Induction therapy including antithymocyte globulin induces marked alterations in T lymphocyte subpopulations after liver transplantation: results of a long-term study

Strategies for Liver Transplantation Tolerance

Liver transplant (LT) recipients require life-long immunosuppression (IS) therapy to preserve allograft function. The risks of chronic IS include an increased frequency of malignancy, infection, renal impairment, and other systemic toxicities. Despite advances in IS, long-term LT outcomes have not been improved over the past three decades. Standard-of-care (SoC) therapy can, in rare cases, lead to development of operational tolerance that permits safe withdrawal of maintenance IS. However, successful IS withdrawal cannot be reliably predicted and, in current prospective studies, is attempted several years after the transplant procedure, after considerable exposure to the cumulative burden of maintenance therapy. A recent pilot clinical trial in liver tolerance induction demonstrated that peri-transplant immunomodulation, using a regulatory T-cell (Treg) approach, can reduce donor-specific alloreactivity and allow early IS withdrawal. Herein we review protocols for active tolerance induction in liver transplantation, with a focus on identifying tolerogenic cell populations, as well as barriers to tolerance. In addition, we propose the use of novel IS agents to promote immunomodulatory mechanisms favoring tolerance. With numerous IS withdrawal trials underway, improved monitoring and use of novel immunomodulatory strategies will help provide the necessary knowledge to establish an active liver tolerance induction protocol for widespread use.

Rapid T cell repopulation after rabbit anti-thymocyte globulin (rATG) treatment is driven mainly by cytomegalovirus

Rabbit anti-thymocyte globulin (rATG) induces a long-lasting lymphocytopenia. CD4(+) T cells remain depleted for up to 2 years, whereas the CD8(+) T cell compartment is refilled rapidly by highly differentiated CD27(-) CD45RA(+) CD57(+) effector-type cells. Because the presence of these highly differentiated CD8(+) T cells has been associated with cytomegalovirus (CMV) infection, we questioned to what extent restoration of CMV T cell immunity contributes to the re-emergence of T cells following rATG treatment. We compared T cell repopulation in six CMV-seropositive patients with CMV reactivation (reactivating CMV(+) ) to that in three CMV(+) patients without reactivation (non-reactivating CMV(+) ), and to that in three CMV-seronegative recipients receiving a kidney from a CMV-seronegative donor (CMV(-/-) ). All patients received rATG because of acute allograft rejection. Total CD4 and CD8 counts, frequency and phenotype of virus-specific CD8(+) T cells were determined. In reactivating CMV(+) patients, total CD8(+) T cells reappeared rapidly, whereas in non-reactivating CMV(+) patients they lagged behind. In CMV(-/-) patients, CD8(+) T cell counts had not yet reached pretransplant levels after 2 years. CMV reactivation was indeed followed by a progressive accumulation of CMV-specific CD8(+) T cells. During lymphocytopenia following rATG treatment, serum interleukin (IL)-7 levels were elevated. Although this was most prominent in the CMV-seronegative patients, it did not result in an advantage in T cell repopulation in these patients. Repopulated CD8(+) T cells showed increased skewing in their Vβ repertoire in both CMV(-/-) and reactivating CMV-seropositive patients. We conclude that rapid T cell repopulation following rATG treatment is driven mainly by CMV.

Deconvoluting post-transplant immunity: cell subset-specific mapping reveals pathways for activation and expansion of memory T, monocytes and B cells

A major challenge for the field of transplantation is the lack of understanding of genomic and molecular drivers of early post-transplant immunity. The early immune response creates a complex milieu that determines the course of ensuing immune events and the ultimate outcome of the transplant. The objective of the current study was to mechanistically deconvolute the early immune response by purifying and profiling the constituent cell subsets of the peripheral blood. We employed genome-wide profiling of whole blood and purified CD4, CD8, B cells and monocytes in tandem with high-throughput laser-scanning cytometry in 10 kidney transplants sampled serially pre-transplant, 1, 2, 4, 8 and 12 weeks. Cytometry confirmed early cell subset depletion by antibody induction and immunosuppression. Multiple markers revealed the activation and proliferative expansion of CD45RO⁺CD62L⁻ effector memory CD4/CD8 T cells as well as progressive activation of monocytes and B cells. Next, we mechanistically deconvoluted early post-transplant immunity by serial monitoring of whole blood using DNA microarrays. Parallel analysis of cell subset-specific gene expression revealed a unique spectrum of time-dependent changes and functional pathways. Gene expression profiling results were validated with 157 different probesets matching all 65 antigens detected by cytometry. Thus, serial blood cell monitoring reflects the profound changes in blood cell composition and immune activation early post-transplant. Each cell subset reveals distinct pathways and functional programs. These changes illuminate a complex, early phase of immunity and inflammation that includes activation and proliferative expansion of the memory effector and regulatory cells that may determine the phenotype and outcome of the kidney transplant.

