Renal transplant patients show variations in their self-reactive repertoires: a serial study

Regulatory/inflammatory cellular response discrimination in operational tolerance

BACKGROUND

Antigen-specific cellular response is essential in immune tolerance. We tested whether antigen-specific cellular response is differentially modulated in operational tolerance (OT) in renal transplantation with respect to critical antigenic challenges in allotransplantation-donor antigens, pathogenic antigens and self-antigens.

METHODS

We analysed the profile of immunoregulatory (REG) and pro-inflammatory (INFLAMMA) cytokines for the antigen-specific response directed to these three antigen groups, by Luminex.

RESULTS

We showed that, in contrast to chronic rejection and healthy individuals, OT gives rise to an immunoregulatory deviation in the cellular response to donor human leucocyte antigen DR isotype peptides, while preserving the pro-inflammatory response to pathogenic peptides. Cellular autoreactivity to the N6 heat shock protein 60 (Hsp60) peptide also showed a REG profile in OT, increasing IL4, IL-5, IL-10 and IL-13.

CONCLUSIONS

The REG shift of donor indirect alloreactivity in OT, with inhibition of interleukin (IL)-1B, IL-8, IL-12, IL-17, granulocyte colony-stimulating factor, Interferon-γ and monocyte chemoattractant protein-1, indicates that this may be an important mechanism in OT. In addition, the differential REG profile of cellular response to the Hsp60 peptide in OT suggests that REG autoimmunity may also play a role in human transplantation tolerance. Despite cross-reactivity of antigen-specific T cell responses, a systemic functional antigen-specific discrimination takes place in OT.

Autoimmune sensitization to cardiac myosin leads to acute rejection of cardiac allografts in miniature swine

BACKGROUND

Recent studies in mice and patients suggest that posttransplantation induction of autoimmune responses to tissue-specific antigens contributes to the rejection of major histocompatibility complex mismatched allotransplants. The relevance of this phenomenon to the rejection of major and minor histocompatibility-mismatched allografts performed in large-animal models remains to be established.

METHODS

Miniature swine were immunized with cardiac myosin (CM) in Freund's adjuvant and received heterotopic, minor antigen-mismatched heart transplants. T-cell (proliferation and delayed type hypersensitivity [DTH]) and B-cell (antibody) responses specific to CM were measured. The rejection of heart transplants was assessed histologically.

RESULTS

Three of four swine that were immunized with CM before receiving a minor antigen-mismatched heart transplant exhibited potent DTH, T-cell proliferation and antibody responses to CM and rejected their grafts acutely. The fourth swine, which failed to mount a significant DTH response to CM and displayed low and transient anti-CM antibody titers, demonstrated long-term allograft survival.

CONCLUSIONS

This large-animal study supports the relevance of autoimmunity to CM in the rejection of minor antigen disparate cardiac allotransplants.

Presentation of self-antigens on MHC class II molecules during dendritic cell maturation

Little is known about how dendritic cells (DCs) maintain a balance between tolerance and immunity for antigens synthesized by DCs themselves. Using transgenic DCs expressing a model self-antigen, in vitro self-peptide-MHC class II complex formation and presentation increased with DC maturation, as for exogenous antigens. In vivo, however, even 'immature' DCs isolated from steady-state lymph nodes expressed MHC at mature cell levels, although many were also CD86 low. Adoptive transfer of naive specific T cells into unstimulated transgenic mice resulted in tolerance. If the mice were also injected with anti-CD40 or Listeria monocytogenes, there was robust specific T cell expansion and inflammation. Thus, DC-endogenous antigens may induce tolerance, but only in the absence of potent maturation stimuli.

Limiting Dilution Analysis of Interleukin-2 Producing Helper T-cell Frequencies as a Tool in Allogeneic Hematopoietic Cell Transplantation

BACKGROUND

A reliable in vitro test that estimates the level of ongoing alloreactivity would be valuable in allogeneic hematopoietic cell transplantation (HCT) as a help to guide clinical interventions such as donor lymphocyte infusions and changes in the immunosuppression. In the present study, the use of limiting dilution analysis of interleukin-2 (IL-2) producing helper T lymphocyte frequencies (HTL assay) as a way to quantify alloreactivity following HCT was investigated.

