Arnaud Delpoux

Inflammatory monocytes are potent antitumor effectors controlled by regulatory CD4+ T cells

The present study evaluates the impact of immune cell populations on metastatic development in a model of spontaneous melanoma [mice expressing the human RET oncogene under the control of the metallothionein promoter (MT/ret mice)]. In this model, cancer cells disseminate early but remain dormant for several weeks. Then, MT/ret mice develop cutaneous metastases and, finally, distant metastases. A total of 35% of MT/ret mice develop a vitiligo, a skin depigmentation attributable to the lysis of normal melanocytes, associated with a delay in tumor progression. Here, we find that regulatory CD4+ T cells accumulate in the skin, the spleen, and tumor-draining lymph nodes of MT/ret mice not developing vitiligo. Regulatory T-cell depletion and IL-10 neutralization led to increased occurrence of vitiligo that correlated with a decreased incidence of melanoma metastases. In contrast, inflammatory monocytes/dendritic cells accumulate in the skin of MT/ret mice with active vitiligo. Moreover, they inhibit tumor cell proliferation in vitro through a reactive oxygen species-dependent mechanism, and both their depletion and reactive oxygen species neutralization in vivo increased tumor cell dissemination. Altogether, our data suggest that regulatory CD4+ T cells favor tumor progression, in part, by inhibiting recruitment and/or differentiation of inflammatory monocytes in the skin.

Highly self-reactive naive CD4 T cells are prone to differentiate into regulatory T cells

Upon activation, naive CD4 T cells differentiate into a variety of T-helper-cell subsets characterized by different cytokine production and functions. Currently, lineage commitment is considered to depend mostly on the environmental context to which naive CD4 T cells are exposed. Here we challenge this model based on the supposed homogeneity of the naive CD4 T-cell compartment. We show that peripheral naive CD4 T cells can be subdivided into two subsets according to Ly-6C expression. Furthermore, the two newly defined subsets (Ly-6C(-) and Ly-6C(+) naive CD4 T cells) are not equal in their intrinsic ability to commit into the induced regulatory T-cell lineage. Finally, phenotypic analysis, imaging and adoptive transfer experiments reveal that Ly-6C expression is modulated by self-recognition, allowing the dichotomization of the naive CD4 T-cell compartment into two cell subsets with distinct self-reactivity. Altogether, our results show that naive CD4 T cells with the highest avidity for self are prone to differentiate into regulatory T cells.

IL-2 and IL-7 Determine the Homeostatic Balance between the Regulatory and Conventional CD4+ T Cell Compartments during Peripheral T Cell Reconstitution

Work over the last decades has led to the identification of the factors that influence the survival and homeostasis of conventional T cells. IL-7 and TCR signaling promote the survival of naive CD4+ and CD8+ T cells in lymphoreplete mice and their proliferation in a lymphopenic environment, whereas survival and homeostatic proliferation of memory CD4+ and CD8+ T cells crucially depend on a combination of IL-7 and IL-15. In contrast, there is little information regarding the factors driving the proliferation of regulatory CD4+ T cells in response to lymphopenia. In this study, we investigated whether regulatory CD4+ T cell proliferation in response to lymphopenia was guided by classical homeostatic resources, such as IL-2, IL-7, or TCR–MHC interactions. Altogether, our data suggest that, although homeostatic proliferation of conventional naive CD4+ T cells is closely related to IL-7 levels, the proliferation of regulatory CD4+ T cells in response to lymphopenia appears to be primarily controlled by IL-2. The capacity of IL-7 to augment conventional T cell proliferation with minimal concomitant regulatory T cell expansion may be clinically exploitable in the treatment of patients with lymphopenia, especially in the case of chronic viral diseases or cancer immunotherapy.

TCR-Signaling Events Are Required for Maintaining CD4 Regulatory T Cell Numbers and Suppressive Capacities in the Periphery

CD4 regulatory T cells (Tregs) can be subdivided into two subsets according to Ly-6C expression in the periphery. Phenotypic analysis, imaging, and adoptive-transfer experiments of peripheral Ly-6C− and Ly-6C+ Tregs reveal that the nonexpression of Ly-6C by ∼70% of peripheral Tregs depends on TCR signaling events. Interestingly, Ly-6C− Tregs express higher surface amounts of key immunosuppressive molecules than do Ly-6C+ Tregs and produce constitutively anti-inflammatory cytokines. In line with their phenotype, Ly-6C+ Tregs exhibit poor suppressive capacities in vitro and in vivo. Finally, although Ly-6C− Tregs maintain their numbers with age, Ly-6C+ Tregs gradually disappear. Altogether, our data strongly suggest that both the survival and suppressive functions of peripheral CD4 Tregs rely on their ability to receive strong TCR signals.

