Effect of FK506 and Anti-CD4 Therapy on Fetal Pig Pancreas Xenografts and Host Lymphoid Cells in NOD/Lt, CBA, and BALB/c Mice

Abstract

Varying doses of FK506, and a cell-depleting anti-CD4 monoclonal antibody, GK1.5, were tested as either monotherapy or in combination for their effect on the survival of renal subcapsular xenografts of organ-cultured fetal pig pancreas in three strains of mice. Subcutaneous injections of FK506 at 4.0 mg/kg/day for 28 d prevented graft rejection to day 35 posttransplantation (i.e., 7 days after cessation of treatment in NOD/Lt, and CBA mice) while BALB/c mice had intact grafts at 28 days. Lower doses were less effective and immunosuppression was less effective in NOD mice than in the other strains. Even 2.0 mg/kg/day of FK506 prevented rejection in CBA mice until day 35, but not in NOD/Lt mice. GK1.5 alone did not prevent rejection in NOD/Lt mice but when a low dose of FK506 (2.0 mg/day) was added, the grafts were present, essentially intact, at 35 days. There were no obvious toxic effects of FK506 in NOD/Lt and CBA mice. With FK506 treatment there was no significant difference in absolute numbers of total leucocytes or lymphocytes in peripheral blood and spleen, but there was a decrease in thymus cellularity. Flow cytometric analysis of lymphocyte subsets in blood and spleen also showed no significant differences, but in the thymus the percentage of immature CD4/CD8 "double positive" cells increased while the more mature CD3"high", and CD4 or CD8 "single-positive" cells decreased. Thus, prolonged discordant xenograft survival in mice is possible and the use of two agents that act on different parts of the immune system allows a reduction in the dose of FK506 to safe levels.

Xenotransplantation of Adult Porcine Islets in Diabetic Mice

“…FK506 is a relatively new immunosuppressive agent that is now undergoing extensive clinical trials, however, its effect on xenografts has been less well studied. Mandel et al reported that Fl<506 at 4 mg/kg/day significantly prolonged the survival of fetal pig pancreas xenograft in 3 strains of mice (18). Earlier, we observed prolonged histological survival of human islets in xenogenic rat recipients treated with FK506 (19).…”

“…Earlier, we also reported the prolongation of human islets in rats for up to 2 months of xenograft under the kidney capsule (19). In the pig to mouse xenograft studies, hyperacute rejection was also present (18). It is apparent that, if hyperacute rejection of xenografts due to preformed natural antibody can be avoided, the major attack on the transplant is T-cell mediated (20,21).…”

Evaluation of Graft‐Host Response for Various Tissue Sources and Animal Models

“…[9][10][11] Long-term human, bovine and porcine islet xenograft survival has been documented in nude mice and rats, suggesting that sufficient islet-specific growth factors are present in xenogeneic recipients. [12][13][14][15][16][17] Adult porcine islets are difficult to isolate and to maintain in vitro; nevertheless, they are extremely promising for eventual clinical application since their glucose-responsiveness is similar to that of humans. 9,10 Isolation of bovine islets is technically easier (than porcine islets), and calf islets are glucose-responsive; 10 however, adult bovine islets are relatively insensitive to glucose.…”

“…9–11 Long‐term human, bovine and porcine islet xenograft survival has been documented in nude mice and rats, suggesting that sufficient islet‐specific growth factors are present in xenogeneic recipients. 12–17…”