Long-term effects of alemtuzumab on regulatory and memory T-cell subsets in kidney transplantation

Second Kidney Transplant Outcomes in Dialysis Dependent Recipients by Induction Type in the United States

BACKGROUND

We examined the association between induction type for a second kidney transplant in dialysis-dependent recipients and the long-term outcomes.

METHODS

Using the Scientific Registry of Transplant Recipients, we identified all second kidney transplant recipients who returned to dialysis before re-transplantation. Exclusion criteria included: missing, unusual, or no-induction regimens, maintenance regimens other than tacrolimus and mycophenolate, and positive crossmatch status. We grouped recipients by induction type into 3 groups: the anti-thymocyte group (N = 9899), the alemtuzumab group (N = 1982), and the interleukin 2 receptor antagonist group (N = 1904). We analyzed recipient and death-censored graft survival (DCGS) using the Kaplan-Meier survival function with follow-up censored at 10 years post-transplant. We used Cox proportional hazard models to examine the association between induction and the outcomes of interest. To account for the center-specific effect, we included the center as a random effect. We adjusted the models for the pertinent recipient and organ variables.

RESULTS

In the Kaplan-Meier analyses, induction type did not alter recipient survival (log-rank P = .419) or DCGS (log-rank P = .146). Similarly, in the adjusted models, induction type was not a predictor of recipient or graft survival. Live-donor kidneys were associated with better recipient survival (HR 0.73, 95% CI [0.65, 0.83], P < .001) and graft survival (HR 0.72, 95% CI [0.64, 0.82], P < .001). Publicly insured recipients had worse recipient and allograft outcomes.

CONCLUSION

In this large cohort of average immunologic-risk dialysis-dependent second kidney transplant recipients, who were discharged on tacrolimus and mycophenolate maintenance, induction type did not influence the long-term outcomes of recipient or graft survival. Live-donor kidneys improved recipient and graft survival.

Distinct association between chronic Epstein-Barr virus infection and T cell compartments from pediatric heart, kidney, and liver transplant recipients

Chronic Epstein-Barr virus (EBV) infection after pediatric organ transplantation (Tx) accounts for significant morbidity and mortality. The risk of complications, such as posttransplant lymphoproliferative disorders, in high viral load (HVL) carriers is the highest in heart Tx recipients. However, the immunologic signatures of such a risk have been insufficiently defined. Here, we assessed the phenotypic, functional, and transcriptomic profiles of peripheral blood CD8+/CD4+ T cells, including EBV-specific T cells, in 77 pediatric heart, kidney, and liver Tx recipients and established the relationship between memory differentiation and progression toward exhaustion. Unlike kidney and liver HVL carriers, heart HVL carriers displayed distinct CD8+ T cells with (1) up-regulation of interleukin-21R, (2) decreased naive phenotype and altered memory differentiation, (3) accumulation of terminally exhausted (TEX PD-1+T-bet-Eomes+) and decrease of functional precursors of exhausted (TPEX PD-1intT-bet+) effector subsets, and (4) transcriptomic signatures supporting the phenotypic changes. In addition, CD4+ T cells from heart HVL carriers displayed similar changes in naive and memory subsets, elevated Th1 follicular helper cells, and plasma interleukin-21, suggesting an alternative inflammatory mechanism that governs T cell responses in heart Tx recipients. These results may explain the different incidences of EBV complications and may help improve the risk stratification and clinical management of different types of Tx recipients.

CD4+CD25+ T regulatory cells in renal transplantation

The immune response to an allograft activates lymphocytes with the capacity to cause rejection. Activation of CD4+CD25+Foxp3+T regulatory cells (Treg) can down-regulate allograft rejection and can induce immune tolerance to the allograft. Treg represent <10% of peripheral CD4+T cells and do not markedly increase in tolerant hosts. CD4+CD25+Foxp3+T cells include both resting and activated Treg that can be distinguished by several markers, many of which are also expressed by effector T cells. More detailed characterization of Treg to identify increased activated antigen-specific Treg may allow reduction of non-specific immunosuppression. Natural thymus derived resting Treg (tTreg) are CD4+CD25+Foxp3+T cells and only partially inhibit alloantigen presenting cell activation of effector cells. Cytokines produced by activated effector cells activate these tTreg to more potent alloantigen-activated Treg that may promote a state of operational tolerance. Activated Treg can be distinguished by several molecules they are induced to express, or whose expression they have suppressed. These include CD45RA/RO, cytokine receptors, chemokine receptors that alter pathways of migration and transcription factors, cytokines and suppression mediating molecules. As the total Treg population does not increase in operational tolerance, it is the activated Treg which may be the most informative to monitor. Here we review the methods used to monitor peripheral Treg, the effect of immunosuppressive regimens on Treg, and correlations with clinical outcomes such as graft survival and rejection. Experimental therapies involving ex vivo Treg expansion and administration in renal transplantation are not reviewed.

CD5 Suppresses IL-15–Induced Proliferation of Human Memory CD8+ T Cells by Inhibiting mTOR Pathways

IL-15 induces the proliferation of memory CD8+ T cells as well as NK cells. The expression of CD5 inversely correlates with the IL-15 responsiveness of human memory CD8+ T cells. However, whether CD5 directly regulates IL-15–induced proliferation of human memory CD8+ T cells is unknown. In the current study, we demonstrate that human memory CD8+ T cells in advanced stages of differentiation respond to IL-15 better than human memory CD8+ T cells in stages of less differentiation. We also found that the expression level of CD5 is the best correlate for IL-15 hyporesponsiveness among human memory CD8+ T cells. Importantly, we found that IL-15–induced proliferation of human memory CD8+ T cells is significantly enhanced by blocking CD5 with Abs or knocking down CD5 expression using small interfering RNA, indicating that CD5 directly suppresses the IL-15–induced proliferation of human memory CD8+ T cells. We also found that CD5 inhibits activation of the mTOR pathway, which is required for IL-15–induced proliferation of human memory CD8+ T cells. Taken together, the results indicate that CD5 is not just a correlative marker for IL-15 hyporesponsiveness, but it also directly suppresses IL-15–induced proliferation of human memory CD8+ T cells by inhibiting mTOR pathways.

