Downregulation of IL-12 and a novel negative feedback system mediated by CD25+CD4+ T cells. Biochem Biophys Res Commun. 2005;330:226-232. [PMID: 15781254 DOI: 10.1016/j.bbrc.2005.02.148]

Nivolumab receptor occupancy on effector regulatory T cells predicts clinical benefit

Immune checkpoint inhibitor discovery represents a turning point in cancer treatment. However, the response rates of solid tumors remain ~10%-30%; consequently, prognostic and immune-related adverse event (irAE) predictors are being explored. The programmed cell death protein 1 (PD-1) receptor occupancy (RO) of PD-1 inhibitors depends on the number of peripheral blood lymphocytes and their PD-1 expression levels, suggesting that the RO may be related to efficacy and adverse events. As PD-1 inhibition affects each T-cell subset differently, the RO of each cell population must be characterized. However, relevant data have not been reported, and the prognostic relevance of this parameter is not known. In this study, we aimed to clarify the association between the nivolumab RO in each T-cell population and patient prognosis and reveal the development of irAEs in nivolumab-treated patients. Thirty-two patients were included in the study, and the mean follow-up period was 364 days. The nivolumab RO on effector regulatory T cells (eTregs) was significantly lower in the group that presented clinical benefits, and a significant negative association was observed between PD-1 occupancy on eTregs and all-cause mortality. The results suggest that the nivolumab RO on eTregs may be a prognostic factor in PD-1 inhibitor therapy, implying that the inhibition of PD-1/PD-ligand 1 (PD-L1) signaling on eTregs may attenuate antitumor effects.

DX5+ CD4+ T cells modulate CD4+ T-cell response via inhibition of IL-12 production by DCs

DX5(+) CD4(+) T cells have been shown to dampen collagen-induced arthritis and delayed-type hypersensitivity reactions in mice. These cells are also potent modulators of T-helper cell responses through direct effects on CD4(+) T cells in an IL-4 dependent manner. To further characterize this T-cell population, we studied their effect on DCs and the potential consequences on T-cell activation. Here, we show that mouse DX5(+) CD4(+) T cells modulate DCs by robustly inhibiting IL-12 production. This modulation is IL-10 dependent and does not require cell contact. Furthermore, DX5(+) CD4(+) T cells modulate the surface phenotype of LPS-matured DCs. DCs modulated by DX5(+) CD4(+) T-cell supernatant express high levels of the co-inhibitor molecules PDL-1 and PDL-2. OVA-specific CD4(+) T cells primed with DCs exposed to DX5(+) CD4(+) T-cell supernatant produce less IFN-γ than CD4(+) T cells primed by DCs exposed to either medium or DX5(-) CD4(+) T-cell supernatant. The addition of IL-12 to the co-culture with DX5(+) DCs restores IFN-γ production. When IL-10 present in the DX5(+) CD4(+) T-cell supernatant is blocked, DCs re-establish their ability to produce IL-12 and to efficiently prime CD4(+) T cells. These data show that DX5(+) CD4(+) T cells can indirectly affect the outcome of the T-cell response by inducing DCs that have poor Th1 stimulatory function.

The Immunomodulatory Effect of You-Gui-Wan on Dermatogoides-pteronyssinus-Induced Asthma

The traditional Chinese medicine You-Gui-Wan (YGW) contains ten species of medicinal plants and has been used to improve health in remissive states of asthma for hundreds of years in Asia. However, little is known about the immunomodulatory mechanisms in vivo. Therefore, this study investigated the pathologic and immunologic responses to YGW in mice that had been repeatedly exposed to Dermatogoides-pteronyssinus (Der p). YGW reduced Der-p-induced airway hyperresponsiveness and total IgE in serum. It also inhibited eosinophil infiltration by downregulating the protein expression of IL-5 in serum and changed the Th2-bios in BALF by upregulating IL-12. Results of the collagen assay and histopathologic examination showed that YGW reduced airway remodeling in the lung. In addition, after YGW treatment there was a relative decrease in mRNA expression of TGF-β1, IL-13, eotaxin, RANTES, and MCP-1 in lung in the YGW group. The results of EMSA and immunohistochemistry revealed that YGW inhibited NF-κB expression in epithelial lung cells. YGW exerts its regulative effects in chronic allergic asthmatic mice via its anti-inflammatory activity and by inhibiting the progression of airway remodeling.

