Characterization of cartilage from H-transferase transgenic pigs

Cartilage engineering is the object of intense research as a result of major medical needs and therapeutic prospects. Porcine xenogeneic cells/tissues may help in the development of clinical applications such as articular cartilage repair. However, unmodified porcine cartilage is rejected in primates by humoral and cellular mechanisms. We previously showed that porcine articular chondrocytes (PAC) isolated from H-transferase (HT) transgenic pigs show markedly reduced expression of the Galalpha1,3Gal antigen (alphaGal) and prolonged survival when transplanted into alpha1,3galactosyltransferase-deficient mice. In this work, we further studied the protective mechanisms of HT transgenic expression in cartilage, particularly its effects on monocyte adhesion. To this end, PAC isolated from control and HT transgenic pigs were assayed for human complement deposition and adhesion to the human monoblastic cell line U937. Consistent with a reduction in complement activation by the classical pathway, the HT transgenic PAC showed a 2-fold reduction in the deposition of complement components C4 and C3 relative to controls. Adhesion of U937 cells to HT PAC was also diminished under various conditions. This reduction was more dramatic at high effector:target ratios and especially observed when combined with anti-alphaGal antibodies (5-fold difference). Nevertheless, this effect was also observed in the absence of anti-alphaGal. antibodies and after tumor necrosis factor treatment. These results suggest that HT expression on porcine chondrocytes protects them from both humoral and cellular rejection.