Thymoglobulin induction in liver transplant recipients with a tacrolimus, mycophenolate mofetil, and steroid immunosuppressive regimen: a five-year randomized prospective study

This randomized, comparative study assessed the long-term efficacy and tolerability of thymoglobulin (TMG) induction in 93 liver transplant patients with an initial regimen of tacrolimus (Tac), mycophenolate mofetil (MMF), and steroids. Forty-four patients were randomly allocated to the TMG+ group, and 49 patients were randomly allocated to the TMG- group. In both groups, Tac was given orally at the initial daily dose of 0.075 mg/kg twice daily, and MMF was given at the initial daily dose of 2 g/day. Steroid withdrawal was planned at 3 months after liver transplantation. The results were evaluated with respect to acute rejection incidence, patient and graft survival, graft function, and medical complications until 5 years or death for all patients. No significant differences were found between groups for the incidence of acute rejection at 5 years (11.4% versus 14.3%), 5-year patient survival (77.3% versus 87.8%), graft function, or postoperative renal function. One patient in the TMG- group underwent retransplantation. There was no difference between groups with respect to the incidence of medical complications, excepted for a higher rate of leukopenia in the TMG+ group, during the 5-year follow-up. In conclusion, the results of this prospective randomized study suggest that the addition of TMG to a triple immunosuppressive regimen (Tac, MMF, and steroids) did not modify the incidence of acute rejection episodes or long-term survival and was responsible for increased leukopenia rates.

CD57+ T lymphocytes and functional immune deficiency

CD57(+) expression in T lymphocytes has been recognized for decades as a marker of in vitro replicative senescence. In recent years, accumulating evidences have pointed on the utility of this marker to measure functional immune deficiency in patients with autoimmune disease, infectious diseases, and cancers. We review here the relevant literature and implications in clinical settings.

Induction of tolerance in solid organ transplantation: the rationale to develop clinical protocols in liver transplantation

Minimization or withdrawal of immunosuppressive treatments after organ transplantation represents a major objective for improving quality of life and long-term survival of grafted patients. Such a goal may be reached under some clinical conditions, particularly in liver transplantation, making these patients good candidates for tolerance trials. In this context in liver transplantation, the central questions are (1) how to promote the natural propensity of the liver graft to be accepted, (2) which type of immunosuppressive drug should be used for induction and maintenance, and (3) which biomarkers could be used to discriminate tolerant patients from those requiring long-term immunosuppression. Induction therapies using aggressive T-cell-depleting agents may favor graft acceptance. However, persistent and/or rapidly reemerging cell lines, such as memory-type cells or CD8(+) T cells, could represent a significant barrier for induction of tolerance. The type of maintenance drugs also remains questionable. Calcineurin inhibitors may be eventually deleterious in the context of tolerance protocols, through inhibitory effects on regulatory T cells, that are not observed with rapamycin. In conclusion, significant efforts must be made to achieve reliable strategies for immunosuppression minimization or withdrawal after organ transplantation into the clinics.

Targeting of natural killer cells by rabbit antithymocyte globulin and campath-1H: similar effects independent of specificity

T cell depleting strategies are an integral part of immunosuppressive regimens widely used in the hematological and solid organ transplant setting. Although it is known to induce lymphocytopenia, little is known about the effects of the polyclonal rabbit antithymocyte globulin (rATG) or the monoclonal anti-CD52 antibody alemtuzumab on Natural Killer (NK) cells in detail. Here, we demonstrate that induction therapy with rATG following kidney/pancreas transplantation results in a rapid depletion of NK cells. Treatment of NK cells with rATG and alemtuzumab in vitro leads to impairment of cytotoxicity and induction of apoptosis even at a 10-fold lower concentration (0.1 microg/ml) compared with T and B cells. By generating Fc-parts of rATG and alemtuzumab we illustrate that their ligation to FcgammaRIII (CD16) is sufficient for the significant induction of degranulation, apoptosis and inflammatory cytokine release (FasL, TNFalpha and IFNgamma) exclusively in CD3(-)CD56(dim) NK cells whereas application of rATG and alemtuzumab F(ab) fragments abolishes these effects. These findings are of general importance as our data suggest that NK cells are also mediators of the clinically relevant cytokine release syndrome and that their targeting by therapeutic antibodies should be considered as they are functionally relevant for the effective clearance of opportunistic viral infections and anti-tumor activity posttransplantation.

