Tolerogenic dendritic cells (tolDCs) that dampen T cell responses can be induced from blood monocytes in vitro using factors such as Vitamin D3 (VitD), dexamethasone, IL-10, or rapamycin. However, challenges remain in obtaining robust and efficient generation of cell therapy-based tolDCs without compromising their viability. We recently reported that CCR2-dependent recruitment of monocytic cells, with the capacity to dampen T-helper responses, occurs in mice treated with a single-stranded oligonucleotide (ssON). Here, we investigated the effects of this immunomodulatory noncoding ssON on differentiating human monocytes towards DC in the presence of IL-4 and GM-CSF (moDC). The moDC differentiated in the presence of ssON upregulated CD1a but also increased their expression of PD-L1. The differentiation of monocytes to moDC in the presence of ssON introduced transcriptomic changes, many of which overlapped with VitD-moDC and resulted in moDCs with altered lipopolysaccharide (LPS)-responsiveness. Moreover, ssON-moDC exhibited a low capacity to stimulate alloreactive T cells in vitro and instead promoted the induction of CD4⁺FoxP3⁺CD25⁺ T cells. Experiments using chemical reagents support a role for PPAR-γ in the generation of ssON-moDC. Collectively, our data show that monocytes differentiated with IL-4, GM-CSF, and ssON generate cells with phenotypic and functional characteristics of tolDCs.

The initial aim of this study on Balb/C mice was to investigate the putative effects on feeding and appetite of isopentenyl pyrophosphate (IPP) and E-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), also known as phosphoantigens (pAgs). HMBPP was recently shown to increase blood meal appetite in malaria mosquitoes. Both IPP and HMBPP are metabolites produced by the normal gut microbiota and apicomplexan parasites such as Plasmodium. To explore potential effects on appetite, male and female mice were treated by gavage with these metabolites, and body mass and gene expression were monitored in brain, stomach and small intestine at 3 h and 7 weeks. Body mass gain did not clearly differ between pAg-treated and water control mice. However, beginning between 4 and 7 weeks, the salivary glands of IPP-treated males began to swell. With the autoimmune Sjögren disease (SjD) in mind, we subsequently investigated the salivary glands after 1, 4 and 7 weeks of IPP treatment. Fast gene set enrichment analysis (FGSEA) of marginal zone B-cell (MZB) transcripts from salivary glands, together with B-cell infiltration in both sexes at 4 weeks, suggested similarities to SjD pathology. Using ELISA, we measured serum autoantibodies against Ro52, Ro60 and La. Multivariate analysis at 7 weeks showed treatment-associated trends: levels of anti-Ro52 and anti-La tended to increase in IPP-treated males, but not in females. Notably, IL-6 serum levels displayed a sex-dependent pattern, and PCA analyses of transcriptomic data from brain, stomach and small intestine—though with some exceptions—also indicated differential responses to pAgs between males and females.

Skin-resident antigen-presenting cells (APC) play an important role in maintaining peripheral tolerance via immune checkpoint proteins and induction of T regulatory cells (Tregs). However, there is a lack of knowledge on how to expand or recruit immunoregulatory cutaneous cells without causing inflammation. Here, it is shown that administration of a non-coding single-stranded oligonucleotide (ssON) leads to CCR2-dependent accumulation of CD45+CD11b+Ly6C+ cells in the skin that express substantial levels of PD-L1 and ILT3. Transcriptomic analyses of skin biopsies reveal the upregulation of key immunosuppressive genes after ssON administration. Functionally, the cutaneous CD11b+ cells inhibit Th1/2/9 responses and promote the induction of CD4+FoxP3+ T-cells. In addition, ssON treatment of imiquimod-induced inflammation results in significantly reduced Th17 responses. It is also shown that induction of IL-10 production in the presence of cutaneous CD11b+ cells isolated after ssON administrations is partly PD-L1 dependent. Altogether, an immunomodulatory ssON is identified that can be used therapeutically to recruit cutaneous CD11b+ cells with the capacity to dampen Th cells.