Determination of the functional status of alloreactive T cells by interferon-gamma kinetics

Role of Regulatory T Cells in Noninherited Maternal Antigen-Related Tolerance in Cord Blood: An in Vitro Study

Cord blood (CB) is an alternative stem cell source for allogeneic hematopoietic stem cell transplantation (HSCT). The unique advantages of using CB as a stem cell source are a degree of permissibility for HLA mismatch, rapid availability, and relatively risk-free cell collection. Because HLA is highly polymorphic and population-specific, optimal HLA-matched unrelated donors or cord blood units (CBUs) might not be available. In view of the possibility that matched CBUs that include noninherited maternal antigens (NIMAs) might contain acceptable HLA mismatches, we attempted to determine the degree of alloreactivity of CB mononuclear cells (MNCs) on stimulation by the maternal, paternal, and unrelated stimulator cells. Suppression of T cell proliferation, cytotoxicity, and a cytokine profile indicating suppressed Th1 and elevated IL-10 and TGF-β1 responses were observed in the mixed lymphocyte reaction in response to NIMAs. The increases in IL-10 and TGF-β1 production may be due to the Th2 response and/or regulatory T cells (Tregs). The reduced IL-10 and TGF-β1 production after CD25 depletion could have been due to removal of Tregs from the CB cells. Thus, Tregs appear to play an important role in the CB MNC response to NIMAs, possibly due to the induction of IL-10 and TGF-β1. We hope that our work can provide some evidence of the beneficial effect of NIMAs.

Effectiveness of topical immunosuppressants in prevention and treatment of rejection in face allotransplantation

BACKGROUND

The use of topical immunosuppressants has been anecdotally reported for the treatment of rejection in vascularized composite allotransplantation. The aim of this study was to evaluate the effectiveness of topical tacrolimus and clobetasol in the prevention and treatment of rejection.

METHODS

Seventy-six hemiface allotransplants, between ACI (RT1) donors and Lewis (RT1) recipients, were performed in 11 groups and treated with topical tacrolimus or clobetasol, or in combination with systemic cyclosporine A and anti-αβ-T-cell receptor antibody for 1 week. Topical treatment increased the survival of the allograft in all groups.

RESULTS

Best outcomes were obtained in the groups treated with systemic therapy and topical tacrolimus. Expression of proinflammatory cytokines interleukin 2, interferon γ, tumor necrosis factor α, and transforming growth factor β correlated with clinical signs of rejection and the final outcomes. Clobetasol application was associated with a marked depletion of lymphocytic populations, and dermal and epidermal atrophy.

CONCLUSIONS

Both topical tacrolimus and clobetasol were effective in treating episodes of acute rejection, and the best outcomes were achieved when their application was initiated after systemic immunosuppression. Topical tacrolimus proved to be a preferable adjunct agent to the systemic therapy by preventing both the local and systemic complications.

Patterns of de novo allo B cells and antibody formation in chronic cardiac allograft rejection after alemtuzumab treatment

Even though the etiology of chronic rejection (CR) is multifactorial, donor specific antibody (DSA) is considered to have a causal effect on CR development. Currently the antibody-mediated mechanisms during CR are poorly understood due to lack of proper animal models and tools. In a clinical setting, we previously demonstrated that induction therapy by lymphocyte depletion, using alemtuzumab (anti-human CD52), is associated with an increased incidence of serum alloantibody, C4d deposition and antibody-mediated rejection in human patients. In this study, the effects of T cell depletion in the development of antibody-mediated rejection were examined using human CD52 transgenic (CD52Tg) mice treated with alemtuzumab. Fully mismatched cardiac allografts were transplanted into alemtuzumab treated CD52Tg mice and showed no acute rejection while untreated recipients acutely rejected their grafts. However, approximately half of long-term recipients showed increased degree of vasculopathy, fibrosis and perivascular C3d depositions at posttransplant day 100. The development of CR correlated with DSA and C3d deposition in the graft. Using novel tracking tools to monitor donor-specific B cells, alloreactive B cells were shown to increase in accordance with DSA detection. The current animal model could provide a means of testing strategies to understand mechanisms and developing therapeutic approaches to prevent chronic rejection.

Dissecting the T Cell Response: Proliferation Assays vs. Cytokine Signatures by ELISPOT

Chronic allograft rejection is in part mediated by host T cells that recognize allogeneic antigens on transplanted tissue. One factor that determines the outcome of a T cell response is clonal size, while another is the effector quality. Studies of alloimmune predictors of transplant graft survival have most commonly focused on only one measure of the alloimmune response. Because differing qualities and frequencies of the allospecific T cell response may provide distinctly different information we analyzed the relationship between frequency of soluble antigen and allo-antigen specific memory IFN-g secreting CD4 and CD8 T cells, their ability to secrete IL-2, and their proliferative capacity, while accounting for cognate and bystander proliferation. The results show proliferative responses primarily reflect on IL-2 production by antigen-specific T cells, and that proliferating cells in such assays entail a considerable fraction of bystander cells. On the other hand, proliferation (and IL-2 production) did not reflect on the frequency of IFN-γ producing memory cells, a finding particularly accentuated in the CD8 T cell compartment. These data provide rationale for considering both frequency and effector function of pre-transplant T cell reactivity when analyzing immune predictors of graft rejection.

