The anti-CD40L monoclonal antibody AT-1501 promotes islet and kidney allograft survival and function in nonhuman primates

Abstract

Prior studies of anti-CD40 ligand (CD40L)-based immunosuppression demonstrated effective prevention of islet and kidney allograft rejection in nonhuman primate models; however, clinical development was halted because of thromboembolic complications. An anti-CD40L-specific monoclonal antibody, AT-1501 (Tegoprubart), was engineered to minimize risk of thromboembolic complications by reducing binding to Fcγ receptors expressed on platelets while preserving binding to CD40L. AT-1501 was tested in both a cynomolgus macaque model of intrahepatic islet allotransplantation and a rhesus macaque model of kidney allotransplantation. AT-1501 monotherapy led to long-term graft survival in both islet and kidney transplant models, confirming its immunosuppressive potential. Furthermore, AT-1501-based regimens after islet transplant resulted in higher C-peptide, greater appetite leading to weight gain, and reduced occurrence of cytomegalovirus reactivation compared with conventional immunosuppression. These data support AT-1501 as a safe and effective agent to promote both islet and kidney allograft survival and function in nonhuman primate models, warranting further testing in clinical trials.

Fig. 1.. In vitro characterization of AT-1501.

(A) CD40L binding potency of AT-1501 (cyan) and Hu5C8 (orange) was determined by ELISA with recombinant human CD40L (rhuCD40L). Abatacept (purple), a variant of CTLA4-Ig that interferes with the CD28-CD80/86 costimulatory pathway, was used as a negative control. A450, absorbance at 450nm. (B) AT-1501 and Hu5C8 binding to human FcγRI, FcγRIIa, FcγRIIIa, and FcγRIIIb was measured by ELISA. (C to F) PAC-1 expression was measured in platelets from healthy controls incubated with soluble CD40L alone (C), Hu5C8 and sCD40L (D), Hu5C8 F(Ab’)2 lacking an Fc region and sCD40L (E), or AT-1501 and sCD40L (F). Blue tracings represent expression of PAC-1 following incubation with 5μg/mL sCD40L alone and red tracings represent expression of PAC-1 following incubation with the indicated combinations. (G) Platelet aggregation was measured in vitro using platelets incubated with the indicated combinations.

Fig. 2.. Effect of AT-1501 monotherapy on survival and function of islets following intrahepatic islet transplantation.

(A) Schematic of the design used to test the effect of AT-1501 monotherapy on NHP intrahepatic allogeneic islet transplant outcomes. Recipients were transplanted with >10,000 IEQ/kg on post-operative day 0 (POD#0). 25 mg/kg AT-1501 were given IV on POD#−1, 0, 3, 10, 18, 23, 28 and every 14 days thereafter. The study was ended on POD#182. (B) Blood glucose, exogenous insulin requirements, C-peptide, and % A1C are shown in all animals that received AT-1501 monotherapy. Fasting (black dots) and post-prandial blood glucose (green line), and exogenous insulin requirements (EIR, blue line) are represented in the upper panels. Fasting (gray bars) and stimulated (black bars) C-peptide and % A1C (red line) are represented in lower panels. Animal H15C102 received a second islet transplant on POD#98 due to acute rejection of the initial graft.

Fig. 3.. AT-1501 compared to conventional immunosuppression following islet transplantation.

(A) Schematic of the design used to test the effect of AT-1501 on NHP intrahepatic allogeneic islet transplant outcomes. Recipients were transplanted with >10,000 IEQ/kg on post-operative day 0 (POD#0). The study was ended on POD#182. (B) Islet graft survival is represented by days with fasting CP > 1ng/mL. (C) The slope of change in body weight is shown for animals in the CIS, Replace Tac, and AT-1501-based groups. (D) Shown is a comparison of metabolic control in animals that became insulin-independent. All data are presented as mean ± SD.

Fig. 4.. AT-1501 monotherapy maintains allograft function following kidney transplantation.

(A) Schematic of immunosuppressive treatment plan. All animals underwent life-sustaining kidney transplantation from an MHC-disparate donor. The study was ended on POD#90. (B) Overall rejection-free survival is shown. Median survival time was undefined for the AT-1501 treatment group. One animal rejected the allograft on POD#56. (C to E) Creatinine concentrations (C), absolute lymphocyte counts (D), and lack of CMV viremia (E) are shown for all four animals. Clinically meaningful CMV viremia was defined as >10,000 copies/ml as indicated by the dotted line. (F and G) T cell (F) and B cell (G) flow crossmatch are shown for all four animals to measure donor-specific antibody. One animal (L172) had increased relative mean fluorescence intensity (MFI) on both T cell and B cell flow crossmatch from POD#42 onwards, coinciding with graft dysfunction and rejection.