Faculty Bibliography

Organ shortage remains a major challenge in transplantation, and gene-edited pig organs offer a promising solution^1-3. Despite gene-editing, the immune reactions following xenotransplantation can still cause transplant failure⁴. To understand the immunological response of a pig-to-human kidney xenotransplantation, we conducted large-scale multi-omics profiling of the xenograft and the host's blood over a 61-day procedure in a brain-dead human (decedent) recipient. Blood plasmablasts, natural killer (NK) cells, and dendritic cells increased between postoperative day (POD)10 and 28, concordant with expansion of IgG/IgA B-cell clonotypes, and subsequent biopsy-confirmed antibody-mediated rejection (AbMR) at POD33. Human T-cell frequencies increased from POD21 and peaked between POD33-49 in the blood and xenograft, coinciding with T-cell receptor diversification, expansion of a restricted TRBV2/J1 clonotype and histological evidence of a combined AbMR and cell-mediated rejection at POD49. At POD33, the most abundant human immune population in the graft was CXCL9+ macrophages, aligning with IFN-γ-driven inflammation and a Type I immune response. In addition, we see evidence of interactions between activated pig-resident macrophages and infiltrating human immune cells. Xenograft tissue showed pro-fibrotic tubular and interstitial injury, marked by S100A6⁵, SPP1⁶ (Osteopontin), and COLEC11⁷, at POD21-POD33. Proteomics profiling revealed human and pig complement activation, with decreased human component after AbMR therapy with complement inhibition. Collectively, these data delineate the molecular orchestration of human immune responses to a porcine kidney, revealing potential immunomodulatory targets for improving xenograft survival.

Xenotransplantation of genetically-modified pig kidneys offers a solution to the scarcity of organs for end-stage renal disease patients.¹ We performed a 61-day alpha-Gal knock-out pig kidney and thymic autograft transplant into a nephrectomized brain-dead human using clinically approved immunosuppression, without CD40 blockade or additional genetic modification. Hemodynamic and electrolyte stability and dialysis independence were achieved. Post-operative day (POD) 10 biopsies revealed glomerular IgM and IgA deposition, activation of early complement components and mesangiolysis with stable renal function without proteinuria, a phenotype not seen in allotransplantation. On POD 33, an abrupt increase in serum creatinine was associated with antibody-mediated rejection and increased donor-specific IgG. Plasma exchange, C3/C3b inhibition and rabbit anti-thymocyte globulin (rATG), completely reversed xenograft rejection. Pre-existing donor-reactive T cell clones expanded progressively in the circulation post-transplant, acquired an effector transcriptional profile and were detected in the POD 33 rejecting xenograft prior to rATG treatment. This study provides the first long-term physiologic, immunologic, and infectious disease monitoring of a pig-to-human kidney xenotransplant and indicates that pre-existing xenoreactive T cells and induced antibodies to unknown epitope(s) present a major challenge, despite significant immunosuppression. It also demonstrates that a minimally gene-edited pig kidney can support long-term life-sustaining physiologic functions in a human.

Vascularized composite allotransplantation (VCA) involves immunologically heterogeneous tissues with a high incidence of acute rejection. Reliable and timely detection of rejection onset remains a major unmet challenge in VCA management. This longitudinal exploratory case study assessed blood- and tissue-derived biomarkers for acute rejection monitoring in a full-face and bilateral hand transplant recipient over 4.6 years. Of these biomarkers, donor-derived cell-free DNA (dd-cfDNA) and short tandem repeats (STR) showed trends toward elevated recipient levels during acute rejection, though differences were not statistically significant. CD8⁺ T-cell percentages increased before acute rejection onset, highlighting a temporal association. Anti-angiotensin II type 1 receptor antibody (AT1R-Ab) levels did not differ significantly between acute rejection and non-rejection episodes, possibly due to prophylactic immune cell depletion. While dd-cfDNA and STR levels correlate with rejection episodes and reflect key graft cellular events, CD8⁺ T-cell dynamics demonstrated the strongest temporal association with rejection episodes in this patient, though no biomarker showed statistically significant differences. These exploratory findings support the need for further longitudinal, multi-patient studies to validate emerging biomarkers and refine rejection monitoring strategies in VCA.

BACKGROUND:Uterus transplantation (UTx) is uniquely positioned at the transition from experimental to clinical reality for women with absolute uterine factor insufficiency. As the technique gains wider clinical adoption, there is a growing need for standardization in both protocols and diagnostics. CONTENT/BACKGROUND:This review describes the current evaluation, monitoring, and emerging diagnostics in UTx across the main phases of care: (a) preoperative evaluation, which includes fertility evaluation and in vitro fertilization, surgical, psychosocial, and donor assessments, as well as donor-recipient matching considerations; (b) perioperative management, which focuses on acute surgical care, initiation of immunosuppression, and early graft evaluation; (c) posttransplant and pregnancy monitoring, which encompasses ongoing immunosuppression evaluation, biopsy interpretation, management of acute rejection, and detection and management of pregnancy and maternal complications; and (d) long-term follow-up, which addresses the potential for repeat pregnancies and planned graft hysterectomy to facilitate immunosuppression withdrawal.The review further explores future directions for clinical diagnostics in UTx, drawing on broader solid organ transplantation experiences. This includes molecular and allele-level human leukocyte antigen matching for recipient-donor compatibility, strategies for immunosuppression minimization, and the development of noninvasive rejection monitoring tools such as donor-derived cell-free DNA and novel blood and urine transcriptomics approaches. SUMMARY/CONCLUSIONS:Standardization of protocols and diagnostics is essential as UTx transitions to routine clinical practice. Emerging molecular diagnostics and noninvasive monitoring tools hold promise for improving graft outcomes and patient care in this evolving field.

