Differential expression of circulating miRNAs after alemtuzumab induction therapy in lung transplantation

Alemtuzumab is a monoclonal antibody targeting CD52, used as induction therapy after lung transplantation (LTx). Its engagement produces a long-lasting immunodepletion; however, the mechanisms driving cell reconstitution are poorly defined. We hypothesized that miRNAs are involved in this process. The expression of a set of miRNAs, cytokines and co-signaling molecules was measured with RT-qPCR and flow cytometry in prospectively collected serum samples of LTx recipients, after alemtuzumab or no induction therapy. Twenty-six LTx recipients who received alemtuzumab and twenty-seven matched LTx recipients without induction therapy were included in the analysis. One year after transplantation four miRNAs were differentially regulated: miR-23b (p = 0.05) miR-146 (p = 0.04), miR-155 (p < 0.001) and miR-486 (p < 0.001). Expression of 3 miRNAs changed within the alemtuzumab group: miR-146 (p < 0.001), miR-155 (p < 0.001) and miR-31 (p < 0.001). Levels of IL-13, IL-4, IFN-γ, BAFF, IL-5, IL-9, IL-17F, IL-17A and IL-22 were different one year after transplantation compared to baseline. In no-induction group, concentration of sCD27, sB7.2 and sPD-L1 increased overtime. Expression of miR-23b, miR-146, miR-486, miR-155 and miR-31 was different in LTx recipients who received alemtuzumab compared to recipients without induction therapy. The observed cytokine pattern suggested proliferation of specific B cell subsets in alemtuzumab group and co-stimulation of T-cells in no-induction group.

No augmentation of indoleamine 2,3-dioxygenase (IDO) activity through belatacept treatment in liver transplant recipients

Belatacept is a second-generation cytotoxic T lymphocyte antigen (CTLA)-4 immunoglobulin (Ig) fusion protein approved for immunosuppression in renal transplant recipients. It was designed intentionally to interrupt co-stimulation via CD28 by binding to its ligands B7·1 and B7·2. Experimental evidence suggests a potential additional mechanism for CTLA-4 Ig compounds through binding to B7 molecules expressed on antigen-presenting cells (APCs) and up-regulation of indoleamine 2,3-dioxygenase (IDO), an immunomodulating enzyme that catalyzes the degradation of tryptophan to kynurenine and that down-regulates T cell immunity. So far it remains unknown whether belatacept up-regulates IDO in transplant recipients. We therefore investigated whether belatacept therapy enhances IDO activity in liver transplant recipients enrolled in a multi-centre, investigator-initiated substudy of the Phase II trial of belatacept in liver transplantation (IM103-045). Tryptophan and kynurenine serum levels were measured during the first 6 weeks post-transplant in liver transplant patients randomized to receive either belatacept or tacrolimus-based immunosuppression. There was no significant difference in IDO activity, as indicated by the kynurenine/tryptophan ratio, between belatacept and tacrolimus-treated patients in per-protocol and in intent-to-treat analyses. Moreover, no evidence was found that belatacept affects IDO in human dendritic cells (DC) in vitro. These data provide evidence that belatacept is not associated with detectable IDO induction in the clinical transplant setting compared to tacrolimus-treated patients.

Regulatory T Cells Promote Natural Killer Cell Education in Mixed Chimeras

Therapeutic administration of regulatory T cells (Tregs) leads to engraftment of conventional doses of allogeneic bone marrow (BM) in nonirradiated recipient mice conditioned with costimulation blockade and mammalian target of rapamycin inhibition. The mode of action responsible for this Treg effect is poorly understood but may encompass the control of costimulation blockade-resistant natural killer (NK) cells. We show that transient NK cell depletion at the time of BM transplantation led to BM engraftment and persistent chimerism without Treg transfer but failed to induce skin graft tolerance. In contrast, the permanent absence of anti-donor NK reactivity in mice grafted with F1 BM was associated with both chimerism and tolerance comparable to Treg therapy, implying that NK cell tolerization is a critical mechanism of Treg therapy. Indeed, NK cells of Treg-treated BM recipients reshaped their receptor repertoire in the presence of donor MHC in a manner suggesting attenuated donor reactivity. These results indicate that adoptively transferred Tregs prevent BM rejection, at least in part, by suppressing NK cells and promote tolerance by regulating the appearance of NK cells expressing activating receptors to donor class I MHC.

Murine models of transplantation tolerance through mixed chimerism: advances and roadblocks

Organ transplantation is the treatment of choice for patients with end-stage organ failure, but chronic immunosuppression is taking its toll in terms of morbidity and poor efficacy in preventing late graft loss. Therefore, a drug-free state would be desirable where the recipient permanently accepts a donor organ while remaining otherwise fully immunologically competent. Mouse studies unveiled mixed chimerism as an effective approach to induce such donor-specific tolerance deliberately and laid the foundation for a series of clinical pilot trials. Nevertheless, its widespread clinical implementation is currently prevented by cytotoxic conditioning and limited efficacy. Therefore, the use of mouse studies remains an indispensable tool for the development of novel concepts with potential for translation and for the delineation of underlying tolerance mechanisms. Recent innovations developed in mice include the use of pro-apoptotic drugs or regulatory T cell (T_reg ) transfer for promoting bone marrow engraftment in the absence of myelosuppression and new insight gained in the role of innate immunity and the interplay between deletion and regulation in maintaining tolerance in chimeras. Here, we review these and other recent advances in murine studies inducing transplantation tolerance through mixed chimerism and discuss both the advances and roadblocks of this approach.

