Identification of Antibodies to DQβ:DRα Interisotypic Heterodimers in Human Sera

BACKGROUND

HLA class II antigens, DR, DQ, and DP, comprised an α and β chains, which typically combine, within the same isotype, to form the major histocompatibility complex:peptide complex. Interisotypic pairing is not commonly observed. Although reports of DQβ:DRα heterodimers exist, the pairing was reported to be unstable and, therefore, not studied to any extent.

METHODS

DQβ:DRα single antigens were produced through transfectant cell lines and used to identify and characterize positive reactive human sera by a multiplex bead-based assay.

RESULTS

Stable DQβ:DRα transfectants were constructed. Cell surface staining with class II-specific monoclonal antibodies revealed that some DQB1 alleles appear to be more efficient in expressing DQβ:DRα heterodimers. Interestingly, alleles within the same serological group varied in their efficiency of forming dimers on the cell surface. For example, DQβ0601:DRα had the highest transfection and cell membrane expression efficiency among 16 common DQB1 alleles tested. In contrast, DQβ0603:DRα-positive transfectants demonstrated minimal surface expression. Assembly of DQβ0601:DRα was not affected by the presence of a DQα chain. DQβ0601:DRα and DQβ0603:DRα single-antigen beads were used to screen human sera. Positive sera were identified that reacted to the unique epitopes of DQβ0601:DRα protein on the cell surface of the transfectants.

CONCLUSIONS

Our studies have demonstrated that unique DQβ:DRα heterodimers can be formed and are stably expressed on the cell surface. Such antigenic combinations, presented on single-antigen beads, demonstrated that patient sera can react with such heterodimers. Investigations on the potential clinical roles of antibodies against such interisotypic heterodimers are now possible.

Safety and efficacy of a reduced frequency viral monitoring strategy for Epstein-Barr virus, cytomegalovirus, and BK polyomavirus post-kidney transplant: A quality assurance initiative

BACKGROUND

There is variability in recommended viral monitoring protocols after kidney transplant. In response to increased demand for laboratory testing during the COVID-19 pandemic, the Transplant Manitoba Adult Kidney Program updated its monitoring protocols for cytomegalovirus (CMV), Epstein-Barr virus (EBV), and BK polyomavirus (BKV) to a reduced frequency.

METHODS

This single-center nested case-control study evaluated 252 adult kidney transplant recipients transplanted from 2015 to 2021, with the updated protocols effective on March 19th 2020. Cases included recipients transplanted after the protocol update who developed CMV, EBV, and BKV DNAemia and were matched to controls with DNAemia transplanted prior to the protocol update. The primary outcome was the difference in maximum DNA load titers between cases and matched controls. Secondary outcomes included time to initial DNAemia detection and DNAemia clearance. Safety outcomes of tissue-invasive viral disease were described.

RESULTS

There were 216 recipients transplanted preupdate and 36 recipients postupdate. There was no difference between cases and controls in maximum or first DNA load titers for EBV, CMV, or BKV. Cases experienced earlier EBV DNAemia detection (26 (IQR 8, 32) vs. 434 (IQR 96, 1184) days, p = .005). Median follow-up was significantly longer for recipients transplanted preupdate (4.3 vs. 1.3 years, p < .0001). After adjusting for follow-up time, there was no difference in DNAemia clearance or tissue-invasive viral disease.

CONCLUSION

Our findings suggest that reduced frequency viral monitoring protocols may be safe and cost-effective. This quality assurance initiative should be extended to detect longer-term and tissue-invasive disease outcomes.

HLA class I peptide polymorphisms contribute to class II DQβ0603:DQα0103 antibody specificity

Antibodies reactive to human leukocyte antigens (HLA) represent a barrier for patients awaiting transplantation. Based on reactivity patterns in single-antigen bead (SAB) assays, various epitope matching algorithms have been proposed to improve transplant outcomes. However, some antibody reactivities cannot be explained by amino acid motifs, leading to uncertainty about their clinical relevance. Antibodies against the HLA class II molecule, DQβ0603:DQα0103, present in some candidates, represent one such example. Here, we show that peptides derived from amino acids 119-148 of the HLA class I heavy chain are bound to DQβ0603:DQα0103 proteins and contribute to antibody reactivity through an HLA-DM-dependent process. Moreover, antibody reactivity is impacted by the specific amino acid sequence presented. In summary, we demonstrate that polymorphic HLA class I peptides, bound to HLA class II proteins, can directly or indirectly be part of the antibody binding epitope. Our findings have potential important implications for the field of transplant immunology and for our understanding of adaptive immunity.

A rational approach to guide cost-effective de novo donor-specific antibody surveillance with tacrolimus immunosuppression

De novo donor-specific antibody (dnDSA) after renal transplantation has been shown to correlate with antibody-mediated rejection and allograft loss. However, the lack of proven interventions and the time and cost associated with annual screening for dnDSA are difficult to justify for all recipients. We studied a well-characterized consecutive cohort (n = 949) with over 15 years of prospective dnDSA surveillance to identify risk factors that would help institute a resource-responsible surveillance strategy. Younger recipient age and HLA-DR/DQ molecular mismatch were independent predictors of dnDSA development. Combining both risk factors into recipient age molecular mismatch categories, we found that 52% of recipients could be categorized as low-risk for dnDSA development (median subclinical dnDSA-free survival at 5 and 10 years, 98% and 97%, respectively). After adjustment, multivariate correlates of dnDSA development included tacrolimus versus cyclosporin maintenance immunosuppression (hazard ratio [HR], 0.37; 95% CI, 0.2-0.6; P < .0001) and recipient age molecular mismatch category: intermediate versus low (HR, 2.48; 95% CI, 1.5-4.2; P = .0007), high versus intermediate (HR, 2.56; 95% CI, 1.6-4.2; P = .0002), and high versus low (HR, 6.36; 95% CI, 3.7-10.8; P < .00001). When combined, recipient age and HLA-DR/DQ molecular mismatch provide a novel data-driven approach to reduce testing by >50% while selecting those most likely to benefit from dnDSA surveillance.

Rationale for the IMAGINE study for chronic active antibody-mediated rejection (caAMR) in kidney transplantation

Chronic active antibody-mediated rejection (caAMR) in kidney transplantation is a major cause of late graft loss and despite all efforts to date, there is no proven effective therapy. Indeed, the Transplant Society (TTS) consensus opinion called for a conservative approach optimizing baseline immunosuppression and supportive care focused on blood pressure, blood glucose, and lipid control. This review provides the rationale and early evidence in kidney transplant recipients with caAMR that supported the design of the IMAGINE study whose goal is to evaluate the potential impact of targeting the IL6/IL6R pathway.

