Detectable plasma severe acute respiratory syndrome coronavirus 2 spike antigen is associated with poor antibody response following third messenger RNA vaccination in kidney transplant recipients

BACKGROUND

Kidney transplant recipients (KTRs) generate lower antibody responses to messenger RNA (mRNA)-based severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination, yet precise mechanisms for this poor response remain uncertain. One potential contributor is suboptimal spike antigen (sAg) translation and expression owing to transplant immunosuppression, which might lead to insufficient exposure to develop humoral and/or cellular immune responses.

METHODS

Within a single-arm clinical trial, 65 KTRs underwent ultrasensitive plasma sAg testing before, and 3 and 14 days after, the third mRNA vaccine doses. Anti-SARS-CoV-2 spike antibodies (anti-receptor binding domain [anti-RBD]) were serially measured at 14 and 30 days post-vaccination. Associations between sAg detection and clinical factors were assessed. Day 30 anti-RBD titer was compared among those with versus without sAg expression using Wilcoxon rank sum testing.

RESULTS

Overall, 16 (25%) KTRs were sAg positive (sAg+) after vaccination, peaking at day 3. Clinical and laboratory factors were broadly similar in sAg(+) versus sAg(-) KTRs. sAg(+) status was significantly negatively associated with day 30 anti-RBD response, with median (interquartile range) 10.8 (<0.4-338.3) U/mL if sAg(+) versus 709 (10.5-2309.5) U/mL if sAg(-) (i.e., 66-fold lower; p = .01).

CONCLUSION

Inadequate plasma sAg does not likely drive poor antibody responses in KTRs, rather sAg detection implies insufficient immune response to rapidly clear vaccine antigen from blood. Other downstream mechanisms such as sAg trafficking and presentation should be explored.

Risk factors and outcomes of bloodstream infection from a urinary source in kidney transplant recipients

BACKGROUND

Bacteriuria is common among kidney transplant recipients (KTR). Risk factors and outcomes associated with bloodstream infection due to a urinary source (BSIU) in KTR are poorly understood.

METHODS

This single center case-control study from 2010 to 2022 compared KTR with BSIU to those with bacteria without bloodstream infection (BU). Multivariable logistic regression identified BSIU risk factors, and Cox models assessed its impact on graft failure.

RESULTS

Among 3435 patients, who underwent kidney transplantation at Emory Hospital, 757 (22%) developed bacteriuria, among whom 142 (18.8%) were BSIU. Male sex, presence of Escherichia coli, Klebsiella pneumoniae, or Pseudomonas species in urine culture, urethral stricture, neuromuscular bladder disorder, and history of diabetes-induced renal failure were independently associated with increased odds of BSIU (Male sex: aOR 2.29, 95% CI 1.52, 3.47, E. coli: aOR 5.14, 95% CI 3.02, 9.13; K. pneumoniae aOR 3.19, 95% CI 1.65, 6.27, Pseudomonas spp aOR 3.06, 95% CI 1.25, 7.18; urethral stricture: 4.10, 95% CI 1.63, 10.3, neuromuscular bladder disorder aOR 1.98, 95% CI 1.09, 3.53, diabetes: aOR 1.64, 95% CI 1.08, 2.49). BSIU was associated with increased hazard of graft failure (HR 1.52, 95% CI 1.05, 2.20).

CONCLUSION

Close monitoring is warranted for male KTR with bacteriuria, those with urine cultures positive for Pseudomonas spp, K. pneumoniae, or E. coli, as well as KTR with a history of diabetes-induced renal failure, urethral stricture, or neuromuscular bladder disorder due to their risk for developing BSIU. Future research should explore strategies to mitigate BSIU risk in these high-risk KTR and reduce the associated risk of long-term graft failure.

The Burden and Impact of Early Post-transplant Multidrug-Resistant Organism Detection Among Renal Transplant Recipients, 2005-2021

Background

Reducing the burden of multidrug-resistant organism (MDRO) colonization and infection among renal transplant recipients (RTRs) may improve patient outcomes. We aimed to assess whether the detection of an MDRO or a comparable antibiotic-susceptible organism (CSO) during the early post-transplant (EPT) period was associated with graft loss and mortality among RTRs.

Methods

We conducted a retrospective cohort study of RTRs transplanted between 2005 and 2021. EPT positivity was defined as a positive bacterial culture within 30 days of transplant. The incidence and prevalence of EPT MDRO detection were calculated. The primary outcome was a composite of 1-year allograft loss or mortality following transplant. Multivariable Cox hazard regression, competing risk, propensity score-weighted sensitivity, and subgroup analyses were performed.

Results

Among 3507 RTRs, the prevalence of EPT MDRO detection was 1.3% (95% CI, 0.91%-1.69%) with an incidence rate per 1000 EPT-days at risk of 0.42 (95% CI, 0.31-0.57). Among RTRs who met survival analysis inclusion criteria (n = 3432), 91% (3138/3432) had no positive EPT cultures and were designated as negative controls, 8% (263/3432) had a CSO detected, and 1% (31/3432) had an MDRO detected in the EPT period. EPT MDRO detection was associated with the composite outcome (adjusted hazard ratio [aHR], 3.29; 95% CI, 1.21-8.92) and death-censored allograft loss (cause-specific aHR, 7.15; 95% CI, 0.92-55.5; subdistribution aHR, 7.15; 95% CI, 0.95-53.7). A similar trend was seen in the subgroup and sensitivity analyses.

Conclusions

MDRO detection during the EPT period was associated with allograft loss, suggesting the need for increased strategies to optimize prevention of MDRO colonization and infection.

Impact of an ultrasensitive Cytomegalovirus quantitative nucleic acid test on Cytomegalovirus detection and therapy in renal transplant recipients

BACKGROUND

Cytomegalovirus (CMV) infection has broad implications for morbidity and mortality in renal transplant recipients (RTR). Routine surveillance for CMV replication with PCR-based quantitative nucleic acid testing (qNAT) assays is standard practice in most transplant centers, but the impact of assay sensitivity on antiviral decision-making and virologic outcomes has not been studied. We investigated the effects of an ultrasensitive CMV qNAT assay on multiple clinical outcomes, including time to detection and duration of CMV DNAemia.

METHODS

We conducted a single-center cohort study contrasting RTRs monitored with a qNAT with a higher lower limit of quantification (LLOQ >300 IU/mL) with those monitored with a more sensitive qNAT (LLOQ >35 IU/mL). Patients were stratified by donor (D)/recipient (R) CMV serostatus (D+/R-: high risk; any R+: moderate risk). CMV viral load monitoring was performed monthly post transplantation, with the primary outcomes being time to CMV DNAemia and its duration.

RESULTS

Total 1382 patients were analyzed from 2014 to 2016 and 2019 to 2021. Moderate-risk RTRs monitored with the more sensitive assay experienced a greater hazard for the development of a first episode of CMV DNAemia (aHR: 1.95, 95% confidence interval [CI]: 1.55-2.46) and an average of 24 (95% CI: 16.40-31.98) additional days of DNAemia. There was no difference in CMV end-organ disease or 1-year all-cause mortality between moderate-risk RTRs.

CONCLUSIONS

The more sensitive assay was associated with earlier detection and extended durations of CMV DNAemia in moderate-risk RTRs, without altering clinical outcomes. These findings inform optimal use of these assays and antiviral stewardship in RTRs.

KEY SUMMARY

The use of ultrasensitive CMV qNAT assays in moderate-risk CMV renal transplant recipients is associated with earlier detection and longer durations of CMV DNAemia without impacting CMV end-organ disease or 1-year mortality.