B-cell response in solid organ transplantation

The transcriptional regulation of B-cell response to antigen stimulation is complex and involves an intricate network of dynamic signals from cytokines and transcription factors propagated from T-cell interaction. Long-term alloimmunity, in the setting of organ transplantation, is dependent on this B-cell response, which does not appear to be halted by current immunosuppressive regimens which are targeted at T cells. There is emerging evidence that shows that B cells have a diverse response to solid organ transplantation that extends beyond plasma cell antibody production. In this review, we discuss the mechanistic pathways of B-cell activation and differentiation as they relate to the transcriptional regulation of germinal center B cells, plasma cells, and memory B cells in the setting of solid organ transplantation.

Concomitant loss of regulatory T and B cells is a distinguishing immune feature of antibody-mediated rejection in kidney transplantation

Although considerable advances have been made in understanding the cellular effector mechanisms responsible for donor-specific antibody generation leading to antibody-mediated rejection (ABMR), the identification of cellular regulators of such immune responses is lacking. To clarify this, we used high dimensional flow cytometry to concomitantly profile and track the two major subsets of regulatory lymphocytes in blood: T regulatory (T_REG) and transitional B cells in a cohort of 96 kidney transplant recipients. Additionally, we established co-culture assays to address their respective capacity to suppress antibody responses in vitro. TREG and transitional B cells were found to be potent suppressors of T follicular helper-mediated B-cell differentiation into plasmablast and antibody generation. TREG and transitional B cells were both durably expanded in patients who did not develop donor-specific antibody post-transplant. However, patients who manifested donor-specific antibody and progressed to ABMR displayed a marked and persistent numerical reduction in TREG and transitional B cells. Strikingly, specific cell clusters expressing the transcription factor T-bet were selectively depleted in both TREG and transitional B-cell compartments in patients with ABMR. Importantly, the coordinated loss of these T-bet⁺CXCR5⁺TREG and T-bet⁺CD21^- transitional B-cell clusters was correlated with increased and inflammatory donor specific antibody responses, more extensive microvascular inflammation and a higher rate of kidney allograft loss. Thus, our study identified coordinated and persistent defects in regulatory T- and B-cell responses in patients undergoing ABMR, which may contribute to their loss of humoral immune regulation, and warrant timely therapeutic interventions to replenish and sustain TREG and transitional B cells in these patients.

Donor-derived regulatory dendritic cell infusion results in host cell cross-dressing and T cell subset changes in prospective living donor liver transplant recipients

Regulatory dendritic cells (DCreg) promote transplant tolerance following their adoptive transfer in experimental animals. We investigated the feasibility, safety, fate, and impact on host T cells of donor monocyte-derived DCreg infused into prospective, living donor liver transplant patients, 7 days before transplantation. The DCreg expressed a tolerogenic gene transcriptional profile, high cell surface programed death ligand-1 (PD-L1):CD86 ratios, high IL-10/no IL-12 productivity and poor ability to stimulate allogeneic T cell proliferation. Target DCreg doses (range 2.5-10 × 10⁶ cells/kg) were achieved in all but 1 of 15 recipients, with no infusion reactions. Following DCreg infusion, transiently elevated levels of donor HLA and immunoregulatory PD-L1, CD39, and CD73 were detected in circulating small extracellular vesicles. At the same time, flow and advanced image stream analysis revealed intact DCreg and "cross-dressing" of host DCs in blood and lymph nodes. PD-L1 co-localization with donor HLA was observed at higher levels than with recipient HLA. Between DCreg infusion and transplantation, T-bet^hi Eomes^hi memory CD8⁺ T cells decreased, whereas regulatory (CD25^hi CD127^- Foxp3⁺ ): T-bet^hi Eomes^hi CD8⁺ T cell ratios increased. Thus, donor-derived DCreg infusion may induce systemic changes in host antigen-presenting cells and T cells potentially conducive to modulated anti-donor immune reactivity at the time of transplant.

Immunosuppression Has Long-Lasting Effects on Circulating Follicular Regulatory T Cells in Kidney Transplant Recipients

Background: FoxP3⁺ follicular regulatory T cells (Tfr) have been identified as the cell population controlling T follicular helper (Tfh) cells and B cells which, are both involved in effector immune responses against transplanted tissue.

Methods: To understand the biology of Tfr cells in kidney transplant patients treated with tacrolimus and mycophenolate mofetil (MMF) combination immunosuppression, we measured circulating (c)Tfh and cTfr cells in peripheral blood by flow cytometry in n = 211 kidney transplant recipients. At the time of measurement patients were 5–7 years after transplantation. Of this cohort of patients, 23.2% (49/211) had been previously treated for rejection. Median time after anti-rejection therapy was 4.9 years (range 0.4–7 years). Age and gender matched healthy individuals served as controls.

Results: While the absolute numbers of cTfh cells were comparable between kidney transplant recipients and healthy controls, the numbers of cTfr cells were 46% lower in immunosuppressed recipients (p < 0.001). More importantly, in transplanted patients, the ratio of cTfr to cTfh was decreased (median; 0.10 vs. 0.06), indicating a disruption of the balance between cTfr and cTfh cells. This shifted balance was observed for both non-rejectors and rejectors. Previous pulse methylprednisolone or combined pulse methylprednisolone + intravenous immunoglobulin anti-rejection therapy led to a non-significant 30.6% (median) and 51.2% (median) drop in cTfr cells, respectively when compared to cTfr cell numbers in transplant patients who did not receive anti-rejection therapy. A history of alemtuzumab therapy did lead to a significant decrease in cTfr cells of 85.8% (median) compared with patients not treated with anti-rejection therapy (p < 0.0001). No association with tacrolimus or MMF pre-dose concentrations was found.

Conclusion: This cross-sectional study reveals that anti-rejection therapy with alemtuzumab significantly lowers the number of cTfr cells in kidney transplant recipients. The observed profound effects by these agents might dysregulate cTfr functions.

Immunosuppressive Agents and Infectious Risk in Transplantation: Managing the "Net State of Immunosuppression"

Successful solid organ transplantation reflects meticulous attention to the details of immunosuppression, balancing risks for graft rejection against risks for infection. The 'net state of immune suppression' is a conceptual framework of all factors contributing to infectious risk. Assays which measure immune function in the immunosuppressed transplant recipient relative to infectious risk and allograft function are lacking. The best measures of integrated immune function may be quantitative viral loads to assess the individual's ability to control latent viral infections. Few studies address adjustment of immunosuppression during active infections. Thus, confronted with infection in solid organ recipients, the management of immunosuppression is based largely on clinical experience. This review examines known measures of immune function and the immunologic effects of common immunosuppressive drugs and available studies reporting modification of drug regimens for specific infections. These data provide a conceptual framework for the management of immunosuppression during infection in organ recipients.

