TMI-Based Dose-Escalated Bone Marrow Transplantation Can Help Preserve the Bone Marrow Microenvironment and Reduce Cellular Senescence in Old Mice

Introduction:Senescence is one of the hallmarks of aging and age-related conditions, including but not limited to, inflammaging, frailty, and various age-related diseases. It has been well-established that radiation and chemotherapy can accelerate senescence. While myeloablative conditioning-based allogeneic hematopoietic cell transplant (HCT) is a curative treatment for patients with leukemia. The dose of total body irradiation (TBI) conditioning has to be reduced in older patients to reduce potential high treatment-related mortality, which may still cause accelerated senescence in aged individuals, resulting in poor survival outcomes. We initiated the testing of a novel total marrow irradiation (TMI) based myeloablative conditioning in older patients to enhance the anti-leukemia effect and overall survival. We hypothesize that this new radiation preconditioning strategy may also reduce radiation-induced senescence in aged individuals compared to TBI to reduce treatment-associated side effects and improve the outcomes of allogeneic HCT. We tested this hypothesis in the present study and further investigated the mechanisms of the effects of TMI-based myeloablative and dose-escalated bone marrow transplantation (BMT) on old mice by examining the changes in expression of various senescence markers and senescence-associated secretory phenotype (SASP) in the bone marrow (BM) and selected organs. Method: The radiation treatment regimens were: TMI (12:4), TMI (16:4) and TBI (12:12), and TBI (16:16), were developed as described (Zuro et al., 2021); i.e. (12:4) means the radiation dose to the BM was 12 Gy and the dose to the organs was 4 Gy. The young (8 weeks old) and aged mice (90 weeks old) of host C57BL/6j (JAX000664, CD45.2) were irradiated in 2 fractions 24h apart, and 25 million whole BM cells from donor (JAX002014, CD45.1) were transplanted by i.v. at 24 h after irradiation. For the hematopoietic stem and progenitor cell (HSPC) population study, more mature hematopoietic progenitors (Lin − Sca-1 −c-Kit + or LK cells) and HSPCs (Lin − Sca-1 + c-Kit + or LSK cells) were examined in BM by flow analysis. Cultured bone marrow mesenchymal stem cells (MSCs) were analyzed for the gene expression of the senescence marker CDNK1a (or p21) and SASP factors MMP13 and CXCL12 by qPCR. For senescence study in organs such as the liver, gut, and spleen, senescence-associated beta-galactosidase (SA-β-gal) staining was performed and expression of the CDNK2a (or p16) was analy