Belatacept with time-limited tacrolimus coimmunosuppression modifies the 3-year risk of eplet mismatch in kidney transplantation

Solid organ transplant donor-recipient eplet mismatch has been correlated with donor-specific antibody (DSA) formation, antibody-mediated rejection, and overall rejection rates. However, studies have been predominantly in patients on tacrolimus-based immunosuppression regimens and have not fully explored differences in ethnically and racially diverse populations. Evidence indicates that patients on belatacept have lower rates of DSA formation, suggesting mediation of the immunogenicity of mismatched human leukocyte antigen polymorphisms. We performed a retrospective, single-center analysis of class II eplet disparity in a cohort of kidney transplant recipients treated using belatacept with tacrolimus induction (Bela/TacTL) or tacrolimus regimens between 2016 and 2019. Bela/TacTL (n = 294) and tacrolimus (n = 294) cohorts were propensity score-matched with standardized difference <0.15. Single-molecule eplet risk level was associated with immune event rates for both groups. In Cox regression analysis stratified by eplet risk level, Bela/TacTL immunosuppression was associated with a decreased rate of DSA (hazard ratio [HR] = 0.4), antibody-mediated rejection (HR = 0.2), and rejection (HR = 0.45). In the low-risk group, cumulative graft failure was lower for patients on Bela/TacTL (P < .02). Analysis of eplet mismatch burden may be a useful adjunct in identifying high-risk populations with increased immunosuppression requirements and should encourage the design of allocation rules to incentivize lower-risk pairings without negatively impacting equity in access.

Costimulatory Blockade and Solid Organ Transplantation: The Past, Present, and Future

Belatacept is the first costimulatory blockade agent clinically approved for transplant immunosuppression. Although more than 10 years of study have demonstrated that belatacept offers superior long-term renal allograft and patient survival compared to conventional calcineurin inhibitor (CNI)-based immunosuppression regimens, the clinical adoption of belatacept has continued to lag because of concerns of an early risk of acute cellular rejection (ACR) and various logistical barriers to its administration. In this review, the history of the clinical development of belatacept is examined, along with the findings of the seminal BENEFIT and BENEFIT-EXT trials culminating in the clinical approval of belatacept. Recent efforts to incorporate belatacept into novel CNI-free immunosuppression regimens are reviewed, as well as the experience of the Emory Transplant Center in using a tapered course of low-dose tacrolimus in belatacept-treated renal allograft patients to garner the long-term outcome benefits of belatacept without the short-term increased risks of ACR. Potential avenues to increase the clinical adoption of belatacept in the future are explored, including surmounting the logistical barriers of belatacept administration through subcutaneous administration or more infrequent belatacept dosing. In addition, belatacept conversion strategies and potential expanded clinical indications of belatacept are discussed for pediatric transplant recipients, extrarenal transplant recipients, treatment of antibody-mediated rejection (AMR), and in patients with failed renal allografts. Finally, we discuss the novel immunosuppressive drugs currently in the development pipeline that may aid in the expansion of costimulation blockade utilization.

Epitope Mapping of SARS-CoV-2 Spike Antibodies in Vaccinated Kidney Transplant Recipients Reveals Poor Spike Coverage Compared to Healthy Controls

Kidney transplant recipients (KTRs) develop decreased antibody titers to SARS-CoV-2 vaccination compared to healthy controls (HCs), but whether KTRs generate antibodies against key epitopes associated with neutralization is unknown. Plasma from 78 KTRs from a clinical trial of third doses of SARS-CoV-2 vaccines and 12 HCs underwent phage display immunoprecipitation and sequencing (PhIP-Seq) to map antibody responses against SARS-CoV-2. KTRs had lower antibody reactivity to SARS-CoV-2 than HCs, but KTRs and HCs recognized similar epitopes associated with neutralization. Thus, epitope gaps in antibody breadth of KTRs are unlikely responsible for decreased efficacy of SARS-CoV-2 vaccines in this immunosuppressed population.

Fecal microbiota transplantation promotes reduction of antimicrobial resistance by strain replacement

Multidrug-resistant organism (MDRO) colonization is a fundamental challenge in antimicrobial resistance. Limited studies have shown that fecal microbiota transplantation (FMT) can reduce MDRO colonization, but its mechanisms are poorly understood. We conducted a randomized, controlled trial of FMT for MDRO decolonization in renal transplant recipients called PREMIX (NCT02922816). Eleven participants were enrolled and randomized 1:1 to FMT or an observation period followed by delayed FMT if stool cultures were MDRO positive at day 36. Participants who were MDRO positive after one FMT were treated with a second FMT. At last visit, eight of nine patients who completed all treatments were MDRO culture negative. FMT-treated participants had longer time to recurrent MDRO infection versus PREMIX-eligible controls who were not treated with FMT. Key taxa (Akkermansia muciniphila, Alistipes putredinis, Phocaeicola dorei, Phascolarctobacterium faecium, Alistipes species, Mesosutterella massiliensis, Barnesiella intestinihominis, and Faecalibacterium prausnitzii) from the single feces donor used in the study that engrafted in recipients and metabolites such as short-chain fatty acids and bile acids in FMT-responding participants uncovered leads for rational microbiome therapeutic and diagnostic development. Metagenomic analyses revealed a previously unobserved mechanism of MDRO eradication by conspecific strain competition in an FMT-treated subset. Susceptible Enterobacterales strains that replaced baseline extended-spectrum β-lactamase-producing strains were not detectable in donor microbiota manufactured as FMT doses but in one case were detectable in the recipient before FMT. These data suggest that FMT may provide a path to exploit strain competition to reduce MDRO colonization.

Letter to the editor: "hook" (prozone) effect in sars-cov-2 anti-spike binding antibody levels following vaccination, infection, or monoclonal antibody in solid organ transplant recipients

Anti-spike binding antibody (Ab) levels are used by some providers to inform COVID-19 risk assessment for solid organ transplant recipients (SOTRs). As has been observed with other Ab assays, in the setting of high binding Ab, quantitative results may demonstrate artifactually low values (i.e., “hook” or prozone effect). Within two studies of SARS-CoV-2 vaccination of SOTRs (an observational cohort and a single-center trial), Ab levels were assessed using the semiquantitative Roche Elecsys anti-SARS-CoV-2 S assay. In the observational cohort, we flagged 9 samples with either a paradoxical decrease or weak (<10x) rise after Tixagevimab/Cilgavimab (T/C) administration. This prompted retesting with up-front 1:50 dilution, with serial dilution performed until returning two results within expected assay variation. Subsequently, all post-vaccination clinical trial samples were retested. Hook effect was suspected if retest level was both ≥15% and ≥200U/mL higher than original level. From the observational cohort, all 9 flagged samples demonstrated a hook effect. Of 377 clinical trial samples (all rerun), 34/377 (9%) demonstrated a hook effect. Among the hook effect samples (n=43), the original median (IQR) titer was 1950 (650 – 4390) U/mL, and upon retesting this increased to 5685 (2981 – 9853) U/mL representing a 1.6 (1.3–6.0)-fold increase (p=0.03). Marked hook effect (>700x increase) was observed in two participants with recent vaccination plus breakthrough infection. Hook effect was observed in SOTRs tested using a SARS-CoV-2 clinical Ab assay in the setting of high analyte. Laboratories and clinicians should be aware of this artifact and consider serial dilution to confirm accurate quantitative results.

