Transition of late-stage effector T cells to CD27+ CD28+ tumor-reactive effector memory T cells in humans after adoptive cell transfer therapy

In humans, the pathways of memory T-cell differentiation remain poorly defined. Recently, adoptive cell transfer (ACT) of tumor-reactive T lymphocytes to metastatic melanoma patients after nonmyeloablative chemotherapy has resulted in persistence of functional, tumor-reactive lymphocytes, regression of disease, and induction of melanocyte-directed autoimmunity in some responding patients. In the current study, longitudinal phenotypic analysis was performed on melanoma antigen-specific CD8+ T cells during their transition from in vitro cultured effector cells to long-term persistent memory cells following ACT to 6 responding patients. Tumor-reactive T cells used for therapy were generally late-stage effector cells with a CD27Lo CD28Lo CD45RA- CD62 ligand- (CD62L-) CC chemokine receptor 7- (CCR7-) interleukin-7 receptor alphaLo (IL-7RalphaLo) phenotype. After transfer, rapid up-regulation and continued expression of IL-7Ralpha in vivo suggested an important role for IL-7R in immediate and long-term T-cell survival. Although the tumor antigen-specific T-cell population contracted between 1 and 4 weeks after transfer, stable numbers of CD27+)CD28+ tumor-reactive T cells were maintained, demonstrating their contribution to the development of long-term, melanoma-reactive memory CD8+ T cells in vivo. At 2 months after transfer, melanoma-reactive T cells persisted at high levels and displayed an effector memory phenotype, including a CD27+ CD28+ CD62L- CCR7- profile, which may explain in part their ability to mediate tumor destruction.     

IL-15 as a mediator of CD4+ help for CD8+ T cell longevity and avoidance of TRAIL-mediated apoptosis

CD4+ helper T cells contribute to the induction and maintenance of antigen-specific CD8+ T cells. Their absence results in short-lived antigen-specific CD8+ T cells and defective secondary CD8+ T cell responses because of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis. Here, we show that IL-15 codelivered with vaccines can overcome CD4+ T cell deficiency for promoting longevity of antigen-specific CD8+ T cells and avoidance of TRAIL-mediated apoptosis. In both priming and secondary responses, IL-15 down-regulates proapoptotic Bax, an intermediate in TRAIL-mediated apoptosis, and increases anti-apoptotic Bcl-X(L) in CD8+ T cells. Thus, IL-15 is sufficient to mimic CD4+ T cell help. Antigen-specific CD4+ T cells induce dendritic cells (DCs) to produce IL-15. IL-15 is also necessary for optimal help, because helper cells do not deliver effective help through IL-15-/- DCs. Therefore, IL-15 codelivered with vaccines can overcome CD4+ helper T cell deficiency for induction of functionally efficient CD8+ T cells and maintenance of CD8+ cytotoxic T lymphocytes (CTLs), and IL-15 is probably one of the natural mediators of help. These findings suggest new vaccine strategies against infections and cancers, especially in individuals with CD4-deficiency.     

CD8+ T cells in HIV disease exhibit cytokine receptor perturbation and poor T cell receptor activation but are responsive to gamma-chain cytokine-driven proliferation

BACKGROUND: Cytokines are important for inducing T cell maturation, proliferation, and survival. Despite the known dysregulation of cytokines in human immunodeficiency virus (HIV) infection, cytokine receptor expression is relatively unexplored. METHODS: We examined maturation markers (naive, central memory, effector memory, and effector); the cytokine receptors interleukin (IL)-2R beta , common gamma (C gamma ) chain, IL-7R alpha , IL-15R alpha; and proliferative responses of T cells in a cohort of HIV-infected pediatric patients (median age, 14.82 years) receiving antiretroviral therapy, arbitrarily designated as immunologic responders (group I) and nonresponders (group II) on the basis of a CD4+ T cell count cutoff of 25%. RESULTS: Patients had increased percentages of effector memory CD8+ T cells, in comparison with those in healthy control subjects, with reduced expression of IL-7R alpha in the central memory and effector memory subsets and of the C gamma chain in all maturation subsets of CD8+ T cells. IL-7R alpha +CD8+ T cell percentages were directly correlated with CD4+ T cell percentages. In immunologic nonresponders, anti-CD3+ or HIV Gag antigen-induced CD8+ T cell proliferation was impaired, but proliferation in response to the homeostatic cytokines IL-2 and IL-15 was preserved.Conclusions. Cytokine receptor deficiencies may contribute to immune deficiency in HIV-infected patients, and gamma -chain-utilizing cytokines may play an important role in vivo in maintaining the memory subsets of T cells in patients with CD4+ T cell deficiency.     