BACKGROUND:Porcine genome editing has revolutionized xenotransplantation, recently enabling the first pig-to-human heart xenotransplants. However, the xeno-immune response in heart xenografts remains largely unexplored. This study aimed to precisely characterize the xeno-immune response and injury in two heart xenografts, transplanted from 10-gene-edited pigs into brain-dead human recipients. METHODS:We analyzed xenograft biopsies at 66-hour post-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, independently from ischemia reperfusion injury and brain death. CONCLUSIONS:Multimodal phenotyping of pig-to-human heart xenografts revealed early signs of xeno-immune response, characterized by mild innate microvascular inflammation, endothelial activation, and molecular signature characteristic of antibody-mediated rejection. Developing such precision diagnostic system could improve graft monitoring in future clinical settings.

Several in-silico methods emerge to assess HLA immunogenicity and stratify immunological risk, including HLA molecular mismatches and HLA evolutionary divergence (HED). However, their added value in risk-stratifying antibody-mediated rejection (AMR) remains uncertain. We include 5159 kidney transplant recipients from four centers. Thirty-three clinical and immunological parameters are assessed, including HLA eplet mismatches, PIRCHE-II scores, and HED. Their associations with AMR are evaluated using Cox models. AMR occurrs in 1024 patients (19.9%). Immunological determinants of AMR include anti-HLA DSA (MFI:500-1400, HR:1.87; MFI > 1400, HR:3.84, p < 0.001) and HLA Class II eplet mismatches (HR:1.02, p < 0.001). HLA-DQB1-derived (HR:1.01, p = 0.005) and HLA-DRB1-derived PIRCHE-II scores (HR:1.01, p = 0.001) are also associated with AMR, while HED is not. These findings remain consistent across centers and subpopulations, including non-sensitized patients (n = 4137). Our findings show that Class II molecular mismatches are independently associated with AMR. HED shows no association, suggesting limited utility for immune-risk stratification at a population level. Clinicaltrials.gov: NCT06436586.

Swine-derived kidneys are a promising alternative organ source for transplantation, but compatibility in the major histocompatibility complex remains an immunological barrier. Furthermore, in repeat transplantations, CD4+ memory T cells can lead to a more rapid immune response against repeated exposure to the same antigens. Several studies have shown that HLA and SLA proteins share overlapping B cell epitopes due to structural or electrostatic similarities, but the role of overlapping T cell epitopes has not been fully explored. This study aims to computationally analyse the potential risk of memory T cell activation in subsequent human-after-swine and swine-after-human transplantation by evaluating shared T cell epitopes between the two graft sources. We show that while HLA and SLA demonstrate striking structural similarities, their linear protein sequences are very distinct, which translates to disparate HLA- and SLA-derived peptidomes and T cell epitopes. By applying the PIRCHE-II Tmem analysis to a simulated panel of recipients receiving repeat transplantations from a human kidney and from a swine xenograft, we observed a median of 1 shared T cell epitope in the cross-species context, compared to a median of 17 shared between two human-derived kidneys. This suggests that a swine xenograft exposes a low risk of T cell memory against a later human donor, and that xenotransplantation may provide an opportunity to receive a graft for highly HLA-sensitised recipients.

Human leukocyte antigen-level matching in US kidney allocation has been deemphasized due to its role in elevating racial disparities. Molecular matching based on eplets might improve risk stratification compared to antigen matching, but the magnitude of racial disparities in molecular matching is not known. To assign eplets unambiguously, we utilized a cohort of 5193 individuals with high-resolution allele-level human leukocyte antigen genotypes from the National Kidney Registry. Using repeated random sampling to simulate donor-recipient genotype pairings based on the ethnic composition of the historical US deceased-donor pool, we profiled the percentage of well-matched donors available for candidates by ethnicity. The prevalence of well-matched donors with 0-DR/DQ eplet mismatch was 3-fold less racially disparate for Black and Asian candidates and 2-fold less for Latino candidates compared to 0-ABDR antigen mismatches. Compared to 0-DR antigen mismatch, 0-DR eplet mismatch was 1.33-fold more racially disparate for Asian and 1.28-fold more for Latino, with similar disparity for Black candidates, whereas 0-DQ eplet mismatch reduced disparities, showing 1.26-fold less disparity for Black, 1.14-fold less for Latino, but 1.26-fold higher for Asian candidates. The prevalence of well-matched donors for candidates of different ethnicities varied according to which molecules were chosen to define a low-risk match.