Characterization of CD28(-)CD4(+) T cells in living kidney transplant patients with long-term allograft acceptance

Costimulatory pathways in kidney transplantation: pathogenetic role, clinical significance and new therapeutic opportunities

Costimulatory pathways play a key role in immunity, providing the second signal required for a full activation of adaptive immune response. Different costimulatory families (CD28, TNF-related, adhesion and TIM molecules), characterized by structural and functional analogies, have been described. Costimulatory molecules modulate T cell activation, B cell function, Ig production, cytokine release and many other processes, including atherosclerosis. Patients suffering from renal diseases present significant alterations of the costimulatory pathways, which might make them particularly liable to infections. These alterations are further pronounced in patients undergoing kidney transplantation. In these patients, different costimulatory patterns have been related to distinct clinical features. The importance that costimulation has gained during the last years has led to development of several pharmacological approaches to modulate this critical step in the immune activation. Different drugs, mainly monoclonal antibodies targeting various costimulatory molecules (i.e. anti-CD80, CTLA-4 fusion proteins, anti-CD154, anti-CD40, etc.) were designed and tested in both experimental and clinical studies. The results of these studies highlighted some criticisms, but also some promising findings and now costimulatory blockade is considered a suitable strategy, with belatacept (a CTLA-4 fusion protein) being approved as the first costimulatory blocker for use in renal transplantation. In this review, we summarize the current knowledge on costimulatory pathways in the setting of kidney transplantation. We describe the principal costimulatory molecule families, their role and clinical significance in patients undergoing renal transplantation and the new therapeutic approaches that have been developed to modulate the costimulatory pathways.

CD40L, CD28, and CTLA-4 expression on CD4+ T cells in kidney graft recipients: A relationship with post-transplantation clinical course

BACKGROUND

Experimental studies have demonstrated that the intensity of alloreactivity against a transplanted organ results from an interaction of positive (CD40/CD40L and B.7/CD28) and inhibitory (B.7/CTLA-4) signals between antigen-presenting cells (APCs) and T lymphocytes.

METHODS

We examined the CD40L, CD28, and both surface (s) and intracellular (i) CTLA-4 expressions on freshly drawn and anti-CD3+rIL-2-stimulated peripheral blood CD4+ T cells in groups of kidney transplant recipients in relation to distinct clinical course using the tri-color immunofluorescence method.

RESULTS

The median proportions of freshly isolated CD3+/CD4+/CTLA-4+ and CD3+/CD4+/CD40L+ cells in all groups of graft recipients were higher than in control subjects. In patients with stable graft function (SGF), non-significantly higher sCTLA-4, significantly higher iCTLA-4 expression, and significantly lower CD40L expression on freshly drawn CD4+ T cells compared with recipients with chronic allograft nephropathy (CAN) were found. Moreover, CD4+ T cells from SGF patients showed a higher potential to express sCTLA-4 and CD40L molecules and to down-regulate the CD28 molecule in response to ex vivo stimulation than those from patients with CAN. In patients without acute graft rejection (NAGR), a markedly higher proportion of freshly drawn CD3+/CD4+/iCTLA-4+ cells compared with patients with acute graft rejection (AGR) and an up-regulation of the median percentage of CD3+/CD4+/CD40L+ cells after ex vivo stimulation was found.

CONCLUSIONS

In patients with SGF, peripheral blood CD4+ T cells exhibited a higher potential to express surface CTLA-4 and CD40L and to down-regulate CD28 costimulatory molecules in response to ex vivo stimulation, indicating a relationship between the expression patterns of both costimulatory and inhibitory molecules in CD4+ T cells and clinical course after renal transplantation.

Induction of obliterative airway disease in murine tracheal allografts by CD8+ CTLs recognizing a single minor histocompatibility antigen

