Human retinal progenitor sheet transplants in immunodeficient retinal degenerate (RD) rats

Abstract

Purpose : To follow the development of human fetal retinal sheet transplants in vivo after transplantation to the subretinal space of immunodeficient RD rats (SD-Foxn1 Tg{S334ter}3Lav = RD nude rats; cross of NIH nude and S334ter-3 rats). Previously, rat retinal sheet transplants restored visual responses.

Methods : Fetal human eyes (11-15.7 weeks gestation, 5 different samples) obtained from an hSCRO-approved supplier were shipped overnight in cold hibernation medium. After dispase treatment, retina with RPE was dissected; and tissue sheets (size 0.8 x 1.3 mm) transplanted on the same day to the subretinal space of 24-31 d old RD nude rats (n=22). Transplanted eyes were imaged by high-resolution spectral-domain optical coherence tomography (SD-OCT; Bioptigen Envisu R2200 SD-OIS) at 1 wk, 1 mo, and up to 7 mo. after transplant at several time points. Four rats with large transplants were recorded for visual responses in the superior colliculus (SC) at 6.7-8.6 mo. post surgery. Rats were euthanized between 0.5 and 8.6 months post surgery for histological evaluation.

Results : Seven of 22 rats developed corneal ulcers which cleared up later upon treatment with betadyne in 3 of 7 rats. SD-OCT scan analysis showed transplant placement in the subretinal space, presence or absence of surgical trauma, and development of laminated areas or rosettes. In 6 rats, transplants had slipped out at the insertion site. 5 rats contained only degenerating transplants. The four 15.7 week gestation transplants all degenerated within 3 months of transplant. In 10 of 18 transplants from 11-12 week donors, large transplants developed, with clear development of plexiform layers first seen in OCT at 3 months post surgery. At 6-8 months post surgery, transplant photoreceptors developed short outer segments. Immunohistochemistry confirmed the formation of retinal layers and photoreceptor maturation of the human grafts. However, all SC recorded rats showed either no or weak responses to bright light. Transplant cells extended processes into the host retina, and transplanted cells migrated into the host retina.

Conclusions : Human fetal retina (11-12 wks gestation) transplanted as sheets to the subretinal space of RD nude rats can develop mature photoreceptors and begin to integrate with the host retina. In the 5 animals with SC recording, such integration did not have a significant effect on functional vision improvement in this RD rat model.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.