Integrative multi-omics profiling in human decedents receiving pig heart xenografts.

In a previous study, heart xenografts from 10-gene-edited pigs transplanted into two human decedents did not show evidence of acute-onset cellular- or antibody-mediated rejection. Here, to better understand the detailed molecular landscape following xenotransplantation, we carried out bulk and single-cell transcriptomics, lipidomics, proteomics and metabolomics on blood samples obtained from the transplanted decedents every 6 h, as well as histological and transcriptomic tissue profiling. We observed substantial early immune responses in peripheral blood mononuclear cells and xenograft tissue obtained from decedent 1 (male), associated with downstream T cell and natural killer cell activity. Longitudinal analyses indicated the presence of ischemia reperfusion injury, exacerbated by inadequate immunosuppression of T cells, consistent with previous findings of perioperative cardiac xenograft dysfunction in pig-to-nonhuman primate studies. Moreover, at 42 h after transplantation, substantial alterations in cellular metabolism and liver-damage pathways occurred, correlating with profound organ-wide physiological dysfunction. By contrast, relatively minor changes in RNA, protein, lipid and metabolism profiles were observed in decedent 2 (female) as compared to decedent 1. Overall, these multi-omics analyses delineate distinct responses to cardiac xenotransplantation in the two human decedents and reveal new insights into early molecular and immune responses after xenotransplantation. These findings may aid in the development of targeted therapeutic approaches to limit ischemia reperfusion injury-related phenotypes and improve outcomes.

The Young Investigator Committee of the International Xenotransplantation Association-Perspective of advancements in the field in 2023.

The 2023 IXA conference, hosted in San Diego, CA, brimmed with excitement against the backdrop of recent innovations in both the pre-clinical and clinical realms with several first-in-human applications of xenotransplantation. The theme, "Pigs are flying," alluded to the adage that xenotransplantation would only become a clinical reality "when pigs fly," suggesting a day that might never come. The event witnessed significant attendance, with 600 participants-the highest in the history of an IXA-IPITA joint congress. Among the attendees were members of the Food and Drug Administration (FDA), the National Institutes of Health (NIH), and corporate sponsors deeply engaged in the field. We summarize the latest topics from the congress, ranging from the pros/cons of decedent models of xenotransplantation and genetic engineering of porcine heart valves, solid organs, and cells for clinical translation and their regulatory and ethical landscape.

Identifying biomarkers of heterogeneity and transplantation efficacy in retinal pigment epithelial cells.

Transplantation of retinal pigment epithelial (RPE) cells holds great promise for patients with retinal degenerative diseases, such as age-related macular degeneration. In-depth characterization of RPE cell product identity and critical quality attributes are needed to enhance efficacy and safety of replacement therapy strategies. Here, we characterized an adult RPE stem cell-derived (RPESC-RPE) cell product using bulk and single-cell RNA sequencing (scRNA-seq), assessing functional cell integration in vitro into a mature RPE monolayer and in vivo efficacy by vision rescue in the Royal College of Surgeons rats. scRNA-seq revealed several distinct subpopulations in the RPESC-RPE product, some with progenitor markers. We identified RPE clusters expressing genes associated with in vivo efficacy and increased cell integration capability. Gene expression analysis revealed lncRNA (TREX) as a predictive marker of in vivo efficacy. TREX knockdown decreased cell integration while overexpression increased integration in vitro and improved vision rescue in the RCS rats.

Immune response, phenotyping and molecular graft surveillance in kidney transplant recipients following severe acute respiratory syndrome coronavirus 2 vaccination.

BACKGROUND: Understanding immunogenicity and alloimmune risk following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination in kidney transplant recipients is imperative to understanding the correlates of protection and to inform clinical guidelines. METHODS: We studied 50 kidney transplant recipients following SARS-CoV-2 vaccination and quantified their anti-spike protein antibody, donor-derived cell-free DNA (dd-cfDNA), gene expression profiling (GEP), and alloantibody formation. RESULTS: Participants were stratified using nucleocapsid testing as either SARS-CoV-2-naïve or experienced prior to vaccination. One of 34 (3%) SARS-CoV-2 naïve participants developed anti-spike protein antibodies. In contrast, the odds ratio for the association of a prior history of SARS-CoV-2 infection with vaccine response was 18.3 (95% confidence interval 3.2, 105.0, p < 0.01). Pre- and post-vaccination levels did not change for median dd-cfDNA (0.23% vs. 0.21% respectively, p = 0.13), GEP scores (9.85 vs. 10.4 respectively, p = 0.45), calculated panel reactive antibody, de-novo donor specific antibody status, or estimated glomerular filtration rate. CONCLUSIONS: SARS-CoV-2 vaccines do not appear to trigger alloimmunity in kidney transplant recipients. The degree of vaccine immunogenicity was associated most strongly with a prior history of SARS-CoV-2 infection.