Premortem anticoagulation timing and dose in donation after circulatory death: multicentre study of associations with graft function

Background:

In controlled donation after circulatory determination of death (DCD), it is common to administer premortem heparin to potential donors. This practice remains controversial because there is limited evidence for it and there is the possibility of inducing hemorrhage. To our knowledge, no previous studies have assessed the effects of heparin timing and dose on graft function.

Methods:

We performed a multicentre cohort study of consecutive DCD donors and the recipients of their organs. Anticoagulation administration was considered early if given near the time of withdrawal of life-sustaining measures and late if delayed until the onset of donor hypoxemia (oxygen saturation < 70%) or hypotension (systolic blood pressure < 60 mm Hg or mean blood pressure < 50 mm Hg). The anticoagulation dose was considered high if it was 300 units/kg or greater.

Results:

Donor anticoagulation data were available for 301 kidney, 75 liver and 46 lung recipients. Heparin was administered in 92% of cases and was most commonly withheld in donors with cerebrovascular causes of death (p = 0.01). Administration was late in 59% and the dose was low in 27%. Among kidney recipients, there were no significant differences in need for dialysis, glomerular filtration rate over the first year after transplantation or graft survival on the basis of whether or not the donor received heparin, the timing of heparin administration or the dose of heparin. Among liver recipients, alkaline phosphatase concentrations over the first year were significantly higher among recipients who received organs from donors to whom lower doses of heparin had been administered.

Conclusion:

Premortem heparin is widely used in DCD cases, but there is variability in timing and dose, which was not associated with kidney outcomes in this study. Donor anticoagulation may have a greater impact in preventing biliary complications following liver transplantation.

The negative impact of T cell-mediated rejection on renal allograft survival in the modern era

The prevalence and long-term impact of T cell-mediated rejection (TCMR) is poorly defined in the modern era of tacrolimus/mycophenolate-based maintenance therapy. This observational study evaluated 775 kidney transplant recipients with serial histology and correlated TCMR events with the risk of graft loss. After a ~30% incidence of a first Banff Borderline or greater TCMR detected on for-cause (17%) or surveillance (13%) biopsies, persistent (37.4%) or subsequent (26.3%) TCMR occurred in 64% of recipients on follow-up biopsies. Alloimmune risk categories based on the HLA-DR/DQ single molecule eplet molecular mismatch correlated with the number of TCMR events (p = .002) and Banff TCMR grade (p = .007). Both a first and second TCMR event correlated with death-censored and all-cause graft loss when adjusted for baseline covariates and other significant time-dependent covariates such as DGF and ABMR. Therefore, a substantial portion of kidney transplant recipients, especially those with intermediate and high HLA-DR/DQ molecular mismatch scores, remain under-immunosuppressed, which in turn identifies the need for novel agents that can more effectively prevent or treat TCMR.

A noninferiority design for a delayed calcineurin inhibitor substitution trial in kidney transplantation

Improving long-term kidney transplant outcomes requires novel treatment strategies, including delayed calcineurin inhibitor (CNI) substitution, tested using informative trial designs. An alternative approach to the usual superiority-based trial is a noninferiority trial design that tests whether an investigational agent is not unacceptably worse than standard of care. An informative noninferiority design, with biopsy-proven acute rejection (BPAR) as the endpoint, requires determination of a prespecified, evidence-based noninferiority margin for BPAR. No such information is available for delayed CNI substitution in kidney transplantation. Herein we analyzed data from recent kidney transplant trials of CNI withdrawal and "real world" CNI- based standard of care, containing subjects with well-documented evidence of immune quiescence at 6 months posttransplant-ideal candidates for delayed CNI substitution. Our analysis indicates an evidence-based noninferiority margin of 13.8% for the United States Food and Drug Administration's composite definition of BPAR between 6 and 24 months posttransplant. Sample size estimation determined that ~225 randomized subjects would be required to evaluate noninferiority for this primary clinical efficacy endpoint, and superiority for a renal function safety endpoint. Our findings provide the basis for future delayed CNI substitution noninferiority trials, thereby increasing the likelihood they will provide clinically implementable results and achieve regulatory approval.

Evidence for the alloimmune basis and prognostic significance of Borderline T cell-mediated rejection

Prognostic biomarkers of T cell-mediated rejection (TCMR) have not been adequately studied in the modern era. We evaluated 803 renal transplant recipients and correlated HLA-DR/DQ molecular mismatch alloimmune risk categories (low, intermediate, high) with the severity, frequency, and persistence of TCMR. Allograft survival was reduced in recipients with Banff Borderline (hazard ratio [HR] 2.4, P = .003) and Banff ≥ IA TCMR (HR 4.3, P < .0001) including a subset who never developed de novo donor-specific antibodies (P = .002). HLA-DR/DQ molecular mismatch alloimmune risk categories were multivariate correlates of Banff Borderline and Banff ≥ IA TCMR and correlated with the severity and frequency of rejection episodes. Recipient age, HLA-DR/DQ molecular mismatch category, and cyclosporin vs tacrolimus immunosuppression were independent correlates of Banff Borderline and Banff ≥ IA TCMR. In the subset treated with tacrolimus (720/803) recipient age, HLA-DR/DQ molecular mismatch category, and tacrolimus coefficient of variation were independent correlates of TCMR. The correlation of HLA-DR/DQ molecular mismatch category with TCMR, including Borderline, provides evidence for their alloimmune basis. HLA-DR/DQ molecular mismatch may represent a precise prognostic biomarker that can be applied to tailor immunosuppression or design clinical trials based on individual patient risk.

What have we learned about how to prevent and treat antibody-mediated rejection in kidney transplantation?

Antibody-mediated rejection (ABMR) in kidney transplantation is a major cause of late graft loss, and despite all efforts to date the "standard of care" remains plasmapheresis, IVIg, and steroids, which itself is based on low quality evidence. This review focuses on the risk factors leading to memory and de novo donor-specific antibody (DSA)-associated ABMR, the optimal prevention strategies for ABMR, and advances in  adjunctive and emerging therapies for ABMR. Because new agents require regulatory approval via a Phase 3 randomized control trial (RCT), an overview of progress in innovative trial design for ABMR is provided. Finally, based on the insights gained in the biology of ABMR, current knowledge gaps are identified for future research that could significantly affect our understanding of how to optimally treat ABMR.

