Immature lung TNFR2- conventional DC 2 subpopulation activates moDCs to promote cyclic di-GMP mucosal adjuvant responses in vivo.

Cyclic dinucleotides (CDNs), including cyclic di-GMP (CDG), are promising vaccine adjuvants in preclinical/clinical trials. The in vivo mechanisms of CDNs are not clear. Here we investigated the roles of lung DC subsets in promoting CDG mucosal adjuvant responses in vivo. Using genetically modified mice and adoptive cell transfer, we identified lung conventional DC 2 (cDC2) as the central player in CDG mucosal responses. We further identified two functionally distinct lung cDC2 subpopulations: TNFR2+pRelB+ and TNFR2-pRelB- cDC2. The TNFR2+ cDC2 were mature and migratory upon intranasal CDG administration while the TNFR2- cDC2 were activated but not mature. Adoptive cell transfer showed that TNFR2- cDC2 mediate the antibody responses of CDG, while the TNFR2+ cDC2 generate Th1/17 responses. Mechanistically, immature TNFR2- cDC2 activate monocyte-derived DCs (moDCs), which do not take up intranasally administered CDG. moDCs promote CDG-induced generation of T follicular helper- and germinal center B cells in the lungs. Our data revealed a previously undescribed in vivo mode of DCs action, whereby an immature lung TNFR2- cDC2 subpopulation directs the non-migratory moDCs to generate CDG mucosal responses in the lung.

The Common R71H-G230A-R293Q Human TMEM173 Is a Null Allele.

TMEM173 encodes MPYS/STING and is an innate immune sensor for cyclic dinucleotides (CDNs) playing a critical role in infection, inflammation, and cancer. The R71H-G230A-R293Q (HAQ) of TMEM173 is the second most common human TMEM173 allele. In this study, using data from the 1000 Genomes Project we found that homozygous HAQ individuals account for ∼16.1% of East Asians and ∼2.8% of Europeans whereas Africans have no homozygous HAQ individuals. Using B cells from homozygous HAQ carriers, we found, surprisingly, that HAQ/HAQ carriers express extremely low MPYS protein and have a decreased TMEM173 transcript. Consequently, the HAQ/HAQ B cells do not respond to CDNs. We subsequently generated an HAQ knock-in mouse expressing a mouse equivalent of the HAQ allele (mHAQ). The mHAQ mouse has decreased MPYS protein in B cells, T cells, Ly6Chi monocytes, bone marrow-derived dendritic cells, and lung tissue. The mHAQ mouse also does not respond to CDNs in vitro and in vivo. Lastly, Pneumovax 23, with an efficacy that depends on TMEM173, is less effective in mHAQ mice than in wild type mice. We conclude that HAQ is a null TMEM173 allele. Our findings have a significant impact on research related to MPYS-mediated human diseases and medicine.

The mucosal adjuvant cyclic di-GMP enhances antigen uptake and selectively activates pinocytosis-efficient cells in vivo.

Effective mucosal adjuvants enhance the magnitude and quality of the vaccine response. Cyclic di-GMP (CDG) is a promising mucosal vaccine adjuvant. However, its in vivo mechanisms are unclear. Here, we showed, in mice, that CDG elicits stronger Ab and TH responses than the mammalian 2'3'-cyclic GMP-AMP (cGAMP), and generated better protection against Streptococcus pneumoniae infection than 2'3'-cGAMP adjuvanted vaccine. We identified two in vivo mechanisms of CDG. First, intranasally administered CDG greatly enhances Ag uptake, including pinocytosis and receptor-mediated endocytosis in vivo. The enhancement depends on MPYS (STING, MITA) expression in CD11C(+) cells. Second, we found that CDG selectively activated pinocytosis-efficient-DCs, leading to T(H) polarizing cytokines IL-12p70, IFNγ, IL-5, IL-13, IL-23, and IL-6 production in vivo. Notably, CDG induces IFNλ, but not IFNß, in vivo. Our study revealed previously unrecognized in vivo functions of MPYS and advanced our understanding of CDG as a mucosal vaccine adjuvant.

MPYS/STING-mediated TNF-α, not type I IFN, is essential for the mucosal adjuvant activity of (3'-5')-cyclic-di-guanosine-monophosphate in vivo.

The bacterial second messenger (3'-5')-cyclic-di-guanosine-monophosphate (CDG) is a promising mucosal adjuvant candidate that activates balanced Th1/Th2/Th17 responses. We showed previously that CDG activates stimulator of IFN genes (STING)-dependent IFN-I production in vitro. However, it is unknown whether STING or IFN-I is required for the CDG adjuvant activity in vivo. In this study, we show that STING(-/-) mice (Tmem173()) do not produce Ag-specific Abs or Th1/Th2/Th17 cytokines during CDG/Ag immunization. Intranasal administration of CDG did not induce TNF-α, IL-1ß, IL-6, IL-12, or MCP-1 production in STING(-/-) mice. Surprisingly, we found that the cytokine and Ab responses were unaltered in CDG/Ag-immunized IFNAR(-/-) mice. Instead, we found that CDG activates STING-dependent, IFN-I-independent TNF-α production in vivo and in vitro. Furthermore, using a TNFR1(-/-) mouse, we demonstrate that TNF-α signaling is critical for CDG-induced Ag-specific Ab and Th1/Th2 cytokine production. This is distinct from STING-mediated DNA adjuvant activity, which requires IFN-I, but not TNF-α, production. Finally, we found that CDG activates STING-dependent, but IRF3 stimulation-independent, NF-κB signaling. Our results established an essential role for STING-mediated TNF-α production in the mucosal adjuvant activity of CDG in vivo and revealed a novel IFN-I stimulation-independent STING-NF-κB-TNF-α pathway.