The Immunosuppressive Effect of CTLA4 Immunoglobulin Is Dependent on Regulatory T Cells at Low But Not High Doses

B7.1/2-targeted costimulation blockade (CTLA4 immunoglobulin [CTLA4-Ig]) is available for immunosuppression after kidney transplantation, but its potentially detrimental impact on regulatory T cells (Tregs) is of concern. We investigated the effects of CTLA4-Ig monotherapy in a fully mismatched heart transplant model (BALB/c onto C57BL/6). CTLA4-Ig was injected chronically (on days 0, 4, 14, and 28 and every 4 weeks thereafter) in dosing regimens paralleling clinical use, shown per mouse: low dose (LD), 0.25 mg (≈10 mg/kg body weight); high dose (HD), 1.25 mg (≈50 mg/kg body weight); and very high dose (VHD), 6.25 mg (≈250 mg/kg body weight). Chronic CTLA4-Ig therapy showed dose-dependent efficacy, with the LD regimen prolonging graft survival and with the HD and VHD regimens leading to >95% long-term graft survival and preserved histology. CTLA4-Ig's effect was immunosuppressive rather than tolerogenic because treatment cessation after ≈3 mo led to rejection. FoxP3-positive Tregs were reduced in naïve mice to a similar degree, independent of the CTLA4-Ig dose, but recovered to normal values in heart recipients under chronic CTLA4-Ig therapy. Treg depletion (anti-CD25) resulted in an impaired outcome under LD therapy but had no detectable effect under HD therapy. Consequently, the immunosuppressive effect of partially effective LD CTLA4-Ig therapy is impaired when Tregs are removed, whereas CTLA4-Ig monotherapy at higher doses effectively maintains graft survival independent of Tregs.

Long-Term Outcomes in Belatacept- Versus Cyclosporine-Treated Recipients of Extended Criteria Donor Kidneys: Final Results From BENEFIT-EXT, a Phase III Randomized Study

In the Belatacept Evaluation of Nephroprotection and Efficacy as First-Line Immunosuppression Trial-Extended Criteria Donors (BENEFIT-EXT), extended criteria donor kidney recipients were randomized to receive belatacept-based (more intense [MI] or less intense [LI]) or cyclosporine-based immunosuppression. In prior analyses, belatacept was associated with significantly better renal function compared with cyclosporine. In this prospective analysis of the intent-to-treat population, efficacy and safety were compared across regimens at 7 years after transplant. Overall, 128 of 184 belatacept MI-treated, 138 of 175 belatacept LI-treated and 108 of 184 cyclosporine-treated patients contributed data to these analyses. Hazard ratios (HRs) comparing time to death or graft loss were 0.915 (95% confidence interval [CI] 0.625-1.339; p = 0.65) for belatacept MI versus cyclosporine and 0.927 (95% CI 0.634-1.356; p = 0.70) for belatacept LI versus cyclosporine. Mean estimated GFR (eGFR) plus or minus standard error at 7 years was 53.9 ± 1.9, 54.2 ± 1.9, and 35.3 ± 2.0 mL/min per 1.73 m² for belatacept MI, belatacept LI and cyclosporine, respectively (p < 0.001 for overall treatment effect). HRs comparing freedom from death, graft loss or eGFR <20 mL/min per 1.73 m² were 0.754 (95% CI 0.536-1.061; p = 0.10) for belatacept MI versus cyclosporine and 0.706 (95% CI 0.499-0.998; p = 0.05) for belatacept LI versus cyclosporine. Acute rejection rates and safety profiles of belatacept- and cyclosporine-based treatment were similar. De novo donor-specific antibody incidence was lower for belatacept (p ≤ 0.0001). Relative to cyclosporine, belatacept was associated with similar death and graft loss and improved renal function at 7 years after transplant and had a safety profile consistent with previous reports.

Anti-OX40L alone or in combination with anti-CD40L and CTLA4Ig does not inhibit the humoral and cellular response to a major grass pollen allergen

BACKGROUND

IgE-mediated allergy is a common disease characterized by a harmful immune response towards otherwise harmless environmental antigens. Induction of specific immunological non-responsiveness towards allergens would be a desirable goal. Blockade of costimulatory pathways is a promising strategy to modulate the immune response in an antigen-specific manner. Recently, OX40 (CD134) was identified as a costimulatory receptor important in Th2-mediated immune responses. Moreover, synergy between OX40 blockade and 'conventional' costimulation blockade (anti-CD40L, CTLA4Ig) was observed in models of alloimmunity.

OBJECTIVE

We investigated the potential of interfering with OX40 alone or in combination with CD40/CD28 signals to influence the allergic immune response.

METHODS

The OX40 pathway was investigated in an established murine model of IgE-mediated allergy where BALB/c mice are repeatedly immunized with the clinically relevant grass pollen allergen Phl p 5. Groups were treated with combinations of anti-OX40L, CTLA4Ig and anti-CD40L. In selected mice, Tregs were depleted with anti-CD25.

RESULTS

Blockade of OX40L alone at the time of first or second immunization did not modulate the allergic response on the humoral or effector cell levels but slightly on T cell responses. Administration of a combination of anti-CD40L/CTLA4Ig delayed the allergic immune response, but antibody production could not be inhibited after repeated immunization even though the allergen-specific T cell response was suppressed in the long run. Notably, additional blockade of OX40L had no detectable supplementary effect. Immunomodulation partly involved regulatory T cells as depletion of CD25(+) cells led to restored T cell proliferation.

CONCLUSIONS AND CLINICAL RELEVANCE

Collectively, our data provide evidence that the allergic immune response towards Phl p 5 is independent of OX40L, although reduction on T cell responses and slightly on the asthmatic phenotype was detectable. Besides, no relevant synergistic effect of OX40L blockade in addition to CD40L/CD28 blockade could be detected. Thus, the therapeutic potential of OX40L blockade for IgE-mediated allergy appears to be ineffective in this setting.

Rapamycin and CTLA4Ig synergize to induce stable mixed chimerism without the need for CD40 blockade

The mixed chimerism approach achieves donor-specific tolerance in organ transplantation, but clinical use is inhibited by the toxicities of current bone marrow (BM) transplantation (BMT) protocols. Blocking the CD40:CD154 pathway with anti-CD154 monoclonal antibodies (mAbs) is exceptionally potent in inducing mixed chimerism, but these mAbs are clinically not available. Defining the roles of donor and recipient CD40 in a murine allogeneic BMT model, we show that CD4 or CD8 activation through an intact direct or CD4 T cell activation through the indirect pathway is sufficient to trigger BM rejection despite CTLA4Ig treatment. In the absence of CD4 T cells, CD8 T cell activation via the direct pathway, in contrast, leads to a state of split tolerance. Interruption of the CD40 signals in both the direct and indirect pathway of allorecognition or lack of recipient CD154 is required for the induction of chimerism and tolerance. We developed a novel BMT protocol that induces mixed chimerism and donor-specific tolerance to fully mismatched cardiac allografts relying on CD28 costimulation blockade and mTOR inhibition without targeting the CD40 pathway. Notably, MHC-mismatched/minor antigen-matched skin grafts survive indefinitely whereas fully mismatched grafts are rejected, suggesting that non-MHC antigens cause graft rejection and split tolerance.

