Rejection Of Solid Organ Allografts Research Articles

In remembrance of things past: memory T cells and transplant rejection.

A cardinal feature of the adaptive immune response is its ability to generate long-lived populations of memory T lymphocytes. Memory T cells are specific to the antigen encountered during the primary immune response and react rapidly and vigorously upon re-encounter with the same antigen. Memory T cells that recognize microbial antigens provide the organism with long-lasting protection against potentially fatal infections. On the other hand, memory T cells that recognize donor alloantigens can jeopardize the survival of life-saving organ transplants. We review here the immunobiology of memory T cells and describe their role in the rejection of solid organ allografts.

Chronic rejection of murine cardiac allografts discordant at the H13 minor histocompatibility antigen correlates with the generation of the H13-specific CD8+ cytotoxic T cells.

Minor histocompatibility antigen (mHag) discordances have been shown to play a critical role in graft-versus-host disease after bone marrow transplantation. However, the role of mHag in rejection of solid-organ allografts remains unknown. Therefore, the goal of this study was to define the role of a single mHag discordance derived from the polymorphic H13 allele in the development of cardiac allograft rejection in mice. The H13a and H13b alleles encode for the SSVVGVWYL (SVL9) and SSVIGVWYL (SIL9) mHag bound to the H2Db molecule, respectively. C56BL/10SnJ (H13a) cardiac allografts were transplanted into congenic B10.CE-H13b Aw(30NX)/Sn (H13b) mice. Allograft function was monitored daily and rejection was defined by cessation of heart beat. Rejection was confirmed histologically. The phenotypic and functional characteristics of the graft-infiltrating cells were analyzed by in situ and in vitro staining with H13a-specific tetramers and by chromium-51 (51Cr)-release assay, respectively. Sixty-five percent of H13-incompatible allografts were rejected in 37.0+/-14.5 days. Sixty-eight percent of the H13a allografts transplanted into H13a-sensitized mice were rejected earlier, in 27.6+/-15.9 days. Rejected allografts showed histopathologic signs of chronic rejection with diffuse mononuclear cell infiltration, concentric intimal hyperplasia, and fibrosis. Both CD8+ (87%) and CD4+ (13%) T cells were observed in rejected allografts. In addition, 60% of the graft-infiltrating CD8+ T cells recognized a H2Db/SVL9 tetramer. Graft-infiltrating CD8+ T cells showed a significant H2Db-restricted, SVL9-specific cytotoxic activity. A single mHag discordance, as demonstrated with H13 disparity, results in the pathogenesis of chronic rejection of major histocompatibility complex-matched vascularized solid-organ allograft.