Comparison of the effects of standard vs low-dose prolonged-release tacrolimus with or without ACEi/ARB on the histology and function of renal allografts

Targeting the renin-angiotensin system and optimizing tacrolimus exposure are both postulated to improve outcomes in renal transplant recipients (RTRs) by preventing interstitial fibrosis/tubular atrophy (IF/TA). In this multicenter, prospective, open-label controlled trial, adult de novo RTRs were randomized in a 2 × 2 design to low- vs standard-dose (LOW vs STD) prolonged-release tacrolimus and to angiotensin-converting enzyme inhibitors/angiotensin II receptor 1 blockers (ACEi/ARBs) vs other antihypertensive therapy (OAHT). There were 2 coprimary endpoints: the prevalence of IF/TA at month 6 and at month 24. IF/TA prevalence was similar for LOW vs STD tacrolimus at month 6 (36.8% vs 39.5%; P = .80) and ACEi/ARBs vs OAHT at month 24 (54.8% vs 58.2%; P = .33). IF/TA progression decreased significantly with LOW vs STD tacrolimus at month 24 (mean [SD] change, +0.42 [1.477] vs +1.10 [1.577]; P = .0039). Across the 4 treatment groups, LOW + ACEi/ARB patients exhibited the lowest mean IF/TA change and, compared with LOW + OAHT patients, experienced significantly delayed time to first T cell-mediated rejection. Renal function was stable from month 1 to month 24 in all treatment groups. No unexpected safety findings were detected. Coupled with LOW tacrolimus dosing, ACEi/ARBs appear to reduce IF/TA progression and delay rejection relative to reduced tacrolimus exposure without renin-angiotensin system blockade. ClinicalTrials.gov identifier: NCT00933231.

HLA-DR/DQ molecular mismatch: A prognostic biomarker for primary alloimmunity

Alloimmune risk stratification in renal transplantation has lacked the necessary prognostic biomarkers to personalize recipient care or optimize clinical trials. HLA molecular mismatch improves precision compared to traditional antigen mismatch but has not been studied in detail at the individual molecule level. This study evaluated 664 renal transplant recipients and correlated HLA-DR/DQ single molecule eplet mismatch with serologic, histologic, and clinical outcomes. Compared to traditional HLA-DR/DQ whole antigen mismatch, HLA-DR/DQ single molecule eplet mismatch improved the correlation with de novo donor-specific antibody development (area under the curve 0.54 vs 0.84) and allowed recipients to be stratified into low, intermediate, and high alloimmune risk categories. These risk categories were significantly correlated with primary alloimmune events including Banff ≥1A T cell-mediated rejection (P = .0006), HLA-DR/DQ de novo donor-specific antibody development (P < .0001), antibody-mediated rejection (P < .0001), as well as all-cause graft loss (P = .0012) and each of these correlations persisted in multivariate models. Thus, HLA-DR/DQ single molecule eplet mismatch may represent a precise, reproducible, and widely available prognostic biomarker that can be applied to tailor immunosuppression or design clinical trials based on individual patient risk.

Carpe diem-Time to transition from empiric to precision medicine in kidney transplantation

The current immunosuppressive pipeline in kidney transplantation is limited. In part, this is due to excellent one-year allograft outcomes with the current standard of care (ie, calcineurin inhibitor in combination with anti-proliferative agents). Despite this success, a recent Federal government-sponsored systematic review has identified gaps/limits in the evidence of what constitutes optimal calcineurin inhibitor use in the short- and long-term. Moreover, recent empiric approaches to minimize/withdraw/convert from calcineurin inhibitors have come with the price of increased alloreactivity. As the time horizon to replace calcineurin inhibitors on a global scale may be distant, the transplant community should seize the opportunity to develop ways to personalize calcineurin inhibitor immunosuppression to the individual-transitioning from empiricism to precision. The authors argue in this viewpoint that the path to precision will require measures capable of detecting subclinical alloreactivity to define adequacy of immunosuppression, as well as novel genetic analytics to accurately define alloimmune risk at the individual level-both approaches will require validation in clinical trials.

Understanding Medication Nonadherence after Kidney Transplant

Alloimmunity remains a barrier to long-term graft survival that necessitates lifelong immunosuppressive therapy after renal transplant. Medication nonadherence has been increasingly recognized as a major impediment to achieving effective immunosuppression. Electronic medication monitoring further reveals that nonadherence manifests early after transplant, although the effect is delayed. The etiology of nonadherence is multifactorial, with the strongest risk factors including past nonadherence and being an adolescent or young adult. Other risk factors with smaller but consistently important effects include minority race/ethnicity, poor social supports, and poor perceived health. In children, risk factors related to parental and child psychologic and behavioral functioning and parental distress and burden are also important. Qualitative systematic reviews highlight the need to tailor interventions to each transplant recipient's unique needs, motivations, and barriers rather than offer a one size fits all approach. To date, relatively few interventions have been studied, and most studies conducted were underpowered to allow definitive conclusions. If the kidney transplant community's goal of "one transplant for life" is to become a reality, then solutions for medication nonadherence must be found and implemented.

Class II Eplet Mismatch Modulates Tacrolimus Trough Levels Required to Prevent Donor-Specific Antibody Development

Despite more than two decades of use, the optimal maintenance dose of tacrolimus for kidney transplant recipients is unknown. We hypothesized that HLA class II de novo donor-specific antibody (dnDSA) development correlates with tacrolimus trough levels and the recipient's individualized alloimmune risk determined by HLA-DR/DQ epitope mismatch. A cohort of 596 renal transplant recipients with 50,011 serial tacrolimus trough levels had HLA-DR/DQ eplet mismatch determined using HLAMatchmaker software. We analyzed the frequency of tacrolimus trough levels below a series of thresholds <6 ng/ml and the mean tacrolimus levels before dnDSA development in the context of HLA-DR/DQ eplet mismatch. HLA-DR/DQ eplet mismatch was a significant multivariate predictor of dnDSA development. Recipients treated with a cyclosporin regimen had a 2.7-fold higher incidence of dnDSA development than recipients on a tacrolimus regimen. Recipients treated with tacrolimus who developed HLA-DR/DQ dnDSA had a higher proportion of tacrolimus trough levels <5 ng/ml, which continued to be significant after adjustment for HLA-DR/DQ eplet mismatch. Mean tacrolimus trough levels in the 6 months before dnDSA development were significantly lower than the levels >6 months before dnDSA development in the same patients. Recipients with a high-risk HLA eplet mismatch score were less likely to tolerate low tacrolimus levels without developing dnDSA. We conclude that HLA-DR/DQ eplet mismatch and tacrolimus trough levels are independent predictors of dnDSA development. Recipients with high HLA alloimmune risk should not target tacrolimus levels <5 ng/ml unless essential, and monitoring for dnDSA may be advisable in this setting.

