Highly sensitized kidney transplant candidates face limited access to compatible organs due to persistent anti-human leukocyte antigen (HLA) antibodies (Abs) and memory B cell (mBc) responses, which are generally not concomitantly targeted by current desensitization therapies. In this single-arm phase 1b/2 trial (NCT05145296), 5 highly sensitized kidney transplant candidates (calculated panel-reactive Ab >99%) were treated with belatacept and daratumumab to evaluate safety and mechanistic efficacy. Serum anti-HLA Ab levels, HLA-specific mBc, and bone marrow (BM)-residing long-lived plasma cells (PCs) were analyzed using single antigen beads, functional B cell assays, and spectral flow cytometry. The regimen was well-tolerated, with no serious adverse events attributable to study drugs. Three of 4 evaluable patients showed substantial serologic response by means of elimination and reductions in mean fluorescence intensity Abs and titers, mainly anti-HLA class I. HLA-specific mBc and CD38+ PC were significantly depleted in responders in peripheral blood and BM. Multidimensional profiling revealed depletion of CD38+ natural killer, T follicular helper, and PC in both peripheral blood and BM, which was accompanied by a reduction in calculated panel-reactive Ab levels, primarily in class I Abs. Dual targeting of T/B cell costimulation and PC using belatacept and daratumumab is a safe and mechanistically effective approach for desensitization in highly sensitized kidney transplant candidates. These findings support further investigation in larger trials.

Despite booster vaccinations, solid organ transplant (SOT) recipients develop suboptimal immunity and remain at risk of severe coronavirus disease 2019 (COVID-19). Chronic immunosuppression and repeated antigen exposure favor T cell exhaustion/senescence, potentially challenging the development of protective immunity. In a prospective multicenter study including 80 naïve SOT patients receiving 5 severe acute respiratory syndrome coronavirus 2 mRNA-based vaccine doses, exhausted/senescent T cell phenotypes were longitudinally profiled at distinct time points, and their impact on antigen-specific immune responses was assessed by antibodies, memory B cells, cytokine-producing T cells, and activation-induced markers on CD4 and CD8 T cells. We observed wide heterogeneity of vaccine-induced adaptive immunity across compartments. T cell exhaustion/senescence did not change after 3 vaccine doses. Notably, high percentages of CD57+, CD57+PD1+, programmed cell death protein 1 (PD1)+, and CD57+TIM3+ exhausted/senescent CD4 T cells at baseline independently predicted poor adaptive functional immune responses despite multiple boosters, regardless of SOT type and immunosuppressive regimen (area under the curve 0.89, 95% confidence interval 0.81-0.97, sensitivity 0.79, specificity 0.92). Such phenotypes were predominantly observed among tacrolimus/mycophenolate-based regimens. Moreover, SOT recipients with high percentages of CD57+, CD57+PD1+, and CD57+TIM3+ exhausted/senescent CD4 T cells at baseline predicted severe COVID-19 (area under the curve 0.88, P < .01). Our study adds preliminary new insight in the field and has clinical implications for risk-stratification against COVID-19 and other viral infections, ultimately guiding decision-making for establishing preventive strategies in SOT patients.

Donor-derived cell-free deoxyribonucleic acid (DNA) (dd-cfDNA) and urinary chemokines are promising noninvasive biomarkers for kidney allograft rejection, but direct comparative data are lacking. In this prospective pilot study, we analyzed 194 biopsies (101 for-cause, 93 surveillance) paired with dd-cfDNA and urinary chemokine (CXCL9, CXCL10, CCL2, VEGF-A) concentrations in kidney transplant recipients. We evaluated their correlation, diagnostic accuracy for rejection phenotypes, and integration into diagnostic models with clinical and immunologic variables. Rejection was diagnosed in 32.5% of biopsies, predominantly antibody-mediated. dd-cfDNA showed strong diagnostic performance in both for-cause (area under the receiver operating characteristic curve [AUC] 0.85) and surveillance (AUC 0.91) biopsies. Conversely, urinary chemokines, particularly the composite Score4, showed accuracy mainly in for-cause biopsies (AUC 0.76). Remarkably, Score4 combined with donor-specific antibodies showed similar performance as dd-cfDNA + donor-specific antibodies (AUC 0.90) in for-cause biopsies. Internal bootstrap validation, including calibration metrics, confirmed the consistency of the models. dd-cfDNA provides robust diagnostic accuracy for kidney allograft rejection across distinct clinical settings. Urinary chemokine measures, especially Score4, may offer valuable diagnostic utility in for-cause biopsies. These findings support context-specific integration of noninvasive biomarkers and represent the first direct comparison of dd-cfDNA and urinary chemokines, informing personalized approaches to rejection monitoring.

