Progression from acute to chronic disease in a murine parent-into-F1 model of graft-versus-host disease

Follicular helper- and peripheral helper-like T cells drive autoimmune disease in human immune system mice

Human immune system (HIS) mice constructed in various ways are widely used for investigations of human immune responses to pathogens, transplants and immunotherapies. In HIS mice that generate T cells de novo from hematopoietic progenitors, T cell-dependent multisystem autoimmune disease occurs, most rapidly when the human T cells develop in the native NOD.Cg- Prkdc scid Il2rg tm1Wjl (NSG) mouse thymus, where negative selection is abnormal. Disease develops very late when human T cells develop in human fetal thymus grafts, where robust negative selection is observed. We demonstrate here that PD-1 + CD4 + peripheral (Tph) helper-like and follicular (Tfh) helper-like T cells developing in HIS mice can induce autoimmune disease. Tfh-like cells were more prominent in HIS mice with a mouse thymus, in which the highest levels of IgG were detected in plasma, compared to those with a human thymus. While circulating IgG and IgM antibodies were autoreactive to multiple mouse antigens, in vivo depletion of B cells and antibodies did not delay the development of autoimmune disease. Conversely, adoptive transfer of enriched Tfh- or Tph-like cells induced disease and autoimmunity-associated B cell phenotypes in recipient mice containing autologous human APCs without T cells. T cells from mice with a human thymus expanded and induced disease more rapidly than those originating in a murine thymus, implicating HLA-restricted T cell-APC interactions in this process. Since Tfh, Tph, autoantibodies and LIP have all been implicated in various forms of human autoimmune disease, the observations here provide a platform for the further dissection of human autoimmune disease mechanisms and therapies.

Murine models of graft versus host disease (GVHD): Focus on ocular GVHD

Graft versus host disease (GVHD) remains a major and serious complication of allogeneic hematopoietic stem cell transplantation. Based on the time of onset, clinical phenotypes, progression kinetics, and pathophysiology, GVHD is stratified into acute, chronic, and overlapping types. The eyes are among the most commonly affected organs in GVHD. Mouse models have played an important role in understanding the several key elements of GVHD pathobiology. The current review discusses the immunology, pathology, and key phenotypic features of mouse models of systemic GVHD. Furthermore, a critical appraisal of mouse models of ocular GVHD (oGVHD) is provided. The disease mechanisms underlying the ocular surface, meibomian gland, and lacrimal gland injury in these models are reviewed, and the relevance of oGVHD murine models to clinical oGVHD is also included.

TIGIT-Fc fusion protein alleviates murine lupus nephritis through the regulation of SPI-B-PAX5-XBP1 axis-mediated B-cell differentiation

OBJECTIVES

T cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif (ITIM) domain (TIGIT) is a newly discovered immune checkpoint (IC) that exhibits immunosuppressive function in the regulation of immune system. Activation of TIGIT signaling has emerged as a promising approach for autoimmune disease immunotherapy, such as systemic lupus erythematosus (SLE).

METHODS

We generated a chimeric protein, TIGIT-immunoglobulin (Ig), by fusing the extracellular domain of murine TIGIT to the Fc region of mouse IgG2a, which was used to investigated the effect of activating the TIGIT signaling in murine lupus models (MRL/lpr and chronic graft-versus-host disease mice). Treated mice were harvested, and samples of serum, kidney, and spleen were collected for outcome evaluation. In vitro treatment of TIGIT-Ig in B cells was used for exploring the roles of TIGIT in toll-like receptor 7 (TLR7)-mediated B cell differentiation and antibody production.

RESULTS

TIGIT-Ig treatment delayed disease progression in both lupus models, accompanied by a decrease in the production of anti-double stranded DNA antibodies (anti-dsDNA), proteinuria, proteinuria/creatinine, and Ig kidney deposition. Additionally, the group treated with TIGIT-Ig displayed a decreased proportion of T helper cell (Th)1 cells, T follicular helper (Tfh) cells, and B-cell subsets, including germinal center B cells (GC B), plasmablasts, and plasma cells, compared to the group treated with control IgG. Interestingly, we also observed an increased proportion of Tregs in the spleen of the TIGIT-Ig group. We have discovered a new way in which activating the TIGIT pathway can regulate B-cell differentiation through the SPI-B-PAX5-XBP1 pathway, resulting in a reduction in autoantibodies.

CONCLUSION

Together, TIGIT may be a promising IC target for SLE treatment.

Novel pre-clinical mouse models for chronic Graft-versus-Host Disease

Despite considerable progress in allogeneic hematopoietic cell transplantation (allo-HCT) has been achieved over the past years, chronic Graft-versus-Host Disease (cGvHD) still contributes to high morbidity rates, thus remaining a major hurdle in allo-HCT patients. To understand the complex pathophysiology of cGvHD and to develop refined prophylaxis and treatment strategies, improved pre-clinical models are needed. In this study, we developed two murine cGvHD models, which display high long-term morbidity but low mortality and depict the heterogeneous clinical manifestations of cGvHD seen in patients. We established a haploidentical C57BL/6→B6D2F1 allo-HCT model that uses myeloablative radiation and G-CSF-mobilized splenocytes as stem cell source and a sub-lethally irradiated Xenograft model, which utilizes the transfer of human peripheral blood mononuclear cells (PBMCs) into NOD scid gamma (NSG)-recipients. We characterized both mouse models to exhibit diverse clinical and histopathological signs of human cGvHD as extensive tissue damage, fibrosis/sclerosis, inflammation and B cell infiltration in cGvHD target organs skin, liver, lung and colon and found a decelerated immune cell reconstitution in the late phase after HCT. Our pre-clinical models can help to gain a deeper understanding of the target structures and mechanisms of cGvHD pathology and may enable a more reliable translation of experimental findings into the human setting of allo-HCT.

Adipose tissue-derived mesenchymal stem cells ameliorate bone marrow aplasia related with graft-versus-host disease in experimental murine models

Graft-versus-host disease (GVHD) constitutes the most frequent complications after the allogeneic hematopoietic stem cell transplantation for a variety of hematological malignancies. In the present study, we explored the prophylactic potential of adipose tissue-derived mesenchymal stem cells (AD-MSCs) in controlling GVHD in murine models with a special focus on bone marrow aplasia related with acute GVHD. The CB6F1 mice were induced GVHD by the injection intravenously of C57BL/6 (B6-Ly-5.1) splenocytes without conditioning irradiation or chemotherapy. AD-MSCs from C3H mice were injected intravenously via tail veins. GVHD was assessed using flowcytometry analysis of peripheral blood cells and histopathologic analysis of target organs. Histopathological analyses revealed that AD-MSCs markedly suppressed the infiltration of lymphocytes into liver as well as the aplasia in bone marrow. This study is the first to clarify the effectiveness of AD-MSCs against bone marrow aplasia in GVHD, supporting a rationale of AD-MSCs for ameliorating bone marrow suppression and infectivity after allo-HSCT in human clinics.

