High incidence of donor-reactive delayed-type hypersensitivity reactivity in transplant patients

Detection of Retinal Pigment Epithelium-Specific Antibody in iPSC-Derived Retinal Pigment Epithelium Transplantation Models

Antibody-mediated rejection is characterized by donor-specific antibody produced by B cells. However, to our knowledge, B cell invasion and antibody in the inflamed retina after transplantation of retinal pigment epithelial (RPE) cells has not been reported. To determine if RPE transplantation could be performed using allografts, we established in vivo immune rejection models with induced pluripotent stem cell (iPSC)-RPE allografts and determined whether RPE-specific antibody could be detected in these models. We detected alloantibodies in the serum from recipient monkeys that had immune attacks in the retina in an immunofluorescent assay using the transplanted iPSC-RPE cells as the antigen. In addition to T cell and antigen-presenting cell immunity, peripheral blood cells and lymph nodes in animal models with allogeneic iPSC-RPE cells also had activated B cells, which were probably secreting alloantibodies. Using serum and transplanted cells, alloreactive antibody can be detected for the diagnosis of immune rejection after transplantation.

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Alloantibodies secreted by B cells target iPSC-derived RPE cells

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Alloantibodies were detected in serum from monkeys receiving RPE allografts

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Blood and lymph nodes in monkeys receiving the grafts contained activated B cells

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B cell-mediated immune attack was attenuated by administration of local steroid

Operational tolerance in kidney transplantation and associated biomarkers

In the 1960s, our predecessors won a historical battle against acute rejection and ensured that transplantation became a common life-saving treatment. In parallel with this success, or perhaps because of it, we lost the battle for long-lived transplants, being overwhelmed with chronic immune insults and the toxicities of immunosuppression. It is likely that current powerful treatments block acute rejection, but at the same time condemn the few circulating donor cells that would have been able to elicit immunoregulatory host responses towards the allograft. Under these conditions, spontaneously tolerant kidney recipients - i.e. patients who maintain allograft function in the absence of immunosuppression - are merely accidents; they are scarce, mysterious and precious. Several teams pursue the goal of finding a biomarker that would guide us towards the 'just right' level of immunosuppression that avoids rejection while leaving some space for donor immune cells. Some cellular assays are attractive because they are antigen-specific, and provide a comprehensive view of immune responses toward the graft. These seem to closely follow patient regulatory capacities. However, these tests are cumbersome, and require abundant cellular material from both donor and recipient. The latest newcomers, non-antigen-specific recipient blood transcriptomic biomarkers, offer the promise that a practicable and simple signature may be found that overcomes the complexity of a system in which an infinite number of individual cell combinations can lead possibly to graft acceptance. Biomarker studies are as much an objective - identifying tolerant patients, enabling tolerance trials - as a means to deciphering the underlying mechanisms of one of the most important current issues in transplantation.

Role of Wnt3a expressed by dendritic cells in the activation of canonical Wnt signaling and generation of memory T cells during primary immune responses

The presence of memory T cells (T_Ms) hinders transplant survival. Dendritic cells (DCs) induce the generation of T_Ms during primary immune responses. However, the specific mechanisms are unclear. In this study, we constructed a Wnt3a-expressing adenovirus and used small interfering RNA (siRNA) targeting Wnt3a to investigate the influence of Wnt3a expression in DCs on the generation of T_Ms during primary immune responses. Our results demonstrated that the Wnt3a expression levels in DCs influenced the generation of T_Ms after 5days in co-culture with naïve T cells through activation of the Wnt canonical pathway. Interleukin-7 secretion levels in supernatants of DC/T_Ns co-cultures showed a similar pattern of Wnt3a expression levels in DCs. These findings provide a better understanding of T_Ms generation mechanisms that might be useful to improve transplant outcomes.

Memory T-cell-specific therapeutics attenuate allograft rejection via mediation of alloreactivity in memory cells

Many means in inbred rodent models promoted long-term graft survival or donor-specific tolerance, but less so in nonhuman primates, outbred rodents or human patients. A diverse repertoire of memory T cells, derived from heterologous immunity or prior to exposure to alloantigen, has been believed to be an important part of this barrier. Memory T cells have a unique capacity to generate effector functions quickly upon re-exposure to antigen, and this capacity is achieved by reduced activation thresholds, and expressed high level trafficking and adhesion molecules, which is likely responsible for their exhibiting differential susceptibility to immune therapeutics compared with naïve T cells. This review outlines recent progress on characteristics of memory T cells and focuses on these potential therapies targeting memory T cells which are likely to ameliorate allograft rejection by inducing transplant tolerance.