Evaluation of C1q Status and Titer of De Novo Donor-Specific Antibodies as Predictors of Allograft Survival

De novo donor-specific antibodies (dnDSAs) that develop after renal transplantation are independent predictors of allograft loss. However, it is unknown if dnDSA C1q status or titer at the time of first detection can independently predict allograft loss. In a consecutive cohort of 508 renal transplant recipients, 70 developed dnDSAs. Histologic and clinical outcomes were correlated with the C1q assay or dnDSA titer. C1q positivity correlated with dnDSA titer (p < 0.01) and mean fluorescence intensity (p < 0.01) and was more common in class II versus class I dnDSAs (p < 0.01). C1q status correlated with tubulitis (p = 0.02) and C4d status (p = 0.03) in biopsies at the time of dnDSA development, but not T cell-mediated rejection (TCMR) or antibody-mediated rejection (ABMR). De novo DSA titer correlated with Banff g, i, t, ptc, C4d scores, TCMR (p < 0.01) and ABMR (p < 0.01). Post-dnDSA graft loss was observed more frequently in recipients with C1q-positve dnDSA (p < 0.01) or dnDSA titer ≥ 1:1024 (p ≤ 0.01). However, after adjustment for clinical phenotype and nonadherence in multivariate models, neither C1q status nor dnDSA titer were independently associated with allograft loss, questioning the utility of these assays at the time of dnDSA development.

Rates and determinants of progression to graft failure in kidney allograft recipients with de novo donor-specific antibody

Understanding rates and determinants of clinical pathologic progression for recipients with de novo donor-specific antibody (dnDSA), especially subclinical dnDSA, may identify surrogate endpoints and inform clinical trial design. A consecutive cohort of 508 renal transplant recipients (n = 64 with dnDSA) was studied. Recipients (n = 388) without dnDSA or dysfunction had an eGFR decline of -0.65 mL/min/1.73 m(2) /year. In recipients with dnDSA, the rate eGFR decline was significantly increased prior to dnDSA onset (-2.89 vs. -0.65 mL/min/1.73 m(2) /year, p < 0.0001) and accelerated post-dnDSA (-3.63 vs. -2.89 mL/min/1.73 m(2) /year, p < 0.0001), suggesting that dnDSA is both a marker and contributor to ongoing alloimmunity. Time to 50% post-dnDSA graft loss was longer in recipients with subclinical versus a clinical dnDSA phenotype (8.3 vs. 3.3 years, p < 0.0001). Analysis of 1091 allograft biopsies found that dnDSA and time independently predicted chronic glomerulopathy (cg), but not interstitial fibrosis and tubular atrophy (IFTA). Early T cell-mediated rejection, nonadherence, and time were multivariate predictors of IFTA. Independent risk factors for post-dnDSA graft survival available prior to, or at the time of, dnDSA detection were delayed graft function, nonadherence, dnDSA mean fluorescence intensity sum score, tubulitis, and cg. Ultimately, dnDSA is part of a continuum of mixed alloimmune-mediated injury, which requires solutions targeting T and B cells.

The Synergistic Effect of Class II HLA Epitope-Mismatch and Nonadherence on Acute Rejection and Graft Survival

Predicting long-term outcomes in renal transplant recipients is essential to optimize medical therapy and determine the frequency of posttransplant histologic and serologic monitoring. Nonadherence and human leukocyte antigen (HLA) mismatch are risk factors that have been associated with poor long-term outcomes and may help individualize care. In the present study, class II HLA mismatches were determined at the HLA epitope level in 195 renal transplant recipients in whom medication adherence was prospectively measured using electronic monitors in medication vial caps. Recipients were grouped by medication adherence and high (≥10 HLA-DR, ≥17 HLA-DQ) or low epitope-mismatch load. We found that the combination of higher epitope mismatch and poor adherence acted synergistically to determine the risk of rejection or graft loss. Nonadherent recipients with HLA-DR epitope mismatch ≥10 had increased graft loss (35% vs. 8%, p < 0.01) compared to adherent recipients with low epitope mismatch. At the HLA-DQ locus nonadherent recipients with HLA-DQ epitope mismatch ≥17 had increased graft loss (33% vs. 10%, p < 0.01) compared to adherent recipients with low epitope mismatch. Subclinical nonadherence early posttransplant combined with HLA class II epitope mismatch may help identify recipients that could benefit from increased clinical, histologic, and serologic monitoring.

Class II HLA epitope matching-A strategy to minimize de novo donor-specific antibody development and improve outcomes

De novo donor-specific antibody (dnDSA) develops in 15-25% of renal transplant recipients within 5 years of transplantation and is associated with 40% lower graft survival at 10 years. HLA epitope matching is a novel strategy that may minimize dnDSA development. HLAMatchmaker software was used to characterize epitope mismatches at 395 potential HLA-DR/DQ/DP conformational epitopes for 286 donor-recipient pairs. Epitope specificities were assigned using single antigen HLA bead analysis and correlated with known monoclonal alloantibody epitope targets. Locus-specific epitope mismatches were more numerous in patients who developed HLA-DR dnDSA alone (21.4 vs. 13.2, p < 0.02) or HLA-DQ dnDSA alone (27.5 vs. 17.3, p < 0.001). An optimal threshold for epitope mismatches (10 for HLA-DR, 17 for HLA-DQ) was defined that was associated with minimal development of Class II dnDSA. Applying these thresholds, zero and 2.7% of patients developed dnDSA against HLA-DR and HLA-DQ, respectively, after a median of 6.9 years. Epitope specificity analysis revealed that 3 HLA-DR and 3 HLA-DQ epitopes were independent multivariate predictors of Class II dnDSA. HLA-DR and DQ epitope matching outperforms traditional low-resolution antigen-based matching and has the potential to minimize the risk of de novo Class II DSA development, thereby improving long-term graft outcome.

Dynamic challenges inhibiting optimal adoption of kidney paired donation: findings of a consensus conference

While kidney paired donation (KPD) enables the utilization of living donor kidneys from healthy and willing donors incompatible with their intended recipients, the strategy poses complex challenges that have limited its adoption in United States and Canada. A consensus conference was convened March 29-30, 2012 to address the dynamic challenges and complexities of KPD that inhibit optimal implementation. Stakeholders considered donor evaluation and care, histocompatibility testing, allocation algorithms, financing, geographic challenges and implementation strategies with the goal to safely maximize KPD at every transplant center. Best practices, knowledge gaps and research goals were identified and summarized in this document.

