Functional Fc gamma receptor gene polymorphisms and donor-specific antibody-triggered microcirculation inflammation

Fc-dependent effector mechanisms may contribute to antibody-mediated rejection (ABMR), and distinct gene polymorphisms modifying the function of Fc gamma receptors (FcγRs) may influence the capability of donor-specific antibodies (DSAs) to trigger inflammation. To evaluate the relevance of functional FcγR variants in late ABMR, 85 DSA-positive kidney allograft recipients, who were recruited upon antibody screening of 741 prevalent patients, were genotyped for polymorphisms in FcγRIIA (FCGR2A-H/R₁₃₁ ; rs1801274), FcγRIIIA (FCGR3A-V/F₁₅₈ ; rs396991), and FcγRIIIB (FCGR3B-neutrophil antigen 1 ([NA1]/NA2; rs35139848). Individuals with high-affinity FCGR3A-V₁₅₈ alleles (V/V₁₅₈ or V/F₁₅₈ ) showed a higher rate (and extent) of peritubular capillaritis (ptc) in protocol biopsies than homozygous carriers of the lower-affinity allele (ptc score ≥1: 53.6% vs 25.9%; P = .018). Associations were independent of C1q-binding to DSA or capillary C4d. In parallel, there was a trend toward increased macrophage- and injury-repair response-associated transcript subsets. Kidney function over 24 months, however, was not different. In support of a functional role of FcγRIIIA polymorphism, NK92 cells expressing FCGR3A-V₁₅₈ produced >2 times as much interferon gamma upon incubation with HLA antibody-coated cells as those expressing FCGR3A-F₁₅₈ . FcγRIIA and FcγRIIIB polymorphisms were not associated with allograft morphology. Our data suggest that the presence of high-affinity FcγRIIIA variants may favor DSA-triggered microcirculation inflammation.

Anti-C1s monoclonal antibody BIVV009 in late antibody-mediated kidney allograft rejection-results from a first-in-patient phase 1 trial

The classical pathway (CP) of complement may contribute to the pathogenesis of antibody-mediated rejection (ABMR). Selective CP blockade may be a promising strategy to counteract rejection. The objective of this first-in-patient phase 1b trial was to evaluate the safety/tolerability and CP-blocking potential of 4 weekly doses (60 mg/kg) of the anti-C1s antibody BIVV009 in complement-mediated disorders. Here we describe the results in a cohort of 10 stable kidney transplant recipients (median of 4.3 years posttransplantation) with late active ABMR and features of CP activation, such as capillary C4d or complement-fixing donor-specific antibodies (DSA). During 7 weeks follow-up, no severe adverse events were reported, and BIVV009 profoundly inhibited overall and DSA-triggered CP activation in serum. Five of 8 C4d-positive recipients turned C4d-negative in 5-week follow-up biopsies, while another 2 recipients showed a substantial decrease in C4d scores. There was, however, no change in microcirculation inflammation, gene expression patterns, DSA levels, or kidney function. In conclusion, we demonstrate that BIVV009 effectively blocks alloantibody-triggered CP activation, even though short-course treatment had no effect on indices of activity in late ABMR. This initial trial provides a valuable basis for future studies designed to clarify the therapeutic value of CP blockade in transplantation. ClinicalTrials.gov NCT#02502903.

Effect of the Anti-C1s Humanized Antibody TNT009 and Its Parental Mouse Variant TNT003 on HLA Antibody-Induced Complement Activation-A Preclinical In Vitro Study

The classic pathway (CP) of complement is believed to significantly contribute to alloantibody-mediated transplant injury, and targeted complement inhibition is currently considered to be a promising approach for preventing rejection. Here, we investigated the mode of action and efficacy of the humanized anti-C1s monoclonal antibody TNT009 and its parental mouse variant, TNT003, in preclinical in vitro models of HLA antibody-triggered CP activation. In flow cytometric assays, we measured the attachment of C1 subcomponents and C4/C3 split products (C4b/d, C3b/d) to HLA antigen-coated flow beads or HLA-mismatched aortic endothelial cells and splenic lymphocytes. Anti-C1s antibodies profoundly inhibited C3 activation at concentrations >20 μg/mL, in both solid phase and cellular assays. While C4 activation was also prevented, this was not the case for C1 subcomponent attachment. Analysis of serum samples obtained from 68 sensitized transplant candidates revealed that the potency of inhibition was related to the extent of baseline CP activation. This study demonstrates that anti-C1s antibodies TNT009 and TNT003 are highly effective in blocking HLA antibody-triggered complement activation downstream of C1. Our results provide the foundation for clinical studies designed to investigate the potential of TNT009 in the treatment or prevention of complement-mediated tissue injury in sensitized transplant recipients.

