375 Long-term survival of pig-to-primate renal xenotransplant using costimulation-blockade immunosuppression
Monday November 16, 2015 from 17:30 to 18:30
Plenary Room 1

Laura B. Higginbotham, United States

Postdoctoral Research Fellow

Emory Transplant Center

Emory University School of Medicine


Long-term survival of pig-to-primate renal xenotransplant using costimulation-blockade immunosuppression

Laura Higginbotham1, Dave Mathews1, Allison Stephenson1, Cynthia Breeden1, Christian P. Larsen1, Mandy L. Ford1, Kenneth A. Newell1, Joseph Tector2, Andrew B. Adams1.

1Emory Transplant Center, Department of Surgery, Emory University School of Medicine, Atlanta, GA, United States; 2Indiana University Health Transplant Institute, Department of Surgery, Indiana University School of Medicine, Indianapolis, IN, United States

Introduction: Xenotransplantation has the potential to alleviate the organ supply shortage, yet its clinical application is largely unrealized. Preclinical kidney xenograft models (pig-to-nonhuman primate) have met limited success largely due to preformed anti-pig antibody and species-specific complement and coagulation proteins. Genetically altered pigs, galactose-α1,3-galactose (Gal) knockouts +/- transgenic expression of complement regulatory proteins, have improved outcomes but median survival times remain limited. We report long-term survival >227 days in pig-to-macaque renal transplantation using Gal knockout / CD55 transgenic pigs and an anti-CD154-based immunosuppression protocol.
Methods: Serum samples from thirty-four rhesus macaque transplant candidates were incubated with porcine GGTA1KO (α-1,3-galactosyltransferase knockout) PBMC (peripheral blood mononuclear cells) and stained with anti-human IgM and IgG to measure preformed anti-pig antibody titers. Results were collected using flow cytometry. Four primates with the lowest preformed IgG titers and one macaque with the highest IgG titers were selected for transplantation. Rhesus macaques then underwent bilateral native nephrectomy followed by life-sustaining renal transplant using a kidney from donor transgenic GGTA1KO/hDAF (α-1,3-galactosyltransferase knockout, human decay-accelerating factor) pigs. Animals were treated with T cell depletion (anti-CD4 and anti-CD8) plus costimulation blockade with either anti-CD154 (n=3) or belatacept (n=2) plus daily mycophenolate mofetil (MMF) and steroids. Percutaneous renal xenograft biopsies were performed at POD 14, 35, 70, 100, and 224. Samples were submitted for H&E, trichrome, PAS, and Von Kossa staining with interpretation by a renal pathologist. CMV titers were measured using quantitative PCR at time of donation in pigs and weekly post-transplant in monkeys. Prophylactic ganciclovir was started in macaque recipients on day of transplant and discontinued when CMV titers were negative on two consecutive measurements. Weekly serum chemistries assessed graft function post-transplant. Serum creatinine >5mg/dL or BUN >100mg/dL on two consecutive measurements defined clinical rejection.
Results: Animals selected for transplant with low anti-pig antibody titers survived significantly longer than the high-titer monkey (MST >90.5 days [n=4]; versus MST=6 days [n=1]; p<0.05). Within the low-titer group, costimulation blockade with anti-CD154 prolonged survival more than belatacept (MST >193.5 days [>227 and 160 days, n=2] versus MST=17.5 days [21 and 14 days, n=2]). One low-titer, anti-CD154 monkey remains ongoing (survival >227 days) with normal xenograft function and normal renal xenograft biopsy at post-transplant day 224. Electrolyte levels remain within expected physiologic parameters with the exception of elevated serum calcium. Despite this, no adverse effects of hypercalcemia are seen including no evidence of calcium deposition in renal biopsy specimens. Quantitative urine protein remains negative. 
Conclusions: Pre-transplant antibody screening and costimulation blockade with anti-CD154 promote renal xenograft survival in a pig-to-macaque kidney transplant model. This description of the longest-reported survival, >227 days, offers promise for further investigation in NHP models as well as future clinical translation.

Lectures by Laura B. Higginbotham

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