Challenges in pig-to-human kidney xenotransplantation – Authors' reply
Authors: Alexandre Loupy, Adam Griesemer, Robert A Montgomery
Journal: The Lancet (2024)

The Correspondence from Liming Cheng and Kai Liu on our Article1Loupy A Goutaudier V Giarraputo A et al.Immune response after pig-to-human kidney xenotransplantation: a multimodal phenotyping study.Lancet. 2023; 402: 1158-1169Summary Full Text Full Text PDF PubMed Google Scholar contains several comments that deserve further discussion. The decision to use thymokidneys from pigs with only the alpha-1, 3-galactosyltransferase antigen knocked out (Gal-KO) was made for several reasons.2Montgomery RA Stern JM Lonze BE et al.Results of two cases of pig-to-human kidney xenotransplantation.N Engl J Med. 2022; 386: 1889-1898Crossref PubMed Scopus (171) Google Scholar First, this herd is being successfully bred, making it easy to rapidly produce Gal-KO pigs at the large scale that is needed if xenotransplantation is to effectively address the shortage of organs for human transplantation. To consistently breed pigs with a substantial number of genetic edits is currently challenging. Second, many patients awaiting transplantation have a low concentration of preformed antibodies to Gal-KO pigs. Therefore, additional genetic modifications might not be required to achieve successful xenotransplantation in these patients. In our study, of two decedent recipients, recipient 1 had a low concentration of preformed antibodies against the Gal-KO kidney, and had only subtle signs of antibody-mediated rejection, and recipient 2 had a moderate concentration of preformed antibodies against the donor, a positive complement-dependent cytotoxicity crossmatch, and had more pronounced signs of antibody-mediated rejection in the glomeruli.1Loupy A Goutaudier V Giarraputo A et al.Immune response after pig-to-human kidney xenotransplantation: a multimodal phenotyping study.Lancet. 2023; 402: 1158-1169Summary Full Text Full Text PDF PubMed Google Scholar In the case of recipient 2, it is likely that a kidney from a triple glycan knockout donor would have resulted in less antibody-mediated damage in the short term. However, preformed antibodies at this concentration can be easily removed from humans with a few plasmapheresis treatments, and anti-carbohydrate antibodies rarely pose a long-term threat. Regarding the immunosuppression used in this study, our short-term follow-up allowed us to use minimal immunosuppression to assess the early effect of the innate immune response. In our long-term decedent studies, we are using immunosuppression intended to provide long-term xenograft survival combined with porcine thymus transplant, which is intended to diminish specific anti-pig T-cell responses and reduce the need for intense immunosuppression long term.3Griesemer AD Hirakata A Shimizu A et al.Results of Gal-knockout porcine thymokidney xenografts.Am J Transplant. 2009; 9: 2669-2678Summary Full Text Full Text PDF PubMed Scopus (95) Google Scholar In their Correspondence, Chih-Yu Yang and colleagues comment on gene homology (and use of the Banff Human Organ Transplant panel adapted for porcine–human cross-species analysis for transcriptomics studies) and the rationale of using fold change. In our study, the differential expression analysis was carried out using the DESeq function (DESeq2 package) and a Wald test to compare gene expression between conditions of interest, after accounting for cross-species hybridisation. Differentially expressed genes were identified from the linear fitting after computing fold change for the contrast of interest and ranking genes with significant changes in expression level by false discovery rate p value, according to previous studies.4Love MI Huber W Anders S Moderated estimation of fold change and dispersion for RNA-seq data with DESeq2.Genome Biol. 2014; 15: 550Crossref PubMed Scopus (46228) Google Scholar, 5Risso D Ngai J Speed TP Dudoit S Normalization of RNA-seq data using factor analysis of control genes or samples.Nat Biotechnol. 2014; 32: 896-902Crossref PubMed Scopus (1153) Google Scholar The results presented in the volcano plots showed how much a gene's expression changed in the comparison between the xenografts with the controls of interest including the preimplantation biopsy from the contralateral kidney from the Gal-KO pigs. Fold change values were presented as a logarithmic scale as shown in figures 3 and 4 and appendix 1 (p 31) of the Article.1Loupy A Goutaudier V Giarraputo A et al.Immune response after pig-to-human kidney xenotransplantation: a multimodal phenotyping study.Lancet. 2023; 402: 1158-1169Summary Full Text Full Text PDF PubMed Google Scholar AG received institutional grants from eGenesis, Choironex, and United Thereapeutics. RAM serves on the advisory board of eGenesis; has been a strategic advisor for Recombinetics; and has received research funds from United Therapeutics. AL declares no competing interests. Challenges in pig-to-human kidney xenotransplantationAlexandre Loupy and colleagues1 reported an exciting breakthrough in porcine kidney xenotransplantation into human recipients. The results in figures 3 and 4 have drawn our attention. The authors observed increased expression of multiple HLA genes by next-generation sequencing. Since the xenografts before implantation (the control group in figure 3A) were taken directly from pigs and had not been perfused with human blood, they are expected to express swine leukocyte antigen (SLA), not HLA. The possibility of cross-reaction between different species is slim because the number of SLA-expressing cells (pig kidney) substantially outweighs any trace of human cells in the transplanted kidney (the experimental group in figure 3A). Full-Text PDF Challenges in pig-to-human kidney xenotransplantationPig-to-human kidney xenotransplantation is our interest, and we read about it endlessly. We read Alexandre Loupy and colleagues' multimodal, in-depth phenotypic analysis of early immune responses in two porcine kidney xenotransplantations to human patients,1 and this pioneering research has important implications for future xenotransplantation. However, we want to present modern immunology research insights to enlighten authors and readers. Full-Text PDF Immune response after pig-to-human kidney xenotransplantation: a multimodal phenotyping studyDespite 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. Full-Text PDF