Elena Crespo

Pretransplant Immediately Early-1-Specific T Cell Responses Provide Protection for CMV Infection After Kidney Transplantation

Cytomegalovirus (CMV) infection is still a major complication after kidney transplantation. Although cytotoxic CMV‐specific T cells play a crucial role controlling CMV survival and replication, current pretransplant risk assessment for CMV infection is only based on donor/recipient (IgG)‐serostatus. Here, we evaluated the usefulness of monitoring pre‐ and 6‐month CMV‐specific T cell responses against two dominant CMV antigens (IE‐1 and pp65) and a CMV lysate, using an IFN‐γ Elispot, for predicting the advent of CMV infection in two cohorts of 137 kidney transplant recipients either receiving routine prophylaxis (n = 39) or preemptive treatment (n = 98). Incidence of CMV antigenemia/disease within the prophylaxis and preemptive group was 28%/20% and 22%/12%, respectively. Patients developing CMV infection showed significantly lower anti‐IE‐1‐specific T cell responses than those that did not in both groups (p < 0.05). In a ROC curve analysis, low pretransplant anti‐IE‐1‐specific T cell responses predicted the risk of both primary and late‐onset CMV infection with high sensitivity and specificity (AUC > 0.70). Furthermore, when using most sensitive and specific Elispot cut‐off values, a higher than 80% and 90% sensitivity and negative predictive value was obtained, respectively. Monitoring IE‐1‐specific T cell responses before transplantation may be useful for predicting posttransplant risk of CMV infection, thus potentially guiding decision‐making regarding CMV preventive treatment.

Prospective assessment of antidonor cellular alloreactivity is a tool for guidance of immunosuppression in kidney transplantation.

Current characterization of the immune risk in renal transplant patients is only focused on the assessment of preformed circulating alloantibodies; however, alloreactive memory T cells are key players in mediating allograft rejection. Immune monitoring of antidonor alloreactive memory/effector T cells using an IFN-γ Elispot has been shown to distinguish patients at risk for immune-mediated graft dysfunction, suggesting a potential tool for immunosuppression individualization. In this nonrandomized study, we prospectively assessed donor and nondonor T-cell alloreactivity in 60 highly alloreactive patients receiving calcineurin inhibitor-based immunosuppression and in non-T-cell alloreactive transplant recipients treated with a calcineurin inhibitor-free regimen. The impact was evaluated using 1-year allograft outcome. We found a strong association between ongoing antidonor T-cell alloreactivity and histological lesions of acute T cell-mediated rejection in 6-month protocol biopsies, distinguishing those patients with better 1-year graft function, regardless of immunosuppression regimen. Interestingly, evidence for enhanced immune regulation, driven by circulating Foxp3-demethylated regulatory T cells, was only observed among patients achieving antidonor T-cell hyporesponsiveness. Thus, prospective evaluation of donor-specific T-cell sensitization may add crucial information on the alloimmune state of transplanted patients to be used in daily clinical practice.

Preformed Frequencies of Cytomegalovirus (CMV)–Specific Memory T and B Cells Identify Protected CMV-Sensitized Individuals Among Seronegative Kidney Transplant Recipients

BACKGROUND Cytomegalovirus (CMV) infection remains a major complication after kidney transplantation. Baseline CMV risk is typically determined by the serological presence of preformed CMV-specific immunoglobulin (Ig) G antibodies, even though T-cell responses to major viral antigens are crucial when controlling viral replication. Some IgG-seronegative patients who receive an IgG-seropositive allograft do not develop CMV infection despite not receiving prophylaxis. We hypothesized that a more precise evaluation of pretransplant CMV-specific immune-sensitization using the B and T-cell enzyme-linked immunospot assays may identify CMV-sensitized individuals more accurately, regardless of serological evidence of CMV-specific IgG titers. METHODS We compared the presence of preformed CMV-specific memory B and T cells in kidney transplant recipients between 43 CMV IgG-seronegative (sR(-)) and 86 CMV IgG-seropositive (sR(+)) patients. Clinical outcome was evaluated in both groups. RESULTS All sR(+) patients showed a wide range of CMV-specific memory T- and B-cell responses. High memory T- and B-cell frequencies were also clearly detected in 30% of sR(-) patients, and those with high CMV-specific T-cell frequencies had a significantly lower incidence of late CMV infection after prophylactic therapy. Receiver operating characteristic curve analysis for predicting CMV viremia and disease showed a high area under the receiver operating characteristic curve (>0.8), which translated into a high sensitivity and negative predictive value of the test. CONCLUSIONS Assessment of CMV-specific memory T- and B-cell responses before kidney transplantation among sR(-) recipients may help identify immunized individuals more precisely, being ultimately at lower risk for CMV infection.

