CD4+ CD28null T cells are not alloreactive unless stimulated by interleukin-15

Recognizing Complexity of CD8 T Cells in Transplantation

The major role of CD8 + T cells in clinical and experimental transplantation is well documented and acknowledged. Nevertheless, the precise impact of CD8 + T cells on graft tissue injury is not completely understood, thus impeding the development of specific treatment strategies. The goal of this overview is to consider the biology and functions of CD8 + T cells in the context of experimental and clinical allotransplantation, with special emphasis on how this cell subset is affected by currently available and emerging therapies.

Terminally differentiated effector memory T cells in kidney transplant recipients: New crossroads

Immunosenescence, the age-related dysregulation of innate and adaptive immunity, impairs immune response and increases inflammation, leading to higher infection and cardiovascular risks, particularly outside the field of transplantation. In kidney transplant recipients (KTRs), conditions like cytomegalovirus infection, old age, uremia, smoking, and diabetes, linked to poor outcomes, are associated with enhanced immunosenescence. Recent studies highlight the pathogenic role of cytotoxic T cells, particularly terminally differentiated effector memory T cells that reexpress CD45RA (TEMRA), in graft dysfunction. A higher proportion of circulating CD8+ TEMRA cells is observed in KTRs with chronic rejection. In antibody-mediated rejection, they invade the graft by superior chemotactic properties and binding to human leukocyte antigen (HLA) antibodies through FcγRIIIa (CD16). Also in microvascular inflammation without donor-specific antibodies, and even in patients without rejection but faster decline of kidney function, intragraft CD8+ TEMRA cells were instrumental. CD8+ TEMRA cells may explain the unresolved dismal graft outcomes associated with donor age and cytomegalovirus-serostatus mismatching and could become a novel therapeutic target in KTRs.

Lowering maintenance immune suppression in elderly kidney transplant recipients; connecting the immunological and clinical dots

The management of long-term immune suppressive medication in kidney transplant recipients is a poorly explored field in the area of transplant medicine. In particular, older recipients are at an increased risk for side effects and have an exponentially increased risk of infection-related death. In contrast, an aged immune system decreases the risk of acute T-cell-mediated rejection in older recipients. Recent advances in alloimmunity research have shown a rapid and substantial decline in polyfunctional, high-risk CD4⁺ T cells post-transplantation. This lowers the direct alloreactivity responsible for T-cell-mediated rejection, also known as donor-specific hyporesponsiveness. Chronic antibody-mediated rejection (c-aABMR) is the most frequent cause of kidney graft loss in the long term. However, in older adults, c-aABMR as a cause of graft loss is outnumbered by death with a functioning graft. In addition, DSA development and a diagnosis of c-aABMR plateau ~10 years after transplantation, resulting in a very low risk for rejection thereafter. The intensity of immune suppression regimes could likely be reduced accordingly, but trials in this area are scarce. Tacrolimus monotherapy for 1 year after transplantation seems feasible in older kidney transplant recipients with standard immunological risk, showing the expected benefits of fewer infections and better vaccination responses.

N6-methyladenosine regulators-related immune genes enable predict graft loss and discriminate T-cell mediate rejection in kidney transplantation biopsies for cause

Objective

The role of m6A modification in kidney transplant-associated immunity, especially in alloimmunity, still remains unknown. This study aims to explore the potential value of m6A-related immune genes in predicting graft loss and diagnosing T cell mediated rejection (TCMR), as well as the possible role they play in renal graft dysfunction.

Methods

Renal transplant-related cohorts and transcript expression data were obtained from the GEO database. First, we conducted correlation analysis in the discovery cohort to identify the m6A-related immune genes. Then, lasso regression and random forest were used respectively to build prediction models in the prognosis and diagnosis cohort, to predict graft loss and discriminate TCMR in dysfunctional renal grafts. Connectivity map (CMap) analysis was applied to identify potential therapeutic compounds for TCMR.

Results

The prognostic prediction model effectively predicts the prognosis and survival of renal grafts with clinical indications (P< 0.001) and applies to both rejection and non-rejection situations. The diagnostic prediction model discriminates TCMR in dysfunctional renal grafts with high accuracy (area under curve = 0.891). Meanwhile, the classifier score of the diagnostic model, as a continuity index, is positively correlated with the severity of main pathological injuries of TCMR. Furthermore, it is found that METTL3, FTO, WATP, and RBM15 are likely to play a pivotal part in the regulation of immune response in TCMR. By CMap analysis, several small molecular compounds are found to be able to reverse TCMR including fenoldopam, dextromethorphan, and so on.

Conclusions

Together, our findings explore the value of m6A-related immune genes in predicting the prognosis of renal grafts and diagnosis of TCMR.