Persistent SARS-CoV-2-specific immune defects in kidney transplant recipients following third mRNA vaccine dose

Kidney transplant recipients (KTRs) show poorer response to SARS-CoV-2 mRNA vaccination, yet response patterns and mechanistic drivers following third doses are ill-defined. We administered third monovalent mRNA vaccines to n = 81 KTRs with negative or low-titer anti-receptor binding domain (RBD) antibody (n = 39 anti-RBDNEG; n = 42 anti-RBDLO), compared with healthy controls (HCs, n = 19), measuring anti-RBD, Omicron neutralization, spike-specific CD8+%, and SARS-CoV-2-reactive T cell receptor (TCR) repertoires. By day 30, 44% anti-RBDNEG remained seronegative; 5% KTRs developed BA.5 neutralization (vs 68% HCs, P < .001). Day 30 spike-specific CD8+% was negative in 91% KTRs (vs 20% HCs; P = .07), without correlation to anti-RBD (rs = 0.17). Day 30 SARS-CoV-2-reactive TCR repertoires were detected in 52% KTRs vs 74% HCs (P = .11). Spike-specific CD4+ TCR expansion was similar between KTRs and HCs, yet KTR CD8+ TCR depth was 7.6-fold lower (P = .001). Global negative response was seen in 7% KTRs, associated with high-dose MMF (P = .037); 44% showed global positive response. Of the KTRs, 16% experienced breakthrough infections, with 2 hospitalizations; prebreakthrough variant neutralization was poor. Absent neutralizing and CD8+ responses in KTRs indicate vulnerability to COVID-19 despite 3-dose mRNA vaccination. Lack of neutralization despite CD4+ expansion suggests B cell dysfunction and/or ineffective T cell help. Development of more effective KTR vaccine strategies is critical. (NCT04969263).

CD28-Selective Inhibition Prolongs Non-Human Primate Kidney Transplant Survival

Costimulation blockade using belatacept results in improved renal function after kidney transplant as well as decreased likelihood of death/graft loss and reduced cardiovascular risk; however, higher rates and grades of acute rejection have prevented its widespread clinical adoption. Treatment with belatacept blocks both positive (CD28) and negative (CTLA-4) T cell signaling. CD28-selective therapies may offer improved potency by blocking CD28-mediated costimulation while leaving CTLA-4 mediated coinhibitory signals intact. Here we test a novel domain antibody directed at CD28 (anti-CD28 dAb (BMS-931699)) in a non-human primate kidney transplant model. Sixteen macaques underwent native nephrectomy and received life-sustaining renal allotransplantation from an MHC-mismatched donor. Animals were treated with belatacept alone, anti-CD28 dAb alone, or anti-CD28 dAb plus clinically relevant maintenance (MMF, Steroids) and induction therapy with either anti-IL-2R or T cell depletion. Treatment with anti-CD28 dAb extended survival compared to belatacept monotherapy (MST 187 vs. 29 days, p=0.07). The combination of anti-CD28 dAb and conventional immunosuppression further prolonged survival to MST ∼270 days. Animals maintained protective immunity with no significant infectious issues. These data demonstrate CD28-directed therapy is a safe and effective next-generation costimulatory blockade strategy with a demonstrated survival benefit and presumed advantage over belatacept by maintaining intact CTLA-4 coinhibitory signaling.

Progress in kidney transplantation: The role for systems immunology

The development of systems biology represents an immense breakthrough in our ability to perform translational research and deliver personalized and precision medicine. A multidisciplinary approach in combination with use of novel techniques allows for the extraction and analysis of vast quantities of data even from the volume and source limited samples that can be obtained from human subjects. Continued advances in microfluidics, scalability and affordability of sequencing technologies, and development of data analysis tools have made the application of a multi-omics, or systems, approach more accessible for use outside of specialized centers. The study of alloimmune and protective immune responses after solid organ transplant offers innumerable opportunities for a multi-omics approach, however, transplant immunology labs are only just beginning to adopt the systems methodology. In this review, we focus on advances in biological techniques and how they are improving our understanding of the immune system and its interactions, highlighting potential applications in transplant immunology. First, we describe the techniques that are available, with emphasis on major advances that allow for increased scalability. Then, we review initial applications in the field of transplantation with a focus on topics that are nearing clinical integration. Finally, we examine major barriers to adapting these methods and discuss potential future developments.

81. Impact of Early Post-Transplant Multidrug-Resistant Organism Detection Among Renal Transplant Recipients, 2005–2021

Background

Understanding the impact of multi-drug resistant organism (MDRO) acquisition on renal transplant recipients (RTR) mortality and allograft function is paramount to mitigating deleterious outcomes. Prior studies have been limited by lack of control groups and sample sizes. We aimed to the assess whether the detection of an MDRO or a susceptible organism during the early post-transplant period was associated with increased mortality and allograft failure among RTRs.

Methods

We performed a retrospective cohort study of RTRs at the Emory University Transplant Center between 2005–2022. Early post-transplant culture positivity was defined as a positive culture within 30 days of renal transplant. The primary outcome was a combined composite of one year- allograft loss and/or mortality following renal transplant. A Kaplan–Meier survival analysis was performed, and differences between survival curves for RTRs with an early post-transplant positive culture (stratified by susceptibility status) and negative control RTRs were assessed using the log-rank test. Multivariable cox proportional hazard and a competing risk analysis were performed.

Results

Among 3,233 RTRs, 259 (8%) had a susceptible organism detected and 35 (1%) had an MDRO detected (Figure 1). Demographic and microbiology characteristics are summarized in Table 1 & 2. One hundred and forty-nine (5%) RTRs experienced the composite outcome, this was experienced more frequently among RTRs with an MDRO detected (14%, 5/35) compared to RTRs with a susceptible organism defected (8%, 21/259) and negative controls (4%, 123/2,939) (Table 3). Significant difference between time from transplantation to the composite outcome when comparing negative controls, MDRO and susceptible organisms RTRs was observed (log rank p < 0.001) (Figure 2). Early post-transplant culture positivity (aHR 1.98 [1.30, 3.04]) and MDRO detection (aHR: 3.20 [1.30, 7.84]) were significantly associated with the composite outcome (Table 4).

Conclusion

MDRO as well as susceptible organism acquisition during the early post-transplant period was associated with increased mortality and allograft loss highlighting the need for increased infection prevention efforts within this vulnerable population.

Disclosures

All Authors: No reported disclosures.

Impact of belatacept and tacrolimus on cytomegalovirus viral load control and relapse in moderate and high-risk cytomegalovirus serostatus kidney transplant recipients

BACKGROUND

Belatacept improves long-term graft survival, but control of some primary viral infections may be impaired. We evaluated the impact of belatacept and tacrolimus on cytomegalovirus (CMV) viral control, remission and relapse in CMV high-risk and moderate-risk recipients.

METHODS

Using a multistate Markov model, we evaluated viral load state transitions of 173 kidney transplant recipients with at least one episode of viremia within 1 year after transplant: state 1, undetectable/low viral load; state 2, moderate viremia; and state 3, severe viremia.

RESULTS

Among high-risk recipients, belatacept-treated recipients exhibited a significantly higher probability of entering moderate viremia (.36; 95% CI = .31, .41) than tacrolimus-treated recipients (.20; 95% CI = .13, .29). The expected number of days in viremic states differed. High-risk belatacept-treated recipients persisted in moderate viremia for significantly longer (128 days, 95% CI = 110, 146) than did tacrolimus-treated recipients (70.0 days, 95% CI = 45.2, 100) and showed a trend of shorter duration in low/undetectable viral load state (172 days, 95% CI = 148, 195) than did tacrolimus-treated recipients (239 days, 95% CI = 195, 277). Moderate-risk recipients showed better viral load control and with no differences by immunosuppression.

CONCLUSION

High-risk belatacept-treated recipients showed defects in sustaining viral control relative to tacrolimus-treated recipients. Avoidance of initial use belatacept in high-risk recipients or development of modified management protocols should be considered.

SARS-CoV-2 coinfections with variant genomic lineages identified by multiplex fragment analysis

Immunocompromised patients can experience prolonged SARS-CoV-2 infections in the setting of a lack of protectivity immunity despite vaccination. As circulating SARS-CoV-2 strains become more heterogeneous, concomitant infection with multiple SARS-CoV-2 variants has become an increasing concern. Immunocompromised patient populations represent potential reservoirs for the emergence of novel SARS-CoV-2 variants through mutagenic change or coinfection followed by recombinatory events. Identification of SARS-CoV-2 coinfections is challenging using traditional next generation sequencing pipelines; however, targeted genotyping approaches can facilitate detection. Here we describe five COVID-19 cases caused by coinfection with different SARS-CoV-2 variants (Delta/Omicron BA.1 and Omicron BA.1/BA.2) as identified by multiplex fragment analysis.