Effect of vitamin D supplementation on Mycobacterium tuberculosis-induced innate immune responses in a Canadian Dené First Nations cohort

Canadian First Nations (FN) population experiences a high burden of tuberculosis. Vitamin D is known to enhance the expression of innate immune effectors, including cathelicidin LL-37, for protection against infections. In this study we performed longitudinal analyses to investigate the impact of vitamin D supplementation on macrophage responses to Mycobacterium tuberculosis (Mtb) lipoprotein (TLR2/1L), in Canadian Dené FN participants compared to Caucasian participants. Serum 25(OH)D and LL-37 levels were evaluated by ELISA. Transcriptional responses and protein expression of TLR2/1L-induced LL-37 and other innate immune cytokines were monitored in monocyte-derived macrophages (MDMs) before and after 8 months of vitamin D supplementation. In this study we showed that serum levels of LL-37 decreased after vitamin D supplementation in both Dené and Caucasian participants. There was no difference in TLR2/1L-induced LL-37 expression in MDMs in the two groups, either pre- or post-vitamin D supplementation. However, vitamin D supplementation markedly enhanced TLR2/1L-induced responses in MDMs e.g. IL-6, IL-12 and IL-23 among Caucasians but not in the Dené participants. In contrast, after vitamin D supplementation TLR2/1L-induced responses e.g. IL-1β, IL-8 and IL-12 were significantly reduced in the Dené MDMs. These results indicate that vitamin D supplementation enhanced TLR2/1L-induced innate immune macrophage responses in the Caucasian but not in the Dené participants. We hypothesize that cytokines may be differentially regulated in Canadian FN compared to Caucasians, in particular those that influence Th-1 and Th-17 responses required for the control of Mtb.

Evolution and clinical pathologic correlations of de novo donor-specific HLA antibody post kidney transplant

The natural history for patients with de novo donor-specific antibodies (dnDSA) and the risk factors for its development have not been well defined. Furthermore, clinical and histologic correlation with serologic data is limited. We studied 315 consecutive renal transplants without pretransplant DSA, with a mean follow-up of 6.2 ± 2.9 years. Protocol (n = 215) and for cause (n = 163) biopsies were analyzed. Solid phase assays were used to screen for dnDSA posttransplant. A total of 47 out of 315 (15%) patients developed dnDSA at a mean of 4.6 ± 3.0 years posttransplant. Independent predictors of dnDSA were HLA-DRβ1 MM > 0 (OR 5.66, p < 0.006); and nonadherence (OR 8.75, p < 0.001); with a strong trend toward clinical rejection episodes preceding dnDSA (OR 1.57 per rejection episode, p = 0.061). The median 10-year graft survival for those with dnDSA was lower than the No dnDSA group (57% vs. 96%, p < 0.0001). Pathology consistent with antibody-mediated injury can occur and progress in patients with dnDSA in the absence of graft dysfunction and furthermore, nonadherence and cellular rejection contribute to dnDSA development and progression to graft loss.

Serum creatinine measurement immediately after cardiac surgery and prediction of acute kidney injury

BACKGROUND

After heart surgery, acute kidney injury (AKI) confers substantial long-term risk of death and chronic kidney disease. We hypothesized that small changes in serum creatinine (SCr) levels measured within a few hours of exit from the operating room could help discriminate those at low versus high risk of AKI.

STUDY DESIGN

Prospective cohort of 350 elective cardiac surgery patients (valve or coronary artery bypass grafting) recruited in Winnipeg, Canada. Baseline SCr level was obtained at the preoperative visit 2 weeks before surgery. The postoperative SCr level was drawn within 6 hours of completion of surgery and then daily while the patient was in the hospital.

PREDICTOR

Immediate (ie, <6 hours) postoperative SCr level change (ΔSCr), categorized as within 10% (reference), decrease >10%, or increase >10% relative to baseline.

OUTCOME

AKI, defined according to the new KDIGO (Kidney Disease: Improving Global Outcomes) consensus definition as an increase in SCr level >0.3 mg/dL within 48 hours or >1.5 times baseline within 1 week.

MEASUREMENTS

We compared the C statistic of logistic models with and without inclusion of immediate postoperative ΔSCr.

RESULTS

After surgery, 176 patients (52%) experienced a decrease >10% in SCr level, 26 (7.4%) experienced an increase >10%, and 143 had ΔSCr within ±10% of baseline. During hospitalization, 53 (14%) developed AKI. Bypass pump time, baseline estimated glomerular filtration rate, and European System for Cardiac Operative Risk Evaluation (euroSCORE) were associated with AKI in a parsimonious base logistic model. Added to the base model, immediate postoperative ΔSCr was associated strongly with subsequent AKI and significantly improved model discrimination over the base model (C statistic, 0.78 [95% CI, 0.71-0.85] vs 0.69 [95% CI, 0.62-0.77]; P < 0.001). A ≥10% SCr level decrease predicted significantly lower AKI risk (OR, 0.37; 95% CI, 0.18-0.76), whereas a ≥10% SCr level increase predicted significantly higher (OR, 6.38; 95% CI, 2.37-17.2) AKI risk compared with the reference category.

LIMITATIONS

We used a surrogate marker of AKI. External validation of our results is warranted.

CONCLUSION

In elective cardiac surgery patients, measurement of immediate postoperative ΔSCr improves prediction of AKI.

Urinary hepcidin-25 and risk of acute kidney injury following cardiopulmonary bypass

BACKGROUND AND OBJECTIVES

Acute kidney injury (AKI) complicating cardiopulmonary bypass (CPB) results in increased morbidity and mortality. Urinary hepcidin-25 has been shown to be elevated in patients who do not develop AKI after CPB using semiquantitative mass spectrometry (SELDI TOF-MS). The goals of this study were to quantitatively validate these findings with ELISA and evaluate the diagnostic performance of hepcidin-25 for AKI.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A nested, case-control analysis of urinary hepcidin-25 in AKI (n = 22) and non-AKI (n = 22) patients was conducted to validate the SELDI TOF-MS data at the following times: preoperatively; the start of CPB; 1 hour on CPB; on arrival to the intensive care unit; and postoperative days (POD) 1 and 3 to 5. The diagnostic performance of hepcidin-25 was then evaluated in the entire prospective observational cohort (n = 338) at POD 1. AKI was defined as Cr >50% from baseline, within 72 hours postoperatively.

