Preferential Priming of Alloreactive T Cells with Indirect Reactivity

The relative contributions of the direct and indirect pathways in alloimmune responses have not been fully elucidated. We report a novel murine TCR transgenic system that can simultaneously track the CD4-direct (CD4-d), CD4-indirect (CD4-i) and CD8-direct (CD8-d) pathways after transplantation. Using this system, we have observed a profoundly greater proliferation of CD4-i T cells relative to CD4-d and CD8-d T cells after transplantation. Furthermore, a much larger proportion of CD4-i T cells attain an effector phenotype. We also analyzed endogenous, wild-type T cells using enzyme-linked immunospot analysis. In naïve mice, T cells with indirect reactivity were undetectable, but T cells with direct reactivity were abundant. However, 10 days after skin or heterotopic heart transplantation, CD4-i T cells comprised approximately 10% of the CD4+ response. Consistent with increased priming of the CD4-i pathway, we observed that the CD4-i T cells were further enriched in the effector cells migrating to the allograft and in memory-like T cells persisting after rejection. Thus, priming of the CD4-i pathway is favored after transplantation, allowing a rare population to rapidly become a major component of the CD4+ T-cell response in acute allograft rejection. The generalizability of this observation to other models remains to be determined.     

Dual effects of the alloresponse by Th1 and Th2 cells on acute and chronic rejection of allotransplants

The contribution of direct and indirect alloresponses by CD4⁺ Th1 and Th2 cells in acute and chronic rejection of allogeneic transplants remains unclear. In the present study, we addressed this question using a transplant model in a single MHC class I‐disparate donor–recipient mouse combination. BALB/c‐dm2 (dm2) mutant mice do not express MHC class I L^d molecules and reject acutely L^d+ skin grafts from BALB/c mice. In contrast, BALB/c hearts placed in dm2 mice are permanently accepted in the absence of chronic allograft vasculopathy. In this model, CD4⁺ T cells are activated following recognition of a donor MHC class I determinant, L^d 61–80, presented by MHC Class II A^d molecules on donor and recipient APC. Pre‐transplantation of recipients with L^d 61–80 peptide emulsified in complete Freund's adjuvant induced a Th1 response, which accelerated the rejection of skin allografts, but it had no effect on cardiac transplants. In contrast, induction of a Th2 response to the same peptide abrogated the CD8⁺ cytotoxic T cells response and markedly delayed the rejection of skin allografts while it induced de novo chronic rejection of heart transplants. This shows that Th2 cells activated via indirect allorecognition can exert dual effects on acute and chronic rejection of allogeneic transplants.     

A pilot study on the immunological effects of oral administration of donor major histocompatibility complex class II peptides in renal transplant recipients

Oral tolerance is an important physiological mechanism of immune hyporesponsiveness to dietary antigens and the commensal flora of the gastrointestinal tract. Feeding of alloantigens, therefore, has the potential to suppress undesirable immune responses after transplantation. To date, there are no published reports on the effects of such an approach in human transplant recipients. In the present pilot study, we demonstrate complete suppression of baseline indirect alloreactivity in patients with chronic renal allograft dysfunction following the oral feeding of low (0.5 mg/d) but not higher (1.0 and 5.0 mg/d) doses of donor major histocompatibility complex (MHC) class II peptides. The regimen was well tolerated with no evidence for sensitization to the donor antigen. Our results indicate that oral feeding of low dose donor MHC peptide may represent a safe and effective therapy to suppress indirect alloreactivity in renal transplant recipients with chronic allograft dysfunction and warrants further clinical investigation.     

Transplantation tolerance: The concept and its applicability

Recent advances have enabled researchers to induce tolerance in animal transplant models. Although it has been relatively easy to do so in rodents, it has been much more difficult to translate such strategies into primates. Understanding the cellular and molecular mechanisms of the alloimmune response has prompted the development of novel strategies that may obviate the need for immunosuppression in humans. Mechanisms of tolerance and promising new therapies, as well as the inherent difficulties in bringing them into clinical practice, are reviewed.     

Exploiting beneficial alloreactive T cells

Although the T-cell response to allogeneic cells is typically regarded as a detrimental phenomenon responsible for rejection of transplanted allografts and graft-vs.-host disease following haematopoietic stem cell transplantation, beneficial components also exist within the alloreactive population. Alloreactive T cells specific for tumour antigens can contribute to the elimination of malignant cells, and alloantigen-specific regulatory T cells can promote transplant tolerance. The challenge is to separate the good from the bad. We review how the identification, isolation and manipulation of beneficial alloreactive T cells has grown from a greater understanding of the molecular basis of the T-cell alloresponse and how alloaggression could be exploited for immunotherapy.     

