Lessons learned from pig hearts genetically modified for the first time in human patients

An international research team said,Graft dysfunction in the compassionate use of transgenic pig-to-human cardiac xenografts: a case report” of lancet The world’s first successful transgenic pig heart transplantation into a human patient revealed the cause of heart failure. A medical scientist at the University of Maryland School of Medicine (UMSOM) performed the procedure. January 2022.

The patient, 57-year-old David Bennett Sr., was treated at the University of Maryland Medical Center. He experienced strong cardiac function almost his 7 weeks post-surgery, with no obvious signs of acute rejection.Sudden onset of heart failure led to his death 2 months after transplantation. Since then, transplant teams have conducted studies of the physiological processes leading to heart failure to identify factors that could be prevented in future transplants to increase the likelihood of long-term success.

“Genetically modified porcine heart xenograft will be performed on January 7, 2022 in a 57-year-old non-ambulatory male patient with end-stage heart failure, receiving venous-arterial extracorporeal membrane oxygenation, who is not an allograft candidate. “This report details our current understanding of the factors that are important for xenotransplantation outcome,” the researchers wrote.

“Physiologic and biochemical parameters critical to the care of all heart transplant recipients were collected by extensive clinical monitoring in the intensive care unit to confirm the cause of xenograft dysfunction. , electron microscopy and quantification of porcine cytomegalovirus or porcine roseolovirus (PCMV/PRV) in xenografts, recipient cells and tissues by DNA PCR and RNA transcription. We performed a study in which we performed intravenous immunoglobulin (IVIG) binding to donor cells and single-cell RNA sequencing of peripheral blood mononuclear cells.”

The graft worked well…but

“After successful xenotransplantation, the graft performed well on echocardiography, and cardiovascular and other organ system function was maintained until postoperative day 47, when diastolic heart failure occurred. Postoperatively. A 50-day endocardial biopsy revealed interstitial edema, erythrocyte extravasation, rare thrombotic microangiopathy, and damaged capillaries with complement deposition.

“An increase in anti-porcine xenoantibodies (predominantly IgG) was detected after IVIG administration for hypogammaglobulinemia and during the first plasmapheresis. showed fibrotic changes consistent with myocardial rigidity in 1. Microbial cell-free DNA testing showed increased titers of PCMV/PRV cell-free DNA.Post-mortem single-cell RNA sequencing showed A duplicate cause was indicated.

“Hyperacute rejection was avoided. We identified potential mediators of the observed endothelial injury. First, extensive endothelial injury indicates antibody-mediated rejection. It may have strongly bound to the donor endothelium and caused immune activation.Finally, reactivation and replication of latent PCMV/PRV in xenografts may have caused a deleterious inflammatory response. The findings point to concrete measures to improve future xenotransplantation outcomes.”

“Our paper provides important insights into how multiple factors may contribute to the deterioration of transplanted hearts,” said lead study author and professor of surgery. Muhammad M. Mohiuddin, Ph.D., Scientific/Program Director of the Cardiac Xenotransplantation Program. at UMSOM. “Our goal is to continue advancing the field while preparing for clinical trials of xenotransplantation involving porcine organs.”

Bennett had end-stage heart failure and was nearing the end of his life, so he was ineligible for a conventional heart transplant. This procedure has been cleared by the FDA under the Extended Access (Considerate Use) provision.

“We are determined to find out what led to the failure of the heart transplant of Mr. Bennett, who performed the heroic act of volunteering for the world’s first heart transplant.” Study co-author Bartley Griffiths, M.D., Ph.D., Professor of Surgery at UMSOM and Distinguished Professor of Transplantation with Thomas E. Hales and Alice Marie Hales, said: “We hope that the next patient will not only survive longer with xenotransplantation, but will return to a normal life and thrive for months or years. ”

To better understand the processes that lead to the failure of porcine heart transplants, the research team performed tests on the limited available tissue of the patient. They mapped the sequence of events that led to heart failure and demonstrated that the heart was functioning well up to 47 days after surgery, using imaging studies such as echocardiography.

A combination of factors caused heart failure

A new study confirms that no signs of acute rejection occurred in the first few weeks after transplantation. A combination of factors likely contributed to Bennett’s heart failure, including poor pre-transplant health that left him severely immunocompromised. This has limited the use of effective anti-rejection therapies used in preclinical studies of xenotransplantation. As a result, the researchers found that patients were likely more vulnerable to organ rejection due to antibodies produced by the immune system. Investigators found indirect evidence of antibody-mediated rejection based on histology, immunohistochemical staining, and single-cell RNA analysis.

Intravenous administration of antibody-containing immunoglobulin (IVIG) may also have contributed to cardiomyocyte damage. Two doses were administered to the patient within two months after transplantation to prevent infection, presumably also eliciting an anti-pig immune response. The research team found evidence of immunoglobulin antibodies targeting the endothelial layer of blood vessels in pig hearts.

Finally, a new study investigated the presence of a latent virus called porcine cytomegalovirus (PCMV) in pig hearts, which may have contributed to transplant failure. Viral activation may have occurred after the patient’s antiviral regimen was reduced to address other health issues. This may have triggered an inflammatory response that caused cell damage. However, there is no evidence that the virus has infected patients or spread to organs other than the heart. An improved PCMV testing protocol was developed for sensitive detection and elimination of latent virus for future xenotransplantation.

“We will learn valuable lessons from this landmark surgery and from this courageous first patient, Dr. Bennett, to better inform future xenotransplantations,” said Mark, Dean of UMSOM. – said T. Gladwin, M.D., vice president of medical affairs at the University of Maryland Baltimore. , Distinguished Professors of John Z. Bowers and Akiko K. Bowers. “In the future, our team of surgeons and scientists will utilize newly designed immune cell assays to more accurately monitor patients in the days, weeks and months following xenotransplantation. This promises to be a truly life-saving innovation, allowing us to more closely manage early signs of rejection.”