A Novel Technique for the Generation of Substantial Numbers of Functional Resident T Cells from Kidney Tissue

Studying functionality and antigen-specificity of resident kidney T cells derived from a kidney biopsy is hampered by the lack of sufficient numbers of T cells obtained by the standard method of enzymatic tissue dissociation. Enzymatic dissociation of kidney tissue was compared to a novel method of whole kidney tissue culture allowing T cells to migrate into the medium in the presence of exogenous IL-2 and IL-15. T cell numbers were quantified and phenotype of resident T cells (CD69+CD103+/−), TCR Vβ repertoire and functional characteristics were analyzed with multi-parameter flow cytometry. Renal tissue culture for four weeks in the presence of exogenous IL-2 and IL-15 yielded significantly higher numbers of T cells (1.3 × 104/mm3) when compared to cultures without exogenous cytokines (71/mm3) or direct isolation by enzymatic dissociation (662/mm3 T cells, p < 0.05). The proportion of T cells with a resident phenotype did not change in the tissue culture; percentages amounted to 87.2% and 85.1%, respectively. In addition, frequencies of CD4+, CD8+, CD4−CD8−, T cells and MAIT T cells remained similar. For both CD4+ and CD8+, T cells had a more differentiated memory phenotype after tissue culture, but the distribution of TCR Vβ families did not change. In addition, the predominant Th1 cytokine secretion profile and poly-functionality of resident kidney T cell remained intact. T cell proliferation potential was not affected, excluding exhaustion and enrichment of BKV- and CMV-reactive resident T cells was observed. In conclusion, the kidney tissue culture method yields significantly increased numbers of resident T cells without major effects on composition and functionality.

Activated CD4+ T Cells and Highly Differentiated Alloreactive CD4+ T Cells Distinguish Operationally Tolerant Liver Transplantation Recipients

Spontaneous operational tolerance to the allograft develops in a proportion of liver transplantation (LT) recipients weaned off immunosuppressive (IS) drugs. Several studies have investigated whether peripheral blood circulating T cells could play a role in the development or identify operational tolerance, but never characterized alloreactive T cells in detail due to the lack of a marker for these T cells. In this study, we comprehensively investigated phenotypic and functional characteristics of alloreactive circulating T cell subsets in tolerant LT recipients (n = 15) using multiparameter flow cytometry and compared these with LT recipients on IS drugs (n = 23) and healthy individuals (n = 16). Activation-induced CD137 was used as a marker for alloreactive T cells upon allogenic stimulation. We found that central and effector memory CD4+ T cells were hyporesponsive against donor and third-party splenocyte stimulation in tolerant LT recipients, whereas an overall hyperresponsiveness was observed in alloreactive terminally differentiated effector memory CD4+ T cells. In addition, elevated percentages of circulating activated T helper cells were observed in these recipients. Lastly, tolerant and control LT recipients did not differ in donor-specific antibody formation. In conclusion, a combination of circulating hyperresponsive highly differentiated alloreactive CD4+ T cells and circulating activated T helper cells could discriminate tolerant recipients from a larger group of LT recipients.

Endogenous memory T cells with donor-reactivity: early post-transplant mediators of acute graft injury in unsensitized recipients

The pretransplant presence of endogenous donor-reactive memory T cells is an established risk factor for acute rejection and poorer transplant outcomes. A major source of these memory T cells in unsensitized recipients is heterologously generated memory T cells expressing reactivity to donor allogeneic MHC molecules. Multiple clinical studies have shown that the pretransplant presence of high numbers of circulating endogenous donor-reactive memory T cells correlates with higher incidence of acute rejection and decreased graft function during the first-year post-transplant. These findings have spurred investigation in preclinical models to better understand mechanisms underlying endogenous donor-reactive memory T-cell-mediated allograft injury in unsensitized graft recipients. These studies have led to the identification of unique mechanisms underlying the activation of these memory T cells within allografts at early times after transplant. In particular, optimal activation to mediate acute allograft injury is dependent on the intensity of ischaemia-reperfusion injury. Therapeutic strategies directed at the recruitment and activation of endogenous donor-reactive memory T cells are effective in attenuating acute injury in allografts experiencing increased ischaemia-reperfusion injury in preclinical models and should be translatable to clinical transplantation.

Acquisition of New Migratory Properties by Highly Differentiated CD4+CD28null T Lymphocytes in Rheumatoid Arthritis Disease

Expanded CD4+CD28^null T lymphocytes are found in the tissues and peripheral blood of patients with many autoimmune diseases, such as rheumatoid arthritis (RA). These highly differentiated cells present potent inflammatory activity and capability to induce tissue destruction, which has been suggested to predispose to the development of more aggressive disease. In fact, preferential migration to inflammatory sites has been proposed to be a contributing factor in the progression of autoimmune and cardiovascular diseases frequently found in these patients. The functional activity of CD4+CD28^null T lymphocytes is largely dependent on interleukin 15 (IL-15), and this cytokine may also act as a selective attractor of these cells to local inflammatory infiltrates in damaged tissues. We have analysed, in RA patients, the migratory properties and transcriptional motility profile of CD4+CD28^null T lymphocytes compared to their counterparts CD28+ T lymphocytes and the enhancing role of IL-15. Identification of the pathways involved in this process will allow us to design strategies directed to block effector functions that CD4+CD28^null T lymphocytes have in the target tissue, which may represent therapeutic approaches in this immune disorder.