Donor CD4 T cells trigger costimulation blockade-resistant donor bone marrow rejection through bystander activation requiring IL-6

Bone marrow (BM) transplantation under costimulation blockade induces chimerism and tolerance. Cotransplantation of donor T cells (contained in substantial numbers in mobilized peripheral blood stem cells and donor lymphocyte infusions) together with donor BM paradoxically triggers rejection of donor BM through undefined mechanisms. Here, nonmyeloablatively irradiated C57BL/6 recipients simultaneously received donor BM (BALB/c) and donor T cells under costimulation blockade (anti-CD154 and CTLA4Ig). Donor CD4, but not CD8 cells, triggered natural killer-independent donor BM rejection which was associated with increased production of IL-6, interferon gamma (IFN-γ) and IL-17A. BM rejection was prevented through neutralization of IL-6, but not of IFN-γ or IL-17A. IL-6 counteracted the antiproliferative effect of anti-CD154 in vitro. Rapamycin and anti-lymphocyte function-associated antigen 1 negated this effect of IL-6 in vitro and prevented BM rejection in vivo. Simultaneous cotransplantation of (BALB/cxB6)F1, recipient or irradiated donor CD4 cells, or late transfer of donor CD4 cells did not lead to BM rejection, whereas cotransplantation of third party CD4 cells did. Transferred donor CD4 cells became activated, rapidly underwent apoptosis and triggered activation and proliferation of recipient T cells. Collectively, these results provide evidence that donor T cells recognizing the recipient as allogeneic lead to the release of IL-6, which abolishes the effect of anti-CD154, triggering donor BM rejection through bystander activation.

Belatacept-based immunosuppression in de novo liver transplant recipients: 1-year experience from a phase II randomized study

This exploratory phase II study evaluated the safety and efficacy of belatacept in de novo adult liver transplant recipients. Patients were randomized (N = 260) to one of the following immunosuppressive regimens: (i) basiliximab + belatacept high dose [HD] + mycophenolate mofetil (MMF), (ii) belatacept HD + MMF, (iii) belatacept low dose [LD] + MMF, (iv) tacrolimus + MMF, or (v) tacrolimus alone. All received corticosteroids. Demographic characteristics were similar among groups. The proportion of patients who met the primary end point (composite of acute rejection, graft loss, death by month 6) was higher in the belatacept groups (42–48%) versus tacrolimus groups (15–38%), with the highest number of deaths and grafts losses in the belatacept LD group. By month 12, the proportion surviving with a functioning graft was higher with tacrolimus + MMF (93%) and lower with belatacept LD (67%) versus other groups (90%: basiliximab + belatacept HD; 83%: belatacept HD; 88%: tacrolimus). Mean calculated GFR was 15–34 mL/min higher in belatacept-treated patients at 1 year. Two cases of posttransplant lymphoproliferative disease and one case of progressive multifocal leukoencephalopathy occurred in belatacept-treated patients. Follow-up beyond month 12 revealed an increase in death and graft loss in another belatacept group (belatacept HD), after which the study was terminated.

Bcl-2 inhibition to overcome memory cell barriers in transplantation

Memory T cells (Tm) represent a major barrier for immunosuppression and tolerance induction after solid organ transplantation. Taking into consideration the critical role of the intrinsic apoptosis pathway in the generation and maintenance of Tm, we developed a new concept to deplete alloreactive Tm by targeting Bcl-2 proteins. The small-molecule Bcl-2/Bcl-XL inhibitor ABT-737 efficiently induced apoptosis in alloreactive Tm in vitro and in vivo and prolonged skin graft survival in sensitized recipients. A short course of ABT-737 induction therapy prevented Tm-mediated resistance in a donor-specific transfusion model and allowed mixed chimerism induction across Tm barriers. Since Bcl-2 inhibitors yielded encouraging safety results in cancer trials, this novel approach might represent a substantial advance to prevent allograft rejection and induce tolerance in sensitized recipients.

Persistent molecular microchimerism induces long-term tolerance towards a clinically relevant respiratory allergen

BACKGROUND

Development of antigen-specific preventive strategies is a challenging goal in IgE-mediated allergy. We have recently shown in proof-of-concept experiments that allergy can be successfully prevented by induction of durable tolerance via molecular chimerism. Transplantation of syngeneic hematopoietic stem cells genetically modified to express the clinically relevant grass pollen allergen Phl p 5 into myeloablated recipients led to high levels of chimerism (i.e. macrochimerism) and completely abrogated Phl p 5-specific immunity despite repeated immunizations with Phl p 5.

OBJECTIVE

It was unclear, however, whether microchimerism (drastically lower levels of chimerism) would be sufficient as well which would allow development of minimally toxic tolerance protocols.

METHODS

Bone marrow cells were transduced with recombinant viruses integrating Phl p 5 to be expressed in a membrane-anchored fashion. The syngeneic modified cells were transplanted into non-myeloablated recipients that were subsequently immunized repeatedly with Phl p 5 and Bet v 1 (control). Molecular chimerism was monitored using flow cytometry and PCR. T cell, B-cell and effector-cell tolerance were assessed by allergen-specific proliferation assays, isotype levels in sera and RBL assays.

RESULTS

Here we demonstrate that transplantation of Phl p 5-expressing bone marrow cells into recipients having received non-myeloablative irradiation resulted in chimerism persisting for the length of follow-up. Chimerism levels, however, declined from transient macrochimerism levels to persistent levels of microchimerism (followed for 11 months). Notably, these chimerism levels were sufficient to induce B-cell tolerance as no Phl p 5-specific IgE and other high affinity isotypes were detectable in sera of chimeric mice. Furthermore, T-cell and effector-cell tolerance were achieved.

