Background and objectives Patients receiving hemodialysis are at high risk for both SARS-CoV-2 infection and severe COVID-19 disease. A life-saving vaccine is available, but sensitivity to vaccines is generally lower in dialysis patients. Little is yet known about antibody responses after COVID-19 vaccination in this vulnerable group. Design, setting, participants, and measurements In this prospective single-center study, we included 22 dialysis patients and 46 healthy controls from Heidelberg University Hospital between December 2020 and February 2021. We measured anti-S1 IgG with a threshold index for detection >1, neutralizing antibodies with a threshold for viral neutralization of ≥30% and antibodies against different SARS-CoV-2 fragments 17-22 days after the first and 18-22 days after the second dose of the mRNA vaccine BNT162b2. Results After the first vaccine dose, 4/22 (18%) dialysis patients compared with 43/46 (93%) healthy controls developed positive anti-S1 IgG, with a median (IQR) anti-S1 IgG index of 0.2 (0.1-0.7) compared with 9 (4-16), respectively. SARS-CoV-2 neutralizing antibodies exceeded the threshold for neutralization in 4/22 (18%) dialysis patients compared with 43/46 (93%) in healthy controls, with a median (IQR) percent inhibition of 11 (3-24) compared with 65 (49-75), respectively. After the second dose, 14/17 (82%) of dialysis patients developed neutralizing antibodies exceeding the threshold for viral neutralization and antibodies against the receptor-binding S1-domain of the spike protein, compared to 46/46 (100%) of healthy controls, respectively. The median (IQR) percent inhibition was 51 (32-86) compared to 98 (97-98) in healthy controls. Conclusions Patients receiving long-term hemodialysis show a reduced antibody response to the first and second doses of the mRNA vaccine BNT162b2. The majority (82%) develop neutralizing antibodies after the second dose, but at lower levels than healthy controls.

Bacterial RNA (bRNA) can induce cytokine production in macrophages and dendritic cells (DCs) through a previously unidentified receptor. Gene expression analysis of murine DCs showed that bRNA induced gene regulation similar to that induced by stimulation of TLR7 with R848. Although TLR7 was dispensable for cytokine induction by bRNA, TLR-associated proteins MyD88 and UNC93B were required. TLR13 is an endosomal murine TLR that has been described to interact with UNC93B with, so far, no characterized ligand. Small interfering RNA against TLR13 reduced cytokine induction by bRNA in DCs. Moreover, Chinese hamster ovary cells transfected with TLR13, but not with TLR7 or 8, could activate NF-κB in response to bRNA or Streptococcus pyogenes in an RNA-specific manner. TLR7 antagonist IRS661 could, in addition, inhibit TLR13 signaling and reduced recognition of whole Gram-positive bacteria by DCs, also in the absence of TLR7. The results identify TLR13 as a receptor for bRNA.

Despite limited data on safety and immunogenicity, heterologous prime-boost vaccination is currently recommended for individuals with ChAdOx1 nCoV-19 prime immunization in certain age groups. In this prospective, single-center study we included 166 health care workers from Heidelberg University Hospital who received either heterologous ChAdOx1 nCoV-19/BNT162b2, homologous BNT162b2 or homologous ChAdOx1 nCoV-19 vaccination between December 2020 and May 2021. We measured anti-S1 IgG, SARS-CoV-2 specific neutralizing antibodies, and antibodies against different SARS-CoV-2 fragments 0–3 days before and 19–21 days after boost vaccination. Before boost, 55/70 (79%) ChAdOx1 nCoV-19-primed compared with 44/45 (98%) BNT162b2-primed individuals showed positive anti-S1 IgG with a median (IQR) anti-S1 IgG index of 1.95 (1.05–2.99) compared to 9.38 (6.26–17.12). SARS-CoV-2 neutralizing antibodies exceeded the threshold in 24/70 (34%) of ChAdOx1 nCoV-19-primed and 43/45 (96%) of BNT162b2-primed individuals. After boosting dose, median (IQR) anti-S1 IgG index in heterologous ChAdOx1 nCoV-19/BNT162b2 vaccinees was 116.2 (61.84–170), compared to 13.09 (7.03–29.02) in homologous ChAdOx1 nCoV-19 and 145.5 (100–291.1) in homologous BNT162b2 vaccinees. All boosted vaccinees exceeded the threshold for neutralization, irrespective of their vaccination scheme. Vaccination was well-tolerated overall. We show that heterologous ChAdOx1 nCoV-19/BNT162b2 vaccination is safe and induces a strong and broad humoral response in healthy individuals.

؊/؊ mDC cultures but was severely reduced in mDC cultures from mice lacking IFN regulatory factor 3. Our observations suggest that mDCs respond to incoming virus via a pathway that differs from the fusion-independent, MyD88-mediated endosomal pathway described for the induction of IFN-␣/␤ in pDCs. We propose that events during or downstream of viral fusion, but prior to replication, can activate IFN-␣/␤ in mDCs. Thus, mDCs may contribute to the antiviral response activated by the immune system at early time points after infection.

