A higher number of infused CD34(+) cells has a positive impact on the clinical outcome after related PBSC transplantation

A high CD34+ cell dose is associated with better disease-free survival in patients with low-risk diseases undergoing peripheral blood stem cell transplantation from HLA-matched related donors

To elucidate the impact of infused CD34⁺ cell doses on transplant outcome, we retrospectively analyzed 851 adult patients who received peripheral blood stem cell transplantation (PBSCT) from human leukocyte antigen (HLA)-matched related donors. The patients were divided into high- and low-CD34 groups at the cutoff value of 4.5 × 10⁶/kg. Overall, the high CD34 group showed early neutrophil and platelet recovery. Stratification of disease risks demonstrated that among the patients with low-risk diseases, the high-CD34 group showed better disease-free survival (DFS) (64.9% vs. 55.5%, P = 0.0415) than did the low-CD34 group, without any increase in graft-versus-host disease (GVHD). Meanwhile, a higher CD34⁺ cell dose had no impacts on the outcomes of patients with high-risk diseases. Multivariate analyses for the patients with low-risk diseases revealed that a high CD34⁺ cell dose (hazard ratio [HR] 0.72, P = 0.048) and development of grade III-to-IV acute GVHD (HR 1.64, P = 0.018) were significantly associated with DFS. An excessive dose of CD34⁺ cells (>8.0 × 10⁶/kg) led to an increase in acute GVHD. By stratification of disease risk, a CD34⁺ cell dose between 4.5 and 8.0 × 10⁶/kg can be suggested for patients with low-risk diseases who undergo PBSCT from HLA-matched related donors.

Transient apoptosis inhibition in donor stem cells improves hematopoietic stem cell transplantation

During hematopoietic stem cell transplantation, a substantial number of donor cells are lost because of apoptotic cell death. Transplantation-associated apoptosis is mediated mainly by the proapoptotic BCL-2 family proteins BIM and BMF, and their proapoptotic function is conserved between mouse and human stem and progenitor cells. Permanent inhibition of apoptosis in donor cells caused by the loss of these BH3-only proteins improves transplantation outcome, but recipients might be exposed to increased risk of lymphomagenesis or autoimmunity. Here, we address whether transient inhibition of apoptosis can serve as a safe but efficient alternative to improve the outcome of stem cell transplantation. We show that transient apoptosis inhibition by short-term overexpression of prosurvival BCL-XL, known to block BIM and BMF, is not only sufficient to increase the viability of hematopoietic stem and progenitor cells during engraftment but also improves transplantation outcome without signs of adverse pathologies. Hence, this strategy represents a promising and novel therapeutic approach, particularly under conditions of limited donor stem cell availability.