Salvianolic acid B ameliorates liver injury in a murine aGvHD model by decreasing inflammatory responses via upregulation of HO-1

Acute graft-versus-host disease (aGvHD) remains lethal, even after allogeneic hematopoietic stem cell transplantation. Inflammatory responses play an important role in aGvHD. Salvianolic acid B (Sal B) has been widely reported to have a major effect on the anti-inflammatory response, but these effects in an aGvHD model have never been reported. B6 donor splenocytes were transplanted into unirradiated BDF1 recipients and liver and serum were collected on day 14 after transplantation with or without Sal B administration. We measured the expression of pro-inflammatory cytokines and chemokines and other manifestations in aGvHD mice after Sal B treatment. Sal B ameliorated liver injury in aGvHD and promoted survival in mice. Sal B treatment resulted in decreased expression of pro-inflammatory cytokines and chemokines whose expressions in liver are normally elevated by aGvHD. Furthermore, Sal B treatment also enhanced PGC-1α expression in liver tissue and HO-1 expression in nonparenchymal cells. In addition, HO-1 inhibitor abrogated the improvement of survival rate of mice with aGvHD. These results indicated that the protective effect of Sal B relies on suppressing the inflammatory response phase in the aGvHD model, presumably by inducing HO-1. Taken together our data showed that Sal B ameliorates liver injury in aGvHD by decreasing inflammatory responses via upregulation of HO-1. It may provide a novel way to deal with this disease.

The immunosuppressive effect of the tick protein, Salp15, is long-lasting and persists in a murine model of hematopoietic transplant

Salp15, a salivary protein of Ixodes ticks, inhibits the activation of naïve CD4 T cells. Treatment with Salp15 results in the inhibition of early signaling events and the production of the autocrine growth factor, interleukin-2. The fate of the CD4 T cells activated in the presence of Salp15 or its long-term effects are, however, unknown. We now show that Salp15 binding to CD4 is persistent and induces a long-lasting immunomodulatory effect. The activity of Salp15 results in sustained diminished cross-antigenic antibody production even after interruption of the treatment with the protein. Transcriptionally, the salivary protein provokes an acute effect that includes known activation markers, such as Il2 or Cd44, and that fades over time. The long-term effects exerted by Salp15 do not involve the induction of either anergy traits nor increased populations of regulatory T cells. Similarly, the treatment with Salp15 does not result in B cell anergy or the generation of myeloid suppressor cells. However, Salp15 induces the increased expression of the ectoenzyme, CD73, in regulatory T cells and increased production of adenosine. Our study provides a profound characterization of the immunomodulatory activity of Salp15 and suggests that its long-term effects are due to the specific regulation of CD73.

A Canine Model of Chronic Graft-versus-Host Disease

In long-term survivors of allogeneic hematopoietic cell transplantation (HCT), chronic graft-versus-host disease (GVHD) is the major cause of morbidity and mortality and a major determinant of quality of life. Chronic GVHD responds poorly to current immunosuppressive drugs, and while T cell depletion may be preventive, this gain is offset by increased relapse rates. A significant impediment to progress in treating chronic GVHD has been the limitations of existing animal models. The goal of this study was to develop a reproducible comprehensive model of chronic GVHD in the dog. Ten recipient dogs received 920 cGy total body irradiation, infusion of marrow, and an infusion of buffy coat cells from a dog leukocyte antigen (DLA)-mismatched unrelated donor. Postgrafting immunosuppression consisted of methotrexate (days 1, 3, 6, 11) and cyclosporine. The duration of cyclosporine administration was limited to 80 days instead of the clinically used 180 days. This was done to contain costs, as chronic GVHD was expected to develop at earlier time points. All recipients were given ursodiol for liver protection. One dog had graft failure and 9 dogs showed stable engraftment. Eight of the 9 developed de novo chronic GVHD. Dogs progressed with clinical signs of chronic GVHD over a period of 43 to 164 (median, 88) days after discontinuation of cyclosporine. Target organs showed the spectrum of chronic GVHD manifestations that are typically seen clinically. These included lichenoid changes of the skin, fasciitis, ocular involvement (xerophthalmia), conjunctivitis, bronchiolitis obliterans, salivary gland involvement, gingivitis, esophageal involvement, and hepatic involvement. Peripheral blood lymphocyte surface antigen expression of CD28 and inducible costimulator was elevated in dogs with GHVD compared with those in normal dogs, but not significantly so. Serum levels of IL-8 and monocyte chemotactic protein-1 in GVHD-affected dogs at time of euthanasia were elevated, whereas levels of IL-15 were depressed compared with those in normal dogs. Results indicate that the canine model is well suited for future studies aimed at preventing or treating chronic GVHD.

The Role of Animal Models in the Study of Hematopoietic Stem Cell Transplantation and GvHD: A Historical Overview

Bone marrow transplantation (BMT) is the only therapeutic option for many hematological malignancies, but its applicability is limited by life-threatening complications, such as graft-versus-host disease (GvHD). The last decades have seen great advances in the understanding of BMT and its related complications; in particular GvHD. Animal models are beneficial to study complex diseases, as they allow dissecting the contribution of single components in the development of the disease. Most of the current knowledge on the therapeutic mechanisms of BMT derives from studies in animal models. Parallel to BMT, the understanding of the pathophysiology of GvHD, as well as the development of new treatment regimens, has also been supported by studies in animal models. Pre-clinical experimentation is the basis for deep understanding and successful improvements of clinical applications. In this review, we retrace the history of BMT and GvHD by describing how the studies in animal models have paved the way to the many advances in the field. We also describe how animal models contributed to the understanding of GvHD pathophysiology and how they are fundamental for the discovery of new treatments.

Immunotherapeutic targeting of LIGHT/LTβR/HVEM pathway fully recapitulates the reduced cytotoxic phenotype of LIGHT-deficient T cells

Tumor necrosis factor (TNF)/TNF receptor (TNFR) superfamily members play essential roles in the development of the different phases of the immune response. Mouse LIGHT (TNFSF14) is a type II transmembrane protein with a C-terminus extracellular TNF homology domain (THD) that assembles in homotrimers and regulates the course of the immune responses by signaling through 2 receptors, the herpes virus entry mediator (HVEM, TNFRSF14) and the lymphotoxin β receptor (LTβR, TNFRSF3). LIGHT is a membrane-bound protein transiently expressed on activated T cells, natural killer (NK) cells and immature dendritic cells that can be proteolytically cleaved by a metalloprotease and released to the extracellular milieu. The immunotherapeutic potential of LIGHT blockade was evaluated in vivo. Administration of an antagonist of LIGHT interaction with its receptors attenuated the course of graft-versus-host reaction and recapitulated the reduced cytotoxic activity of LIGHT-deficient T cells adoptively transferred into non-irradiated semiallogeneic recipients. The lack of LIGHT expression on donor T cells or blockade of LIGHT interaction with its receptors slowed down the rate of T cell proliferation and decreased the frequency of precursor alloreactive T cells, retarding T cell differentiation toward effector T cells. The blockade of LIGHT/LTβR/HVEM pathway was associated with delayed downregulation of interleukin-7Rα and delayed upregulation of inducible costimulatory molecule expression on donor alloreactive CD8 T cells that are typical features of impaired T cell differentiation. These results expose the relevance of LIGHT/LTβR/HVEM interaction for the potential therapeutic control of the allogeneic immune responses mediated by alloreactive CD8 T cells that can contribute to prolong allograft survival.

