Emerging possibilities in the development and function of regulatory T cells

Targeting of CD25 and glucocorticoid-induced TNF receptor family-related gene-expressing T cells differentially modulates asthma risk in offspring of asthmatic and normal mother mice

Immunological mechanisms leading to increased asthma susceptibility in early life remain obscure. In this study, we examined the effects of neonatal Ab treatments targeting T cell populations on the development of an asthma syndrome. We used a model of increased asthma susceptibility where offspring of asthmatic BALB/c mother mice are more prone (than normal pups) to develop the disease. Neonatal pretreatment of naive pups with mAb directed against the IL-2Ralpha chain (CD25), the costimulatory molecule glucocorticoid-induced TNFR family related gene, and the inhibitory molecule CTLA-4 elicited contrasting effects in offspring depending on the mother's asthma status. Specifically, neonatal CD25(high) T cell depletion stimulated asthma susceptibility in normal offspring whereas it ameliorated the condition of pups born of asthmatic mothers. Conversely, glucocorticoid-induced TNFR family related gene ligation as a primary signal reduced the spleen cellularity and largely abrogated asthma susceptibility in asthma-prone offspring, without inducing disease in normal pups. Striking changes in Th1/Th2 cytokine levels, especially IL-4, followed mAb pretreatment and were consistent with the impact on asthma susceptibility. These results point to major differences in neonatal T cell population and responsiveness related to maternal asthma history. Interventions that temporarily remove and/or inactivate specific T cell subsets may therefore prove useful to attenuate early life asthma susceptibility and prevent the development of Th2-driven allergic airway disease.

A regulatory T cell-dependent novel function of CD25 (IL-2Ralpha) controlling memory CD8(+) T cell homeostasis

A massive systemic expansion of CD8(+) memory T (T(M)) cells and a remarkable increase in circulating IL-2 were observed only in IL-2Ralpha (CD25) knockout (KO) mice but not in IL-2 KO and scurfy mice, although all three mutants lack regulatory T (Treg) cells. However, both phenotypes were suppressed by the transfer of Treg cells. The data presented indicate that Treg cell deficiency drives naive T cells to T(M) cells. The lack of high-affinity IL-2R in IL-2Ralpha KO mice increases circulating IL-2 that is then preferentially used by CD8(+) T(M) cells through its abundant low-affinity IL-2R, resulting in systemic CD8(+) T(M) cell dominance. Our study demonstrates the critical control of CD8(+) T(M) cell homeostasis by a Treg cell-dependent novel function of CD25 and resolves its mechanism of action.

Rapamycin Promotes Emergence of IL-10-Secreting Donor Lymphocyte Infusion-Derived T Cells Without Compromising Their Graft-Versus-Leukemia Reactivity

BACKGROUND

There are limited data examining the effects of pharmacological immunosuppression on the in vivo fate of donor lymphocyte infusions (DLI)-derived T cells, their function, and their antitumor efficacy.

METHODS

We addressed this question in a murine model in which DLI is given to stable mixed chimeras resulting in lymphohematopoietic graft-versus-host (LH-GVH) response. In this model, LH-GVH potency can be directly measured as the kinetics of conversion to full donor chimerism and can be correlated with associated graft-versus-leukemia (GVL) reactivity.

RESULTS

We found discordance in DLI-mediated LH-GVH reactivity depending on the timing of rapamycin (RAPA) administration. Delayed administration of RAPA in contrast to its early administration at the time of adoptive transfer did not interfere with conversion to full donor chimerism. Moreover, delayed administration of RAPA preserved the GVL reactivity of DLI. Analysis of the long-term chimeras showed that regardless of RAPA administration, adoptively transferred T cells mediating the LH-GVH response contribute minimally to the reconstitution of the peripheral T-cell compartment and exhibit profound hyporesponsiveness and decreased production of interleukin (IL)-2 on restimulation in vitro. However, we observed only in the RAPA-treated chimeras that the remaining hyporesponsive DLI-derived CD4+ T cells secrete large amounts of IL-10, a known immunoregulatory cytokine.

CONCLUSIONS

We conclude that delayed administration of RAPA after DLI does not interfere with their LH-GVH reactivity but promotes the emergence of IL-10-secreting DLI-derived CD4+ T cells that might contribute to the drug's known ability to promote bilateral donor host tolerance without interfering with GVL reactivity.

