Intravital imaging of spatiotemporal engraftment dynamics of transplanted hematopoietic stem and progenitor cells

Abstract

Bone marrow (BM) is commonly utilized in the clinical situation in the form of bone marrow transplantation (BMT) to treat patients with various hematological disorders. Unfortunately, a number of post-transplant complications mainly occur due to lack of initial engraftment at early post-transplant phase, which has been a critical limiting factor for achieving successful BMT outcomes. However, underlying cellular engraftment dynamics which be the beginning point to alleviate several complications and enhance hematopoietic recov-ery have not been fully identified yet. In this research, we performed a longitudinal in vivo imaging of spatio-temporal cellular behaviors of transplanted BM cells during early engraftment by utilizing a custom-built real-time laser-scanning confocal microscopy system. We successfully performed a longitudinal nuclear-cytoplasmic visualization of transplanted BM cells with a H2B-GFP/β-actin-DsRed double-transgenic mouse model and fluorescently labeled vasculature landmark. Longitudinal in vivo BM monitoring clearly delineated the dynamic cellular behaviors of transplant BM dur-ing engraftment including cluster formation, migration, active proliferation, and differentiation into certain cell types in vivo. We visualized multi-phase spatiotemporal cellular dynamics of transplanted hematopoietic stem and progen-itor cells (HSPCs) during early engraftment. A daily longitudinal wide-area intravital imaging of host cranial BM until post-transplant day 10 identified two distinctive behaviors of transplanted HSPC groups including cluster formation and cluster dissociation in vivo. Especially, in vivo cellular dynamics of cluster formation followed by cluster dissociation and serial de novo cluster formation around the dissociation spot were ob-served with coordinated vascular dynamics. Finally, we performed a multi-position long-term time-lapse in vivo visualization of transplanted HSPCs on transplant day 2-4 when the cluster formation occurred, which revealed three collective spatiotemporal cellular phases of initial engraftment with distinct cellular density positively coordinated with proliferation rate and negatively correlated with migration velocity.