Background & Aims Hepatitis D virus (HDV) superinfection in patients with hepatitis B virus (HBV) is associated with rapid progression to liver cirrhosis and hepatocellular carcinoma. Treatment options are limited, and no vaccine is available. Although HDV-specific CD8 + T cells are thought to control the virus, little is known about which HDV epitopes are targeted by virus-specific CD8 + T cells or why these cells ultimately fail to control the infection. We aimed to define how HDV escapes the CD8 + T-cell–mediated response. Methods We collected plasma and DNA samples from 104 patients with chronic HDV and HBV infection at medical centers in Europe and the Middle East, sequenced HDV, typed human leukocyte antigen (HLA) class I alleles from patients, and searched for polymorphisms in HDV RNA associated with specific HLA class I alleles. We predicted epitopes in HDV that would be recognized by CD8 + T cells and corresponded with the identified virus polymorphisms in patients with resolved (n = 12) or chronic (n = 13) HDV infection. Results We identified 21 polymorphisms in HDV that were significantly associated with specific HLA class I alleles ( P < .005). Five of these polymorphisms were found to correspond to epitopes in HDV that are recognized by CD8 + T cells; we confirmed that CD8 + T cells in culture targeted these HDV epitopes. HDV variant peptides were only partially cross-recognized by CD8 + T cells isolated from patients, indicating that the virus had escaped detection by these cells. These newly identified HDV epitopes were restricted by relatively infrequent HLA class I alleles, and they bound most frequently to HLA-B. In contrast, frequent HLA class I alleles were not associated with HDV sequence polymorphisms. Conclusions We analyzed sequences of HDV RNA and HLA class I alleles that present epitope peptides to CD8 + T cells in patients with persistent HDV infection. We identified polymorphisms in the HDV proteome that associate with HLA class I alleles. Some variant peptides in epitopes from HDV were only partially recognized by CD8 + T cells isolated from patients; these could be mutations that allow HDV to escape the immune response, resulting in persistent infection. HDV escape from the immune response was associated with uncommon HLA class I alleles, indicating that HDV evolves, at the population level, to evade recognition by common HLA class I alleles.

Vaccination against SARS-CoV-2 infection is currently approved and shows favorable outcomes, but little known about antibody responses in solid organ transplant recipients, since these patients are known to have an impaired immune response upon vaccination and have not been included in admission studies. We therefore analyzed immunogenicity in 43 liver transplant (LT) recipients in a median of 15 days (IQR, 12–24) after receiving two doses of the mRNA-based SARS-CoV-2 vaccine BNT162b2 following the standard protocol, and compared these results to a control group consisting of 20 healthcare workers (HCWs). Thirty-four of the 43 (79%) LT recipients developed antibodies, compared to 20 out of 20 (100%) in the control group (p = 0.047). The median SARS-CoV-2 IgG titer was significantly lower in the LT recipients compared to the control group (216 vs. >2080 BAU/mL, p = 0.0001). Age and sex distribution was similar in the LT patients that developed antibodies after vaccination compared to those who did not. Interestingly, the patients who received mycophenolate mofetil exhibited a reduced vaccination response compared to the other LT patients (5 of 11 (45.5%) vs. 29 of 32 (90.6%), p = 0.004). In conclusion, our data reveal lower immunogenicity of SARS-CoV-2 vaccine BNT162b2 in LT patients compared to the control group, but still show superior results compared to other solid organ transplant recipients reported so far.

SARS-CoV-2 infection is known to lead to severe morbidity and mortality in patients with liver cirrhosis. For this reason, vaccination of these patients against COVID-19 is widely recommended. However, data regarding immunogenicity in patients with liver cirrhosis is limited and even less is known about the kinetics of antibody response, as well as the optimal timing of booster immunization. We analyzed immunogenicity in 110 patients with liver cirrhosis after receiving two doses of the mRNA-based vaccine BNT162b2 following the standard protocol and compared these results to a control group consisting of 80 healthcare workers. One hundred and six patients with liver cirrhosis (96%) developed antibodies against SARS-CoV-2, compared to 79 (99%) in the control group (p = 0.400). Still, the median SARS-CoV-2 IgG titer was significantly lower in patients with liver cirrhosis compared to the control group (939 vs. 1905 BAU/mL, p = 0.0001). We also analyzed the strength of the antibody response in relation to the time between the second dose and antibody detection. Antibody titers remained relatively stable in the control group while showing a rapid and significant decrease in patients with liver cirrhosis. In conclusion, our data reveals a favorable initial outcome after vaccination with the COVID-19 vaccine BNT162b2 in cirrhotic patients but show a rapid deterioration of the antibody response after time, thereby giving a strong hint towards the importance of early booster immunization for this group of patients.

