Autoreactivity to self H-2Kb peptides in TAP1 mice. Intravenous administration of H-2Kb class I-derived peptides induces long-term survival of grafts from C57BL/6 donors

We and others have previously shown that TAP1-/- mice (H-2b) reject grafts from donors without major histocompatibility complex (MHC) disparity that express wild-type levels of H-2b class I molecules (C57BL/6, TAP1+/+ mice). In this same model, we also showed that subcutaneous priming of TAP1-/- mice with synthetic peptides derived from the H-2Kb molecule accelerated graft rejection and that in vivo depletion of CD4+ T cells induced a significant prolongation of graft survival, suggesting an important role for CD4 T cells. We hypothesize that, in this model, rejection is triggered by the recognition of class I molecules or derived peptides, in an inflammatory microenvironment, by a functionally altered autoreactive T-cell repertoire that escapes the control of peripheral regulatory mechanisms. In the present study, we analysed the cellular autoreactivity induced by synthetic peptides derived from the H-2Kb sequence in naive and TAP1-/- mice transplanted with C57BL/6 grafts, and investigated whether intravenous modulation of autoreactivity to these peptides induced transplantation tolerance. We showed that TAP1-/- mice have peripheral autoreactive T cells that recognize H-2Kb peptides. A significant amplification of proliferation against these peptides was detected in TAP1-/- mice that rejected grafts, indicating that the inflammatory context of transplantation induced peripheral expansion of these autoreactive T cells. Furthermore, intravenous injection of H-2Kb-derived peptides significantly prolonged graft survival in some animals. In these mice (> 100 days graft survival), we observed intragraft inhibition of interferon-gamma and interleukin-10 expression, suggesting that these cytokines have an active role during the rejection. In conclusion, our present data indicate that inflammatory autoreactive T cells directed against H-2Kb peptides can be inhibited in the periphery to prolong graft survival in TAP1-/- mice.     

The effect of locally synthesised complement on acute renal allograft rejection

The complement system of components and receptors is one of the earliest forms of defence. Excessive or inappropriate activation can result in tissue damage, classically illustrated in immune-mediated nephritis. In addition, complement forms a bridge between innate and adaptive immunity, helping to prepare and focus T and B lymphocyte responses. More recent research in renal allograft models has shown that complement-inhibited and complement-deficient animals have reduced inflammatory injury and lowered antidonor immune responses. Furthermore, it is known that the transplanted kidney is a significant site of local synthesis of C3, although until recently the relative contribution of locally produced C3 to transplant injury was unknown. Current evidence indicates that defective local synthesis of C3 both reduces tissue injury and lowers the antidonor T cell response, substantially increasing graft survival. Among various possible explanations to account for these findings, the data favours a direct effect of complement on alloreactive T cell stimulation. Study of complement gene regulation by common immunosuppressive agents suggests that they do not influence local complement synthesis. Alternative approaches are therefore required to control the local effect of complement in the extravascular tissue compartment of the graft.     

落新妇甙对大鼠肺移植排斥反应的抑制作用

目的:探讨落新妇甙对大鼠肺移植排斥反应的抑制作用。方法:采用大鼠左侧单肺移植模型。随机将肺移植后的40只大鼠分为4组:A组肺移植后用生理盐水(1ml/天)灌胃,B组肺移植后用环孢素A(5mg/kg/天)灌胃,C组肺移植后用落新妇甙(1ml/kg/天)灌胃,D组肺移植后用环孢素A(2.5mg/kg/天)及落新妇甙(1ml/kg/天)灌胃。术后第10天切取移植肺观察肺急性排斥反应分级情况。结果:B组、C组及D组移植肺排斥反应分级均低于A组(P<0.05～0.01);D组移植肺急性排斥反应最轻,优于C组(P<0.05)和B组(P<0.01)。结论:落新妇甙对肺移植排斥反应有较强的抑制作用,并与环孢素A有协同作用。     

Belatacept in kidney transplantation and its limitations

Introduction: Since the approval of belatacept in 2011 for use in the setting of de novo kidney transplantation, this CD80/86 – CD28 co-stimulation blocker has been shown to be a valuable treatment option for maintenance immunosuppression.

Areas covered: In this setting, belatacept has been associated with superior glomerular filtration rate as compared to calcineurin inhibitor-based treatments because of the absence of nephrotoxicity. Additionally, belatacept avoids the cardiovascular side effects (e.g. hypertension and dyslipidemia) caused by a CNI-based-regimen. Nevertheless, belatacept-treated recipients have a higher rate of acute rejections and a higher risk of lymphoproliferative disorders.

Expert opinion: Data suggest a benefit from early conversion vs. late conversion of belatacept in a conversion setting following CNI-related toxicity. Randomized studies are currently comparing belatacept to tacrolimus, instead of cyclosporine, as was done in the Belatacept Evaluation of Nephroprotection and Efficacy as a First-line Immunosuppression Trial (BENEFIT). The benefits and limitations of belatacept seem to be the same when tacrolimus is used instead of cyclosporine.

Finally, we also report in this review on the immunological data available so far that explain belatacept’s limitations and the higher rate of acute rejection. The goal is to find the optimal immunosuppressive strategy to improve efficacy and safety at post-transplantation.     