In This Issue: From Basic Immunology to Oncogenesis and Inflammation

This issue of the International Reviews of Immunology features very diverse topics from basic immunology to inflammation, oncogenesis and immunopathology. Specifically, this volume hosts reviews describing the role of TCRγδ T cells, the significance of Epstein Barr virus-associated miRNAs and the genetic basis of Hashimoto's thyroiditis along with other reviews on the topics mentioned above.     

Potential and limitations of regulatory T-cell therapy in solid organ transplantation

Over the past few years, the therapeutic potential of Treg has been highlighted in the field of autoimmune diseases and after allogeneic transplantation. The first hurdle for the therapeutic use of Treg is their insufficient numbers in non-manipulated individuals, in particular when facing strong immune activation and expanding effector cells, such as in response to an allograft. Here we review current approaches being explored for Treg expansion in the perspective of clinical therapeutic protocols. We describe different Treg subsets that could be suitable for clinical application, as well as discuss factors such as the required dose of Treg, their antigen-specificity and in vivo stability, that have to be considered for optimal Treg-based immunotherapy in transplantation. Since Treg may not be sufficient as stand-alone therapy for solid organ transplantation in humans, we draw attention to possible hurdles and combination therapy with immunomodulatory drugs that could possibly improve the in vivo efficacy of Treg.     

Biased TCR gene usage in alloreactive T cells specific for a structurally dissimilar MHC alloantigen

Two models of allorecognition of MHC molecules have been proposed.One emphasizes specificity for MHC molecule-bound peptfdes andthe other for exposed MHC polymorphisms. We predicted that thelatter model would predominate in responder:stimulator combinationswhose MHC molecules differed extensively in their TCR-contactingsurfaces and that this would be reflected in biased TCR usage.Two panels of anti-DR11 T cell clones were generated, one froma DR17 and the other from a DR15 responder. The TCR-contactingsurfaces of DR17 and DR11 have multiple differences, and thoseof DR15 and DR11 are very similar. TCR analysis by polymerasechain reaction amplification and mAb staining revealed thatfive out of nine DR17 anti-DRH clones used the Vß13and two the Vß6, family. In contrast seven differentVß families were used by the eight DR15 anti-DR11clones. A similar bias In TCR Vp usage was observed in the polycionalDR17 and DR11 T cell lines from which the clones were derived,and in a second DR17 anti-DR11 line from a different individual.These results support the concept that specificity for the foreignMHC structure itself may play an important role in the alloresponsebetween respondere and stimulators with structurally dissimilarMHC molecules.     

术前输注负载供者抗原的受者未成熟树突状细胞延长移植心存活时间的实验研究

目的:利用负载供者抗原的受者未成熟树突状细胞(imDC)干扰T细胞抗原间接识别途径,观察对同种异体移植心存活时间的影响。方法:用低剂量粒细胞-巨噬细胞集落刺激因子(GM-CSF)培养受者小鼠骨髓源性imDC,并在培养过程中加入供者可溶性抗原共同孵育,流式细胞术检测细胞表型,观察其在体外刺激自体T细胞增殖的能力,并于术前1周将约2.0×106个树突状细胞(DC)输入受者体内,观察其对同种异体移植心存活时间的影响。结果:受者DC可通过共同孵育的方式有效负载供者抗原,负载供者抗原的受者imDC在体外不能有效刺激自体T细胞活化增殖,将其于术前输入受者体内,移植心的存活时间由(7.2±1.7)天延长至(17.7±3.3)天。结论:术前输注负载供者抗原的受者imDC,可明显延长移植心的存活时间。     

Indirect Recognition of T-Cell Epitopes Derived from the α3 and Transmembrane Domain of HLA-A2

Indirect allorecognition has been implicated in the mechanism of chronic rejection and alloantibody formation but precise definition of the epitopes involved has been limited. We have undertaken a detailed assessment of the antigenic properties of peptides derived from HLA-A2. Candidate epitopes were identified in vitro by assessment of MHC class II binding. The immune response to these epitopes was determined in patients awaiting a renal transplant by the assessment of PBMC activation using gamma-interferon ELISPOT. Twenty-two of fifty-five patients responded to peptides from HLA-A2 and this was associated with but not confined to those who had made antibody to HLA-A2 (14/18). Nineteen of twenty-two patients responded to peptides derived from the hypervariable alpha1 and alpha2 domains and 18/22 responded to peptides from the alpha 3 and transmembrane domain, the sequences of which show little polymorphism. In six patients, the sequence of these peptides was identical to self, that is, the response was autoimmune. The finding of indirect epitopes derived from regions of MHC class I that exhibit little polymorphism provides a novel perspective on the immune response to alloantigen and has potential implications for the development of specific therapies.