Targeting inflammation and immune activation to improve CTLA4-Ig-based modulation of transplant rejection

For the last few decades, Calcineurin inhibitors (CNI)-based therapy has been the pillar of immunosuppression for prevention of organ transplant rejection. However, despite exerting effective control of acute rejection in the first year post-transplant, prolonged CNI use is associated with significant side effects and is not well suited for long term allograft survival. The implementation of Costimulation Blockade (CoB) therapies, based on the interruption of T cell costimulatory signals as strategy to control allo-responses, has proven potential for better management of transplant recipients compared to CNI-based therapies. The use of the biologic cytotoxic T-lymphocyte associated protein 4 (CTLA4)-Ig is the most successful approach to date in this arena. Following evaluation of the BENEFIT trials, Belatacept, a high-affinity version of CTLA4-Ig, has been FDA approved for use in kidney transplant recipients. Despite its benefits, the use of CTLA4-Ig as a monotherapy has proved to be insufficient to induce long-term allograft acceptance in several settings. Multiple studies have demonstrated that events that induce an acute inflammatory response with the consequent release of proinflammatory cytokines, and an abundance of allograft-reactive memory cells in the recipient, can prevent the induction of or break established immunomodulation induced with CoB regimens. This review highlights advances in our understanding of the factors and mechanisms that limit CoB regimens efficacy. We also discuss recent successes in experimentally designing complementary therapies that favor CTLA4-Ig effect, affording a better control of transplant rejection and supporting their clinical applicability.

hlaR: A rapid and reproducible tool to identify eplet mismatches between transplant donors and recipients

Eplet mismatch load, both overall and at the single molecule level, correlates with transplant recipient outcomes. However, precise eplet assessment requires high-resolution HLA typing of both the donor and recipient. Anything less than high-resolution typing requires imputation of HLA types. The currently available methods to identify eplet mismatch are both tedious and demanding. Therefore, we developed a software package and user-friendly web application (hlaR), that simplifies the workflow of eplet analysis, provides functions to impute high-resolution from low-resolution data and calculates both overall and single molecule eplet mismatch for single or multiple donor recipient pairs. Compared to manual assessments using currently available tools (namely, HLAMatchMaker), hlaR resulted in only minimal discrepancy in eplet mismatches (mean absolute difference of 0.56 for class I and 0.86 for class II for unique sum across loci). Additionally, output of the single molecule eplet function compared well to manual calculation, with an average single antigen count increase of 0.19. Importantly, the hlaR tool permits rapid and reproducible imputation and eplet mismatch including comparison between eplet reference tables (e.g. HLAMatchMaker version 2 or 3). Users can import data from a spreadsheet rather than relying on keystroke entry of individual donor and recipient data, thus reducing the risk of data entry errors. The resulting improved scalability of the hlaR tool is highlighted by plotting analysis time against the size of the input dataset. The new hlaR tool can provide eplet mismatch data with a streamlined workflow. With decreased effort from the end user, eplet matching and mismatch load data can be further incorporated into both research and clinical use.

Fecal Microbiota Transplantation Donor Screening Updates and Research Gaps for Solid Organ Transplant Recipients

In this review, we discuss stool donor screening considerations to mitigate potential risks of pathogen transmission through fecal microbiota transplant (FMT) in solid organ transplant (SOT) recipients. SOT recipients have a higher risk for Clostridioides difficile infection (CDI) and are more likely to have severe CDI. FMT has been shown to be a valuable tool in the treatment of recurrent CDI (RCDI); however, guidelines for screening for opportunistic infections transmitted through FMT are underdeveloped. We review reported adverse effects of FMT as they pertain to an immunocompromised population and discuss the current understanding and recommendations for screening found in the literature while noting gaps in research. We conclude that while FMT is being performed in the SOT population, typically with positive results, there remain many unanswered questions which may have major safety implications and warrant further study.

Temporal trends and current use of de novo belatacept in kidney transplant recipients in the United States

The adoption of de novo belatacept in kidney transplant (kTx) recipients was hampered by an increased risk of acute cellular rejection (ACR) with variation in adopted belatacept based immunosuppressive therapies across centers. We used data from the Scientific Registry of Transplant Recipients (SRTR) to evaluate the temporal trends in belatacept use and describe the associated induction and maintenance regimens in US adult kTx recipients transplanted between June 2011 and December 2018. The number of patients receiving de novo-belatacept based immunosuppressive therapy increased from .74% in 2011 to 3.11% in 2016. In 2016, 66/207 centers used de novo belatacept-based regimen with 3.03% using it in over 50% of their patients. The use of T-cell depleting agents increased with time. Since 2012, the rate of calcineurin inhibitor (CNI) use in combination with belatacept remained stable around 50% and ∼30% remained under belatacept/CNI combination at 1-year post-transplantation. The adoption of belatacept as de novo immunosuppressive regimen has been slow and its use remains low in the United States. Various regimens have been used to modulate the risk of ACR. Further studies evaluating the long-term outcomes of these regimens and assessing their safety especially with regard to the risk of infection are needed.

Every 2-month belatacept maintenance therapy in kidney transplant recipients greater than 1-year posttransplant: A randomized, noninferiority trial

Belatacept results in improved kidney transplant outcomes, but utilization has been limited by logistical barriers related to monthly (q1m) intravenous infusions. Every 2-month (q2m) belatacept has potential to increase utilization, therefore we conducted a randomized noninferiority trial in low immunologic risk renal transplant recipients greater than 1-year posttransplant. Patients on belatacept were randomly assigned to q1m or q2m therapy. The primary objective was a noninferiority comparison of renal function (eGFR) at 12 months with a noninferiority margin (NIM) of 6.0 ml/min/1.73 m² . One hundred and sixty-six participants were randomized to q1m (n = 82) or q2m (n = 84) belatacept, 163 patients received treatment, and 76 q1m and 77 q2m subjects completed the 12-month study period. Every 2-month belatacept was noninferior to q1m, as the difference in mean eGFR adjusted for baseline renal function did not exceed the NIM. Two-month dosing was safe and well tolerated, with no patient deaths or graft losses. Four rejection episodes and three cases of donor-specific antibodies (DSAs) occurred among q2m subjects; however, only one rejection and one instance of DSA were observed in subjects adherent to the study protocol. Every 2-month belatacept therapy may facilitate long-term utilization of costimulation blockade, but future multicenter studies with long-term follow-up will further elucidate immunologic risk. (ClinicalTrials.gov NCT02560558).

A Roadmap for Innovation to Advance Transplant Access and Outcomes: A Position Statement From the National Kidney Foundation

Over the past 65 years, kidney transplantation has evolved into the optimal treatment for patients with kidney failure, dramatically reducing suffering through improved survival and quality of life. However, access to transplant is still limited by organ supply, opportunities for transplant are inequitably distributed, and lifelong transplant survival remains elusive. To address these persistent needs, the National Kidney Foundation convened an expert panel to define an agenda for future research. The key priorities identified by the panel center on the needs to develop and evaluate strategies to expand living donation, improve waitlist management and transplant readiness, maximize use of available deceased donor organs, and extend allograft longevity. Strategies targeting the critical goal of decreasing organ discard that warrant research investment include educating patients and clinicians about potential benefits of accepting nonstandard organs, use of novel organ assessment technologies and real-time decision support, and approaches to preserve and resuscitate allografts before implantation. The development of personalized strategies to reduce the burden of lifelong immunosuppression and support "one transplant for life" was also identified as a vital priority. The panel noted the specific goal of improving transplant access and graft survival for children with kidney failure. This ambitious agenda will focus research investment to promote greater equity and efficiency in access to transplantation, and help sustain long-term benefits of the gift of life for more patients in need.

