The road to xenotransplantation

International Xenotransplantation Association (IXA) Position Paper on Kidney Xenotransplantation

Porcine kidney xenotransplantation for end-stage renal disease (ESRD) has reached the stage of clinical testing following major advances in donor pig genetic modifications and effective immunosuppressive strategies through decades of rigorous translational research. Reports of pig kidney xenograft survival beyond 1 year post-transplant in nonhuman primate (NHP) models justify optimism for its potential as an alternative to allotransplantation. In the United States, experimental transplantations of genetically engineered (GE) porcine kidneys into brain-dead subjects and a small number of ESRD patients have shown no evidence of hyperacute rejection and adequate pig kidney function for up to several months. Here we discuss pre-clinical/clinical results, infectious disease, ethical, and regulatory considerations, and propose evidence-based recommendations. For initial clinical trials in kidney xenotransplantation, we make the following recommendations: (i) transplantation with organs from a triple knockout (TKO) donor pig, preferably with added human transgenes, (ii) an immunosuppressive regimen with induction therapy to deplete T (and possibly B) cells, and maintenance therapy based on a cluster of differentiation (CD)40/CD154 co-stimulation pathway blockade, (iii) the patient should be fully acceptable as a candidate for allotransplantation but should be unlikely ever to receive an allograft. Patients aged 60-69 years (extendable to 40-75 years, if one of the criteria mentioned below is present), of blood group B or O, and with diabetes are most at risk in this regard. Other patients who could be considered are (i) those who have lost two or more previous kidney allografts from recurrent disease in the graft, (ii) those with broad human leukocyte antigen (HLA)-reactivity but no evidence of anti-pig antibodies, including swine leukocyte antigen (SLA), and (iii) those with failing vascular access. Clinical pilot studies in carefully and highly selected patients with no alternative therapy will provide the foundation upon which to base subsequent formal expanded clinical trials.

International Xenotransplantation Association (IXA) Position Paper on Kidney Xenotransplantation

Porcine kidney xenotransplantation for end-stage renal disease (ESRD) has reached the stage of clinical testing following major advances in donor pig genetic modifications and effective immunosuppressive strategies through decades of rigorous translational research. Reports of pig kidney xenograft survival beyond 1 year posttranplant in nonhuman primate (NHP) models justify optimism for its potential as an alternative to allotransplantation. In the United States, experimental transplantations of genetically engineered (GE) porcine kidneys into brain-dead subjects and a small number of ESRD patients have shown no evidence of hyperacute rejection and adequate pig kidney function for up to several months. Here we discuss pre-clinical/clinical results, infectious disease, ethical, and regulatory considerations, and propose evidence-based recommendations. For initial clinical trials in kidney xenotransplantation, we make the following recommendations: (i) transplantation with organs from a triple knockout (TKO) donor pig, preferably with added human transgenes, (ii) an immunosuppressive regimen with induction therapy to deplete T (and possibly B) cells, and maintenance therapy based on a cluster of differentiation (CD)40/CD154 co-stimulation pathway blockade, (iii) the patient should be fully acceptable as a candidate for allotransplantation but should be unlikely ever to receive an allograft. Patients aged 60-69 years (extendable to 40-75 years, if one of the criteria mentioned below is present), of blood group B or O, and with diabetes are most at risk in this regard. Other patients who could be considered are (i) those who have lost two or more previous kidney allografts from recurrent disease in the graft, (ii) those with broad human leukocyte antigen (HLA)-reactivity but no evidence of anti-pig antibodies, including swine leukocyte antigen (SLA), and (iii) those with failing vascular access. Clinical pilot studies in carefully and highly selected patients with no alternative therapy will provide the foundation upon which to base subsequent formal expanded clinical trials.

Cellular dynamics in pig-to-human kidney xenotransplantation

BACKGROUND

Xenotransplantation of genetically engineered porcine organs has the potential to address the challenge of organ donor shortage. Two cases of porcine-to-human kidney xenotransplantation were performed, yet the physiological effects on the xenografts and the recipients' immune responses remain largely uncharacterized.

METHODS

We performed single-cell RNA sequencing (scRNA-seq) and longitudinal RNA-seq analyses of the porcine kidneys to dissect xenotransplantation-associated cellular dynamics and xenograft-recipient interactions. We additionally performed longitudinal scRNA-seq of the peripheral blood mononuclear cells (PBMCs) to detect recipient immune responses across time.

FINDINGS

Although no hyperacute rejection signals were detected, scRNA-seq analyses of the xenografts found evidence of endothelial cell and immune response activation, indicating early signs of antibody-mediated rejection. Tracing the cells' species origin, we found human immune cell infiltration in both xenografts. Human transcripts in the longitudinal bulk RNA-seq revealed that human immune cell infiltration and the activation of interferon-gamma-induced chemokine expression occurred by 12 and 48 h post-xenotransplantation, respectively. Concordantly, longitudinal scRNA-seq of PBMCs also revealed two phases of the recipients' immune responses at 12 and 48-53 h. Lastly, we observed global expression signatures of xenotransplantation-associated kidney tissue damage in the xenografts. Surprisingly, we detected a rapid increase of proliferative cells in both xenografts, indicating the activation of the porcine tissue repair program.

CONCLUSIONS

Longitudinal and single-cell transcriptomic analyses of porcine kidneys and the recipient's PBMCs revealed time-resolved cellular dynamics of xenograft-recipient interactions during xenotransplantation. These cues can be leveraged for designing gene edits and immunosuppression regimens to optimize xenotransplantation outcomes.

FUNDING

This work was supported by NIH RM1HG009491 and DP5OD033430.

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.

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.