HUMAN ANTI-PIG T-CELL MEDIATED CYTOTOXICITY

Miniature swine have a variety of advantages as potential donors for h uman xenotransplantation, including size, physiological similarities, and breeding characteristics. To investigate the nature of the human a nti-pig xenogeneic cellular response, we performed standard Cr-51-rele ase cell-mediated lympholysis (CML) experiments. The major histocompat ibility complex (MHC) allele specificity of the xenogeneic cellular re sponse was tested on porcine target cells of three distinct homozygous MHC haplotypes (SLA(aa), SLA(cc), SLA(dd)) and three intra-MHC recomb inant haplotypes (SLA(ii), SLA(gg), SLA(kk)), Obtained from our herd o f partially inbred miniature swine. After stimulation with irradiated porcine peripheral blood mononuclear cells (PBMC) of SLA(aa) haplotype , a strong nonspecific cytotoxic response of the bulk culture against xenogeneic targets of all three haplotypes was observed. However, SLA allele specificity could be demonstrated after T cell enrichment, and mapping experiments revealed predominantly SLA class I restriction of xenoreactive cytotoxic T lymphocytes (CTLs), although some class II re striction was also observed. The experiments were repeated in the pres ence of anti-T cell monoclonal antibodies, anti-CD3 (OKT3), anti-CD2 ( 35.1), anti-CD4 (OKT4), or anti-CD8 (OKT8). The bulk xenogeneic CML wa s not inhibited by any of the anti-T cell antibodies tested. However, after T cell-enrichment, lysis of porcine targets was significantly in hibited by anti-CD3 or anti-CD8 antibody and partially inhibited by an ti-CD2 antibody. In comparable assays, the human allogeneic CML was bl ocked by anti-CD3 and anti-CD8, but not by anti-CD2 or anti-CD4 antibo dies. Finally, the cytotoxic activity of A3b3, a human CD4(+) T-cell c lone, was tested. A3b3 lysed xenogeneic targets of SLA(aa) haplotype, but not SLA(cc) or allogeneic targets, and was inhibited by anti-CD4, anti-CD2, and anti-CD3 antibodies, but not by anti-CD8. With the aid o f intra-MHC recombinant haplotypes, the xenogeneic CML reactivity of A 3b3 was mapped to SLA class II, suggesting direct xenogeneic recogniti on of porcine MHC class II antigens by human T cells. Thus, the human anti-pig cell-mediated cytotoxic response is similar in magnitude to c omparable allogeneic responses, and involves both SLA class I and clas s II restricted T-cell mediated cytotoxicity, as well as additional no nspecific killing, possibly by NK cells.