Transregulation of memory CD8 T-cell proliferation by IL-15Ralpha+ bone marrow-derived cells

Interleukin 15 (IL-15) and the IL-15 receptor alpha (IL-15Ralpha) chain are both required for the basal proliferation of memory CD8 T cells, but which cell types are required to express IL-15 or IL-15Ralpha to mediate this proliferation is not known. Using bone marrow (BM) chimeras, we showed that virus-specific CD8 memory T-cell proliferation was driven by IL-15 produced by either BM-derived or parenchymal cells. Experiments using mixed BM chimeras showed that IL-15Ralpha expression by memory CD8 T cells was not required for their division. In addition, wild-type memory CD8 T cells did not divide after transfer into IL-15Ralpha(-/-) mice. Further analyses demonstrated that IL-15Ralpha(+) BM-derived cells were crucial in driving memory CD8 T-cell division in the spleen while both parenchymal and BM-derived cells promoted memory cell division in the lung. Proliferation in response to soluble IL-15 in vivo required expression of IL-15Ralpha by opposing cells and IL-15Rbeta by CD8 memory cells, indicating that IL-15 interacted directly with the T cells. These results indicate that transpresentation of IL-15 by IL-15Ralpha on BM-derived cells mediates the basal proliferation of memory CD8 T cells.     

CD4+ T cell regulation of CD25 expression controls development of short-lived effector CD8+ T cells in primary and secondary responses

Both CD4⁺ T cell help and IL-2 have been postulated to “program” activated CD8⁺ T cells for memory cell development. However, the linkage between these two signals has not been well elucidated. Here we have studied effector and memory CD8⁺ T cell differentiation following infection with three pathogens (Listeria monocytogenes, vesicular stomatitis virus, and vaccinia virus) in the absence of both CD4⁺ T cells and IL-2 signaling. We found that expression of CD25 on antigen-specific CD8⁺ T cells peaked 3–4 days after initial priming and was dependent on CD4⁺ T cell help, likely through a CD28:CD80/86 mediated pathway. CD4⁺ T cell or CD25-deficiency led to normal early effector CD8⁺ T cell differentiation, but a subsequent lack of accumulation of CD8⁺ T cells resulting in overall decreased memory cell generation. Interestingly, in both primary and recall responses KLRG1^high CD127^low short-lived effector cells were drastically diminished in the absence of IL-2 signaling, although memory precursors remained intact. In contrast to previous reports, upon secondary antigen encounter CD25-deficient CD8⁺ T cells were capable of undergoing robust expansion, but short-lived effector development was again impaired. Thus, these results demonstrated that CD4⁺ T cell help and IL-2 signaling were linked via CD25 up-regulation, which controls the expansion and differentiation of antigen-specific effector CD8⁺ T cells, rather than “programming” memory cell traits.     

In vitro human memory CD8 T cell expansion in response to cytomegalovirus requires CD4+ T cell help

Requirements for human memory CD8(+) T cell expansion are incompletely understood. We found that human cytomegalovirus (HCMV) induced expansion of memory CD8(+) T cells in vitro without requiring intracellular viral peptide synthesis. Peptide-major histocompatibility complex class I tetramer binding confirmed expansion of cells with HCMV-peptide specificity. Expansion of memory CD8(+) T cells was completely dependent on the presence and function of CD4(+) T cells, whose "help" also could be induced by exposure to irrelevant antigen. Recombinant interleukin (IL)-2 or IL-15 could substitute for help provided by CD4(+) T cells, whereas CD8(+) T cell expansion was blocked by anti-IL-2 but not anti-IL-15 antibody. Human memory CD8(+) T cells expand dramatically in vitro in response to cross-presentation of HCMV antigens, and, in contrast to observations made in murine systems, this proliferation was critically dependent on CD4(+) T cells that provide essential IL-2. Thus, in humans, cross-presentation and expansion of memory CD8(+) T cells may be compromised in disease states that result in deficits in CD4(+) T cell numbers or function, such as may be seen in human immunodeficiency virus type 1 infection.     