Enhancing the Value of Histopathological Assessment of Allograft Biopsy Monitoring

Traditional histopathological allograft biopsy evaluation provides, within hours, diagnoses, prognostic information, and mechanistic insights into disease processes. However, proponents of an array of alternative monitoring platforms, broadly classified as "invasive" or "noninvasive" depending on whether allograft tissue is needed, question the value proposition of tissue histopathology. The authors explore the pros and cons of current analytical methods relative to the value of traditional and illustrate advancements of next-generation histopathological evaluation of tissue biopsies. We describe the continuing value of traditional histopathological tissue assessment and "next-generation pathology (NGP)," broadly defined as staining/labeling techniques coupled with digital imaging and automated image analysis. Noninvasive imaging and fluid (blood and urine) analyses promote low-risk, global organ assessment, and "molecular" data output, respectively; invasive alternatives promote objective, "mechanistic" insights by creating gene lists with variably increased/decreased expression compared with steady state/baseline. Proponents of alternative approaches contrast their preferred methods with traditional histopathology and: (1) fail to cite the main value of traditional and NGP-retention of spatial and inferred temporal context available for innumerable objective analyses and (2) belie an unfamiliarity with the impact of advances in imaging and software-guided analytics on emerging histopathology practices. Illustrative NGP examples demonstrate the value of multidimensional data that preserve tissue-based spatial and temporal contexts. We outline a path forward for clinical NGP implementation where "software-assisted sign-out" will enable pathologists to conduct objective analyses that can be incorporated into their final reports and improve patient care.

Inclusion body myositis: clinical features and pathogenesis

Inclusion body myositis (IBM) is often viewed as an enigmatic disease with uncertain pathogenic mechanisms and confusion around diagnosis, classification and prospects for treatment. Its clinical features (finger flexor and quadriceps weakness) and pathological features (invasion of myofibres by cytotoxic T cells) are unique among muscle diseases. Although IBM T cell autoimmunity has long been recognized, enormous attention has been focused for decades on several biomarkers of myofibre protein aggregates, which are present in <1% of myofibres in patients with IBM. This focus has given rise, together with the relative treatment refractoriness of IBM, to a competing view that IBM is not an autoimmune disease. Findings from the past decade that implicate autoimmunity in IBM include the identification of a circulating autoantibody (anti-cN1A); the absence of any statistically significant genetic risk factor other than the common autoimmune disease 8.1 MHC haplotype in whole-genome sequencing studies; the presence of a marked cytotoxic T cell signature in gene expression studies; and the identification in muscle and blood of large populations of clonal highly differentiated cytotoxic CD8⁺ T cells that are resistant to many immunotherapies. Mounting evidence that IBM is an autoimmune T cell-mediated disease provides hope that future therapies directed towards depleting these cells could be effective.

Association of More Intensive Induction With Less Acute Rejection Following Intestinal Transplantation: Results of 445 Consecutive Cases From a Single Center

BACKGROUND

In intestinal transplantation, acute cellular rejection (ACR) remains a significant challenge to achieving long-term graft survival. It is still not clear which are the most important prognostic factors.

METHODS

We performed a Cox multivariable analysis of the hazard rates of developing any ACR, severe ACR, and cause-specific graft loss during the first 60 months posttransplant among 445 consecutive intestinal transplant recipients at our institution since 1994. Of particular interest was to determine the prognostic influence of induction type: rabbit antithymocyte globulin (rATG; 2 mg/kg × 5)/rituximab (150 mg/m × 1; begun in 2013), alemtuzumab (2001-2011), and less intensive forms.

RESULTS

First ACR and severe ACR occurred in 61.3% (273/445) and 22.2% (99/445) of cases. The following 3 multivariable predictors were associated with significantly lower hazard rates of developing ACR and severe ACR: transplant type modified multivisceral or full multivisceral (P = 0.0009 and P < 0.000001), rATG/rituximab induction (P < 0.000001 and P < 0.01), and alemtuzumab induction (P = 0.004 and P = 0.07). For both ACR and severe ACR, the protective effects of rATG/rituximab and alemtuzumab were highly significant (P ≤ 0.000005 for ACR; P ≤ 0.01 for severe ACR) but only during the first 24 days posttransplant (when the ACR hazard rate was at its peak). The prognostic effects of rATG/rituximab and alemtuzumab on ACR/severe ACR disappeared beyond 24 days posttransplant (ie, nonproportional hazards). While significant protective effects of both rATG/rituximab and alemtuzumab existed during the first 6 months posttransplant for the hazard rate of graft loss-due-to-rejection (P = 0.01 and P = 0.003), rATG/rituximab was additionally associated with a consistently lower hazard rate of graft loss-due-to-infection (P = 0.003). All significant effects remained after controlling for the propensity-to-be-transplanted since 2013.

CONCLUSIONS

More intensive induction was associated with a significant lowering of ACR risk, particularly during the early posttransplant period.

Regulatory dendritic cells for promotion of liver transplant operational tolerance: Rationale for a clinical trial and accompanying mechanistic studies

Dendritic cells (DC) are rare, bone marrow (BM)-derived innate immune cells that critically maintain self-tolerance in the healthy steady-state. Regulatory DC (DCreg) with capacity to suppress allograft rejection and promote transplant tolerance in pre-clinical models can readily be generated from BM precursors or circulating blood monocytes. These DCreg enhance allograft survival via various mechanisms, including promotion of regulatory T cells. In non-human primates receiving minimal immunosuppressive drug therapy (IS), infusion of DCreg of donor origin, one week before transplant, safely prolongs renal allograft survival and selectively attenuates anti-donor CD8+ memory T cell responses in the early post-transplant period. Based on these observations, and in view of the critical need to reduce patient dependence on non-specific IS agents that predispose to cardiometabolic side effects and renal insufficiency, we will conduct a first-in-human safety and preliminary efficacy study of donor-derived DCreg infusion to achieve early (18 months post-transplant) complete IS withdrawal in low-risk, living donor liver transplant recipients receiving standard-of-care IS (mycophenolate mofetil, tacrolimus and steroids). We will test the hypothesis that, although donor-derived DCreg are short-lived, they will induce robust donor-specific T cell hyporesponsiveness. We will examine immunological mechanisms by sequential analysis of blood and tissue samples, incorporating cutting-edge technologies.

