(P-BT-6) CD34 Cells Likely Out-of-kilter When Graft Platelet Concentrations Went Extremes

Impaired post-thaw CD34 cell (postCD34) viability in autologous haematopoietic stem cell transplant (ASCT) could indicate delayed engraftment. Therefore, procedures that can promote better cell recovery after cryopreservation and thawing, have been explored. However, the known variables such as the white cell (WCC) content of the graft,  explain only part of the results observed in the clinical practice. In this study, we explored another less commonly investigated factor that could be impacting the graft cell quality, such as how platelets might be involved. Therefore, we conducted this study to closely examine the effects of graft platelet concentration on CD34 cells of patients submitted to stem cell collection and cryopreservation.

Study

Design/Methods:

Medical records from adult patients  submitted to peripheral blood stem cell collection, cryopreservation, and post-thaw recovery assessment for treatment of lymphoma and multiple myeloma at the Christchurch and Waikato Hospitals, New Zealand, from January 2020 to October 2023, were retrospectively reviewed. Patient demographic data, including gender and age at stem cell harvesting, stem cell yield, white cell and platelet concentration of the graft were analysed. A total of 82 patients with a total of 150 collections were included in the study.

Results/Findings:

A significant negative correlation between platelet count and postCD34 recovery (r = -0.18, p = 0.0278), in addition to a known negative correlation between WCC and postCD34 recovery (r = -0.30, p = 0.0002). The G1 and G6 groups with extreme platelet counts (< 500 x 10⁹/L and >= 2500 x 10⁹/L respectively) stood out from the remaining groups with reduced postCD34 recovery. A multivariate regression analysis of postCD34 recovery confirmed that there were significant statistical interactions between diagnosis (or cancer type) and platelet group. 

Conclusions:

Examining potential roles of graft platelet count in relation to postCD34 recovery and issues in apheresis stem cell collection and processing, instead of finding a replication of the reported negative correlation of platelet count with postCD34 viability, we discovered that postCD34 recovery was clearly reduced when platelet count went either very high (i.e. the G6 group) or very low (i.e. the G1 group). It was further discovered that the G1 group was enriched with collections from NHL and Hodgkin patients and the G6 group was enriched with collections from Myeloma patients, and both groups had elevated male preponderance. Therefore, we hypothesized that graft platelet concentrations probably indicated CD34 cell state (e.g. cell cycle and cell adhesion highly related to platelet functions) that sustained when platelet concentrations were within a niche range but went out of kilter otherwise, which however needs further investigation to prove.