The role of minor histocompatibility Ag (mHAg)-specific CD8+ CTLs in the pathogenesis of chronic lung allograft rejection (bronchiolitis obliterans syndrome) remains to be elucidated. Thus, the goal of this study was to define the role of a single mHAg mismatch at the polymorphic H13 allele in the development of obliterative airway disease (OAD) after murine heterotopic tracheal transplantation. The H13a and H13b alleles encode for the SSVVGVWYL (SVL9) and SSVIGVWYL (SIL9) mHAgs, respectively, presented in the context of the H2Db MHC class I molecule. Toward this, C56BL/10SnJ (H13a) tracheal allografts were transplanted into congenic B10.CE-H13b Aw(30NX)/Sn (H13b) recipients. The allografts were harvested at 30, 60, and 90 days after transplantation, and OAD lesions (epithelial damage, cellular infiltration, and luminal fibrosis) were confirmed histologically. Selected groups of mice were immunized (s.c.) or tolerized (i.v.) with the SVL9 peptide before transplantation. This single mHAg mismatch induced the development of OAD within 90 days. SVL9 immunization significantly accelerated the kinetics of the OAD lesions. In contrast, SVL9 tolerization completely abrogated the development of OAD. This was correlated with a complete abrogation of H13a-specific CD8+ CTL responses with a significant reduction in the frequency of IFN-gamma-producing CTLs and the activation of TGF-beta-producing CD8+ T cells. In conclusion, a single mHAg mismatch can induce the development of OAD. These data also suggest that mHAg-reactive CD8+ CTLs may play an important role in the pathogenesis of chronic lung allograft rejection in humans.

Kidney Transplant Patients with Long-Term Graft Survival Have Altered Expression of Molecules Associated with T-Cell Activation

BACKGROUND

Patients with long-term functioning organ allografts may have developed different mechanisms that explain the lack of graft rejection. However, it is not known how these mechanisms interplay or whether one of them predominates in such situations.

METHODS

The authors analyzed the expression of T-cell surface molecules involved in alloantigen recognition, signal transduction, co-stimulation, and activation markers on circulating T cells from patients with normal kidney function 10 or more years after transplantation, short-term survival (1-4 years), and chronic rejection and from healthy adults. The percentage and the median fluorescent intensity of each marker were determined by flow cytometry. Proliferative response against specific and third-party donors and mitogenic stimulation were also determined.

RESULTS

Peripheral blood lymphocytes from patients with long-term surviving kidneys had decreased expression of T-cell receptor (TCR)-alphabeta (P < 0.01), CD3epsilon (P < 0.05), and CD3 zeta-chains (P < 0.001); diminished percentages of CD4(+)CD28(+) (P < 0.001) cells; and increased expression of CTLA-4(+) (P < 0.01) on CD3(+) cells. CD4(+)CD25(+)CD69(+) cells were also increased in long-term surviving patients. Long-term surviving patients had decreased donor-specific proliferative responses.

CONCLUSIONS

The decreased expression of TCR-alphabeta and epsilon- and zeta-chains on circulating T cells of long-term surviving patients suggests that these cells may have defects in alloantigen recognition or signal transduction that may result in decreased numbers of T cells expressing co-stimulatory molecules and activation markers as well as a decreased specific proliferative response. The decrease in the percentage of CD28(+) cells and the increase in CD4(+)CD25(+)CD69(+) cells suggest that regulatory mechanisms of the immune response are still active in such patients.

Long time follow up of CD28- CD4+ T cells in living kidney transplant patients

We previously reported that the CD28(-) CD4(+) T cell subpopulation was expanded in the kidney allograft patients with long graft survival, although these T cells were rarely found in patients with graft survival <5 yr. To understand the CD28(-) CD4(+) T cells in the long-term acceptance of kidney allografts, we examined functions of this population and performed a 4 yr follow up study. Peripheral blood mononuclear cells (PBMC) were obtained from 47 long-term living related kidney allograft recipients. CD28(+) CD4(+) and CD28(-) CD4(+) T cells purified by cell sorting were analyzed for expression of V(beta) repertoire. Donor-specific response was examined in mixed lymphocyte reaction (MLR). A follow up study with long-term kidney allograft patients was performed for 4 yr about the rate of CD28(-) CD4(+) T cells. Eleven patients were examined by MLRs against donors and third party. Four patients with a marked increase of CD28(-) CD4(+) T cells showed the donor-specific responses appeared to be lower when compared with third party-specific responses. Freshly sorted CD28(-) CD4(+) T cells showed a restricted V(beta) repertoire, whereas the V(beta) usage of CD28(+) CD4(+) T cells from the same patients was much diversified. Such difference in V(beta) repertoire was not evident between the two populations from healthy control. A follow up study showed the ratio of CD28(-) CD4(+) T cells appeared to be lower in patients who were suspected of chronic rejection. These unusual CD4(+) T cells might be related to the long-term acceptance of human transplant allografts.