We have previously characterized mouse CMV (MCMV)–encoded immune-evasive IFN signaling inhibition and identified the viral protein pM27 as inducer of proteasomal degradation of STAT2. Extending our analysis to STAT1 and STAT3, we found that MCMV infection neither destabilizes STAT1 protein nor prevents STAT1 tyrosine Y701 phosphorylation, nuclear translocation, or the capability to bind γ-activated sequence DNA-enhancer elements. Unexpectedly, the analysis of STAT3 revealed an induction of STAT3 Y705 phosphorylation by MCMV. In parallel, we found decreasing STAT3 protein amounts upon MCMV infection, although STAT3 expression normally is positive autoregulative. STAT3 phosphorylation depended on the duration of MCMV infection, the infectious dose, and MCMV gene expression but was independent of IFNAR1, IL-10, IL-6, and JAK2. Although STAT3 phosphorylation did not require MCMV immediate early 1, pM27, and late gene expression, it was restricted to MCMV-infected cells and not transmitted to bystander cells. Despite intact STAT1 Y701 phosphorylation, IFN-γ–induced target gene transcription (e.g., IRF1 and suppressor of cytokine signaling [SOCS] 1) was strongly impaired. Likewise, the induction of STAT3 target genes (e.g., SOCS3) by IL-6 was also abolished, indicating that MCMV antagonizes STAT1 and STAT3 despite the occurrence of tyrosine phosphorylation. Consistent with the lack of SOCS1 induction, STAT1 phosphorylation was prolonged upon IFN-γ treatment. We conclude that the inhibition of canonical STAT1 and STAT3 target gene expression abrogates their intrinsic negative feedback loops, leading to accumulation of phospho–tyrosine-STAT3 and prolonged STAT1 phosphorylation. These findings challenge the generalization of tyrosine-phosphorylated STATs necessarily being transcriptional active and document antagonistic effects of MCMV on STAT1/3-dependent target gene expression.

Viruses and hosts are situated in a molecular arms race. To avoid morbidity and mortality, hosts evolved antiviral restriction factors. These restriction factors exert selection pressure on the viruses and drive viral evolution toward increasingly efficient immune antagonists. Numerous viruses exploit cellular DNA damage-binding protein 1 (DDB1)-containing Cullin RocA ubiquitin ligases (CRLs) to induce the ubiquitination and subsequent proteasomal degradation of antiviral factors expressed by their hosts. To establish a comprehensive understanding of the underlying protein interaction networks, we performed immuno-affinity precipitations for a panel of DDB1-interacting proteins derived from viruses such as mouse cytomegalovirus (MCMV, Murid herpesvirus [MuHV] 1), rat cytomegalovirus Maastricht MuHV2, rat cytomegalovirus English MuHV8, human cytomegalovirus (HCMV), hepatitis B virus (HBV), and human immunodeficiency virus (HIV). Cellular interaction partners were identified and quantified by mass spectrometry (MS) and validated by classical biochemistry. The comparative approach enabled us to separate unspecific interactions from specific binding partners and revealed remarkable differences in the strength of interaction with DDB1. Our analysis confirmed several previously described interactions like the interaction of the MCMV-encoded interferon antagonist pM27 with STAT2. We extended known interactions to paralogous proteins like the interaction of the HBV-encoded HBx with different Spindlin proteins and documented interactions for the first time, which explain functional data like the interaction of the HIV-2-encoded Vpr with Bax. Additionally, several novel interactions were identified, such as the association of the HIV-2-encoded Vpx with the transcription factor RelA (also called p65). For the latter interaction, we documented a functional relevance in antagonizing NF-κB-driven gene expression. The mutation of the DDB1 binding interface of Vpx significantly impaired NF-κB inhibition, indicating that Vpx counteracts NF-κB signaling by a DDB1- and CRL-dependent mechanism. In summary, our findings improve the understanding of how viral pathogens hijack cellular DDB1 and CRLs to ensure efficient replication despite the expression of host restriction factors.