Cultured keratinocyte grafts are recognized, but not rejected by CD8+ T cells in vivo.

It has been shown in the mouse that cultured keratinocyte allografts [fully major histocompatibility complex (MHC) mismatched] survive for at least 100 days without evidence of rejection. In an attempt to analyze the immune mechanisms underlying this phenomenon we have investigated the induction of tolerance to such grafts. Primary cultures of BALB/c keratinocytes were prepared using irradiated 3T3 feeder cells, and the cultured cell sheets were grafted, using a silicone transplantation chamber, onto CBA recipients. After the cultured grafts had been in place for 4-6 weeks full-thickness tail skin from BALB/c donors was grafted onto the dorsal flank opposite the cultured graft. The median graft survival time of these full-thickness allografts was 15.5 days compared to 13 days in the control group. These data show that in the absence of Langerhans cells and MHC class II expression, keratinocytes expressing class I and minor histocompatibility antigens induce a prolonged survival of full-thickness skin allografts. The results from experiments in which T cell subsets were depleted in vivo suggest that CD8+ cells (a) recognize the class I alloantigens of the cultured graft, (b) do not reject the cultured graft and (c) do not progress further in their maturation pathway. We propose that these CD8+ T cells might have been partially primed by receiving only the first signal of activation and that they may be equivalent to "poised" cytotoxic T cells. These CD8+ cells can reject non cultured full-thickness skin grafts, and do so more effectively after removing CD4+ cells.