Implications of defective immune responses in SARS-CoV-2 vaccinated organ transplant recipients

Organ transplant patients have poor immune responses to COVID-19 vaccines; thus designing vaccine strategies to protect this vulnerable population from SARS-CoV-2 infection is crucial.

Optimization of de novo belatacept-based immunosuppression administered to renal transplant recipients

Kidney transplant recipients administered belatacept-based maintenance immunosuppression present with a more favorable metabolic profile, reduced incidence of de novo donor-specific antibodies (DSAs), and improved renal function and long-term patient/graft survival relative to individuals receiving calcineurin inhibitor (CNI)-based immunosuppression. However, the rates and severity of acute rejection (AR) are greater with the approved belatacept-based regimen than with CNI-based immunosuppression. Although these early co-stimulation blockade-resistant rejections are typically steroid sensitive, the higher rate of cellular AR has led many transplant centers to adopt immunosuppressive regimens that differ from the approved label. This article summarizes the available data on these alternative de novo belatacept-based maintenance regimens. Steroid-sparing, belatacept-based immunosuppression (following T cell-depleting induction therapy) has been shown to yield AR rates comparable to those seen with CNI-based regimens. Concomitant treatment with belatacept plus a mammalian target of rapamycin inhibitor (mTORi; sirolimus or everolimus) has yielded AR rates ranging from 0 to 4%. Because the optimal induction agent and number of induction doses; blood levels of mTORi; and dose, duration, and use of corticosteroids have yet to be determined, larger prospective clinical trials are needed to establish the optimal alternative belatacept-based regimen for minimizing early cellular AR occurrence.

CMV Status Drives Distinct Trajectories of CD4+ T Cell Differentiation

Cytomegalovirus (CMV) is one of the most commonly recognized opportunistic pathogens and remains the most influential known parameter in shaping an individual's immune system. As such, T cells induced by CMV infection could have a long-term impact on subsequent immune responses. Accumulating evidence indicates that memory T cells developed during past bacterial and viral infection can cross-react with unrelated pathogens, including transplant antigens, and can alter responses to de novo infections, vaccines, cancers, or rejection. Therefore, careful examination of T cell responses elicited by CMV is warranted to understand their potentially beneficial or harmful roles in future major immune events. Our detailed exploration of the distribution, phenotype, TCR repertoire and transcriptome of CD4+ T cells within CMV seropositive healthy individuals using high-dimensional flow cytometry and single cell multi-omics sequencing reveals that CMV seropositivity has highly significant age-independent effects, leading to a reduction in CD4+ naïve T cells and an expansion of CD4+ effector memory T cells and CD45RA+ effector memory T cells. These induced CD4+ effector memory T cells undergo a specific differentiation trajectory resulting in a subpopulation of CD57+CD27-CD28-CD244+ CD4+ T cells with cytotoxic function and TCR oligoclonality for optimal controlled coexistence with cytomegalovirus. Through gene set enrichment analysis, we found that this subpopulation is similar to virus-specific CD8+ T cells and T cells that mediate acute rejection in patients using tacrolimus and belatacept, a selective costimulation blocker. Together, these data suggest that memory CD4+ T cells induced by cytomegalovirus are formed via a distinct differentiation program to acquire cytotoxic function and can be potentially detrimental to transplant patients adopting costimulation blockade immunosuppressive regimen.

Phase 3 trial of human islet-after-kidney transplantation in type 1 diabetes

Allogeneic islet transplant offers a minimally invasive option for β cell replacement in the treatment of type 1 diabetes (T1D). The CIT consortium trial of purified human pancreatic islets (PHPI) in patients with T1D after kidney transplant (CIT06), a National Institutes of Health-sponsored phase 3, prospective, open-label, single-arm pivotal trial of PHPI, was conducted in 24 patients with impaired awareness of hypoglycemia while receiving intensive insulin therapy. PHPI were manufactured using standardized processes. PHPI transplantation was effective with 62.5% of patients achieving the primary endpoint of freedom from severe hypoglycemic events and HbA_1c  ≤ 6.5% or reduced by ≥ 1 percentage point at 1 year posttransplant. Median HbA_1c declined from 8.1% before to 6.0% at 1 year and 6.3% at 2 and 3 years following transplant (P < .001 for all vs baseline), with related improvements in hypoglycemia awareness and glucose variability. The improved metabolic control was associated with better health-related and diabetes-related quality of life. The procedure was safe and kidney allograft function remained stable after 3 years. These results add to evidence establishing allogeneic islet transplant as a safe and effective treatment for patients with T1D and unstable glucose control despite intensive insulin treatment, supporting the indication for PHPI in the post-renal transplant setting.

CMV high-risk status and posttransplant outcomes in kidney transplant recipients treated with belatacept

INTRODUCTION

Cytomegalovirus (CMV) remains associated with poor outcomes after kidney transplantation (kTx). The impact of belatacept on CMV infection remains understudied. In this study, we assessed the impact of belatacept on patient and graft survivals.

METHODS

CMV seronegative kTx recipients were included. Patient and graft survival were studied using Kaplan-Meier method, log-rank test. Cox models were used to compare outcomes by CMV risk and immunosuppressive regimen. Incidence and persistence of CMV viremia under belatacept vs tacrolimus were compared.

RESULTS

Among 308 CMV seronegative recipients, 168 CMV high-risk and 203 belatacept-treated patients were included. High-risk CMV status was associated with lower patient survival and graft survival. Among the CMV high-risk group, patients treated with belatacept presented a higher incidence of CMV viremia, a higher rate of first-line treatment failure and a longer time to virus clearance. They had a nonsignificant trend toward a lower graft survival.

CONCLUSION

Belatacept-based maintenance immunosuppression is associated with an increased risk of CMV primary-infection and a prolonged course of viral replication in CMV high-risk patients. Further studies are needed to confirm the nonsignificant trend towards a lower graft survival in CMV high-risk patients treated with belatacept and whether it is explained by the higher risk of CMV reactivation and infection.

Avoidance of CNI and steroids using belatacept-Results of the Clinical Trials in Organ Transplantation 16 trial

Immunosuppression devoid of corticosteroids has been investigated to avoid long-term comorbidities. Likewise, alternatives to calcineurin inhibitors have been investigated as a strategy to improve long-term kidney function following transplanion. Costimulatory blockade strategies that include corticosteroids have recently shown promise, despite their higher rates of early acute rejection. We designed a randomized clinical trial utilizing depletional induction therapy to mitigate early rejection risk while limiting calcineurin inhibitors and corticosteroids. This trial, Clinical Trials in Organ Transplantation 16 (CTOT-16), sought to evaluate novel belatacept-based strategies employing tacrolimus and corticosteroid avoidance. Sixty-nine kidney transplant recipients were randomized from 4 US transplant centers comparing a control group of with rabbit antithymocyte globulin (rATG) induction, rapid steroid taper, and maintenance mycophenolate and tacrolimus, to 2 arms using maintenance belatacept. There were no graft losses but there were 2 deaths in the control group. However, the trial was halted early because of rejection in the belatacept treatment groups. Serious adverse events were similar across groups. Although rejection was not uniform in the belatacept maintenance therapy groups, the frequency of rejection limits the practical implementation of this strategy to avoid both calcineurin inhibitors and corticosteroids at this time.

