Effects of CD34+ cell dose on engraftment and long-term outcomes after allogeneic bone marrow transplantation

Background: The number of CD34(+) cells in the graft is generally associated with time to engraftment and survival in transplantation using cord blood or allogeneic peripheral blood stem cells. However, the significance of abundant CD34(+) in bone marrow transplantation (BMT) remained unclear. Methods: We retrospectively reviewed 207 consecutive adult patients who underwent their first BMT at Jichi Medical University between January 2009 and June 2021. Results: The median nucleated cell count (NCC) and CD34(+) cell dose were 2.17 x 10(8)/kg (range .56-8.52) and 1.75 x 10(6)/kg (.21-5.84), respectively. Compared with 104 patients in the low CD34(+) group (below the median), 103 patients in the high CD34(+) group (above the median) showed faster engraftment at day +28 in terms of neutrophil (84.6% vs. 94.2%; p = .001), reticulocyte (51.5% vs. 79.6%; p < .001), and platelet (39.4% vs. 72.8%; p < .001). There were no significant differences in overall survival, relapse, nonrelapse mortality, acute or chronic graft-versus-host disease, or infectious complications between the two groups in univariate and multivariate analyses. Low or high NCC had no significant effect on overall survival, nonrelapse mortality, cumulative incidence of relapse and graft-versus-host disease, either. While a positive correlation was observed between NCC and the CD34(+) cell dose, a high CD34(+) cell dose was associated with rapid hematopoietic recovery, even in patients with NCC below the median. Conclusion: Measurement of CD34(+) cell dose in addition to NCC was useful for predicting hematopoietic recovery, but seemed to have little influence on the long-term outcome in BMT.