Desensitization With Proteasome Inhibition and Costimulation Blockade Modulates the Xenoreactive Humoral Response in Nonhuman Primate Xenotransplantation.

INTRODUCTION

"Delayed" antibody-mediated xenograft rejection is one of the most important obstacles to clinical application of pig organ xenografts. The aim of this study was to assess the impact of a structured desensitization regimen including proteasome inhibition and next-generation costimulation blockade on xenoreactive antibodies.

METHODS

Rhesus macaques with moderate-high pre-treatment xenoreactive antibody titers (N = 2) were selected. Recipients received twice-weekly carfilzomib (20 mg/m), anti-CD154 (20 mg/kg) every other week, and CD4 and CD20 lymphocyte cell depletion. Bone marrow was acquired to assess plasma cell depletion in response to proteasome inhibition. A flow cytometry-based xenoreactive crossmatch assay was performed to assess levels of circulating xenoreactive antibodies.

RESULTS

The desensitization regimen resulted in a >50% depletion of CD38+CD27+ bone marrow plasma cells; these changes were progressive over the duration of the desensitization treatment period. The desensitization strategy and plasma cell depletion resulted in a progressive reduction in anti-pig IgG antibodies. Following xenotransplantation, both desensitized recipients demonstrated superior graft survival to a highly xenoreactive recipient (MST 30 days vs. 6 days), but neither desensitized recipient experienced prolonged graft survival.

CONCLUSIONS

A structured desensitization regimen including proteasome inhibition and costimulation blockade results in plasma cell depletion and resultant reduction in circulating xenoreactive anti-pig IgG antibodies, with a modest improvement in xenograft survival. This desensitization regimen has promise for pig-to-NHP xenotransplant models.