The impact of belatacept on third-party HLA alloantibodies in highly sensitized kidney transplant recipients

Recent evidence suggests that belatacept reduces the durability of preexisting antibodies to class I and class II human leukocyte antigens (HLAs). In this case series of 163 highly sensitized kidney transplant candidates whose calculated panel-reactive antibody (cPRA) activity was ≥98% to 100%, the impact of belatacept on preexisting HLA antibodies was assessed. Of the 163 candidates, 72 underwent transplantation between December 4, 2014 and April 15, 2017; 60 of these transplanted patients remained on belatacept consecutively for at least 6 months. We observed a decrease in the breadth and/or strength of HLA class I antibodies as assessed by FlowPRA in belatacept-treated patients compared to controls who did not receive belatacept. Specifically, significant HLA antibody reduction was evident for class I (P < .0009). Posttransplant belatacept-treated patients also had a clinically significant reduction in their cPRA compared to controls (P < .01). Collectively, these findings suggest belatacept can reduce HLA class I antibodies in a significant proportion of highly sensitized recipients and could be an option to improve pretransplant compatibility with organ donors.

Belatacept and CD28 Costimulation Blockade: Preventing and Reducing Alloantibodies over the Long Term

Purpose of Review

Highlight developments in T and B cell biology that are helping elucidate the mechanisms underlying CD28 pathway blockade-mediated inhibition of alloantibodies in transplantation, and discuss recent clinical observations on the impact of belatacept on de novo and established HLA antibodies.

Recent Findings

The identification of T follicular helper cells as the CD4+ T cell subset required for optimal humoral immunity, along with newly identified roles for CD28 and the B7 molecules on B cell lineage cells has begun to pave the way for improved understanding and discovery of the mechanisms of CD28 costimulation blockade-mediated antibody inhibition. There has been resurgent clinical interest in the ability of belatacept to attenuate alloantibody responses. New reports have continued to document its ability to prevent de novo antibody responses, and more recent studies have surfaced exploring its potential to control nascent or pre-existing HLA antibodies.

Summary

A growing understanding of the mechanisms of anti-CD28-mediated alloantibody inhibition and continued clinical successes will guide the clinical optimization of belatacept and next generation CD28 blockers to prevent and reduce alloantibodies over the long-term.

Abatacept as rescue immunosuppression after calcineurin inhibitor treatment failure in renal transplantation

A majority of kidney transplant recipients receive calcineurin inhibitor-based immunosuppression. However, some do not tolerate calcineurin inhibitors and require other immunosuppressive strategies. Until recently, alternative approaches have been associated with inferior outcomes, but recent methods have effectively utilized belatacept in calcineurin inhibitor-intolerant patients. Though promising, belatacept uptake has been limited by higher acute rejection rates, unavailability due to production shortages, and logistical challenges as a result of intravenous infusion requirements. Interestingly, its predecessor abatacept is clinically available in subcutaneous formulation to treat autoimmune disorders but has not been used in clinical transplantation. Here we report on a series of 9 calcineurin inhibitor-intolerant transplant recipients converted to abatacept early after transplant as rescue immunosuppression during periods of belatacept unavailability. Retrospective review revealed successful allograft salvage and 100% patient and graft survival (median 115 months) after conversion to abatacept. Patients received abatacept for a median duration of 82 months with stable, long-term renal allograft function, a single cellular rejection episode, and no clinically apparent protective immunity concerns. Hence our findings suggest that future clinical studies utilizing abatacept either de novo or as conversion therapy in transplant recipients should be considered.

Long-term survival of pig-to-rhesus macaque renal xenografts is dependent on CD4 T cell depletion

The shortage of available organs remains the greatest barrier to expanding access to transplant. Despite advances in genetic editing and immunosuppression, survival in experimental models of kidney xenotransplant has generally been limited to <100 days. We found that pretransplant selection of recipients with low titers of anti-pig antibodies significantly improved survival in a pig-to-rhesus macaque kidney transplant model (6 days vs median survival time 235 days). Immunosuppression included transient pan-T cell depletion and an anti-CD154-based maintenance regimen. Selective depletion of CD4⁺ T cells but not CD8⁺ T cells resulted in long-term survival (median survival time >400 days vs 6 days). These studies suggested that CD4⁺ T cells may have a more prominent role in xenograft rejection compared with CD8⁺ T cells. Although animals that received selective depletion of CD8⁺ T cells showed signs of early cellular rejection (marked CD4⁺ infiltrates), animals receiving selective CD4⁺ depletion exhibited normal biopsy results until late, when signs of chronic antibody rejection were present. In vitro study results suggested that rhesus CD4⁺ T cells required the presence of SLA class II to mount an effective proliferative response. The combination of low pretransplant anti-pig antibody and CD4 depletion resulted in consistent, long-term xenograft survival.

Corticosteroids and methotrexate as adjuvants to costimulation blockade in non-human primate renal transplantation

Belatacept, the CD28-B7 costimulation pathway inhibitor, has been approved as a calcineurin inhibitor (CNI) alternative in kidney transplantation. Although costimulation blockade (CoB) allows for CNI avoidance, it is associated with increased rates of early rejection, prompting a search for agents to pair with belatacept. Methotrexate (MTX) is an antimetabolite that has been found to be complimentary with abatacept, a lower affinity CD28-B7-specific analogue of belatacept, in the treatment of rheumatoid arthritis (RA). We examined whether this synergy would extend to prevention of kidney allograft rejection. Rhesus macaques underwent kidney transplantation treated with abatacept maintenance therapy with either a steroid taper, MTX, or both. The combination of abatacept maintenance with steroids prolonged graft survival compared to untreated historical controls and previous reports of abatacept monotherapy. The addition of MTX did not provide additional benefit. These data demonstrate that abatacept with adjuvant therapy may delay the onset of acute rejection, but fail to show synergy between abatacept and MTX beyond that of steroids. These findings indicate that MTX is unlikely to be a suitable adjuvant to CoB in kidney transplantation, but also suggest that with further modification, a CoB regimen used for advanced RA may suffice for RA patients requiring kidney transplantation.

CD122 signaling in CD8+ memory T cells drives costimulation-independent rejection

Interrupting T cell costimulatory signals as a strategy to control undesired immune responses, such as occur in autoimmunity or transplantation, has the potential to alleviate many of the unwanted side effects associated with current immunosuppressive therapies. Belatacept, a high-affinity version of CTLA4-Ig that blocks ligand ligation to CD28, has been approved for use in kidney transplant recipients. Despite the long-term benefits associated with its use, such as improved renal function and lower cardiovascular risk, a subset of patients treated with belatacept experience elevated rates of acute T cell-mediated rejection, tempering enthusiasm for its use. Here we demonstrate that costimulation-independent T cell alloreactivity relies on signaling through CD122, the shared IL-2 and IL-15 receptor β-chain. Combined costimulatory and CD122 blockade improved survival of transplanted tissue in mice and nonhuman primates by controlling proliferation and effector function of CD8+ T cells. The high-affinity IL-2 receptor was dispensable for memory CD8+ T cell responses, whereas signaling through CD122 as a component of the high-affinity IL-15 receptor was critical for costimulation-independent memory CD8+ T cell recall, distinguishing specific roles for IL-2 and IL-15 in T cell activation. These studies outline a novel approach for clinical optimization of costimulatory blockade strategies in transplantation by targeting CD122.