Sirolimus and islet transplants

IMMUNOSUPPRESSION is a critical determinant of the success of islet transplants. Tailoring immunosuppression to the specific setting of marginal mass islet cell transplants in autoimmune type 1 diabetic recipients would likely increase the safety, success rate, and applicability of such transplants. Tailored immunosuppression would ideally inhibit antigen-independent innate immune responses during the engraftment of transplanted islets, control alloimmune responses, and thwart autoimmune responses without diabetogenic and nephrotoxic side effects. Rejectionfree protocols need to be administered until markers of imminent islet rejection are validated or until robust function of a dysfunctional graft is restored. Sirolimus is a macrocyclic lactone with potent immunosuppressive properties. Its mechanism of action involves the blockade of IL-2 and other T-cell growth factor-mediated signal transduction and the inhibition of cell cycle progression. Sirolimus is conceivably the single most important contribution to the immunosuppressive armamentarium in islet transplantation. The immunosuppressive synergism between sirolimus and cyclosporin A (CsA) markedly reduces the incidence of solid organ and islet allograft rejection; it also enables steroids to be avoided and CsA doses to be profoundly reduced. In vitro studies suggested competitive inhibition between sirolimus and tacrolimus. Synergism between those two drugs was demonstrated in rat transplant models. The synergism between sirolimus (and other mammalian targets of rapamycin antagonists) and sphingosine 1-phosphate receptor agonists enables both steroids and calcineurin inhibitors to be avoided, thereby protecting allografts from rejection as well as from diabetogenic and nephrotoxic side effects. The synergism between sirolimus and selective blockers of costimulatory pathways helps induce immunologic tolerance and may, in the future, facilitate minimization or discontinuation of maintenance immunosuppression. The distinctive profile of sirolimus suggests an important role for it as an immunosuppressive and tolerogenic agent for diabetic recipients of islet transplants. Studies of the tolerogenic potential of sirolimus have been performed predominantly in cardiac and islet transplant models in mice. Sirolimus was used at a dose of 0.2 mg/kg/d intraperitoneally (IP) daily for the first 3 days, then every other day until the advent of hyperglycemia. It markedly prolonged the survival of islet allografts across a complete major histocompatibility barrier in interleukin (IL)-2 / and IL-4 / double knockout mice. Thus, sirolimus blocks T-cell growth factor signals beyond IL-2 and IL-4, especially IL-7 and IL-15; these rapamycin-sensitive T-cell growth factor signals are critical in the execution of islet allograft rejection. Combined costimulatory blockade (anti-CD154 monoclonal antibody and CTLA4-Ig) and sirolimus monotherapy 0.2 mg/kg/d IP on days 0, 1, 2, then every other day through day 14 posttransplant both facilitated indefinite survival of cardiac allografts in the Balb/c to C3H/He strain combination. Adding CsA, but not sirolimus, to treatment with anti-CD154 monoclonal antibody and CTLA4-Ig blocked the capacity of costimulatory blockade to produce permanent engraftment. Subsequently, islet transplant experiments were conducted in IL-2-deficient mice treated with sirolimus, and cardiac allograft transplant experiments in Bcl-XL transgenic mice treated with costimulatory blockade. Those experiments assessed the importance of alloreactive T-cell pool size, and more specifically activated-induced cell death of alloreactive T cells (in peripheral tolerance induction). They confirmed the hypothesis that sirolimus blocks the proliferative component of IL-2 signaling but does not inhibit priming of activation-induced cell death. They also demonstrated that deletion of activated T cells, through activation-induced cell death or growth factor withdrawal, is necessary to achieve peripheral tolerance across major histocompatibility barriers. The efficacy of sirolimus in preventing spontaneous and recurrent autoimmune diabetes has been studied in NOD mice, a clinically relevant model of autoimmune type 1 diabetes. Sirolimus was administered per os (PO) 3 times per week from 8 to 10 weeks of age; it prevented onset of autoimmune diabetes in 90% of NOD mice at a dose of 0.6

Heterogeneity of T cell clones specific for a single indirect alloantigenic epitope (I-Ab/H-2Kd54-68) that mediate transplant rejection.