Loss of host-microbiota balance promotes gut inflammation, colitis and inflammatory bowel disease. Yet, whether host or microbial factors are the critical driver of the pathology remains unclear. Here, we investigate how cardiolipin maintains metabolic fitness of regulatory T (Treg) cells to preserve gut-immune homeostasis. We discover that deleting the cardiolipin-synthesizing enzyme protein tyrosine phosphatase mitochondrial 1 (PTPMT1) in T cells predisposes mice to colitis due to impaired Treg cell function in the absence of dysbiosis. Subsequent pathobiont infections accelerate the progression and severity of gut inflammation. Mechanistically, the absence of cardiolipin impairs Treg cell metabolic fitness and triggers a maladaptive integrated stress response, which can be reversed pharmacologically or genetically, restoring gut homeostasis and extending lifespan in PTPMT1 ΔT mice. Barth syndrome, a genetic disorder marked by severe cardiolipin deficiency, also exhibits gastrointestinal symptoms and inflammation associated with helper T cell imbalance and an active integrated stress response signature. Overall, these results suggest that a cardiolipin-mediated mitonuclear axis in T cells preserves gut-immune homeostasis and dictates outcome in pathobiont infections.

IntroductionRisk stratification for CMV infection in lung transplantation (LT) currently relies on determining donor and recipient CMV IgG before transplantation. However, it has been observed that some patients who test positive for CMV-specific humoral response before kidney transplantation (KT) exhibit a weak or absent CMV-specific cellular response. The significance of this observation in LT is still unknown.MethodsThis prospective, multicenter, observational study evaluated the agreement between CMV IgG serology and specific cell-mediated response (specific T cell Enzyme-Linked ImmunoSpot Assay, ELISPOT, against CMV pp65 and IE-1 antigens) in 121 patients on the waiting list for LT.ResultsOne hundred and four (86%) patients were seropositive for CMV. Discordant humoral and cellular immunologic responses were observed, 29% of seropositive patients had a weak ELISPOT response to IE-1 and 39% to pp65. In 22% of seropositive patients, there was a weak or no response to both antigens. All seronegative patients did not respond to either antigen.ConclusionsTherefore, over 20% of CMV seropositive LT candidates showed weak CMV-specific cellular immune responses despite detectable serological memory against CMV. This may be important in assessing the risk of developing a CMV infection after transplantation.

Introduction:The interferon gamma (IFN-γ) enzyme-linked immunosorbent spot is a highly sensitive immune assay that enables the assessment of cytomegalovirus (CMV)-specific cell-mediated immunity (CMI) and can identify at-risk transplant patients of CMV infection; however, its clinical implementation remains elusive. Methods:We developed a novel CMV-CMI risk-score based on the standardized T-SPOT.CMV assay against 2 CMV antigens (immediate-early protein 1 [IE-1] and 65 kDa phosphoprotein [pp65]), a biomarker predicting CMV infection, both high viral replication, and disease by performing a pooled analysis of 570 kidney transplants participating in different clinical trials and subsequently validating it in 146 consecutives solid organ transplants (SOT) in an interventional trial. By incorporating clinical variables into the CMV-CMI risk-score, we built an integrative prognostic system quantifying the risk of CMV infection (CMV-PrognosTIC score) using elastic net penalized regression analysis. Results:In the pooled derivation cohort, whereas specific IE-1/pp65-specific CMV-CMI frequencies independently correlated with high risk of CMV infection (areas under the curve [AUCs]: 0.694, P < 0.0001; 0.719, P < 0.0001, respectively), by combining both responses, 3 CMV-CMI risk-scores appeared, accurately discriminating low-risk (LR) from intermediate-risk (IR) and high-risk (HR) patients (98.7% negative predictive value [NPV], 97.2% sensitivity). Its prospective implementation guiding decision-making in an independent SOT cohort confirmed the very high NPV and sensitivity identifying LR patients. By integrating type of preventive therapy, patient age, and donor (D) and recipient (R) CMV-serostatus to the CMV-CMI risk-score, we generated a global risk-prognostic model showing accurate discrimination and calibration in both derivation (AUC: 0.807) and validation cohorts (AUC: 0.719). Conclusion:We developed a robust CMV-PrognosTIC score to quantify the risk of CMV infection in SOT, which may be readily implemented in clinical transplantation to personalize CMV preventive therapies.