Effect of the iChoose Kidney decision aid in improving knowledge about treatment options among transplant candidates: A randomized controlled trial

We previously developed a mobile- and web-based decision aid (iChoose Kidney) that displays individualized risk estimates of survival and mortality, for the treatment modalities of dialysis versus kidney transplantation. We examined the effect of iChoose Kidney on change in transplant knowledge and access to transplant in a randomized controlled trial among patients presenting for evaluation in three transplant centers. A total of 470 patients were randomized to standard transplantation education (control) or standard education plus iChoose Kidney (intervention). Change in transplant knowledge (primary outcome) among intervention versus control patients was assessed using nine items in pre- and postevaluation surveys. Access to transplant (secondary outcome) was defined as a composite of waitlisting, living donor inquiries, or transplantation. Among 443 patients (n = 226 intervention; n = 216 control), the mean knowledge scores were 5.1 ± 2.1 pre- and 5.8 ± 1.9 postevaluation. Change in knowledge was greater among intervention (1.1 ± 2.0) versus control (0.4 ± 1.8) patients (P < .0001). Access to transplantation was similar among intervention (n = 168; 74.3%) versus control patients (n = 153; 70.5%; P = .37). The iChoose Kidney decision aid improved patient knowledge at evaluation, but did not impact transplant access. Future studies should examine whether combining iChoose Kidney with other interventions can increase transplantation. (Clinicaltrials.gov NCT02235571).

Transplant Center Patient Navigator and Access to Transplantation among High-Risk Population: A Randomized, Controlled Trial

BACKGROUND AND OBJECTIVES

Barriers exist in access to kidney transplantation, where minority and patients with low socioeconomic status are less likely to complete transplant evaluation. The purpose of this study was to examine the effectiveness of a transplant center-based patient navigator in helping patients at high risk of dropping out of the transplant evaluation process access the kidney transplant waiting list.

DESIGN, SETTING, PARTICIPANTS & MEASUREMENTS

We conducted a randomized, controlled trial of 401 patients (n=196 intervention and n=205 control) referred for kidney transplant evaluation (January 2013 to August 2014; followed through May 2016) at a single center. A trained navigator assisted intervention participants from referral to waitlisting decision to increase waitlisting (primary outcome) and decrease time from referral to waitlisting (secondary outcome). Time-dependent Cox proportional hazards models were used to determine differences in waitlisting between intervention and control patients.

RESULTS

At study end, waitlisting was not significantly different among intervention (32%) versus control (26%) patients overall (P=0.17), and time from referral to waitlisting was 126 days longer for intervention patients. However, the effectiveness of the navigator varied from early (<500 days from referral) to late (≥500 days) follow-up. Although no difference in waitlisting was observed among intervention (50%) versus control (50%) patients in the early period (hazard ratio, 1.03; 95% confidence interval, 0.69 to 1.53), intervention patients were 3.3 times more likely to be waitlisted after 500 days (75% versus 25%; hazard ratio, 3.31; 95% confidence interval, 1.20 to 9.12). There were no significant differences in intervention versus control patients who started evaluation (85% versus 79%; P=0.11) or completed evaluation (58% versus 51%; P=0.14); however, intervention patients had more living donor inquiries (18% versus 10%; P=0.03).

CONCLUSIONS

A transplant center-based navigator targeting disadvantaged patients improved waitlisting but not until after 500 days of follow-up. However, the absolute effect was relatively small.

Emergency department use among kidney transplant recipients in the United States

Patients with end-stage renal disease use the emergency department (ED) at a 6-fold higher rate than do other US adults. No national studies have described ED use rates among kidney transplant (KTx) recipients, and the factors associated with higher ED use. We examined a cohort of 132 725 adult KTx recipients in the United States Renal Data System (2005-2013). Data on ED visits, hospitalization, and outpatient nephrology visits were obtained from Medicare claims databases. Nearly half (46.1%) of KTx recipients had at least one ED visit (1.61 ED visits/patient-year [PY]), and 39.7% of ED visits resulted in hospitalization in the first year posttransplantation. ED visit rate was high in the first 30 days (5.26 visits/PY) but declined substantially thereafter (1.81 visits/PY in months 1-3; 1.13 visits/PY in months 3-12 posttransplantation). ED visit rates were higher in the first 30 days versus rates for dialysis patients but less than half the rate thereafter. Female sex, public insurance, medical comorbidities, longer pretransplantation dialysis vintage, and delayed graft function were associated with higher ED use in the first year post-KTx. Policies and strategies addressing potentially preventable ED visits should be promoted to help improve patient care and increase efficient use of ED resources.

Outcomes at 7 years post-transplant in black vs nonblack kidney transplant recipients administered belatacept or cyclosporine in BENEFIT and BENEFIT-EXT

Clinical outcomes are generally worse for black vs nonblack renal allograft recipients. In BENEFIT and BENEFIT-EXT, recipients were randomized to belatacept more intense-based, belatacept less intense-based, or cyclosporine-based immunosuppression. At year 7, belatacept was associated with superior graft survival vs cyclosporine in BENEFIT (recipients of living or standard criteria deceased donor kidneys); belatacept was associated with similar graft survival vs cyclosporine in BENEFIT-EXT (recipients of extended criteria donor kidneys). In both studies, renal function was superior for belatacept-treated vs cyclosporine-treated patients. Seven-year outcomes were examined by race post hoc in each study. The effect of race and treatment on time to death or graft loss was compared using Cox regression. The interaction between treatment and race was also considered. Glomerular filtration rate (GFR) was estimated from months 1 to 84 using a repeated-measures model. In total, 8.3% (55/666) and 13.1% (71/543) of patients in BENEFIT and BENEFIT-EXT, respectively, were black. Time to death or graft loss was similar in blacks and nonblacks. For both subgroups, estimated mean GFR increased over 7 years for belatacept, but declined for cyclosporine. Outcomes were similar in belatacept-treated black and nonblack patients. Due to the small number of black patients, these results must be interpreted with caution.

Belatacept Combined With Transient Calcineurin Inhibitor Therapy Prevents Rejection and Promotes Improved Long-Term Renal Allograft Function

Belatacept, a T cell costimulation blocker, demonstrated superior renal function, lower cardiovascular risk, and improved graft and patient survival in renal transplant recipients. Despite the potential benefits, adoption of belatacept has been limited in part due to concerns regarding higher rates and grades of acute rejection in clinical trials. Since July 2011, we have utilized belatacept-based immunosuppression regimens in clinical practice. In this retrospective analysis of 745 patients undergoing renal transplantation at our center, we compared patients treated with belatacept (n = 535) with a historical cohort receiving a tacrolimus-based protocol (n = 205). Patient and graft survival were equivalent for all groups. An increased rate of acute rejection was observed in an initial cohort treated with a protocol similar to the low-intensity regimen from the BENEFIT trial versus the historical tacrolimus group (50.5% vs. 20.5%). The addition of a transient course of tacrolimus reduced rejection rates to acceptable levels (16%). Treatment with belatacept was associated with superior estimated GFR (belatacept 63.8 mL/min vs. tacrolimus 46.2 mL/min at 4 years, p < 0.0001). There were no differences in serious infections including rates of cytomegalovirus or BK viremia. We describe the development of a costimulatory blockade-based strategy that ultimately allows renal transplant recipients to achieve calcineurin inhibitor-free immunosuppression.

Lessons Learned: Early Termination of a Randomized Trial of Calcineurin Inhibitor and Corticosteroid Avoidance Using Belatacept

The intent of this National Institutes of Health-sponsored study was to compare a belatacept-based immunosuppressive regimen with a maintenance regimen of tacrolimus and mycophenolate. Nineteen primary, Epstein-Barr virus-immune renal transplant recipients with a negative cross-match were randomized to one of three groups. All patient groups received perioperative steroids and maintenance mycophenolate mofetil. Patients in groups 1 and 2 were induced with alemtuzumab and maintained on tacrolimus or belatacept, respectively. Patients in group 3 were induced with basiliximab, received 3 mo of tacrolimus, and maintained on belatacept. There was one death with a functioning allograft due to endocarditis (group 1). There were three graft losses due to vascular thrombosis (all group 2) and one graft loss due to glomerular disease (group 1). Biopsy-proven acute cellular rejection was more frequent in the belatacept-treated groups, with 10 treated episodes in seven participants compared with one episode in group 1; however, estimated GFR was similar between groups at week 52. There were no episodes of posttransplant lymphoproliferative disorder or opportunistic infections in any group. Protocol enrollment was halted prematurely because of a high rate of serious adverse events. Such negative outcomes pose challenges to clinical investigators, who ultimately must weigh the risks and benefits in randomized trials.