Lymphocyte-polarized dendritic cells are highly effective in inducing tumor-specific CTLs

High activity of dendritic cells (DCs) in inducing cytotoxic T cells (CTLs) led to their application as therapeutic cancer vaccines. The ability of DCs to produce IL-12p70 is one of the key requirements for effective CTL induction and a predictive marker of their therapeutic efficacy in vivo. We have previously reported that defined cocktails of cytokines, involving TNFα and IFNγ, induce mature type-1 polarized DCs (DC1s) which produce strongly elevated levels of IL-12 and CXCL10/IP10 upon CD40 ligation compared to "standard" PGE₂-matured DCs (sDCs; matured with IL-1β, IL-6, TNFα, and PGE₂) and show higher CTL-inducing activity. Guided by our observations that DC1s can be induced by TNFα- and IFNγ-producing CD8⁺ T cells, we have tested the feasibility of using lymphocytes to generate DC1s in a clinically-compatible process, to limit the need for clinical-grade recombinant cytokines and the associated costs. CD3/CD28 activation of bulk lymphocytes expanded them and primed them for effective production of IFNγ and TNFα following restimulation. Restimulated lymphocytes, or their culture supernatants, enhanced the maturation status of immature (i)DCs, elevating their expression of CD80, CD83 and CCR7, and the ability to produce IL-12p70 and CXCL10 upon subsequent CD40 ligation. The "lymphocyte-matured" DC1s showed elevated migration in response to the lymph-node-directing chemokine, CCL21, when compared to iDCs. When loaded with antigenic peptides, supernatant-matured DCs induced much high levels of CTLs recognizing tumor-associated antigenic epitope, than PGE₂-matured DCs from the same donors. These results demonstrate the feasibility of generation of polarized DC1s using autologous lymphocytes.

The dendritic cell-regulatory T lymphocyte crosstalk contributes to tumor-induced tolerance

Tumor cells commonly escape from elimination by innate and adaptive immune responses using multiple strategies among which is the active suppression of effector immune cells. Regulatory T lymphocytes (Treg) and tolerogenic dendritic cells play essential roles in the establishment and persistence of cancer-induced immunosuppression. Differentiating dendritic cells (DCs) exposed to tumor-derived factors may be arrested at an immature stage becoming inept at initiating immune responses and may induce effector T-cell anergy or deletion. These tolerogenic DCs, which accumulate in patients with different types of cancers, are also involved in the generation of Treg. In turn, Treg that expand during tumor progression contribute to the immune tolerance of cancer by impeding DCs' ability to orchestrate immune responses and by directly inhibiting antitumoral T lymphocytes. Herein we review these bidirectional communications between DCs and Treg as they relate to the promotion of cancer-induced tolerance.

Relationship between inflammatory bowel disease and immuno-regulatory cells in intestinal mucosa

Inflammatory bowel disease (IBD) includes Crohn's disease (CD) and ulcerative colitis (UC). Although the precise etiopathogenesis of IBD remains unclear, dysfunctions of the immune system has been seen as an important factor. Participation of immuno-regulatory cells and multiple cytokines in immunoreactions and inflammatory process has nowadays become one of the hot spots in research into the immunopathogenesis of IBD. This paper reviewed the function of immuno-regulatory cells in IBD.

Suppression of mature dendritic cell function by regulatory T cells in vivo is abrogated by CD40 licensing