Immune response after pig-to-human kidney xenotransplantation: a multimodal phenotyping study.

BACKGROUND: Cross-species immunological incompatibilities have hampered pig-to-human xenotransplantation, but porcine genome engineering recently enabled the first successful experiments. However, little is known about the immune response after the transplantation of pig kidneys to human recipients. We aimed to precisely characterise the early immune responses to the xenotransplantation using a multimodal deep phenotyping approach. METHODS: We did a complete phenotyping of two pig kidney xenografts transplanted to decedent humans. We used a multimodal strategy combining morphological evaluation, immunophenotyping (IgM, IgG, C4d, CD68, CD15, NKp46, CD3, CD20, and von Willebrand factor), gene expression profiling, and whole-transcriptome digital spatial profiling and cell deconvolution. Xenografts before implantation, wild-type pig kidney autografts, as well as wild-type, non-transplanted pig kidneys with and without ischaemia-reperfusion were used as controls. FINDINGS: The data collected from xenografts suggested early signs of antibody-mediated rejection, characterised by microvascular inflammation with immune deposits, endothelial cell activation, and positive xenoreactive crossmatches. Capillary inflammation was mainly composed of intravascular CD68+ and CD15+ innate immune cells, as well as NKp46+ cells. Both xenografts showed increased expression of genes biologically related to a humoral response, including monocyte and macrophage activation, natural killer cell burden, endothelial activation, complement activation, and T-cell development. Whole-transcriptome digital spatial profiling showed that antibody-mediated injury was mainly located in the glomeruli of the xenografts, with significant enrichment of transcripts associated with monocytes, macrophages, neutrophils, and natural killer cells. This phenotype was not observed in control pig kidney autografts or in ischaemia-reperfusion models. INTERPRETATION: Despite favourable short-term outcomes and absence of hyperacute injuries, our findings suggest that antibody-mediated rejection in pig-to-human kidney xenografts might be occurring. Our results suggest specific therapeutic targets towards the humoral arm of rejection to improve xenotransplantation results. FUNDING: OrganX and MSD Avenir.

Pig-to-human heart xenotransplantation in two recently deceased human recipients.

Genetically modified xenografts are one of the most promising solutions to the discrepancy between the numbers of available human organs for transplantation and potential recipients. To date, a porcine heart has been implanted into only one human recipient. Here, using 10-gene-edited pigs, we transplanted porcine hearts into two brain-dead human recipients and monitored xenograft function, hemodynamics and systemic responses over the course of 66 hours. Although both xenografts demonstrated excellent cardiac function immediately after transplantation and continued to function for the duration of the study, cardiac function declined postoperatively in one case, attributed to a size mismatch between the donor pig and the recipient. For both hearts, we confirmed transgene expression and found no evidence of cellular or antibody-mediated rejection, as assessed using histology, flow cytometry and a cytotoxic crossmatch assay. Moreover, we found no evidence of zoonotic transmission from the donor pigs to the human recipients. While substantial additional work will be needed to advance this technology to human trials, these results indicate that pig-to-human heart xenotransplantation can be performed successfully without hyperacute rejection or zoonosis.

Staged Endovascular and Surgical Management of a Mycotic Pseudoaneurysm After Pancreas Transplant.

Mycotic pseudoaneurysms are a rare, life-threatening complication after pancreas transplant. There have been limited reports of endovascular treatment of mycotic pseudoaneurysms in pancreas transplant recipients. Herein, we report on a case of a mycotic pseudoaneurysm from Pseudomonas aeruginosa after pancreas transplant. A 53-year-old male recipient underwent an uneventful simultaneous pancreas and kidney transplant. He was readmitted 48 days posttransplant with fevers and rigors. Pan-cultures were performed and broad-spectrum antibiotics were initiated. Imaging studies demonstrated a large mycotic pseudoaneurysm arising from the right common iliac artery adjacent to the arterial Y-graft anastomosis of the transplant pancreas. Endovascular stent placement was used to exclude the pseudoaneurysm prior to transplant pancreatectomy. During pancreatectomy, the lateral wall of the common iliac artery was found to be necrotic with significant exposure of the endovascular stent. After ligation and excision of the common iliac artery, a femorofemoral bypass was performed to revascularize the lower extremity. This case report highlights the advantage of a staged endovascular and surgical management strategy for complex mycotic pseudoaneurysms after pancreas transplant.