The immunological monitoring of kidney and liver transplants in adult and pediatric recipients

Over the last half century, kidney and liver transplantation have been recognized as the treatment of choice for adult and children with end-stage renal or liver failure. Infants present a relative naïve immune system, but they are capable of mounting both cellular and humoral immune responses to the foreign antigens presented by the allograft. Immune monitoring is a way of measuring functional and molecular correlates of immune reactivity which may provide clinically useful information for identifying patients who have an increase risk of acute rejection prior to clinical symptoms or develop transplant tolerance. However, although numerous assays have been shown to predict rejection, to date no assays have been demonstrated to detect or predict transplantation tolerance. This is a summary of the published literature on promising antigen-specific and non-antigen-specific assays used for immunological monitoring in solid organ transplantation. This work also attempts to review their applicability to pediatric transplantation, specifically, pediatric kidney and liver recipients.

Successful reduction of immunosuppression in older renal transplant recipients who exhibit donor-specific regulation

BACKGROUND

We hypothesized that T-regulatory cells specific for donor alloantigens would protect a renal transplant during partial withdrawal of immunosuppression.

METHODS

To test this hypothesis, 32 renal transplant recipients aged 55 years and older with excellent renal function were tested for donor-specific regulation (DSR) by trans-vivo delayed type hypersensitivity assay at the time of enrollment (T=0) and 6 months later (T=6). Twenty-two patients had prednisone withdrawn during a 3-month period, whereas 10 controls were maintained on triple therapy (prednisone, cyclosporine, and mycophenolate).

RESULTS

Of 22 patients in the steroid withdrawal group, 10 were DSR+ and 12 were DSR- at the time of enrollment (T=0). None of the DSR+ patients experienced acute rejection, nor did any have donor-specific human leukocyte antigen (HLA) antibody during or after withdrawal. Of 12 DSR- patients, three developed acute rejection, which were reversed with bolus steroid treatment, and four were donor-specific antibody+ at T=0 or T=6. Two years later, 80% (8 of 10) of DSR+ patients in the withdrawal group remain steroid free while maintaining excellent renal function, as compared with only 58% (7 of 12) DSR- patients. Patient survival at 4 years was similar for DSR+ (9 of 10) and DSR- (11 of 12) patients in the withdrawal group. Patients maintained on triple therapy remained rejection free during the 4-year follow-up regardless of initial DSR status, with patient survival rate of 70% (7 of 10).

CONCLUSIONS

DSR before steroid withdrawal may identify a subset of transplant patients who could benefit from reduction of immunosuppression without elevated risk of rejection or deteriorating renal function.

Accommodation of grafts: implications for health and disease

Accommodation refers to the acquired resistance of a graft to immune-mediated injury. It is typically observed after antibodies that would cause rejection of a graft are removed from a recipient and then later return. In addition to being induced in this manner, accommodation can occur spontaneously, without depleting antibodies. Indeed, we postulate spontaneous accommodation may be the most common outcome of clinical organ transplantation. The paper reviews the current understanding of accommodation, emphasizing recent advances and important questions. Among the recent advances are the discoveries of potentially broader relevance of accommodation for biology and immunology and pathways by which accommodation may be achieved. To investigate these pathways and to understand how accommodation begins and how it evolves, clinical organ transplants might offer a useful and incisive model.

