Myeloid-Derived Suppressor Cells Are Increased in Lung Transplant Recipients and Regulated by Immunosuppressive Therapy.

Lung transplantation remains as a primary treatment for end-stage lung diseases. Although remarkable improvement has been achieved due to the immunosuppressive protocols, long-term survival for lung transplant recipients (LTR) is still limited. In the last few decades, an increasing interest has grown in the study of dysregulation of immune mechanisms underlying allograft failure. In this regard, myeloid-derived suppressor cells (MDSCs) could play an important role in the promotion of graft tolerance due to their immune regulatory function. Here, we describe for the first time circulating subsets MDSCs from LTR at several time points and we evaluate the relationship of MDSCs with sort-term lung transplant outcomes. Although no effect of MDSCs subsets on short-term clinical events was observed, our results determine that Mo-MDSCs frequencies are increased after acute cellular rejection (ACR), suggesting a possible role for Mo-MDSCs in the development of chronic lung allograft dysfunction (CLAD). Therefore, whether MDSCs subsets play a role as biomarkers of chronic rejection remains unknown and requires further investigations. Also, the effects of the different immunosuppressive treatments on these subpopulations remain under research and further studies are needed to establish to what extend MDSCs immune modulation could be responsible for allograft acceptance.

Acute Rejection Following Kidney Transplantation: State-of-the-Art and Future Perspectives.

Although acute renal graft rejection rate has declined in the last years, and because an adequate therapy can improve graft outcome, its therapy remains as one of the most significant challenges for pharmacists and physicians taking care of transplant patients. Due to the lack of evidence highlighted by the available metaanalyses, we performed a narrative review focused on the basic mechanisms and current and future therapies of acute rejection in kidney transplantation. According to Kidney Disease/Improving Global Outcomes (KDIGO) guidelines, both clinical and subclinical acute rejection episodes should be treated. Usually, high dose steroids and basal immunosuppression optimization are the first line of therapy in treating acute cellular rejection. Rabbit antithymocytic polyclonal globulins are used as rescue therapy for recurrent or steroid-resistant cellular rejection episodes. Current standard-of-care (SOC) therapy for acute antibody-mediated rejection (AbMR) is the combination of plasma exchange with intravenous immunoglobulin (IVIG). Since a significant rate of AbMR does not respond to SOC, different studies have analyzed the role of new drugs such as Rituximab, Bortezomib, Eculizumab and C1 inhibitors. Lack of randomized controlled trials and heterogenicity among performed studies limit obtaining definite conclusions. Data about new direct and indirect B cell and plasma cell depleting agents, proximal and terminal complement blockers, IL-6/IL-6R pathway inhibitors and antibody removal agents, among other promising drugs, are reviewed.

Author Correction: Human neutrophils phagocytose and kill Acinetobacter baumannii and A. pittii.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Number of Antibody-verified Eplet in HLA-C Locus as an Independent Factor of T-cell-Mediated Rejection After Liver Transplantation.

BACKGROUND: HLA mismatching is a risk factor for graft rejection in solid organ transplantation. Its definition is being rethought with the introduction of the eplets in organ allocation. The eplets are highly polymorphic regions of the HLA molecule that help to explain cross-reactivity of HLA antigens. The effect of eplet mismatch is well documented in renal and lung transplantation but there is no clear evidence in liver transplantation. METHODS: Forty-three consecutive liver-graft donor/recipient pairs performed at our center from 2016 to 2018 were HLA typed. The quantification of antibody-verified eplets (VerEp) mismatch was performed with HLA-matchmaker 2.1 version. RESULTS: A total of 9 patients suffered an episode of T-cell-mediated rejection (TCMR). No significant differences were observed in the number of A, B, DRB, DQA, and DQB VerEp. However, the mean of mismatches VerEp in locus C (VerEpC) was significantly increased in patients with acute rejection: 3.89 (1.36) versus 2.32 (1.82), P = 0.021. A total of 22 patients with high load of VerEpC (>2) had an increased risk of TCMR (P = 0.008). The time of TCMR-free after liver transplant was statistically reduced in high-load VerEpC group (log-rank test P = 0.019). Multivariate analysis demonstrated that high load of VerEpC was independently associated with TCMR (P = 0.038). CONCLUSIONS: Patients with no or 1 eplet mismatch at the C locus are less likely to suffer TCMR after liver transplantation.

Late Plasma Cell Depletion After Thymoglobulin Induction in Kidney Transplant Recipients.