Results of Two Cases of Pig-to-Human Kidney Xenotransplantation.

BACKGROUND: Xenografts from genetically modified pigs have become one of the most promising solutions to the dearth of human organs available for transplantation. The challenge in this model has been hyperacute rejection. To avoid this, pigs have been bred with a knockout of the alpha-1,3-galactosyltransferase gene and with subcapsular autologous thymic tissue. METHODS: We transplanted kidneys from these genetically modified pigs into two brain-dead human recipients whose circulatory and respiratory activity was maintained on ventilators for the duration of the study. We performed serial biopsies and monitored the urine output and kinetic estimated glomerular filtration rate (eGFR) to assess renal function and xenograft rejection. RESULTS: The xenograft in both recipients began to make urine within moments after reperfusion. Over the 54-hour study, the kinetic eGFR increased from 23 ml per minute per 1.73 m2 of body-surface area before transplantation to 62 ml per minute per 1.73 m2 after transplantation in Recipient 1 and from 55 to 109 ml per minute per 1.73 m2 in Recipient 2. In both recipients, the creatinine level, which had been at a steady state, decreased after implantation of the xenograft, from 1.97 to 0.82 mg per deciliter in Recipient 1 and from 1.10 to 0.57 mg per deciliter in Recipient 2. The transplanted kidneys remained pink and well-perfused, continuing to make urine throughout the study. Biopsies that were performed at 6, 24, 48, and 54 hours revealed no signs of hyperacute or antibody-mediated rejection. Hourly urine output with the xenograft was more than double the output with the native kidneys. CONCLUSIONS: Genetically modified kidney xenografts from pigs remained viable and functioning in brain-dead human recipients for 54 hours, without signs of hyperacute rejection. (Funded by Lung Biotechnology.).

Intraoperative Verapamil Fails to Reduce Delayed Graft Function in Donation After Circulatory Death Renal Allografts.

BACKGROUND: The shortage of transplantable organs has led to increased utilization of kidneys that may be particularly vulnerable to ischemia-reperfusion injury (IRI) and delayed graft function (DGF). Kidneys from donation after circulatory death (DCD) donors have additional IRI from donor procurement that results in increased risk of DGF. Verapamil may reduce IRI in kidney allografts when given at the time of organ reperfusion. This study sought to determine if intraoperative administration of verapamil (Ver) could reduce the risk of DGF in DCD kidney transplants. METHODS: A single-center retrospective matched cohort study was performed of 93 Ver (-) kidney transplant recipients compared with 93 Ver (+) kidney transplant recipients, matched by donor age, Kidney Donor Profile Index, and DCD status. Covariates that could impact DGF risk were evaluated by univariate and multivariate logistic regression analyses. RESULTS: The Ver (-) and Ver (+) matched cohorts did not have any significant differences in the demographic covariates. There was no difference in DGF rate between the Ver cohorts in either the overall study population or within the DCD subgroup. There was a trend toward reduced DGF in the Ver (+) cohort for cold ischemia time (CIT) ≤24 h, but this failed to achieve statistical significance. On multivariate analysis, only CIT was found to be independently associated with DGF. CONCLUSIONS: Intraoperative verapamil failed to reduce DGF risk in DCD kidney allografts. Limitations to this study include nonrandomization for the intraoperative administration of verapamil and the mean CIT >24 h in the study population. Only CIT was an independent prognosticator for DGF on multivariate analysis in a cohort matched for DCD status, consistent with prior studies.

Caregiver exposure to hepatitis C virus following transplantation with hepatitis C viremic donor organs: A case series.