Evaluation of immune regulation in transplant patients using the trans vivo delayed type hypersensitivity assay

Allograft recipient IL-10 and/or transforming growth factor-beta (TGF-beta) dependent anti-inflammatory T-cell delayed type hypersensitivity (DTH) responses to donor derived antigens, or regulatory T-cell responses, have been demonstrated in rodents and transplant patients using a previously described trans vivo DTH assay. We used this assay to determine the incidence of recipient anti-inflammatory T-cell responses to donor antigens in a large cohort (n = 420) of primary kidney and simultaneous kidney-pancreas transplant patients tested a mean of 4.8 years after transplantation. The results were compared with clinical outcomes and the presence of detectable circulating alloantibodies. We found an unexpectedly high incidence (21.9%) of this anti-inflammatory T-cell response to donor antigens in these recipients. There was a significant correlation between this T-cell phenotype and the presence of detectable circulating alloantibodies (p = 0.03). There was no correlation between this T-cell phenotype and the degree of HLA mismatch. In addition, the presence of an anti-inflammatory DTH response to donor antigens did not correlate with an improved clinical outcome at a median of nearly 5 years after transplantation. These findings suggest that detection of an anti-inflammatory T-cell response to donor antigens does not identify patients that have developed graft protective, regulatory T-cell responses.

Mouse strain and injection site are crucial for detecting linked suppression in transplant recipients by trans-vivo DTH assay

Chemokine-driven accumulation of lymphocytes, mononuclear and polymorphonuclear proinflammatory cells in antigenic tissue sites is a key feature of several types of T-cell-dependent autoimmunity and transplant rejection pathology. It is now clear that the immune system expends considerable energy to control this process, exemplified by the sequential layers of regulatory cell input, both innate and adaptive, designed to prevent a classical Type IV or 'delayed-type' hypersensitivity (DTH) reaction from occurring in the visual field of the eye. Yet, despite an abundance of in vitro assays currently available to the human T-cell immunologist, none of them adequately models the human DTH response and its various control features. The theme of this article is that it is relatively easy to model the effector side of the human DTH response with xenogeneic adoptive transfer models. However, we show that in order to detect inhibition of a recall DTH in response to colocalized donor antigen (linked suppression)--a characteristic feature of peripheral tolerance to an organ transplant--both the challenge site and the immunocompetence of the mouse adoptive host are critical factors limiting the sensitivity of the trans-vivo DTH test.

Controlling the generation and function of human CD8+ memory T cells in vitro with immunosuppressants

BACKGROUND

Memory T cells play a pivotal role in acute and chronic rejection of transplanted organs. Novel therapies such as alemtuzumab and the identification of heterologous memory have highlighted their importance following transplantation. Unlike naive T cells, the influence of immunosuppressive agents on the de novo generation of memory T cells and on the function of pre-existing memory T cells is poorly understood.

METHOD

CD8 effector memory T cells (Tem, CD45RA, CCR7) were generated by stimulating peripheral blood mononuclear cells for five days with anti-CD3 and anti-CD28 monoclonal antibodies, followed by nine days of rest. The influence of immunosuppression on this was assessed by flow cytometry. Tem that had been naturally formed in vivo were used to study the influence of the same agents on the function (intracellular interferon-gamma production) of Tem cells.

RESULTS

Whereas all the immunosuppressive agents tested inhibited the expansion of CD8 Tem population by influencing their proliferation and apoptosis, the calcineurin inhibitors were better at controlling their function. Furthermore, Tem generated despite the presence of tacrolimus were functional and did not exhibit drug resistance.

CONCLUSIONS

Immunosuppressive agents differ in their ability to control the generation and function of CD8 Tem; the calcineurin inhibitors being the most efficacious. This may be of importance when tailoring immunosuppressants for transplant recipients, particularly in those where there is pre-existing immunological memory or in those receiving T-cell depleting therapies, which skews the immune repertoire towards memory.

The impact of memory T cells on rejection and the induction of tolerance

Accumulating evidence suggests that alloreactive memory T cells (Tm) may be generated in transplant recipients that have not previously been exposed to alloantigen through mechanisms such as cross-reactivity and homeostatic proliferation. The presence of Tm correlates with both acute and chronic rejection episodes and, furthermore, may be responsible for the failure to induce tolerance in large animal and clinical settings. A clearer understanding of how Tm function and their requirements to mount an effective response to alloantigen will be key to further attempts to translate tolerance induction protocols from the experimental setting to the clinic.

How can we measure immunologic tolerance in humans?

