CD4+CD45RO+CD25-/lowCD127+: CD4+CD45RO+CD25hiCD127-/low Ratio in Peripheral Blood A Useful Biomarker to Detect Cardiac Allograft Vasculopathy in Heart Transplanted Patients

The Presence of a Marked Imbalance Between Regulatory T Cells and Effector T Cells Reveals That Tolerance Mechanisms Could Be Compromised in Heart Transplant Children

Regulatory T cells (Treg) are crucial for the induction and maintenance of graft tolerance. In pediatric heart transplant procedures, the thymus is routinely excised, removing the primary source of T-cell replenishment. Consequently, thymectomy joined to the effects of immunosuppression on the T-cell compartment may have a detrimental impact on Treg values, compromising the intrinsic tolerance mechanisms and the protective role of Treg preventing graft rejection in heart transplant children.

Profiling circulating T follicular helper cells and their effects on B cells in post-cardiac transplant recipients

Background

To evaluate circulating T follicular helper (cTfh) cells and characterize their function in chronic-phase recipients after heart transplantation.

Methods

Participants were divided into healthy control (HC, n=40), preoperative (Pre, n=40), and post-transplantation chronic-phase recipient (1-year, n=40) groups. The percentages of cTfh cell subsets and CD19⁺ B cell subsets were measured using flow cytometry. In vitro co-culture experiments were performed using cTfh cells and B cells isolated by fluorescence-activated cell sorting. Plasma concentrations of IL-21, chemokine ligand 13 (CXCL13), immunoglobulin G1 (IgG1), and immunoglobulin G3 (IgG3) were quantified using enzyme-linked immunosorbent assays (ELISA).

Results

cTfh and programmed cell death protein 1-positive (PD-1⁺) cTfh cells, the cTfh17/cTfh ratio, and class-switched memory B cells in peripheral blood were significantly increased in the 1-year group versus the HC and Pre groups (P<0.01), whereas the cTfh1/cTfh ratio and number of naïve B cells were significantly decreased in the 1-year group. Co-culture experiments showed that cTfh cells promoted B cell differentiation to plasmablasts. In the 1-year group, cTfh and PD-1⁺ cTfh cell numbers were positively correlated with plasmablasts in CD19⁺ B cells (P<0.01). The cTfh17/cTfh ratio was positively correlated with IgG3 concentrations in plasma (P<0.01). The plasma concentrations of interleukin-21 (IL-21) and CXCL13 in the 1-year group were increased compared to the HC and Pre groups (P<0.05). Chronic-phase recipients had increased proportions of CD4⁺CXCR5⁺ and CD4⁺CXCR5⁺PD-1⁺ cTfh cells, with a cTfh1-to-cTfh17 subtype conversion. An increased number of cTfh cells was positively correlated with B cell differentiation to plasmablasts, class-switched memory B cells, and greater IgG production.

Conclusions

During the chronic phase, the proportion of cTfh cells increased and enhanced B cell responses. The cTfh-related soluble factors CXCL13 and IL-21 may regulate the immunopathogenesis of chronic immune injury. Thus, cTfh cells may drive long-term immune rejection in chronic-phase recipients after heart transplantation.

Novel Cytokine Score and Cardiac Allograft Vasculopathy

To date, there are no established noninvasive biomarkers available for prediction of cardiac allograft vasculopathy (CAV) after orthotopic heart transplantation (OHT). Inflammatory processes are supposed to play a central role in the pathogenesis of CAV. Recent studies have suggested that immune mediators could serve as biomarkers for cardiovascular diseases. We hypothesized particular cytokines or a combination thereof may serve as noninvasive biomarkers for CAV. Plasma cytokines were screened from 27 patients with CAV and 27 patients without CAV after OHT. The concentrations of interleukins-4, -6, -10, -21, -23, -31, -33, interferon gamma, tumor necrosis factor alpha, and the soluble activation marker CD40 ligand were determined using Luminex-based multiplex analyses. Although concentrations of all cytokines except interferon gamma were on average higher in the CAV group, there were no significant differences between the groups for any 1 cytokine. Using a binary logistic regression model, we were able to develop a probability score for detecting patients at elevated risk for advanced CAV with a sensitivity of 92.31% and a specificity of 60.71% (receiver-operating characteristic area under the curve 0.799 ± 0.06; p<0.0001). In conclusion, analyzing the concentration of specific inflammatory cytokines could be meaningfully included in evaluation of CAV after OHT.

High-Sensitivity Troponin T and Soluble Form of AXL as Long-Term Prognostic Biomarkers after Heart Transplantation

Antecedents

Cardiac allograft vasculopathy (CAV) is a frequent complication limiting the long-term (>1 year) survival after heart transplantation (HTx). CAV is initiated by endothelial dysfunction and can lead to severe cardiovascular (CV) complications. Since CAV is often clinically silent, biomarkers could help identifying HTx patients at risk of CAV and their severe complications.

Aim

Evaluate the clinical yield of high-sensitivity cardiac troponin T (hs-cTnT), marker of cardiomyocyte damage, and the soluble form of AXL (sAXL), biomarker of endothelial dysfunction, to assess the prognosis of long-term cardiovascular (CV) events occurring after HTx.

Methods

96 patients were evaluated at least > 1 year after HTx. CAV was evaluated by coronary angiography or multisliced tomography, and hs-cTnT and sAXL measured 6 months before or after CAV evaluation. Patients were followed during 42 ± 15 months for a combined end point including cardiac death, angina or acute myocardial infarction, left ventricular ejection fraction < 50%, or heart failure not due to an acute rejection.

