Faculty Bibliography

BACKGROUND/UNASSIGNED:Imlifidase is an IgG-cleaving endopeptidase conditionally approved in Europe for desensitization of highly sensitized patients before kidney transplantation. We present 5-y outcomes and donor-specific antibody (DSA) levels for clinical trial participants from a single site who received imlifidase for desensitization before incompatible transplantation (NCT02790437). METHODS/UNASSIGNED:Imlifidase was administered up to 24 h before living or deceased donor kidney transplantation. DSAs were monitored before transplantation, at days 7 and 28, and at 5 y posttransplant. RESULTS/UNASSIGNED:At 5 y, 7 of 8 participants were alive. One of these 7 had suboptimal graft function secondary to donor-derived disease but remained dialysis independent. Three participants had antibody-mediated rejection (AMR), which occurred in the first 30 d in all cases and was successfully treated. No new episodes of suspected or biopsy-proven AMR occurred after 30 d posttransplant. Seven participants had DSA rebound. DSAs commonly persisted 5 y posttransplant, although they were generally lower strength compared with pre-imlifidase. Dilution studies of sensitized serum enabled the identification of lower AMR risk phenotypes for persisting DSAs. Severe and/or opportunistic infections were not observed at greater than expected frequency. CONCLUSIONS/UNASSIGNED:Five-year outcomes of imlifidase-enabled incompatible transplants are overall favorable. DSA rebound is common, but antibody strength lessens in the long term, and longitudinally persisting DSAs did not lead to premature graft failure.

High human leukocyte antigen (HLA) sensitization limits access to compatible transplantation. New CD38-targeting agents have been shown to reduce anti-HLA antibodies, although with important interpatient variability. Thus, pretreatment identification of responder and nonresponder (NR) patients is needed for treatment decision-making. We analyzed 26 highly sensitized (HS) patients from 2 desensitization trials using anti-CD38 monoclonal antibodies. Hierarchical clustering identified 3 serologic responder groups: high responders, low responders, and NR. Spectral flow cytometry and functional HLA-specific memory B cell (mBC) assessment were first conducted on peripheral blood mononuclear cells and bone marrow samples from 16 patients treated with isatuximab (NCT04294459). Isatuximab effectively depleted bone marrow plasma cells, peripheral CD38-expressing plasmablasts, plasma cells, transitional B cells, and class-switch mBCs, ultimately reducing frequencies of HLA-specific immunoglobulin G (IgG)-producing mBCs. Multidimensional spectral flow cytometry with partial least squares discriminant analysis revealed that pretreatment abundance of specific circulating mBC phenotypes, especially CD38neg class-switch mBCs, accurately distinguished between high serologic responders and low responders or NR (AUC 0.958, 0.860-1.000, P = .009), who also displayed significantly lower frequencies of HLA-specific IgG-producing mBCs (P < .0001). This phenotypical mBC signature predicting response to therapy was validated in an external HS patient cohort (n = 10) receiving daratumumab (NCT04204980). This study identifies critical circulating mBC subset phenotypes that distinguish HS patients with successful serologic responses to CD38-targeting desensitization therapies, potentially guiding treatment decision-making.

UNLABELLED:(N = 24 patients) among functioning grafts. DSA rebounded with levels progressively decreasing over time and no increase in DSA seen between 3 and 5 years. No AMR occurred between 3 and 5 years. Furthermore, no additional safety signals assessed as related to imlifidase were reported in this cohort. At 5 years, highly-HLA sensitized patients who underwent imlifidase desensitization prior to transplantation demonstrated excellent patient and graft survival, despite their high-risk immunological profile. Imlifidase offers a viable and effective treatment option for highly sensitized patients to achieve life-saving transplantation and continued optimism is warranted. CLINICAL TRIAL/UNASSIGNED:ClinicalTrials.gov (NCT02790437), EudraCT Number: 2016-002064-13.

The demand for transplant organs far exceeds the available supply. In the United States alone, more than 90,000 patients are currently on the kidney transplant waitlist, yet only about one third of them will ever receive a transplant. Xenotransplantation, organ transplants from gene edited pigs, offers a potential solution to this shortage. Successful investigational transplants of pig kidneys into brain-dead recipients and expanded access cases involving living human recipients have resulted in the green-lighting of the first human clinical trials. Using the benchmark of 2-year survival of non-human primates in pre-clinical studies, we developed a tool that can identify individual wait-listed patients predicted to have a shorter life expectancy than with a xenotransplant, utilizing Random Survival Forest, DeepSurv and Cox Proportional-Hazards models. We found that it is hard to identify patients that reach clinical equipoise unless the expected xenograft survival exceeds two years, with the Random Survival Forest model identifying less than 5% of such patients. Few patients would benefit based on survival alone and potential beneficiaries are spread across more than 200 transplant centers. Several incentives could allow more patients to reach equipoise. At the same benchmark of 2-year xenograft survival, keeping patients inactive on the waitlist while they have a functioning xeno-kidney increases the percentage achieving equipoise by up to 1.7% across cohorts. Granting patients with failed xenografts the same priority as prior living donors increases this by up to 17.9%, while assigning them the highest priority raises it by up to 28.5%. We are able, however, to identify phenotypes that have a high mortality and low transplant rates in the current allocation system that could serve as acceptable candidates; while not achieving equipoise, they would enjoy the benefits of being dialysis free.