METHODS

Serial HTL assays were performed following allogeneic HCT with myeloablative or nonmyeloablative conditioning in 26 patients with hematologic malignancies.

RESULTS

Deviations from single-hit kinetics were frequently observed in the HTL assays and a nonlinear model was therefore used for analysis. The results of this analysis suggested the presence of an inhibitory cell population. Inhibition was observed in the majority of patients and was not restricted to a specific transplant regimen. Inhibition occurred more often with high frequencies of IL-2 producing cells, indicating a physiological role of the putative inhibitory cell population in the regulation of an immune response. Higher frequencies of IL-2 producing cells were observed in patients with acute graft-versus-host disease grades II-IV than in patients with grades 0-I (P = 0.046), indicating that the degree of ongoing alloreactivity is indeed quantified by the HTL assay.

CONCLUSIONS

We find that the HTL assay may yield interesting insight into regulation of immune responses following allogeneic HCT, but because of the complexity of the results obtained, its use as a routine procedure to guide immunosuppression cannot be recommended.

T-cell autoreactivity to Hsp in human transplantation may involve both proinflammatory and regulatory functions

Heat shock proteins (Hsp) are moving from the category of basically intracellular chaperone molecules to important proteins in both innate and acquired immune responses, with great potential for clinical application as immunomodulators. Both proinflammatory and regulatory Hsp-reactive T cells have been described in animal models of autoimmune diseases. To investigate the role of autoreactivity to Hsp60 and Hsp70 in human transplantation, we analyzed, sequentially, peripheral blood mononuclear cell proliferation and cytokine production before and at different time points after renal transplantation, as well as the modulation of proliferation to Hsp in the presence of exogenous cytokines. Proliferation to Hsp60 and Hsp70 in the pretransplantation (pre-Tx) period was significantly associated with rejection episodes in the first months post-Tx. In contrast, IL-4 production was significantly associated with absence of rejection. Addition of exogenous IL-4 distinctly modulated the proliferative response to Hsp60; inhibiting proliferation in 83% of patients in the early post-Tx period (0-6 months), in which rejection episodes occurred, and inducing proliferation in 62.5% of patients in the later period (>12-24 months), when no rejection was observed. Characterization of autoreactive anti-Hsp60 regulatory T cells may permit new approaches to control the proinflammatory response to the graft, as well as aggressive autoimmunity.

Modulation of tissue-specific immune response to cardiac myosin can prolong survival of allogeneic heart transplants

The role of immune response to tissue-specific Ags in transplant rejection is poorly defined. We have previously reported that transplantation of cardiac allografts triggers a CD4(+) Th1 cell response to cardiac myosin (CM), a major contractile protein of the heart, and that pretransplant activation of proinflammatory CM-specific T cells accelerates rejection. In this study, we show that administration of CM together with IFA (CM/IFA) can prevent acute rejection of an allogeneic heart transplant. Prolongation of cardiac graft survival is associated with activation of CM- and allo-specific T cells secreting type 2 cytokines (IL-4, IL-5) and reduction of the frequency of proinflammatory IFN-gamma-secreting (type 1) alloreactive T cells. Blocking of IL-4 cytokine with Abs abrogates the prolongation. CM/IFA treatment prevents acute rejection of MHC class I-mismatched, but not fully mismatched grafts. However, if donor heart is devoid of MHC class II expression, CM-IFA administration delays rejection of fully allogeneic cardiac transplants. This finding suggests that the effect of CM modulation depends on the type (direct vs indirect) and strength of recipient's CD4(+) T cell alloresponse. Our results underscore the important role of host immunity to tissue-specific Ags in the rejection of an allograft. This study demonstrates that modulation of the immune response to a tissue-specific Ag can significantly prolong cardiac allograft survival, an observation that may have important implications for the development of novel selective immune therapies in transplantation.