Potential Beneficial Effects of Cytomegalovirus Infection after Transplantation

Cytomegalovirus (CMV) infection can cause significant complications after transplantation, but recent emerging data suggest that CMV may paradoxically also exert beneficial effects in two specific allogeneic transplant settings. These potential benefits have been underappreciated and are therefore highlighted in this review. First, after allogeneic hematopoietic stem cell transplantation (HSCT) for acute myeloid leukemia (AML) using T-cell and natural killer (NK) cell-replete grafts, CMV reactivation is associated with protection from leukemic relapse. This association was not observed for other hematologic malignancies. This anti-leukemic effect might be mediated by CMV-driven expansion of donor-derived memory-like NKG2C⁺ NK and Vδ2^negγδ T-cells. Donor-derived NK cells probably recognize recipient leukemic blasts by engagement of NKG2C with HLA-E and/or by the lack of donor (self) HLA molecules. Vδ2^negγδ T cells probably recognize as yet unidentified antigens on leukemic blasts via their TCR. Second, immunological imprints of CMV infection, such as expanded numbers of Vδ2^negγδ T cells and terminally differentiated TCRαβ⁺ T cells, as well as enhanced NKG2C gene expression in peripheral blood of operationally tolerant liver transplant patients, suggest that CMV infection or reactivation may be associated with liver graft acceptance. Mechanistically, poor alloreactivity of CMV-induced terminally differentiated TCRαβ⁺ T cells and CMV-induced IFN-driven adaptive immune resistance mechanisms in liver grafts may be involved. In conclusion, direct associations indicate that CMV reactivation may protect against AML relapse after allogeneic HSCT, and indirect associations suggest that CMV infection may promote allograft acceptance after liver transplantation. The causative mechanisms need further investigations, but are probably related to the profound and sustained imprint of CMV infection on the immune system.

Allo-HLA Cross-Reactivities of Cytomegalovirus-, Influenza-, and Varicella Zoster Virus-Specific Memory T Cells Are Shared by Different Healthy Individuals

Virus-specific T cells can recognize allogeneic HLA (allo-HLA) through TCR cross-reactivity. The allospecificity often differs by individual (private cross-reactivity) but also can be shared by multiple individuals (public cross-reactivity); however, only a few examples of the latter have been described. Because these could facilitate alloreactivity prediction in transplantation, we aimed to identify novel public cross-reactivities of human virus-specific CD8⁺ T cells directed against allo-HLA by assessing their reactivity in mixed-lymphocyte reactions. Further characterization was done by studying TCR usage with primer-based DNA sequencing, cytokine production with ELISAs, and cytotoxicity with ⁵¹ chromium-release assays. We identified three novel public allo-HLA cross-reactivities of human virus-specific CD8⁺ T cells. CMV B35/IPS CD8⁺ T cells cross-reacted with HLA-B51 and/or HLA-B58/B57 (23% of tetramer-positive individuals), FLU A2/GIL (influenza IMP[58-66] HLA-A*02:01/GILGFVFTL) CD8⁺ T cells with HLA-B38 (90% of tetramer-positive individuals), and VZV A2/ALW (varicella zoster virus IE62[593-601] HLA-A*02:01/ALWALPHAA) CD8⁺ T cells with HLA-B55 (two unrelated individuals). Cross-reactivity was tested against different cell types including endothelial and epithelial cells. All cross-reactive T cells expressed a memory phenotype, emphasizing the importance for transplantation. We conclude that public allo-HLA cross-reactivity of virus-specific memory T cells is not uncommon and may create novel opportunities for alloreactivity prediction and risk estimation in transplantation.

Janus kinase inhibition for immunosuppression in solid organ transplantation: Is there a role in complex immunologic challenges?

Inhibition of the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway for immunosuppression in solid organ transplantation is appealing due to its specificity for immune cell function, particularly for JAK3. This is due to its unique association with only the common gamma chain (γ_c). The γ_c is an appealing immunosuppression target in transplantation because of the critically important lymphokines that act at it, including IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21. Tofacitinib was initially purported to selectively inhibit solely JAK3, but subsequent analyses have also demonstrated its activity at the other members of the JAK family. Clinical outcomes have validated tofacitinib's pan-JAK activity in kidney transplantation after demonstrating an increased risk of infection and malignancy as compared to CNI-based regimens. After these trials, tofacitinib investigation for use in transplantation has effectively ceased. However, a post-hoc analysis has shed new light on the monitoring of tofacitinib exposure in order to predict infection and oncologic events. With new methods to monitor tofacitinib exposure, clinicians may be able to effectively reduce toxicities while providing a high level of immunosuppression. The purpose of this review to identify when, and for whom, JAK inhibitors may provide benefit in solid organ transplantation.

Impact of Immune-Modulatory Drugs on Regulatory T Cell

Immunosuppression strategies that selectively inhibit effector T cells while preserving and even enhancing CD4FOXP3 regulatory T cells (Treg) permit immune self-regulation and may allow minimization of immunosuppression and associated toxicities. Many immunosuppressive drugs were developed before the identity and function of Treg were appreciated. A good understanding of the interactions between Treg and immunosuppressive agents will be valuable to the effective design of more tolerable immunosuppression regimens. This review will discuss preclinical and clinical evidence regarding the influence of current and emerging immunosuppressive drugs on Treg homeostasis, stability, and function as a guideline for the selection and development of Treg-friendly immunosuppressive regimens.

Graft-infiltrating host dendritic cells play a key role in organ transplant rejection

Successful engraftment of organ transplants has traditionally relied on preventing the activation of recipient (host) T cells. Once T-cell activation has occurred, however, stalling the rejection process becomes increasingly difficult, leading to graft failure. Here we demonstrate that graft-infiltrating, recipient (host) dendritic cells (DCs) play a key role in driving the rejection of transplanted organs by activated (effector) T cells. We show that donor DCs that accompany heart or kidney grafts are rapidly replaced by recipient DCs. The DCs originate from non-classical monocytes and form stable, cognate interactions with effector T cells in the graft. Eliminating recipient DCs reduces the proliferation and survival of graft-infiltrating T cells and abrogates ongoing rejection or rejection mediated by transferred effector T cells. Therefore, host DCs that infiltrate transplanted organs sustain the alloimmune response after T-cell activation has already occurred. Targeting these cells provides a means for preventing or treating rejection.

