Evidence for Microchimerism in Baboon Recipients of Pig Hearts

How to Detect Porcine Endogenous Retrovirus (PERV) Infections in Patients After Transplantation of Pig Organs

Porcine endogenous retroviruses (PERVs) are integrated into the genome of all pigs and can infect human cells in culture. However, no PERV infections have been reported in recipients following preclinical or clinical xenotransplantation or deliberate infection experiments. Detection of PERV infection in transplanted recipients is challenging due to microchimerism, such as the presence of pig cells containing PERV proviruses in the recipient. Based on our previous publications on PERV detection in xenotransplant recipients, particularly from the first clinical trials, we developed a comprehensive strategy to screen for PERV infections. Recipients can be monitored for increasing levels of viral genomic RNA and mRNA using real-time reverse transcriptase (RT)-PCR, which can indicate PERV expression and replication. To test this strategy, explanted pig hearts and organs from baboons after pig heart transplantation were analyzed. No PERV genomic RNA or mRNA was detected in these tissues, although both were found in PERV-producing human control cells. Screening for antibodies against PERV as indirect evidence of infection is the method of choice. Recombinant viral proteins were prepared for use in Western blot assays. Animal antisera generated through immunization with recombinant PERV proteins served as positive controls. No antibodies against PERV were detected in transplanted baboons, even though microchimerism was observed in many of the animals' organs. For effective antibody screening, at least two PERV proteins should be used as antigens.

Monitoring for PERV Following Xenotransplantation

Porcine endogenous retroviruses (PERVs) are integrated in the genome of all pigs. PERV-A, PERV-B and PERV-C can be released as infectious virus particles and PERV-A and PERV-B can infect human cells in culture. PERV-C does not infect human cells, but high-titer recombinant PERV-A/C can infect them. Retroviruses are able to induce immunosuppression and/or tumors in the infected host. Numerous methods have been developed to study PERV in donor pigs. No PERV infections were observed in infection experiments as well as in preclinical and clinical xenotransplantation trials. Despite this, several strategies have been developed to prevent PERV infection of the recipient. PCR-based and immunological methods are required to screen xenotransplant recipients. Since the proviruses are integrated into the pig genome, PERV infection has to be distinguished from microchimerism, e.g., the presence of pig cells in the recipient, which is common in xenotransplantation. Sensitive PCR methods using pig short interspersed nuclear elements (SINE) sequences allow to detect pig cells easily. Virus infection can also be detected by an increase of viral genomic or mRNA in human cells. The method of choice, however, is to screen for specific antibodies against PERV using different recombinant PERV proteins, purified viruses or peptides.

Mitigating Cross-Species Viral Infections in Xenotransplantation: Progress, Strategies, and Clinical Outlook

Xenotransplantation holds great promise as a solution to address the critical shortage of organs, but it raises concerns regarding the potential transmission of porcine viruses to recipients, leading to infections and even zoonotic diseases. Data used in this review were mainly from literature of Pubmed database. Keywords included xenotransplantation, infection, virus, and epidemiology. The original articles and critical reviews selected were relevant to this review's theme. We review the major viral infections of concern in xenotransplantation, their risk of transmission, diagnosis, treatment, and ways to prevent infection. Then, we pivot to a comprehensive overview of the current status of xenotransplantation. In addition, we offer our own insights and recommendations for propelling xenotransplantation forward, transitioning from preclinical experiments to the critical phase of clinical trials. Viral infections pose considerable safety concerns within xenotransplantation, particularly with the possibility of emerging or currently unidentified viruses. Clinical trials serve as a crucial platform to progress the safety standards of xenotransplantation. However, further studies and dedicated efforts are required to effectively translate findings into practical applications that can improve safety measures in this field.