INTRODUCTION:Xenotransplantation has emerged as a promising solution to organ shortage, generating numerous publications. However, no studies have analyzed the research dynamics of xenotransplantation research. We aimed to systematically assess xenotransplantation publication activity. METHODS:A systematic literature search was conducted up to November 22, 2024. Studies on xenotransplantation of solid organs and islets of Langerhans from animals to humans, or perfusion with human blood or its derivatives were included. Publication information, publishing journal, publication type, organ, donor species, and topics studied were extracted. RESULTS:Of 2944 publications, 706 met inclusion criteria: 41.2% original articles, 41.1% reviews, 14.2% publications without original data, 1.6% case reports, 1.3% research letters, 0.6% systematic reviews/meta-analyses. Publication activity displayed two peaks: in the 1990s, driven by the gene editing advancements, and in the early 2020s, following the first pig-to-human transplantation. The top five publishing countries were the USA with (48.2%), Germany (10.2%), UK (5.4%), Sweden (4.8%), and China (4.2%). Xenotransplantation journal accounted for 19.7% of publications, transplantation journals for 27.6%, and general medical journals for 5.4%. Islets of Langerhans were studied in 23.1% of studies, and the most studied organs were heart (21.2%), followed by kidney (17.1%), liver (12.2%), and lung (6.2%). The most represented thematic groups were rejection, immune mechanisms, overall challenges, gene editing, current research, and prospects. CONCLUSION:This first systematic assessment of xenotransplantation research highlights its growing global interest and evolving focus areas. The low proportion of publications with original data underscores the need for more original research. Limited representation in general medical journals highlights the importance of engaging a broader audience as clinical trials approach.

The degree of immunological compatibility between donors and recipients greatly impacts allograft survival. In the United States kidney allocation system, HLA antigen-level matching has been shown to cause ethnic disparities and thus, has been de-emphasised. However, priority points are still awarded for antigen-level zero-ABDR matching, zero-DR matching and one-DR matching. Recently, the degree of HLA molecular (eplet) mismatch has emerged as a more accurate measure of immunological risk, and eplet mismatch load has gained attention as a possible biomarker to improve HLA compatibility. However, little is known about the frequency of eplets in population groups, which is a necessary step to ensure that candidates from any ethnical background can have similar chances at a well-matched organ. Eplet frequencies were estimated using HLA alleles in the Common, Intermediate and Well-Documented (CIWD) 3.0.0 catalogue for six population groups: African-American (AFA), Asian-Pacific Islander (API), European/European descent (EURO), Middle East/North Coast of Africa (MENA), Hispanic/Latino (HIS) and Native-American (NAM). We determined that 98.6% (484 out of 491) of HLA eplets are expressed by the common HLA alleles in all population groups. Of the seven eplets that were expressed by less common HLA alleles, six were Class I eplets and one was expressed by HLA-DQB1 alleles and most were expressed by HLA alleles that were more commonly observed in European/European descent populations. Our observations indicate that HLA eplets will not cause any significant disparity if applied to HLA molecular compatibility, regardless of the ethnic origin of both recipients and donors.

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/RESULTS: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/BACKGROUND:This work was supported by NIH RM1HG009491 and DP5OD033430.

BACKGROUND:Antibody-mediated rejection (ABMR) poses a barrier to long-term graft survival and is one of the most challenging events after kidney transplantation. Removing donor specific antibodies (DSA) through therapeutic plasma exchange (PLEX) is a cornerstone of antibody depletion but has inconsistent effects. Imlifidase is a treatment currently utilized for desensitization with near-complete inactivation of DSA both in the intra- and extravascular space. METHODS:This was a 6-month, randomized, open-label, multicenter, multinational trial conducted at 14 transplant centers. Thirty patients were randomized to either imlifidase or PLEX treatment. The primary endpoint was reduction in DSA level during the 5 days following the start of treatment. RESULTS:Despite considerable heterogeneity in the trial population, DSA reduction as defined by the primary endpoint was 97% for imlifidase compared to 42% for PLEX. Additionally, imlifidase reduced DSA to noncomplement fixing levels, whereas PLEX failed to do so. After antibody rebound in the imlifidase arm (circa days 6-12), both arms had similar reductions in DSA. Five allograft losses occurred during the 6 months following the start of ABMR treatment-four within the imlifidase arm (18 patients treated) and one in the PLEX arm (10 patients treated). In terms of clinical efficacy, the Kaplan-Meier estimated graft survival was 78% for imlifidase and 89% for PLEX, with a slightly higher eGFR in the PLEX arm at the end of the trial. The observed adverse events in the trial were as expected, and there were no apparent differences between the arms. CONCLUSION/CONCLUSIONS:Imlifidase was safe and well-tolerated in the ABMR population. Despite meeting the primary endpoint of maximum DSA reduction compared to PLEX, the trial was unsuccessful in demonstrating a clinical benefit of imlifidase in this heterogenous ABMR population. TRIAL REGISTRATION/BACKGROUND:EudraCT number: 2018-000022-66, 2020-004777-49; ClinicalTrials.gov identifier: NCT03897205, NCT04711850.