The Effect of Cortex/Medulla Proportions on Molecular Diagnoses in Kidney Transplant Biopsies: Rejection and Injury Can Be Assessed in Medulla

Histologic assessment of kidney transplant biopsies relies on cortex rather than medulla, but for microarray studies, the proportion cortex in a biopsy is typically unknown and could affect the molecular readings. The present study aimed to develop a molecular estimate of proportion cortex in biopsies and examine its effect on molecular diagnoses. Microarrays from 26 kidney transplant biopsies divided into cortex and medulla components and processed separately showed that many of the most significant differences were in glomerular genes (e.g. NPHS2, NPHS1, CLIC5, PTPRO, PLA2R1, PLCE1, PODXL, and REN). Using NPHS2 (podocin) to estimate proportion cortex, we examined whether proportion cortex influenced molecular assessment in the molecular microscope diagnostic system. In 1190 unselected kidney transplant indication biopsies (Clinicaltrials.govNCT01299168), only 11% had <50% cortex. Molecular scores for antibody-mediated rejection, T cell-mediated rejection, and injury were independent of proportion cortex. Rejection was diagnosed in many biopsies that were mostly or all medulla. Agreement in molecular diagnoses in paired cortex/medulla samples (23/26) was similar to biological replicates (32/37). We conclude that NPHS2 expression can estimate proportion cortex; that proportion cortex has little influence on molecular diagnosis of rejection; and that, although histology cannot assess medulla, rejection does occur in medulla as well as cortex.

[Kidney paired donation. Combination with extracorporeal desensitization]

BACKGROUND

Live kidney donation represents the gold standard for renal replacement therapy. Due to ABO and HLA incompatibility between donor and recipient pairs, one third of possible transplantations cannot be performed. Kidney exchange programs in combination with extracorporeal desensitization have been introduced to enable successful kidney transplantation in such circumstances.

OBJECTIVE

This review discusses the current indications, methods, ethical problems and results within such programs.

MATERIALS AND METHODS

Relevant Medline articles were analyzed and personal experiences of the authors are included in this article.

RESULTS

Kidney exchange programs in combination with extracorporeal desensitization enable successful transplantation for most patients.

DISCUSSION

The best combinations of existing strategies have to be defined and newly arisen ethical questions have to be answered.

Value of routine voiding cystourethrography after renal transplantation

The impact of vesicoureteral reflux (VUR) on renal allograft outcomes is debatable, with small cohort studies reporting controversial results. The objective of this retrospective study was to evaluate long-term clinical effects of early VUR in a large cohort of kidney transplant patients. Posttransplantation voiding cystourethrography was used to evaluate 646 consecutive kidney transplant recipients before discharge. The study endpoints included VUR grade, death-censored graft or patient survival, renal function, proteinuria and occurrence of urinary tract infections (UTIs). Of the 646 recipients, 263 (40.7%) were diagnosed with VUR. VUR grade II was most common (19.8%), followed by grades III (10.2%), I (7.9%) and IV (2.8%). VUR was less common in transplantations performed by experienced compared to inexperienced surgeons (36% vs. 48%; p = 0.004). VUR did not affect death-censored graft or patient survival and was not associated with proteinuria or occurrence of UTIs. Patients with VUR had a lower eGFR at 1 year after transplantation than did patients without VUR (60 vs. 52 mL/min/1.73 m(2) ; p = 0.02), although this difference was not observed at 3 and 5 years after transplantation. We conclude that early VUR, a common finding among renal transplant patients, may not have a meaningful impact on long-term transplant outcomes.

Desensitization and crossmatch conversion in deceased donor kidney transplantation

Recipient allosensitization represents a major barrier to transplantation. Sensitized patients awaiting a deceased donor kidney transplant often face unacceptably long waiting times and are more prone to rejection, even in the absence of a positive crossmatch (XM). Two major strategies have been shown to facilitate the access to transplantation: specific allocation programs designed to enhance the availability of a well-matched allograft; and recipient desensitization to decrease levels of humoral alloreactivity. Over the last two to three decades, a variety of desensitization strategies have been published. Such protocols are based on the use of apheresis for direct alloantibody removal from the circulation, or high dose intravenous immunoglobulin and/or CD20 antibody rituximab for modulation of B cell immunity. An attractive approach may be the application of apheresis for rapid desensitization, with or without XM conversion, immediately before transplantation, a particular challenge because of the short interval between the transplant offer and surgery. It was shown that with currently available treatment strategies many high risk patients can be successfully transplanted within an acceptable time period. However, there is still a need for further improvement, as rejection and graft loss rates may be considerably higher than those documented for non-sensitized patients. Future studies will have to establish more precise diagnostic criteria to optimize treatment allocation and monitoring. Moreover, systematic trials are needed to assess the efficiency of innovative treatment concepts, such as the use of agents that directly affect alloantibody-producing plasma cells.