Primary vascularization of the graft determines the immunodominance of murine minor H antigens during organ transplantation

Grafts can be rejected even when matched for MHC because of differences in the minor histocompatibility Ags (mH-Ags). H4- and H60-derived epitopes are known as immunodominant mH-Ags in H2(b)-compatible BALB.B to C57BL/6 transplantation settings. Although multiple explanations have been provided to explain immunodominance of Ags, the role of vascularization of the graft is yet to be determined. In this study, we used heart (vascularized) and skin (nonvascularized) transplantations to determine the role of primary vascularization of the graft. A higher IFN-γ response toward H60 peptide occurs in heart recipients. In contrast, a higher IFN-γ response was generated against H4 peptide in skin transplant recipients. Peptide-loaded tetramer staining revealed a distinct antigenic hierarchy between heart and skin transplantation: H60-specific CD8(+) T cells were the most abundant after heart transplantation, whereas H4-specific CD8(+) T cells were more abundant after skin graft. Neither the tissue-specific distribution of mH-Ags nor the draining lymph node-derived dendritic cells correlated with the observed immunodominance. Interestingly, non-primarily vascularized cardiac allografts mimicked skin grafts in the observed immunodominance, and H60 immunodominance was observed in primarily vascularized skin grafts. However, T cell depletion from the BALB.B donor prior to cardiac allograft induces H4 immunodominance in vascularized cardiac allograft. Collectively, our data suggest that immediate transmigration of donor T cells via primary vascularization is responsible for the immunodominance of H60 mH-Ag in organ and tissue transplantation.

Cytokine kinetics profiling in pediatric renal transplant recipients

Pediatric renal transplant recipients experience side effects of immunosuppression. Few immunoassays exist which can assess the adequacy of immunosuppression. We developed a CKT, whereby cytokine levels are measured in a five-day mixed lymphocyte reaction. We describe the in vitro cytokine responses to donor and third-party antigen in a pilot study of nine children after living-donor renal transplantation. The CKT identified five patterns of IFN-gamma secretion relative to donor and third-party alloantigen: no response to alloantigen (n = 2), hypo-response to donor (n = 3), equal response (n = 1), hyper-response to donor (n = 1), and intermediate response (n = 2). IL-2 and IL-13 patterning correlated with IFN-gamma expression. Two of nine subjects had acute rejection, which correlated with intermediate and hyper-responsive profiles. No rejection occurred during immunosuppression or donor-specific hypo-responsiveness. Significant immunosuppression was universal early after transplantation. Two of four children showed strong pretransplant responses to donor, which were regained three months post-transplant, and associated with rejection in one subject. The CKT reflects the level of immunosuppression and may offer a method to assess the adequacy of immunosuppression. A pattern of complete non-responsiveness or hypo-responsiveness correlated with lack of acute rejection. The CKT may prove useful in titrating immunosuppression and in improving live donor selection.

Memory T-cell-specific therapeutics in organ transplantation

PURPOSE OF REVIEW

This review details the role of memory T cells in physiologic and allospecific immunity, and summarizes the effects of immunosuppressive agents used to manipulate their function in the context of organ transplantation.

RECENT FINDINGS

Memory T cells are lymphocytes with characteristics that are thought to promote anamnestic immune responses. They have a unique capacity to generate rapid effector functions upon secondary exposure to a pathogen, and this capacity is achieved through truncated requirements for antigen presentation, reduced activation thresholds, and enhanced trafficking and adhesion mechanisms. In general, these same mechanisms also appear to evoke improved efficiency in mediating allograft rejection. The phenotype of these cells has been increasingly well defined and associated with a characteristic pattern of susceptibility to immunosuppressive agents. This knowledge is now being exploited in the development of immune therapeutic regimens to selectively mollify T memory cell effects.

SUMMARY

A specific targeting of memory T cells has potential to prevent allograft rejection in a more precise manner than current means of immunosuppression. However, these benefits will be balanced by the reciprocal risk of susceptibility to recurrent infection.