The priming of CD4+ effector T cells (T(eff)) in vivo is induced by mature dendritic cells (DC) and controlled by CD4+CD25+Foxp3+ regulatory T cells (T(reg)). It remains unclear,however, how T(eff) priming vs T(reg) suppression are regulated during Ag presentation by DC in secondary lymphoid organs at the simultaneous presence of T(eff) and T(reg). In this study, we used an peptide-specific DO11.10 TCR-transgenic adoptive transfer model to follow the T(eff) priming kinetics and the mechanisms of suppression by T(reg). T(reg) activation was slower as compared with T(eff) and could not influence the early T(eff) expansion but limited the T(eff) response leading to lower T(eff) numbers in the memory phase. DC-T(reg) cell contacts remained unaltered during suppression by T(reg) and led to a down-regulation of the costimulatory molecules CD80, CD86, PD-L1, and PD-L2 but not MHC II, CD40, ICOS-L, or CD70 from the mature DC surface. This effect was observed only after DC maturation with TNF or LPS but not after additional CD40 licensing. Together, our data indicate that T(reg) suppression against nonself Ags in vivo occurs delayed due to the slower T(reg) response, is mediated to a large extent through DC modulation, but is controlled by the type of DC maturation.

The cross-talk between dendritic and regulatory T cells: good or evil?

Immune responses against pathogens require fine regulation to avoid excessive inflammation, which could be harmful to the host. Moreover, the immune system must be tolerant to nonpathogenic antigens to prevent allergy, autoimmunity, and transplant rejection. There is accumulating evidence that interactions between dendritic cells (DC) and regulatory T (Treg) cells play a crucial role in the balance between immune response and tolerance. Communications between these cells are complex, bidirectional, and mediated by soluble or cell surface molecules. The maturation status of DC, which may be influenced by different microenvironmental factors, is considered as an important checkpoint for the induction of peripheral tolerance through modifications of the activation status of T cells. Moreover, several lines of experimental evidence suggest that different subsets or the functional status of DC are also involved in the promotion of Treg cell differentiation. A better knowledge of the regulatory mechanisms of the immune response induced or inhibited by DC via their interactions with Treg cells could be relevant for the development of new, immunotherapeutic approaches.

Tumor-derived CD4(+)CD25(+) regulatory T cell suppression of dendritic cell function involves TGF-beta and IL-10

CD4(+)CD25(+) regulatory T cells have been characterized as a critical population of immunosuppressive cells. They play a crucial role in cancer progression by inhibiting the effector function of CD4(+) or CD8(+) T lymphocytes. However, whether regulatory T lymphocytes that expand during tumor progression can modulate dendritic cell function is unclear. To address this issue, we have evaluated the inhibitory potential of CD4(+)CD25(+) regulatory T cells from mice bearing a BCR-ABL(+) leukemia on bone marrow-derived dendritic cells. We present data demonstrating that CD4(+)CD25(+)FoxP3(+) regulatory T cells from tumor-bearing animals impede dendritic cell function by down-regulating the activation of the transcription factor NF-kappaB. The expression of the co-stimulatory molecules CD80, CD86 and CD40, the production of TNF-alpha, IL-12, and CCL5/RANTES by the suppressed DC is strongly down-regulated. The suppression mechanism requires TGF-beta and IL-10 and is associated with induction of the Smad signaling pathway and activation of the STAT3 transcription factor.

Regulatory T-cell physiology and application to treat autoimmunity

Endowed with the ability to actively suppress an immune response, regulatory T cells (Tregs) hold the promise of halting ongoing pathogenic autoimmunity and restoring self-tolerance in patients suffering from autoimmune diseases. Through many in vitro and in vivo studies, we have learned that Tregs can function in the lymph nodes as well as in the peripheral tissues. In vivo, Tregs act through dendritic cells to limit autoreactive T-cell activation, thus preventing their differentiation and acquisition of effector functions. By limiting the supply of activated pathogenic cells, Tregs prevent or slow down the progression of autoimmune diseases. However, this protective mechanism appears insufficient in autoimmune individuals, likely because of a shortage of Tregs cells and/or the development and accumulation of Treg-resistant pathogenic T cells over the long disease course. Thus, restoration of self-tolerance in these patients will likely require purging of pathogenic T cells along with infusion of Tregs with increased ability to control ongoing tissue injury. In this review, we highlight advances in dissecting Treg function in vivo in autoimmune settings and summarize multiple studies that have overcome the limitations of the low abundance of Tregs and their hypoproliferative phenotype to develop Treg-based therapies.