Risk factors for recurrence of primary sclerosing cholangitis after liver transplantation

Orthotopic liver transplantation (OLT) is the only effective treatment for end-stage liver disease due to primary sclerosing cholangitis (PSC). Recurrence of PSC has recently emerged as a leading cause of allograft failure in the long term. There is limited data on risk factors for recurrence of PSC. We performed a retrospective analysis of 69 consecutive patients who underwent a first OLT for PSC over a 14-year period. Baseline characteristics and clinical and laboratory test results post-LT were recorded. Cholangiograms and liver histopathology were reviewed in a blinded manner by an experienced radiologist and hepatopathologist. Recurrent PSC was diagnosed using previously published Mayo Clinic cholangiographic or histologic criteria. Of 69 patients, 7 (10%) developed recurrent PSC at a median of 68 months (range, 24-134 months) post-LT. The following variables were associated with recurrent PSC in our cohort: presence of human leukocyte antigen (HLA)-DRB1*08 (29% versus 2%; P= 0.026; odds ratio [OR], 24.4; 95% confidence interval [CI], 1.8-318.1), acute cellular rejection (ACR) (71% versus 22%; P= 0.015; OR, 8.7; 95% CI, 1.5-49.9), and steroid-resistant ACR (29% versus 0%; P= 0.012). Despite the strong linkage disequilibrium between DRB1*08 and DQB1*04, DRB1*08-positive subjects with recurrence were negative for DQB1*04, whereas the single DRB1*08-positive subject without recurrent PSC was positive for DQB1*04. A history of ACR and presence of HLA-DRB1*08 are associated with increased risk of recurrent PSC, suggesting an immunologic mechanism for this syndrome. Further studies are required to confirm these observations and to understand the underlying mechanisms.

Interindividual variability in the concentration-effect relationship of antilymphocyte globulins - a possible influence of FcgammaRIIIa genetic polymorphism

AIMS

Polyclonal antilymphocyte globulins (ALGs) are currently used in transplantation, but the sources of interindividual variability of their effect are poorly understood. No pharmacokinetic-pharmacodynamic (PK-PD) study of ALG is available. Moreover, the genetic polymorphism of FcgammaRIIIa, a receptor for the Fc portion of immunoglobulins involved in antibody-dependent cellular cytotoxicity (ADCC), may influence their concentration-effect relationship.

METHODS

Fourteen kidney transplant patients treated by horse ALG were included in a prospective, noncomparative study. A population two-compartment PK model including a time dependence of the central volume of distribution was developed. Total lymphocyte count was used as biomarker of effect. Concentration-effect data were described using a physiological indirect response model, combining concentration-dependent and -independent inhibitions of lymphocyte input into the circulation. In addition, six kidney transplant patients in whom ALG concentrations were not available were included retrospectively. All patients were genotyped for FCGR3A.

RESULTS

Both the PK and the PK-PD model described the data satisfactorily and showed high interindividual variability. Asymptotic T(1/2)-alpha and T(1/2)-beta-values were 1.3 and 25 days, respectively. The concentration of ALG leading to a 50% inhibition of lymphocyte input (IC(50)) was lower in FCGR3A-V carriers than in FCGR3A-F/F patients (383 +/- 199 vs. 593 +/- 209 mg l(-1), P = 0.008).

CONCLUSIONS

This is the first description of the ALG effect on lymphocyte count using PK-PD modelling. Our results show that part of the variability in their concentration-effect relationship may be explained by FcgammaRIIIa genetic polymorphism and therefore that horse ALG may deplete lymphocytes by ADCC.

