Selective expansion of memory CD4(+) T cells by mitogenic human CD28 generates inflammatory cytokines and regulatory T cells

Costimulatory signals are important for development of effector and regulatory T cells. In this case, CD28 signaling is usually considered inert in the absence of signaling through the TCR. By contrast, mitogenic rat CD28 mAb reportedly expand regulatory T cells without TCR stimulation. We found that a commercially available human CD28 mAb (ANC28) stimulated PBMC without TCR co-ligation or cross-linking; ANC28 selectively expanded CD4(+)CD25(+)FOXP3(-) (Teff) and CD4(+)CD25(+)FOXP3(+) (Treg) cells. ANC28 stimulated the CD45RO(+) CD4(+) (memory) population, whereas CD45RA(+)CD4(+) (naive) cells did not respond. ANC28 also induced inflammatory cytokines. Treg induced by ANC28 retain the Treg phenotype longer than costimulated Treg. Treg induced by ANC28 suppressed CD25(-) T cells through a contact-dependent mechanism. Purity influenced the response of CD4(+)CD25(+ )cells because bead-purified CD4(+)CD25(+ )cells (85-90% pure) responded strongly to ANC28, whereas 98% pure FACS-sorted CD4(+)CD25(bright) (Treg) did not respond. Purified CD4(+)CD25(int) cells responded similarly to the bead-purified CD4(+)CD25(+) cells. Thus, pre-activated CD4(+) T cells (CD25(int)) respond to ANC28 rather than Treg (CD25(bright)). The ability of ANC28 to expand both effectors producing inflammatory cytokines as well as suppressive regulatory T cells might be useful for ex vivo expansion of therapeutic T cells.     

Efficient expansion of regulatory T cells in vitro and in vivo with a CD28 superagonist

CD4(+)CD25(+) T cells play a central role in the suppression of autoimmunity and inflammation, making their in vivo expansion a highly attractive therapeutic target. By phenotyping with a novel rat CTL antigen-4 (CTLA-4)-specific monoclonal antibody (mAb) and functional in vitro assays, we here first establish that rat CD4(+)CD25(+) T cells correspond to the regulatory T cells (Treg cells) described in mice and humans: they constitutively express CTLA-4, produce IL-10 but not IL-2, and are able to suppress the proliferation of costimulated CD25-negative indicator cells. Furthermore, we show that rat Treg cells respond less well than CD25(-) T cells to conventional costimulation, but are readily expanded in vitro with "superagonistic" CD28-specific mAb which are potent mitogens for all T cells without the need for TCR engagement. In vivo, functional Treg cells are preferentially expanded by CD28 stimulation over other T cell subsets, leading to a 20-fold increase within 3 days in response to a single antibody dose. These data suggest that CD28-driven activation of Treg cells may be highly effective in the treatment of inflammatory and autoimmune diseases.     

Ethylenecarbodiimide-coupled allogeneic antigen presenting cells induce human CD4+ regulatory T cells

Adoptive transfer of naturally occurring CD4(+)CD25(+) regulatory T cells can tolerize transplantation alloresponses in animal models. However isolation of these cells in sufficient numbers from humans is cumbersome and prone to contamination with alloreactive CD25(+) T cells. Incubation of ethylenecarbodiimide-coupled antigen presenting cells (APC) with na?ve T cells and antigen has been shown to induce tolerance in various experimental models. We therefore investigated whether ECDI-coupled allogeneic APC were able to induce an expandable human CD4(+) Treg population. CD4(+) and CD4(+) CD25(-) cells cultured for 5 days with ECDI-treated human PBMC exhibited potent suppressive capacity in a mixed lymphocyte reaction. Induction of these ECDI-Tregs was associated with up-regulation of Foxp3 mRNA and protein expression and they maintained high expression of CD62L and CD27 as well as low CD127 expression. ECDI-treated APC displayed reduced expression of the co-stimulatory signaling molecules CD40 and CD80, and failed to stimulate proliferation and cytokine secretion in co-cultured CD4(+) T cells. Restimulation in the presence of rapamycin and hrIL-2 led to expansion of ECDI-Tregs with increasing Foxp3 levels and suppressive activity significantly higher than expanded naturally occurring CD4(+)CD25(+) Tregs. In summary these findings support the hypothesis that ECDI-coupled APC can convert na?ve CD4(+) T cells into functional Tregs with different phenotypic characteristics than naturally occurring CD4(+)CD25(+) Tregs. These inducible Tregs could provide a novel approach that might facilitate the translation of ex vivo generated and expanded Tregs into clinical settings.     