Peritransplant immunoadsorption for positive crossmatch deceased donor kidney transplantation

Various desensitization protocols were shown to enable successful living donor kidney transplantation across a positive complement-dependent cytotoxicity crossmatch (CDCXM). Positive crossmatch transplantation, however, is less well established for deceased donor transplantation. We report a cohort of 68 deceased donor renal allograft recipients who, on the basis of broad sensitization (lymphocytotoxic panel reactivity ≥40%), were subjected to a protocol of peritransplant immunoadsorption (IA). Treatment consisted of a single session of immediate pretransplant IA (protein A) followed by posttransplant IA and antilymphocyte antibody therapy. Twenty-one patients had a positive CDCXM, which could be rendered negative by pretransplant apheresis. Solid phase HLA antibody detection revealed preformed donor-specific antibodies (DSA) in all 21 CDCXM-positive and in 30 CDCXM-negative recipients. At 5 years, overall graft survival, death-censored graft survival and patient survival were 63%, 76% and 87%, respectively, without any differences between CDCXM-positive, CDCXM-negative/DSA-positive and CDCXM-negative/DSA-negative recipients. Furthermore, groups did not differ regarding rates of antibody-mediated rejection (24% vs. 30% vs. 24%, p = 0.84), cellular rejection (14% vs. 23% vs. 18%, p = 0.7) or allograft function (median 5-year serum creatinine: 1.3 vs. 1.8 vs. 1.7 mg/dL, p = 0.62). Our results suggest that peritransplant IA is an effective strategy for rapid desensitization in deceased donor transplantation.

Posttransplant HLA alloreactivity in stable kidney transplant recipients-incidences and impact on long-term allograft outcomes

Humoral alloreactivity is well established to predict adverse allograft outcomes. However, in some recipients, alloantibodies may also occur in the absence of graft dysfunction. We evaluated if and how often complement- and noncomplement-fixing alloantibodies are detectable in stable recipients and whether, in this context, they affect long-term outcomes. Sera obtained from 164 kidney transplant recipients at 2, 6 and 12 months were evaluated by FlowPRA screening and single-antigen testing for detection of IgG- or C4d-fixing HLA panel reactivity and donor-specific antibodies (DSA). Applying stringent criteria, we selected 34 patients with an uneventful 1-year course (no graft dysfunction or rejection) and excellent graft function at 12 months [estimated glomerular filtration rate (eGFR) >or=60 mL/min and proteinuria <or=0.5 g/24 h]. Nine (27%) and 5 (15%) of these recipients tested positive by [IgG] and [C4d]FlowPRA screening, respectively. In five cases, DSA were identified. Frequencies of positive test results and DSA binding intensities were not significantly lower than those documented for patients who did not fulfill the above criteria. In recipients with an excellent 1-year course, FlowPRA reactivity was not associated with lower eGFR or increased protein excretion during 68-month median follow-up. Our results suggest cautious interpretation of antibody monitoring in patients with normal-functioning grafts.

In vitro detection of C4d-fixing HLA alloantibodies: associations with capillary C4d deposition in kidney allografts

Capillary C4d deposition is a valuable marker of antibody-mediated rejection (AMR). In this analysis, flow cytometric detection of alloantibody-triggered C4d deposition to HLA antigen-coated microparticles ([C4d]FlowPRA) was evaluated for its value as a marker for C4d deposition in renal allografts. For comparative analysis, 105 first renal biopsies performed for graft dysfunction and an equal number of concurrent sera were subjected to immunohistochemistry and [C4d] plus standard [IgG]FlowPRA, respectively. C4d deposition/fixation was detected in 17 biopsies and, applying [C4d]FlowPRA HLA class I and II screening, also in a small number of corresponding sera (N = 20). IgG reactivity detected by standard [IgG]FlowPRA was more frequent (49% of sera). Comparing [C4d]FlowPRA screening with capillary C4d staining, we found a high level of specificity (0.92 [95% confidence interval: 0.86-0.98]), which far exceeded that calculated for [IgG]FlowPRA (0.60 [0.50-0.70]). [IgG]FlowPRA screening, however, turned out to be superior in terms of sensitivity (0.94 [0.83-1.05] vs. 0.76 [0.56-0.97] calculated for C4d-fixing panel reactivity). Remarkably, posttransplant single antigen testing for identification of complement-fixing donor-specific alloreactivities failed to improve the predictive value of FlowPRA-based serology. In conclusion, our results suggest that detection of complement-fixing HLA panel reactivity could provide a specific tool for monitoring of C4d-positive AMR.

The cellular lesion of humoral rejection: predominant recruitment of monocytes to peritubular and glomerular capillaries

Accumulation of inflammatory cells within capillaries is a common morphologic feature of humoral renal allograft rejection and is most easily appreciated if it occurs in glomeruli. The aim of our study was to determine the amount and composition of immune cells within glomeruli and peritubular capillaries (PTC) in cellular and humoral allograft rejection. Immunofluorescent double-labeling for CD31 and CD3 or CD68 was used for phenotyping and enumerating immune cells within glomeruli and PTC. The major findings are: (1) accumulation of immune cells in PTC is far more common than it would be anticipated based on the assessment by conventional histology; (2) it is not the absolute number of immune cells accumulating within capillaries, but rather the composition of the intracapillary cell population that distinguishes humoral rejection from cellular rejection and (3) in C4d positive biopsies a predominantly monocytic cell population accumulates not only within glomeruli but also within PTC. The median value of monocyte/T-cell ratio within PTC was 2.3 in C4d positive biopsies but only 1 (p = 0.0008) in C4d negative biopsies. Given their prominent presence within capillaries and their extensive biological versatility monocytes might contribute to the capillary damage observed in acute and chronic allograft rejection.