Long-Term Cell Monitoring of Kidney Recipients After an Antilymphocyte Globulin Induction With and Without Steroids

BACKGROUND

Because of several side effects, the corticosteroid usage has been minimized in kidney transplantation. The increased acute rejection episodes associated with their withdrawal may counterbalance with induction treatment using polyclonal antilymphocyte globulin (ALG). The effects of ALG on blood cell phenotype have already been the subject of several reports. However, to date, no data are available concerning the comparison of blood phenotype when ALG is given with or without steroids and no gene profiling study has been performed.

METHODS

We report here on a longitudinal blood cell analysis of a selected cohort of kidney recipients enrolled in a randomized study of steroid avoidance or withdrawal (during 6 months) during ALG induction.

RESULTS

In the two groups, ALG quickly and massively depleted all the T cells and natural killer cells, but not B cells. Interestingly, the lymphopenia-driven homeostatic proliferation of CD4 and CD8T cells strongly differed with persistent low CD4 (including CD25CD4) T-cell counts. Effector memory CD8T cells reappeared rapidly. ALG induced apoptosis-associated molecules and increased myeloid cell genes. However, few genes were found differentially expressed with a low fold ratio between the two groups during and at distance of corticotherapy.

CONCLUSION

Thus initial steroid avoidance or withdrawal associated with ALG induction has a weak influence on phenotype and transcriptional pattern of blood leukocytes. In contrast, ALG therapy induces an early and strong depletion of all T-cell subsets with contrasted long-lasting homeostatic regulation.

Contrasting CD25hiCD4+T cells/FOXP3 patterns in chronic rejection and operational drug-free tolerance

BACKGROUND

Although immunosuppression withdrawal in kidney recipients usually leads to rejection, in some patients it does not, leading to a state of clinical operational tolerance.

METHODS

We compared these highly contrasted situations by analyzing blood cell phenotype and transcriptional patterns in drug-free spontaneously tolerant kidney recipients, recipients with chronic rejection, recipients with stable graft function under standard or minimal immunosuppression and healthy individuals

RESULTS

The blood cell phenotype of clinically tolerant patients did not differ from that of healthy individuals. In contrast, recipients with chronic rejection had significantly less CD25hiCD4+T cells and lower levels of FOXP3 transcripts compared with clinically tolerant recipients. Patients with chronic rejection also displayed CD25-CD4+T cells expressing NKG2D+CD94+ and CD57+CD27-CD28- cytotoxic-associated markers (P<0.05).

CONCLUSION

These data show that whereas clinically tolerant recipients displayed normal levels of CD25hiCD4+T cells and FOXP3 transcripts, chronic rejection is associated with a decrease in CD25hiCD4+T cells and FOXP3 transcripts, suggesting that clinically "operational tolerance" may be due to a maintained phenomenon of natural tolerance that is lacking in patients with chronic rejection.

Immunosuppressive agents in solid organ transplantation: Mechanisms of action and therapeutic efficacy

Effective immunosuppression is an essential pre-requisite for successful organ transplantation and improvements in outcome after transplantation have to a large extent been dependent on developments in immunosuppressive therapy. Here we provide an overview of the different immunosuppressive agents currently used in solid organ transplantation. A historical perspective on the development of immunosuppression for organ transplantation is followed by a review of the individual agents, with a focus on their mechanism of action and efficacy. Steroids, anti-proliferative agents (azathioprine and mycophenolate), calcineurin inhibitors (cyclosporine and tacrolimus) and TOR inhibitors (sirolimus and everolimus) are discussed along with both polyclonal and monoclonal antibody preparations. Many of the key clinical trials that underpin current clinical usage of these agents are described and side-effects of the different agents are highlighted. Finally, a number of newer agents still in various stages of clinical development are briefly considered.

Biological effects of induction immunosuppression

The concept of induction immunosuppression is evolving. Once used to buttress the inadequacies of past maintenance immunosuppressive regimens, it is now being used to permit effective maintenance immunosuppression using ever decreasing amounts of modern agents. In addition to lymphocyte depletion, with which it was once synonymous, it is now recognized that induction immunosuppression is associated with a host of non-depletional effects such as receptor modulation and blockade, which profoundly alter the lymphocyte's capacity to mount an effective response. Additionally, the recent focus on the effect of induction agents on antigen presenting cells and on regulatory factors controlling homeostatic repopulation may ultimately permit a safer, more refined and more effective approach to induction immunosuppression.