Human anti-porcine T cell response: blocking with anti-class I antibody leads to hyporesponsiveness and a switch in cytokine production.

Intervention in the molecular interactions that lead to an immune response is possible at various stages of Ag recognition and T cell activation. Perturbation of the interaction of the TCR with the MHC/peptide ligand complex is one approach that has shown promise for autoimmunity and graft rejection in blocking T cell-activated responses. In this study, we investigated the effect of altering the target MHC class I molecule by blocking with Abs. We established a system that analyzed the human T cell response against MHC class I+/class II- porcine stimulatory cell targets. The primary human response against porcine smooth muscle cells was CD8+ T cell dependent. In the presence of F(ab')2 fragments of the MHC class I-reactive Ab, PT-85, the proliferative response was inhibited and production of IL-2 and IFN-gamma was blocked. Moreover, in a secondary response, proliferation was reduced and type 1 cytokine levels were inhibited. In contrast, levels of IL-10 and IL-4 were sustained or slightly increased. These findings indicate that Ab against MHC class I blocked the recognition of porcine cells by the human CD8+ T cells and altered the cytokine secretion profile. Thus, a single treatment with PT-85 F(ab')2 directed against the MHC class I molecule provides an attractive approach to the induction of T cell tolerance that may provide long-term graft survival in porcine-to-human cell transplantation.

Porcine repeat element DNA: in situ detection of xenotransplanted cells.

Using a digoxygenin-labelled DNA probe derived from the porcine repeat element PRE-1, we have developed a protocol for the detection of transplanted porcine islets and hepatocytes against a background of murine host tissue. Analysis of this probe by Southern blotting indicated that PRE-1 hybridizes to pig genomic DNA but not to human or mouse DNA. On tissue sections, hybridizing probe was detected using alkaline phosphatase-conjugated antidigoxygenin antibody visualized with 5-bromo-4-chloro-3-indolyl-phosphate/4-nitro-blue tetrazolium chloride (BCIP/NBT) substrate. We have demonstrated sensitive and highly specific staining of porcine nuclei in fixed, paraffin embedded tissue sections, and have applied the technique to detect porcine pancreatic islets and hepatocytes transplanted into murine kidney and spleen. Application of this technique include detection of transplanted cells or organs across the variety of xenogeneic barriers.