Low-dose peripheral blood stem cell graft after high-dose chemotherapy - an evaluation of hematopoietic reconstitution.

Background: High-dose (HD) chemotherapy followed by autologous blood stem-cell transplantation (ASCT) is the standard treatment for multiple myeloma (MM) patients. However, the collection of sufficient peripheral blood stem cell (PBSC) grafts can be challenging, and the question arises whether reinfusion of low-dose grafts will lead to a hematopoietic recovery.
Methods: The hematopoietic recovery of 148 MM patients who underwent HD melphalan chemotherapy and received PBSC transplants with varying CD34+ cells doses (3-4 × 10 ⁶ [n = 86], 2-2.5 × 10 ⁶ [n = 53], < 2 × 10 ⁶ [n = 9] per kg body weight [bw]) was analyzed in this retrospective single-center study.
Results: All patients reached hematopoietic reconstitution, even those who received < 2 × 10 ⁶ CD34+ cells/kg bw. 62 (42%) patients received granulocyte-colony-stimulating factor (G-CSF). The median duration to leukocyte recovery ≥1.0 × 10 ⁹ /L was 12 days in every group. The median duration to platelet recovery ≥20 × 10 ⁹ /L was 11, 13 and 13 days, respectively. In the multivariate analysis, a low number of reinfused CD34+ cells was associated with prolonged time until leukocyte reconstitution (p = 0.010, HR 0.607) and platelet recovery (p < 0.001, HR 0.438). G-CSF support significantly accelerated leukocyte (p < 0.001, HR 16.742) but not platelet reconstitution.
Conclusion: In conclusion, reinfusion of low- and even very-low-dose PBSC grafts leads to sufficient hematopoietic reconstitution. No severe adverse events were observed during or after HD chemotherapy and ASCT in the analyzed cohort. While the impact of CD34+ cell dose is marginal, G-CSF significantly accelerates the leukocyte recovery.