Belatacept and sirolimus prolong nonhuman primate islet allograft survival: adverse consequences of concomitant alefacept therapy

Abstract

Calcineurin inhibitors (CNI) and steroids are known to promote insulin resistance, and their avoidance after islet transplantation is preferred from a metabolic standpoint. Belatacept, a B7-specific mediator of costimulation blockade (CoB), is clinically indicated as a CNI alternative in renal transplantation, and we have endeavored to develop a clinically translatable, belatacept-based regimen that could obviate the need for both CNIs and steroids. Based on the known synergy between CoB and mTOR inhibition, we studied rhesus monkeys undergoing MHC-mismatched islet allotransplants treated with belatacept and the mTOR inhibitor, sirolimus. To extend prior work on CoB-resistant rejection, some animals also received CD2 blockade with alefacept (LFA3-Ig). Nine rhesus macaques were rendered diabetic with streptozotocin and underwent islet allotransplantation. All received belatacept and sirolimus; six also received alefacept. Belatacept and sirolimus significantly prolonged rejection-free graft survival (median 225 days compared to 8 days in controls receiving basiliximab and sirolimus; p = 0.022). The addition of alefacept provided no additional survival benefit, but was associated with Cytomegalovirus reactivation in four of six animals. No recipients produced donor-specific alloantibodies. The combination of belatacept and sirolimus successfully prevents islet allograft survival in rhesus monkeys, but induction with alefacept provides no survival benefit and increases the risk of viral reactivation.

Figure 1. Treatment with belatacept and sirolimus prolongs islet allograft survival and prevents donor specific alloantibody

The immunosuppression regimen of belatacept and intramuscular sirolimus (A) significantly prolongs islet allograft survival compared to historic controls that received basiliximab and sirolimus(16) (p=0.022) and (B) prevents the formation of donor specific alloantibody at the time of rejection as measured by anti-rhesus IgG. (C) Fasting blood glucose (FBG) graphs (solid line) for transplant recipients receiving belatacept and sirolimus reveal that two recipients (RMt12 and RCd13) rejected their grafts after all immunosuppression was withdrawn and one recipient (RYo12) rejected its graft after rapamycin levels waned (dashed line) but while still on belatacept therapy.

Figure 2. The addition of alefacept provides no survival benefit

(A) Adding alefacept to the regimen of belatacept and intramuscular sirolimus results in worse survival (p=0.036). (B) Fasting blood glucose (FBG) graphs (solid line) for transplant recipients receiving alefacept, belatacept and sirolimus show that three recipients (RZw11, RVw11 and RRRp12) rejected their grafts prior to cessation of sirolimus (dashed line), one recipient (RDp12) rejected its graft after rapamycin levels waned while still receiving belatacept, and one recipient (RAg12) rejected its graft following cessation of all immunosuppression.

Figure 3. Treatment with alefacept results in CD2 blockade

(A) Treatment with alefacept resulted in a marked decrease in CD2 expression as measured by mean fluorescence intensity (MFI) on CD4⁺ and CD8⁺ naïve (T_Naive), central memory (T_CM) and effector memory (T_EM) T cells. (B) This effect is not seen in animals treated with belatacept and sirolimus alone.

Figure 4. CMV reactivation may have contributed to worse graft survival in the cohort receiving alefacept

(A) Clinically significant Cytomegalovirus (CMV) reactivation (as measured by PCR and expressed as copies/mL) in the cohort receiving alefacept, belatacept and sirolimus may have contributed to worse survival compared to the transplant recipients receiving belatacept and sirolimus alone (B), which experienced no clinically significant viral reactivation.