DAP12 is an ITAM-containing adaptor molecule conveying activating properties to surface receptors on many cell types. We show here that DAP12 paradoxically down-modulates plasmacytoid dendritic cell (pDC) cytokine production in vivo during murine CMV (MCMV) infection. Higher levels of IFN-αβ and IL-12 were detected upon MCMV infection or CpG treatment in DAP12-deficient (DAP12°) mice as compared with wild-type (WT) mice. This resulted from altered homeostasis and enhanced responsiveness of pDCs in DAP12° animals. Increased numbers of pDCs were observed in the periphery of both naive and MCMV-infected DAP12° mice. A higher proportion of pDCs was activated in infected DAP12° mice, as demonstrated by intracellular staining using an optimized protocol for simultaneous detection of IFN-α and IFN-β. The homeostasis of WT and DAP12° pDCs did not differ in mixed bone marrow chimeric mice. In addition, a similar efficiency of pDC differentiation was observed in vitro in Fms-like tyrosine kinase receptor 3 ligand cultures of WT and DAP12° bone marrow cells. This suggests that DAP12 signaling effects on pDC homeostasis are indirect. In contrast, in response to CpG, DAP12-mediated effects on both IL-12 and IFN-αβ production were intrinsic to the pDCs. However, in response to MCMV, only IL-12 but not IFN-αβ production was affected by pDC-intrinsic DAP12 signaling. Thus, DAP12 signaling in pDCs can mediate different regulatory effects on their functions, depending on the mechanisms of pDC activation. The potential implications of the regulation of pDC functions by DAP12 for promoting health over disease are discussed.

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Background and objectivesAntibody response after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination is impaired in kidney transplant recipients. Emerging variants, such as B.1.617.2 (δ), are of particular concern because of their higher transmissibility and partial immune escape. Little is known about protection against these variants in immunocompromised patients.Design, setting, participants, & measurementsIn this prospective two-center study, antispike 1 IgG and surrogate neutralizing antibodies were measured in 173 kidney transplant recipients and 166 healthy controls with different vaccination schedules. In addition, different SARS-CoV-2 epitope antibodies from 135 vaccinated kidney transplant recipients were compared with antibodies in 25 matched healthy controls after second vaccination. In 36 kidney transplant recipients with seroconversion, neutralization against B.1.1.7 (α), B.1.351 (β), and B.1.617.2 (δ) was determined on VeroE6 cells and compared with neutralization in 25 healthy controls.ResultsKidney transplant recipients had significantly lower seroconversion rates compared with healthy controls. After the second vaccination, antispike 1, antireceptor-binding domain, and surrogate neutralizing antibodies were detectable in 30%, 27%, and 24% of kidney transplant recipients, respectively. This compares with 100%, 96%, and 100% in healthy controls, respectively (P<0.001). Neutralization against B.1.1.7 was detectable in all kidney transplant recipients with seroconversion, with a median serum dilution that reduces infection of cells by 50% of 80 (interquartile range, 80–320). In contrast, only 23 of 36 (64%) and 24 of 36 (67%) kidney transplant recipients showed neutralization against B.1.351 and B.1.617.2, respectively, with median serum dilutions that reduce infection of cells by 50% of 20 (interquartile range, 0–40) and 20 (interquartile range, 0–40), respectively. Neutralization against different variants was significantly higher in healthy controls (P<0.001), with all patients showing neutralization against all tested variants.ConclusionsSeroconverted kidney transplant recipients show impaired neutralization against emerging variants of concern after standard two-dose vaccination.Clinical Trial registry name and registration number:Observational study to assess the SARS-CoV-2 specific immune response in kidney transplant recipients (COVID-19 related immune response), DRKS00024668

STAT1 mediates signaling in response to IFN-α, -β, and -γ, cytokines required for protective immunity against several viral, bacterial, and eukaryotic pathogens. The protective role of STAT1 in the control of intranasal infection with the obligate intracellular bacterium Chlamydia pneumoniae was analyzed. IFN-γ−/− or IFN-γ receptor (R)−/− mice were highly susceptible to infection with C. pneumoniae. We found that STAT1−/− mice were even more susceptible to C. pneumoniae than IFN-γ−/− or IFN-γR−/− mice. Phosphorylation of STAT1 was detected in the lungs of C. pneumoniae-infected wild-type, IFN-γR−/−, and IFN-αβR−/− mice, but not in mice lacking both IFN-αβR and IFN-γR. In line with this, IFN-αβR−/−/IFN-γR−/− mice showed increased susceptibility to infection compared with IFN-γR−/− mice. However, C. pneumoniae-infected IFN-αβR−/− or IFN regulatory factor 3−/− mice showed no increased susceptibility and similar IFN-γ expression compared with wild-type mice. CD4+ or CD8+ cells released IFN-γ in vivo and conferred protection against C. pneumoniae in a STAT1-independent manner. In contrast, STAT1 mediated a nonredundant protective role of nonhemopoietic cells but not of hemopoietic cells. Nonhemopoietic cells accounted for the expression of STAT1-mediated indoleamine 2, 3-dioxygenase and the p47 GTPase LRG-47, but not inducible NO synthase mRNA. In summary, we demonstrate that STAT1 mediates a cooperative effect of IFN-αβ and IFN-γ on nonhemopoietic cells, resulting in protection against C. pneumoniae.