Direct-acting antiviral (DAA) therapeutics have ushered in an era in which transplanting organs from donors infected with hepatitis C virus (HCV+) into recipients without (HCV-) is an increasingly common practice. Rare but potentially life-threatening events have been reported in recipients of HCV+ organs. Since 2018 at our institution, 182 HCV- patients have received HCV+ donor organs. Here, we retrospectively reviewed cases in which recipients' family member caregivers reported sustaining needlestick exposures at home following discharge of the transplant recipient from the hospital. Caregiver needlestick exposures were passively reported in three cases of HCV+ into HCV- transplants (1.64% of such cases at our center). In all instances, the exposed individuals were aiding in diabetic management and the exposure occurred via lancets or insulin needles. In one case, the recipient viral load was undetectable at the time of the exposure but in the other two, recipients were viremic, putting their family members at risk to contract HCV infection. Surveillance for the exposed individuals was undertaken and no transmissions occurred. For centers performing HCV+ into HCV- transplants, it is important that informed consent includes discussion of potential secondary risks to family members and caregivers. Further, protocols for postexposure surveillance and for the acquisition of DAA treatment in the event of a secondary transmission should be in place.

Assessing patient perception of risk in ocular stem cell therapies.

A wide variety of stem cell-derived therapies are under development for the treatment of retinal degeneration. In order to better understand patient perspectives about these therapies, we assessed risk tolerance using an in-person survey of 178 patients at an academic eye center. Risk of malignancy served as a hypothetical, readily understood, and serious adverse event to be considered in trade for potential visual improvement from a stem cell-derived treatment. The results indicate that patients were willing to trade visual improvement against a risk of malignancy that far exceeds actual risk. Two novel findings were that older patients and those with an intermediate level of visual loss were particularly risk tolerant. The quantitative survey results provide a step toward understanding patient perspectives that will, over the long term, guide the development of ocular stem cell-derived therapies.

The eyeball's connected to the brain ball.

How does the human eye develop in concert with the brain to create a functioning visual system? In this issue of Cell Stem Cell, Gabriel et al. (2021) report the development of eye-like structures from forebrain organoids with light sensitivity, signal processing, and connectivity, which moves us toward answering this complex question.

Clinical and Financial Implications of 2 Treatment Strategies for Donor-derived Hepatitis C Infections.

Transplanting hepatitis C viremic donor organs into hepatitis C virus (HCV)-negative recipients is becoming increasingly common; however, practices for posttransplant direct-acting antiviral (DAA) treatment vary widely. Protracted insurance authorization processes for DAA therapy often lead to treatment delays. METHODS: At our institution, 2 strategies for providing DAA therapy to HCV- recipients of HCV+ transplants have been used. For thoracic organ recipients, an institution-subsidized course of initial therapy was provided to ensure an early treatment initiation date. For abdominal organ recipients, insurance approval for DAA coverage was sought once viremia developed, and treatment was initiated only once the insurance-authorized supply of drug was received. To evaluate the clinical impact of these 2 strategies, we retrospectively collected data pertaining to the timing of DAA initiation, duration of recipient viremia, and monetary costs incurred by patients and the institution for patients managed under these 2 DAA coverage strategies. RESULTS: One hundred fifty-two transplants were performed using HCV viremic donor organs. Eighty-nine patients received DAA treatment without subsidy, and 62 received DAA treatment with subsidy. One patient who never developed viremia posttransplant received no treatment. Subsidizing the initial course enabled earlier treatment initiation (median, 4 d [interquartile range (IQR), 2-7] vs 10 [IQR, 8-13]; P < 0.001) and shorter duration of viremia (median, 16 d [IQR, 12-29] vs 36 [IQR, 30-47]; P < 0.001). Institutional costs averaged $9173 per subsidized patient and $168 per nonsubsidized patient. Three needlestick exposures occurred in caregivers of viremic patients. CONCLUSIONS: Recipients and their caregivers stand to benefit from earlier DAA treatment initiation; however, institutional costs to subsidize DAA therapy before insurance authorization are substantial. Insurance authorization processes for DAAs should be revised to accommodate this unique patient group.

Impact of the 2014 kidney allocation system changes on trends in A2/A2B into B kidney transplantation and organ procurement organization reporting of donor subtyping.

The current kidney allocation system (KAS) preferentially allocates kidneys from blood type A2 or A2B (A/A2B) donors to blood type B candidates. We used national data to evaluate center-level performance of A2/A2B to B transplants, and organ procurement organization (OPO) reporting of type A or AB donor subtyping, in 5-year time periods prior to (2009-2014) and following (2015-2019) KAS implementation. The number of centers performing A2/A2B to B transplants increased from 17 pre-KAS to 76 post-KAS, though this still represents only a minority of centers (7.3% pre-KAS and 32.6% post-KAS). For high-performing centers, the median net increase in A2/A2B to B transplants was 19 cases (range -2-72) per center in the 5 years post-KAS. The median net increase in total B recipient transplants was 21 cases (range -17-119) per center. Despite requirements for performance of subtyping, in 2019 subtyping was reported on only 56.4% of A/AB donors. This translates into potential missed opportunities for B recipients, and even post-KAS up to 2322 A2/A2B donor kidneys may have been allocated for transplantation as A/AB. Further progress must be made both at center and OPO levels to broaden implementation of A2/A2B to B transplants for the benefit of underserved recipients.