Preformed circulating HLA-specific memory B cells predict high risk of humoral rejection in kidney transplantation

The accurate evaluation of donor-specific antibodies (DSAs) has allowed a precise identification of sensitized patients at risk of antibody-mediated rejection (ABMR). However, the scale of the humoral response is not always fully addressed, as it excludes the complete memory B-cell (mBC) pool such as that caused by antigen-specific mBC. Using a novel B-cell ELISpot assay approach, we assessed circulating mBC frequencies against class I and II HLA antigens in highly sensitized and nonsensitized patients in the waiting list for kidney transplantation. Also, kidney transplant patients undergoing ABMR were evaluated for the presence of donor-specific mBCs both at the time of rejection and before transplantation. For this purpose, 278 target HLA-sp antigens from 70 patients were studied and compared to circulating HLA-sp antibodies. Both class I and II HLA-sp mBC frequencies were identified in highly sensitized individuals but not in nonsensitized and healthy individuals, many years after first sensitization. Also, high donor-specific mBC responses were clearly found both during ABMR and before transplantation, regardless of circulating DSA. The higher the donor-specific mBC response, the more aggressive the allograft rejection. Thus, assessing donor-specific mBC frequencies may be relevant to better refine patient alloimmune-risk stratification, and provides new insight into the mechanisms of the adaptive humoral alloimmune response taking place in kidney transplantation.

Pre-transplant donor-specific T-cell alloreactivity is strongly associated with early acute cellular rejection in kidney transplant recipients not receiving T-cell depleting induction therapy.

Preformed T-cell immune-sensitization should most likely impact allograft outcome during the initial period after kidney transplantation, since donor-specific memory T-cells may rapidly recognize alloantigens and activate the effector immune response, which leads to allograft rejection. However, the precise time-frame in which acute rejection is fundamentally triggered by preformed donor-specific memory T cells rather than by de novo activated naïve T cells is still to be established. Here, preformed donor-specific alloreactive T-cell responses were evaluated using the IFN-γ ELISPOT assay in a large consecutive cohort of kidney transplant patients (n = 90), to assess the main clinical variables associated with cellular sensitization and its predominant time-frame impact on allograft outcome, and was further validated in an independent new set of kidney transplant recipients (n = 67). We found that most highly T-cell sensitized patients were elderly patients with particularly poor HLA class-I matching, without any clinically recognizable sensitizing events. While one-year incidence of all types of biopsy-proven acute rejection did not differ between T-cell alloreactive and non-alloreactive patients, Receiver Operating Characteristic curve analysis indicated the first two months after transplantation as the highest risk time period for acute cellular rejection associated with baseline T-cell sensitization. This effect was particularly evident in young and highly alloreactive individuals that did not receive T-cell depletion immunosuppression. Multivariate analysis confirmed preformed T-cell sensitization as an independent predictor of early acute cellular rejection. In summary, monitoring anti-donor T-cell sensitization before transplantation may help to identify patients at increased risk of acute cellular rejection, particularly in the early phases after kidney transplantation, and thus guide decision-making regarding the use of induction therapy.

Human CMV-specific T-cell responses in kidney transplantation; toward changing current risk-stratification paradigm.

Despite the great efficacy of current antiviral preventive strategies, hCMV infection is still a major complication after renal transplantation, significantly challenging patient and graft survival. This issue seems to be explained because of the rather poor immunologic monitoring of the antiviral immune response. An important body of evidence has shown that monitoring the hCMV‐specific T‐cell response, at different time points of the transplant setting, seems to add crucial information for predicting the risk of viral infection, thus potentially helping individualization of therapeutic decision‐making in clinical transplantation. While several immune‐cellular assays have shown its capability for accurately monitoring hCMV‐specific T‐cell responses, only few such as the IFN‐γ ELISPOT and the ELISA based technology assays might be reliable for its application in the clinic. Nonetheless, an important effort has to be made among the transplant community to standardize and validate such immune assays. Noteworthy, large‐scale prospective randomized trials are highly warranted to ultimately introduce them in current clinical practice as a part of the highly desired personalized medicine.

Molecular and Functional Noninvasive Immune Monitoring in the ESCAPE Study for Prediction of Subclinical Renal Allograft Rejection.

Background Subclinical acute rejection (sc-AR) is a main cause for functional decline and kidney graft loss and may only be assessed through surveillance biopsies. Methods The predictive capacity of 2 novel noninvasive blood biomarkers, the transcriptional kidney Solid Organ Response Test (kSORT), and the IFN-&ggr; enzyme-linked immunosorbent spot assay (ELISPOT) assay were assessed in the Evaluation of Sub-Clinical Acute rejection PrEdiction (ESCAPE) Study in 75 consecutive kidney transplants who received 6-month protocol biopsies. Both assays were run individually and in combination to optimize the use of these techniques to predict sc-AR risk. Results Subclinical acute rejection was observed in 22 (29.3%) patients (17 T cell–mediated subclinical rejection [sc-TCMR], 5 antibody-mediated subclinical rejection [sc-ABMR]), whereas 53 (70.7%) showed a noninjured, preserved (stable [STA]) parenchyma. High-risk (HR), low-risk, and indeterminate-risk kSORT scores were observed in 15 (20%), 50 (66.7%), and 10 (13.3%) patients, respectively. The ELISPOT assay was positive in 31 (41%) and negative in 44 (58.7%) patients. The kSORT assay showed high accuracy predicting sc-AR (specificity, 98%; positive predictive value 93%) (all sc-ABMR and 58% sc-TCMR showed HR-kSORT), whereas the ELISPOT showed high precision ruling out sc-TCMR (specificity = 70%, negative predictive value = 92.5%), but could not predict sc-ABMR, unlike kSORT. The predictive probabilities for sc-AR, sc-TCMR, and sc-ABMR were significantly higher when combining both biomarkers (area under the curve > 0.85, P < 0.001) and independently predicted the risk of 6-month sc-AR in a multivariate regression analysis. Conclusions Combining a molecular and immune cell functional assay may help to identify HR patients for sc-AR, distinguishing between different driving alloimmune effector mechanisms.