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.

Immunoadsorption in severe C4d-positive acute kidney allograft rejection: a randomized controlled trial

Antibody-mediated rejection (AMR) frequently causes refractory graft dysfunction. This randomized controlled trial was designed to evaluate whether immunoadsorption (IA) is effective in the treatment of severe C4d-positive AMR. Ten out of 756 kidney allograft recipients were included. Patients were randomly assigned to IA with protein A (N = 5) or no such treatment (N = 5) with the option of IA rescue after 3 weeks. Enrolled recipients were subjected to tacrolimus conversion and, if indicated, 'anti-cellular' treatment. All IA-treated patients responded to treatment. One death unrelated to IA occurred after successful reversal of rejection. Four control subjects remained dialysis-dependent. With the exception of one patient who developed graft necrosis, non-responders were subjected to rescue IA, however, without success. Because of a high graft loss rate in the control group the study was terminated after a first interim analysis. Even though limited by small patient numbers, this trial suggests efficiency of IA in reversing severe AMR.

Pivotal role of complement-fixing HLA alloantibodies in presensitized kidney allograft recipients

Recipient presensitization represents a major risk factor for kidney allograft loss. Complement fixation may be a critical attribute of deleterious alloantibodies. We investigated clinical impact of complement-fixing HLA presensitization employing [C4d]FlowPRA, a novel assay permitting selective detection of HLA panel reactive antibody (PRA)-triggered C4 complement split product deposition. A cohort of 338 kidney transplants was evaluated for presensitization applying [C4d]FlowPRA together with [IgG]FlowPRA and complement-dependent cytotoxicity (CDC)-PRA. Analysis of HLA class I alloreactivities revealed a high incidence of C4d-positive graft dysfunction in [IgG]FlowPRA(+)/[C4d]FlowPRA(+) and [IgG]FlowPRA(+)/[C4d]FlowPRA(-) recipients (23% and 22% vs. 3% in [IgG]FlowPRA(-) patients). Only patients with complement-fixing HLA class I immunization had inferior graft survival [75% (3 years) vs. 91% and 89%, respectively (p=0.036)]. Despite frequent finding of capillary C4d deposition (28%), complement-fixing HLA class II immunization was not associated with inferior survival rates. This may have been due to reduction of clinical effects by intense immunosuppression in presensitized patients. Evaluating CDC, 29% of CDC-PRA(+)/[C4d]FlowPRA(+) recipients had C4d-positive graft dysfunction. For these patients 3-year graft survival was worst, followed by CDC-PRA(+)/[C4d]FlowPRA(-) and CDC-PRA(-) patients (76% vs. 81% vs. 90%, p=0.014). Results highlight a strong impact of complement-fixing HLA presensitization. Discerning complement-activating abilities of HLA alloantibodies, [C4d]FlowPRA may help identify recipients at particularly high risk for graft rejection and loss.

Endothelial C4d deposition is associated with inferior kidney allograft outcome independently of cellular rejection

BACKGROUND

Capillary deposition of complement split product C4d has been suggested to be a valuable marker for humoral rejection. In this retrospective study we evaluated the clinical impact of C4d deposition in renal allografts with special emphasis on associations between C4d staining patterns and histological features of acute rejection.

METHODS

One hundred and two allograft biopsies obtained from 61 kidney transplants (1-532 days after transplantation; median 14 days) were examined by immunohistochemistry on routine paraffin sections using a novel anti-C4d polyclonal antibody (C4dpAb).

RESULTS

Fourty-two of 102 biopsies showed endothelial C4d deposits in peritubular capillaries (PTC). Histopathological analysis revealed a significantly lower frequency of positive C4d staining in biopsies with rather than in those without acute cellular rejection defined by the Banff grading schema (P<0.01). For clinical evaluation, patients were classified according to C4d staining in allografts (C4d(PTC) positive in at least one biopsy, n=31 vs C4d(PTC) negative in all biopsies, n=30). C4d(PTC) positive patients had significantly higher serum creatinine levels than C4d negative patients. Even in the absence of morphological evidence for rejection, differences in serum creatinine levels between C4d(PTC) positive and negative recipients were significant (6 months: 2.01+/-0.75 vs 1.41+/-0.27 mg/dl; 12 months: 1.95+/-0.60 vs 1.36+/- 0.34 mg/dl; 18 months: 1.98+/-0.50 vs 1.47+/-0.31 mg/dl; P<0.05). All patients with rejection resistant to conventional therapy (n=4) were in the C4d(PTC) positive subgroup. All recipients with panel reactive antibodies (PRA) >50% (n=8) were C4d(PTC) positive.