Activation of naive and memory T cells by interleukin-15

Interleukin-15 (IL-15), a product of monocytes and other cells, has biological activities similar to those of IL-2, including growth stimulation of activated T cells, induction of cytolytic effector cells, and B-cell costimulation for proliferation and lg production. We report that IL-15 at optimal concentrations rapidly induced memory (CD45RO+) CD4+ and CD8+ T cells and naive (CD45RO-) CD8+ T cells to express the CD69 activation marker followed by proliferation. By contrast, IL-15 failed to induce naive (CD45RO-) CD4+ T cells to express CD69 or to proliferate. Similar findings were obtained with IL- 2. Unlike the other T-cell subsets, CD4+ T cells with a naive phenotype expressed little or no IL-2R beta chain, a shared component of the IL-2 and IL-15 receptors required for receptor function. A monoclonal antibody to the IL-2R beta chain, Mik beta 1, reduced CD69 expression and proliferation in CD4+ memory, CD8+ memory, and CD8+ naive T cells activated by IL-15. These results confirm the biological similarities of IL-2 and IL-15. They further document that the pool of naive CD4+ cells, unlike the pool of memory CD4+, memory CD8+, and naive CD8+ cells, is not regulated directly by the T-cell growth factors IL-2 or IL-15.     

IL-15 enhances the in vivo antitumor activity of tumor-reactive CD8+ T cells

IL-15 and IL-2 possess similar properties, including the ability to induce T cell proliferation. However, whereas IL-2 can promote apoptosis and limit CD8(+) memory T cell survival and proliferation, IL-15 helps maintain a memory CD8(+) T cell population and can inhibit apoptosis. We sought to determine whether IL-15 could enhance the in vivo function of tumor/self-reactive CD8(+) T cells by using a T cell receptor transgenic mouse (pmel-1) whose CD8(+) T cells recognize an epitope derived from the self/melanoma antigen gp100. By removing endogenous IL-15 by using tumor-bearing IL-15 knockout hosts or supplementing IL-15 by means of exogenous administration, as a component of culture media or as a transgene expressed by adoptively transferred T cells, we demonstrate that IL-15 can improve the in vivo antitumor activity of adoptively transferred CD8(+) T cells. These results provide several avenues for improving adoptive immunotherapy of cancer in patients.     

Interleukin 7 reduces the levels of spontaneous apoptosis in CD4+ and CD8+ T cells from HIV-1-infected individuals

Apoptosis has been suggested as one of the major mechanisms of CD4+ T cell depletion during the course of HIV type 1 (HIV-1) infection. Here, we show that interleukin 7 (IL-7), a nonredundant cytokine that plays essential roles in the generation and homeostasis of the T cell compartment of the immune system, exerts strong antiapoptotic effects ex vivo on both CD4+ and CD8+ T cells derived from HIV-1-infected subjects. The level of IL-7-mediated reduction of apoptosis was inversely correlated with the number of circulating CD4+ T cells, indicating a higher sensitivity to IL-7 effects in patients with more advanced disease. The antiapoptotic effect of IL-7 was uncoupled from the induction of cellular proliferation or endogenous HIV-1 replication. These results provide a further rationale for consideration of IL-7 as an agent of immune reconstitution in HIV-1 infection.     

Bone marrow retaining colitogenic CD4+ T cells may be a pathogenic reservoir for chronic colitis

BACKGROUND & AIMS: Although bone marrow (BM) is known as a primary lymphoid organ, it also is known to harbor memory T cells, suggesting that this compartment is a preferential site for migration and/or selective retention of memory T cells. We here report the existence and the potential ability to induce colitis of the colitogenic BM CD4+ memory T cells in murine colitis models. METHODS: We isolated BM CD4+ T cells obtained from colitic severe combined immunodeficient mice induced by the adoptive transfer of CD4+ CD45RB(high) T cells and colitic interleukin (IL)-10(-/-) mice that develop colitis spontaneously, and analyzed the surface phenotype, cytokine production, and potential activity to induce colitis. Furthermore, we assessed the role of IL-7 to maintain the colitogenic BM CD4+ T cells. RESULTS: A high number of CD4+ T cells reside in the BM of colitic severe combined immunodeficient mice and diseased IL-10(-/-) mice, and they retain significant potential to induce type-1 T helper-mediated colitis in an IL-7-dependent manner. These resident BM CD4+ T cells have an effector memory (T(EM); CD44(high)CD62L(-)IL-7R(high)) phenotype and preferentially are attached to IL-7-producing BM cells. Furthermore, the accumulation of BM CD4+ T(EM) cells was decreased significantly in IL-7-deficient recipients reconstituted with the colitogenic lamina propria CD4+ T(EM) cells. CONCLUSIONS: Collectively, these findings suggest that BM-retaining colitogenic CD4+ memory T cells in colitic mice play a critical role as a reservoir for persisting lifelong colitis.     