RESULTS

Urinary hepcidin-25/Cr ratio was significantly elevated in all patients at POD 1 compared with baseline (P < 0.0005) and was also significantly elevated in non-AKI versus AKI patients at POD 1 (P < 0.0005). Increased log(10) hepcidin-25/Cr ratio was strongly associated with avoidance of AKI on univariate analysis. On multivariate analysis, the log(10) hepcidin-25/Cr ratio (P < 0.0001) was associated with avoidance of AKI with an area under the curve of 0.80, sensitivity 0.68, specificity 0.68, and negative predictive value 0.96.

CONCLUSIONS

Elevated urinary hepcidin-25 on POD 1 is a strong predictor of avoidance of AKI beyond postoperative day 1.

Functional gene polymorphisms in canadian aboriginal populations with high rates of tuberculosis

The present study determined whether a pattern of functional single-nucleotide polymorphisms (SNPs) was present that could predispose a Dené cohort to a suboptimal response to Mycobacterium tuberculosis. Compared with a Caucasian cohort, the Dené and Cree were found to maintain a significantly higher frequency of SNPs associated with low expression of vitamin D receptor (VDR), interferon (IFN)-gamma (+874), and tumor necrosis factor-alpha (-308) and high production of monocyte chemoattractant protein (MCP)-1 (-2518) and interleukin (IL)-6 (-174). Given the roles played by IFN-gamma and VDR in facilitating macrophage containment of M. tuberculosis and the opposing role of MCP-1 and IL-6, the observed allelic variation by ethnicity may in part contribute to the high rates of tuberculosis among the Dené.

Biologically variable bypass reduces enzymuria after deep hypothermic circulatory arrest

BACKGROUND

Renal injury is common after open-heart surgery. Cardiopulmonary bypass contributes to the problem. We compared conventional nonpulsatile perfusion (NP) to biologically variable perfusion (BVP), which uses a computer controller to restore physiological beat-to-beat variability to roller pump flow. We hypothesized BVP would decrease renal injury after deep hypothermic circulatory arrest.

METHODS

Pigs were randomly assigned to either BVP (n = 9) or NP (n = 9), cooled, arrested at 18 degrees C (1 hour), reperfused, and rewarmed and maintained normothermic (3 hours). Additional pigs had NP for a similar time as above, but without circulatory arrest (n = 3), or were sham-treated without bypass (n = 3). Hemodynamics, acid-base status, temperature, and urine volumes were measured. Urinary enzyme markers of tubular injury were compared post-hoc for gamma glutamyl transpeptidase, alkaline phosphatase, and glutathione S-transferase and by urine proteomics using mass spectrometry.

RESULTS

Urine output at 1 hour after arrest was 250 +/- 129 mL with BVP versus 114 +/- 66 mL with NP (p < 0.02). All three renal enzyme markers were higher with NP after arrest compared with BVP. In animals on bypass without arrest or those sham-treated, no elevations were seen in renal enzymes. Urine proteomics revealed abnormal proteins, persisting longer with NP. Biologically variable perfusion decreased cooling to 21.0 +/- 9.0 minutes versus 31.7 +/- 7.5 minutes (p < 0.002), and decreased rewarming to 22.1 +/- 3.9 minutes versus 31.2 +/- 5.1 minutes (p < 0.002).

CONCLUSIONS

Biologically variable perfusion improved urine output, decreased enzymuria, and attenuated mass spectrometry urine protein signal with more rapid temperature changes. This strategy could potentially shorten bypass duration and may decrease renal tubular injury with deep hypothermic circulatory arrest.

Evolution of HLA antibody detection: technology emulating biology

New technological advances in the field of histocompatibility have provided an approach to systematically address the specificity of positive lymphocyte crossmatches. These approaches can now confirm whether a positive crossmatch is (or is not) due to class I and/or class II antibodies directed against donor HLA antigens. The information gained from the application of these sensitive and specific technologies can be used to predict crossmatch results for highly sensitized patients. In summary, these emerging technologies have provided the tools to reliably determine the clinical relevance of a positive lymphocyte crossmatch.

Prevalence and treatment of decreased bone density in renal transplant recipients: a randomized prospective trial of calcitriol versus alendronate

BACKGROUND

Reduced bone mineral density (BMD) is common in long-term renal transplant recipients and results in a high incidence of fractures. The optimal therapy for these patients is not known.

METHODS

Baseline BMD determinations were obtained in 211 long-term adult renal transplant recipients. One hundred and seventeen patients with a reduced BMD (T score < or = -1) were randomly assigned to treatment with alendronate and calcium (n=60) versus calcitriol and calcium (n=57). Of these, 46 and 51 patients, respectively, completed 1 year of treatment. Forty-nine patients who were not eligible or did not consent to the trial were followed prospectively.

RESULTS

Reduced baseline BMD (T score < or = -1) was present in 159 (78.7%) of patients at the lumbar spine or femur. There was no significant loss of BMD in the prospectively followed patients during 2.7 years. The average lumbar BMD increased from 0.984+/-0.149 to 1.025+/-0.143 g/cm2 (P<0.001) with alendronate and from 1.014+/-0.15 to 1.034+/-0.146 g/cm2 (P=0.002) with calcitriol. BMD at the femur increased from 0.809+/-0.092 to 0.836+/-0.107 g/cm2 (P<0.001) with alendronate and from 0.830+/-0.144 to 0.857+/-0.125 g/cm2 (P=0.023) with calcitriol.

CONCLUSIONS

One year of treatment with alendronate or calcitriol, both with calcium supplementation, resulted in significant increases in BMD at the lumbar spine and femur, with a trend toward alendronate being more effective at the spine (P=0.082). Further studies are needed to determine whether BMDs continue to increase after 1 year and whether there is any additional benefit to combining vitamin D and alendronate. Larger studies are needed to determine whether treatment decreases fracture rates.

