Cellular response in rabbit eyes after human fetal RPE cell transplantation

Background: This study was carried our to study inflammatory and proliferat ive cellular responses in the rabbit eye after subretinal transplantation o f human fetal retinal pigment epithelial (HFRPE) cells. Methods: 5-Bromo-2- deoxyuridine (BrdU)-labeIed HFRPE cells were injected subretinally into rab bit eyes at three different concentrations. Macrophage, glial, and prolifer ative responses of the eye tissues were studied by immunohistochemistry and light microscopy at different times after the surgery. Results: In transpl anted eyes, the HFRPE cells were distributed irregularly either as multilay ers or monolayers. In eyes receiving high-density cell suspensions, retinal breaks were seen. No retinal breaks were noted in the eyes receiving low-d ensity HFRPE cell suspensions. The highest intensity of inflammatory respon se was seen at 4-14 days after surgery, with greater expression in transpla nted eyes receiving high-density cell suspensions. The host cellular respon se was characterized initially by local infiltration of the retina and subr etinal space by macrophages and glial cells. After day 14, a decline in the number of donor cells was noted in all eyes. At later stages the host cell ular response was characterized mainly by local choroidal thickening and in filtration by inflammatory cells. Proliferative response was expressed main ly by retinal cells. Conclusion: Initial inflammatory and proliferative res ponses after the xenogenic human to rabbit HFRPE cell transplantation were expressed by retinal cells with later involvement of the choroid. Our resul ts showed a decline in the number of donor cells starting from day 14 after the transplantation. This may suggest a possibility of rejection. The init ial quantity of injected cells may be critical for the intensity of the imm une and inflammatory responses.