Inhibition of BTK and ITK with Ibrutinib Is Effective in the Prevention of Chronic Graft-versus-Host Disease in Mice

Bruton’s Tyrosine Kinase (BTK) and IL-2 Inducible T-cell Kinase (ITK) are enzymes responsible for the phosphorylation and activation of downstream effectors in the B-cell receptor (BCR) signaling and T cell receptor (TCR) signaling pathways, respectively. Ibrutinib is an FDA-approved potent inhibitor of both BTK and ITK that impairs B-cell and T-cell function. CD4 T cells and B cells are essential for the induction of chronic graft-versus-host disease (cGVHD). We evaluated these targets by testing the ability of Ibrutinib to prevent or ameliorate cGVHD, which is one of the major complications for patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). We found that Ibrutinib significantly alleviated cGVHD across four different mouse models, accompanied by increased long-term survival and reduced clinical score. The clinical improvements in Ibrutinib-treated recipients were associated with decreased serum-autoantibodies, costimulatory molecule activation, B-cell proliferation, and glomerulonephritis compared to vehicle controls. Ibrutinib was also able to alleviate the clinical manifestations in acute GVHD (aGVHD), where the recipients were given grafts with or without B cells, suggesting that an inhibitory effect of Ibrutinib on T cells contributes to a reduction in both aGVHD and cGVHD pathogenesis. An effective prophylactic regimen is still lacking to both reduce the incidence and severity of human cGVHD following allo-HSCT. Our study shows that Ibrutinib is an effective prophylaxis against several mouse models of cGVHD with minimal toxicity and could be a promising strategy to combat human cGVHD clinically.

Thiol/redox metabolomic profiling implicates GSH dysregulation in early experimental graft versus host disease (GVHD)

Graft-versus-host disease (GVHD) is a common complication of allogeneic bone marrow transplantation (BMT). Upregulation of inflammatory cytokines precedes the clinical presentation of GVHD and predicts its severity. In this report, thiol/redox metabolomics was used to identify metabolic perturbations associated with early preclinical (Day+4) and clinical (Day+10) stages of GVHD by comparing effects in Syngeneic (Syn; major histocompatibility complex- identical) and allogeneic transplant recipients (Allo BMT) in experimental models. While most metabolic changes were similar in both groups, plasma glutathione (GSH) was significantly decreased, and GSH disulfide (GSSG) was increased after allogeneic compared to syngeneic recipient and non-transplant controls. The early oxidation of the plasma GSH/GSSG redox couple was also observed irrespective of radiation conditioning treatment and was accompanied by significant rise in hepatic protein oxidative damage and ROS generation. Despite a significant rise in oxidative stress, compensatory increase in hepatic GSH synthesis was absent following Allo BMT. Early shifts in hepatic oxidative stress and plasma GSH loss preceded a statistically significant rise in TNF-α. To identify metabolomic biomarkers of hepatic GVHD injury, plasma metabolite concentrations analyzed at Day+10 were correlated with hepatic organ injury. GSSG (oxidized GSH) and β-alanine, were positively correlated, and plasma GSH cysteinylglycine, and branched chain amino acids were inversely correlated with hepatic injury. Although changes in plasma concentrations of cysteine, cystathionine (GSH precursors) and cysteinylglycine (a GSH catabolite) were not significant by univariate analysis, principal component analysis (PCA) indicated that accumulation of these metabolites after Allo BMT contributed significantly to early GVHD in contrast to Syn BMT. In conclusion, thiol/redox metabolomic profiling implicates that early dysregulation of host hepatic GSH metabolism and oxidative stress in sub-clinical GVHD before elevated TNF-α levels is associated with GVHD pathogenesis. Future studies will probe the mechanisms for these changes and examine the potential of antioxidant intervention strategies to modulate GVHD.

Rosiglitazone prevents graft-versus-host disease (GVHD)

The effect of rosiglitazone, an agonist of peroxisome proliferator-activated receptor-γ (PPARγ), was investigated in a mouse parent-to-F1 GVHD model. Rosiglitazone inhibited mixed lymphocyte reactions, inducing enhanced apoptosis in CD4+, CD8+, and B220+ cells, but not in NK1.1+, Mac-1+, CD4+/CD25+ and CD3+/NK1.1+ cells. Rosiglitazone administration prevented GVHD in the liver, skin, spleen and intestine. Rosiglitazone inhibited GVHD-induced increases in serum levels of tumor necrosis factor-alpha, interferon-gamma, interleukin (IL)-6, and IL-12, and the GVHD-induced decreases in transforming growth factor-beta and IL-10. Immunophenotyping of splenic leukocytes demonstrated that while rosiglitazone treatment increased the population percentages of both donor and host CD4+/CD25+ and CD3+/NK1.1+ cells, the treatment resulted in lower fractions of both donor and host CD8+ cells. Rosiglitazone inhibited the GVHD-induced decreases in the expression of phosphatase and tensin homologue deleted on chromosome 10 (PTEN), as well as the GVHD-induced increase in the splenic p-Akt and nuclear factor-kappa B expression. These results indicate that rosiglitazone and PPARγ activation may be useful in protecting the host from GVHD.

T cells, murine chronic graft-versus-host disease and autoimmunity

The chronic graft-versus-host disease (cGVHD) in mice is characterized by the production of autoantibodies and immunopathology characteristic of systemic lupus erythematosus (lupus). The basic pathogenesis involves the cognate recognition of foreign MHC class II of host B cells by alloreactive CD4 T cells from the donor. CD4 T cells of the host are also necessary for the full maturation of host B cells before the transfer of donor T cells. CD8 T cells play critical roles as well. Donor CD8 T cells that are highly cytotoxic can ablate or prevent the lupus syndrome, in part by killing recipient B cells. Host CD8 T cells can reciprocally downregulate donor CD8 T cells, and thus prevent them from suppressing the autoimmune process. Thus, when the donor inoculum contains both CD4 T cells and CD8 T cells, the resultant syndrome depends on the balance of activities of these various cell populations. For example, in one cGVHD model (DBA/2(C57BL/6xDBA/2)F1, the disease is more severe in females, as it is in several of the spontaneous mouse models of lupus, as well as in human disease. The mechanism of this female skewing of disease appears to depend on the relative inability of CD8 cells of the female host to downregulate the donor CD4 T cells that drive the autoantibody response. In general, then, the abnormal CD4 T cell help and the modulating roles of CD8 T cells seen in cGVHD parallel the participation of T cells in genetic lupus in mice and human lupus, although these spontaneous syndromes are presumably not driven by overt alloreactivity.

