The relationship of CD34+ dosage and platelet recovery following high dose chemotherapy and autologous CD34+ reinfusion in multiple myeloma

Autologous hematopoietic stem cell transplantation (ASCT) is an established treatment for multiple myeloma (MM), yet the impact of transplanted CD34+ cell dose remains unresolved, especially in patients over the age of 65 years. Data was collected from 207 consecutive ASCT patients to determine the relationship between CD34+ infusion count and short-term and long-term platelet recovery. For MM patients under the age of 65 years (n = 155), CD34+ dosage correlates with time to platelet engraftment (p < 0.001) and platelet count at 30 days (p = 0.003), but not with long-term platelet counts at 180 or 360 days from the CD34+ reinfusion. For MM patients aged 65 years or older (n = 46), CD34+ dosage did not correlate with time to platelet engraftment, but did correlate with both short-term and long-term platelet counts at 30 (p < 0.001), 180 (p = 0.021), and 360 days (p = 0.005). Exploratory regression analysis was done to explore platelet stability following the current minimum CD34+ dosage reinfusion. For MM patients under the age of 65 years, the minimum standard CD34+ dosage of 2 × 10⁶ cells/kg was sufficient for a timing to platelet engraftment of <21 days and short-term platelets count ≥150 × 10⁹/L at 30 days. Alternatively, for MM patients aged 65 years or older, the CD34+ dosage of 2 × 10⁶ cells/kg was insufficient for platelet counts ≥150 × 10⁹/L at 30 and only marginally attainable at 360 days suggesting that in elderly MM patients a higher CD34+ dosage may be required for platelet recovery and possibly long-term platelet stability.