND Hematopoietic stem cell mobilization and leukapheresis in adult beta-thalassemia patients have been recently optimized in the context of clinical trials for obtaining hematopoietic stem cells for thalassemia gene therapy. In some patients, however, CD34+ cell yield was poor despite successful mobilization and the modification of apheresis settings was mandatory for harvest rescue. STUDY DESIGN AND METHODS The data of twenty adult β-thalassemia patients who were enrolled in a clinical trial for optimizing mobilization strategies for stem cell gene therapy were analyzed. The aim of this post-hoc analysis was to assess how certain hematological and/or clinical parameters may correlate with low collection efficiency in the presence of adequate numbers of circulating stem cells, after pharmacological mobilization and standard leukapheresis procedures. RESULTS Four patients among 19 optimally mobilized with Plerixafor or remobilized with G-CSF+Plerixafor patients demonstrated disproportionally poor CD34+ cell harvest, with respect to their circulating CD34+ cells after mobilization. All four patients who had undergone splenectomy presented at baseline and before first apheresis with lymphocytosis resulting in a lymphocyte/neutrophil ratio well above 1 and marked reticulocytosis as compared to patients with optimal mobilization/CD34+ cell harvest. Such unexpected expansion of specific cell populations disrupted the normal cell layer separation and necessitated modification of the apheresis settings in order to rescue the harvests. CONCLUSIONS By close examination of certain hematological and/or clinical parameters prior to leukapheresis, patients who, in spite of adequate mobilization are at risk for poor CD34+ cell harvests, may be identified and harvest failure can be prevented by adjusting of the apheresis settings.

Successful hematopoietic stem cell mobilization and apheresis collection using plerixafor alone in sickle cell patients

“…Third, based on the observation that HSPCs were already mobilized at 4 hours after plerixafor, earlier than previously described, we implemented an earlier apheresis start time 4 hours after plerixafor administration. 21 †HbS was measured at the end of red cell exchange within 1 week of collection.…”

“…Previous reports of predictors of collection efficiency postulated that the lymphocyte to neutrophil ratios would predict poor collectors. 21 We calculated these ratios (Table 2), but did not find sustained values greater than 1. A single value for patient 1 was found to be 2.2 only at initiation of apheresis, and fell below 1 at all other times.…”

“…Between 2.5 to 3.5 blood volumes were processed (Table 2). Given the poor yield of CD34 1 cells in the apheresis product, we altered our collection strategy based on reports of collections in patients with b thalassemia [19][20][21][22] or microcytosis 23 that suggested altered sedimentation of HSCs. In these patient populations, interface parameters of 5% to 10% were reported to improve recovery of CD34 1 cells.…”

Plerixafor enables safe, rapid, efficient mobilization of hematopoietic stem cells in sickle cell disease patients after exchange transfusion

“… 5 Considering the typical proportion of HSPC that can be corrected in gene therapy clinical trials (~50% of CD34 + HSPC) and an average recovery of 70% of CD34 + cells post-selection, a minimum harvest of ~6×10 6 CD34 + cells/kg would be required. For reasons that have not been completely elucidated, as for thalassemic patients, 6 – 7 the recovery of HSPC from SCD patients’ BM is peculiarly low (M. Cavazzana, unpublished data ). In our ongoing gene therapy trial (HGB-205, ClinicalTrials.gov number, NCT02151526), two BM harvests (each requiring an exchange transfusion program before general anesthesia) were needed to obtain enough cells to transplant the three SCD patients enrolled.…”

Providing the Starting Material to the Manufacturer of an Approved and Commercially Available Autologous CAR-T Cell Treatment

“…-Check the MCV to rule out the presence of beta thalassemia minor. Microcytosis leads to abnormal sedimentation behaviour, necessitating modification of apheresis settings (Constantinou et al 2017). -Note height and weight and calculate total blood volume.…”