Belatacept-Resistant Rejection Is Associated With CD28+ Memory CD8 T Cells

Recently, newer therapies have been designed to more specifically target rejection in an effort to improve efficacy and limit unwanted toxicity. Belatacept, a CD28-CD80/86 specific reagent, is associated with superior patient survival and graft function compared with traditional therapy, but its adoption as a mainstay immunosuppressive therapy has been tempered by increased rejection rates. It is essential that the underlying mechanisms associated with this rejection be elucidated before belatacept is more widely used. To that end, we designed a study in a nonhuman primate kidney transplant model where animals were treated with either a belatacept- or a tacrolimus-based immunosuppressive regimen. Interestingly, we found that elevated pretransplant frequencies of CD28⁺ CD8⁺ T_EMRA cells are associated with rejection on belatacept but not tacrolimus treatment. Further analysis showed that the CD28⁺ CD8⁺ T_EMRA cells rapidly lose CD28 expression after transplant in those animals that go on to reject with the allograft infiltrate being predominantly CD28^- . These data suggest that CD28⁺ memory T cells may be resistant to belatacept, capable of further differentiation including loss of CD28 expression while maintaining effector function. The unique signaling requirements of CD28⁺ memory T cells provide opportunities for the development of targeted therapies, which may synergize with belatacept to prevent costimulation-independent rejection.

Increased Pretransplant Frequency of CD28+ CD4+ TEM Predicts Belatacept-Resistant Rejection in Human Renal Transplant Recipients

While most human T cells express the CD28 costimulatory molecule constitutively, it is well known that age, inflammation, and viral infection can drive the generation of CD28^null T cells. In vitro studies have demonstrated that CD28^null cell effector function is not impacted by the presence of the CD28 costimulation blocker belatacept. As such, a prevailing hypothesis suggests that CD28^null cells may precipitate costimulation blockade-resistant rejection. However, CD28⁺ cells possess more proliferative and multifunctional capacity, factors that may increase their ability to successfully mediate rejection. Here, we performed a retrospective immunophenotypic analysis of adult renal transplant recipients who experienced acute rejection on belatacept treatment as compared to those who did not. Intriguingly, our findings suggest that patients possessing higher frequency of CD28⁺ CD4⁺ T_EM prior to transplant were more likely to experience acute rejection following treatment with a belatacept-based immunosuppressive regimen. Mechanistically, CD28⁺ CD4⁺ T_EM contained significantly more IL-2 producers. In contrast, CD28^null CD4⁺ T_EM isolated from stable belatacept-treated patients exhibited higher expression of the 2B4 coinhibitory molecule as compared to those isolated from patients who rejected. These data raise the possibility that pretransplant frequencies of CD28⁺ CD4⁺ T_EM could be used as a biomarker to predict risk of rejection following treatment with belatacept.

Costimulation Blockade in Autoimmunity and Transplantation: The CD28 Pathway

T cell activation is a complex process that requires multiple cell signaling pathways, including a primary recognition signal and additional costimulatory signals. TCR signaling in the absence of costimulatory signals can lead to an abortive attempt at activation and subsequent anergy. One of the best-characterized costimulatory pathways includes the Ig superfamily members CD28 and CTLA-4 and their ligands CD80 and CD86. The development of the fusion protein CTLA-4-Ig as an experimental and subsequent therapeutic tool is one of the major success stories in modern immunology. Abatacept and belatacept are clinically approved agents for the treatment of rheumatoid arthritis and renal transplantation, respectively. Future interventions may include selective CD28 blockade to block the costimulatory potential of CD28 while exploiting the coinhibitory effects of CTLA-4.

Fc-Silent Anti-CD154 Domain Antibody Effectively Prevents Nonhuman Primate Renal Allograft Rejection

The advent of costimulation blockade provides the prospect for targeted therapy with improved graft survival in transplant patients. Perhaps the most effective costimulation blockade in experimental models is the use of reagents to block the CD40/CD154 pathway. Unfortunately, successful clinical translation of anti-CD154 therapy has not been achieved. In an attempt to develop an agent that is as effective as previous CD154 blocking antibodies but lacks the risk of thromboembolism, we evaluated the efficacy and safety of a novel anti-human CD154 domain antibody (dAb, BMS-986004). The anti-CD154 dAb effectively blocked CD40-CD154 interactions but lacked crystallizable fragment (Fc) binding activity and resultant platelet activation. In a nonhuman primate kidney transplant model, anti-CD154 dAb was safe and efficacious, significantly prolonging allograft survival without evidence of thromboembolism (Median survival time 103 days). The combination of anti-CD154 dAb and conventional immunosuppression synergized to effectively control allograft rejection (Median survival time 397 days). Furthermore, anti-CD154 dAb treatment increased the frequency of CD4⁺ CD25⁺ Foxp3⁺ regulatory T cells. This study demonstrates that the use of a novel anti-CD154 dAb that lacks Fc binding activity is safe without evidence of thromboembolism and is equally as potent as previous anti-CD154 agents at prolonging renal allograft survival in a nonhuman primate preclinical model.

First-Year Waitlist Hospitalization and Subsequent Waitlist and Transplant Outcome

Frailty is associated with inferior survival and increased resource requirements among kidney transplant candidates, but assessments are time-intensive and costly and require direct patient interaction. Waitlist hospitalization may be a proxy for patient fitness and could help those at risk of poor outcomes. We examined United States Renal Data System data from 51 111 adult end-stage renal disease patients with continuous Medicare coverage who were waitlisted for transplant from January 2000 to December 2011. Heavily admitted patients had higher subsequent resource requirements, increased waitlist mortality and decreased likelihood of transplant (death after listing: 1-7 days: hazard ratio [HR] 1.24, 95% confidence interval [CI] 1.20-1.28; 8-14 days: HR 1.49, 95% CI 1.42-1.56; ≥15 days: HR 2.07, 95% CI 1.99-2.15; vs. 0 days). Graft and recipient survival was inferior, with higher admissions, although survival benefit was preserved. A model including waitlist admissions alone performed better (C statistic 0.76, 95% CI 0.74-0.80) in predicting postlisting mortality than estimated posttransplant survival (C statistic 0.69, 95% CI 0.67-0.73). Although those with a heavy burden of admissions may still benefit from kidney transplant, less utility is derived from allografts placed in this population. Current kidney allocation policy, which is based in part on longevity matching, could be significantly improved by consideration of hospitalization records of transplant candidates.

Interruption of OX40L signaling prevents costimulation blockade-resistant allograft rejection

The potential of costimulation blockade to serve as a novel transplant immunosuppression strategy has been explored for over 20 years, culminating in the recent clinical approval of belatacept for renal transplant patients. Despite improving long-term graft function and survival compared with calcineurin inhibitors, clinical acceptance of belatacept has been hindered by elevated rates of acute rejection. We examined the signaling pathways required to activate costimulation blockade-resistant alloreactive T cells and identified the OX40/OX40L secondary costimulatory pathway as a promising target. We next sought to improve the clinical efficacy of traditional costimulation blockade using belatacept by coupling it with anti-OX40L. Using a murine transplant model, we demonstrate that combined blockade enhances the suppression of alloreactive T cell proliferation and effector functions including both cytokine release and cytotoxic degranulation. We also show that anti-OX40L may be particularly useful in targeting alloreactive memory T cell responses that are relatively unaffected by traditional costimulation blockade regimens. Finally, we translated this therapy to a clinically relevant nonhuman primate renal transplant model, validating the efficacy of this regimen in a potentially novel steroid- and calcineurin inhibitor-free immunosuppression regimen.