Selective blockade of herpesvirus entry mediator-B and T lymphocyte attenuator pathway ameliorates acute graft-versus-host reaction

The cosignaling network mediated by the herpesvirus entry mediator (HVEM; TNFRSF14) functions as a dual directional system that involves proinflammatory ligand, lymphotoxin that exhibits inducible expression and competes with HSV glycoprotein D for HVEM, a receptor expressed by T lymphocytes (LIGHT; TNFSF14), and the inhibitory Ig family member B and T lymphocyte attenuator (BTLA). To dissect the differential contributions of HVEM/BTLA and HVEM/LIGHT interactions, topographically-specific, competitive, and nonblocking anti-HVEM Abs that inhibit BTLA binding, but not LIGHT, were developed. We demonstrate that a BTLA-specific competitor attenuated the course of acute graft-versus-host reaction in a murine F(1) transfer semiallogeneic model. Selective HVEM/BTLA blockade did not inhibit donor T cell infiltration into graft-versus-host reaction target organs, but decreased the functional activity of the alloreactive T cells. These results highlight the critical role of HVEM/BTLA pathway in the control of the allogeneic immune response and identify a new therapeutic target for transplantation and autoimmune diseases.

The parent-into-F1 murine model in the study of lupus-like autoimmunity and CD8 cytotoxic T lymphocyte function

The transfer of homozygous C57Bl/6 (B6) or DBA/2 (DBA) parental strain T cells into normal B6D2F1 mice in the parent-into-F1 (p → F1) model results in a graft-vs.-host disease (GVHD) that takes one of the following two forms: (a) acute GVHD seen with B6 → F1 mice and mediated by donor CD8 cytotoxic T cells that eliminate host lymphocytes and (b) a chronic lupus-like GVHD seen with DBA → F1 mice and mediated by donor CD4 T cell cognate help to autoreactive B cells resulting in autoantibody production and renal disease similar to human lupus. Importantly, these two phenotypes can be distinguished by flow cytometry as early as 2 weeks after donor cell transfer. The p → F1 model can be used to screen for agents that alter lupus development. Additionally, the model is useful for preclinical screening of biologic agents with immunomodulatory potential. Agents that selectively inhibit CD8 T cell function will convert acute GVHD to chronic GVHD in B6 → F1 mice. Conversely, agents that promote CD8 CTL function will convert chronic GVHD to acute GVHD in DBA → F1 mice. Agents that completely suppress T cell function will block both phenotypes. The model is also useful for examining the effects of T cell mutations by transferring mutant T cells into wild-type hosts and assessing the effects on disease phenotype. Differences observed from wild-type T cells → F1 can be directly ascribed to alterations in mutant T cell function. Because of the early 2-week phenotype development, the p → F1 model is well suited to screening of potential immunomodulatory therapeutic compounds and the assessment of T cell mutations on in vivo function.

B- and T-lymphocyte attenuator targeting protects against the acute phase of graft versus host reaction by inhibiting donor anti-host cytotoxicity

BACKGROUND

B- and T-lymphocyte attenuator (BTLA) functions as a coinhibitory/costimulatory molecule that belongs to the immunoglobulin superfamily and exhibits a pattern of expression restricted to the hematopoietic compartment. Engagement of BTLA by its ligand, herpes virus entry mediator (HVEM), delivers negative signals to T cells, whereas engagement of HVEM receptor on T cells by surface BTLA expressed on other immune cells costimulates T activation. Previous work has reported that parental donor BTLA knock-out or HVEM knock-out T cells adoptively transferred into nonirradiated F1 recipient mice survived poorly, and the rejection of host hematopoietic cells was attenuated compared with F1 recipients receiving wild-type T cells.

METHODS

Parent into nonirradiated immunocompetent F1 murine model of acute graft versus host reaction, which is induced with the adoptive transfer of splenocytes from donor B6 mice (H-2(b)) into F1 recipients (BALB/c×B6, H-2(d/b)), was used as an experimental approach to test the therapeutic effect of targeting BTLA during the course of an allogeneic immune response.

RESULTS

We herein provide evidence that administration of an anti-BTLA monoclonal antibody leads to significant reduction of donor anti-host allogeneic immune response against bone marrow and thymus during the acute phase of graft versus host reaction in a parent into nonirradiated F1 murine model of alloreactivity. Anti-BTLA protection against donor anti-host hematopoietic cell rejection correlated with impaired anti-host cytotoxic T-lymphocyte activity than reduction in T-cell number infiltrating host tissues.

CONCLUSIONS

These findings place BTLA receptor as a potential immunoregulatory target for the modulation of cytotoxic T-lymphocyte-mediated alloresponses.

Mouse models of graft-versus-host disease: advances and limitations

The limiting factor for successful hematopoietic stem cell transplantation (HSCT) is graft-versus-host disease (GvHD), a post-transplant disorder that results from immune-mediated attack of recipient tissue by donor T cells contained in the transplant. Mouse models of GvHD have provided important insights into the pathophysiology of this disease, which have helped to improve the success rate of HSCT in humans. The kinetics with which GvHD develops distinguishes acute from chronic GvHD, and it is clear from studies of mouse models of GvHD (and studies of human HSCT) that the pathophysiology of these two forms is also distinct. Mouse models also further the basic understanding of the immunological responses involved in GvHD pathology, such as antigen recognition and presentation, the involvement of the thymus and immune reconstitution after transplantation. In this Perspective, we provide an overview of currently available mouse models of acute and chronic GvHD, highlighting their benefits and limitations, and discuss research and clinical opportunities for the future.

