How, where and when to screen for porcine cytomegalovirus (PCMV) in donor pigs for xenotransplantation

Abstract

Porcine cytomegalovirus (PCMV) that is actually a porcine roseolovirus (PRV) is a common herpesvirus in domestic pigs and wild boars. In xenotransplantation, PCMV/PRV has been shown to significantly reduce the survival time of pig kidneys and hearts in preclinical trials with different non-human primates. Furthermore, PCMV/PRV has been transmitted in the first pig to human heart xenotransplantation and contributed to the death of the patient. Although transmitted to the recipient, there is no evidence that PCMV/PRV can infect primate cells including human cells. Since PCMV/PRV is a roseolovirus closely related to the human herpesviruses 6 and 7, antiviral drugs against human CMV are not effective. However, there are well described strategies to eliminate the virus from pig facilities. In order to detect the virus and to eliminate it, highly sensitive detection methods and the knowledge, how, where and when to screen the donor pigs is required. Here, a comparative testing of different organs from pigs of different age using PCR-based and immunological methods was performed. Testing young piglets, PCMV/PRV was well detected by PCR in blood, bronchoalveolar lavage fluid, tonsils and heart. In adult animals, detection by PCR was in most cases not successful, because the virus was in latency. Therefore, detection of antibodies against selected recombinant proteins corresponding to epitopes detected by nearly all infected animals in a Western blot assays is advantageous. Immunological testing on the other hand is not beneficial in young animals. Piglets might have PCMV/PRV-specific antibodies that they obtained from the infected mother by the colostrum. Using a thoughtful combination of PCR-based and immunological methods, detection of PCMV/PRV in donor pigs for xenotransplantation is feasible and a controlled elimination of the virus by early weaning or other methods is possible.

Porcine cytomegalovirus/porcine roseolovirus (PCMV/PRV): A threat for xenotransplantation?

“…So far, such serological detection methods have been developed in the context of research projects and are not widely available nor easy to implement. A recent paper highlights the importance of the combined use of the two methods 21 . As the disease never has been perceived to be a major danger for commercial breading, the interest to develop widely available and validated assays has been very limited.…”

“…A recent paper highlights the importance of the combined use of the two methods. 21 As the disease never has been perceived to be a major danger for commercial breading, the interest to develop widely available and validated assays has been very limited. The recent transmission of PCMV/PRV to the first patient transplanted with a pig heart, 3 but also the previous transplantations of pig hearts and kidneys into non-human primates [22][23][24] have clearly shown the need to reliably diagnose PCMV/PRV.…”

Early testing of porcine organ xenotransplantation products in humans: Microbial safety as illustrated for porcine cytomegalovirus

“…The experience in the UMD heart patient underscores the need to have methods available to detect the virus in latency: various assays have been developed including assays with high sensitivity and allowing to detect of the virus in its latent phase 63–65 . Also, an optimal strategy in testing animals should be in place 66 …”

“…In this respect, it seems obvious that the latency in a pig in the animal facility is not restricted to a single animal but can be expected in other pigs as well. In this interpretation, it is clear that organs from animals with latent presence of PCMV should not be used in studies in humans; this simple requirement asks for sensitive assays and appropriate testing strategies 66 and the correct material from animals to be used in screening and monitoring. Noteworthy, this experience in a single patient does not align with the outcomes in nonhuman primate studies, at least at two institutions (UAB and UMD) using organs from animals from the same facility.…”

“…In conclusion, the POC studies summarized in this report bring xenotransplantation a step further to clinical application: most important, the data do not block but facilitate the next phase. A major lesson learned from the study at UMD is that virus safety is pivotal for the success of xenotransplantation 1,51 and that testing should be done with assays of the highest quality and following an optimal strategy in the animal testing protocol 63–66 . There are still hurdles to overcome before a porcine solid organ xenotransplantation product will enter clinical medicine.…”