The cGAS/STING Pathway Detects Streptococcus pneumoniae but Appears Dispensable for Antipneumococcal Defense in Mice and Humans

Streptococcus pneumoniae is a frequent colonizer of the upper respiratory tract and a leading cause of bacterial pneumonia. The innate immune system senses pneumococcal cell wall components, toxin, and nucleic acids, which leads to production of inflammatory mediators to initiate and control antibacterial defense. Here, we show that the cGAS (cyclic GMP-AMP [cGAMP] synthase)-STING pathway mediates detection of pneumococcal DNA in mouse macrophages to primarily stimulate type I interferon (IFN) responses. Cells of human individuals carrying HAQ TMEM173, which encodes a common hypomorphic variant of STING, were largely or partly defective in inducing type I IFNs and proinflammatory cytokines upon infection. Subsequent analyses, however, revealed that STING was dispensable for restricting S. pneumoniae during acute pneumonia in mice. Moreover, explorative analyses did not find differences in the allele frequency of HAQ TMEM173 in nonvaccinated pneumococcal pneumonia patients and healthy controls or an association of HAQ TMEM173 carriage with disease severity. Together, our results indicate that the cGAS/STING pathway senses S. pneumoniae but plays no major role in antipneumococcal immunity in mice and humans.

Downregulation of Membrane Trafficking Proteins and Lactate Conditioning Determine Loss of Dendritic Cell Function in Lung Cancer

Restoring antigen presentation for efficient and durable activation of tumor-specific CD8⁺ T-cell responses is pivotal to immunotherapy, yet the mechanisms that cause subversion of dendritic cell (DC) functions are not entirely understood, limiting the development of targeted approaches. In this study, we show that bona fide DCs resident in lung tumor tissues or DCs exposed to factors derived from whole lung tumors become refractory to endosomal and cytosolic sensor stimulation and fail to secrete IL12 and IFNI. Tumor-conditioned DC exhibited downregulation of the SNARE VAMP3, a regulator of endosomes trafficking critical for cross-presentation of tumor antigens and DC-mediated tumor rejection. Dissection of cell-extrinsic suppressive pathways identified lactic acid in the tumor microenvironment as sufficient to inhibit type-I IFN downstream of TLR3 and STING. DC conditioning by lactate also impacted adaptive function, accelerating antigen degradation and impairing cross-presentation. Importantly, DCs conditioned by lactate failed to prime antitumor responses in vivo These findings provide a new mechanistic viewpoint to the concept of DC suppression and hold potential for future therapeutic approaches.Significance: These findings provide insight into the cell-intrinsic and cell-extrinsic mechanisms that cause loss of presentation of tumor-specific antigens in lung cancer tissues. Cancer Res; 78(7); 1685-99. ©2018 AACR.

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, Ly6C^hi 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.