Selective Blockade of CD28/B7/CTLA4 Pathway With Monovalent Anti-CD28 Versus Targeting of B7 With Belatacept, in Kidney Allograft in Non-Human Primate, After CNI Weaning.

Abstract

Targeting the CD28/B7/CTLA-4 costimulation pathway with the fusion protein CTLA4-Ig (Belatacept) in association with mycofenolate mofetil (MMF), is a less toxic alternative to calcineurin inhibitors (CNI). However, B7-specific blocking strategies inhibit CTLA-4 signals crucial to the function of regulatory T cells (Tregs). We previously showed in a model of kidney allograft in non-human primate (NHP) that a monovalent antibody fragment against CD28, which selectively blocks CD28 without affecting CTLA4, increased intragraft and peripheral blood Tregs and delayed acute rejection as single therapy and synergized with CNI to prevent efficiently acute rejection. In the current study, we performed a comparison of FR104, a monovalent pegylated Fab'anti-CD28 antagonist antibody with B7 blockade in kidney allograft in the baboon. Biologics were used de novo together with an initial 1 month treatment of low dose tacrolimus, weaned thereafter between months 1 and 2. After 2 months, therefore, recipients were under monotherapy with their biologics. In case of acute rejection, animals were treated with bolus of steroids. In the Belatacept group (n=3), two recipients developed severe acute rejection before or during CNI weaning (day 15 and 43) and bolus of steroid were ineffective. Histological examination confirmed rejection (Banff classification IIB: i3t2v2 and i3t3v2). The third recipient was lost on day 70 for pyelonephritis. In FR104-treated baboons (n=2), one animal developed an acute rejection episode during the CNI weaning period, but steroids bolus was able to reverse this episode. These two first FR104-treated recipients still have a stable kidney function 6 and 8 months post-transplantation. Interestingly, on the 1 and 3-months protocol biopsies, both FR104-treated recipients displayed an interstitial infiltration. Immuno-phenotyping analyses, emphasizing on peripheral Treg count (CD4+CD127lowCD25+) by flow cytometry, did not reveal any difference between the two biologics. These results suggest that the selective blockade of CD28 was efficient to allow reducing immunosuppression and maintaining recipients under this single therapy. Additional experiments are necessary to confirm the data and to further understand the mechanisms of action, in particular Tregs quantification in the biopsy. DISCLOSURES:Poirier, N.: Employee, Effimune SAS. Vanhove, B.: Stockholder, Effimune SAS.