One of the complexities of solid organ allograft rejection is the inherent diversity of the specific T cell antigenic epitopes that participate in this response, including the role of direct alloantigen recognition and indirect recognition of donor-derived peptides in recipient antigen-presenting cells. To probe the role of distinct T cell receptor (TCR) avidity differences and the role of cytokine expression patterns of different effector T cells that may participate in allograft rejections, we have identified a dominant allopeptide derived from the H-2Kd molecule, recognized by H-2b CD4 T cells in the context of syngeneic I-Ab. To identify a stimulatory peptide derived from the H-2Kd molecule, a panel of synthetic overlapping peptides was screened for immunogenicity and a panel of T cell clones established. These clones were characterized for TCR Vbeta usage by mAb staining and/or reverse transcribed-polymerase chain reaction analysis, peptide dose sensitivity as a marker of TCR avidity, cytokine expression phenotype in vitro, and their ability to mediate rejection of a vascularized cardiac allograft after adoptive transfer to immunodeficient mice. The H-2Kd54-68 peptide was identified as a dominant stimulatory peptide by the ability of T cells from C57BL/6 (H-2b) mice primed by a combination of allogeneic spleen cell injection and mixed peptide immunization to mount an in vitro proliferative response and interferon-gamma production by peptide stimulation. Furthermore, direct immunization with synthetic H-2Kd54-68 peptide of normal C57BL/6 mice resulted in accelerated rejection of both skin and cardiac allografts from B10.D2 (H-2d) mice, but not 3rd party B10.BR (H-2k) grafts. A panel of 15 distinct CD4+ clones specific for H-2Kd54-68 peptide were established and shown to utilize a variety of TCR Vbeta and different apparent TCR avidities to H-2Kd54-68 peptide when stimulated in vitro. To characterize these clones further, two clones were chosen based on the difference of avidity to H-2Kd54-68 peptide. The cytokine expression pattern was determined and indirect alloantigen specificity confirmed by analysis of responses to purified peptide and B10.D2 spleen cells using normal H.2b and I-Abeta chain knockout mice as APC donors. Both of these T cell clones were able to mediate rejection of B10.D2, but not B10.BR hearts, in immunodeficient mice, but the morphological pattern of T cell infiltration was distinct. These results demonstrate the potential importance of fine dissection of the alloantigeneic response to solid organ transplants and provide unique insights into the role of TCR avidity and cytokine expression patterns in different morphological patterns of transplant rejection.

The abrogation of allosensitization following the induction of mixed allogeneic chimerism.

The association of preformed anti-donor Abs with the hyperacute rejection of bone marrow and solid organ allografts and the persistence of the anti-donor immune response secondary to immunologic memory make allosensitization an absolute contraindication to transplantation. Mixed allogeneic (A + B-->A) bone marrow chimerism has been demonstrated to confer donor-specific tolerance in nonsensitized recipients, but has not been evaluated in the setting of allosensitization. The current study documents that despite significant anti-donor sensitization, mixed allogeneic engraftment is possible and provides a marked advantage over fully allogeneic (B-->A) models. Moreover, the acceptance of donor skin grafts and loss of circulating anti-donor Abs suggest that allosensitization can be abrogated with the induction of stable mixed allogeneic chimerism.

Preferential production of IgG2 antibodies by parenchymal lung B-lymphocytes during lung allograft rejection

Lung transplantation has become an increasingly utilized modality for the treatment of various endstage pulmonary diseases. However, the lung is more prone to rejection than other solid organ allografts, likely due to the many immunocompetent cells in the donor lung. The immune mechanisms that mediate solid organ allograft rejection are believed to involve the presentation of donor alloantigens to recipient lymphocytes stimulating both cellular and humoral immunity. The cellular immune response to lung alloantigen can be due to the stimulation of either T-helper-1 type (Thl) lymphocytes which produce gamma interferon (γIFN) and interleukin (IL-2), or T-helper-2 type (Th2) lymphocytes which produce interleukins 4, 5, and 10. Investigators have demonstrated that solid organ allograft rejection was associated with upregulated Thl lymphocyte activation in vivo. Th1 and Th2 cytokines lead to the production of distinct IgG subtypes. γIFN stimulates IgG2a production in murine studies. and IgG2 production in human studies. IL-4 induces IgG1 production in murine studies. Similar to cellular immunity, humoral activity during allograft rejection has also been demonstrated to be secondary to Th1 lymphocyte activation. For example, Kupiec-Weglinski et al demonstrated that IgG alloantibody production was the result of enhanced γIFN production during cardiac allograft rejection in rats. Similarly, in a murine model of liver allograft rejection, only IgG2a antibodies were deposited in the rejecting allograft, and we reported that increased IgG2 concentrations in allograft bronchoalveolar lavage fluid (BAL) coincided with human lung allograft rejection. Other investigators have reported that the presence of large numbers of B-lymphocytes at the sites of rejection activity may be associated with a refractory response to immunosuppressive therapy, and possibly the development of obliterative bronchiolitis (0B). However, it is not known if B-lymphocytes present at the sites of rejection activity actually synthesize IgG antibodies. In addition, the source of increased IgG2 concentrations in allograft BAL fluid during rejection, ie, local production by parenchymal lung lymphocytes or passive transudation from serum, has not been evaluated. The purpose of the current study was to determine if lung allograft B-lymphocytes synthesize IgG antibodies during rejection and assess if IgG2 is preferentially produced.