Expansion of CD4+CD25+ suppressive regulatory T cells from rhesus macaque peripheral blood by FN18/antihuman CD28-coated Dynal beads

CD4(+)CD25(+) regulatory T cells (Tregs) play an important role in allograft and self-tolerance and thus have potential therapeutic application in transplantation, autoimmunity, and allergy. Although nonhuman primate (NHP) provide the most accepted preclinical models for translational studies in allograft tolerance and infectious diseases, CD4(+)CD25(+) Tregs have been rarely studied in NHP. The low frequencies of Tregs in peripheral blood will likely necessitate ex vivo expansion to enable Tregs adaptive immune therapy in NHP and humans. Tregs were isolated by magnetic and flow sorting and then stimulated weekly with antirhesus CD3 clone FN18 and antihuman CD28-coated Dynal beads plus 100 U/ml rhIL-2. Under these conditions, the Tregs were expanded 300- to 2000-fold in 4 weeks. Expanded CD4(+)CD25(+) Tregs expressed high to moderate levels of FOXP3 as well as CD95, CD62L, CD69, and CCR7 surface antigens. Expanded rhesus Tregs were anergic and suppressed the proliferation of autologous peripheral blood mononuclear cells (PBMC) in a dose-dependent fashion, and the suppression was partially reversed by anti-transforming growth factor (TGF)-beta1 neutralizing antibody (Ab). These results demonstrate that rhesus macaque suppressive regulatory CD4(+)CD25(+)FOXP3(+) Tregs can be efficiently expanded in vitro under rhesus-specific stimulation, which enables preclinical testing of Treg therapy in the NHP model.     

Equine CD4(+) CD25(high) T cells exhibit regulatory activity by close contact and cytokine-dependent mechanisms in vitro

Horses are particularly prone to allergic and autoimmune diseases, but little information about equine regulatory T cells (Treg) is currently available. The aim of this study therefore was to investigate the existence of CD4(+) Treg cells in horses, determine their suppressive function as well as their mechanism of action. Freshly isolated peripheral blood mononuclear cells (PBMC) from healthy horses were examined for CD4, CD25 and forkhead box P3 (FoxP3) expression. We show that equine FoxP3 is expressed constitutively by a population of CD4(+) CD25(+) T cells, mainly in the CD4(+) CD25(high) subpopulation. Proliferation of CD4(+) CD25(-) sorted cells stimulated with irradiated allogenic PBMC was significantly suppressed in co-culture with CD4(+) CD25(high) sorted cells in a dose-dependent manner. The mechanism of suppression by the CD4(+) CD25(high) cell population is mediated by close contact as well as interleukin (IL)-10 and transforming growth factor-β1 (TGF-β1) and probably other factors. In addition, we studied the in vitro induction of CD4(+) Treg and their characteristics compared to those of freshly isolated CD4(+) Treg cells. Upon stimulation with a combination of concanavalin A, TGF-β1 and IL-2, CD4(+) CD25(+) T cells which express FoxP3 and have suppressive capability were induced from CD4(+) CD25(-) cells. The induced CD4(+) CD25(high) express higher levels of IL-10 and TGF-β1 mRNA compared to the freshly isolated ones. Thus, in horses as in man, the circulating CD4(+) CD25(high) subpopulation contains natural Treg cells and functional Treg can be induced in vitro upon appropriate stimulation. Our study provides the first evidence of the regulatory function of CD4(+) CD25(+) cells in horses and offers insights into ex vivo manipulation of Treg cells.     