Donor CD8 T cells and IFN-gamma are critical for sex-based differences in donor CD4 T cell engraftment and lupus-like phenotype in short-term chronic graft-versus-host disease mice

The transfer of unfractionated DBA/2J (DBA) splenocytes into B6D2F(1) (DBA → F(1)) mice results in greater donor CD4 T cell engraftment in females at day 14 that persists long-term and mediates greater female lupus-like renal disease. Although donor CD8 T cells have no demonstrated role in lupus pathogenesis in this model, we recently observed that depletion of donor CD8 T cells prior to transfer eliminates sex-based differences in renal disease long-term. In this study, we demonstrate that greater day 14 female donor CD4 engraftment is also critically dependent on donor CD8 T cells. Male DBA → F(1) mice exhibit stronger CD8-dependent day 8-10 graft-versus-host (GVH) and counter-regulatory host-versus-graft (HVG) responses, followed by stronger homeostatic contraction (days 10-12). The weaker day 10-12 GVH and HVG in females are followed by persistent donor T cell activation and increasing proliferation, expansion, and cytokine production from days 12 to 14. Lastly, greater female day 14 donor T cell engraftment, activation, and cytokine production were lost with in vivo IFN-γ neutralization from days 6 to 14. We conclude the following: 1) donor CD8 T cells enhance day 10 proliferation of donor CD4 T cells in both sexes; and 2) a weaker GVH/HVG in females allows prolonged survival of donor CD4 and CD8 T cells, allowing persistent activation. These results support the novel conclusion that sex-based differences in suboptimal donor CD8 CTL activation are critical for shaping sex-based differences in donor CD4 T cell engraftment at 2 wk and lupus-like disease long-term.

Characterization of murine non-adherent bone marrow cells leading to recovery of endogenous hematopoiesis

Non-adherent bone marrow-derived cells (NA-BMCs) are a mixed cell population that can give rise to multiple mesenchymal phenotypes and that facilitates hematopoietic recovery. We characterized NA-BMCs by flow cytometry, fibroblast colony-forming units (CFU-f), real-time PCR, and in in vivo experiments. In comparison to adherent cells, NA-BMCs expressed high levels of CD11b(+) and CD90(+) within the CD45(+) cell fraction. CFU-f were significantly declining over the cultivation period, but NA-BMCs were still able to form CFU-f after 5 days. Gene expression analysis of allogeneic NA-BMCs compared to bone marrow (BM) indicates that NA-BMCs contain stromal, mesenchymal, endothelial cells and monocytes, but less osteoid, lymphoid, and erythroid cells, and hematopoietic stem cells. Histopathological data and analysis of weight showed an excellent recovery and organ repair of lethally irradiated mice after NA-BMC transplantation with a normal composition of the BM.

Implications of the parent-into-F1 model for human lupus pathogenesis: roles for cytotoxic T lymphocytes and viral pathogens

PURPOSE OF REVIEW

The central role of CD4 T cells in lupus pathogenesis is well recognized; however, the mechanism by which CD4 T cells lose tolerance and promote humoral autoimmunity remains unclear. This review examines mechanisms elucidated in the parent-into-F1 model of lupus and their possible parallels in human lupus pathogenesis.

RECENT FINDINGS

In the parent-into-F1 model, lupus results from the transfer of normal, foreign reactive CD4 T cells targeted to intrinsically normal F1 B cells. Transfer of normal CD8 T cells prevents lupus, whereas transfer of CD8 T cells with killing defects does not but is correctable with additional in-vivo enhancement of CD8 cytotoxic T lymphocyte (CTL) function. The parent-into-F1 model has two major similarities to Epstein-Barr virus infection: CD4 T-cell-driven polyclonal B-cell hyperactivity and a critical dependence on CD8 CTL for elimination of activated B cells. These similarities are discussed in relation to human lupus pathogenesis.

SUMMARY

Work in the parent-into-F1 model supports the idea that lupus may result from defective CD8 T-cell function and that therapeutic enhancement of CD8 effectors with selective targeting to autoreactive B cells may be beneficial. Despite strong evidence linking Epstein-Barr virus infection with human lupus, the exact nature of this link requires further study.

Subclinical GvHD in non-irradiated F1 hybrids: severe lymphoid-tissue GvHD causing prolonged immune dysfunction

GvHD is an important complication of allogeneic hematopoietic SCT. Parent-in-F1 models are frequently used to study GvHD immunobiology; the characteristics of parent-in-F1 GvHD vary between strain combinations and induction protocols. Here, we observed that a high-dose challenge of non-irradiated B6DBA2F1 and B6SJLF1 recipients with C57BL/6 splenocytes left the majority of recipients clinically healthy, while inducing progressive high-grade donor T-cell chimerism. We investigated this previously undescribed pattern of parent-in-F1 T-cell alloreactivity and studied the effect of serial parental splenocyte infusions on epithelial and lymphohematopoietic tissues. The majority of recipients of 4 weekly splenocyte infusions showed long-term survival with gradual establishment of high-grade donor chimerism and without any signs of epithelial-tissue GvHD. A minority of recipients showed BM failure type of GvHD and, respectively, graft rejection. Moreover, long-term F1 chimeras showed protracted pancytopenia, and in peripheral lymphoid tissues severe lymphopenia and near-complete eradication of APCs and dysfunction in antigen-presenting capacity in remaining APC. Hematopoiesis and lymphoid tissue composition recovered only after multilineage donor chimerism had established. In conclusion, we report on a novel type of parent-in-F1 hybrid GvHD, where a cumulative high dose of C57BL/6 parental splenocytes in non-irradiated F1 mice induces subclinical but severe hematolymphoid-tissue GvHD, causing prolonged immuno-incompetence.

Slow down and survive: Enigmatic immunoregulation by BTLA and HVEM

B and T lymphocyte associated (BTLA) is an Ig domain superfamily protein with cytoplasmic immunoreceptor tyrosine-based inhibitory motifs. Its ligand, herpesvirus entry mediator (HVEM), is a tumor necrosis factor receptor superfamily member. The unique interaction between BTLA and HVEM allows for a system of bidirectional signaling that must be appropriately regulated to balance the outcome of the immune response. HVEM engagement of BTLA produces inhibitory signals through SH2 domain-containing protein tyrosine phosphatase 1 (Shp-1) and Shp-2 association, whereas BTLA engagement of HVEM produces proinflammatory signals via activation of NF-kappaB. The BTLA-HVEM interaction is intriguing and quite complex given that HVEM has four other ligands that also influence immune responses, the conventional TNF ligand LIGHT and lymphotoxin alpha, as well as herpes simplex virus glycoprotein D and the glycosylphosphatidylinositol-linked Ig domain protein CD160. BTLA-HVEM interactions have been shown to regulate responses in several pathogen and autoimmune settings, but our understanding of this complex system of interactions is certainly incomplete. Recent findings of spontaneous inflammation in BTLA-deficient mice may provide an important clue.

Advances in lupus stemming from the parent-into-F1 model

The parent-into-F1 model has led to important advances in our understanding of lupus. Here, we review the work in murine lupus that elucidated the role of T cells and supported the conclusion that the parent-into-F1 model of induced lupus compares favorably with de facto gold standard spontaneous models of lupus. Then we focus on recent work in parent-into-F1 mice, which has yielded novel insights into unresolved controversies, such as the role of apoptosis in the pathogenesis of lupus and lupus in patients receiving TNF blockade. Finally, the review considers the evidence that supports a potential role for CD8 T cells, both cytotoxic and memory cells, in mediating disease remission.