Ten years of Orthoclone OKT3 (muromonab-CD3): a review.

Many important advances in transplantation have been made during the last decade. The introduction of Orthoclone OKT3 into clinical trials and its subsequent approval by the Food and Drug Administration in 1985 for use as an antirejection agent for renal transplantation were landmarks in the field of clinical transplantation of solid organs. In the decade since the approval of OKT3 for clinical use, much has been learned and written about OKT3. OKT3 now is considered a safe and effective agent for prophylaxis and first-line treatment of acute rejection of solid organ allografts. In this article, the development and use of OKT3 over the last 10 years, as well as the present status and future implications of immune therapy with OKT3, are reviewed.

Ten Years of Orthoclone OKT3 (Muromonab-CD3): A Review

Many important advances in transplantation have been made during the last decade. The introduction of Orthoclone OKT3 into clinical trials and its subsequent approval by the Food and Drug Administration in 1985 for use as an antirejection agent for renal transplantation were landmarks in the field of clinical transplantation of solid organs. In the decade since the approval of OKT3 for clinical use, much has been learned and written about OKT3. OKT3 now is considered a safe and effective agent for prophylaxis and first-line treatment of acute rejection of solid organ allografts. In this article, the development and use of OKT3 over the last 10 years, as well as the present status and future implications of immune therapy with OKT3, are reviewed.

Extracorporeal photochemotherapy: A scientific overview

Extracorporeal photochemotherapy was developed for treatment of cutaneous T-cell lymphoma (CTCL). Several independent and multicenter trials using lymphapheresis with 8-methoxypsoralen (8-MOP) activated by shortwave ultraviolet light have demonstrated the clinical benefit of this modality for treatment of advanced CTCL. Recently, trials using the combination of photochemotherapy and recombinant interferons or photochemotherapy and low doses of methotrexate have been initiated to enhance the response to photopheresis. Also, a multicenter study evaluating a new 8-MOP formulation that could be added into the leukocyte/plasma fractions prior to ultraviolet exposure is in progress in CTCL patients. The applications of photochemotherapy in the treatment of other disorders of T-cells are being examined in ongoing clinical trials. Pilot studies have been completed and controlled trials are under way in patients with autoimmune diseases. Important information has emerged regarding the potential use of photopheresis for prevention of solid organ allograft rejection. Several investigators have undertaken pilot studies comparing the efficacy of photochemotherapy with the conventional immunosuppressive therapy for treatment of cardiac transplant rejection. It is hoped that photochemotherapy can induce an immune tolerance in the allograft setting and therefore eliminate or reduce the use of cyclosporin. Other considerations have led to the use of photochemotherapy in the prevention and treatment of graft-versus-host disease after alloeneic and unrelated donor marrow transplantation. Randomized studies are required to evaluate the impact of photochemotherapy on the course of graft-versus-host disease and overall survival.