Expanded murine regulatory T cells: analysis of phenotype and function in contact hypersensitivity reactions

Regulatory T cells (Treg) exert suppressive functions in the periphery of the body for the maintenance of tolerance. The functional analysis of Treg is hampered by the fact that only small numbers (5%-10% among the CD4(+) T cells) of Treg exist in peripheral blood and tedious isolation methods further reduce the yield of high-purity Treg. We therefore set out to expand isolated murine Treg in ex vivo cultures with help of anti-CD3/anti-CD28 antibodies in the presence of IL-2. Our expansion-protocol described herein resulted in a 200-fold expansion of Treg and does not involve feeder cells, beads or other cellular compounds that would interfere with further in vivo use of the expanded cells. Expanded Treg could even be stored in liquid nitrogen and thawed without loss of function. Functional analysis revealed that expanded Treg are superior suppressors of T cell functions in vitro and in vivo and when applied in a model for contact hypersensitivity reactions, Treg were able to suppress the ear swelling reaction significantly. Thereby the expanded Treg home to secondary lymphoid organs in similar manner as observed for freshly isolated Treg. Accordingly, the expansion procedure does not effect the expression of specific homing markers. Thus, this protocol will facilitate the production of Treg as an "off-the-shelf reagent" and offers the possibility to explore the application of Treg as a cellular therapeutic in several allergic and autoimmune diseases.     

Vasoactive intestinal peptide induces regulatory T cells during experimental autoimmune encephalomyelitis

CD4(+)CD25(+) regulatory T cells (Treg) control the immune response to a variety of antigens, including self-antigens. Several models support the idea of the peripheral generation of CD4(+)CD25(+) Treg from CD4(+)CD25(-) T cells. Little is known about the endogenous factors and mechanisms controlling the peripheral expansion of CD4(+)CD25(+) Treg. In this study we report on the capacity of the vasoactive intestinal peptide (VIP), an immunosuppressive neuropeptide, to induce functional Treg in vivo during the development of experimental autoimmune encephalomyelitis (EAE), a multiple sclerosis model. The administration of VIP to EAE mice results in the expansion of the CD4(+)CD25(+), Foxp3-expressing T cells in the periphery and the nervous system, which inhibit encephalitogenic T cell activation. In addition to the increase in the number of CD4(+)CD25(+) Treg, VIP induces more efficient suppressors on a per cell basis. The VIP-generated CD4(+)CD25(+) Treg transfer suppression and significantly ameliorate the progression of the disease.     

Comparative study of regulatory T cells expanded ex vivo from cord blood and adult peripheral blood

In this study, we expanded regulatory T cells (Tregs) ex vivo from CD4(+) CD25(+) T cells from cord blood (CB) and CD4(+) CD25(+) CD127(-) T cells from adult peripheral blood (APB) and compared the suppressive functions of the newly generated Tregs. The Tregs from CB and APB were expanded either in two cycles with a polyclonal stimulus or in two cycles with an alloantigen stimulus in the first cycle and a polyclonal stimulus in the second cycle. Cell yield after Treg expansion with polyclonal stimulation was greater than that of Tregs expanded with combined alloantigen and polyclonal stimulation. The expanded Tregs expressed high levels of Foxp3, CD39 and cytotoxic T-lymphocyte antigen-4 and low levels of CD127, interleukin-2 and interferon-γ. After two cycles of expansion, the CB Tregs maintained expression of the GARP gene and showed greater suppressive function than APB Tregs. The CB Tregs that were expanded with two cycles of polyclonal stimulation suppressed not only the polyclonal antigen-driven responder T (T(resp)) cell proliferation but also the HLA mismatched dendritic cell-driven T(resp) cell proliferation. When CB and APB Tregs were expanded with a primary alloantigen stimulus followed by a secondary polyclonal stimulus, the Tregs showed a potent, antigen-specific suppressive capacity. The Tregs expanded with two cycles of polyclonal stimulation from both CB and APB alleviated acute graft-versus-host disease symptoms and prolonged survival in a murine model of graft-versus-host disease. In conclusion, CB Tregs expanded with two cycles of polyclonal stimulation had a stronger immunosuppressive function than APB Tregs. It is feasible to obtain human functional alloantigen-specific Tregs expanded ex vivo from CB and APB in large numbers.     