CONCLUSIONS AND CLINICAL RELEVANCE

Low levels of persistent molecular chimerism are sufficient to induce long-term tolerance in IgE-mediated allergy. These results suggest that it will be possible to develop minimally toxic conditioning regimens sufficient for low level engraftment of genetically modified bone marrow.

Resistance to ABT-737 in activated T lymphocytes: molecular mechanisms and reversibility by inhibition of the calcineurin-NFAT pathway

Dynamic regulation of the intrinsic apoptosis pathway controls central and peripheral lymphocyte deletion, and may interfere with the pro-apoptotic potency of B-cell lymphoma 2 inhibitors such as ABT-737. By following a T-cell receptor (TCR) transgenic population of alloantigen-specific T cells, we found that sensitivity to ABT-737 radically changed during the course of allo-specific immune responses. Particularly, activated T cells were fully resistant to ABT-737 during the first days after antigen recognition. This phenomenon was caused by a TCR–calcineurin–nuclear factor of activated T cells-dependent upregulation of A1, and was therefore prevented by cyclosporine A (CsA). As a result, exposure to ABT-737 after alloantigen recognition induced selection of alloreactive T cells in vivo, whereas in combination with low-dose CsA, ABT-737 efficiently depleted alloreactive T cells in murine host-versus-graft and graft-versus-host models. Thus, ABT-737 resistance is not a prerogative of neoplastic cells, but it physiologically occurs in T cells after antigen recognition. Reversibility of this process by calcineurin inhibitors opens new pharmacological opportunities to modulate this process in the context of cancer, autoimmunity and transplantation.

Treg-therapy allows mixed chimerism and transplantation tolerance without cytoreductive conditioning

Establishment of mixed chimerism through transplantation of allogeneic donor bone marrow (BM) into sufficiently conditioned recipients is an effective experimental approach for the induction of transplantation tolerance. Clinical translation, however, is impeded by the lack of feasible protocols devoid of cytoreductive conditioning (i.e. irradiation and cytotoxic drugs/mAbs). The therapeutic application of regulatory T cells (Tregs) prolongs allograft survival in experimental models, but appears insufficient to induce robust tolerance on its own. We thus investigated whether mixed chimerism and tolerance could be realized without the need for cytoreductive treatment by combining Treg therapy with BM transplantation (BMT). Polyclonal recipient Tregs were cotransplanted with a moderate dose of fully mismatched allogeneic donor BM into recipients conditioned solely with short-course costimulation blockade and rapamycin. This combination treatment led to long-term multilineage chimerism and donor-specific skin graft tolerance. Chimeras also developed humoral and in vitro tolerance. Both deletional and nondeletional mechanisms contributed to maintenance of tolerance. All tested populations of polyclonal Tregs (FoxP3-transduced Tregs, natural Tregs and TGF-beta induced Tregs) were effective in this setting. Thus, Treg therapy achieves mixed chimerism and tolerance without cytoreductive recipient treatment, thereby eliminating a major toxic element impeding clinical translation of this approach.

Short-term effects of high-dose zoledronic acid treatment on bone mineralization density distribution after orthotopic liver transplantation

Patients with "hepatic" bone disease exhibit increased fracture incidence. The effects on bone material properties, their changes due to orthotopic liver transplantation (OLT), as well as zolendronate (ZOL) treatment have not yet been investigated. We studied bone mineralization density distribution (BMDD) in paired transiliacal biopsies (at and 6 months after OLT) from patients (control CON n = 18, treatment group ZOL n = 21, the latter treated with i.v. ZOL at doses of 4 mg/month) for how bone at the material level was affected by the "hepatic" disease in general, as well as by OLT and ZOL in particular. (1) BMDD parameters at baseline reflected disturbed bone matrix mineralization in "hepatic" bone disease combined with low turnover. Trabecular bone displayed a decrease in mean and most frequent calcium concentration (Ca(MEAN) -2.9% and Ca(PEAK) -2.8%, respectively; both P < 0.001), increased heterogeneity of mineralization (Ca(WIDTH) +12.2%, P = 0.01), and increased percentage of bone areas with low mineralization (Ca(LOW) +32.4%, P = 0.02) compared to normal; however, there were no differences compared to cortical bone. (2) Six months after OLT, ZOL-treated trabecular bone displayed reduced Ca(LOW) (-32.0%, P = 0.047), cortical bone increased Ca(MEAN) (+4.2%, P = 0.009), increased Ca(PEAK) (+3.3%, P = 0.040), and decreased Ca(LOW) (-55.7, P = 0.038) compared to CON and increased Ca(MEAN) compared to baseline (+1.9, P = 0.032) without any signs of hyper- or defective mineralization. These changes as consequence of the antiresorptive action of ZOL visible already after 6 months result in beneficial effects on bone matrix mineralization, likely contributing to the significant decrease in fracture incidence observed in these patients 2 years post transplantation.

Prophylactic bisphosphonate treatment prevents bone fractures after liver transplantation

A randomized controlled prospective open-label single center trial was performed. At the time of transplantation patients were randomly assigned to one of two treatment arms: The study group of 47 patients received zoledronic acid (ZOL, 8 infusions at 4 mg during the first 12 months after LT), calcium (1000 mg/d) and vitamin D (800 IE/d). The control group consisted of 49 patients who received calcium and vitamin D at same doses (CON). The incidence of bone fractures or death was predefined as the primary endpoint. Secondary endpoints included bone mineral density (BMD), serum biochemical markers of bone metabolism, parameters of trabecular bone histomorphometry and mineralization density distribution (BMDD). Patients were followed up for 24 months. Analysis was performed on an intention-to-treat basis. The primary endpoint fracture or death was reached in 26% of patients in the ZOL group and 46% in the CON group (p = 0.047, log rank test). Densitometry results were different between the groups at the femoral neck at 6 months after LT (mean+/-SD BMD ZOL: 0.80 +/- 0.19 g/cm2 vs. CON: 0.73 +/- 0.14 g/cm2, p = 0.036). Mixed linear models of biochemical bone markers showed less increase of osteocalcin in the ZOL group and histomorphometry and BMDD indicated a reduction in bone turnover. Prophylactic treatment with the bisphosphonate zoledronic acid reduces bone turnover and fractures after liver transplantation.