Defective in vitro IL-2 production in lupus is an early but secondary event paralleling disease activity: evidence from the murine parent-into-F1 model supports staging of IL-2 defects in human lupus

T cell defects are a well described feature of both human and murine lupus however their exact significance is unclear. Evidence from an induced model of lupus, the P --> F1 model of chronic lupus-like GVHD demonstrates that a secondary inducible T cell defect in in vitro IL-2 and CTL responses occurs early in the course of lupus-like disease and well in advance of clinical disease. Defective Th cell function was probed using a novel approach categorizing the response to two stimuli:1) the MHC self restricted response, termed self +X; and 2) the allogeneic response. Using this approach, lupus mice exhibited similar in vitro Th cell pattern i.e. an absent S+X response but preserved allogeneic (termed -/+). In contrast, human lupus patients exhibited three possible response patterns, +/+, - /+ or -/- with more severe in vitro T cell impairment correlated with more severe disease. Similarly, patients with other T cell mediated conditions i.e. HIV infection or renal allograft recipients, also exhibited more severe in vitro T cell impairment with greater disease activity or greater immunosuppression respectively. The similar Th response patterns in human and murine T cell mediated conditions indicates that the underlying mechanisms involved are not disease specific but instead reflect common immune responses and validate the use of the P --> F1 model for future studies of T cell mediated conditions. These results support the use of prospective monitoring of IL-2 responses in lupus patients. Successful adaptation of this approach to the clinical setting could allow not only earlier therapeutic intervention and reduced organ damage but also earlier tapering of pharmacological agents and reduced untoward effects.

Allogeneic non-adherent bone marrow cells facilitate hematopoietic recovery but do not lead to allogeneic engraftment

Background

Non adherent bone marrow derived cells (NA-BMCs) have recently been described to give rise to multiple mesenchymal phenotypes and have an impact in tissue regeneration. Therefore, the effects of murine bone marrow derived NA-BMCs were investigated with regard to engraftment capacities in allogeneic and syngeneic stem cell transplantation using transgenic, human CD4⁺, murine CD4^−/−, HLA-DR3⁺ mice.

Methodology/Principal Findings

Bone marrow cells were harvested from C57Bl/6 and Balb/c wild-type mice, expanded to NA-BMCs for 4 days and characterized by flow cytometry before transplantation in lethally irradiated recipient mice. Chimerism was detected using flow cytometry for MHC-I (H-2D[b], H-2K[d]), mu/huCD4, and huHLA-DR3). Culturing of bone marrow cells in a dexamethasone containing DMEM medium induced expansion of non adherent cells expressing CD11b, CD45, and CD90. Analysis of the CD45⁺ showed depletion of CD4⁺, CD8⁺, CD19⁺, and CD117⁺ cells. Expanded syngeneic and allogeneic NA-BMCs were transplanted into triple transgenic mice. Syngeneic NA-BMCs protected 83% of mice from death (n = 8, CD4⁺ donor chimerism of 5.8±2.4% [day 40], P<.001). Allogeneic NA-BMCs preserved 62.5% (n = 8) of mice from death without detectable hematopoietic donor chimerism. Transplantation of syngeneic bone marrow cells preserved 100%, transplantation of allogeneic bone marrow cells 33% of mice from death.

Conclusions/Significance

NA-BMCs triggered endogenous hematopoiesis and induced faster recovery compared to bone marrow controls. These findings may be of relevance in the refinement of strategies in the treatment of hematological malignancies.

Mouse models of bone marrow transplantation

Over the last 50 years, mouse models of bone marrow transplantation have provided the critical links between graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) pathophysiology and clinical practice. The initial insight from mouse models that GVHD and GVL were T cell dependent has long been confirmed clinically. More recent translations from mouse models have included the important role of inflammatory cytokines in GVHD. Newly developed concepts relating to the ability of antigen presenting cell (APC) and T cell subsets to mediate GVHD now promise significant clinical advances. The ability to use knockout and transgenic approaches to dissect mechanisms of GVHD and GVL mean that mouse systems will continue as the predominant preclinical platform. The basic transplant approach in these models, coupled with modern "real-time" immunologic imaging of GVHD and GVL is discussed.

CTL-promoting effects of CD40 stimulation outweigh B cell-stimulatory effects resulting in B cell elimination and disease improvement in a murine model of lupus

CD40/CD40L signaling promotes both B cell and CTL responses in vivo, the latter being beneficial in tumor models. Because CTL may also limit autoreactive B cell expansion in lupus, we asked whether an agonist CD40 mAb would exacerbate lupus due to B cell stimulation or would improve lupus due to CTL promotion. These studies used an induced model of lupus, the parent-into-F1 model in which transfer of DBA/2 splenocytes into B6D2F1 mice induces chronic lupus-like graft-vs-host disease (GVHD). Although agonist CD40 mAb treatment of DBA-->F1 mice initially exacerbated B cell expansion, it also strongly promoted donor CD8 T cell engraftment and cytolytic activity such that by 10 days host B cells were eliminated consistent with an accelerated acute GVHD. CD40 stimulation bypassed the requirement for CD4 T cell help for CD8 CTL possibly by licensing dendritic cells (DC) as shown by the following: 1) greater initial activation of donor CD8 T cells, but not CD4 T cells; 2) earlier activation of host DC; 3) host DC expansion that was CD8 dependent and CD4 independent; and 4) induction of acute GVHD using CD4-depleted purified DBA CD8+ T cells. A single dose of CD40 mAb improved lupus-like renal disease at 12 wk, but may not suffice for longer periods consistent with a need for continuing CD8 CTL surveillance. These results demonstrate that in the setting of lupus-like CD4 T cell-driven B cell hyperactivity, CTL promotion is both feasible and beneficial and the CTL-promoting properties of CD40 stimulation outweigh the B cell-stimulatory properties.

The influence of CD4 T-cell subsets on control of CD4 T-cell-mediated graft-versus-host disease

In this study, we tested the effect of different T-cell subpopulations on antigen driven effector cell expansion in lymphopenic hosts, making use of an experimental model of graft-versus-host disease (GVHD). Fluorescence-activated cell sorted (FACS) naïve CD4 T cells from C57BL/6 mice, transferred into lymphopenic F1 (C57BL/6 x BALB/c) Rag-deficient hosts, proliferated extensively and migrated systemically causing acute GVHD within 4 weeks after transfer. Adoptive hosts of CD4 memory T cells on the other hand developed milder symptoms of GVHD with later onset. T-cell expansion and migration to peripheral sites as well as development of GVHD were prevented when naïve T cells were transferred together with CD4(+) CD25(+) T cells, but co-transfer of memory T cells with naïve T cells could not prevent GVHD, although its onset was delayed. OX40, a costimulatory marker that is upregulated at an early time point after T-cell activation and enhances T-cell proliferation, cytokine secretion and survival, was strongly upregulated during GVH responses. Naïve T cells deficient in OX40 expression caused markedly reduced GVH in onset and severity despite some level of expansion in the adoptive host, suggesting an important role of this molecule in the immune pathology of GVHD.

