Vascular Cell Adhesion Molecule 1-Mediated Targeting of Human Hematopoietic Stem Cells to Bone Marrow Is Effective in Conferring Regeneration and Survival in Lethally Irradiated Mice

Abstract

Bone marrow (BM) transplantation has been used to treat malignant and nonmalignant BM-related disorders. Although an effective strategy, the procedure is associated with numerous complications, including graft rejection and nonspecific stem cell distribution. Avoidance of immune graft rejection has downsized the quantity of available stem cells, whereas nonspecific distribution necessitates the infusion of increased stem cell doses. A dual-purpose approach is needed to reduce the stem cell dose for transplantation. This used cell encapsulation and BM targeting to increase the quantity of transplanted stem cells reaching the BM. Cells were encapsulated with different biomaterials-chitosan (CS), polyallylamine hydrochloride (PAH), polystyrene sulfonate (PSS), and liposomes-and assessed for interaction with immune system components. The biomaterials were conjugated with vascular cell adhesion molecule 1 (VCAM1), a peptide that binds to BM-specific cell surface molecule, and evaluated for a successful transplantation. Encapsulated cells showed reduced interaction with antibody and cytokine without adverse effects on viability. Constitutive expression of VCAM1 was found to be specific on human bone marrow endothelial cells and was used for targeting by conjugating VCAM1-binding peptide to encapsulated cells. Peptide-conjugated-encapsulated stem cell formulations transplanted in irradiated mice with or without treatment with radioprotectant amifostine showed an increased percentage of cells reaching bone marrow. Post-transplantation survival along with blood count of neutrophils, platelets, and leukocytes was also enhanced for VCAM1-binding peptide-conjugated formulations with 100% survival demonstrated by peptide-conjugated CS/PSS/CS encapsulation formulation in irradiated mice for 4 weeks. Encapsulated cells retained their viability with increased shielding to the immune system, ensuring that graft rejection can be avoided. Transplanted encapsulated stem cells were distributed in a higher percentage to BM when conjugated to VCAM1-binding peptide, which could enable the use of lower stem cell doses. The peptide-conjugated CS/PSS/CS encapsulation system conferred 100% survival in irradiated mice, with increased regeneration demonstrating the ability to treat radiation-exposed victims.