Indoleamine 2,3-dioxygenase in hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) is complicated by unwelcome side-effects that arise on the basis of an altered immune system. Infectious complications and alloreactive T-cell responses trigger a process of ongoing immune activation and inflammation. Negative-feedback mechanisms to counteract inflammation involve the induction of the immunoregulatory enzyme indoleamine 2,3-dioxygenase (IDO), which mediates anti-inflammatory activities and T-cell inhibition via tryptophan catabolism. However, persistent immune activation and generalized release of pro-inflammatory cytokines deviate immune regulation towards chronic suppression incapable to abrogate the inflammatory response. This review focuses on the unique role of tryptophan catabolism in modulating inflammatory processes and T-cell responses after HSCT.

Present status at the Vienna Transplantation Center after four thousand renal transplantations

The Division of Transplantation at the Medical University of Vienna, Austria was established by Dr Franz Piza, who performed the first deceased donor kidney transplantation in Vienna in 1965. During the next 43 years, 4,849 transplants were performed at this unit. Data were analysed in the time period 1993-2006 for 2,165 deceased donor transplants (1,734 first and 431 regrafts) and 263 living donor transplants. Long-term follow-up was available for more than 95% of all grafts and all recipients had at least 9 months of follow-up. Two- and 6-year graft survival rates were 81.4% and 66.3%, respectively, for first deceased donor grafts, 76.1% and 61.8% for regrafts and 91.5% and 79.1% for living transplants. Appropriate immunosuppression, HLA matching and crossmatching supported by solid basic scientific research have proved successful in achieving good graft survival at our unit.

The advantage of allocating kidneys from old cadaveric donors to old recipients: a single-center experience

BACKGROUND

In January 1999 a new kidney allocation program was launched by the Eurotransplant Foundation, the 'Eurotransplant Senior Program' (ESP). Cadaveric donors above the age of 65 yr are allocated to kidney transplant recipients of the same age group.

METHODS

Using a single-center database, 91 patients who underwent first renal transplantation at the age of 65 yr and older in the years 1999-2002 were identified. Fifty-six patients were transplanted through ESP allocation (study group) and 35 patients (control group) via normal Eurotransplant Kidney Allocation System (ETKAS) procedure.

RESULTS

Age, sex and comorbid conditions did not differ by group. The rate of acute rejection episodes, primary non-function, delayed graft function, perioperative mortality did not differ by group. Serum creatinine was significantly lower in the ETKAS group (1.3 vs. 1.9 mg/dL; p=0.015) from six months after the transplantation on. Overall graft survival at six yr was 56% in the ETKAS group and 52% in the ESP group. With 73% in the ETKAS group and 71% in the ESP group, cumulative patient survival according to the Kaplan-Meier estimation was not statistically different at five yr.

CONCLUSIONS

We did not find a relevant difference in the outcome between young and old kidney transplants in old recipients after this long observation period.

Role of CD40-CD154 pathway in the rejection of concordant and discordant xenogeneic islets

BACKGROUND

Costimulatory blockade has been shown to allow long-term survival of xenogeneic islets. The aim of the present study was to evaluate the role of recipient CD40 and CD154 in the rejection process of concordant and discordant islet xenotransplantation (Tx).

METHODS

Diabetic C57BL/6 mice, CD40- or CD154 knockout (KO) mice were transplanted with either concordant rat or discordant human islets.

EXPERIMENTAL DESIGN

group 1, control (ie, C57BL/6 mice received islet Tx without therapy); group 2, C57BL/6 mice received islet Tx with anti-CD154 monoclonal Ab (mAb) therapy; group 3, CD40 KO mice; and group 4, CD154 KO mice were used as recipients without therapy. Mouse anti-rat mixed lymphocyte reactions (MLR) were performed using mouse splenocytes obtained from animals transplanted with rat islets in groups 1 to 4.

RESULTS

In group 2, short-term anti-CD154 mAb therapy significantly prolonged rat-to-mouse and human-to-mouse xenograft survival, compared to controls. In CD40-KO and CD154-KO recipients, survival of concordant or discordant islets was not prolonged significantly compared to control groups. Mouse anti-donor rat cellular responses were reduced approximately 50% in group 2 but remained unmodified in groups 3 and 4, when compared to group 1.

CONCLUSIONS

Improved graft survival and reduced MLR responses against donor cells in vitro among the anti-CD154 mAb-treated mice could be explained by specific targeting of activated T cells with subsequent inactivation by anergy and/or elimination by apoptosis, or complement- or cellular-mediated mechanisms. Rejection of xenografts and strong MLR responses against donor cells in vitro in CD40 or CD154 KO animals is possible through efficient activation of alternate pathways of costimulation.

Phylogenetic disparity influences the predominance of direct over indirect pathway of antigen presentation in islet xenotransplantation

BACKGROUND

Cellular immunity plays a major role in rejection of xenografted islets. Depending on the phylogenetical disparity, direct or indirect antigen presentation is predominant. The aim of this study was to analyze in vitro the predominance of direct or indirect presentation, and in vivo the effect of macrophage depletion on concordant and discordant islet xenograft survival.

MATERIALS AND METHODS

In vitro, we performed mouse antirat and mouse antihuman mixed lymphocyte reactions (MLR) after depletion of responder or stimulator antigen-presenting cells. In vivo, streptozotocin-induced diabetic C57BL/6 mice were treated by gadolinium chloride to deplete macrophages and rat or human islets were transplanted under the kidney capsule. Islet function was followed by glycemia and xenografts were analyzed at regular intervals for histology.

RESULTS

Mouse antirat MLR showed a predominant direct antigen presentation pathway, whereas in mouse antihuman MLR, direct and indirect pathways were similarly involved. Survival of rat islets was not modified by GdCl therapy. In contrast, survival of human islets was significantly prolonged in GdCl-treated mice. Macrophage infiltration was decreased in concordant and discordant GdCl-treated xenografts at day 4, compared to controls. At day 15, macrophage infiltration was similar in all groups.

DISCUSSION

Our results indicate that direct antigen presentation is dominant in rejection of concordant islet xenografts and cannot be influenced by host macrophage depletion. Both direct and indirect antigen presentation are involved in rejection of discordant xenogeneic islets. Macrophage depletion or inhibition should be considered as therapeutic tool for discordant islet xenotransplantation.