CONCLUSIONS

Our data indicate that endothelial C4d deposition is associated with inferior graft outcome. We provide evidence that this immunohistochemical finding and its clinical impact are not associated with morphological signs of cellular rejection.

Long-term evaluation of proliferative donor antigen-specific reactivity in cadaveric kidney transplant recipients

Development of donor-specific proliferative hyporeactivity has been evaluated in many studies for its usefulness in identifying transplant recipients at low risk of immunological complications. These studies often result in controversial conclusions, however. The authors claim that the discrepancy in the predictive value of mixed lymphocyte culture- (MLC) reactivity might partly be due to differences in presentation and interpretation of results. The purpose of this study is to investigate the usefulness of a normalized evaluation of antigen-specific donor-reactivity in a small number of kidney transplant recipients. This could then serve as a basis for an extended clinical study. Ten cadaveric kidney recipients were tested for proliferative reactivity to donor- and third-party antigens up to 20 months posttransplantation. Expressing donor-specific reactivity as a relation between the percentage of pretransplant responses towards donor splenocytes and the percentage of pretransplant responses towards third-party donor cells should minimize influences of e. g. uremia, current immunosuppression or infections on the evaluation of specific reactivity and thus should allow an evaluation of the donor-specificity of T-cell alloresponses independently of fluctuations in global responsiveness. Four of ten recipients acquired a state of donor-specific hyporeactivity ( < 75 % relative specific reactivity) at 20 months post-transplantation (61 +/- 12%, mean +/- SD). Six patients were classified non-hyporeactive (98 +/- 10% mean relative specific reactivity). Relative specific reactivity did not correlate with the levels of general reactivity. Three of the four hyporeactive and four of the six non-hyporeactive patients developed acute rejection. Stable graft function at 20 months posttransplantation (serum creatinine < or = 2 mg/dl) was not closely related to the reactivity status, as five of eight patients with well-functioning grafts did not develop relative specific hyporeactivity. One recipient with chronic rejection was classified hyporeactive. One non-hyporeactive patient lost his graft due to non-immunological causes. Our data suggest that post-transplant relative specific reactivity does not predict acute rejection. Downregulation of donor-specific reactivity might not be a prerequisite for stable graft function but could help identifying recipients who require less immunosuppression. This, however, remains to be established in a prospective immunosuppression-weaning study.

Impaired phosphate handling of renal allografts is aggravated under rapamycin-based immunosuppression

BACKGROUND

Impaired phosphate handling of the renal allograft is a common problem and of multifactorial origin. The aim of the study was to elucidate whether a rapamycin- or a mycophenolate-based immunosuppressive therapy aggravates the renal phosphate leak in kidney transplant recipients.

METHODS

Renal phosphate handling was determined in thirty-eight cadaveric allograft recipients, with good renal function at 8, 12, 20 and 28 weeks after transplantation. Nineteen patients (group 1) received triple immunosuppression with rapamycin, cyclosporine and prednisolone, nineteen other transplant recipients received mycophenolate mofetil, cyclosporine and prednisolone immunosuppression (group 2), and six healthy subjects (group 3) served as controls. After 12 weeks of stable graft function, group 1 patients were divided further into two subgroups. Ten patients were kept on their immunosuppressive regimen (group 1A), whereas the remaining nine randomly chosen subjects had their cyclosporine withdrawn; they were thus maintained on a dual immunosuppression regimen with prednisolone and a higher dosage of rapamycin (group 1B).

RESULTS

Renal phosphate reabsorption was significantly lower in group 1 at 8 and 12 weeks after transplantation as compared with groups 2 and 3. At 20 weeks after transplantation, patients with rapamycin-based immunosuppression (groups 1A and 1B) continued to exhibit hypophosphataemia and impaired renal phosphate handling. Group 1B had the lowest TmP/ GFR compared with all groups. At 28 weeks, renal phosphate reabsorption and plasma phosphate levels were no longer different between patient groups and controls.

CONCLUSION

These data suggest that rapamycin-based immunosuppression prolongs the phosphate leak of the allografted kidney, leading to low serum phosphate levels during the first weeks after transplantation.

Anti-inflammatory effects of sodium butyrate on human monocytes: potent inhibition of IL-12 and up-regulation of IL-10 production

Cytokines are critical in regulating unresponsiveness versus immunity towards enteric antigens derived from the intestinal flora and ingested food. There is increasing evidence that butyrate, a major metabolite of intestinal bacteria and crucial energy source for gut epithelial cells, also possesses anti-inflammatory properties. Its influence on cytokine production, however, is not established. Here, we report that butyrate strongly inhibits interleukin-12 (IL-12) production by suppression of both IL-12p35 and IL-12p40 mRNA accumulation, but massively enhances IL-10 secretion in Staphylococcus aureus cell-stimulated human monocytes. The effect of butyrate on IL-12 production was irreversible upon the addition of neutralizing antibodies to IL-10 or transforming growth factor b1 and of indomethacin. In anti-CD3-stimulated peripheral blood mononuclear cells, butyrate enhanced IL-10 and IL-4 secretion but reduced the release of IL-2 and interferon-g. The latter effect was in part a result of suppressed IL-12 production but also a result of inhibition of IL-12 receptor expression on T cells. These data demonstrate a novel anti-inflammatory property of butyrate that may have broad implications for the regulation of immune responses in vivo and could be exploited as new therapeutic approach in inflammatory conditions.