High numbers of differentiated CD28null CD8+ T cells are associated with a lowered risk for late rejection and graft loss after kidney transplantation

Background

The hypothesis was tested that parameters of an aged T-cell compartment associate with the risk for late rejection after kidney transplantation.

Methods

Recipients of a kidney transplant in the period 2007–2013 were (N = 365) were included. T cells were characterized prior to transplantation by flow cytometry as naive (CD45RO^-CCR7⁺), central-memory (CD45RO⁺CCR7⁺), effector-memory (CD45RO^-CCR7^-) or terminally differentiated CD8⁺ Temra (CD45RO^-/CCR7^-/CD28^-) cells. T cell telomere length and thymic output were assessed prior to transplantation in 202 recipients. Follow-up was until December 2018. The date of the first time of biopsy-proven late rejection (>6 months after transplantation) was used to calculate the rejection-free survival time.

Results

Fifty cases of biopsy-proven rejection were recorded. Thymic output and T cell telomere length did not associate with late rejection-free survival. However, the percentage and absolute numbers of CD8⁺Temra and CD28null CD8⁺ T cells were significantly lower in patients with late rejection. Specifically, in the highest tertile of percentages of CD28null CD8⁺ T cells, the cumulative incidence of late rejection at 5 and 10 years was only 5% and 8% compared to 16% and 20% in the middle to lowest tertile (p = 0.002). Multivariate proportional hazard analysis showed that percentage and absolute number of CD28null CD8⁺ T cells remained significantly associated with late rejection and rejection-related graft loss.

Conclusion

High numbers of differentiated CD28null CD8⁺ T cells decrease the risk for late rejection and rejection-related graft loss after kidney transplantation.

Impact of preformed T-cell alloreactivity by means of donor-specific and panel of reactive T cells (PRT) ELISPOT in kidney transplantation

Donor-specific (d-sp) interferon gamma enzyme-linked immunosorbent spot (d-sp ELISPOT) and Panel of reactive T-cell (PRT) ELISPOT assays have been developed to detect alloreactive memory T (Tmem) cells in order to estimate the risk of acute rejection after kidney transplantation. Adding IL15 to the PRT assay (PRT+IL15) may uncover the presence of pathogenic alloreactive CD28^-Tmem. Face-to-face comparisons of these assays have not been done yet. We performed pre-transplant d-sp ELISPOT and PRT assays (±IL15, against six B-cell lines) in 168 consecutive kidney transplant recipients and evaluated the multivariable-adjusted associations with biopsy-proven acute rejection (BPAR), de novo donor-specific antibodies (DSA), and eGFR decline over a 48-month follow-up period. D-sp ELISPOT was positive in 81 (48%) subjects, while 71 (42%) and 81 (48%) subjects displayed positive PRT and PRT+IL15, respectively. Their median [interquartile range] numerical test result was 23 [6–65], 18 [8–37], and 26 [10–45] spots/3x10⁵ PBMCs, respectively. The number of PRT spots were weakly correlated with those of d-sp ELISPOT, but highly correlated with PRT+IL15 (rho = 0.96, P<0.001). d-sp ELISPOT, but not PRT (±IL15) was independently associated with BPAR (adjusted Odds Ratio of BPAR associated with d-sp ELISPOT positivity: 4.20 [95%CI: 1.06 to 21.73; P = 0.041]). Unlike d-sp ELISPOT, median PRT and PRT+IL15 were independently associated with higher Δ3-48month eGFR decline post-transplantation (for both assays, about -3mL/min/1.73m2 per one standard deviation unit increase in the spot number). Pre-transplant T-cell immune-monitoring using d-sp ELISPOT and PRT assays identifies kidney transplant candidates at high risk of BPAR and worse kidney allograft progression.

Cardiovascular disease after transplantation: an emerging role of the immune system

Cardiovascular disease (CVD) after transplantation remains a major concern. Little is known about what drives the increased cardiovascular risk in transplant recipients apart from traditional risk factors. The immune system is involved in the pathogenesis of hypertension, atherosclerosis, and coronary artery disease in the general population. Recently, inhibition of interleukin 1 - β by canakinumab versus placebo decreased the incidence of cardiovascular events. Emerging evidence points to a role of adaptive cellular immunity in the development of CVD. Especially, expansion of pro-inflammatory and antiapoptotic cytotoxic CD4⁺ CD28^null T cells is closely associated with incident CVD in various study populations including transplant recipients. The association of cytomegalovirus exposure with increased cardiovascular mortality might be explained by its capacity to upregulate these cytotoxic cells. Also, humoral immunity seems to be relevant for cardiovascular outcome in transplant recipients. Panel-reactive antibodies at baseline and donor-specific antibodies are independently associated with poor cardiovascular outcome after kidney transplantation. Cardiovascular effects of immunosuppressive drugs and statins do not only imply indirect positive or negative effects on traditional cardiovascular risk factors but also intrinsic immunological effects. How immunosuppressive drugs modify atherosclerosis largely remains elusive.