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A strategy for inhibiting CD40 has been considered as an alternative approach for immunosuppression because of undesirable effects of anti-CD154 monoclonal antibodies (mAbs). Previously, we demonstrated that ASKP1240, which is a fully human anti-CD40 mAb, significantly prolonged kidney and liver allograft survival in cynomolgus monkeys without causing thromboembolic complications. Herein, we evaluated the effect of ASKP1240 on pancreatic islet transplantation (PITx) in cynomolgus monkeys. Diabetes was induced by total pancreatectomy, and islet allografts were transplanted into the liver. Following PITx (8201-12 438 IEQ/kg), blood glucose levels normalized promptly in all animals. Control islet allografts were rejected within 9 days (n = 3), whereas ASKP1240 (10 mg/kg) given on postoperative days 0, 4, 7, 11 and 14 (induction treatment, n = 5) significantly prolonged graft survival time (GST) to >15, >23, 210, 250 and >608 days, respectively. When ASKP1240 (5 mg/kg) was administered weekly thereafter up to post-PITx 6 months (maintenance treatment, n = 4), GST was markedly prolonged to >96, >115, 523 and >607 days. During the ASKP1240 treatment period, both anti-donor cellular responses and development of anti-donor antibodies were abolished, and no serious adverse events were noted. ASKP1240 appears to be a promising candidate for immunosuppression in clinical PITx.

Blockade of CD40-CD154 signaling pathway is an attractive strategy to induce potent immunosuppression and tolerance in organ transplantation. Due to its strong immunosuppressive effect shown in nonhuman primate experiments, anti-CD154 monoclonal antibodies (mAbs) have been tried in clinical settings, but it was interrupted by unexpected thromboembolic complications. Thus, inhibition of the counter molecule, CD40, has remained an alternative approach. In the previous preliminary study, we have shown that 4D11, a novel fully human anti-CD40 mAb, has a fairly potent immunosuppressive effect on kidney allograft in nonhuman primates. In this study, we aimed to confirm the efficacy and untoward events of the 2-week induction and 180-day maintenance 4D11 treatments. In both, 4D11 significantly suppressed T-cell-mediated alloimmune responses and prolonged allograft survival. Addition of weekly 4D11 administration after the induction treatment further enhanced graft survival. Complete inhibition of both donor-specific Ab and anti-4D11 Ab productions was obtained only with higher-dose maintenance therapy. No serious side effect including thromboembolic complications was noted except for a transient reduction of hematocrit in one animal, and decrease of peripheral B-cell counts in all. These results indicate that the 4D11 appears to be a promising candidate for immunosuppression in clinical organ transplantation.

In order to obviate a small-for-size graft syndrome (SFSGS), a portacaval (PC) shunt had been considered in a case of adult-to-adult living donor liver transplantation (AA-LDLT). In a recent AA-LDLT case, we adopted the PC shunt to resolve SFSGS; however, graft atrophy was observed in the late period of LDLT, thereby resulting in liver dysfunction. Due to the surgical closure of the PC shunt at 11 months post-LDLT, the graft regenerated gradually and resulted in the recovery of the liver function. This experience indicates that the portacaval shunt would overcome SFSGS in the early period of LDLT, while it would cause the graft atrophy and the graft dysfunction in the late period of LDLT.