Prevention and treatment of allograft rejection in organ transplant recipients relies primarily on non-antigen-specific immunosuppression, with all its associated potential hazards and costs. Currently, the status of the recipient immune response is measured by monitoring pharmacologic drug levels and clinical/pathologic evaluation of graft function. Development of reliable assays that can measure accurately the status of the immune response not only would help clinicians customize the prescription of immunosuppressive drugs in individual patients but also may allow their complete withdrawal in some patients with immunologic tolerance. Furthermore, these assays would facilitate the safe evaluation of novel tolerogenic regimens. Achieving this goal has proved to be very difficult because it requires both a more in-depth understanding of complex mechanisms of tolerance and also identification of transplant patients with acquired tolerance to an allograft that can be studied. This review discusses the current understanding of tolerance mechanisms and outlines the unique and specific challenges in development of tolerance/monitoring assays in the field of transplantation. In addition, several of the most promising candidate assays are discussed in detail.

Tolerance Assays: Measuring the Unknown

Distinguishing transplant recipients who will benefit from a reduction in, or even the withdrawal of, immunosuppression from those who require intensive, lifelong immunosuppression will be dependent on developing strategies for immune monitoring. Currently, no assays have been shown to accurately predict the development or presence of donor-specific tolerance in humans after transplantation. In this overview we describe and discuss those assays that we believe may be useful for identifying tolerant transplant recipients. Validation of "tolerance" assays will be critical for the safe development of tolerance regimens in humans.

The autoimmune response to vimentin after renal transplantation in nonhuman primates is immunosuppression dependent

BACKGROUND

Chronic allograft nephropathy (CAN) is a common late complication of kidney transplantation. Antibodies to both human leukocyte antigen and nonhuman leukocyte antigen antigens have been implicated in the development of this condition. Here we investigated the presence of antivimentin antibodies in nonhuman primate recipients of kidney allografts as a possible predictor of CAN and the effects of immunosuppression.

METHODS

Thirty seven rhesus monkeys received a kidney allograft to study the potency of several different immunosuppressive regimens (conventional immunosuppression, n=19, vs. costimulatory blockade, n=18). Monkeys were tested for antivimentin antibody by enzyme-linked immunosorbent assay and for anti-donor antibody by staining donor spleen cells with recipient serum. The appearance of antibodies was correlated with the graft pathology in biopsy and necropsy material.

RESULTS

Antivimentin antibodies were found in 31 of 37 animals, whereas only 15 of 32 animals made anti-donor antibodies. Conventional immunosuppression did not prevent antivimentin antibody formation. Costimulation blockade, in particular blocking CD40 and CD86, significantly delayed or prevented antivimentin antibody formation, but did not prevent CAN. Antivimentin antibodies were not significantly associated with development of CAN.

CONCLUSIONS

We postulate that vimentin acts as an autoantigen after renal transplantation; it elicits an autoimmune response that is not regulated by cyclosporine. This autoimmune response may be part of the complex immunologic events occurring posttransplantation and may contribute to the development of CAN, but cannot be considered as a major cause of CAN because this condition also develops without antivimentin antibodies.

A renewable source of donor cells for repetitive monitoring of T- and B-cell alloreactivity

A major impediment to repetitive monitoring of alloreactivity or tolerance is the limited supply of donor cells available for assays of host-versus-graft T- and B-cell reactivity. In this paper, we describe the use of CD40L stimulated CD19(+) B cells as targets or stimulators in flow cytometric crossmatching (FXM), mixed lymphocyte reactivity and IFN-gamma ELISPOT assays. Stimulated B cells (sBc) express high levels of MHC class I and II, as well as the costimulatory molecules CD80 and CD86. They can be polyclonally expanded and frozen for later use. We describe the use of sBc in ELISPOT, mixed lymphocyte cultures and FXM. CD4(+) T cells exposed to sBc express a similar cytokine profile as those stimulated with unfractionated PBMC. We further analyzed T- and B-cell responses in 14 patients on the renal transplant waiting list, finding that those with an elevated panel reactive antibody (PRA) (>60%) had higher alloreactive T-cell precursor frequencies as measured by CDFSE MLR and IFN-gamma ELISPOT. We conclude that sBc are a renewable source of donor-specific target/stimulator cells for use in repetitive and coordinate assays of B- and T-cell alloreactivity.