Exacerbation of myocardial injury in transgenic mice overexpressing FGF-2 is T cell dependent

Fibroblast growth factor-2 (FGF-2) is cardioprotective when added exogenously, stimulates cardiac myocyte proliferation, and is a mediator of tissue repair after injury. Furthermore, transgenic (TG) mice overexpressing FGF-2 in cardiac muscle demonstrate increased resistance to injury in an isolated heart model of ischemia-reperfusion. We investigated how increasing the endogenous FGF-2 levels in the heart affects the extent of myocardial damage induced by isoproterenol in vivo. Histopathological evaluation of hearts after intraperitoneal injection of isoproterenol yielded significantly higher scores for myocardial damage in FGF-2 TG lines compared with non-TG mice. After 1 day, FGF-2 TG mouse hearts displayed more cellular infiltration correlating with increased tissue damage. Immunostaining of non-TG and FGF-2 TG mouse hearts showed the presence of leukocytes in the infiltrate, including T cells expressing FGF receptor-1. Treatment of mice with T cell suppressors cyclosporin A and anti-CD3epsilon significantly decreased the level of myocardial injury observed after isoproterenol and equalized the histopathology scores in FGF-2 TG and non-TG hearts. These data demonstrate a direct T cell involvement in the response to isoproterenol-induced injury in vivo. Moreover, the findings indicate that the exacerbation of myocardial damage in FGF-2 TG mice was dependent on T cell infiltration, implicating FGF-2 in the inflammatory response seen in cardiac tissue after injury in vivo.

IL-2 receptor-targeted cytolytic IL-2/Fc fusion protein treatment blocks diabetogenic autoimmunity in nonobese diabetic mice

High affinity IL-2R5 is present on recently activated but not on resting or memory T cells. Selective targeting of T cells bearing high affinity IL-2R is an attractive therapy for many T cell-dependent cytopathic disease processes. A variety of rodent mAbs directed against the alpha-chain of the IL-2R, as well as IL-2 fusion toxins, have been used in animals and humans to achieve selective immunosuppression. Here we report on the development of a novel IL-2R targeting agent, a cytolytic chimeric IL-2/Fc fusion protein. This immunoligand binds specifically and with high affinity to IL-2R and is structurally capable of recruiting host Ab-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity activities. The Ig component ensures an extended circulating t1/2 of 25 h following systemic administration. To subsequently explore the mechanisms of the antidiabetogenic effects of IL-2/Fc, we have mutated the FcR binding and complement C1q binding (Fc-/-) domains of the Fc fragment to render the Fc unable to direct Ab-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity activities. In a model of passive transfer of diabetes in nonobese diabetic mice, lytic IL-2/Fc, but not nonlytic IL-2/Fc-/-, exhibited striking antidiabetogenic effects. Together with the negligible potential of IL-2/Fc for immunogenicity, this finding forecasts that cytolytic IL-2/Fc may offer a new therapeutic approach for selective targeting of auto and alloimmune T cells.

IL-2 Receptor-Targeted Cytolytic IL-2/Fc Fusion Protein Treatment Blocks Diabetogenic Autoimmunity in Nonobese Diabetic Mice

High affinity IL-2R5 is present on recently activated but not on resting or memory T cells. Selective targeting of T cells bearing high affinity IL-2R is an attractive therapy for many T cell-dependent cytopathic disease processes. A variety of rodent mAbs directed against the α-chain of the IL-2R, as well as IL-2 fusion toxins, have been used in animals and humans to achieve selective immunosuppression. Here we report on the development of a novel IL-2R targeting agent, a cytolytic chimeric IL-2/Fc fusion protein. This immunoligand binds specifically and with high affinity to IL-2R and is structurally capable of recruiting host Ab-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity activities. The Ig component ensures an extended circulating t1/2 of 25 h following systemic administration. To subsequently explore the mechanisms of the antidiabetogenic effects of IL-2/Fc, we have mutated the FcR binding and complement C1q binding (Fc−/−) domains of the Fc fragment to render the Fc unable to direct Ab-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity activities. In a model of passive transfer of diabetes in nonobese diabetic mice, lytic IL-2/Fc, but not nonlytic IL-2/Fc−/−, exhibited striking antidiabetogenic effects. Together with the negligible potential of IL-2/Fc for immunogenicity, this finding forecasts that cytolytic IL-2/Fc may offer a new therapeutic approach for selective targeting of auto and alloimmune T cells.

IL-2 and IL-4 double knockout mice reject islet allografts: a role for novel T cell growth factors in allograft rejection

T cell growth factors (TCGFs) play a critical role in allograft rejection by promoting the activation and proliferation of alloreactive T cells. To determine whether IL-2 and IL-4 are of quintessential importance in allograft rejection and to identify possible alternative TCGFs, we have bred IL-2(-/-) and IL-4(-/-) double knockout (DKO) mice and studied islet allograft rejection using the DKO mice as allograft recipients. Although mononuclear leukocytes from DKO mice did not mount a proliferative response in vitro in response to anti-CD3 stimulation, crude islet allografts were vigorously rejected by DKO mice (mean survival time 17 +/- 7, n = 8) as compared with wild-type controls (mean survival time 13 +/- 4, n = 7). Treatment of DKO mice with anti-CD3 or rapamycin markedly prolonged the islet allograft survival. An analysis of intragraft cytokine gene transcripts showed robust expression of IL-7 and IL-15. In contrast, intragraft IL-9 gene transcripts were not detected in either wild-type or DKO mice. Provision of exogenous IL-2, IL-4, IL-7, or IL-15, but not IL-9, supports the proliferation of anti-CD3 activated DKO splenic leukocytes in vitro. Blocking the common gamma c of IL-2 receptor, a shared essential signaling component by receptors for IL-2, IL-4, IL-7, IL-9, and IL-15, prolonged the survival of islet allografts in DKO mice. Hence, a T cell dependent allograft rejection enabled by rapamycin-sensitive signals or signals mediated by binding of the gamma c chain occurs in the absence of both IL-2 and IL-4. Non-T cell-derived TCGFs, especially IL-7 and IL-15, may play an active role in supporting allograft rejection.

IL-2 and IL-4 Double Knockout Mice Reject Islet Allografts: A Role for Novel T Cell Growth Factors in Allograft Rejection

T cell growth factors (TCGFs) play a critical role in allograft rejection by promoting the activation and proliferation of alloreactive T cells. To determine whether IL-2 and IL-4 are of quintessential importance in allograft rejection and to identify possible alternative TCGFs, we have bred IL-2−/− and IL-4−/− double knockout (DKO) mice and studied islet allograft rejection using the DKO mice as allograft recipients. Although mononuclear leukocytes from DKO mice did not mount a proliferative response in vitro in response to anti-CD3 stimulation, crude islet allografts were vigorously rejected by DKO mice (mean survival time 17 ± 7, n = 8) as compared with wild-type controls (mean survival time 13 ± 4, n = 7). Treatment of DKO mice with anti-CD3 or rapamycin markedly prolonged the islet allograft survival. An analysis of intragraft cytokine gene transcripts showed robust expression of IL-7 and IL-15. In contrast, intragraft IL-9 gene transcripts were not detected in either wild-type or DKO mice. Provision of exogenous IL-2, IL-4, IL-7, or IL-15, but not IL-9, supports the proliferation of anti-CD3 activated DKO splenic leukocytes in vitro. Blocking the common γc of IL-2 receptor, a shared essential signaling component by receptors for IL-2, IL-4, IL-7, IL-9, and IL-15, prolonged the survival of islet allografts in DKO mice. Hence, a T cell dependent allograft rejection enabled by rapamycin-sensitive signals or signals mediated by binding of the γc chain occurs in the absence of both IL-2 and IL-4. Non-T cell-derived TCGFs, especially IL-7 and IL-15, may play an active role in supporting allograft rejection.