Mechanisms involved in the establishment of tolerance through costimulatory blockade and BMT: lack of requirement for CD40L-mediated signaling for tolerance or deletion of donor-reactive CD4+ cells

We have previously shown that high levels of multiline-age mixed hematopoietic chimerism and systemic T-cell tolerance can be achieved in mice without myeloablation through the use of anti-CD40L and costimulatory blockade alone (plus CTLA4Ig) or with recipient CD8 depletion and allogeneic bone marrow transplantation. Chimeric mice permanently accept donor skin grafts (> 100 days), and rapidly reject third-party grafts. The mechanisms by which costimulatory blockade facilitates the engraftment of allogeneic hematopoietic cells have not been defined. To further understand the in vivo mechanisms by which the administration of anti-CD40L mAb facilitates the engraftment of donor bone marrow and rapidly tolerizes CD4+ T cells, we analyzed the establishment of chimerism and tolerance in CD40L -/- mice. We demonstrate here that anti-CD40L mAb treatment is required only to prevent CD40L/CD40 interactions, and that no signal to the T cell through CD40L is necessary for the induction of CD4+ tolerance. Peripheral deletion of donor-reactive CD4+ T cells occurs rapidly in CD40L -/- mice receiving bone marrow transplantation (BMT), indicating that this deletion in the presence of anti-CD40L is not due to targeting of activated CD4+ cells by the antibody. Complete CD4+ cell tolerance is observed by both skin graft acceptance and in vitro assays before deletion is complete, indicating that additional mechanisms play a role in inducing CD4+ T-cell tolerance as the result of BMT in the presence of CD40/CD40L blockade.

Transplantation tolerance induced by mixed chimerism

Although short- and long-term results after organ transplantation have improved considerably in recent years, morbidity and mortality rates in graft recipients remain high. The induction of lifelong donor-specific tolerance would dramatically improve outcome after organ transplantation. Although many tolerance protocols have been successful in rodent studies, most of these approaches have failed when attempted in large animals or humans. Robust tolerance, in contrast, has been demonstrated with mixed chimerism regimens not only in rodents but also in large animal models, including non-human primates. Furthermore, mixed chimerism protocols have been developed that would be feasible in cadaveric, and thus in thoracic, transplantation. The induction of mixed hematopoietic chimerism is therefore an attractive experimental approach for development of clinical tolerance protocols. One of the obstacles to widespread clinical application of this concept is the remaining toxicity of the host conditioning. Recent advances, however, have led to substantially milder protocols that could become clinically acceptable in the foreseeable future. This article provides a short overview of the basic mechanisms by which immunologic tolerance may be induced, describes the concept of mixed chimerism as a promising approach for clinical tolerance induction, and reviews recent progress in developing clinically feasible mixed chimerism protocols.

Mixed chimerism and transplantation tolerance

Achieving transplantation tolerance is an important goal in the effort to reduce long-term morbidity and mortality in organ transplant recipients. Robust, lifelong, donor-specific tolerance can be reliably achieved by induction of mixed chimerism in various animal models. To date, the clinical application of these proto-cols has been impeded partly by the potential toxicity of the required host conditioning regimens and the lack of successful studies in large animals. This article reviews the progress achieved in recent years in developing considerably milder conditioning protocols in rodents, and in extending some of these models to achieve permanent mixed chimerism and tolerance in large animals. Advances in the induction of xenogeneic tolerance through mixed chimerism are also discussed.

Peripheral deletion after bone marrow transplantation with costimulatory blockade has features of both activation-induced cell death and passive cell death

Two major pathways of death of previously activated T cells have been described: activation-induced cell death can be triggered by restimulating activated T cells with high concentrations of Ag, is Fas-dependent, is not influenced by proteins of the Bcl family, and is blocked by cyclosporin A; in contrast, passive cell death is induced by the withdrawal of growth factors and activation stimuli, is Fas-independent, and is blocked by Bcl family proteins. We examined the role of these two forms of cell death in the peripheral deletion of donor-reactive host T cells after allogeneic bone marrow transplantation and costimulatory blockade with anti-CD154 plus CTLA4Ig in two murine models. The substantial decline in donor-reactive CD4 cells seen in wild-type recipients 1 wk after bone marrow transplantation with costimulatory blockade was largely inhibited in Fas-deficient recipients and in Bcl-x(L)-transgenic recipients. We observed these effects both in a model involving low-dose total body irradiation and a conventional dose of bone marrow, and in a radiation-free regimen using high-dose bone marrow transplantation. Furthermore, cyclosporin A did not completely block the deletion of donor-reactive CD4(+) T cells in recipients of bone marrow transplantation with costimulatory blockade. Thus, the deletion of donor-reactive T cells occurring early after bone marrow transplantation with costimulatory blockade has features of both activation-induced cell death and passive cell death. Furthermore, these in vivo data demonstrate for the first time the significance of in vitro results indicating that proteins of the Bcl family can prevent Fas-mediated apoptosis under certain circumstances.

The critical role of mouse CD4+ cells in the rejection of highly disparate xenogeneic pig thymus grafts