An essential role for Rxr alpha in the development of Th2 responses

A viable hypomorphic allele of mouse retinoid X receptor alpha (Rxralpha) was created by random germline mutagenesis. The mutation (I273N) alters the ligand binding and heterodimerization domain, and causes a 90% decline in ligand-inducible transactivation. Homozygotes develop progressive alopecia and dermal cysts, and progressive exaggeration of Th1 and loss of Th2 responses to antigen. Th1 skewing is directly caused by aberrant function of both antigen-presenting cells and naïve CD4 T cells; the predominant Th1 response to antigen is attributable to decreased suppression of regulatory T cells in mutant mouse. Dietary depletion of vitamin A in Th2-prone wild-type mice mimics the immune phenotype caused by the mutation. Hence, RXRalpha plays an important post-developmental role in the regulation of adaptive immune responses, and provides a plausible link between nutritional environment and the type of adaptive response that results from immunization.

Imaging the function of regulatory T cells in vivo

Despite extensive research on regulatory T cells (Tregs) since their rebirth more than twenty years ago, the cellular and molecular mechanisms by which they act to suppress immune responses remain largely elusive. In vitro suppression assays are instrumental in the functional identification of these cells. However, suppressive mechanisms defined in in vitro assays might not be relevant to situations in vivo. Advances in live tissue and intravital imaging technologies combined with the ability to grow large numbers of Tregs for in vivo experimentation have created an opportunity to analyze Treg function in vivo in their native environment in real-time. Two-photon laser-scanning microscopic studies of Treg control of lymph node priming suggest that Tregs exert their function by limiting T helper (Th) cell access to dendritic cells (DCs). In the absence of Tregs, Th cells initially form transient interactions with DCs that lead to arrest of the Th cells and to the formation of stable conjugates between Th cells and DCs. In the presence of increasing number of Tregs, Th cell arrest and their prolonged contacts with DCs are progressively inhibited. The reduced DC contacts in the presence of Tregs are associated with suppressed proliferation and differentiation of Th cells. Expansion of such analysis to peripheral tissues together with the development of functional reporter mice will help to further elucidate the mode of operation of Tregs in vivo.

Potential Mechanisms of Photopheresis in Hematopoietic Stem Cell Transplantation

Immune tolerance describes specific unresponsiveness to antigens. In clinical situations such as graft-versus-host disease it may be useful to capitalize on these pre-existing tolerance mechanisms to treat patients. Extracorporeal photopheresis is a pheresis treatment whereby the approximately 5 x 10(9) leukocytes are treated with a photoactivatable compound (8-methoxypsoralen) and UVA light, and immediately returned to the patient in a closed-loop, patient-connected system. This therapy induces apoptosis of virtually all the treated leukocytes. There is growing evidence that infusion of apoptotic cells may trigger certain tolerance mechanisms and, thus, be of therapeutic use in graft-versus-host disease. These apoptotic cells are taken up by phagocytes (antigen-presenting cells) in the body of the patient. Apoptotic cell engagement has been reported to induce several changes and functional activities in the engulfing antigen-presenting cell. These antigen-presenting cells: (1) decrease production of proinflammatory cytokines; (2) increase production of anti-inflammatory cytokines; (3) lower ability to stimulate T-cell responses; (4) delete CD8 T effector cells; and (5) induce regulatory T cells. Any and all of these mechanisms could explain the noted effect in graft-versus-host disease. It is still unclear which one or ones are truly responsible. Ongoing studies in animals and human trials will ultimately unravel these details.

How do CD4+CD25+ regulatory T cells control autoimmunity?

Any scientist opening up an immunology journal today will observe immediately that suppressor T cells, renamed 'regulatory T cells' (Tregs) have become a central concept in the immunology lexicon. Hundreds of Treg publications over the past few years have validated the existence of this unique T cell lineage armed with an ability to regulate autoimmunity. The CD4(+)CD25(+)Foxp3(+) Treg subset develops in the thymus, can be induced in the periphery during the course of normal immune responses and utilizes a T cell repertoire skewed towards autoantigens. Despite these advances, however, there is still controversy over their mechanism of action. This confusion stems from the differences observed in in vitro versus in vivo studies. Recent in vivo analyses support a model in which Tregs directly or indirectly alter the activation and differentiation of pathogenic T cells through an effect on antigen presenting cells.