IMMUNOGENICITY OF CULTURED KERATINOCYTE ALLOGRAFTS DEFICIENT IN MAJORHISTOCOMPATIBILITY COMPLEX ANTIGENS

Background: Full-thickness (FT) and cultured keratinocyte (CK) allogra fts have been used as temporary skin replacements in patients with mas sive burns, but these grafts are ultimately rejected after restoration of host immunocompetence. Genetic engineering has permitted the creat ion of knockout (KO) mice deficient in class I or class TI major histo compatibility antigens, This study examines the immunogenicity of such grafts to determine if these genetically modified keratinocytes could be used for permanent wound coverage. Methods: Host sensitization to alloantigen was assessed by second-set rejection. CBA mice (n = 111) w ere primed with flank grafts consisting of FT and CK allografts from n ormal C57BL/6 donors, MT and CK class I KO allografts, FT and CK class II KO allografts, and CK autografts, Three weeks later, hosts were ch allenged with normal tail allografts and observed for second-set rejec tion. Median graft survival was analyzed by chi(2) and Wilcoxon rank t ests, In the second experiment, cytotoxic T lymphocytes (CTLs) were ha rvested from CBA mice (n = 28) 3 weeks after flank grafting. CTL effec ters were tested on radiolabeled targets at various ratios in a Cr-51 release assay. Dilution curves of CTL activity were compared by analys is of variance. Results: Hosts primed with CK or FT allografts demonst rated accelerated rejection of second-set tail grafts compared with ho sts covered with CBA autografts. CK knockout grafts were less immunoge nic than FT knockout skin; class II KO allografts were considerably le ss immunogenic than class I KO allografts, CTL activity against the kn ockout CK allografts was negligible compared with that of hosts primed with normal allografts or FT knockout allografts. Conclusion: Althoug h full-thickness knockout skin retains substantial immunogenicity, cul tured keratinocytes deficient in class II antigens fail to prime for a ccelerated second-set rejection and do not elicit a CTL response in th e graft recipient. This lack of immunogenicity may permit the indefini te survival of allogeneic knockout keratinocytes in patients requiring massive wound excision and coverage.