Effect of anti-CD4 monoclonal antibody administration on rat small bowel allograft survival and circulating leukocyte populations

This study assessed the effect of an anti-rat CD4 monoclonal antibody (OX38 ) on heterotopic small bowel allograft rejection. Fully allogeneic small bo wel transplants were performed in the PVG-to-DA-rat strain combination. Ani mals received either i) short course (days -1, 0 and 1) of 1 mg/kg per day OX38, ii) short course of 5 mg/kg per day or iii) extended course (days -2, -1, 0, 1, 2 and twice weekly thereafter) of 1 mg/kg per day. Both the high dose (13 days) and extended low-dose (12 days) courses prolonged graft sur vival compared to untreated control animals (7 days). The low-dose, short-c ourse treatment had no effect. Similar regimens were given to animals that did not receive transplants and in which peripheral blood CD4(+) cell count s fell to between 20 and 55% of pretreatment levels and 20-30% of binding s ites were blocked. In summary, anti-CD4 monoclonal antibody therapy delayed rejection of rat small bowel allografts; however, long-term survival was n ot achieved.