Results

51 patients (53%) presented CAV at evaluation; 21 of them had CV events. Hs-cTnT (56 ± 45 versus 20 ± 18 ng/L; p = 0.04) and sAXL concentrations (98 ± 51 versus 26 ± 26 ng/L; p = 0.01) were significantly higher in patients with CV events. Hs-cTnT (HR 1.03; 95% CI 1.015–1.042, p = 0.0001) and sAXL (HR 1.01; 95% CI 1.001–1.019, p = 0.02) were independent predictors of CV events. A hs-cTnT concentration < 21 ng/L, detected by AUC ROC, predicted the absence of CV events with a predictive value of 91%; sAXL did not add more predictive value to hs-cTnT. Survival free of CV events was 92% in patients with hs-cTnT < 21 ng/L and 57% in those with hs-cTnT > 21 ng/L (p < 0.001).

Conclusion

Hs-cTnT, but not sAXL, measured during the long-term follow-up of HTx patients appears as a helpful biomarker to identify patients at low risk of adverse CV outcomes.

Regulatory T Cells as Biomarkers for Rejection and Immunosuppression Tailoring in Solid Organ Transplantation

The use of biomarkers to tailor immunosuppression and to predict graft and patient outcomes using biological samples obtained by non-invasive tests is one of the main objectives in solid organ transplantation. Although biopsies give the most accurate information, they are clearly invasive and are associated with potentially adverse effects. To date, regulatory T cells have been shown to play a role in allograft protection; for this reason, extensive research has been performed to define them as biomarkers. However, studies of the measurement of these cells in peripheral blood as biomarkers in solid organ transplantation have been very limited and still not validated in prospective randomized large cohorts with the use of standardized methodology. Such poor evidence has been almost exclusively obtained in renal transplantation. Available data summarized here point for their use as biomarkers in different clinical settings with discordant data in many cases.

In Vivo Development of Transplant Arteriosclerosis in Humanized Mice Reflects Alloantigen Recognition and Peripheral Treg Phenotype of Lung Transplant Recipients

Experimentally, regulatory T cells inhibit rejection. In clinical transplantations, however, it is not known whether T cell regulation is the cause for, or an epiphenomenon of, long-term allograft survival. Here, we study naïve and alloantigen-primed T cell responses of clinical lung transplant recipients in humanized mice. The pericardiophrenic artery procured from human lung grafts was implanted into the aorta of NODrag^-/- /IL-2rγc^-/- mice reconstituted with peripheral blood mononuclear cells (PBMCs) from the respective lung recipient. Naïve or primed allogeneic PBMCs procured 21 days post-lung transplantation with or without enriching for CD4⁺ CD25^high T cells were used. Transplant arteriosclerosis was assessed 28 days later by histology. Mice reconstituted with alloantigen-primed PBMCs showed significantly more severe transplant arteriosclerosis than did mice with naïve PBMCs (p = 0.005). Transplant arteriosclerosis was equally suppressed by enriching for autologous naïve (p = 0.012) or alloantigen-primed regulatory T cells (Tregs) (p = 0.009). Alloantigen priming in clinical lung recipients can be adoptively transferred into a humanized mouse model. Transplant arteriosclerosis elicited by naïve or alloantigen-primed PBMCs can be similarly controlled by potent autologous Tregs. Cellular therapy with expanded autologous Tregs in lung transplantation might be a promising future strategy.

Current diagnostic and treatment strategies for cardiac allograft vasculopathy

Heart transplantation remains the most durable treatment for end-stage heart disease that is not amenable to coronary revascularization or anti-arrhythmic therapies. Cardiac allograft vasculopathy (CAV) remains one of the main contributors to morbidity and mortality post heart transplant. Nonimmune and immune factors that influence CAV can be modified after a heart transplant. Given the potential silent nature of CAV in the denervated heart, early diagnosis of CAV is critical. Diagnosis and treatment of CAV remain key areas of investigation to improve patient care and quality of life post heart transplant. While repeat heart transplantation is an option in the treatment of significant CAV, outcomes following retransplantation are inferior to outcomes following first heart transplant. Repeat heart transplantation is limited to a select group of patients after index heart transplant.

Augmentation of Transient Donor Cell Chimerism and Alloantigen-Specific Regulation of Lung Transplants in Miniature Swine

Donor alloantigen infusion induces T cell regulation and transplant tolerance in small animals. Here, we study donor splenocyte infusion in a large animal model of pulmonary transplantation. Major histocompatibility complex-mismatched single lung transplantation was performed in 28 minipigs followed by a 28-day course of methylprednisolone and tacrolimus. Some animals received a perioperative donor or third party splenocyte infusion, with or without low-dose irradiation (IRR) before surgery. Graft survival was significantly prolonged in animals receiving both donor splenocytes and IRR compared with controls with either donor splenocytes or IRR only. In animals with donor splenocytes and IRR, increased donor cell chimerism and CD4(+) CD25(high+) T cell frequencies were detected in peripheral blood associated with decreased interferon-γ production of leukocytes. Secondary third-party kidney transplants more than 2 years after pulmonary transplantation were acutely rejected despite maintained tolerance of the lung allografts. As a cellular control, additional animals received third-party splenocytes or donor splenocyte protein extracts. While animals treated with third-party splenocytes showed significant graft survival prolongation, the subcellular antigen infusion showed no such effect. In conclusion, minipigs conditioned with preoperative IRR and donor, or third-party, splenocyte infusions may develop long-term donor-specific pulmonary allograft survival in the presence of high levels of circulating regulatory T cells.