OBJECTIVES: Induction therapy with rabbit antithymocyte globulin is frequently used in kidney transplant recipients and contributes to regulating the humoral alloantibody response. However, the effect of rabbit antithymocyte globulin on B-cell subpopulations, including plasma cells, has not been previously studied in humans in vivo. MATERIALS AND METHODS: We prospectively studied a cohort of 39 adult kidney transplant recipients. Twenty patients received rabbit antithymocyte globulin as induction therapy. Peripheral blood samples were obtained pretransplant and at 6 and 12 months posttransplant. T and B cells were acquired by flow cytometry. RESULTS: Total lymphocytes and CD3 and CD4 cells significantly decreased at 6 and 12 months only in patients who received rabbit antithymocyte globulin. In contrast, the CD19 population did not change after rabbit antithymocyte globulin induction. One-year circulating plasma cells remained significantly lower than pretransplant levels in patients who received rabbit antithymocyte globulin. We observed sig-nificant differences in plasma cell numbers at 12 months after transplant between patients who received rabbit antithymocyte globulin and those patients who did not receive it (median of 5 and interquartile range of 3-17 vs median of 25 and interquartile range of 12-35; P = .001). CONCLUSIONS: Rabbit antithymocyte globulin induction leads to a late reduction in the number of circulating plasma cells at 1 year after kidney transplant. This effect can contribute to down-regulation of the humoral alloantibody response.

NFκB activation in differentiating glioblastoma stem-like cells is promoted by hyaluronic acid signaling through TLR4.

We have previously described that the NFκB pathway is upregulated during differentiation of glioblastoma stem-like cells (GSCs) which keeps differentiating GSCs in a proliferative astrocytic precursor state. However, extracellular signals and cellular mediators of this pathway are not clear yet. Here, we show that TLR4 is a key factor to promote NFκB activation in differentiating GSCs. TLR4 is upregulated during differentiation of GSCs and promotes transcriptional activation of NFκB as determined by luciferase-reporter assays and expression of NFκB target genes. Downregulation of TLR4 by shRNAs or blockade with anti-TLR4 specific antibodies drastically inhibited NFκB activity which promoted further differentiation and reduced proliferation of GSCs. We found that hyaluronic acid (HA), a main component of brain extracellular matrix, triggers the TLR4-NFκB pathway in differentiating GSCs. Moreover, HA is synthesized and released by GSCs undergoing differentiation and leads to transcriptional activation of NFκB, which is inhibited following downregulation of TLR4 or blockade of HA synthesis. Thus, we have demonstrated that during the process of differentiation, GSCs upregulate TLR4 and release the TLR4 ligand HA, which activates the TLR4-NFκB signaling pathway. This strategy may efficiently be used by differentiating GSCs to maintain their proliferative potential and consequently their tumorigenic capacity.

Human neutrophils phagocytose and kill Acinetobacter baumannii and A. pittii.

Acinetobacter baumannii is a common cause of health care associated infections worldwide. A. pittii is an opportunistic pathogen also frequently isolated from Acinetobacter infections other than those from A. baumannii. Knowledge of Acinetobacter virulence factors and their role in pathogenesis is scarce. Also, there are no detailed published reports on the interactions between A. pittii and human phagocytic cells. Using confocal laser and scanning electron microscopy, immunofluorescence, and live-cell imaging, our study shows that immediately after bacteria-cell contact, neutrophils rapidly and continuously engulf and kill bacteria during at least 4 hours of infection in vitro. After 3 h of infection, neutrophils start to release neutrophil extracellular traps (NETs) against Acinetobacter. DNA in NETs colocalizes well with human histone H3 and with the specific neutrophil elastase. We have observed that human neutrophils use large filopodia as cellular tentacles to sense local environment but also to detect and retain bacteria during phagocytosis. Furthermore, co-cultivation of neutrophils with human differentiated macrophages before infections shows that human neutrophils, but not macrophages, are key immune cells to control Acinetobacter. Although macrophages were largely activated by both bacterial species, they lack the phagocytic activity demonstrated by neutrophils.

Within-Patient Variability in Tacrolimus Blood Levels Predicts Kidney Graft Loss and Donor-Specific Antibody Development.

