Abstract 27: Physiologic Oxygen Expansion Enhances Lymphocyte and Neutrophil Recovery Following Transplantation

Abstract Introduction Expeditious recovery of lymphocytes after hematopoietic cell transplantation is a major determinant of patient outcome. There are few efficient clinical therapies to enhance lymphocyte recovery, indicating a clear unmet need. Ex vivo expansion of cord blood (CB) units is an approved therapy to increase numbers of hematopoietic stem and progenitor cells, but impact on lymphocyte recovery remains uncertain. Moreover, culture in physioxic (physiological oxygen) conditions results in increased lymphoid-biased RNA levels. Objectives We hypothesize that ex vivo expansion in physioxic conditions will increase lymphoid-biased cells and increase lymphocyte counts post-transplantation (PT). The objective of this study is to increase lymphocyte numbers following transplantation without sacrificing reconstitution of potent hematopoietic cells. Methods Three independent transplants were conducted. 1) Murine lineage- bone marrow (BM) was expanded for 7 days then transplanted into lethally irradiated mice with/without additional common lymphoid progenitors (CLPs). 2) Murine lineage- BM was expanded in 1%, 3%, 5%, 14%, and 21% O2 for 7 days and transplanted into lethally irradiated mice. 3) Human CD34+ CB cells were expanded for 7 days in 1%, 3%, 5%, 14%, and 21% O2 and transplanted into NSG mice. Unexpanded BM or CB cells were used as controls. Results Additional CLPs did not contribute to lymphocyte recovery. Mice transplanted with expanded BM had increased lymphocyte counts compared to transplantations with unexpanded BM at weeks 2 and 5 PT via complete blood count (CBC) and increased B-cell reconstitution in the spleen, BM, and peripheral blood (PB) at weeks 2, 5, and 8 PT. LSK (Lin- SCA1+ cKIT+) and neutrophil frequencies were increased at 3% O2 in the BM and 5% O2 in the PB, respectively. Compared to 21% O2, CB cells expanded at 1%, 3%, 5%, 14% O2 had increased neutrophil and lymphocyte frequencies in the PB at weeks 2 and 10, respectively, and demonstrated greater recovery than unexpanded at week 2. Discussion Expansion increases lymphocyte counts via CBC and immunophenotyping. Physioxic expansion increases numbers of potent hematopoietic cell subpopulations and frequencies of specific lymphocyte compartments in multiple organs. Thus, expansion under physioxia is a viable strategy to enhance recovery of lymphocytes PT.