Alemtuzumab as Antirejection Therapy: T Cell Repopulation and Cytokine Responsiveness

Supplemental digital content is available in the text.

Background

Alemtuzumab induction therapy in kidney transplant patients results in T cell depletion followed by slow immune reconstitution of memory T cells with reduced immune functions. The kinetics and functional characteristics of T cell reconstitution when alemtuzumab is given during immune activation, ie, as antirejection therapy, are unknown.

Methods

Patients (n = 12) with glucocorticoid-resistant or severe vascular kidney transplant rejection were treated with alemtuzumab. Flow cytometric analysis was performed on whole blood to measure cell division by the marker Ki-67, and cytokine responsiveness by IL-2–mediated and IL-7–mediated phosphorylation of signal transducer and activator of transcription 5 of T cells before and during the first year after rejection therapy.

Results

At 1 year after alemtuzumab antirejection therapy, the total T cell population recovered to baseline level. Repopulation of CD4+ and CD8+ T cells was associated with increased percentages of Ki-67+ proliferating T cells (P < 0.05). In addition, both populations showed a phenotypic shift toward relatively more memory T cells (P < 0.01). At the functional level, IL-7 reactivity of CD4+ memory T cells was diminished, reflected by a decreased capacity to phosphorylate signal transducer and activator of transcription 5 during the first 6 months after alemtuzumab treatment (P < 0.05), whereas reactivity to IL-2 was preserved. CD8+ T cells were affected in terms of both IL-2 and IL-7 responses (both P < 0.05). After reconstitution, relatively more regulatory T cells were present, and a relatively high proportion of Ki-67+ T cells was observed.

Conclusions

Preliminary data from this small series suggest that alemtuzumab antirejection therapy induces homeostatic proliferation of memory and regulatory T cells with diminished responsiveness to the homeostatic cytokine IL-7. IL-2 responsiveness was affected in repopulated CD8+ T cells.

T Cell Response in Patients with Implanted Biological and Mechanical Prosthetic Heart Valves

The study was aimed at assessing T cell subsets of peripheral blood from recipients of long-term functioning (more than 60 months) biological and mechanical heart valve prostheses. The absolute and relative number of CD4 and CD8 T cell subsets was analyzed: naïve (N, CD45RA⁺CD62L⁺), central memory (CM, CD45RA⁻CD62L⁺), effector memory (EM, CD45RA⁻CD62L⁻), and terminally differentiated CD45RA-positive effector memory (TEMRA, CD45RA⁺CD62L⁻) in 25 persons with biological and 7 with mechanical prosthesis compared with 48 apparently healthy volunteers. The relative and absolute number of central memory and naïve CD3⁺CD8⁺ in patients with biological prosthesis was decreased (p < 0.001). Meanwhile the number of CD45RA⁺CD62L⁻CD3⁺CD8⁺ and CD3⁺CD4⁺ was increased (p < 0.001). Patients with mechanical prosthesis had increased absolute and relative number of CD45RA⁺CD62L⁻CD3⁺CD8⁺ cells (p = 0.006). Also the relative number of CD3⁺CD4⁺ cells was reduced (p = 0.04). We assume that altered composition of T cell subsets points at development of xenograft rejection reaction against both mechanical and biological heart valve prostheses.

Prospective Clinical Testing of Regulatory Dendritic Cells in Organ Transplantation

Dendritic cells (DC) are rare, professional antigen-presenting cells with ability to induce or regulate alloimmune responses. Regulatory DC (DCreg) with potential to down-modulate acute and chronic inflammatory conditions that occur in organ transplantation can be generated in vitro under a variety of conditions. Here, we provide a rationale for evaluation of DCreg therapy in clinical organ transplantation with the goal of promoting sustained, donor-specific hyporesponsiveness, while lowering the incidence and severity of rejection and reducing patients’ dependence on anti-rejection drugs. Generation of donor- or recipient-derived DCreg that suppress T cell responses and prolong transplant survival in rodents or non-human primates has been well-described. Recently, good manufacturing practice (GMP)-grade DCreg have been produced at our Institution for prospective use in human organ transplantation. We briefly review experience of regulatory immune therapy in organ transplantation and describe our experience generating and characterizing human monocyte-derived DCreg. We propose a phase I/II safety study in which the influence of donor-derived DCreg combined with conventional immunosuppression on subclinical and clinical rejection and host alloimmune responses will be examined in detail.

Lymphocyte depletion and repopulation after chemotherapy for primary breast cancer

Background

Approximately 30 % of breast cancer patients receive chemotherapy, yet little is known about influences of current regimens on circulating lymphocyte levels and phenotypes. Similarly, clinico-pathological factors that modify these influences, and implications for future immune health remain mainly unexplored.

Methods

We used flow-cytometry to assess circulating lymphocyte levels and phenotypes in 88 primary breast cancer patients before chemotherapy and at time-points from 2 weeks to 9 months after chemotherapy completion. We examined circulating titres of antibodies against pneumococcal and tetanus antigens using ELISAs.

Results

Levels of B, T and NK cells were significantly reduced 2 weeks after chemotherapy (p < 0.001). B cells demonstrated particularly dramatic depletion, falling to 5.4 % of pre-chemotherapy levels. Levels of all cells recovered to some extent, although B and CD4⁺ T cells remained significantly depleted even 9 months post-chemotherapy (p < 0.001). Phenotypes of repopulating B and CD4⁺ T cells were significantly different from, and showed no sign of returning to pre-chemotherapy profiles. Repopulating B cells were highly depleted in memory cells, with proportions of memory cells falling from 38 % to 10 % (p < 0.001). Conversely, repopulating CD4⁺ T cells were enriched in memory cells, which increased from 63 % to 75 % (p < 0.001). Differences in chemotherapy regimen and patient smoking were associated with significant differences in depletion extent or repopulation dynamics. Titres of anti-pneumococcal and anti-tetanus antibodies were both significantly reduced post-chemotherapy and did not recover during the study (p < 0.001).

Conclusion

Breast cancer chemotherapy is associated with long-term changes in immune parameters that should be considered during clinical management.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-015-0669-x) contains supplementary material, which is available to authorized users.

