A Comparative Analysis of Engraftment Outcomes for Recipients of Allogeneic Hematopoietic Stem Cell Transplants (allo HSCT) and Post-Transplant Cyclophosphamide (PTCy) Based on Ideal Body Weight (IBW) or Actual Body Weight (ABW) Dosing of CD34-Positive Stem Cells

Introduction Previous studies have demonstrated that CD34+ cell doses using IBW are more predictive of engraftment than ABW, with 2 × 106 CD34 cells/Kg of IBW established as the minimal target. This has not been reevaluated, however, in the setting of PTCy for GVHD prophylaxis. Therefore, as part of a quality assurance project, we performed a retrospective study to examine whether there was a significant difference between times to absolute neutrophil count (ANC) and platelet count (PLT) engraftment in 122 consecutive patients receiving myeloablative (MA) conditioning allo HSCT at our institution who received PTCy as part of their GVHD prophylaxis. Objective To determine whether stem cell dosing based on IBW or ABW is preferable in patients undergoing allo HSCT who received PTCy for GVHD prophylaxis. Methods We retrospectively reviewed the records of 122 consecutive patients who received MA conditioning allo HSCT in the Fox Chase-Temple Bone Marrow Transplant Program between 1/2015 and 8/2023, given PTCy as part of the GVHD prophylaxis. 3 × 106 CD34 cells/Kg of IBW cell doses were planned for each patient. In this retrospective analysis, however, we calculated the dose given based on both IBW and ABW. Times to ANC recovery ≥ 500/uL for 3 consecutive days and PLT recovery to ≥ 20/uL for 3 consecutive days with no transfusion for 7 days were then compared for the two categories based on cell doses of <2, 2-3, 3.1-4 and >4 × 106 CD34 cells/Kg. These data were further evaluated based on type of transplant donors: matched related (MRD), Haplo-identical (Haplo), matched unrelated (MUD) and mismatched unrelated (MMUD). Statistical differences were assessed using T-Test Calculator for 2 Independent Means (2-tailed), and One-Way ANOVA to compare means of three or more groups. Results Table 1 shows the distribution of patients based on type of transplant and CD34+ cell doses infused based on IBW and ABW. Only two patients were given < 2 × 106 CD34 cells/kg when using ABW, and the majority in each group received >4 × 106 CD34 cells/kg. One of the patients who received < 2 × 106 CD34 cells/kg ABW did experience late graft failure after initial engraftment.Table 2 shows the ANC recovery medians for each group and Table 3 the median PLT engraftment times. No significant differences were seen between any of the groups. We next evaluated engraftment time based on stem cell source or degree of matching for IBW vs. ABW stem cell dosing, and again no significant differences were seen. Conclusions Our findings confirm that IBW-based stem cell dosing should remain the standard of care for MA transplants, even when PTCy is utilized for GVHD prophylaxis. These results should be interpreted with caution, however, since all but two patients in our series received at least 2 × 106 CD34 cells/kg ABW.