How We Do It: Implementing a Virtual, Multi-Institutional Collaborative Education Model for the COVID-19 Pandemic and Beyond.

OBJECTIVE: To describe the implementation of a virtual, multi-institutional educational collaboration involving over 50 general surgery residency programs during the COVID-19 pandemic that enabled enhanced learning for surgical residents despite social-distancing requirements. DESIGN: Description of Virginia Commonwealth University's virtual educational augmentation program and the development of a collaborative teaching network during the coronavirus pandemic. SETTING: This collaboration was initiated by Virginia Commonwealth University's Department of Surgery, Richmond, VA, and grew to include general surgery residency programs from across the nation. PARTICIPANTS: General surgery residents and faculty from Departments of General Surgery were recruited locally via direct emails and nationally via the Association of Program Directors' listserv and Twitter. In total, 52 institutions participated from every part of the country. RESULTS: A virtual, multi-institutional collaborative lecture series was initiated that grew to involve over 50 general surgery residency programs, allowing for daily didactics by experts in their fields during the initial surge of the COVID-19 pandemic, while maintaining social distancing and the provision of essential clinical care. CONCLUSION: A multi-institutional collaboration enabled continued didactic education during the coronavirus pandemic, vastly broadening the expertise, scope and variety available to residents, while decreasing burden on faculty. We believe this can serve as a framework for future multi-institutional collaborations that extend beyond the COVID-19 era.

Multi-institutional Collaborative Surgery Education Didactics: Virtual Adaptations During a Global Pandemic.

OBJECTIVE: The COVID-19 pandemic has disrupted graduate medical education, impacting Accreditation Council for Graduate Medical Education (ACGME)-mandated didactics. We aimed to study the utility of 2 methods of virtual learning: the daily National Surgery Resident Lecture Series (NSRLS), and weekly "SCORE School" educational webinars designed around the Surgical Council on Resident Education (SCORE) curriculum. DESIGN AND SETTING: NSRLS: The National Surgery Resident Lecture Series was a daily virtual educational session initially led by faculty at an individual surgical residency program. Thirty-eight lectures were assessed for number of live viewings (March 23, 2020-May 15, 2020). SCORE SCHOOL: Attendance at eleven weekly SCORE educational webinars was characterized into live and asynchronous viewings (May 13, 2020-August 5, 2020). Each 1-hour live webinar was produced by SCORE on a Wednesday evening and featured nationally recognized surgeon educators using an online platform that allowed for audience interaction. RESULTS: NSRLS: There were a mean of 71 live viewers per NSRLS session (range 19-118). Participation began to decline in the final 2 weeks as elective case volumes increased, but sessions remained well-attended. SCORE SCHOOL: There were a range of 164-3889 live viewers per SCORE School session. Sessions have most commonly been viewed asynchronously (89.8% of viewings). Live viewership decreased as the academic year ended and then rebounded with the start of the new academic year (range 4.9%-27%). Overall, the eight webinars were viewed 11,135 times. Each webinar continues to be viewed a mean of 43 times a day (range 0-102). Overall, the eleven webinars have been viewed a total of 22,722 times. CONCLUSIONS: Virtual didactics aimed at surgical residents are feasible, well-attended (both live and recorded), and have high levels of viewer engagement. We have observed that careful coordination of timing and topics is ideal. The ability for asynchronous viewing is particularly important for attendance. As the COVID-19 pandemic continues to disrupt healthcare systems, training programs must continue to adapt to education via virtual platforms.

Pseudocyst of Pancreas Transplant Allograft: A Case Report.