Detection of Virus-Specific CD8+ T Cells With Cross-Reactivity Against Alloantigens: Potency and Flaws of Present Experimental Methods

Supplemental digital content is available in the text.

Virus-specific T cells have the intrinsic capacity to cross-react against allogeneic HLA antigens, a phenomenon known as heterologous immunity. In transplantation, these cells may contribute to the alloimmune response and negatively impact graft outcome. This study describes the various techniques that can be used to detect heterologous immune responses of virus-specific CD8⁺ T cells against allogeneic HLA antigens. The strengths and weaknesses of the different approaches are discussed and illustrated by experimental data.

CMV Primary Infection Is Associated With Donor-Specific T Cell Hyporesponsiveness and Fewer Late Acute Rejections After Liver Transplantation

Viral infections, including cytomegalovirus (CMV), abrogate transplantation tolerance in animal models. Whether this also occurs in humans remains elusive. We investigated how CMV affects T cells and rejection episodes after liver transplantation (LT). Phenotype and alloreactivity of peripheral and allograft-infiltrating T cells from LT patients with different CMV status were analyzed by flow cytometry. The association of CMV status with early and late acute rejection was retrospectively analyzed in a cohort of 639 LT patients. CMV-positivity was associated with expansion of peripheral effector memory T cell subsets after LT. Patients with CMV primary infection showed donor-specific CD8(+) T cell hyporesponsiveness. While terminally differentiated effector memory cells comprised the majority of peripheral donor-specific CD8(+) T cells in CMV primary infection patients, they were rarely present in liver allografts. Retrospective analysis showed that R(-) D(+) serostatus was an independent protective factor for late acute rejection by multivariate Cox regression analysis (hazard ratio [HR] = 0.18, 95% CI = 0.04-0.86, p = 0.015). Additionally, CMV primary infection patients showed the highest Vδ1/Vδ2 γδ T cell ratio, which has been shown to be associated with operational tolerance after LT. In conclusion, our data suggest that CMV primary infection may promote tolerance to liver allografts, and CMV status should be considered when tapering or withdrawing immunosuppression.

Lymphocytes as an Indicator for Initial Kidney Function: A Single Center Analysis of Outcome after Alemtuzumab or Basiliximab Induction

Alemtuzumab, an anti-CD52 T-cell and B-cell depleting monoclonal antibody, is established for induction therapy in renal transplantation (KTx). We herein provide a comparative analysis between alemtuzumab and basiliximab induction therapy and correlate lymphocyte depletion and recovery with the clinical course after KTx. This is a single center retrospective analysis of 225 patients/consecutive kidney transplantations treated with alemtuzumab for lymphocyte depletion and 205 recipients treated with basiliximab. Mean lymphocyte counts were 22.8 ± 9.41% before Tx and 2.61 ± 3.11% between week 1 and week 3 in the alemtuzumab group and 23.77 ± 10.42% before Tx and 13.92 ± 8.20% in the basiliximab group. Delayed graft function (DGF), cytomegalovirus (CMV) status, and recipient age showed a significant correlation with lymphocyte counts in the alemtuzumab group only. The outcome was read in reference to the velocity of lymphocyte recovery and in comparison to the control group. Lymphocyte counts early after transplantation, following alemtuzumab treatment, could be identified as a predictive factor for kidney function early after transplantation. A detailed analysis of phenotype and function of lymphocytes after alemtuzumab induction together with a correlation with the clinical course is warranted.

Recollective homeostasis and the immune consequences of peritransplant depletional induction therapy

One's cellular immune repertoire is composed of lymphocytes in multiple stages of maturation - the dynamic product of their responses to antigenic challenges and the homeostatic contractions necessary to accommodate immune expansions within physiologic norms. Given that alloreactivity is predominantly a cross-reactive phenomenon that is stochastically distributed throughout the overall T-cell repertoire, one's allospecific repertoire is similarly made up of cells in a variety of differentiation states. As such, the continuous expansion and elimination of activated memory populations, producing a 'recollective homeostasis' of sorts, has the potential over time to alter the maturation state and effector composition of both ones protective and alloreactive T-cell repertoire. Importantly, a T cell's maturation state significantly influences its response to numerous immunomodulatory therapies used in organ transplantation, including depletional antibody induction. In this review, we discuss clinically utilized depletional induction strategies, how their use alters a transplant recipient's cellular immune repertoire, and how a recipient's repertoire influences the clinical effects of induction therapy.

Homeostatic expansion as a barrier to lymphocyte depletion strategies

PURPOSE OF REVIEW

Following lymphodepletion, lymphocytes repopulate the immune space both through enhanced thymopoiesis and proliferation of residual nondepleted peripheral lymphocytes. The term homeostatic proliferation (alternatively homeostatic expansion or lymphopenia-induced proliferation) refers to the latter process. Homeostatic proliferation is especially relevant to reconstitution of the lymphocyte compartment following immunodepletion therapy in transplantation. Repopulating lymphocytes can skew toward an effector memory type capable of inducing graft rejection, autoimmunity, or, in the case of allogeneic bone marrow transplantation, graft versus host disease. Here we review recent studies exploring the biologic mechanisms underlying homeostatic proliferation and explore implications for therapy in transplantation.

RECENT FINDINGS

Two immune-depleting agents, alemtuzumab and rabbit antithymocyte globulin, have been well characterized in their abilities to induce an effector-memory phenotype in repopulating lymphocytes. Additionally, we have gained new understandings of the mechanisms by which the cytokines interleukin-7 and interleukin-15 regulate this process. Recent studies have also explored the functions of noncytokine and signaling molecules in lymphopenia-induced proliferation. Finally, we have seen the promise and limitations of several therapeutic approaches, including recombinant interleukin-7 therapy, CD8-targeted antibodies, and peri-transplant cyclophosphamide, to treat posttransplant lymphopenia and reduce the risks of immune dysregulation following homeostatic proliferation.

SUMMARY

Immune dysfunction following homeostatic proliferation is a special challenge in transplantation. A deeper understanding of the underlying biology has led to a number of promising new therapies to overcome this problem.

A randomized pilot study of donor stem cell infusion in living-related kidney transplant recipients receiving alemtuzumab

BACKGROUND

Transplant tolerance would remove the need for maintenance immunosuppression while improving survival and quality of life.