Expression of vascular cell adhesion molecule-1 in kidney allograft rejection

VCAM-1, a leukocyte adhesion molecule expressed by cytokine-activated endothelial cells in culture, may mediate mononuclear leukocyte infiltration in vessels and interstitium in solid organ allograft rejection. Using the avidin-biotin immunoperoxidase technique and an affinity-purified rabbit polyclonal antisera to recombinant human VCAM (rVCAM Ab) which works in methyl Carnoy's fixed tissues, we studied the expression of this molecule in biopsies of transplanted kidneys (N = 34) with and without features of rejection and allograft nephrectomies (N = 17) as well as nontransplanted control tissues (N = 26). The rVCAM Ab showed a population of reactive endothelial cells limited to sites of prominent subendothelial leukocytic cell infiltration in arteries and veins, and occasional peritubular capillaries (PTC) in rejecting allografts. Endothelial expression of VCAM was rarely identified in biopsies showing interstitial rejection only or cyclosporine toxicity, usually in PTC, and was only rarely encountered in nontransplanted control tissues. Apparent de novo expression of VCAM-1 by arterial smooth muscle cells and mesangial cells was present in cases of severe rejection. In addition, a population of cells (DC) with dendritic morphology was identified by rVCAM Ab within sites of lymphoid cell aggregation in rejecting allografts. Further evidence that these cells represent true DC was obtained by identification of VCAM-1 positive, morphologically similar cells in both germinal centers and interfollicular areas of all seven reactive lymph nodes tested; and by similar staining of these cells in the allografts and lymph nodes by antibodies to nerve growth factor receptor and the complement receptor CR1, previously shown to recognize DC. DCs were generally not seen in uninflamed normal control organs or portions of allografts uninvolved by lymphoid aggregates. Enhanced tubular epithelial cell expression of VCAM-1 was also present in rejecting allografts. All staining could be abolished by absorption of the antisera with VCAM-1 transfected, but not ICAM-1 or ELAM-1 transfected, CHO cells. In situ hybridization studies utilizing a cDNA probe to human VCAM-1 demonstrated mRNA production by glomerular, tubular and vascular cells corresponding to sites where the protein was immunohistochemically localized.(ABSTRACT TRUNCATED AT 400 WORDS)

Therapeutic Applications of Photopheresis

Photopheresis is a useful therapy for advanced cutaneous T-cell lymphoma, particularly for Sezary syndrome. Additional conditions in which clinical studies have suggested a therapeutic role for photopheresis include certain autoimmune diseases and reversal of rejection of solid organ allografts. Because photopheresis is extremely well tolerated and evidence is lacking for a direct immunosuppressive effect produced by this therapy, randomized trials should be pursued to determine the full spectrum of clinical benefit of this novel therapeutic modality.

Prostaglandin E 2 inhibits in vitro and in vivo lymphocyte responses in allogeneic transplantation

Prostaglandin E, (PGE 2) has been shown to have a clear role in the suppression of immune responses after burn and trauma injury. This probably results from inhibition of interleukin-2 production. This study examined the effects of PGE 2 in vivo on the survival of solid-organ allografts and in vitro on the rat allogeneic mixed lymphocyte response. Administration of 16,16-dimethyl prostaglandin E 2 (DMPGE 2), a stable analogue of PGE 2, significantly prolonged the survival of heterotopic cardiac allografts from ACI to LBN rats: 10.4 ± 1.7 days versus 5.7 ± 1.1 days (mean ± standard error of the mean) ( p <- 0.001). In 1 animal, DMPGE 2 apparently ied to the induction of long-term tolerance. Mixed lymphocyte cultures using splenocytes from naive LBN and ACI rats to which DMPGE 2 was added showed a dose-dependend suppression of the mixed lymphocyte response with concentrations as low as 1 × 10 −7 mol/L. Splenocytes harvested from treated animals with functioning but histologically rejecting hearts demonstrated a marked decrease in mixed lymphocyte response to donor (ACI) stimulators compared with naive LBN controls (3,804 ± 603 versus 27,395 ± 2,668 cpm, n = 4), but maintained a normal response to (third-party (Wistar Furth) stimulators. We conclude that DMPGE 2 suppressed solid-organ allograft rejection, inhibited the allogeneic mixed lymphocyte response, and induced donor-specific in vitro hyporesponsiveness.