De novo use of a generic formulation of tacrolimus versus reference tacrolimus in kidney transplantation: evaluation of the clinical results, histology in protocol biopsies, and immunological monitoring.

The use of generic formulations of immunosuppressive drugs in renal transplantation has been and still is a controversial subject. The lack of clinical studies about safety and efficacy in transplant patients is one of the factors restricting the diffusion of generic drugs in the renal transplant field. Since March 2013, our transplant unit has incorporated generic tacrolimus (Adoport®; Sandoz), replacing the one we were currently using (Prograf®; Astellas). When carrying out our retrospective analysis comparing the two different formulations, we evaluated several clinical results: tacrolimus trough concentrations (C0) at 5–7 days; 1, 3, and 6 months post‐transplantation; concentration/dose ratio at 6 months; acute rejection incidence; delayed graft function (DGF); renal function (as CKD‐EPI); and proteinuria at 6 months in 120 patients (1:1 ratio of Prograf® versus Adoport®), noticing no important differences. We also evaluated the results of protocol biopsies at 6 months in a subgroup of patients, thus verifying the safety and efficacy of this particular generic drug versus the reference product on a histological basis as well. No difference in the development of dnDSA (de novo donor‐specific antibody) was found between the two groups.

Effector Antitumor and Regulatory T Cell Responses Influence the Development of Nonmelanoma Skin Cancer in Kidney Transplant Patients

Background Chronic immunosuppression promotes nonmelanocytic squamous cell carcinoma (SCC) after kidney transplantation. Adaptive and innate immunity play a key role controlling tumor growth and are influenced by different immunosuppressive agents. We hypothesized that functional impairment of tumor-specific T cell responses due to calcineurin inhibitors (CNI) could contribute to SCC development, whereas conversion to mammalian target of rapamycin inhibitors (mTOR-i) could recover this protective immune response. Methods Peripheral tumor-specific T cell responses against main SCC-derived antigens using the IFN-&ggr; enzyme-linked immunospot assay and intratumor (IT) and circulating immune phenotypes (CD4 + T, CD8 + T, CD20 + B, CD56 + NK, FOXP3 + regulatory T [Treg] cells) were explored in a cross-sectional analysis in 59 kidney transplant patients with SCC on CNI (KT-CNI-SCC) or mTOR-i (KT-mTORi-SCC), 25 nontransplants developing SCC (NoKT-SCC) and 6 healthy controls. Moreover, 25 KT-CNI-SCC were switched to mTOR-i and evaluated after 12 months. Results Kidney transplant patients showed lower IT infiltrates and tumor-specific T cell responses than NoKT-SCC, and intratumoral and circulating FOXP3 + Treg cells were higher in KT-mTORi-SCC (P < 0.05). Tumor-specific T cell responses were significantly lower in KT-CNI-SCC than KT-mTORi-SCC and NoKT-SCC and predicted SCC relapses (area under the curve = 0.837; P < 0.05). One-year after mTOR-i conversion, a significant increase in FOXP3 + Treg cell numbers and tumor-specific T cell responses were observed, reaching similar levels than KT-mTORi-SCC and NoKT-SCC patients. Conclusions Tumor-specific T cell responses are strongly impaired in CNI-treated patients but recover after mTOR-i conversion, reducing SCC relapses.

Biomarkers to assess donor-reactive T-cell responses in kidney transplant patients.

Different to antibody-mediated rejection (ABMR), T-cell mediated rejection (TCMR) still unpredictably occurs after kidney transplantation in a great part because of a poor immunologic evaluation of the cellular allogeneic immune response. However, in the last years, important efforts have focused on the development of novel and more sensitive assays to monitor T-cell alloimmune responses at different biological levels that may improve the understanding of the functional status of the cellular immune compartment in patients undergoing organ transplantation. In this direction, immune assays evaluating T-cell proliferation, intracellular ATP release, multiparameter flow cytometry, profiling T-cell receptor repertoires and measurements of frequencies of cytokine-producing T-cells using an IFN-γ enzyme-linked immunospot assay (IFN-γ ELISPOT) have been reported showing interesting associations between the cellular alloimmune response and kidney transplant outcomes. In summary, an important progress has been made in the assessment of alloreactive T-cell responses in the context of organ transplantation using novel immune assays at different biological levels. However, there is an urgent need for prospective, randomized clinical studies to validate these encouraging preliminary data to ultimately introduce them in current clinical practice for refining current immune-risk stratification in kidney transplantation.