Background. The pig is currently considered to be the most likely candidate for a xenogenic-organ source. Anti-pig human T-cell response via co-stimulatory molecules has been studied with great interest. The soluble form of porcine CD80 has recently been cloned and characterized, but the sequence of the transmembrane form has not been determined. The purpose of this study was to investigate the functional interaction between porcine CD80 and human T cells using the full-length clone of porcine CD80. Materials and Methods. Specific complementary DNA (cDNA) clones encoding porcine CD80 were isolated and sequenced using rapid amplification of cDNA ends-polymerase chain reaction. Polymerase chain reaction-amplified cDNA coding for the open reading frame of the porcine CD80 transmembrane form was subcloned into an expression vector and then transfected into Chinese hamster ovary (CHO) cells. CHO cells transfected with porcine CD80 (CHO-pCD80) were co-cultured with human CD4+ T cells and then interleukin-2 secretion was measured and transferred pCD80 expression in these human T cells was detected by flow cytometry. Results. We cloned and determined the complete nucleotide sequence for the transmembrane form of porcine CD80. Results from our T-cell co-stimulatory assay showed significant interleukin-2 production when co-stimulated with CHO-pCD80. Human naïve CD4+ T cells acquired xenogenic pCD80 molecules in the process of T-cell activation. Conclusions. Findings from this study seem to suggest that pCD80 has the functional ability to regulate human anti-pig cellular response. In addition, genetic manipulation of porcine co-stimulatory molecules offers a potentially new therapeutic strategy to prevent xenogeneic rejection across species.