Interferon-gamma receptor signaling is not required in the effector phase of the alloimmune response

BACKGROUND

Gene transcripts for the Thl cytokines interleukin (IL)-2 and interferon-gamma (IFN-gamma) are frequently detected during allograft rejection. The relative importance of these cytokines in facilitating allograft rejection is unclear. Recently, we have shown that IL-2-deficient mice reject islet allografts. In the IL-2-deficient system, IFN-gamma gene transcripts are abundantly expressed.

METHODS

To determine the relative importance of IFN-gamma-dependent effector mechanisms in mediating allograft rejection, the present study utilized IFN-gamma receptor-deficient mice as islet allograft recipients. Grafts were analyzed by immunohistology, and cytokine expression was measured by competitive template reverse transcriptase polymerase chain reaction.

RESULTS

IFN-gamma receptor-deficient mice reject islet allografts by a process that is T cell-dependent. Although IFN-gamma receptor signaling is absent, these mice do not show a clear Th2 type response.

CONCLUSION

Although the signals evoked through the IFN-gamma receptor may play a role, they are not essential to allograft rejection.

Distinct mechanisms for the induction and maintenance of allograft tolerance with CTLA4-Fc treatment

A murine CTLA4/Fc gamma2a heavy chain (mCTLA4-Fc) chimeric fusion molecule was used in B6AF1 recipients of BALB/c pancreatic islet allografts to study the induction and maintenance of tolerance following inhibition of the CD28-B7 pathway for T cell activation. Donor-specific tolerance was achieved by administering 100 microg of mCTLA4-Fc on alternate days for 14 days (8 total doses) or a single 500 microg dose of mCTLA4-Fc on day 2 after transplant. Tolerance was mediated by long-lived peripheral lymphocytes and showed features of organ and alloantigen specificity. Whereas tolerance could not be established in allograft recipients receiving simultaneous mCTLA4-Fc and rIL-2, previously tolerant animals did not reject their grafts when given IL-2, suggesting that the induction and maintenance phases of tolerance were distinct and separate. The maintenance of donor-specific tolerance was an active immunologic process that was CD4+ T cell dependent and could be adoptively transferred to naive lymphocytes, but could not be explained by apoptosis or deletion of alloreactive T cells. Although an IL-2-sensitive mechanism such as anergy may contribute toward the induction of tolerance, its maintenance involves active suppression.

Distinct mechanisms for the induction and maintenance of allograft tolerance with CTLA4-Fc treatment

A murine CTLA4/Fc gamma2a heavy chain (mCTLA4-Fc) chimeric fusion molecule was used in B6AF1 recipients of BALB/c pancreatic islet allografts to study the induction and maintenance of tolerance following inhibition of the CD28-B7 pathway for T cell activation. Donor-specific tolerance was achieved by administering 100 microg of mCTLA4-Fc on alternate days for 14 days (8 total doses) or a single 500 microg dose of mCTLA4-Fc on day 2 after transplant. Tolerance was mediated by long-lived peripheral lymphocytes and showed features of organ and alloantigen specificity. Whereas tolerance could not be established in allograft recipients receiving simultaneous mCTLA4-Fc and rIL-2, previously tolerant animals did not reject their grafts when given IL-2, suggesting that the induction and maintenance phases of tolerance were distinct and separate. The maintenance of donor-specific tolerance was an active immunologic process that was CD4+ T cell dependent and could be adoptively transferred to naive lymphocytes, but could not be explained by apoptosis or deletion of alloreactive T cells. Although an IL-2-sensitive mechanism such as anergy may contribute toward the induction of tolerance, its maintenance involves active suppression.

CTLA4Ig attenuates accelerated rejection (presensitization) in the mouse islet allograft model

BACKGROUND

Sensitization to donor antigens is a problem of growing magnitude in clinical transplantation. At a molecular level, this is due to the interaction between antigen bearing antigen-presenting cells and recipient T cells and involves both antigen presentation and co-stimulation.

METHODS

Allogeneic islet transplantation was performed using DBA/2J donors and B6AF1 recipients. Four weeks before transplantation, recipient animals were given donor-specific transfusion (DST) alone, DST + CTLA4Ig, DST + control IgG, or no treatment. Graft loss was defined as a blood glucose >300 mg/100 ml.

RESULTS

Administration of DST + control IgG 4 weeks before transplantation resulted in accelerated rejection due to presensitization (median survival time of 8 days, compared with 14.5 days for the no-treatment group). Animals treated with CTLA4Ig in combination with DST had a median survival time of 12 days, compared with 8 days for DST + IgG.

CONCLUSIONS

CTLA4Ig attenuates the tempo of accelerated rejection in this islet allograft model of presensitization, but does not prolong allograft survival as compared with no treatment.

A noncytolytic IL-10/Fc fusion protein prevents diabetes, blocks autoimmunity, and promotes suppressor phenomena in NOD mice

We have been successful in our efforts to develop a long lived noncytolytic murine IL-10/Fc fusion protein. In the nonobese diabetic mouse (NOD) model, administration of IL-10/Fc from 5 to 25 wk of age completely prevented the occurrence of diabetes. Moreover, these mice remained disease-free long after cessation of IL-10/Fc therapy. Immunohistochemistry studies show that IL-10/Fc treatment inhibits expression of TNF-alpha, proinflammatory cytokine, as well as Th1-type cytokines, IL-2 and IFN-gamma, but promotes expression of IL-4 and IL-10, Th2-type cytokines, by islet-infiltrating leukocytes. In an adoptive transfer model of diabetes in NOD mice, we found that: 1) IL-10/Fc treated hosts bear leukocytes that block expression of diabetes and 2) these leukocytes persisted even 8 wk after cessation of IL-10/Fc treatment. The potent antidiabetogenic effects provided by IL-10/Fc in the NOD model, together with its apparent lack of systemic toxicity, are notable.