EFFECT OF GK1.5 MONOCLONAL ANTIBODY DOSAGE ON SURVIVAL OF PIG PROISLET XENOGRAFTS IN CD4+ T CELL-DEPLETED MICE

Abstract

Treatment of CBA/H mice with 5 injections of anti-CD4 (GK1.5 mAb) terminating on day 10 posttransplant resulted in long-term survival (≥6 weeks) of fetal pig proislet (pancreatic islet precursor) xenografts. The GK1.5 mAb dose determined the duration of CD4⁺ T cell depletion and the extent to which the survival of pig proislet xenografts was prolonged. Sustained depletion of CD4⁺ T cells (0%, 1%, and 9% of total T cells in peripheral lymph nodes at 2, 4, and 6 weeks, respectively) and survival of proislet xenografts at 6 weeks posttransplant was observed when transplant recipients were treated with 5.4 mg GK1.5 mAb/injection. Treatment of transplanted mice with a suboptimal dose of GK1.5 mAb (0.2 mg/injection) resulted in the same level of depletion at 2 weeks posttransplant but a more rapid recovery of CD4⁺ T cells in the periphery (24% of total T cells at 4 weeks) and only temporary prolongation in xenograft survival (>4 weeks). Control xenografts showed evidence of graft destruction by as early as 6–7 days posttransplant and were completely rejected by 2 weeks. The rejection reaction consisted predominantly of CD4⁺ T cells, eosinophils and F4/80-positive macrophages. Only small numbers of CD8⁺ T cells were identified. CD4⁺ T cells therefore represented the major T cell component of the cellular infiltrate. In contrast, surviving xenografts in GK1.5 mAb-treated recipient mice showed essentially an absence of CD4⁺ T cells but presence of CD8⁺ T cells. This finding may be attributable to the increase (1.7–3.1-fold) in the absolute size of the population of CD8⁺ T cells in the periphery following GK1.5 mAb treatment in vivo. Compared with isolated fetal pig proislets, which contained only a small population of insulin-producing cells in addition to glucagon-and somatostatin-positive cells, surviving pig proislet xenografts contained mainly insulin-positive beta cells with smaller populations of glucagon- and somatostatin-positive cells. Fetal pig proislets therefore differentiate into insulin-producing islet tissue posttransplant and thus show evidence of normal development of endocrine function.