الفهرس 
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Abstract
Antibody-mediated rejection (AMR) is a unique, significant, and often severe form of allograft rejection that is not amenable to treatment with standard immunosuppressive medications. Significant advances have occurred in our ability to predict patients at risk for, and to diagnose, AMR. These advances include the development of newer anti-human leukocyte antigen (HLA)-antibody detection techniques and assays for non-HLA antibodies associated with AMR. The patho physiology of AMR suggests a prime role for antibodies, B cells and plasma cells, but other effector molecules, especially the complement system, point to potential targets that could modify the AMR process. An emerging and potentially larger problem is the development of chronic AMR (CAMR) resulting from de novo donor-specific anti-HLA antibodies (DSA) that emerge more than 100 days posttransplantation.
Biomarkers (proteomics) may serve not only as diagnostic parameters but also as predictive biomarkers that anticipate the subsequent development of sub-clinical and clinical acute rejection. Towards these objectives, we and others have investigated the hypotheses that urine and peripheral blood cell profiles offer a noninvasive means of predicting the development of acute rejection and are diagnostic of biopsy confirmed acute rejection.
Early diagnosis and treatment are essential for salvaging grafts undergoing acute antibodymediated rejection. Treatments include removal of antibodies by plasmapheresis or immunoadsorption, high-dose pulses of glucocorticoids, intravenous immune globulin, and antiproliferative agents. Supplementary therapies include rituximab. Or antilymphocyte antibody, if there is concurrent T-cell mediated rejection. These treatments can be useful when given as prophylaxis to highly sensitized or ABO-mismatched recipients.
Eculizumab (a monoclonal antibody that inhibits the cleavage of C5) and bortezomib (a proteasome inhibitor that can inhibit plasma cells) are new, investigational agents that have shown promise in preliminary studies of antibody-mediated acute rejection, but the results require confirmation.
Immune tolerance is principally mediated via central and peripheral mechanisms. Central tolerance normally leads to the intrathymic deletion of T cells recognizing thymus-expressed autoantigens with high avidity, so that potentially deleterious antigen-reactive T cells will not reach the periphery. Since the early observations by Medawar and colleagues
Currently, three main approaches are being explored for Treg expansion in the perspective of therapeutic protocols: ex-vivo nTreg expansion, ex-vivo conversion of naïve T cells to iTreg and in vivo expansion of nTreg and/or induction of iTreg. The first method requires selection of highly purified nTreg prior to in vitro expansion for subsequent adoptive transfer. Purity is a critical issue as even a few contaminating effector T cells might expand in vivo and cause unwanted immune pathologies. As discussed, different surface markers have to be combined to purify human nTreg from the peripheral blood, including CD25hi and CD127low expression, CD45RA+, CD27, CD39, CD49b, folate receptor 4 (FR4) or PD-1.88–91 Good manufacturing practice (GMP) accepted isolation strategies are based on CliniMACS (Miltenyi®) protocols, using antibody cocktails with magnetic microbeads and columns. However, these immunomagnetic techniques do not allow the same broad multiparameter selection as compared to flow cytometry cell sorting. Thus, these approaches may lead to poor nTreg purity and still need to be optimized. Once selected, nTreg have to be expanded to the yields needed for clinical application and transfer into patients. We and others have described robust protocols to expand nTreg in vitro in great numbers without loss of their suppressive function
In brief, these strategies are based on the use of donor-derived APC, recipient-derived APC pulsed with donor antigens or surrogate APC (such as anti-CD3/CD28 coated beads) in the presence of high amounts of exogenous IL-2.
The second approach is based on the induction of iTreg in vitro from naïve CD4+ T cells or by forcing Foxp3 expression by viral transduction.
Finally, the third strategy consists in expanding nTreg and/or de novo generation of iTreg in vivo. This would alleviate the need for GMP cell isolation and cumbersome ex-vivo manipulations, thus rendering the therapy more clinically applicable. Blocking the T cell costimulatory signaling pathways (CD28:CD80/CD86, CD154:CD40, OX40:OX40L, ICOS: ICOSL, CD27:CD70) at the time of transplantation and donor-antigen encounter has been shown to facilitate donor-specific iTreg conversion and/or preferential proliferation of nTreg, while inducing anergy of alloantigen-specific effector T-cells.
Current studies suggest that effector T cells and nTreg have qualitative and quantitative differences in TCR stimulation and costimulatory molecules requirements, and thus could be differentially targeted.
Besides costimulatory blockade, T-cell depletion induction therapies (e.g., anti-CD3, anti-CD52 monoclonal antibodies or polyclonal anti-thymocyte globulins) are used in clinical SOT to prevent acute rejection. These therapies induce profound and durable (weeks to months) reduction of circulating lymphocytes capable of mounting an alloresponse. Recent data suggest that T-cell depletion protocols allow preferential expansion of Treg once lymphocytes gradually repopulate the host, thus skewing the Treg/effector T cell ratio towards tolerance. In these studies, the increased frequency of Treg was neither fully explained by their homeostatic proliferation in a lymphopenic environment nor preferential sparing by the depleting antibody.
Although the underlying mechanisms need to be clarified, the induction of apoptotic cells in vivo (as would occur with cell-depleting agents) leads to TGFβ secretion by phagocytes (immature DC, macrophages) involved in clearing these cells, thus favoring iTreg generation and expansion. The uptake of apoptotic cells may also help to maintain DC in an immature state (low level of surface MHC II and costimulatory molecules), favoring tolerance.
Besides induction therapies, maintenance immunosuppressive drugs such as mammalian target of rapamycin (mTOR) inhibitors (e.g., sirolimus, everolimus), allow preferential expansion of nTreg and iTreg that promote antigen-specific transplantation tolerance.
Finally, as stressed before, in vivo homeostasis and expansion of Treg is highly dependent on IL-2. Thus, the administration of IL-2 could be combined to these immunomodulatory approaches and is under investigation in stringent experimental allotransplantation models.
Chronic allograft injury severely impedes successful kidney transplantation.
Deciphering the mechanisms of such late graft loss would enable more personalized treatment strategies but is hindered by the difficulty in assigning specific diagnoses. Recently, chronic allograft nephropathy (CAN), the nonspecific term used to describe all manners of late graft scarring, was ousted for the term ”interstitial fibrosis and tubular atrophy” (IF/TA), to be used in cases in which no underlying cause can be identified.
We have identified TRIB1 mRNA as a potential minimally invasive biomarker of chronic AMR because it is upregulated in the peripheral blood, where it displays high sensitivity and specificity. Although it is unlikely that TRIB1 is a stand-alone biomarker for chronic AMR, so far we have been unable to identify other molecules that show the same expression profile, even among well-characterized markers such as Granzyme B (data not shown); however, in the event of other biomarkers’ being identified, TRIB1 could form part of a panel of genes, as in the case of the Cardiac Allograft Rejection Gene Expression Observation (CARGO) study.
CAMR has a poor prognosis, with no well-defined treatment protocol. A pilot study, conducted by Billing et al., investigated the use of IVIG with rituximab in six patients (ages 10–26) who had evidence of CAMR.