Michael DiVita

Xenotransplantation represents a promising strategy to address the organ shortage. Immune tolerance has been achieved with thymic xenotransplantation in preclinical models offering the possibility of reducing or eliminating immunosuppression. Here we report on the outcome of a composite α1,3-galactosyltransferase knockout (GGTA1KO) porcine thymus plus kidney (thymokidney) xenotransplant in a 54-year-old woman with congestive heart failure and dialysis-dependent renal failure who also received a left ventricular assist device (LVAD) implant under an FDA expanded access, single patient IND. Early peripheral blood T-cell recovery after depletion was characterized by naïve recent thymic emigrants (RTEs). T cell clones detected post-transplant and not in pre-transplant populations did not infiltrate the kidney extensively and peripheral blood mixed lymphocyte reaction (MLR) assays demonstrated evolving donor-specific hyporesponsiveness. Collectively, these data indicate that human T cells developed de novo in the porcine thymus and were tolerant of the source pig antigens.

BACKGROUND: Porcine genome editing has revolutionized xenotransplantation, recently enabling the first pig-to-human heart xenotransplants. However, the xenoimmune response in heart xenografts remains largely unexplored. This study aimed to precisely characterize the xenoimmune response and injury in 2 heart xenografts transplanted from 10-gene–edited pigs into brain-dead human recipients. METHODS: We analyzed xenograft biopsy specimens 66 hours after reperfusion using a multimodal phenotyping approach combining morphological evaluation, immunophenotyping, ultrastructural assessment, automated quantification of multiplex immunofluorescence staining, and gene expression profiling. Xenografts before implantation and wild-type pig hearts with and without ischemia/reperfusion injury and brain death were used as controls. RESULTS: Both xenografts showed evidence of endothelial activation and mild microvascular inflammation without capillary C4d deposition. Immune infiltrates were mainly composed of CD15+ and CD68+ innate immune cells. Ultrastructural assessment showed endothelial swelling with occasional intravascular leucocytes. Deep learning–based automated multiplex immunofluorescence analysis confirmed that microvascular inflammation was primarily associated with CD15+ and CD68+ innate immune cells. Both xenografts showed increased expression of genes and pathways associated with monocyte/macrophage activation, neutrophil activation, interferon-gamma response, natural killer cell burden, endothelial activation, apoptosis, and injury repair. This phenotype was absent in all control pig hearts independent of ischemia/reperfusion injury and brain death. CONCLUSIONS: Multimodal phenotyping of pig-to-human heart xenografts revealed early signs of xenoimmune response, characterized by mild innate microvascular inflammation, endothelial activation, and a molecular signature characteristic of antibody-mediated rejection. Developing such a precision diagnostic system could improve graft monitoring in future clinical settings.

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.

A 35-year-old obese male [body mass index (BMI) 35 kg/m²] with no prior medical history presented with acute-onset substernal chest pain. He had chills, cough, and dyspnoea that started a week previously. He denied any prior history of chest pain or syncope. He was afebrile, heart rate 104 b.p.m., and blood pressure 100/54 mmHg. Physical examination was unremarkable except for mild distress. The electrocardiogram was suggestive of acute infero-posterior ST-elevation myocardial infarction (STEMI) (Panel A).

Acute severe mitral regurgitation (MR) associated with cardiogenic shock is a life-threatening emergency. Traditional teaching has focused on the need for emergent coronary angiography and/or intra-aortic balloon counterpulsation in preparation for emergent open-heart surgery for repair/replacement. Unfortunately, emergent open-heart surgery in patients with acute MR complicated by cardiogenic shock is associated with 25–46% perioperative mortality. New devices have provided additional options for stabilization prior to emergent surgery which facilitate improved outcomes. We present two cases of acute severe MR resulting in cardiogenic shock and profound hypoxaemia. TandemHeart^® mechanical circulatory support with an oxygenator spliced into the circuit, akin to veno-arterial extracorporeal membrane oxygenation (ECMO), facilitated haemodynamic stabilization and decongestion of the lungs facilitating successful bridge to mitral valve surgery. Successful discharge to home was achieved in both patients with good neurological outcomes and sustained long-term functional recovery at 18 and 14 months, respectively. Selective use of the TandemHeart^®, with or without ECMO, facilitates management of the critically ill cardiogenic shock patient with acute severe MR.