Increased peripheral expansion of naive CD4+ T cells in vivo after IL-2 treatment of patients with HIV infection

Intermittent interleukin-2 (IL-2) therapy has been shown to increase the number of CD4+ T cells, preferentially cells with a naive phenotype, in patients with HIV infection. For this report we investigated the mechanism underlying this expansion by studying the relative roles of peripheral expansion and thymic output. In a cohort of six patients receiving IL-2 over a period of 1 year, the mean number of naive CD4+ T cells increased from 139 to 387 cells per microl while levels of T cell receptor rearrangement excision circles (TRECs) declined from 47,946 to 26,510 copies per 10(6) naive T cells, thus making it unlikely that the CD4+ T cell count increases were secondary to increase in thymic output. To examine directly the impact of IL-2 on peripheral expansion, peripheral blood mature, naive CD4+ T cells were labeled ex vivo with 5-bromodeoxyuridine as well as stained directly for Ki67. These studies revealed a 7-fold increase in the percentage of 5-bromodeoxyuridine-positive cells and a 20-40-fold increase in Ki67 staining in the naive CD4+ T cell pool in the setting of IL-2 administration. This degree of increase in mature CD4+ T cell turnover induced by IL-2 does not compromise the future replicative potential of these cells, because longitudinal measurements of telomere length went from 6,981 to 7,153 bp after 1 year of IL-2 therapy. These data strongly suggest that much of the increase in CD4+ cells associated with IL-2 treatment is caused by peripheral expansion of existing naive CD4+ T cells rather than increased thymic output and that these increases occur without compromising the potential of these cells for further cell division.     

Innate CD4+CD25+ regulatory T cells are required for oral tolerance and inhibition of CD8+ T cells mediating skin inflammation

To elucidate the role of CD4+CD25+ regulatory T cells in oral tolerance, we used the model of contact hypersensitivity (CHS) to 2,4-dinitrofluorobenzene (DNFB), which is mediated by CD8+ Tc1 effector cells independently of CD4+ T-cell help. Conversely to normal mice, invariant chain knock-out (KO) (Ii degrees / degrees ) mice, which are deficient in CD4+ T cells, cannot be orally tolerized and develop a chronic hapten-specific CHS response. Transfer of naive CD4+ T cells before hapten gavage into Ii degrees / degrees mice restores oral tolerance by a mechanism independent of interleukin-10 (IL-10) production by CD4+ T cells. That naturally occurring CD4+CD25+ T cells are critical for oral tolerance induction is demonstrated by the finding that (1) transfer of CD4+CD25+ but not CD4+CD25- T cells into Ii degrees / degrees recipients completely prevents the CHS response and skin infiltration by CD8+ T cells, by blocking development of hapten-specific CD8+ T cells; (2) in vivo depletion of CD4+CD25+ cells by antibody treatment in normal mice impairs oral tolerance; and (3) CD4+CD25+ T cells inhibit hapten-specific CD8+ T-cell proliferation and interferon gamma (IFN gamma) production, in vitro. These data show that naturally occurring CD4+CD25+ T cells are instrumental for orally induced tolerance and are key actors for the control of antigen-specific CD8+ T-cell effectors mediating skin inflammation.     

Foxp3+ CD25- CD4 T cells constitute a reservoir of committed regulatory cells that regain CD25 expression upon homeostatic expansion

