Immunogenicity of Retinal Progenitor Cells Seeded on Biodegradable Polymers

Abstract

Abstract: : Purpose: To study the immunobiology of the retinal progenitor cells seeded on biodegradable polymers by transplantation into the kidney subcapsular space in mice. Methods: Retinal progenitor cells (RPCs) harvested from the retina of postnatal day 1 EGFP (Enhanced Green Fluorescence Protein) mice (C57BL/6 background) were isolated and maintained in culture. RPCs were seeded on biodegradable PLGA polymers (50:50 glycolic acid: lactic acid; 40kDa) and were maintained in vitro for 1 week. A 1 mm² piece of the RPCs / polymer composite was transplanted into the kidney subcapsular space in either syngeneic (C57BL/6) or allogeneic (BALB/c) mice. The animals were sacrificed at 1, 2, 4, 6 and 8 weeks post- transplantation (wpt). The kidney receiving the composite graft was evaluated for EGFP fluorescence and then fixed in 4% paraformaldehyde and cryosectioned for immunostaining. GS lectin and antibodies against MHC II (IA^b for C57BL/6 and IA^d for BALB/c) mice were used to detect infiltration of recipient derived immune cells. Antibodies against neurofilament, GFAP, nestin and recoverin were used to determine the differentiation status of the RPCs in the polymer. Some animals at 4 wpt were used for the detection of delayed hypersensitivity by challenge with either allogeneic spleen cells (C57BL/6) or RPCs. Results: EGFP fluorescence was detected in RPCs / polymer in all grafts up to 8 wpt. The polymer became increasingly translucent and disappeared at 8 wpt. Cells were found positive to neurofilament and GFAP at all time points. Recoverin⁺ cells in the polymer were only found at 2 and 4 wpt. GS lectin and MHC II⁺ cells were found at 2 wpt and onward. However, there is no delayed hypersensitivity specific to either allogeneic antigens or to RPC antigens. Conclusions: Biodegradable polymers are effectively degraded and absorbed by the host kidney over time without any apparent immune response. RPCs possess immune privilege properties. Biodegradable polymers provide an alternate method for delivery of progenitor cell populations, and may be useful in retinal transplantation.

Keywords: transplantation • immune tolerance/privilege • retina