Murine models of chronic graft-versus-host disease: insights and unresolved issues

Chronic graft-versus-host-disease (cGVHD) is a major barrier to successful allogeneic hematopoietic stem cell transplantation (allo-HSCT), with highly variable clinical presentations. The pathophysiology of cGVHD remains relatively poorly understood. The utilization of murine models to study cGVHD encompasses experimental challenges distinct from those that have been successfully used to study acute GVHD (aGVHD). Nevertheless, despite these challenges, murine models of cGVHD have contributed to the understanding of cGVHD, and highlight its mechanistic complexity. In this article, insights into the pathophysiology of cGVHD obtained from murine studies are summarized in the context of their relevancy to clinical cGVHD. Despite experimental limitations, current and future models of murine cGVHD will continue to provide insights into the understanding of clinical cGVHD and provide information for new therapeutic interventions.

Blockade of chronic graft-versus-host disease by alloantigen-induced CD4+CD25+Foxp3+ regulatory T cells in nonlymphopenic hosts

CD4(+)CD25(+) regulatory T cells (Tregs) are well known to suppress immunopathology induced in lymphopenic animals following T cell reconstitution, including acute graft-versus-host disease (GVHD) post-bone marrow transplantation. The regulatory potential of this subset in nonlymphopenic hosts and in chronic, Th2-mediated GVHD is less clear. We have generated alloantigen-specific cells from CD4(+)CD25(+) populations stimulated with MHC-disparate dendritic cells and found them to express a stable Treg forkhead box p3(+) phenotype with enhanced suppressive activity mediated by cell contact. When transferred into nonlymphopenic F1 hosts, nonspecific Tregs proliferated as rapidly as CD4(+)CD25(-) cells but displayed distinct growth kinetics in vitro. Tregs, expanded in response to alloantigen in vitro, displayed greatly enhanced suppressive activity, which was partially antigen-specific. They were effective inhibitors of chronic GVHD, blocking donor cell engraftment, splenomegaly, autoantibody production, and glomerulonephritis. CD25(+) and CD25(-) cells were equally susceptible to inhibition by immunosuppressive drugs targeting TCR signaling and rapamycin, but Tregs were resistant to inhibition by dexamethasone. The data indicate that alloantigen-driven expansion, rather than homeostatic proliferation, is key to the effectiveness of CD4(+)CD25(+) Tregs in GVHD and suggest that cellular therapy with alloantigen-induced Tregs in combination with glucocorticoid treatment would be effective in prevention of chronic GVHD after immune reconstitution.

Unexpected role of B and T lymphocyte attenuator in sustaining cell survival during chronic allostimulation

B and T lymphocyte attenuator (BTLA; CD272) can deliver inhibitory signals to B and T cells upon binding its ligand herpesvirus entry mediator. Because CD28, CTLA-4, programmed death-1, and ICOS regulate the development of acute graft-vs-host disease (GVHD), we wished to assess if BTLA also played a role in this T cell-mediated response. In the nonirradiated parental-into-F1 model of acute GVHD, BTLA+/+ and BTLA-/- donor lymphocytes showed equivalent engraftment and expansion during the first week of the alloresponse. Unexpectedly, BTLA-/- donor T cells failed to sustain GVHD, showing a decline in surviving donor cell numbers beginning at day 9 and greatly reduced by day 11. Similarly, inhibition of BTLA-herpesvirus entry mediator engagement by in vivo administration of a blocking anti-BTLA Ab also caused reduced survival of donor cells. Microarray analysis revealed several genes that were differentially expressed by BTLA-/- and BTLA+/+ donor CD4+ T cells preceding the decline in BTLA-/- donor T cells. Several genes influencing Th cell polarization were differentially expressed by BTLA+/+ and BTLA-/- donor cells. Additionally, the re-expression of the IL-7Ralpha subunit that occurs in BTLA+/+ donor cells after 1 wk of in vivo allostimulation was not observed in BTLA-/- donor CD4+ cells. The striking loss of BTLA-/- T cells in this model indicates a role for BTLA activity in sustaining CD4+ T cell survival under the conditions of chronic stimulation in the nonirradiated parental-into-F1 GVHD.

Allogeneic bone marrow transplantation in models of experimental autoimmune encephalomyelitis: evidence for a graft-versus-autoimmunity effect

Autologous hematopoietic stem cell transplantation (HSCT) is being explored in the treatment of severe multiple sclerosis (MS), and is based on the concept of "resetting" the immune system. The use of allogeneic HSCT may offer additional advantages, such as the replacement of the autoreactive immune compartment by healthy allogeneic cells and development of a graft-versus-autoimmunity (GVA) effect. However, in clinical practice, the genetic susceptibility to MS of allogeneic stem cell donors is generally unknown, and GVA may therefore be an important mechanism of action. Experimental autoimmune encephalomyelitis (EAE)-susceptible and -resistant mouse strains were used to determine the roles of genetic susceptibility, level of donor-chimerism, and alloreactivity in the therapeutic potential of syngeneic versus allogeneic bone marrow transplant (BMT) for EAE. After transplantation and EAE induction, animals were evaluated for clinical EAE and ex vivo myelin oligodendrocyte glycoprotein-specific proliferation. Early after BMT, both syngeneic and allogeneic chimeras were protected from EAE development. On the longer term, allogeneic but not syngeneic BMT conferred protection, but this required high-level donor-chimerism from EAE-resistant donors. Importantly, when EAE-susceptible donors were used, robust protection from EAE was obtained when active alloreactivity, induced by donor lymphocyte infusions, was provided. Our findings indicate the requirement of a sufficient level of donor-chimerism from a nonsusceptible donor in the therapeutic effect of allogeneic BMT. Importantly, the data indicate that, independently of genetic susceptibility, active alloreactivity is associated with a GVA effect, thereby providing new evidence to support the potential role of allogeneic BMT in the treatment of MS.

The Parent-into-F1 Model of Graft-vs-Host Disease as a Model of In Vivo T Cell Function and Immunomodulation

Since its description roughly 30 years ago, the parent-into-F1 model of graft-vs.-host disease has provided insights into the mechanisms of in vivo T cell activation and the pathogenesis of autoimmune conditions. A new and emerging role for the P-->F1 model is one of identifying agents with immunomodulatory activity and defining in vivo mechanisms that promote cell mediated or antibody mediated immune responses. Because F1 mice are not irradiated prior to donor cell transfer, the P-->F1 model has in the past not been strictly analogous to human hematopoetic stem cell transplantation. However with the advent of newer non-myeloablative conditioning regimens, the model may assume more relevance. In this article, we first provide a review of relevant earlier fundamental observations followed by a summary of recent work from our laboratory in which acute and chronic GVHD in this model have been used not only to study normal T cell responses in vivo but also to define mechanisms important in the pathogenesis of autoimmunity and immunomodulation.

