Logical modelling of in vitro differentiation of human monocytes into dendritic cells unravels novel transcriptional regulatory interactions.

Dendritic cells (DCs) are the major specialized antigen-presenting cells, thereby connecting innate and adaptive immunity. Because of their role in establishing adaptive immunity, they constitute promising targets for immunotherapy. Monocytes can differentiate into DCs in vitro in the presence of colony-stimulating factor 2 (CSF2) and interleukin 4 (IL4), activating four signalling pathways (MAPK, JAK/STAT, NFKB and PI3K). However, the downstream transcriptional programme responsible for DC differentiation from monocytes (moDCs) remains unknown. By analysing the scientific literature on moDC differentiation, we established a preliminary logical model that helped us identify missing information regarding the activation of genes responsible for this differentiation, including missing targets for key transcription factors (TFs). Using ChIP-seq and RNA-seq data from the Blueprint consortium, we defined active and inactive promoters, together with differentially expressed genes in monocytes, moDCs and macrophages, which correspond to an alternative cell fate. We then used this functional genomic information to predict novel targets for previously identified TFs. By integrating this information, we refined our model and recapitulated the main established facts regarding moDC differentiation. Prospectively, the resulting model should be useful to develop novel immunotherapies targeting moDCs.

Flagellin is a Th1 polarizing factor for human CD4+ T cells and induces protection in a murine neonatal vaccination model of rotavirus infection.

Neonates have an increased susceptibility to infections, particularly those caused by intracellular pathogens, leading to high morbidity and mortality rates. This is partly because of a poor response of neonatal CD4+ T cells, leading to deficient antibody production and a low production of IFN-γ, resulting in deficient elimination of intracellular pathogens. The poor memory response of human neonates has underpinned the need for improving vaccine formulations. Molecular adjuvants that improve the response of neonatal lymphocytes, such as the ligands of toll-like receptors (TLRs), are attractive candidates. Among them, flagellin, the TLR5 ligand, is effective at very low doses; prior immunity to flagellin does not impair its adjuvant activity. Human CD4+ and CD8+ T cells express TLR5. We found that flagellin induces the expression of IFN-γ, IL-1ß and IL-12 in mononuclear cells from human neonate and adult donors. When human naïve CD4+ T cells were activated in the presence of flagellin, there was high level of expression of IFN-γ in both neonates and adults. Furthermore, flagellin induced IFN-γ production in Th1 cells obtained from adult donors; in the Th2 population, it inhibited IL-4 cytokine production. Flagellin also promoted expression of the IFN-γ receptor in naive CD4+ T cells from neonates and adults. To test the adjuvant capacity of flagellin in vivo, we used a murine neonate vaccination model for infection with rotavirus, a pathogen responsible for severe diarrhea in young infants. Using the conserved VP6 antigen, we observed an 80% protection against rotavirus infection in the presence of flagellin, but only in those mice previously primed in the neonatal period. Our data suggest that flagellin could be an attractive adjuvant for achieving a Th1 response.

CD8+ T Cells from Human Neonates Are Biased toward an Innate Immune Response.

To better understand why human neonates show a poor response to intracellular pathogens, we compared gene expression and histone modification profiles of neonatal naive CD8+ T cells with that of their adult counterparts. We found that neonatal lymphocytes have a distinct epigenomic landscape associated with a lower expression of genes involved in T cell receptor (TCR) signaling and cytotoxicity and a higher expression of genes involved in the cell cycle and innate immunity. Functional studies corroborated that neonatal CD8+ T cells are less cytotoxic, transcribe antimicrobial peptides, and produce reactive oxygen species. Altogether, our results show that neonatal CD8+ T cells have a specific genetic program biased toward the innate immune response. These findings will contribute to better diagnosis and management of the neonatal immune response.

Heterologous prime-boost oral immunization with GK-1 peptide from Taenia crassiceps cysticerci induces protective immunity.

Oral immunization is a goal in vaccine development, particularly for pathogens that enter the host through the mucosal system. This study was designed to explore the immunogenic properties of the Taenia crassiceps protective peptide GK-1 administered orally. Mice were orally immunized with the synthetic GK-1 peptide in its linear form with or without the Brucella lumazine synthase (BLS) protein adjuvant or as a chimera recombinantly bound to BLS (BLS-GK-1). Mice were boosted twice with GK-1 only at 15-day intervals. A significant rate of protection of 64.7% was achieved in GK-1-immunized mice, and that rate significantly increased to 91.8 and 96% when mice were primed with GK-1 coadministered with BLS as an adjuvant and BLS as a carrier, respectively. Specific antibodies and T cell activation and proliferation accompanied the protection induced, revealing the potent immunogenicity of GK-1. Through immunohistochemical studies, GK-1 was detected in T and B cell zones of the Peyer's patches (PP) and mesenteric lymph nodes. In the latter, abundant proliferating cells were detected by 5'-bromo-2'-deoxyuridine incorporation. No proliferation was detected in PP. Altogether, these results portray the potent immunogenic properties of GK-1 administered orally and reinforce the usefulness of BLS as an adjuvant and adequate vaccine delivery system for oral vaccines.

CD43 signals induce Type One lineage commitment of human CD4+ T cells.

BACKGROUND: The activation and effector phenotype of T cells depend on the strength of the interaction of the TcR with its cognate antigen and additional signals provided by cytokines and by co-receptors. Lymphocytes sense both the presence of an antigen and also clues from antigen-presenting cells, which dictate the requisite response. CD43 is one of the most abundant molecules on the surface of T cells; it mediates its own signalling events and cooperates with those mediated by the T cell receptor in T cell priming. We have examined the role of CD43 signals on the effector phenotype of adult CD4+ and CD8+ human T cells, both alone and in the presence of signals from the TcR. RESULTS: CD43 signals direct the expression of IFNgamma in human T cells. In freshly isolated CD4+ T cells, CD43 signals potentiated expression of the IFNgamma gene induced by TcR activation; this was not seen in CD8+ T cells. In effector cells, CD43 signals alone induced the expression of the IFNgamma gene in CD4+ T cells and to a lesser extent in CD8+ cells. The combined signals from CD43 and the TcR increased the transcription of the T-bet gene in CD4+ T cells and inhibited the transcription of the GATA-3 gene in both populations of T cells, thus predisposing CD4+ T cells to commitment to the T1 lineage. In support of this, CD43 signals induced a transient membrane expression of the high-affinity chains of the receptors for IL-12 and IFNgamma in CD4+ T cells. CD43 and TcR signals also cooperated with those of IL-12 in the induction of IFNgamma expression. Moreover, CD43 signals induced the co-clustering of IFNgammaR and the TcR and cooperated with TcR and IL-12 signals, triggering a co-capping of both receptors in CD4+ populations, a phenomenon that has been associated with a T1 commitment. CONCLUSION: Our results suggest a key role for CD43 signals in the differentiation of human CD4+ T cells into a T1 pattern.