Katia Gagne

Highly Altered Vβ Repertoire of T Cells Infiltrating Long-Term Rejected Kidney Allografts

Chronic rejection represents a major cause of long-term kidney graft loss. T cells that are predominant in long-term rejected kidney allografts (35 ± 10% of area infiltrate) may thus be instrumental in this phenomenom, which is likely to be dependant on the indirect pathway of allorecognition only. We have analyzed the variations in T cell repertoire usage of the Vβ chain at the complementary determining region 3 (CDR3) level in 18 human kidney grafts lost due to chronic rejection. We observed a strongly biased intragraft TCR Vβ usage for the majority of Vβ families and also a very high percentage (55%) of Vβ families exhibiting common and oligoclonal Vβ-Cβ rearrangements in the grafts of patients with chronic rejection associated with superimposed histologically acute lesions. Furthermore, Vβ8 and Vβ23 families exhibited common and oligoclonal Vβ-Jβ rearrangements in 4 of 18 patients (22%). Several CDR3 amino acid sequences were found for the common and oligoclonal Vβ8-Jβ1.4 rearrangement. Quantitative PCR showed that biased Vβ transcripts were also overexpressed in chronically rejected kidneys with superimposed acute lesions. In contrast, T lymphocytes infiltrating rejected allografts with chronic rejection only showed an unaltered Gaussian-type CDR3 length distribution. This pattern suggests that late graft failure associated with histological lesions restricted to Banff-defined chronic rejection does not involve T cell-mediated injury. Thus, our observation suggests that a limited number of determinants stimulates the recipient immune system in long-term allograft failure. The possibility of a local response against viral or parenchymatous cell-derived determinants is discussed.

Direct Recognition of Foreign MHC Determinants by Naive T Cells Mobilizes Specific Vβ Families Without Skewing of the Complementarity-Determining Region 3 Length Distribution

The capacity of T cells to interact with nonself-APC, also referred to as direct allorecognition, is an essential feature of the cellular response involved in graft rejection. However, there is no study on TCR repertoire biases associated with direct restricted T cell activation. In this paper, we have addressed the impact of direct recognition on the whole naive T cell repertoire, using a new approach that provides, for the first time, an integrated depiction of the quantitative and qualitative alterations in the TCR Vβ transcriptome. This method can differentiate resting patterns from polyclonally activated ones, as evidenced by superantigen usage. According to this new readout, we show that direct recognition of nonself-MHC molecules triggers mRNA accumulation of several TCR Vβ families, specific to the combination studied. Moreover, in marked contrast to the situation that prevails in indirect allorecognition, T cell activation through the direct presentation pathway was not associated with skewing of the complementarity determining region (CDR) 3 length distribution. Altogether, these data argue for the significance of TCR contacts with the MHC framework in direct allorecognition. In addition, the TCR diversity mobilized by this interaction and the massive TCRβ mRNA accumulation observed after a few days of culture suggest that a significant proportion of naive T cells receive a signal leading to TCRβ transcriptional activation even though only a few of them engage in mitosis.

T cell response in xenorecognition and xenografts: a review

Xenotransplantation has recently become a subject of interest for the transplantation community due to the current organ shortage, which could be partially or even totally solved by the development of this strategy. The humoral response, which arises as a result of species disparities, is the major obstacle to the success of xenotransplantation. However, if the use of different strategies such as plasmapheresis, immunoadsorption, the utilization of organs from transgenic pigs for complement regulatory molecules and new immunosuppressive drugs, may allow to overcome or reduce the early antibody mediated rejections (hyperacute or acute vascular rejection), delayed responses based on cellular activations will still occur. In this review, despite the fact that different cell populations have been shown to be implicated in these phenomena (NK, granulocytes, macrophages), we will focus on recent published information concerning T cell response only, in xenorecognition.

T-cell-mediated rejection of vascularized xenografts in the absence of induced anti-donor antibody response.

