Researchers have uncovered and then overcome an obstacle that has led to the failure of pioneering efforts in xenotransplantation, in which an animal kidney is transplanted into a human.
More than 800,000 Americans have late-stage kidney disease yet only 3 percent receive a transplant each year, according to the U.S. Centers for Disease Control and Prevention. To boost the supply of available organs, experts are exploring the use of genetically modified pig kidneys. The genetic changes are meant to keep the human immune system from recognizing the animal organ as foreign and attacking it to cause rejection. However, recipients' immune reactions can still lead to organ damage and failure after the surgery.
To better understand the immune mechanisms behind xenotransplant rejection, a new investigation, led by NYU Langone Health researchers, explored the transplantation of a genetically engineered pig kidney into a brain-dead recipient with a beating heart and on a ventilator and whose family donated his body to science. For 61 days after the surgery, the team was able to collect samples of tissue, blood, and body fluid at a pace that is impossible to safely maintain in primates or living patients. As a result, they had a rare opportunity to trace the network of interactions that occur among immune cells when a pig organ is being tolerated by a human and when it undergoes a rejection episode.
In the first of two reports published online November 13 in the journal Nature, the study authors created a detailed map of both human and pig kidney immune activity in response to the transplant. They found that rejection was driven by antibodies—immune proteins that "tag" foreign substances for later destruction—as well as by T cells, which target and kill specific invaders.
Once the researchers uncovered this set of reactions, they for the first time successfully reversed the rejection using a combination of drugs approved by the Food and Drug Administration to temper both the antibody and T cell activity. There was no evidence of permanent damage or reduced kidney function after the intervention.
Our results better prepare us for anticipating and addressing harmful immune reactions during pig-organ transplantation in living humans. This sets the stage for more successful clinical trials in the near future."
Robert Montgomery, MD, PhD, study lead author, the H. Leon Pachter, MD, Professor of Surgery at NYU Grossman School of Medicine
The findings also confirmed that a pig kidney can effectively serve as a replacement for a human kidney, says Dr. Montgomery, who is also the chair of the Department of Surgery and director of NYU Langone Transplant Institute.
The second report in Nature outlines immune activity in greater detail, says Dr. Montgomery, who is a co-author. The research team conducted a multi-omics analysis, which integrates information about gene function, gene expression (activity level), and proteins, as well as other data, to gain a holistic understanding of complex mechanisms at work in the immune system.
Measuring about 5,100 expressed human and pig genes in the pig xenograft, the authors identified every type of immune cell in the tissue, tracked immune behavior over the two-month period, and observed the organ rejection in day-by-day snapshots.
The analysis revealed three major immune responses against the pig kidney: on postoperative day (POD) 21, driven by a part of the human recipient's immune system that responds generally to intruders (innate) rather than to a specific target; on POD 33, driven by a specific population of human white blood cells that engulf invaders (macrophages); and on POD 45, driven mostly by the human T cell response. Dr. Montgomery says that by measuring levels of various blood biomarkers the researchers were able to spot these attacks up to five days before they were clinically visible in the tissue.
"Our multi-omics analysis uncovers various biomarkers that shows promise as an early-warning system for pig organ rejection," said study co-lead author Eloi Schmauch, PhD, from the Keating Lab in the Department of Surgery.
"The specific immune reactions revealed in our investigation provide clear pig and human targets for therapies to improve the success of xenotransplantation to address the dire shortage of available organs," said study senior author Brendan Keating, PhD, a faculty member in the Department of Surgery.
According to Dr. Keating, now that the researchers understand which antibodies and T cells are damaging the transplanted pig kidney, they next plan to investigate what molecules the immune response is targeting through the different layers of DNA, RNA, and protein datasets generated.
Dr. Keating says future studies in other human decedents and in live patients are needed to confirm the findings.
The gene edited pig organ was provided by Revivicor, a subsidiary of United Therapeutics. Funding for the studies was provided by National Institutes of Health grants U19AI191396, P30CA016087, R01AI144522, S10RR027050, and S10OD020056. Additional study funding was provided by Yosemite, United Therapeutics, Imam Abdulrahman bin Faisal University, the Vaisala Fund, the Aarne Koskelon Foundation, the Antti and Tyyne Soininen Foundation, and the Finnish Cultural Foundation.
Dr. Montgomery consults with and holds roles with ProCure On-Demand; the Spanish Society of Transplantation; the Transplant Society; LiveOnNY; the National Kidney Foundation; Sanofi-Aventis U.S.; Lung Biotechnology, a subsidiary of United Therapeutics; and PBC BioMed. He has also previously served on the advisory boards for the biotechnology companies eGenesis and Recombinetics. The terms and conditions of all of these relationships are being managed in accordance with NYU Langone Health policies and procedures.
Megan Sykes, MD, at Columbia University in New York City, is the senior author on the clinical study.
Brian Piening, PhD; at Providence Health in Portland, Oregon, is co-lead author of the multi-omics study.
Alexey Stukalov, PhD; Serafim Batzoglou, PhD; Shadi Ferdosi, PhD; and Asim Siddiqui, PhD; all at Seer in San Francisco, were key study collaborators.
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