Expression of the IL-2 receptor alpha chain (CD25) by peripheral CD4 T cells follows cellular activation. However, CD25 expression by CD4 cells is widely used as a marker to identify regulatory T cells (T(R)), although cells with regulatory properties are also found in the CD4+CD25- subset. By using in vivo functional assays and Foxp3 expression as a faithful marker of T(R) differentiation, we have evaluated the requirements for CD25 expression by peripheral T(R). We first show that in vivo depletion of CD25+ cells prevents the development of spontaneous encephalomyelitis in recombination-activating gene (RAG)-deficient anti-myelin basic protein T cell antigen receptor (TCR) transgenic mice, and allows disease induction in otherwise healthy RAG-competent transgenic mice. Similar treatment in normal thymectomized animals is followed by the fast recovery of a normal number of CD25+ T(R). Consistently, Foxp3-expressing T(R) encompassed in the CD25- cell population convert to CD25+ after homeostatic expansion and are selectable by IL-2 in vitro. Surface expression of CD25 on T(R) is controlled by the activity of conventional CD4 cells and is fully labile because it can be lost and regained without affecting the functional potential of the cells. These findings reveal that Foxp3-expressing CD25- cells constitute a peripheral reservoir of differentiated T(R), recruited to the CD25+ pool upon homeostatic expansion and/or activation. This analysis, together with the notion that physiological commitment of T(R) takes place exclusively in the thymus should help for the interpretation of experiments assessing peripheral T(R) differentiation from naive CD4 T cells, defined as CD25-.     

Decreased numbers of signal-joint T cell receptor excision circle-containing CD4+ and CD8+ cells in systemic lupus erythematosus patients

Systemic lupus erythematosus (SLE) patients have a decreased number of peripheral blood T cells containing signal-joint T cell receptor excision circles (Sj TRECs), which are considered an indicator of thymic output. The objective of this study was to investigate the mechanism of the decrease in such T cells. Peripheral blood T cells from SLE patients were classified into CD4+ and CD8+ cells. Sj TREC levels were measured by real-time PCR. Telomerase activity was determined by the telomeric repeat amplification protocol assay. The numbers of Sj TREC containing CD4+ and CD8+ cells were lower in the peripheral blood of SLE patients than in the controls. A correlation was found between the numbers of Sj TREC-positive CD4+ and CD8+ cells. The level of TRECs is influenced by an increase in cell division. To examine this increase, telomerase activity as an indicator of cell division was measured simultaneously; however, there was no correlation between the Sj TREC level and telomerase activity. These results suggest that decreased thymic output occurs in SLE patients.     

IL-15 induces antigen-independent expansion and differentiation of human naive CD8+ T cells in vitro

Recent studies in mice have shown that although interleukin 15 (IL-15) plays an important role in regulating homeostasis of memory CD8+ T cells, it has no apparent function in controlling homeostatic proliferation of naive T cells. We here assessed the influence of IL-15 on antigen-independent expansion and differentiation of human CD8+ T cells. Both naive and primed human T cells divided in response to IL-15. In this process, naive CD8+ T cells successively down-regulated CD45RA and CD28 but maintained CD27 expression. Concomitant with these phenotypic changes, naive cells acquired the ability to produce interferon gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha), expressed perforin and granzyme B, and acquired cytotoxic properties. Primed CD8+ T cells, from both noncytotoxic (CD45RA-CD27+) and cytotoxic (CD45RA+CD27-) subsets, responded to IL-15 and yielded ample numbers of cytokine-secreting and cytotoxic effector cells. In summary, all human CD8+ T-cell subsets had the ability to respond to IL-15, which suggests a generic influence of this cytokine on CD8+ T-cell homeostasis in man.     

IL-7 receptor alpha chain expression distinguishes functional subsets of virus-specific human CD8+ T cells

Virus-specific CD8+ T cells emerge after infection with herpesviruses and maintain latency to these persistent pathogens. It has been demonstrated that murine memory CD8+ T-cell precursors specific for acute lymphocytic choriomeningitis virus express interleukin-7 receptor alpha (IL-7Ralpha), and IL-7 is involved in maintaining memory populations after the clearance of antigen. To investigate whether human CD8+ T cells reactive toward persistent viruses are maintained similarly, we analyzed IL-7Ralpha expression and function on these virus-specific cells. During primary infection, all cytomegalovirus (CMV)-specific CD8+ T cells and most Epstein-Barr virus (EBV)-specific CD8+ T cells lacked IL-7Ralpha expression. Only some virus-specific T cells expressed IL-7Ralpha late after viral replication became undetectable. CD8+ T cells specific for cleared viruses, influenza (FLU), and respiratory syncytial virus (RSV) all expressed IL-7Ralpha. Remarkably, the percentage of IL-7Ralpha- CMV-specific T cells correlated with the height of viral replication in the acute phase. Virus-specific IL-7Ralpha+ cells proliferated vigorously in response to IL-7, IL-15, or peptide, whereas IL-7Ralpha- cells required both peptide and helper-cell activation or IL-2 or IL-15 for optimal expansion. Our data suggest that although IL-7 is essential for the maintenance of memory cells in the absence of antigen, CD8+ T cells specific for latent viruses need T-cell receptor activation plus helper factors to persist.     