Treatment of C4d-positive acute humoral rejection with plasmapheresis and rabbit polyclonal antithymocyte globulin

BACKGROUND

Alloantibody-mediated acute rejection is a major cause of renal allograft loss despite aggressive therapy. Patients with humoral rejection can be identified with high sensitivity and specificity by the presence of peritubular capillary C4d staining on renal biopsy and donor-specific anti-human leukocyte antigen antibodies. Standard therapy for acute humoral rejection (AHR) has been removal of donor-specific antibodies by plasmapheresis (PPH) in conjunction with intravenous immunoglobulin therapy. We describe a series of seven patients with C4d positive AHR who received combined therapy with PPH and polyclonal rabbit antithymocyte globulin (rATG).

METHODS

PPH (1.4 volume exchange) was initiated on diagnosis of AHR on an alternate day basis for a mean number of 6.8 treatments, in conjunction with rATG (0.75 mg/kg/day 5-10 days) until the serum creatinine returned to 120% of nadir.

RESULTS

The nadir posttreatment creatinine was significantly lower than pretreatment creatinine (1.0+/-1.2 vs. 2+/-1.4, P <0.007) with only one episode of graft loss. On follow-up there was no difference in renal allograft survival between the AHR group and the 60 patients without AHR who underwent transplantation during the same period. We describe the ability of rATG to induce apoptosis in vitro peripheral blood and activated B cells.

CONCLUSION

Combination therapy using PPH and rATG is an effective means of reversing AHR in renal allografts.

Immune regulation and graft survival in kidney transplant recipients are both enhanced by human leukocyte antigen matching

We hypothesized that donor/recipient sharing of the human leukocyte antigen (HLA) involved in allopeptide presentation to the T regulatory cell increases the incidence of immune regulation, thus contributing to long-term graft survival. Peripheral blood mononuclear cells (PBMC) were obtained from 40 living related donor (LRD) and 31 cadaver renal transplant recipients. The trans vivo delayed type hypersensitivity (DTH) assay was used to assign patients to regulator, nonregulator, and sensitized categories. In a large cohort (n=1934 patients), primary graft survival and rejection episodes were analyzed using a log rank test for comparison with the DTH results. The highest incidence of regulated anti-donor DTH was observed in the LRD HLA-identical group (6/6; 100%) followed by the LRD HLA 1 haplotype matched group (18/27; 67%). Within the cadaver population, two DR-matched recipients had a higher frequency of regulated anti-donor DTH (6/11; 55%) than 1 & 0 DR-matched recipients (3/18; 17%). In a multivariate model, matching for HLA-DR alone, or for DR plus DQ was significantly (p=0.045, p=0.041) correlated with DTH regulation. The better HLA-matched groups showed the highest incidence of DTH regulation and, in a larger retrospective analysis, displayed better graft survival and freedom from acute rejection (p<0.0001). HLA matching, and HLA-DR matching in particular, correlates with the incidence of immune regulation after kidney transplantation.

Evidence that humoral allograft rejection in lung transplant patients is not histocompatibility antigen-related

We have recently recognized humoral rejection (HR) in lung allograft recipients and its association with acute and chronic graft dysfunction. We have shown that C4d, a stable marker of classic complement activation, is deposited in lung allografts, correlating with clinical rejection and parenchymal injury. The antigenic target may be endothelium in the setting of recurrent acute rejection while varying components of the bronchial wall may be important in chronic graft dysfunction. We sought to establish whether there is a role for antibodies with histocompatibility antigen specificity in the lung humoral allograft phenomenon. Flow cytometric and ELISA assays to assess donor-specific antigens were conducted on sera from 25 lung transplant recipients who had experienced one or more episodes of clinical rejection; in addition, the serum samples were tested for evidence of antiendothelial cell antibody activity. Morphologically, each case had biopsies showing septal capillary injury with significant deposits of immunoreactants with microvascular localization and positive indirect immunofluorescent antiendothelial cell antibody assay. Panel-reactive antibody testing showed absence of MHC Class I/II alloantibodies; ELISA based crossmatch detecting donor-specific MHC Class I/II specific antibodies was negative. HR can occur in the absence of antibodies with HLA specificity; antigenic targets may be of endothelial cell origin.