Despite major advancements in transplant rejection physiopathology and the refinement of immunosuppressive therapies over the past decades, improvements in graft and patient survival remains limited. A potential explanation is the insufficient implementation of biomarkers for individualized alloimmune risk stratification in clinical transplantation. Enormous efforts have focused in the last decades on developing sensitive and specific biomarkers to enable more personalized, non-invasive rejection diagnostics and informed treatment decisions in the transplant process. These biomarkers have distinct purposes; pre-transplantation, biomarkers aim to improve current donor-recipient immunological matching and rule out preformed anti-donor immune memory, whereas post-transplantation, their main aim focuses on identifying anti-donor alloimmune activation and on-going subclinical rejection in a non-invasive manner. This review summarizes the most advanced biomarkers and immune assays in the field, categorizing them by their diagnostic, prognostic, and predictive capabilities, and discusses their current validation status and integration into clinical trial designs aimed at improving transplant outcomes. Among them, we here highlight those assessing alloimmune susceptibility or activation, such as donor/recipient HLA molecular matching, donor (HLA/non-HLA)-specific antibodies (DSA), donor-reactive memory T and B cells, peripheral gene expression profiling (GEP) as well as some specific circulating immune cell phenotypes; and furthermore, we discuss those biomarkers diagnosing on-going subclinical graft injury, including donor-derived cell-free DNA (dd-cfDNA), and urinary chemokines or transcriptional biomarkers. Most importantly, these biomarkers are often complementary: some reflect ongoing alloimmune responses and may guide immunosuppression decisions, while others may provide early warnings of allograft injury prior to clinical manifestation. While some have progressed to advanced validation stages with strong diagnostic and prognostic value, others remain in early development. Rigorous interventional clinical trials are warranted to establish their clinical utility and define their role in transplant precision medicine to ultimately improve current clinical outcomes.

Cytomegalovirus (CMV) infection is associated with poor kidney transplant outcomes. While innate and adaptive immune cells have been implicated in its prevention, an in-depth characterization of the in vivo kinetics of multiple cell subsets and their role in protecting against CMV infection has not been achieved. Here, we performed high-dimensional immune phenotyping by mass cytometry, and functional assays, on 112 serially collected samples from CMV seropositive kidney transplant recipients. Advanced unsupervised deep learning analysis was used to assess immune cell populations that significantly correlated with prevention against CMV infection and anti-viral immune function. Prior to infection, kidney transplant recipients who developed CMV infection showed significantly lower CMV-specific cell-mediated immune (CMI) frequencies than those that did not. A broad diversity of circulating cell subsets within innate and adaptive immune compartments were associated with CMV infection or protective CMV-specific CMI. While percentages of CMV (tetramer-stained)-specific T cells associated with high CMI responses and clinical protection, circulating CD3+CD8midCD56+ NK-T cells overall strongly associated with low CMI and subsequent infection. However, three NK-T cell subsets sharing the CD11b surface marker associated with CMV protection and correlated with strong anti-viral CMI frequencies in vitro. These data were validated in two external independent cohorts of kidney transplant recipients. Thus, we newly describe the kinetics of a novel NK-T cell subset that may have a protective role in post-transplantation CMV infection. Our findings pave the way to more mechanistic studies aimed at understanding the function of these cells in protection against CMV infection.

