Immune responses to osteochondral allografts: nature and significance.

Osteochondral allografts evoke immune responses. The nature of these immune responses and their biologic significance are still only partially understood. It is clear, however, that cell surface antigens of the major histocompatibility complex represented on the cellular elements of bone grafts cause T-cell activation, specifically those of the suppressor/cytotoxic phenotype. In numerous animal models, the most immunogenic bone allografts (mismatched, fresh) have demonstrated the poorest clinical and biologic outcomes, while more closely matched and/or grafts treated to reduce immunogenicity (frozen, freeze-dried) have more successfully incorporated. These observations support the hypothesis that immune responses against bone-graft related antigens have biologic significance and that reducing these responses may improve clinical results.