fibroblasts used in tissue engineering may be allogeneic or autologous. in contrast to allogeneic cells, autologous fibroblasts carry no risk of rejection or risk of cross-infection. however, there is often a delay in culturing autologous cells in order to obtain sufficient cell numbers, whereas allogeneic cells are cryopreserved and therefore readily available. for permanent engraftment, autologous fibroblasts are necessary.