Non-invasive biomarkers are promising tools for improving kidney allograft rejection monitoring, but their clinical adoption requires more evidence in specifically designed studies. To address this unmet need, we designed the EU-TRAIN study, a large prospective multicentric unselected cohort funded by the European Commission. Here, we included consecutive adult patients who received a kidney allograft in nine European transplant centers between November 2018 and June 2020. We prospectively assessed gene expression levels of 19 blood messenger RNAs, four antibodies targeting non-human leukocyte antigen (HLA) endothelial antigens, together with circulating anti-HLA donor-specific antibodies (DSA). The primary outcome was allograft rejection (antibody-mediated, T cell-mediated, or mixed) in the first year post-transplantation. Overall, 412 patients were included, with 812 biopsies paired with a blood sample. CD4 gene expression was significantly associated with rejection, while circulating anti-HLA DSA had a significant association with allograft rejection and a strong association with antibody-mediated rejection. All other tested biomarkers, including AKR1C3, CD3E, CD40, CD8A, CD9, CTLA4, ENTPD1, FOXP3, GZMB, ID3, IL7R, MS4A1, MZB1, POU2AF1, POU2F1, TCL1A, TLR4, and TRIB1, as well as antibodies against angiotensin II type 1 receptor, endothelin 1 type A receptor, C3a and C5a receptors, did not show significant associations with allograft rejection. The blood messenger RNAs and non-HLA antibodies did not show an additional value beyond standard of care monitoring parameters and circulating anti-HLA DSA to predict allograft rejection in the first year post-transplantation. Thus, our results open avenues for specifically designed studies to demonstrate the clinical relevance and implementation of other candidate non-invasive biomarkers in kidney transplantation practice.

Emerging data suggest that costimulation blockade with belatacept effectively controls humoral alloimmune responses. However, whether this effect may be deleterious for protective anti-infectious immunity remains poorly understood. We performed a mechanistic exploratory study in 23 kidney transplant recipients receiving either the calcineurin-inhibitor tacrolimus (Tac, n=14) or belatacept (n=9) evaluating different cellular immune responses after influenza vaccination such as activated T follicular Helper (Tfh), plasmablasts and H1N1 hemagglutinin (HA)-specific memory B cells (HA+mBC) by flow-cytometry, and anti-influenza antibodies by hemagglutination inhibition test (HI), at baseline and days 10, 30 and 90 post-vaccination. The proportion of CD4+CD54RA-CXCR5+ Tfh was lower in belatacept than Tac patients at baseline (1.86%[1.25-3.03] vs 4.88%[2.40-8.27], p=0.01) and remained stable post-vaccination. At M3, HA+mBc were significantly higher in Tac-treated patients (0.56%[0.32-1.49] vs 0.27%[0.13-0.44], p=0.04) and correlated with activated Tfh numbers. When stratifying patients according to baseline HA+mBc frequencies, belatacept patients with low HA+mBC displayed significantly lower HA+mBc increases after vaccination than Tac patients (1.28[0.94-2.4] vs 2.54[1.73-5.70], p=0.04). Also, belatacept patients displayed significantly lower seroprotection rates against H1N1 at baseline than Tac-treated patients (44.4% vs 84.6%) as well as lower seroconversion rates at days 10, 30 and 90 after vaccination (50% vs 0%, 63.6% vs 0%, and 63.6% vs 0%, respectively). We show the efficacy of belatacept inhibiting T-dependent antigen-specific humoral immune responses, active immunization should be highly encouraged before starting belatacept therapy.

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.

Background. Infliximab selectively targets recently activated effector cells and, as an induction agent, might enable the safe elimination of mycophenolate from maintenance immunosuppression in kidney transplantation. Methods. This is a phase II international multicenter open-label single-arm confidence interval (CI)-based clinical trial of the BIO-DrIM EU consortium aimed at assessing the efficacy and safety of rabbit antithymocyte globulin and infliximab induction in kidney transplantation. Sixty-seven primary kidney transplant recipients at low risk (panel-reactive antibodies <20%, no donor-specific antibodies [DSA]) received rabbit antithymocyte globulin (2 x 1.5 mg/kg, postoperative days 0 and 1) and infliximab (5 mg/kg, postoperative day 2), followed by mycophenolate-free tacrolimus-based immunosuppression for 12 mo. The primary endpoint was efficacy failure, defined as a composite of acute rejection, graft loss, or poor graft function (estimated glomerular filtration rate <40 mL/min) at 12 mo and was based on the endpoint of the comparator study. Additionally, a historical propensity-matched control cohort was established. Results. Primary endpoint occurred in 22 of 67 patients (32.84%), with upper bound of an exact 1-sided 95% CI of 43.47%, which met the predefined criteria (efficacy failure of <40% and upper-bound 95% CI of <50%) and was similar in the historical matched cohort. By 12 mo, 79.1% of patients remained on the study protocol. Lower rates of BK replication (6% versus 22.4%; P = 0.013) but higher rates of de novo DSAs (11.9% versus 1.5%; P = 0.039) were observed in the study cohort. Conclusions. A similar efficacy of the study immunosuppression regimen to the comparator study and the historical matched cohort was found. However, a higher de novo DSA emergence points to an increased risk of antibody-mediated rejection (NCT04114188).