Characterization of T-regulatory cells, induced by immature dendritic cells, which inhibit enteroantigen-reactive colitis-inducing T-cell responses in vitro and in vivo

Regulatory T (Treg) cells, derived from co-cultures of unfractionated CD4(+) T cells and immature dendritic cells (DC), suppress enteroantigen-induced proliferation of CD4(+) CD25(-) T cells. The DC-induced Treg cells are a mixture of CD25(+) (10-20%) and CD25(-) (80-90%) T cells. However, all the suppressor activity in vitro and in vivo resides in the CD25(+) T-cell subset. The CD25(+) DC-induced Treg cells can inhibit enteroantigen-induced proliferation in vitro through a transwell membrane, and their function does not appear to depend on previous activation. DC-induced CD25(+) Treg cells display a naive phenotype, expressing high levels of CD45RB and l-selectin (CD62L). In addition, the DC-induced Treg cells mediate a stronger suppressive activity than prototype CD25(+) regulatory T cells. The DC-induced Treg cells, and hereof purified CD25(+) and CD25(-) T-cell fractions, were co-injected into severe combined immunodeficiency (SCID) mice with colitis-inducing CD4(+) CD25(-) T cells. Both unfractionated CD4(+) and purified CD25(+) Treg cells fully protected the recipients against the development of colitis. In contrast, co-transfer of fractionated CD25(-) T cells offered no protection against disease development. Enterobacterial antigen-exposed CD4(+) T cells of the protected mice secreted higher levels of interleukin-10 and lower levels of interferon-gamma than the unprotected mice. The present data demonstrate DC-induced CD4(+) CD25(+) Treg cells, which phenotypically and functionally differ from the generally accepted prototype of CD25(+) Treg cells. These data may initiate new procedures for the expansion of Treg cells for clinical use.     

Glucocorticoid amplifies IL-2-dependent expansion of functional FoxP3(+)CD4(+)CD25(+) T regulatory cells in vivo and enhances their capacity to suppress EAE

IL-2 is crucial for the production of CD4(+)CD25(+) T regulatory (Treg) cells while important for the generation of effective T cell-mediated immunity. How to exploit the capacity of IL-2 to expand Treg cells, while restraining activation of T effector (Teff) cells, is an important and unanswered therapeutic question. Dexamethasone (Dex), a synthetic glucocorticoid steroid, has been reported to suppress IL-2-mediated activation of Teff cells and increase the proportion of Treg cells. Thus, we hypothesized that glucocorticoids may be useful as costimulants to amplify IL-2-mediated selective expansion of Treg cells. We show in this study that short-term simultaneous administration of Dex and IL-2 markedly expanded functional suppressive Foxp3(+)CD4(+)CD25(+) T cells in murine peripheral lymphoid tissues. In a myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (EAE) mouse model, we observed that splenic CD4(+)CD25(+) T cells failed to suppress the proliferation of CD4(+)CD25(-) T cells. Pretreatment with Dex/IL-2 remarkably increased the proportion of CD4(+)FoxP3(+) cells and partially restored the function of splenic CD4(+)CD25(+) T cells, and inhibited the development of EAE. Therefore, the combination of glucocorticoid and IL-2, two currently used therapeutics, may provide a novel approach for the treatment of autoimmune diseases, transplant rejection and graft-vs.-host disease.     

Flow cytometry-based methods for studying signaling in human CD4+CD25+FOXP3+ T regulatory cells

T regulatory (Treg) cells have a fundamental role in the establishment and maintenance of peripheral tolerance. It is well established that Treg cells have a phenotype and function that is distinct from conventional T effector cells, although how these two T cell subsets differ in terms of molecular signaling cascades remains largely unknown. Analysis of signaling events in Treg cells using classical biochemistry has been hampered due to difficulties in isolating homogeneous populations and limited cell numbers. In order to overcome these challenges, we defined the optimal conditions for culture, in vitro expansion, and stimulation of human CD4(+)CD25(+) Treg and T effector cells to study intracellular signaling events by flow cytometry. In order to avoid the pitfalls associated with cell isolation based on CD25 expression, we developed methodology to analyze subpopulations of FOXP3 positive and negative cells from ex vivo CD4(+) T cells. In addition to examination of ex vivo cells, we optimized expansion conditions for analysis of signaling in Treg and T effector cell lines. Using these methods, we found that human FOXP3(+) Treg cells displayed a greater capacity to phosphorylate the extracellular regulated kinase (ERK) compared to T effector cells, upon TCR-mediated activation. In contrast, FOXP3(+) Treg cells showed a significantly diminished capacity to phosphorylate AKT. This methodology provides a foundation for future investigation into the molecular events that regulate the phenotype and function of Treg cells, and may ultimately lead to the identification of Treg-cell specific therapeutic targets.     