Suppression of primary T-cell responses and induction of alloantigen-specific hyporesponsiveness in vitro by the Janus kinase inhibitor tyrphostin AG490

BACKGROUND

Tyrphostin AG490 has recently been shown to block interleukin (IL)-2 receptor gamma-chain-associated Janus kinase 3. Here, we analyzed the effect of AG490 on T-cell alloresponses in vitro.

METHODS

For the evaluation of T-cell activation, DNA synthesis, surface marker expression, cytokine secretion, intracellular calcium mobilization, early protein tyrosine phosphorylation, and apoptosis were measured.

RESULTS

AG490 effectively inhibited T-cell proliferation in human mixed lymphocyte culture (MLC) even when added 4 days after culture initiation. Inhibition of IL-2-dependent proliferation in T-cell blasts and the incapability of IL-2 or IL-15 to restore proliferation in AG490-treated MLC suggests interference with cytokine receptor signaling. T-cell receptor-triggered early protein tyrosine phosphorylation, calcium mobilization, up-regulation of CD69, and initial CD25 expression were not affected. Interestingly, AG490 substantially inhibited production of IL-2 and interferon-gamma in T cells stimulated with alloantigen or via CD3 and CD28. In CD28-independent activation models (e.g., stimulation with phorbol myristate acetate plus ionomycin), however, cytokine secretion was not inhibited. Pretreatment of primary MLC with AG490 resulted in substantial down-regulation of secondary responses to cells from the original donor as opposed to third-party cells or phytohemagglutinin. Unresponsiveness was induced also in T cells stimulated with CD3 monoclonal antibody. Induction of apoptosis in polyclonally activated T cells and the incapability of IL-2 to reverse specific hyporesponsiveness, suggest programmed cell death as an important mechanism underlying antigen-specific down-regulation of alloresponses.

CONCLUSIONS

We demonstrate that AG490 blocks different manifestations of T-cell activation. This and its ability to induce alloantigen-specific hyporesponsiveness point to a potential use for interfering with alloreactivities in vivo.

Role of humoral immune reactions as target for antirejection therapy in recipients of a spousal-donor kidney graft

Excellent graft outcome has been reported for spousal-donor kidney transplantation. In husband-to-wife transplantation, however, a tendency toward inferior graft survival has been described for recipients who were previously pregnant. In our series of spousal-kidney transplantations (nine transplantations; three female recipients), actual graft survival is 100% (median observation time, 339 days). Five patients experienced early allograft rejection. In four transplant recipients, rejection was easily reversible by conventional antirejection therapy. In a multiparous recipient, however, mild interstitial allograft rejection associated with early graft dysfunction was resistant to anticellular treatment (antilymphocyte antibody, tacrolimus rescue therapy). The particular finding of polymorphonuclear neutrophils in peritubular capillaries and the finding of diffuse capillary deposits of the complement split product, C4d, in a posttransplantation biopsy specimen suggested a role of antibody-mediated graft injury. Retrospective flow cytometry cross-matching showed the presence of preformed immunoglobulin G (IgG) antibodies to HLA class I antigens that were not detectable by pretransplantation lymphocytotoxic cross-match testing or screening for panel reactive antibodies. After transplantation, however, complement-fixing antibodies, also presumably triggered by reexposure to spousal-donor HLA antigens, could be detected in the patient's serum. These findings suggested antibody-mediated allograft rejection and led to the initiation of immunoadsorption therapy (14 sessions) with staphylococcal protein A. Selective removal of recipient IgG resulted in complete reversal of graft dysfunction. Our findings suggest that in husband-to-wife transplantation, donor-specific antibodies, presumably triggered by previous pregnancies, might occasionally induce sustained allograft dysfunction. Thus, in this particular setting, a detailed immunologic and histopathologic work-up regarding antibody-mediated allograft dysfunction is warranted because immunoadsorption may be a highly effective treatment modality.

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.

n-butyrate downregulates the stimulatory function of peripheral blood-derived antigen-presenting cells: a potential mechanism for modulating T-cell responses by short-chain fatty acids