BACKGROUND: Pancreatic pseudocysts are rarely reported complications of pancreas transplant. CASE: We present a case of a patient with simultaneous pancreas and kidney transplant with bladder exocrine drainage who developed reflux pancreatitis and symptomatic pancreatic pseudocyst as a result of neuropathic bladder, 15 years after the original transplant. He was initially managed with percutaneous aspiration and drainage along with Foley catheter placement to help with bladder emptying. But the pseudocyst recurred after drains and Foley were removed. Eventually, he underwent an enteric conversion of the pancreas allograft with resolution of his symptoms and the pseudocyst. CONCLUSIONS: Enteric conversion should be considered in cases of bladder-drained pancreas transplants with recurrent reflux pancreatitis and/or pseudocyst formation.

Traumatic Decompression of the Jejunum: A Case of Small Bowel Perforation From High-Speed Motor Vehicle Crash.

We present a rare case of a focal perforation of the jejunum after a high-speed motor vehicle crash. A 60-year-old restrained rear seat passenger presented with severe abdominal pain. She was hemodynamically stable and underwent the traditional trauma workup. CT scan of the abdomen showed large-volume free intraperitoneal air and L4/L5 compression fractures. Given the peritoneal physical exam finding and free air on CT scan she was taken emergently to the operating room. Operative exploration revealed free intraperitoneal air upon entry into the abdominal cavity as well as murky fluid throughout the mid abdomen. A focal perforation was discovered on the antimesenteric surface of a segment of jejunum. The perforation was repaired primarily in two layers and the abdomen was closed. Postoperative course was uncomplicated. Antibiotics were continued for 4 days. Focal perforation of the small bowel from high-speed blunt trauma is a rare isolated injury. Close attention to physical exam and radiologic findings allows for early diagnosis and treatment of these injuries.

Epigenomic and Transcriptomic Changes During Human RPE EMT in a Stem Cell Model of Epiretinal Membrane Pathogenesis and Prevention by Nicotinamide.

Epithelial to mesenchymal transition (EMT) is a biological process involved in tissue morphogenesis and disease that causes dramatic changes in cell morphology, migration, proliferation, and gene expression. The retinal pigment epithelium (RPE), which supports the neural retina, can undergo EMT, producing fibrous epiretinal membranes (ERMs) associated with vision-impairing clinical conditions, such as macular pucker and proliferative vitreoretinopathy (PVR). We found that co-treatment with TGF-ß and TNF-α (TNT) accelerates EMT in adult human RPE stem cell-derived RPE cell cultures. We captured the global epigenomic and transcriptional changes elicited by TNT treatment of RPE and identified putative active enhancers associated with actively transcribed genes, including a set of upregulated transcription factors that are candidate regulators. We found that the vitamin B derivative nicotinamide downregulates these key transcriptional changes, and inhibits and partially reverses RPE EMT, revealing potential therapeutic routes to benefit patients with ERM, macular pucker and PVR.

Impact of CMV Reactivation, Treatment Approaches, and Immune Reconstitution in a Nonmyeloablative Tolerance Induction Protocol in Cynomolgus Macaques.

BACKGROUND: Cytomegalovirus (CMV) infection is a serious complication in immunosuppressed patients, specifically transplant recipients. Here, we describe the development and use of an assay to monitor the incidence and treatment of CMV viremia in a Cynomolgus macaque model of bone marrow transplantation (BMT) for tolerance induction. We address the correlation between the course of viremia and immune reconstitution. METHODS: Twenty-one animals received a nonmyeloablative conditioning regimen. Seven received cyclosporine A for 28 days and 14 received rapamycin. A CMV polymerase chain reaction assay was developed and run twice per week to monitor viremia. Nineteen recipients were CMV seropositive before BMT. Immune reconstitution was monitored through flow cytometry and CMV viremia was tracked via quantitative polymerase chain reaction. RESULTS: Recipients developed CMV viremia during the first month post-BMT. Two animals developed uncontrollable CMV disease. CMV reactivation occurred earlier in cyclosporine A-treated animals compared with those receiving rapamycin. Post-BMT, T-cell counts remained significantly lower compared with pretransplant levels until CMV reactivation, at which point they increased during the viremic phase and approached pretransplant levels 3 months post-BMT. Management of CMV required treatment before viremia reached 10 000 copies/mL; otherwise clinical symptoms were observed. High doses of ganciclovir resolved the viremia, which could subsequently be controlled with valganciclovir. CONCLUSIONS: We developed an assay to monitor CMV in Cynomolgus macaques. CMV reactivation occurred in 100% of seropositive animals in this model. Rapamycin delayed CMV reactivation and ganciclovir treatment was effective at high doses. As in humans, CD8 T cells proliferated during CMV viremia.