Long-term survival of fetal pig thymus (FP THY) grafts and efficient repopulation of mouse CD4+ T cells is achieved in thymectomized (ATX) B6 mice that receive T and NK cell depletion by injection of a cocktail of mAbs (GK1.5, 2.43, 30-H12, and PK136) and fetal pig thymus/liver (FP THY/LIV) grafts. The requirement for each mAb in this conditioning regimen in order to avoid the rejection of FP THY grafts has not yet been defined. In our present studies, CD4 cell-depleted ATX B6 mice and euthymic MHC class II-deficient (IIKO) mice were employed to investigate the role of mouse CD4+ cells in the rejection of FP THY grafts in vivo. After grafting FP THY/LIV to CD4+ cell-depleted ATX B6 mice, efficient repopulation of mouse CD4+ T cells was observed in the periphery. However, only two of four mice had remaining FP THY grafts by 17 weeks post-implantation, and these were of poor quality, whereas four of four T and NK cell-depleted ATX B6 mice had well-developed FP THY grafts. Furthermore, three of four FP THY/LIV-grafted, CD4+ cell-depleted ATX B6 mice rejected donor MHC-matched pig skin grafts. In contrast, three of three FP THY/LIV grafted, T and NK cell-depleted, ATX B6 mice accepted donor MHC-matched pig skin grafts, suggesting that optimal tolerance to xenogeneic pig antigens was not achieved in mice conditioned only with anti-CD4 mAb. ATX B6 mice treated with only anti-CD8 mAb rejected FP THY completely by 6 weeks post-grafting, a time when CD4+ cell-depleted ATX B6 mice had well-vascularized FP THY grafts. In addition, when euthymic IIKO mice were pre-treated with the standard conditioning regimen that includes four different mAbs, FP THY grafts survived and supported the repopulation of mouse CD4+ T cells in the periphery, while high levels of mouse CD8+ T cells developed in host thymi. These studies suggest that mouse CD4+ T cells play a critical role in the acute rejection of xenogeneic FP THY grafts. Without help from CD4+ cells, mouse CD8+ cells, NK, NK/T, and TCR(gamma/delta)+ T cells do not mediate acute rejection of FP THY grafts. Furthermore, our results suggest that other cell subsets besides CD4+ T cells play a role in the delayed rejection of highly disparate xenogeneic FP THY grafts.

Allogeneic bone marrow transplantation with co-stimulatory blockade induces macrochimerism and tolerance without cytoreductive host treatment

Allogeneic bone marrow transplantation (in immunocompetent adults) has always required cytoreductive treatment of recipients with irradiation or cytotoxic drugs to achieve lasting engraftment at levels detectable by non-PCR-based techniques ('macrochimerism' or 'mixed chimerism'). Only syngeneic marrow engraftment at such levels has been achieved in unconditioned hosts. This requirement for potentially toxic myelosuppressive host pre-conditioning has precluded the clinical use of allogeneic bone marrow transplantation for many indications other than malignancies, including tolerance induction. We demonstrate here that treatment of naive mice with a high dose of fully major histocompatibility complex-mismatched allogeneic bone marrow, followed by one injection each of monoclonal antibody against CD154 and cytotoxic T-lymphocyte antigen 4 immunoglobulin, resulted in multi-lineage hematopoietic macrochimerism (of about 15%) that persisted for up to 34 weeks. Long-term chimeras developed donor-specific tolerance (donor skin graft survival of more than 145 days) and demonstrated ongoing intrathymic deletion of donor-reactive T cells. A protocol of high-dose bone marrow transplantation and co-stimulatory blockade can thus achieve allogeneic bone marrow engraftment without cytoreduction or T-cell depletion of the host, and eliminates a principal barrier to the more widespread use of allogeneic bone marrow transplantation. Although efforts have been made to minimize host pre-treatment for allogeneic bone marrow transplantation for tolerance induction, so far none have succeeded in eliminating pre-treatment completely. Our demonstration that this can be achieved provides the rationale for a safe approach for inducing robust transplantation tolerance in large animals and humans.

Stable prodrugs of n-butyric acid: suppression of T cell alloresponses in vitro and prolongation of heart allograft survival in a fully allogeneic rat strain combination

n-Butyric acid has previously been shown in vitro to suppress T cell alloresponses and beyond that to induce a state of alloantigen-specific hyporesponsiveness suggesting a potential relevance for suppressing alloresponses also in vivo. The clinical use of butyrate salt derivatives, however, is limited by an extremely short half-life due to rapid metabolism. This prompted us to investigate the effect of butyric acid derivatives with prolonged residence time in vivo on T cell alloresponses in vitro and further to explore the immunosuppressive capacity of esterified n-butyric acid in vivo. First, the effect of three butyric acid esters, i.e. glucose pentabutyrate, diacetone glucose butyrate and tributyrin on T cell proliferation in a human mixed lymphocyte culture (MLC) was evaluated. All three derivatives were found to inhibit T cell alloresponses in a concentration-dependent manner. Based on the ED50 values, glucose pentabutyrate was found to be most effective in inhibiting T cell alloreactivity in vitro (11 microM), followed by diacetone glucose butyrate (122 microM), tributyrin (146 microM) and sodium butyrate (539 microM). Because of its favourable in vitro properties, glucose pentabutyrate was chosen for in vivo experiments. To test the effect of this compound on allograft survival in vivo, in the second part of this study, heterotopic heart transplants were performed in a high responder fully allogeneic rat strain combination (Brown Norway to Lewis strain rats). We found that intraperitoneal (i.p.) injection of glucose pentabutyrate at 500 mg/kg/day (day 0 and daily up to 12 days posttransplant) induced a significant prolongation of allograft survival as compared to animals treated with vehicle (glycerol formal, i.p.) alone (14.1+/-6.3 versus 9.6+/-3.2 days, p = 0.036), whereby at lower dosage (100 mg/kg/day) no such effect was observed (10.2+/-2.1 days, p = 0.21). Our findings suggest that stable prodrugs of n-butyric acid might have potential clinical relevance for inhibiting alloresponses in vivo.

Anti-CD154 or CTLA4Ig obviates the need for thymic irradiation in a non-myeloablative conditioning regimen for the induction of mixed hematopoietic chimerism and tolerance

BACKGROUND

Thymic irradiation (TI) or repeated administration of T cell-depleting monoclonal antibodies (TCD mAbs) is required in a previously described non-myeloablative regimen allowing allogeneic marrow engraftment with stable mixed chimerism and tolerance. As both treatments might be associated with toxicity in the clinical setting, we evaluated whether T-cell costimulatory blockade could be used to replace them.

METHODS

C57BL/6 mice received depleting anti-CD4 and anti-CD8 mAbs on day -5, 3 Gy whole body irradiation (day 0), and 15x10(6) fully MHC-mismatched, B10.A bone marrow cells. In addition, hosts were injected with an anti-CD154 mAb (day 0) and/or CTLA4Ig (day +2). Chimerism in peripheral blood was followed by flow cytometric (FACS) analysis, and tolerance was assessed by skin grafting, and also by mixed lymphocyte reaction (MLR) and cell-mediated lympholysis (CML) assays. The frequency of certain Vbeta families was determined by FACS to assess deletion of donor-reactive T cells.