T cells are considered to play a major indirect role in the pathogenesis of xenograft vascular rejection, by promoting the induction of anti‐donor antibodies that trigger complement‐ and antibody‐dependent cell cytotoxicity. However, how vigorous the T cell xenoresponse is in vivo, and whether, besides their helper function, T cells are capable of directly affecting the graft is still unclear. We have previously shown that cyclosporine A (CsA) withdrawal in accommodated cardiac xenograft recipient allows for a rapid and dense T‐cell infiltration, concomitant to an acute graft rejection. In this paper we further characterize the role of T cells in this rejection process and we demonstrate that adoptive transfer of CD4+ T cells in irradiated recipients of long‐term cardiac xenografts is sufficient to trigger acute rejection, in the absence of any detectable induced anti‐hamster antibody response. Therefore, our data suggest that unusually strong T‐cell response will be another major barrier to xenotransplantation, even if antibody‐mediated vascular rejection is controlled.

TGF‐β1 and donor dendritic cells are common key components in donor‐specific blood transfusion and anti‐class II heart graft enhancement, whereas tolerance induction also required inflammatory cytokines down‐regulation

Heart allograft tolerance in adult recipients can be induced in the LEW.1W to LEW.1A congeneic strain combination by pre‐graft donor‐specific blood transfusion (DST). Long‐term survivors accept LEW.1W graft but reject third party skin grafts. As tolerant recipients of heart allografts showed an increase in anti‐donor class II antibodies, we hypothesize that these antibodies could be instrumental in tolerance induction. However, anti‐donor MHC class II alone prolonged graft survival but did not induce heart allograft tolerance in this combination. We analyzed the immune response patterns in heart allograft recipients following the injection of anti‐donor class II antibodies (prolongation) or DST priming (tolerance). As suggested by the different phenomena, several immunological patterns were strikingly different between the two models. In strong contrast to DST‐tolerant recipients, at 5 days after transplantation, neither Th1u2009/u2009Th2 nor inflammatory cytokines were inhibited in recipients treated with anti‐donor class II antibodies, in which only prolongation of graft survival was induced. Nevertheless, in both models, depletion of resident dendritic cells (DC) from donor hearts inhibited tolerance induction (DST) or shortened allograft survival (anti‐donor class II antibodies). Moreover, TGF‐β1 was not down‐regulated and administration of neutralizing anti‐TGF‐β1 antibody, which inhibited tolerance induction (DST), also shortened allograft survival (anti‐donor class II antibodies). These results suggest that, in these two MHC class II‐restricted models, both TGF‐β1 and donor DC have a pivotal role in prolonging graft survival. However, in the days following transplantation, further inhibition of inflammatory cytokine production, particularly Th1 and macrophage‐derived cytokines is required for tolerance induction.

Identification of immunodominant donor MHC peptides following rejection and donor strain transfusion‐induced tolerance of heart allografts in adult rats

Pre‐graft priming of heart allograft recipients with donor strain blood induces tolerance in 100u2009% of adult rats in the congenic LEW.1W to LEW.1A combination. This tolerant state is specific for donor MHC antigens as third‐party blood transfusions fail to induce tolerance, and third‐party skin grafts are promptly rejected by tolerant graft recipients. In this study we have characterized the immunodominant donor (RT1u) class I and II allogenic peptides which elicit an in vitro proliferative response to splenocytes from recipients (RT1a) undergoing acute rejection or tolerant to a LEW.1A cardiac allograft. Paradoxically, splenocytes from tolerant animals responded more vigorously to a broader set of donor peptides than splenocytes from rejecting animals. In addition, several of these peptides were observed to be stimulatory only for tolerant splenocytes. These findings suggest that regulatory cells may be involved in tolerance induction or maintenance and are selected by specific motifs, which could be utilized for manipulating the immune system of graft recipients.

Different patterns of TCR beta chain regulation following allo- and xeno-transplantation.

Abstract:u2002 Background:u2002 In the concordant hamster‐to‐rat cardiac xenograft model, recipients treated with cobra venom factor for the first 10u2003days following transplantation and daily with Cyclosporine A (CsA) do not reject their grafts. However, when CsA is withdrawn on day 40, an acute cellular rejection occurs within 4u2003±u20031u2003days. Allografts performed in the same conditions are rejected within 18u2003±u20034u2003days.