CD4+CD25+FoxP3+ regulatory T cells enhance the allogeneic activity of endothelial-specific CD8+/CD28-CTL

Numerous data indicate that CD4+CD25+FoxP3+ regulatory T cells (Treg cells) can attenuate alloresponses of conventional T lymphocytes against professional antigen-presenting cells and thus qualify for clinical use in various transplant settings. However, it is unknown whether Treg cells also influence T cell-endothelial cell interactions. CD8+ PBMC (CD8+ PBMC, CTL) from healthy human donors were stimulated for 7 days with an allogeneic microvascular endothelial cell line (CDC/EU. HMEC-1, an immortalized human microvascular endothelial cell line, further referred to as HMEC) and additional endothelial cell types and analysed for their lytic activity against these target cells in the presence or absence of Treg cells. Addition of Treg cells (1:1:1) to the CTL/HMEC co-cultures in the efferent immune phase (day -1 prior to the assay) led to an increased cytotoxicity against HMEC. In contrast, Treg cells alone did not lyse HMEC. Treg cell-mediated enhancement of CTL activity was endothelial cell specific since lysis of HLA-matched Epstein-Barr virus-transformed B lymphoblastoid cells (B-LCL) was not influenced by the addition of Treg cells. Further analysis of CD28-positive and CD28-negative CTL sub-populations revealed that only the CD28-negative CTL showed an increased activity against HMEC after Treg cell co-culture. Although there is no doubt about the potential therapeutic efficacy of Treg cells to ameliorate outcome of allogeneic transplants, the endothelium might require additional protective interventions to prevent endothelial cell type-specific alloreactivity.     

Endogenous CD4(+) CD25(+) regulatory T cells have a limited role in the control of Trypanosoma cruzi infection in mice

Infection with the protozoan parasite Trypanosoma cruzi results in a robust and multifaceted immune response that controls parasite load but is unable to completely clear infection, resulting in parasite persistence and a chronic illness known as Chagas' disease in humans. The severity of Chagas' disease is correlated with persistent parasitism of muscle, neuronal, and gut tissues. The natural immunomodulatory function of endogenous CD4(+) CD25(+) regulatory T cells (Treg cells) to limit hyperactive immune responses may be exploited by microbes to persist despite host responses. In this study, we show that Treg cells are not necessary for T. cruzi evasion of immune responses during acute or chronic infection. In vivo anti-CD25 monoclonal antibody-mediated depletion of Treg cells from mice prior to challenge with a lethal strain or prior to and during acute infection with a nonlethal strain of parasite neither improved nor worsened the outcome of immune responses: differences in parasitemia, kinetics of antigen-specific CD8(+) T-cell expansion, and CD8(+) T-cell effector function (both in vivo and ex vivo) were of similar magnitudes for both depleted and control groups. Furthermore, depletion of CD25(+) cells from chronically infected mice did not enhance immune responses of muscle-derived CD8(+) T cells, nor could FoxP3 mRNA/scurfin-expressing leukocytes be isolated from muscle tissue. Based on the results of this study, it is concluded that Treg cells do not appear to play a major role in regulating CD8(+) T-cell effector responses during the acute phase of infection or in the muscles of mice during chronic T. cruzi infection.     

Mannose-capped lipoarabinomannan- and prostaglandin E2-dependent expansion of regulatory T cells in human Mycobacterium tuberculosis infection

We evaluated the role of regulatory T cells (CD4(+) CD25(+) Foxp3(+) cells, Tregs) in human Mycobacterium tuberculosis infection. Tregs were expanded in response to M. tuberculosis in healthy tuberculin reactors, but not in tuberculin-negative individuals. The M. tuberculosis mannose-capped lipoarabinomannan (ManLAM) resulted in regulatory T cell expansion, whereas the M. tuberculosis 19-kDa protein and heat shock protein 65 had no effect. Anti-IL-10 and anti-TGF-beta alone or in combination, did not reduce expansion of Tregs. In contrast, the cyclooxygenase enzyme-2 inhibitor NS398 significantly inhibited expansion of Tregs, indicating that prostaglandin E2 (PGE2) contributes to Treg expansion. Monocytes produced PGE2 upon culturing with heat-killed M. tuberculosis or ManLAM, and T cells from healthy tuberculin reactors enhanced PGE2 production by monocytes. Expanded Tregs produced significant amounts of TGF-beta and IL-10 and depletion of Tregs from PBMC of these individuals increased the frequency of M. tuberculosis-responsive CD4(+) IFN-gamma cells. Culturing M. tuberculosis-expanded Tregs with autologous CD8(+) cells decreased the frequency of IFN-gamma(+)cells. Freshly isolated PBMC from tuberculosis patients had increased percentages of Tregs, compared to healthy tuberculin reactors. These findings demonstrate that Tregs expand in response to M. tuberculosis through mechanisms that depend on ManLAM and PGE2.     