RESULTS

Chimerism was transient and tolerance was not present in animals receiving TCD mAbs on day -5 without costimulatory blockade. The addition of anti-CD154 and CTLA4Ig, alone or in combination, reliably permitted induction of high levels of stable (>6 months) multi-lineage chimerism, with specific tolerance to skin grafts and donor antigens by MLR and CML assays. Long-term chimeras showed deletion of donor-reactive CD4+ peripheral blood lymphocytes, splenocytes, and mature thymocytes. Administration of TCD mAbs only 1 day before bone marrow transplantation plus anti-CD154 also allowed induction of permanent chimerism and tolerance.

CONCLUSIONS

One injection of anti-CD154 or CTLA4Ig overcomes the need for TI or prolonged host TCD in a preclinical model for the induction of mixed chimerism and deletional tolerance and thus further decreases the toxicity of this protocol. Achievement of tolerance with conditioning given over 24 hr suggests applicability to cadaveric organ transplantation.

Extrathymic T cell deletion and allogeneic stem cell engraftment induced with costimulatory blockade is followed by central T cell tolerance

A reliable, nontoxic method of inducing transplantation tolerance is needed to overcome the problems of chronic organ graft rejection and immunosuppression-related toxicity. Treatment of mice with single injections of an anti-CD40 ligand antibody and CTLA4Ig, a low dose (3 Gy) of whole body irradiation, plus fully major histocompatibility complex-mismatched allogeneic bone marrow transplantation (BMT) reliably induced high levels (>40%) of stable (>8 mo) multilineage donor hematopoiesis. Chimeric mice permanently accepted donor skin grafts (>100 d), and rapidly rejected third party grafts. Progressive deletion of donor-reactive host T cells occurred among peripheral CD4(+) lymphocytes, beginning as early as 1 wk after bone marrow transplantation. Early deletion of peripheral donor-reactive host CD4 cells also occurred in thymectomized, similarly treated marrow recipients, demonstrating a role for peripheral clonal deletion of donor-reactive T cells after allogeneic BMT in the presence of costimulatory blockade. Central intrathymic deletion of newly developing T cells ensued after donor stem cell engraftment had occurred. Thus, we have shown that high levels of chimerism and systemic T cell tolerance can be reliably achieved without myeloablation or T cell depletion of the host. Chronic immunosuppression and rejection are avoided with this powerful, nontoxic approach to inducing tolerance.

Separate regulation of peripheral hematopoietic and thymic engraftment

Long-term multilineage chimerism, indicating pluripotent hematopoietic stem cell engraftment, was achieved in an Ly5-congenic strain combination without irradiation or other host conditioning when a large number of donor marrow cells (1.4-2x10(8)) was administered. However, the initial (2-4 weeks posttransplantation) percentages of T and B lymphocytes of donor origin were markedly lower than those of myeloid lineages. Steady-state levels of donor and host repopulation of all lineages were reached by 7 to 15 weeks posttransplantation and remained relatively constant for at least 41 weeks. B cell chimerism was similar to that seen in myeloid lineages at steady state. In contrast, long-term donor representation in the T cell lineage was much lower than in the B cell or myeloid lineages. Host treatment with depleting anti-T cell monoclonal antibodies increased the donor contribution to early T cell repopulation, but long-term T cell chimerism was still significantly lower in all lymphohematopoietic tissues, including the thymus, than B cell or myeloid cell chimerism. Pretreatment of hosts with 3.5 Gy of local irradiation to the thymic region further increased the donor contribution to initial T cell repopulation, which equaled that of other lineages at 4 to 7 weeks. However, donor representation in the T cell lineage declined by the time steady-state chimerism was attained and was lower than donor representation in the B cell or myeloid lineages. A higher dose of thymic irradiation (7 Gy) led to a reduction in this discrepancy, so that levels of donor thymopoiesis and hematopoiesis in other lineages were similar by 23 to 27 weeks posttransplantation. The differential contribution of adult donor marrow to long-term, steady-state thymopoiesis vs. hematopoiesis in other lineages under certain conditions in this competitive repopulation assay suggests that functionally distinguishable progenitors are responsible for these activities.

Lung transplantation for primary pulmonary hypertension and giant pulmonary artery aneurysm

We report the case of an 18-year-old patient with a giant pulmonary artery aneurysm and primary pulmonary hypertension who was successfully treated with bilateral lung transplantation and complete reconstruction of the pulmonary artery.

Incidence and outcome of major non-pulmonary surgical procedures in lung transplant recipients

OBJECTIVE

Pulmonary transplant recipients are at high risk from various conditions requiring surgical intervention. As little is known about their exact incidence and course, we examined such procedures in detail.

METHODS AND PATIENTS

We have retrospectively analyzed major nonpulmonary surgical procedures performed in 124 consecutive patients who received an isolated lung transplant at the University of Vienna between 1989 and December 1995. Twenty-two patients underwent a total of 28 major interventions (22/124 = 17.7%), resulting in an incidence of one procedure every 5.8 patient years of follow-up. The mean interval between transplantation and intervention was 17.9 months (range 3 days to 62 months) with six interventions being carried out during the first month after transplantation. Fourteen emergency operations were performed, the remaining 14 procedures were carried out electively. Overall, 15 abdominal procedures, four thoracic, four orthopedic, two gynecological, one neurosurgical, one urological and one plastic surgery were performed.

RESULTS

There was no intraoperative death. Perioperatively, five surgery related deaths were observed (5/28, related mortality 17.9%) with multiple organ failure as the cause of death in all cases. All of these deaths followed emergency operations (5/14 = 35.7%) and all were observed in patients with septic abdominal complications. In contrast, even very extensive procedures were performed electively without related mortality (0/14, P = 0.02). During the first month after transplantation, major surgery was associated with a 50% (3/6) mortality, for late interventions mortality was 9.1% (2/22; P = 0.047).

CONCLUSIONS

Pulmonary transplant recipients showed a high incidence of conditions requiring surgical intervention. As expected, septic complications, especially during the immediate post transplant period, carried a very poor prognosis. However, it was reassuring to observe that even extensive surgical procedures could be performed safely without associated mortality in the elective setting.