BACKGROUND: Lack of adherence to immunosuppressive drugs is a risk factor for development of de novo donor-specific antibodies (dnDSA) and can contribute to antibody-mediated rejection and graft loss. Moreover, nonadherence is the main determinant of immunosuppressive drug level variability. High intrapatient variability of tacrolimus relates to a worse outcome in transplant recipients through unknown mechanisms. We hypothesized that a high within-patient variability of tacrolimus could increase the rate of dnDSA development and contribute to further death-censored graft loss (DCGL). METHODS: We included 310 adult renal transplants receiving twice-daily tacrolimus throughout their first posttransplant year, with (1) at least 3 blood trough levels available to calculate coefficient of variation (CV) from month 4 to 12, (2) graft survival longer than 1 year, and (3) absence of pretransplant DSA. The dnDSA were analyzed in sera at 1, 3, and 5 years and around 6 month before the last follow-up visit or graft loss by single-antigen beads. RESULTS: During the follow-up, 53 patients lost their graft excluding death. A total of 116 patients (37.4%) had a CV greater than 30% and 39 (12.6%) developed dnDSA. Coefficient of variation greater than 30% (hazards ratio, 2.613; 95% confidence interval, 1.361-5.016; P = 0.004) independently related to DCGL. Acute rejection, re-transplant and CV greater than 30% (hazards ratio, 2.925; 95% confidence interval, 1.473-5.807; P = 0.002) were the only variables related to dnDSA development by Cox regression analysis. CONCLUSIONS: Tacrolimus level variability is a strong risk factor for dnDSA development and DCGL. Variability must be added to the current monitoring of kidney transplant recipients due to its relationship with adherence and to graft outcome.

Predictive factors of allosensitization in renal transplant patients switched from calcineurin to mTOR inhibitors.

Conversion of kidney-transplant recipients from calcineurin inhibitors to mTOR inhibitors has been suggested to be a risk factor for increased alloimmune response. We have analyzed the development of new HLA-antibodies (HLA-Abs) early after conversion in 184 patients converted in stable phase at our hospital and compared with a control group of nonconverted comparable 63 transplants. Using single-antigen solid-phase immunoassay analysis, a preconversion and a 3-6 months postconversion sera were prospectively analyzed in every patient for the appearance of new HLA-Abs. Renal function at 2 years postconversion and cumulative graft survival were compared between groups. In 16 patients, new HLA-Abs (3-DSA and 13-NonDSA), not present at the moment of conversion, were detected (8.7% vs. 3.1% in the control group). The type of mTORi used, type of CNI preconversion, the presence of steroids, time of conversion, or indication for conversion did not have influence on this effect but the presence of HLA-Abs before conversion highly correlated with the appearance of new specificities. Patients with de novo HLA-Abs showed a trend to worst graft function and survival. In conclusion, conversion to mTORi can be followed by early appearance of de novo HLA-Abs, especially in patients with HLA-Abs preconversion, and this complication should be screened early after conversion.

Cellular immunotolerance in the transplant.

In humans, a state of operational tolerance has been observed in some recipients who anecdotally or experimentally abandoned their immunosuppressive treatment. Besides, advances in the understanding of the immune response and the continuous appearance of new biological molecules have boosted the growing interest in transferring the knowledge concerning immune tolerance from experimental models to clinical transplantation. Most of the strategies for inducing tolerance target the T-lymphocytes, especially T CD4(+) since they play a central role in the regulation of the immune response. However, an effective tolerogenic treatment must also take into account the role of alloantibody producing B-lymphocytes, which have been shown to play a fundamental role in chronic rejection phenomena. There are multiple regulation and silencing mechanisms that operate both during lymphocyte ontogeny in the bone marrow and thymus (central tolerance) and in the periphery (peripheral tolerance). These regulatory mechanisms include the destruction of APCs by cytotoxic lymphocytes, suppressive cytokines, and activation-induced cell death, among others. However, the mechanism that in recent years has come to be attributed the greatest role has been the active suppression of the response by T-lymphocytes themselves. These lymphocytes are named as regulatory T cells that include Tregs CD4(+)CD25(+), Tr1 cells and Th3. The great therapeutic potential of regulatory lymphocyte populations for the control of allogeneic rejection is evident and several clinical trials in humans have been started to be implemented using populations of both Tregs and Tr1 cells for the prevention of allogeneic reactions.

The impact of Th17 cells on transplant rejection and the induction of tolerance.

PURPOSE OF REVIEW: This review aims to provide an overview of the latest evidence for the involvement of Th17 cells in the rejection of solid organ allografts. It will also consider the implications of the relationship between the differentiation pathways of Th17 and regulatory T cells (Tregs), as well as their plasticity in the context of transplantation tolerance. RECENT FINDINGS: In the absence of the Th1 lineage in vivo, Th17 cells are capable of rejecting cardiac allografts, showing the capacity of Th17 cells to cause allograft rejection, at least in experimental models. Th17 cells are relatively unsusceptible to suppression by Tregs, although this may be context dependent. Furthermore, addition of inflammatory signals to a Treg-inducing environment leads to Th17 development and established Tregs can be converted to Th17 cells under inflammatory conditions. SUMMARY: The capacity of Th17 cells to cause allograft rejection is becoming increasingly clear. However, the role and contribution of Th17 cells in allograft rejection in the presence of the full orchestra of T helper cells remains elusive. The apparent resistance of Th17 to be suppressed by Tregs may pose a hurdle for effective immunosuppression and tolerance inducing protocols. Furthermore, the close developmental pathways of Th17 and Tregs and the ability of Tregs to convert into Th17 cells in the presence of inflammatory signals may impede the establishment of specific unresponsiveness to donor alloantigens in vivo.