Initiation of adaptive immune responses by transcutaneous immunization

The development of new, effective, easy-to-use and lower-cost vaccination approaches for the combat against malignant and infectious diseases is a pre-eminent need: cancer is a leading cause of morbidity in the Western World; there are numerous pathogenic diseases for which we still have no protective or therapeutic cure; and the financial limitations of developing countries to fight these diseases. In this mini-review we focus on transcutaneous immunization (TCI), a relatively new route for antigen delivery. TCI protocols appear to be particularly promising by gaining access to skin resident APC, which are highly efficient for the initiation of humoral and/or cellular immune responses. Consisting of an adjuvant as a stimulus in combination with an antigen which defines the target, TCI offers a most attractive immunization strategy to mount highly specific full-blown adaptive immune responses. As a topically applicable cell-free adjuvant/antigen mixture, TCI might be suitable to improve patient compliance, as well as feasible economically for the use in Third World countries. In addition, this non-invasive procedure might increase the safety of vaccinations by eliminating the risk of infections related to the recycling and improper disposal of needles. The dissection of antigen and adjuvant is important because it allows "free" combinations in contrast to classical immunizations which are based on application of the pathogen of interest. The most relevant ways and means to find new, effective pathogenic target antigens are "reverse vaccinology" and the direct peptide-epitope identification from MHC molecules with mass-spectrometry. Due to these efficient approaches the variety of antigenic epitopes for potential protective/therapeutic use is perpetually expanding. The most studied adjuvants in TCI approaches are cholera toxin (CT) and its less toxic relative, the heat-labile enterotoxin (LT). Both CT and LT can serve as antigen as well. In contrast to these large proteins, which can only penetrate "pre-treated" skin barrier, the immune response modifier, TLR7 agonist R-837 (Imiquimod) is a small compound adjuvant that easily passages non-disrupted epidermis. It remains currently elusive which cells of the complex-structured "skin-associated lymphoid tissue" (SALT) respond to the adjuvant and which APC carries the antigen to the draining lymphnodes for subsequent initiation of adaptive immune responses.

Tumor Evasion of the Immune System by Converting CD4+CD25− T Cells into CD4+CD25+ T Regulatory Cells: Role of Tumor-Derived TGF-β

CD4+CD25+ T regulatory (T(reg)) cells were initially described for their ability to suppress autoimmune diseases in animal models. An emerging interest is the potential role of T(reg) cells in cancer development and progression because they have been shown to suppress antitumor immunity. In this study, CD4+CD25- T cells cultured in conditioned medium (CM) derived from tumor cells, RENCA or TRAMP-C2, possess similar characteristics as those of naturally occurring T(reg) cells, including expression of Foxp3, a crucial transcription factor of T(reg) cells, production of low levels of IL-2, high levels of IL-10 and TGF-beta, and the ability to suppress CD4+CD25- T cell proliferation. Further investigation revealed a critical role of tumor-derived TGF-beta in converting CD4+CD25- T cells into T(reg) cells because a neutralizing Ab against TGF-beta, 1D11, completely abrogated the induction of T(reg) cells. CM from a nontumorigenic cell line, NRP-152, or irradiated tumor cells did not convert CD4+CD25- T cells to T(reg) cells because they produce low levels of TGF-beta in CM. Finally, we observed a reduced tumor burden in animals receiving 1D11. The reduction in tumor burden correlated with a decrease in tumor-derived TGF-beta. Treatment of 1D11 also reduced the conversion of CD4+ T cells into T(reg) cells and subsequent T(reg) cell-mediated suppression of antitumor immunity. In summary, we have demonstrated that tumor cells directly convert CD4+CD25- T cells to T(reg) cells through production of high levels of TGF-beta, suggesting a possible mechanism through which tumor cells evade the immune system.

Regulatory T cells as potential immunotherapy in allergy

PURPOSE OF REVIEW

CD4 regulatory T cells are fundamental for the induction and maintenance of immunological tolerance to self and foreign-antigens, including allergens. Here we discuss recent advances in the field of regulatory T cells and how this knowledge can be exploited to treat and prevent allergy.

RECENT FINDINGS

Current research suggest that naturally occurring CD4CD25 regulatory T cells together with inducible IL-10-producing CD4 regulatory T cells actively control allergic responses and that their function or numbers may contribute to the development or progression of allergy. Indeed, successful treatment of allergy by allergen-specific immunotherapy may depend on the induction of IL-10 secreting CD4 T cells. Work has begun to reveal the impact of various pharmaceutical treatments on naturally occurring CD25 regulatory T cells. In addition, recent findings point to an important role for toll-like receptors in the tuning of regulatory T cell function and homeostasis. This may link the hygiene hypothesis to regulatory T cells and open up new possibilities for early intervention in allergic disease.

SUMMARY

The identification of a role for regulatory T cells in allergic disease has provided a host of new therapeutic possibilities, with the potential prospect of safe and long-term alleviation of allergic diseases.

CD4+CD25+FoxP3+ T lymphocytes fail to suppress myelin basic protein-induced proliferation in patients with multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disorder directed against self antigens of the central nervous system. CD4(+)CD25(+)FoxP3(+) regulatory T cell (T(reg)) mediated suppression is an essential mechanism of self-tolerance. We studied whether changes in the suppressive function of a mixture of CD25(high) and CD25(intemediate) expressing T(reg) cells in myelin basic protein (MBP)-induced proliferation occurred in untreated MS patients. Suppression of MBP-induced proliferation was observed in 13 out of 29 (45%) MS patients; this was significantly (p<0.05) less compared with 17 out of 19 (89%) healthy individuals. Relative T(reg) counts was significantly increased in MS patients (mean+/-S.D.; 20+/-8%) compared with healthy individuals (15+/-5%). These findings suggest that impaired T(reg) function may be involved in pathogenesis of MS.