HUMAN NK CELL AND ADCC REACTIVITY AGAINST XENOGENEIC PORCINE TARGET-CELLS INCLUDING FETAL PORCINE ISLET CELLS

In vitro studies of human NK cell-mediated cytotoxicity and ADCC again st porcine target cells were performed. Stimulation of human PBMC resp onder cells with either allogeneic or xenogeneic porcine cells led to a marked increase in NK cell reactivity, Maximum reactivity was reache d following 3-6 days of in vitro culture. The sensitivity of target ce lls ranked as follows: K562 > porcine PHA-induced lymphoblasts > resti ng porcine PBMC. Limiting dilution analysis showed that allo-and xeno- stimulation in vitro led to differentiation of similar frequencies of effector NK cells. Split culture experiments showed that single NK eff ector cells were cytotoxic against both K562 and porcine lymphoblasts, demonstrating that individual NK cells lack species specificity. NK e ffector cell generation stimulated by xenogeneic cells was cyclosporin A (CsA) sensitive and dependent on the presence of autologous respond er T lymphocytes, a dependence that was completely reconstituted by th e sole addition of human IL-2. Xenostimulation of enriched CD3+ cells also led to a preferential appearance of CD16+ or CD56+ lymphoblasts. Natural xenoreactive human anti-porcine antibodies are mainly of IgM a nd IgG2 subclasses, but antibodies in xenoimmunised patients reactive against porcine lymphocytes and fetal porcine islet cells were also of IgG1 and IgG3 subclasses. The same subclass distribution was found am ong antibodies specific for gal alpha 1,3 gal epitopes as shown by tes ts performed with alpha 1,3 galactosyltransferase-transfected Raji cel ls (human Burkitt lymphoma cells). Natural antibodies did not mediate ADCC, whereas gal alpha 1,3 gal-specific antibodies in sera from xenoi mmunised patients did. Fetal porcine islet cells were sensitive to hum an NK cell-mediated cytotoxicity and to ADCC mediated by xenoimmune se ra.