Delivery of human adipose-derived stromal cells within in situ forming chitosan/PEG-PTMC hydrogels induces adverse outcomes in a femoral artery ligation model in athymic nu/nu mice

The delivery of human adipose-derived stromal cells (hASCs) to ischemic tissues represents a promising strategy to promote vascular regeneration for patients with critical limb ischemia (CLI). Building on previous work, this study focused on the in vivo characterization of a hydrogel cell delivery platform for hASCs composed of peptide-functionalized methacrylated glycol chitosan (MGC-RGD) and a terminally acrylated triblock copolymer of poly(ethylene glycol) and poly(trimethylene carbonate) (PEG(PTMC-A)2) in athymic nu/nu mice with femoral artery ligation-induced critical limb ischemia (FAL-CLI). This immunodeficient mouse strain was selected to enable human cell transplantation in a model with conserved monocyte/macrophage function, recognizing that macrophages are key regulators of the biomaterial implant response, as well as vascular repair and regeneration. The hASCs were engineered to co-express tdTomato and firefly luciferase to enable longitudinal cell tracking using bioluminescence imaging (BLI). Interestingly, the hASCs were better retained following delivery in saline compared to hydrogel delivery. However, laser Doppler perfusion imaging (LDPI) analysis indicated that the restoration of hindlimb perfusion was similar between the two cell treatment groups. Critically, delivery of the hASCs within the hydrogels was associated with adverse outcomes only observed within this treatment group, including severe swelling, discoloration, and necrosis, which necessitated early euthanasia of some mice. CD45 staining supported that the combination of the cells and the hydrogels induced an inflammatory host response. These findings contrast with previous positive results when the platform was tested for hASC delivery in more severely immunocompromised NOD/SCID mice with FAL-CLI, as well as allogeneic rat ASC delivery in a healthy immunocompetent rat model. Overall, this study emphasizes the potential importance of testing cell delivery platforms in pre-clinical disease models that have retained host immune cell function, especially for immunomodulatory cell populations such as ASCs.