IntroductionSolid organ transplant (SOT) recipients display weak seroconversion and neutralizing antibody (NAb) responses after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination and remain at risk of severe coronavirus disease 2019 (COVID-19). While B-cell memory is the hallmark of serological immunity, its role in driving successful vaccine responses and providing immune protection in SOT patients remains unclear.MethodsWe investigated the function and interplay of SARS-CoV-2-specific memory B cells (mBc), different cytokineproducing T cells, and cross-reactive NAb in driving seroconversion and protection against COVID-19 in two cohorts. First, we studied a large cohort of 148 SOT recipients and 32 immunocompetent individuals who underwent several vaccinations. Subsequently, we assessed 25 SOT patients participating in a randomized controlled trial to compare two different immunosuppressive strategies for allowing successful seroconversion and memory-cell responses after booster vaccination.ResultsWe corroborate previous findings that B- and T-cell memory responses are weaker and more delayed in SOT patients than in immunocompetent (IC) individuals; however, within the SOT cohort, we found that these responses are relatively stronger and more robust in patients not receiving mycophenolate mofetil (MMF)-based therapies. Anti- spike IgG titers strongly correlated with RBD-specific IgG-producing mBc, with both displaying broad viral cross reactivity. Prebooster SARS-CoV-2-specific mBc and IL-2- producing T cells accurately predicted Nab seroconversion (AUC, 0.828) and protection against severe COVID-19. While switching unresponsive SOT patients from calcineurin inhibitors (CNI)/MMF to a low-exposure CNI/mTOR-i regimen favored wider SARS-CoV-2-specific immune responses after a fourth booster vaccination, preformed RBD-specific mBc predicted NAb seroconversion.DiscussionOur study adds new insights into the pathobiology of immune memory and highlights the pivotal role of SARS-CoV-2-specific mBc in promoting immune protection inSOT patients.

BACKGROUND:Dysregulated inflammatory responses and oxidative stress are key pathogenic drivers of chronic inflammatory diseases such as liver cirrhosis (LC). Regulatory T cells (Tregs) are essential to prevent excessive immune activation and maintain tissue homeostasis. While inflammatory cues are well known to modulate the function and stability of Tregs, the extent to which Tregs are influenced by oxidative stress has not been fully explored.METHODS:The phenotypic and functional properties of CD4+CD25+CD127lo/- Tregs isolated from patients with LC were compared to healthy controls (HC). Treg redox state was investigated by characterizing intracellular reactive oxygen species (ROS), NADPH oxidase-2 (Nox2) activity, mitochondrial function, morphology, and nuclear factor-erythroid 2-related factor (Nrf2) antioxidant signalling. The relevance of Nrf2 and its downstream target, Heme-oxygenase-1 (HO-1), in Treg function, stability, and survival, was further assessed using mouse models and CRISPR/Cas9-mediated HO-1 knock-out.FINDINGS:Circulating Tregs from LC patients displayed a reduced suppressive function, correlating with liver disease severity, associated with phenotypic abnormalities and increased apoptosis. Mechanistically, this was linked to a dysregulated Nrf2 signalling with resultant lower levels of HO-1, enhanced Nox2 activation, and impaired mitochondrial respiration and integrity. The functional deficit in LC Tregs could be partially recapitulated by culturing control Tregs in patient sera.INTERPRETATION:Our findings reveal that Tregs rely on functional redox homeostasis for their function, stability, and survival. Targeting Treg specific anti-oxidant pathways may have therapeutic potential to reverse the Treg impairment in conditions of oxidative damage such as advanced liver disease.FUNDING:This study was funded by the Wellcome Trust (211113/A/18/Z).