Despite the enormous therapeutic potential of bone marrow transplants, the procedure carries significant risks of morbidity and mortality. Some of the risks are associated with the cytoreductive conditioning regimen that clinicians must use to clear niche space and promote donor cell engraftment. Without high-dose radiation or chemotherapy, donor bone marrow cells fail to engraft in host bone marrow. Other risks are associated with transplanting donor T cells, which cause an immune response against host tissue. However, depleting T cells from transplants causes a further increase in engraftment failure. Therefore, there is a pressing medical need to develop new methods to increase donor cell engraftment in bone marrow transplants. This proposal describes a novel strategy of therapeutic delivery that may find wide application in transplant biology. CD47 is a ubiquitously expressed "don't eat me signal" that negative regulates macrophage activation and phagocytosis. Cell surface CD47 expression is a necessary factor for hematopoietic stem cell engraftment in wild- type mice and a sufficient factor to promote the engraftment of MOLM-13 cell line in immunodeficient mice. Therefore, we are developing protein-based strategies to artificially increase CD47 protein levels on the donor cell surface. Using biotin- streptavidin crosslinking, we have successfully increased cell surface display of CD47 and we are actively characterizing the effects. Additionally, capitalizing on the highly selective chemistry of cystein thiols, we have engineered a site for the specific modification of recombinant CD47 protein with a synthetic lipid, which can subsequently be anchored into the plasma membrane. We propose to treat donor bone marrow cells ex vivo with both of these strategies in order to evade innate immunosurveillance and promote donor cell engraftment.
Despite the enormous therapeutic potential of bone marrow transplants in treating genetic disease and blood cancers, the procedure carries significant risks of morbidity and mortality. This project seeks to develop novel biochemical tools that mitigate these risks and prevent transplant failure.