Human CD4 T Cells From Thymus and Cord Blood Are Convertible Into CD8 T Cells by IL-4.

Commitment to the CD4+ or CD8+ T cell lineages is linked to the acquisition of a functional program broadly defined by helper and cytotoxic properties, respectively. The mechanisms underlying these processes in the human thymus remain largely unclear. Moreover, recent thymic emigrants are thought to have some degree of plasticity, which may be important for the shaping of the immune system and adjustment to specific peripheral needs. We show here that IL-4 induces proliferation-independent de novo synthesis of CD8αß in human CD4 single-positive (SP) thymocytes, generating a stable CD8SP population that features a diverse TCRαß repertoire, CD4 expression shut-down and ThPOK downregulation. IL-4 also promotes an innate-like program in both CD4SP and CD8SP thymocytes, characterized by Eomes upregulation in the absence of T-bet, in line with its recognized role in the generation of thymic innate-like CD8+ T cells. The clinical relevance of these findings is further supported by the profile of IL-4 production and IL-4 receptor expression that we identified in the human thymus. Importantly, human cord blood CD4+ T cells preserve the ability to generate Eomes+ CD8+ T cells in the presence of IL-4, with implications in neonatal immunity. Our results support a role for IL-4 in the dynamic regulation of human thymocyte plasticity and identify novel strategies to modulate immune responses.

Human naïve regulatory T-cells feature high steady-state turnover and are maintained by IL-7.

Naïve FoxP3-expressing regulatory T-cells (Tregs) are essential to control immune responses via continuous replenishment of the activated-Treg pool with thymus-committed suppressor cells. The mechanisms underlying naïve-Treg maintenance throughout life in face of the age-associated thymic involution remain unclear. We found that in adults thymectomized early in infancy the naïve-Treg pool is remarkably well preserved, in contrast to conventional naïve CD4 T-cells. Naïve-Tregs featured high levels of cycling and pro-survival markers, even in healthy individuals, and contrasted with other circulating naïve/memory CD4 T-cell subsets in terms of their strong γc-cytokine-dependent signaling, particularly in response to IL-7. Accordingly, ex-vivo stimulation of naïve-Tregs with IL-7 induced robust cytokine-dependent signaling, Bcl-2 expression, and phosphatidylinositol 3-kinase (PI3K)-dependent proliferation, whilst preserving naïve phenotype and suppressive capacity. Altogether, our data strongly implicate IL-7 in the thymus-independent long-term survival of functional naïve-Tregs, and highlight the potential of targeting the IL-7 pathway to modulate Tregs in different clinical settings.

Thymic HIV-2 infection uncovers posttranscriptional control of viral replication in human thymocytes.

UNLABELLED: A unique HIV-host equilibrium exists in untreated HIV-2-infected individuals. This equilibrium is characterized by low to undetectable levels of viremia throughout the disease course, despite the establishment of disseminated HIV-2 reservoirs at levels comparable to those observed in untreated HIV-1 infection. Although the clinical spectrum is similar in the two infections, HIV-2 infection is associated with a much lower rate of CD4 T-cell decline and has a limited impact on the mortality of infected adults. Here we investigated HIV-2 infection of the human thymus, the primary organ for T-cell production. Human thymic tissue and suspensions of total or purified CD4 single-positive thymocytes were infected with HIV-2 or HIV-1 primary isolates using either CCR5 or CXCR4 coreceptors. We found that HIV-2 infected both thymic organ cultures and thymocyte suspensions, as attested to by the total HIV DNA and cell-associated viral mRNA levels. Nevertheless, thymocytes featured reduced levels of intracellular Gag viral protein, irrespective of HIV-2 coreceptor tropism and cell differentiation stage, in agreement with the low viral load in culture supernatants. Our data show that HIV-2 is able to infect the human thymus, but the HIV-2 replication cycle in thymocytes is impaired, providing a new model to identify therapeutic targets for viral replication control. IMPORTANCE: HIV-1 infects the thymus, leading to a decrease in CD4 T-cell production that contributes to the characteristic CD4 T-cell loss. HIV-2 infection is associated with a very low rate of progression to AIDS and is therefore considered a unique naturally occurring model of attenuated HIV disease. HIV-2-infected individuals feature low to undetectable plasma viral loads, in spite of the numbers of circulating infected T cells being similar to those found in patients infected with HIV-1. We assessed, for the first time, the direct impact of HIV-2 infection on the human thymus. We show that HIV-2 is able to infect the thymus but that the HIV-2 replication cycle in thymocytes is impaired. We propose that this system will be important to devise immunotherapies that target viral production, aiding the design of future therapeutic strategies for HIV control.

Human regulatory T-cell development is dictated by Interleukin-2 and -15 expressed in a non-overlapping pattern in the thymus.

