Transplanted fetal fibroblasts: Survival and distribution over time in normal adult dermis compared with autogenic, allogenic, and xenogenic adult fibroblasts

Cell therapy is a widely applicable therapeutic approach using cells and ce ll elements, frequently from fetal or young animals, for their beneficial e ffects. This study evaluated the host response to and tolerance of transpla nted fetal skin fibroblasts. Cultured fibroblasts from adult rabbit skin (a utogenic and allogenic), 21-day fetal rabbit skin (allogenic), and adult pi g skin (xenogenic) were labeled with a fluorescent vital dye CM-Dil, inject ed intradermally into the dorsal skin of adult rabbits at multiple sites an d then biopsied over an 8-week period. Each cell type showed a biphasic dis tribution curve with an early phase (0 to 28 days) and a late phase (28 to 56 days). In the early phase, cells showed a rise and fall in total cell de nsity (reflecting an increase and then a decrease in total cell number), fo llowed by a slow decrease in cell density with cells still detectable at 56 days. Fetal cells showed the highest survival at the end of the study. Non e of the groups showed clinical or histologic signs of acute inflammation o r rejection. This study demonstrated that (1) transplanted fibroblasts are well tolerated by an immunologically competent host, (2) CM-Dil-labeled cel ls are detectable in vivo for at least 8 weeks, and (3) fetal fibroblasts h ave a distribution and survival profile that is distinct from that of adult fibroblasts.