METHODS

A prospective, randomized pilot study was undertaken to assess the safety and efficacy of donor stem cell infusion (DSCI) in living-related kidney transplant recipients treated with alemtuzumab (C1H) induction and tacrolimus and mycophenolate maintenance with switch to sirolimus and weaning over 2 years.

RESULTS

Four patients received DSCI; five patients were controls. Graft failure occurred in two patients in the DSCI arm. Recurrence of glomerular disease occurred in two DSCI recipients, leading to graft loss in one. Biopsy-proven acute rejection episodes occurred in three patients (two in the DSCI vs. one in the control). One DSCI patient, with recurrence, subsequently developed antibody-mediated rejection leading to graft failure. In the remaining two DSCI patients, weaning was attempted but was not successful. All (4 of 4) DSCI patients had biopsy-proven chronic allograft injury and/or recurrence.

CONCLUSION

DSCI with C1H induction and a steroid-free maintenance regimen in a small group of patients failed to induce tolerance, with suboptimal patient and graft survival. The results do not justify extension of this particular trial and underscore the importance of patient selection, specifically avoidance of patients with glomerulopathies whose recurrence may obscure potential benefit.

Increased numbers of circulating CD8 effector memory T cells before transplantation enhance the risk of acute rejection in lung transplant recipients

The effector and regulatory T cell subpopulations involved in the development of acute rejection episodes in lung transplantation remain to be elucidated. Twenty-seven lung transplant candidates were prospectively monitored before transplantation and within the first year post-transplantation. Regulatory, Th17, memory and naïve T cells were measured in peripheral blood of lung transplant recipients by flow cytometry. No association of acute rejection with number of peripheral regulatory T cells and Th17 cells was found. However, effector memory subsets in acute rejection patients were increased during the first two months post-transplant. Interestingly, patients waiting for lung transplant with levels of CD8⁺ effector memory T cells over 185 cells/mm³ had a significant increased risk of rejection [OR: 5.62 (95% CI: 1.08-29.37), p=0.04]. In multivariate analysis adjusted for age and gender the odds ratio for rejection was: OR: 5.89 (95% CI: 1.08-32.24), p=0.04. These data suggest a correlation between acute rejection and effector memory T cells in lung transplant recipients. The measurement of peripheral blood CD8⁺ effector memory T cells prior to lung transplant may define patients at high risk of acute lung rejection.

Inhibitory effects of belatacept on allospecific regulatory T-cell generation in humans

BACKGROUND

It is unclear if new costimulatory blockade agents, such as the cytotoxic T lymphocyte-associated antigen 4-Ig molecule belatacept (BEL), promote or inhibit the potential for immunologic tolerance in transplantation. We therefore tested the in vitro effects of BEL on human regulatory T cells (Tregs) in mixed lymphocyte reactions (MLR) alone and in combination with maintenance agents used in transplant recipients.

METHODS

BEL, mycophenolic acid (MPA), and sirolimus, either alone or in combination, were added to healthy volunteer Treg-MLR, testing (a) H-TdR incorporation for inhibition of lymphoproliferation and (b) flow cytometry to analyze for newly generated CD4+ CD25(high) FOXP3+ Tregs in carboxyfluorescein succinimidyl ester-labeled MLR responders. In addition, the modulatory effects of putative Tregs generated in the presence of these drugs were also tested using the lymphoproliferation and flow cytometric assays.

RESULTS

In comparison with medium controls, BEL dose-dependently inhibited both lymphoproliferation and Treg generation in human leukocyte antigen DR matched and mismatched MLRs either alone or in combination with MPA or sirolimus. However, MPA alone inhibited lymphoproliferation but significantly enhanced Treg generation at subtherapeutic concentrations (P<0.01). In addition, purified CD4+ CD127- cells generated in MLR in the presence of MPA and added as third component modulators in fresh MLRs significantly enhanced newly developed Tregs in the proliferating responder cells compared with those generated with BEL or medium controls.

CONCLUSIONS

BEL alone and in combination with agents used in transplant recipients inhibits the in vitro generation of human Tregs. BEL might therefore be a less optimal agent for tolerance induction in human organ transplantation.

Post-transplant repopulation of naïve and memory T cells in blood and lymphoid tissue after alemtuzumab-mediated depletion in heart-transplanted cynomolgus monkeys

Repopulation of memory T cells (Tmem) in allograft recipients after lymphodepletion is a major barrier to transplant tolerance induction. Ineffective depletion of naïve T cells (Tn) and Tmem may predispose to repopulation of Tmem after transplantation. Cynomolgus macaque monkeys given heart allografts were lymphodepleted using Alemtuzumab (Campath-1H; anti-CD52). Peripheral blood (PB) and lymph nodes (LN) were analyzed for CD95(-) (Tn) and CD95(+) cells (Tmem), one day, one month and up to three months after Alemtuzumab infusion. CD52 expression, susceptibility to Alemtuzumab cytotoxicity and pro-apoptotic caspase-3 were evaluated in Tn and Tmem. In vivo, Alemtuzumab induction profoundly depleted lymphocytes in PB (99% reduction) but exerted a lesser effect in LN (70% reduction), with similar depletion of Tn and Tmem subsets. After transplantation, Tmem comprised the majority of lymphocytes in PB and LN. In vitro, LN T cells were more resistant to Alemtuzumab-mediated cytotoxicity than PB lymphocytes. CD4(+) Tn and Tmem were equally susceptible to Alemtuzumab-mediated cytotoxicity, whereas CD8(+) Tn were more resistant than CD8(+) Tmem. However, no significant differences in CD52 expression between lymphocyte subsets in PB and LN were observed. Caspase-3 expression was higher in PB than LN T cells. CD4(+) and CD8(+) Tn expressed lower levels of Caspase-3 than Tmem, in both PB and LN. Thus, after Alemtuzumab infusion, residual Tn in secondary lymphoid tissue may predispose to rapid recovery of Tmem in allograft recipients.

Elevation of CD4+ differentiated memory T cells is associated with acute cellular and antibody-mediated rejection after liver transplantation

BACKGROUND

It is now well known that the outcome after allogeneic transplantation, such as incidence of acute rejections, very much depends on the individual's immune reactivity status. There is also increasing evidence that the presence of preexisting memory T cells can affect antigraft immune responses.