Immune phenotype predicts risk for posttransplantation squamous cell carcinoma.

Cutaneous squamous cell cancer (SCC) affects up to 30% of kidney transplant recipients (KTRs) within 10 years of transplantation. There are no reliable clinical tests that predict those who will develop multiple skin cancers. High numbers of regulatory T cells associate with poor prognosis for patients with cancer in the general population, suggesting their potential as a predictive marker of cutaneous SCC in KTRs. We matched KTRs with (n = 65) and without (n = 51) cutaneous SCC for gender, age, and duration of immunosuppression and assessed several risk factors for incident SCC during a median follow-up of 340 days. Greater than 35 peripheral FOXP3(+)CD4(+)CD127(low) regulatory T cells/microl, <100 natural killer cells/microl, and previous SCC each significantly associated with increased risk for new cutaneous SCC development (hazard ratio [HR] 2.48 [95% confidence interval (CI) 1.04 to 5.98], HR 5.6 [95% CI 1.31 to 24], and HR 1.33 [95% CI 1.15 to 1.53], respectively). In addition, the ratio of CD8/FOXP3 expression was significantly lower in cutaneous SCC excised from KTRs (n = 25) compared with matched SCC from non-KTRs (n = 25) and associated with development of new cutaneous SCCs. In summary, monitoring components of the immune system can predict development of cutaneous SCC among KTRs.

Regulatory T cells in renal transplantation and modulation by immunosuppression.

The poor long-term graft survival rate counteracts the important advance that transplantation is for end-stage renal disease patients. This is mainly due to the employment of immunosuppression that inhibits nonspecifically the alloimmune response to avoid graft rejection, but, at the same time, brings a number of adverse effects leading to chronic rejection. Thus, the major goal in transplantation is to reach an absence of immune response towards donor alloantigens without the need of long-term immunosuppressant drugs. In recent years, regulatory T cells, mainly those with a CD4CD25FOXP3 phenotype (named as Tregs), have demonstrated an inhibitory effect on immune responses against donor alloantigens. As a consequence, they are a potential tool in the development of transplant tolerance in vivo. Most of the evidence comes from experimental models, although recent works address the role of Tregs in the clinical arena of transplantation. In such a setting, the coexistence of immunosuppression in almost 100% patients is an essential factor to consider. Recent findings show that different drugs favor the induction and maintenance of Tregs in renal transplant recipients. Among them, mammalian target of rapamycin inhibitors seem to better promote the development of Tregs at present. The present work reviews all the evidence published up to date about Tregs in human renal transplantation with a special focus on the effect of clinical protocols of immunosuppression.

Calcineurin inhibitors, but not rapamycin, reduce percentages of CD4+CD25+FOXP3+ regulatory T cells in renal transplant recipients.

BACKGROUND: Immunosuppression in renal transplantation, although manageable in the short-term, is a major hurdle for long-term graft survival. Recently, increased frequencies of CD4CD25 regulatory T cells (Tregs) have been described as an additional mechanism that induces alloimmune tolerance. METHODS: We assessed 64 renal transplant recipients with stable renal function for at least one year. Patients were divided into two groups according to the immunosuppression they were receiving at the moment of the study: one consisted of patients receiving rapamycin (Rapa) but not calcineurin inhibitors (CNI), and the other group received CNI but not Rapa. The Rapa group was further divided into three subgroups according to their previous experience with CNI: CNI-free, CNI withdrawal, and CNI conversion. Frequencies of blood Tregs were studied by flow cytometry after staining with monoclonal antibodies specific for different markers of Tregs. RESULTS: Frequencies of CD4 T cells with regulatory phenotype and function were significantly decreased in peripheral blood of renal transplant patients receiving CNI compared with those receiving Rapa. This effect was independent of an early exposure to CNI because the CNI-free patients in the Rapa group showed similar frequencies of Tregs to the CNI withdrawal and CNI conversion groups. CONCLUSIONS: CNI, but not Rapa, induce a decrease of circulating Tregs in stable renal transplant recipients. Thus, Rapa might be further explored in strategies using preservation of Tregs for transplant tolerance. Furthermore, quantification of blood Tregs may be a suitable tool to identify renal transplant recipients who may be candidates for reduced immunosuppression.