Unaltered graft survival and intragraft lymphocytes infiltration in the cardiac allograft of Cxcr3-/- mouse recipients

Previous studies showed that absence of chemokine receptor Cxcr3 or its blockade prolong mouse cardiac allograft survival. We evaluated the effect of the CXCR3 receptor antagonist MRL-957 on cardiac allograft survival, and also examined the impact of anti-CXCR3 mAb in human CXCR3 knock-in mice. We found only a moderate increase in graft survival (10.5 and 16.6 days, p < 0.05) using either the antagonist or the antibody, respectively, compared to control (8.7 days). We re-evaluated cardiac allograft survival with two different lines of Cxcr3(-/-) mice. Interestingly, in our hands, neither of the independently derived Cxcr3(-/-) lines showed remarkable prolongation, with mean graft survival of 9.5 and 10.8 days, respectively. There was no difference in the number of infiltrating mononuclear cells, expansion of splenic T cells or IFN-gamma production of alloreactive T cells. Mechanistically, an increased other chemokine receptor fraction in the graft infiltrating CD8 T cells in Cxcr3(-/-) recipients compared to wild-type recipients suggested compensatory T-cell trafficking in the absence of Cxcr3. We conclude Cxcr3 may contribute to, but does not govern, leukocyte trafficking in this transplant model.

Role for nitric oxide in hookworm-associated immune suppression

Hookworm infection is a major cause of anemia and malnutrition in resource-poor countries. Human and animal studies suggest that infection with these intestinal nematodes is associated with impaired cellular immunity, characterized by reduced lymphocyte proliferation in response to both parasite and heterologous antigens. We report here data from studies aimed at defining mechanisms through which hookworms modulate the host cellular immune response. Splenocytes and mesenteric lymph node (MLN) cells from hamsters infected with Ancylostoma ceylanicum showed minimal proliferation in response to mitogen at days 20 and 30 postinfection (p.i.), with partial recovery noted at day 70 p.i. The proliferative capacity of enriched splenocyte T-cell preparations from infected animals following stimulation with hookworm antigens was partially restored in the presence of antigen-presenting cells from uninfected hamsters. Analysis by fluorescence-activated cell sorting revealed that hookworm infection is associated with reduced percentages of both CD4(+) and surface immunoglobulin G-positive lymphocytes in the spleen and MLN cells. Splenocytes from infected hamsters also secreted more nitric oxide (NO) in culture than did those from naïve animals. Inhibition of NO secretion was associated with partial restoration of the proliferative capacity of splenocytes from infected animals in response to concanavalin A, suggesting a role for NO in mediating this effect. Together, these data demonstrate that hookworm infection is associated with impaired function of antigen-presenting cells and depletion of important lymphocyte subpopulations and also suggests a role for NO in parasite-induced immunosuppression.

Rapid quantification of naive alloreactive T cells by TNF-alpha production and correlation with allograft rejection in mice

Allograft transplantation requires chronic immunosuppression, but there is no effective strategy to evaluate the long-term maintenance of immunosuppression other than assessment of graft function. The ability to monitor naive alloreactive T cells would provide an alternative guide for drug therapy at early, preclinical stages of graft rejection and for evaluating tolerance-inducing protocols. To detect and quantify naive alloreactive T cells directly ex vivo, we used the unique ability of naive T cells to rapidly produce TNF-alpha but not IFN-gamma. Naive alloreactive T cells were identified by the production of TNF-alpha after a 5-hour in vitro stimulation with alloantigen and were distinguished from effector/memory alloreactive T cells by the inability to produce IFN-gamma. Moreover, naive alloreactive T cells were not detected in mice tolerized against specific alloantigens. The frequency of TNF-alpha-producing cells was predictive for rejection in an in vivo cytotoxicity assay and correlated with skin allograft rejection. Naive alloreactive T cells were also detected in humans, suggesting clinical relevance. We conclude that rapid production of TNF-alpha can be used to quantify naive alloreactive T cells, that it is abrogated after the induction of tolerance, and that it is a potential tool to predict allograft rejection.

Development of tolerogenic strategies in the clinic

The study of tolerance in the clinic can be divided into three areas: (i) focused evaluation of existing tolerant transplant recipients as to their mechanism of tolerance; (ii) prospective tolerance trials, such as combined bone marrow and kidney transplantation as well as T cell depletion followed by subsequent weaning of immunosuppression; and (iii) immunologic assays to assess the likelihood of rejection or tolerance. Frankly, a very small number of patients have been transplanted with the intention of removing all immunosuppressive therapy, but several clinical trials with this aim are currently in progress, largely sponsored by the Immune Tolerance Network, a joint venture between the National Institutes of Health and the Juvenile Diabetes Research Foundation. Similarly, a reliable assay to assess tolerance has not yet been developed but a variety of approaches towards assessing rejection, and in some cases tolerance, are being developed. It would be accurate to state that many of the experimental and preclinical approaches to the induction of tolerance have resulted in better immunosuppression for human transplantation, but reliable tolerance strategies in humans have not yet been achieved. Combined bone marrow and kidney transplantation may be considered as one exception to this, but such a strategy is not generally applicable to the vast majority of solid organ transplant recipients. This review will summarize efforts to date, particularly focusing on kidney transplantation.