METHODS

In a prospective study, we monitored peripheral CD4 and CD8 central memory, effector memory, and terminal differentiated effector memory (TEMRA) T cells in 55 patients who underwent deceased liver transplantation and received conventional immunosuppressive treatment with or without basiliximab induction. The primary endpoint of the study was acute allograft rejection during a 1-year follow-up period.

RESULTS

We observed significantly increased proportions of CD4 and CD8 TEMRA cells in patients before transplantation compared with healthy controls (P=0.006 and 0.009, respectively). This characteristic was independent of the underlying disease. In patients with no signs of acute rejection, we observed an immediate reduction of CD4 TEMRA cells. In contrast, patients who experienced acute cellular rejection, and especially antibody-mediated rejection, displayed persistent elevated TEMRA cells (P=0.017 and 0.027, respectively). Basiliximab induction therapy did not influence CD4 and CD8 TEMRA numbers.

CONCLUSIONS

Conventional immunosuppressive or basiliximab treatment cannot control the persistence of TEMRA T cells, which may contribute to acute cellular rejection and antibody-mediated rejection after liver transplantation. In the future, specific targeting of TEMRA cells in selected patients may prevent the occurrence of difficult to treat steroid-resistant rejections, thereby leading to improved patient outcome.

Ex vivo-expanded cynomolgus macaque regulatory T cells are resistant to alemtuzumab-mediated cytotoxicity

Alemtuzumab (Campath-1H) is a humanized monoclonal antibody (Ab) directed against CD52 that depletes lymphocytes and other leukocytes, mainly by complement-dependent mechanisms. We investigated the influence of alemtuzumab (i) on ex vivo-expanded cynomolgus monkey regulatory T cells (Treg) generated for prospective use in adoptive cell therapy and (ii) on naturally occurring Treg following alemtuzumab infusion. Treg were isolated from PBMC and lymph nodes and expanded for two rounds. CD52 expression, binding of alemtuzumab and both complement-mediated killing and Ab-dependent cell-mediated cytotoxicity (ADCC) were compared between freshly isolated and expanded Treg and effector T cells. Monkeys undergoing allogeneic heart transplantation given alemtuzumab were monitored for Treg and serum alemtuzumab activity. Ex vivo-expanded Treg showed progressive downregulation of CD52 expression, absence of alemtuzumab binding, minimal change in complement inhibitory protein (CD46) expression and no complement-dependent killing or ADCC. Infusion of alemtuzumab caused potent depletion of all lymphocytes, but a transient increase in the incidence of circulating Treg. After infusion of alemtuzumab, monkey serum killed fresh PBMC, but not expanded Treg. Thus, expanded cynomolgus monkey Treg are resistant to alemtuzumab-mediated, complement-dependent cytotoxicity. Furthermore, our data suggest that these expanded monkey Treg can be infused into graft recipients given alemtuzumab without risk of complement-mediated killing.

Preexisting epithelial diversity in normal human livers: a tissue-tethered cytometric analysis in portal/periportal epithelial cells

Routine light microscopy identifies two distinct epithelial cell populations in normal human livers: hepatocytes and biliary epithelial cells (BECs). Considerable epithelial diversity, however, arises during disease states when a variety of hepatocyte-BEC hybrid cells appear. This has been attributed to activation and differentiation of putative hepatic progenitor cells (HPC) residing in the canals of Hering and/or metaplasia of preexisting mature epithelial cells. A novel analytic approach consisting of multiplex labeling, high-resolution whole-slide imaging (WSI), and automated image analysis was used to determine if more complex epithelial cell phenotypes preexist in normal adult human livers, which might provide an alternative explanation for disease-induced epithelial diversity. "Virtually digested" WSI enabled quantitative cytometric analyses of individual cells displayed in a variety of formats (e.g., scatterplots) while still tethered to the WSI and tissue structure. We employed biomarkers specifically associated with mature epithelial forms (HNF4α for hepatocytes, CK19 and HNF1β for BEC) and explored for the presence of cells with hybrid biomarker phenotypes. The results showed abundant hybrid cells in portal bile duct BEC, canals of Hering, and immediate periportal hepatocytes. These bipotential cells likely serve as a reservoir for the epithelial diversity of ductular reactions, appearance of hepatocytes in bile ducts, and the rapid and fluid transition of BEC to hepatocytes, and vice versa.

CONCLUSION

Novel imaging and computational tools enable increased information extraction from tissue samples and quantify the considerable preexistent hybrid epithelial diversity in normal human liver. This computationally enabled tissue analysis approach offers much broader potential beyond the results presented here.

Phase I study of alemtuzumab for therapy of steroid-refractory chronic graft-versus-host disease

Steroid-refractory chronic graft-versus-host disease (cGVHD) carries a poor prognosis with no agreed upon algorithm for treatment. Because both B and T cells contribute to the pathophysiology of cGVHD, we conducted a phase I study in subjects with steroid-refractory cGVHD using the anti-CD52 antibody alemtuzumab to transiently deplete most mononuclear subsets. Three regimens were investigated in a 3+3 dose-escalation design: 3 mg × 6 (dose level 1), 3 mg × 1, then 10 mg × 5 (dose level 2) and 3 mg × 1, 10 mg × 1, then 30 mg × 4 (dose level 3) administered over 4 weeks. The maximum tolerated dose of alemtuzumab was dose level 2. Thirteen patients were assessable for toxicities, which were primarily infectious and hematologic. Rates of infectious complications in the first 12 weeks were 0% at dose level 1 (n = 3), 50% at dose level 2 (1 death, n = 6), and 75% at dose level 3 (2 deaths, n = 4). Of 10 patients assessable for response, 7 (70%) responded at 12 weeks, with a 30% complete response rate. Four subjects reduced steroid dose or discontinued an immunosuppressant at 12 weeks. The median decrease in steroid dose at 1 year was 61.6%. Infectious complications occurred predominantly in the first 3 months after therapy, but full B and T cell recovery took well over 12 months. Immunophenotypic profiling revealed early recovery by natural killer cells and relative sparing of CD4+ and CD8+ central memory T cell subsets. Our study indicates that therapy with alemtuzumab for steroid-refractory cGVHD is tolerable with close attention to dosing and may be active in subjects who have failed multiple therapies. The pattern of lymphocyte recovery after alemtuzumab will inform the biology and future therapy of cGVHD. The use of alemtuzumab in the context of therapy for cGVHD deserves study in larger phase II trials.