IL-35 is a novel cytokine with therapeutic effects against collagen-induced arthritis through the expansion of regulatory T cells and suppression of Th17 cells

Epstein-Barr virus-induced gene 3 (EBI3) and the p35 subunit of IL-12 have been reported to form a heterodimeric hematopoietin in human and mouse. We have constructed a heterodimeric protein covalently linking EBI3 and p35, to form a novel cytokine which we now call IL-35. The Fc fusion protein of IL-35 induced proliferation of murine CD4(+)CD25(+) and CD4(+)CD25(-) T cells when stimulated with immobilized anti-CD3 and anti-CD28 antibodies in vitro. The IL-35-expanded CD4(+)CD25(+) T cell population expressed Foxp3 and produced elevated levels of IL-10, whereas the IL-35-induced CD4(+)CD25(-) T cells produced IFN-gamma but not IL-4. The in vitro expanded CD4(+)CD25(+) T cells retained their suppressive functions against CD4(+)CD25(-) effector cells. Furthermore, when cultured with soluble anti-CD3 antibody and antigen-presenting cells, IL-35 suppressed the proliferation of CD4(+)CD25(-) effector cells. Moreover, IL-35 inhibited the differentiation of Th17 cells in vitro. In vivo, IL-35 effectively attenuated established collagen-induced arthritis in mice, with concomitant suppression of IL-17 production but enhanced IFN-gamma synthesis. Thus, IL-35 is a novel anti-inflammatory cytokine suppressing the immune response through the expansion of regulatory T cells and suppression of Th17 cell development.     

CD4+CD25+ T regulatory cells inhibit cytotoxic activity of T CD8+ and NK lymphocytes in the direct cell-to-cell interaction

There are reports suggesting an influence of CD4(+)CD25(+) T regulatory cells (Treg) on cytotoxic lymphocytes. The aim of the study was to evaluate such an influence. Cytotoxic activity was examined in the cultures of peripheral blood mononuclear cells (PBMC) as well as in the cultures of separate T CD8(+) or NK cells mixed with Treg and other subpopulations of PBMC. We found that the production of IFNgamma, perforin and cytotoxic activity of T CD8(+) or NK cells were decreased in the presence of Treg, however, the percentage of conjugates formed by cytotoxic cells with target cells during cytotoxic reaction was decreased only in the cultures of T CD8(+) cells. Inhibition of the cytotoxic reactions in the presence of Treg cells was found to be associated with the generation of conglomerates formed by CD4(+)CD25(+) and the cytotoxic cells, as observed under the fluorescence microscope. Treg produced IL10 when mixed with the cytotoxic lymphocytes, however, an addition of anti-IL10 mAb into the cultures did not affect the results. It is concluded that Treg were able to inhibit both T CD8+ and NK lymphocyte cytotoxic activities in a direct cell-to-cell interaction. Treg decreased the number of T CD8+ cells attached to the target cells, while the mechanism underlying a decrease in NK cytotoxicity remained unclear.     

树突状细胞扩增抗原特异性CD4+ CD25+调节性T细胞研究进展

CD4+CD25+调节性T细胞(Tr)是同时具有免疫低反应性和免疫抑制性功能两大特征的T细胞.研究证实,CD4+ CD25+ Tr在抑制器官特异性自身免疫性疾病及GVHD是抗原特异性的,因此,应用器官特异性而不是多克隆性的Tr将大大促进以Tr为基础的免疫治疗.而具有调节活性的CD4+ CD25+ Tr仅占人类外周血CIM+ T细胞的1%～2%,因此,研究体外大量扩增的方法 对于以Tr基础的治疗至关重要.研究表明,树突状细胞(DC)作为机体强有力的专职抗原递呈细胞可以扩增具有抗原特异性的CD4+ CD25+ Tr且能增加后者的抑制活性,这为治疗自身免疫性疾病及GVHD提供了新的治疗前景.