Modulation of proliferative T-cell responses by n-butyrate has been suggested to result from direct interference with cell cycle progression. Considering the important role of antigen-presenting cells (APC) in T-cell activation, we were particularly interested in studying the impact of n-butyrate on these cells. We demonstrated that pretreatment of human peripheral blood mononuclear cells (PBMC) or monocytes with this agent resulted in a dose- and time-dependent downregulation of their capability to stimulate T-cell responses with a similar pattern of inhibition when this agent was present throughout the culture period. Pretreatment with n-butyrate was effective in preventing both alloresponses and T-cell proliferation to immobilized anti-CD3 monoclonal antibody (mAb) suggesting alteration of costimulatory function. Flow cytometric analysis revealed that interferon-gamma (IFN-gamma)-induced upregulation of B7-1 expression on monocytes was profoundly inhibited by n-butyrate. Furthermore, this agent significantly suppressed the expression of intercellular adhesion molecule-1 (ICAM-1) or lymphocyte function-associated antigen-3 (LFA-3). In contrast, constitutive as well as cytokine-induced expression of B7-2 was enhanced by n-butyrate. Additionally, in monocytes, but not in T cells, treatment with n-butyrate led to significant alteration of membrane integrity owing to apoptotic cell death. Our findings indicate that modulation of T-cell responses by n-butyrate could also result from altered APC function, possibly as a consequence of downregulating distinct adhesion and/or costimulatory receptors as well as of inducing apoptosis. A potential clinical relevance of short-chain fatty acids for reducing T-cell-mediated immune reactions via modulating APC function is speculated.

Induction of alloantigen-specific hyporesponsiveness in vitro by n-butyrate: antagonistic effect of cyclosporin A

The short-chain fatty acid n-butyrate has recently been shown in vitro to specifically downregulate T cell reactivity to nominal antigen or to alloantigen, which possibly results from inhibition of cell cycle progression in early G1 phase during antigen contact. In the present study, we investigated the effect of cyclosporin A (CyA) on the modulation of alloreactivity in human mixed lymphocyte culture (MLC) by n-butyrate. Whereas in primary culture, CyA additively enhanced inhibition of DNA synthesis by n-butyrate, the effect of this agent on secondary T cell reactivity was clearly antagonized by CyA. Thus, specific downregulation of proliferative responsiveness to restimulation with antigen from the original donor, observed in cultures pretreated with n-butyrate alone, was at least partially prevented by the addition of CyA to the primary culture. Our in vitro finding indicates that specific downregulation of T cell alloreactivity by n-butyrate might depend on a calcium-dependent T cell receptor (TCR)-mediated signal sensitive to the immunosuppressive action of CyA.

Specific down-regulation of proliferative T cell alloresponsiveness by interference with CD2/LFA-3 and LFA-1/ICAM-1 in vitro

T cell activation requires Ag contact with the TCR in the presence of costimulatory signals provided by APCs. When Ag is presented without costimulation, T cells are functionally inactivated. Here we demonstrate that interference with distinct adhesion molecules during Ag contact using mAbs leads to Ag-specific functional inactivation of alloreactive T cells. We found that the presence of a mixture of mAbs specific for CD2, LFA-3, LFA-1 alpha- and beta-chain, and ICAM-1 during primary MLC leads to down-regulation of secondary proliferative responses to Ag from the donor used for priming. Cells from pretreated cultures proliferated well, however, when stimulated with Ag from third party donors, mitogens, or mitogenic CD3 mAb. Because specific reactivity could be restored by addition of IL-2 to restimulation cultures, altered secondary responsiveness appeared to be caused by anergy and not by elimination of specific clones. Furthermore, specific down-regulation of alloresponsiveness was prevented by addition of IL-2 to primary cultures in the presence of mAb. Interference by mAb with either CD2/LFA-3, LFA-1/ICAM-1, CD2/LFA-1, or LFA-3/ICAM-1 had a substantial, though less pronounced effect on secondary responsiveness. After pretreatment with the Ab mixture, CTL generation was substantially but incompletely down-regulated against the original and third party donors. Because a decrease in the reactivity of unstimulated responders by culture was also observed, these findings might be explained by the loss of cytotoxic precursors after culturing under nonstimulating conditions. In conclusion, our data demonstrate that T cells enter a state of anergy when T cell activation is modulated by simultaneous interference with distinct adhesion molecules during Ag contact, which thus might reflect at least partly overlapping functions of particular receptor-ligand pairs in T cell costimulation.

Co-ligation of CD31 and Fc gamma RII induces cytokine production in human monocytes

The CD31 (PECAM-1) cell surface glycoprotein is considered to be involved in intercellular recognition and adhesion. Cytokines play a major role in cellular interactions, and therefore it was of interest to study whether engagement of CD31 affects synthesis and release of proadhesive cytokines. Here we demonstrate that immobilized CD31 mAb 1B5 induces the release of TNF-alpha, IL-1 beta, and IL-8 from human PBMCs. CD11b mAb VIM12 and HLA-D mAb VID1, both of which are of the same Ig subclass as mAb 1B5 (IgG1), as well as nonbinding isotype control mAb VIAP, were ineffective. That the effect was caused by the mAb, but not endotoxin contamination, was shown by negative Limulus amebocyte lysate tests and coculture with polymyxin B, which did not abolish TNF-alpha release. Cytokine production through intact mAb 1B5 was completely blocked by soluble F(ab) fragments of anti-IgG Fc gamma RII mAb IV.3, suggesting a significant contribution of that FcR. Cross-linking of neither CD31 nor Fc gamma RII molecules with the respective F(ab) fragments induced TNF-alpha release, but nonbinding control IgG1 Ab was able to restore the response of PBMC to 1B5 F(ab) fragments, when both Ab preparations were coated concomitantly. Therefore, only coligation of CD31 and Fc gamma RII appears to transduce activation signals leading to cytokine production. Our findings thus indicate a novel functional aspect of CD31 molecules that might play an important role in the propagation of an ongoing immune response as well as in the regulation of cell-cell interactions during inflammatory reactions.