Thymus-derived FOXP3-expressing regulatory T-cells (tTregs) are master orchestrators of physiological and pathological immune responses, thus constituting ideal targets for the treatment of autoimmunity. Despite their clinical importance, the developmental program governing their differentiation in the human thymus remains poorly understood. Here, we investigated the role of common gamma-chain cytokines in human tTreg differentiation, by performing gain- and loss-of-function experiments in 3D and 2D postnatal thymic cultures. We identified IL-2 and IL-15 as key molecular determinants in this process and excluded a major function for IL-4, IL-7 and IL-21. Mechanistically, IL-2 and IL-15 were equally able to drive tTreg precursor differentiation into FOXP3(+) cells, and promote tTreg proliferation and survival. Both cytokines also increased the expression levels of molecules associated with effector function within FOXP3(+) subsets, supporting their involvement in tTreg functional maturation. Furthermore, we revealed that IL-2 and IL-15 are expressed in a non-overlapping pattern in the human thymus, with the former produced mainly by mature αß and γδ thymocytes and the latter by monocyte/macrophages and B lymphocytes. Our results identify core mechanisms dictating human tTreg development, with IL-2 and IL-15 defining specific niches required for tTreg lineage stabilization and differentiation, with implications for their therapeutic targeting in autoimmune conditions.

Delta-like 1-mediated Notch signaling enhances the in vitro conversion of human memory CD4 T cells into FOXP3-expressing regulatory T cells.

FOXP3-expressing regulatory T cells (Treg) are essential for the prevention of autoimmunity and were shown to be reduced and/or dysfunctional in several autoimmune diseases. Although Treg-based adoptive transfer represents a promising therapy, the large cell number required to achieve clinical efficacy constitutes an important limitation. Therefore, novel strategies to generate bona fide in vitro-induced Treg (iTreg) are critical. In this study, we report that human memory CD4 T cells can be efficiently converted into iTreg, and that Delta-like 1 (DL1)-mediated Notch signaling significantly enhances this process. The iTreg generated in the presence of DL1 featured higher levels of Treg function-associated molecules and were efficient suppressors. Importantly, these iTreg displayed a stable phenotype in long-term cultures, even in the presence of proinflammatory cytokines. Additionally, DL1 potentiated FOXP3 acquisition by memory CD4 cells through the modulation of the TGF-ß signaling pathway and of Foxp3 transcription. Our data demonstrate that iTreg can be efficiently induced from memory CD4 cells, a subset enriched in relevant specificities for targeting in autoimmune diseases, and that DL1 enhances this process. DL1 also enhanced the proliferation and Treg function-associated marker expression of ex vivo-stimulated human circulating FOXP3(+) cells. Manipulation of the Notch signaling pathway constitutes a promising approach to boost the in vitro generation of iTreg and ex vivo Treg expansion, thus facilitating the establishment of effective Treg-based adoptive therapy in autoimmune diseases.

Enteric mucosa integrity in the presence of a preserved innate interleukin 22 compartment in HIV type 1-treated individuals.

BACKGROUND: Interleukin 22 (IL-22) is emerging as a key cytokine for gut epithelial homeostasis and mucosal repair. Gut disruption is a hallmark of human immunodeficiency virus (HIV) infection. Here, we investigated IL-22 production and gut mucosal integrity in HIV type 1 (HIV-1)-infected individuals receiving long-term antiretroviral therapy (ART). METHODS: Biopsy specimens from 37 individuals who underwent colonoscopy primarily for cancer screening and from 17 HIV-1-infected and 20 healthy age-matched controls were assessed. RESULTS: We found significant depletion of sigmoid IL-22-producing CD4(+) T cells (T-helper type 22 [Th22] cells) even after prolonged ART, contrasting with the apparently normal compartments of regulatory and interleukin 17 (IL-17)-producing CD4(+) T cells, as well as total mucosal CD4(+) T cells. Despite the preferential Th22 cell depletion, IL-22 production by innate lymphoid cells (ILCs) was similar to that observed in HIV-1-seronegative subjects, and transcription of genes encoding molecules relevant for IL-22 production (ie, AHR, IL23, IL23R, IL1B, IL6, and TGFB1) was preserved. Remarkably, levels of transcripts of IL-22-target genes (ie, REG3G, DEFB4A, S100A9, MUC1, and MUC13) were unaltered, suggesting an adequate production of antimicrobial peptides and mucins. In agreement, enteric epithelial architecture was fully preserved. CONCLUSIONS: Despite the reduced Th22 cell subset, innate IL-22-mediated mechanisms, essential for sigmoid mucosa integrity, were fully operational in long-term-treated HIV-1-infected individuals. Our data highlight IL-22 production by ILCs as an important target for therapies aimed at facilitating human mucosal reconstitution.