Immune response by host after allogeneic chondrocyte transplant to the cartilage

Chondrocytes constitutively express class I and, in some species, class II major histocompatibility complex (MHC). It is also possible that they possess specific differentiation antigen(s). Furthermore, lymphocytic cells, corresponding to NK cells, display spontaneous cytotoxic activity against chondrocytes. Studies on articular cartilage repair by transplants of allogeneic chondrocytes were mainly done on non-inbred animals, such as rabbits and hens. Surprisingly, only in single instances these transplants were rejected. In inbred rats, allogeneic chondrocytes transplanted into full-thickness defects in articular cartilage immediately after isolation evoked systemic immunological reaction and produced cartilage was rejected. Combined immunosuppression with cyclosporin A and cladribine did not prevent rejection of such transplants. Mechanical separation of transplants from bone marrow prevented sensitization of recipients and rejection of the produced cartilage. Successful allogeneic chondrocyte transplants in rabbits and hens could be tentatively explained by a certain degree of inbreeding among experimental animals, by the use of chondrocytes cultivated before grafting in artificial scaffolds and thus protected by matrix produced in vitro, and also by creation of a temporary mechanical barrier between transplant and bone marrow by tissues damaged during preparation of the defect.