An Irradiation-Free Nonmyeloablative Bone Marrow Transplantation Model: Importance of the Balance between Donor T-cell Number and the Intensity of Conditioning

BACKGROUND

Animal allogeneic bone marrow transplantation (BMT) models with nonmyeloablative conditioning regimens have so far required irradiation or antibodies in addition to immunosuppressive drugs for engraftment. Moreover, although it is known that the balance between donor T-cell number and the dose of immunosuppressive drugs would be critical for engraftment, it has not been experimentally clarified in a nonmyeloablative regimen.

METHODS

We used C57BL/6 mice as donors and DBA/2 mice as recipients with a nonmyeloablative regimen including fludarabine (Flu) and cyclophosphamide (CPA) without irradiation or antibodies. To determine the adequate doses, we injected recipients with various doses of Flu and CPA, and 2x10 bone marrow cells (BMC) and 5x10 splenocytes (SC). Furthermore, using T-cell-depleted BMC and enriched T cells, we investigated the balance between donor T-cell number and the dose of Flu.

RESULTS

Doses of Flu at 150 mg/kg/dayx6 and CPA at 150 mg/kg/dayx2 were most appropriate for engraftment with low mortality. All mice appropriately pretreated and transplanted with both BMC and SC exhibited complete donor chimeras. Donor cell engraftment was not enhanced by any increase of BMC transplanted, and dose escalation of donor T cells but not BMC led to the reduction of Flu dose required for engraftment of donor cells.

CONCLUSIONS

We have established a murine nonmyeloablative BMT model in a fully MHC-mismatched combination for donor cell engraftment with complete donor chimerism. Simultaneously, we have quantitatively demonstrated that the balance between donor T-cell number and the dose of immunosuppressive drugs is critical for stable engraftment.

Donor T cells lacking Fas ligand and perforin retain the capacity to induce severe GvHD in minor histocompatibility antigen mismatched bone-marrow transplantation recipients

Graft-versus-host disease (GvHD) is a frequent impediment to therapeutically successful allogeneic bone-marrow transplantation (BMT). This investigation further examines the roles of two potential donor cytotoxic effector mechanisms previously implicated in tissue pathogenesis. Cytotoxically double deficient (B6-cdd) T cells (lacking functional fas ligand and perforin) and wild-type (B6-wt) donor T-cell transplantation in a minor antigen-mismatched BMT model (C57BL/6 --> C3H.SW) resulted in similar mortality and weight loss. Histopathologic findings revealed mononuclear infiltrates and cellular atrophy in GvHD target tissues (liver, stomach) in recipients of B6-wt and B6-cdd donor T cells. Both recipients also exhibited GvH-associated lymphohematopoietic compartment (LHC) alterations as evidenced by inverted CD4:CD8 ratios and B-cell hypoplasia. Notably, transplants using recombinant inbred mHAg disparate recipients demonstrated that B6-cdd T cells induced lethal GvHD in CXBE but not CXBG recipients: the same pattern induced by B6-wt T cells. This observation is consistent with previous findings that cytotoxic T lymphocyte (CTL) responses against CXBG and CXBE antigens did not correlate with GvH responses in these strains. In contrast with the typical pattern of donor T-cell expansion and contraction, T cells lacking perforin and FasL function exhibited extensive expansion postBMT. In summary, these findings support the notion that donor anti-host cytotoxicity by way of the two major pathways is not a prerequisite for induction of GvHD. In addition, the results suggest that this model will be useful to investigate the regulation of allogeneic donor T-cell expansion after major histocompatibility complex-matched allogeneic BMT.

CD4+ and CD8+ Regulatory T Cells Generated Ex Vivo with IL-2 and TGF-β Suppress a Stimulatory Graft-versus-Host Disease with a Lupus-Like Syndrome

Regulatory T cells generated ex vivo from conventional mouse T cells have been used to prevent and alter the course of a stimulatory graft-vs-host disease with a lupus-like syndrome. DBA/2 mouse T cells induce this syndrome when injected into (DBA/2 x C57BL/6) F(1) mice. Stimulating DBA/2 T cells with irradiated C57BL/6 in the presence of IL-2 and TGF-beta induced both CD4(+) and CD8(+) cells to develop potent suppressive activity and enhanced their survival. The IL-2 and TGF-beta-treated T cells lost their ability to induce graft-vs-host disease and, instead, prevented other parental T cells from inducing lymphoid hyperplasia, B cell activation, and an immune complex glomerulonephritis. Moreover, a single transfer of TGF-beta-conditioned T cells to animals that had already developed anti-dsDNA Abs decreased the titer, suppressed proteinuria, and doubled survival. This study raises the possibility that autologous regulatory T cells generated ex vivo have the potential to be used as an adoptive immunotherapy to induce allograft tolerance and to control autoimmunity.

CD8+ immunoregulatory cells in the graft-versus-host reaction: CD8 T cells activate dendritic cells to secrete interleukin-12/interleukin-18 and induce T helper 1 autoantibody

Initiation of cell-mediated immunity or autoimmunity requires secretion of interleukin (IL)-12 from dendritic cells (DC), which drives the generation of T helper 1 (Th1) effector cells in synergy with IL-18. Induction of IL-12 can be triggered by microbial stimuli but also requires signals from activated T cells. We investigated interactions between alloreactive CD4 and CD8 T cells in mixed lymphocyte reactions (MLR) in vitro and in the graft-versus-host reaction (GVHR) in vivo. In a parent-into-F1 model of GVHR, donor CD8 cells were found to suppress the hyper-immunoglobulin E (IgE) syndrome, anti-DNA immunoglobulin G1 (IgG1) autoantibodies and donor CD4-cell expansion, but were essential for Th1-dependent immunoglobulin G2a (IgG2a) autoantibody production and release of serum IL-12 p40. In vitro, addition of alloreactive CD8 cells to CD4 cells and mature DC enhanced Th1 development. CD4 and CD8 T cells induced IL-18 from DC and primed for IL-12 p70 secretion via interferon-gamma (IFN-gamma) or tumour necrosis factor-alpha (TNF-alpha). However CD8 T cells, but not CD4 cells, released IFN-gamma/TNF-alpha after primary stimulation. The data suggest that rapid release of inflammatory cytokines from central memory-type CD8 cells early in immunity is critical for induction of Th1 cells via DC activation and IL-12 production. This pathway could provide a means for amplification of cell-mediated autoimmunity in the absence of microbial stimuli.