Central memory self/tumor-reactive CD8+ T cells confer superior antitumor immunity compared with effector memory T cells

Central memory CD8+ T cells (T(CM)) and effector memory CD8+ T cells (T(EM)) are found in humans and mice; however, their relative contributions to host immunity have only recently been examined in vivo. Further, the ability of T(CM) to treat an established tumor or infection has yet to be evaluated. To address the therapeutic potential of different tumor-reactive CD8+ T cell memory subsets, we used an established model for the in vitro generation of T(CM) and T(EM) by using IL-15 and IL-2, respectively. Adoptively transferred T(CM) exhibited a potent in vivo recall response when combined with tumor-antigen vaccination and exogenous IL-2, leading to the eradication of large established tumors. By contrast, T(EM) were far less effective on a per-cell basis. Microarray analysis revealed that the signature of highly in vivo effective antitumor T cells included the overexpression of genes responsible for trafficking to secondary lymphoid tissues. This gene expression profile correctly predicted the in vitro and in vivo lymphoid-homing attributes of tumor-reactive T cells. Furthermore, we found that homing to secondary lymphoid tissue is required for optimal tumor treatment. Our findings indicated that highly in vivo effective antitumor T cells were those that initially targeted secondary lymphoid tissue, rather than tumor sites, as had previously been postulated. Thus, tumor-reactive CD8+ T cell populations with the phenotypic and functional attributes of T(CM) may be superior to T(EM)/effector T cells for adoptive immunotherapies using concomitant tumor-antigen vaccination.     

Potent induction of long-term CD8+ T cell memory by short-term IL-4 exposure during T cell receptor stimulation

An important goal of vaccination is to achieve long-term survival of functional memory T cells. Using a MHC-compatible adoptive transfer system, we show here that a short, 3-day IL-4 but not IL-2 or IL-12 exposure during in vitro T cell receptor stimulation of naive CD8(+) T cells induced long-lasting in vivo memory. Such long-term memory CD8(+) T cells expressed antigen-specific cytotoxicity and the potential for IFN-gamma and IL-4 production. Our results support the concept that functional T cell longevity can be regulated by cytokines during initial antigen encounter and provide a rational foundation for vaccine development. They also may have implications in formulating optimal therapeutic regimens of ex vivo expanded autologous cancer- and HIV-specific CD8(+) T cells. In addition, the availability of large numbers of memory CD8(+) T cells generated through our high-efficiency system should facilitate progress in the molecular dissection of CD8(+) T cell memory development.     

CD4+CD25+ T regulatory cells control anti-islet CD8+ T cells through TGF-beta-TGF-beta receptor interactions in type 1 diabetes

Pancreatic lymph node-derived CD4+CD25+ T regulatory (Treg) cells inhibit in situ differentiation of islet-reactive CD8+ T cells into cytotoxic T lymphocytes, thereby preventing diabetes progression. The mechanism by which these Treg cells suppress anti-islet CD8+ T cells is unknown. Here, we show by using a CD8+ T cell-mediated model of type 1 diabetes that transforming growth factor (TGF)-beta-TGF-beta receptor signals are critical for CD4+CD25+ Treg cell regulation of autoreactive islet-specific cytotoxic T lymphocytes. Transgenic expression of tumor necrosis factor alpha from birth to 25 days of age in the islets of B6 mice that constitutively express CD80 on their beta cells results in accumulation of CD4+CD25+TGF-beta+ cells exclusively in the islets and pancreatic lymph nodes, which delays diabetes progression. In contrast, expression of tumor necrosis factor alpha until 28 days of age prevents islet accumulation of CD4+CD25+TGF-beta+ Treg cells, resulting in acceleration to diabetes. Furthermore, adoptive transfer experiments demonstrated that CD4+CD25+ Treg cells could not control na?ve or activated islet-reactive CD8+ T cells bearing a dominant negative TGF-beta receptor type II. Our data demonstrate that, in vivo, TGF-beta signaling in CD8+ T cells is critical for CD4+CD25+ Treg cell suppression of islet-reactive CD8+ T cells in type 1 diabetes.