Granzyme B and perforin can be used as predictive markers of acute rejection in heart transplantation

We have investigated perforin and granzyme B expression in graft-infiltrating lymphocytes of patients who underwent heart transplantation. Those proteins are commonly present in the cytoplasmic granules of cytotoxic T lymphocytes and are released upon effector-target cell interaction. From 28 patients 103 endomyocardial biopsies were obtained and examined by histology and immunocytochemical analysis using relevant monoclonal antibodies. We found that “high” biopsy histological grades were associated with perforin and granzyme B expression in graft-infiltrating lymphocytes of patients with acute severe rejection crisis. In contrast, these markers were not detected in patients without rejection or during graft stabilization. Interestingly, in patients with mild rejection and “low” histological grades, two groups could be distinguished with a differential expression of the two intracytoplasmic proteins. The presence of perforin and granzyme B-expressing cells was found to be predictive of rapid progression to severe rejection, so that this situation required additional treatment; in contrast, their absence seemed to correlate with a good graft outcome without additional treatment. Moreover, perforin and granzyme B expression seemed to be down-regulated by immunosuppressive drugs, which coincided with graft stabilization. In conclusion, our data suggest that detection of granzyme B and perforin in graft-infiltrating lymphocytes might be helpful for routinely monitoring heart transplant patients.     

Platelet-specific alloantigens in cadaveric renal transplantation. A prospective study. Effect of HPA-5b mismatch in acute vascular rejection of renal allografts

This prospective study comprised 166 renal allograft-recipient pairs that were studied for human platelet alloantigens (HPA) 1-3 and 5, which have been shown to be expressed by adhesion molecules of the vascular endothelium. Four of the five (80%) HPA-5a5a regraft recipients developing acute vascular rejection (AVR) had received an HPA-5b-incompatible graft in contrast to one of the 32 (3%) regraft recipients without rejection. The occurrence of AVR was not explained by the degree of HLA mismatches. All four regraft recipients of an HPA-5b-mismatched graft with AVR were HLA-A3,B7, and the combination of HLA-A3 and/or B7 match and an HPA-5b-mismatched graft was associated with AVR. No antibodies against HPA-5b were detected in the patients with AVR of an HPA-5b-mismatched graft. These preliminary findings suggest that HPA-5b is a minor histocompatibility antigen involved in the development of AVR.     

Acute rejection of vascular heart allografts by perforin-deficient mice

To study the role of perforin in cell-mediated graft rejection, vascularized hearts were grafted to perforin-deficient C57BL/6 and control C57BL/6 recipient mice. Fully allogeneic heart grafts (BALB/c) were acutely rejected by both recipients within 6 days. Peritoneal exudate lymphocytes from control mice but not from perforin-deficient mice exhibit a strong alloreactive cytotoxic activity in vitro. Histological analysis of the rejected tissues demonstrated extensive mononuclear cell infiltrates in both recipients. Flow cytometry analysis and immunohistology of graft-infiltrating cells showed similar proportions of lymphocyte subsets (CD8 ≧ CD4). Collectively, these data indicate that perforin is not essential in the cell-mediated acute rejection of a fully mismatched heart allograft. However, perforin-dependent effector mechanisms appeared to be limiting in the T cellmediated rejection of heart allografts differing only at a single major histocompatibility complex class I antigen (bm1), because these grafts survived longer (mean 87.8 days) in perforin-deficient than in control mice (mean 31.5 days).     

Reduction of Extended‐Release Tacrolimus Dose in Low‐Immunological‐Risk Kidney Transplant Recipients Increases Risk of Rejection and Appearance of Donor‐Specific Antibodies: A Randomized Study

The aim of this study (ClinicalTrials.gov, NCT01744470) was to determine the efficacy and safety of two different doses of extended‐release tacrolimus (TacER) in kidney transplant recipients (KTRs) between 4 and 12 mo after transplantation. Stable steroid‐free KTRs were randomized (1:1) after 4 mo: Group A had a 50% reduction in TacER dose with a targeted TacER trough level (C₀) >3 μg/L; group B had no change in TacER dose (TacER C₀ 7–12 μg/L). The primary outcome was estimated GFR at 1 year. Of 300 patients, the intent‐to‐treat analysis included 186 patients (group A, n = 87; group B, n = 99). TacER C₀ was lower in group A than in group B at 6 mo (4.1 ± 2.7 vs. 6.7 ± 3.9 μg/L, p < 0.0001) and 12 mo (5.6 ± 2.0 vs. 7.4 ± 2.1 μg/L, p < 0.0001). Estimated GFR was similar in both groups at 12 mo (group A, 56.0 ± 17.5 mL/min per 1.73 m²; group B, 56.0 ± 22.1 mL/min per 1.73 m²). More rejection episodes occurred in group A than group B (11 vs. 3; p = 0.016). At 1 year, subclinical inflammation occurred more frequently in group A than group B (inflammation score [i] >0: 21.4% vs. 8.8%, p = 0.047; tubulitis score [t] >0: 19.6% vs. 8.7%, p = 0.076; i + t: 1.14 ± 1.21 vs. 0.72 ± 1.01, p = 0.038). Anti‐HLA donor‐specific antibodies appeared only in group A (6 vs. 0 patients, p = 0.008). TacER C₀ should be maintained >7 μg/L during the first year after transplantation in low‐immunological‐risk, steroid‐free KTRs receiving a moderate dose of mycophenolic acid.