Co-ligation of CD31 and Fc gamma RII induces cytokine production in human monocytes

The CD31 (PECAM-1) cell surface glycoprotein is considered to be involved in intercellular recognition and adhesion. Cytokines play a major role in cellular interactions, and therefore it was of interest to study whether engagement of CD31 affects synthesis and release of proadhesive cytokines. Here we demonstrate that immobilized CD31 mAb 1B5 induces the release of TNF-alpha, IL-1 beta, and IL-8 from human PBMCs. CD11b mAb VIM12 and HLA-D mAb VID1, both of which are of the same Ig subclass as mAb 1B5 (IgG1), as well as nonbinding isotype control mAb VIAP, were ineffective. That the effect was caused by the mAb, but not endotoxin contamination, was shown by negative Limulus amebocyte lysate tests and coculture with polymyxin B, which did not abolish TNF-alpha release. Cytokine production through intact mAb 1B5 was completely blocked by soluble F(ab) fragments of anti-IgG Fc gamma RII mAb IV.3, suggesting a significant contribution of that FcR. Cross-linking of neither CD31 nor Fc gamma RII molecules with the respective F(ab) fragments induced TNF-alpha release, but nonbinding control IgG1 Ab was able to restore the response of PBMC to 1B5 F(ab) fragments, when both Ab preparations were coated concomitantly. Therefore, only coligation of CD31 and Fc gamma RII appears to transduce activation signals leading to cytokine production. Our findings thus indicate a novel functional aspect of CD31 molecules that might play an important role in the propagation of an ongoing immune response as well as in the regulation of cell-cell interactions during inflammatory reactions.

Specific down-regulation of proliferative T cell alloresponsiveness by interference with CD2/LFA-3 and LFA-1/ICAM-1 in vitro

T cell activation requires Ag contact with the TCR in the presence of costimulatory signals provided by APCs. When Ag is presented without costimulation, T cells are functionally inactivated. Here we demonstrate that interference with distinct adhesion molecules during Ag contact using mAbs leads to Ag-specific functional inactivation of alloreactive T cells. We found that the presence of a mixture of mAbs specific for CD2, LFA-3, LFA-1 alpha- and beta-chain, and ICAM-1 during primary MLC leads to down-regulation of secondary proliferative responses to Ag from the donor used for priming. Cells from pretreated cultures proliferated well, however, when stimulated with Ag from third party donors, mitogens, or mitogenic CD3 mAb. Because specific reactivity could be restored by addition of IL-2 to restimulation cultures, altered secondary responsiveness appeared to be caused by anergy and not by elimination of specific clones. Furthermore, specific down-regulation of alloresponsiveness was prevented by addition of IL-2 to primary cultures in the presence of mAb. Interference by mAb with either CD2/LFA-3, LFA-1/ICAM-1, CD2/LFA-1, or LFA-3/ICAM-1 had a substantial, though less pronounced effect on secondary responsiveness. After pretreatment with the Ab mixture, CTL generation was substantially but incompletely down-regulated against the original and third party donors. Because a decrease in the reactivity of unstimulated responders by culture was also observed, these findings might be explained by the loss of cytotoxic precursors after culturing under nonstimulating conditions. In conclusion, our data demonstrate that T cells enter a state of anergy when T cell activation is modulated by simultaneous interference with distinct adhesion molecules during Ag contact, which thus might reflect at least partly overlapping functions of particular receptor-ligand pairs in T cell costimulation.

Mode of action of coumarin in immune cells

In order to characterize further the mode of action of coumarin, binding studies were undertaken using human monocytes and radioactively labelled drug. Since coumarin is only a small compound and we wanted to exclude possible artefacts due to variations in size or conformation, the drug was produced by synthesis in the presence of radioactive 14C. Adding increasing amounts of a mixture of labelled and unlabelled drug to monocytes resulted in saturating conditions only at rather high concentrations. Performing Scatchard analysis demonstrated that binding sites for coumarin appeared to be present in relatively high numbers (7.5 x 10(8)/cell) but their affinity was rather low (K alpha approximately 2 x 10(2) M-1). Inhibition studies with 7-hydroxycoumarin revealed that an approximately four times higher molar concentration of the derivative was necessary to cause 50% displacement of coumarin from its binding site. These results indicate that binding of the drug to cells is characterized by high-capacity but low-affinity conditions. This would be compatible with the hypothesis that coumarin interacts with ubiquitous intracellular receptor proteins able to interact with aromatic hydrocarbons, which might form the basis for enzyme induction, and leads to the effects observed in vitro and in vivo.