FOXO1 opposition of CD8+ T cell effector programming confers early memory properties and phenotypic diversity

Significance Acute infection with intracellular pathogen results in the expansion and effector differentiation of pathogen-specific CD8+ T cells, most of which die after pathogen clearance. The factors and steps controlling CD8+ T cell differentiation in response to acute infection are not fully understood. We find FOXO1 and TCF7 drive postinfection immune memory characteristics in cells expressing low TIM3, where TCF7 actively down-regulates the cytotoxic molecule GZMB and reduces terminally differentiated KLRG1high effector abundance. We further report the creation of a continuum of CD8+ T cell phenotypes, ranging from terminal effector cells to long-lived immune-memory cells, dependent on FOXO1 and TCF7. We conclude FOXO1 and TCF7 are essential to oppose cytotoxic/terminal differentiation programs and enable full phenotypic diversity of postinfection CD8+ T cells. The factors and steps controlling postinfection CD8+ T cell terminal effector versus memory differentiation are incompletely understood. Whereas we found that naive TCF7 (alias “Tcf-1”) expression is FOXO1 independent, early postinfection we report bimodal, FOXO1-dependent expression of the memory-essential transcription factor TCF7 in pathogen-specific CD8+ T cells. We determined the early postinfection TCF7high population is marked by low TIM3 expression and bears memory signature hallmarks before the appearance of established memory precursor marker CD127 (IL-7R). These cells exhibit diminished TBET, GZMB, mTOR signaling, and cell cycle progression. Day 5 postinfection, TCF7high cells express higher memory-associated BCL2 and EOMES, as well as increased accumulation potential and capacity to differentiate into memory phenotype cells. TCF7 retroviral transduction opposes GZMB expression and the formation of KLRG1pos phenotype cells, demonstrating an active role for TCF7 in extinguishing the effector program and forestalling terminal differentiation. Past the peak of the cellular immune response, we report a gradient of FOXO1 and TCF7 expression, which functions to oppose TBET and orchestrate a continuum of effector-to-memory phenotypes.

Continuous activity of Foxo1 is required to prevent anergy and maintain the memory state of CD8+ T cells

Upon infection with an intracellular pathogen, cytotoxic CD8+ T cells develop diverse differentiation states characterized by function, localization, longevity, and the capacity for self-renewal. The program of differentiation is determined, in part, by FOXO1, a transcription factor known to integrate extrinsic input in order to specify survival, DNA repair, self-renewal, and proliferation. At issue is whether the state of T cell differentiation is specified by initial conditions of activation or is actively maintained. To study the spectrum of T cell differentiation, we have analyzed an infection with mouse cytomegalovirus, a persistent-latent virus that elicits different cytotoxic T cell responses characterized as acute resolving or inflationary. Our results show that FOXO1 is continuously required for all the phenotypic characteristics of memory-effector T cells such that with acute inactivation of the gene encoding FOXO1, T cells revert to a short-lived effector phenotype, exhibit reduced viability, and manifest characteristics of anergy.

Foxp3-independent loss of regulatory CD4+ T-cell suppressive capacities induced by self-deprivation

In the periphery, Foxp3 expression is considered sufficient to maintain natural regulatory CD4+ T‐cell suppressive function. In this study, we challenge this model. Indeed, in mouse chimeras in which major histocompatibility complex (MHC) class II expression is restricted to the thymus, peripheral regulatory CD4+ T cells lack suppressive activity. In addition, regulatory CD4+ T cells recovered 5 days after transfer into recipient mice lacking expression of MHC class II molecules (self‐deprived) are unable to inhibit the proliferative response of conventional CD4+ T cells both in vitro and in vivo. Disruption of TCR/MHC class II interactions rapidly leads to alterations in the regulatory CD4+ T‐cell phenotype, the ability to respond to stimulation and to produce interleukin‐10, and the transcriptional signature. Interestingly, self‐deprivation does not affect Foxp3 expression indicating that in regulatory CD4+ T cells, self‐recognition induces unique transcriptional and functional features that do not rely on Foxp3 expression.

Profiling the lymphoid-resident T cell pool reveals modulation by age and microbiota

Despite being implicated in non-lymphoid tissues, non-recirculating T cells may also exist in secondary lymphoid organs (SLO). However, a detailed characterization of this lymphoid-resident T cell pool has not yet been done. Here we show that a substantial proportion of CD4 regulatory (Treg) and memory (Tmem) cells establish long-term residence in the SLOs of specific pathogen-free mice. Of these SLOs, only T cell residence within Peyer’s patches is affected by microbiota. Resident CD4 Treg and CD4 Tmem cells from lymph nodes and non-lymphoid tissues share many phenotypic and functional characteristics. The percentage of resident T cells in SLOs increases considerably with age, with S1PR1 downregulation possibly contributing to this altered homeostasis. Our results thus show that T cell residence is not only a hallmark of non-lymphoid tissues, but can be extended to secondary lymphoid organs.Non-circulating, tissue-resident T cells have been reported for non-lymphoid organs, but their characterization and regulation in secondary lymphoid organs (SLO) are still lacking. Here the authors show that age and microbiota both exert SLO-specific effects for the various tissue-resident T cell subsets.