Identification of tell-tale patterns in the 3' non-coding region of hantaviruses that distinguish HCPS-causing hantaviruses from HFRS-causing hantaviruses

Selective Depletion of ZAP-Binding CpG Motifs in HCV Evolution

Hepatitis C virus (HCV) is a bloodborne pathogen that can cause chronic liver disease and hepatocellular carcinoma. The loss of CpGs from virus genomes allows escape from restriction by the host zinc-finger antiviral protein (ZAP). The evolution of HCV in the human host has not been explored in the context of CpG depletion. We analysed 2616 full-length HCV genomes from 1977 to 2021. During the four decades of evolution in humans, we found that HCV genomes have become significantly depleted in (a) CpG numbers, (b) CpG O/E ratios (i.e., relative abundance of CpGs), and (c) the number of ZAP-binding motifs. Interestingly, our data suggests that the loss of CpGs in HCV genomes over time is primarily driven by the loss of ZAP-binding motifs; thus suggesting a yet unknown role for ZAP-mediated selection pressures in HCV evolution. The HCV core gene is significantly enriched for the number of CpGs and ZAP-binding motifs. In contrast to the rest of the HCV genome, the loss of CpGs from the core gene does not appear to be driven by ZAP-mediated selection. This work highlights CpG depletion in HCV genomes during their evolution in humans and the role of ZAP-mediated selection in HCV evolution.

CpG content in the Zika virus genome affects infection phenotypes in the adult brain and fetal lymph nodes

Increasing the number of CpG dinucleotides in RNA viral genomes, while preserving the original amino acid composition, leads to impaired infection which does not cause disease. Beneficially, impaired infection evokes antiviral host immune responses providing a cutting-edge vaccine approach. For example, we previously showed that CpG-enriched Zika virus variants cause attenuated infection phenotypes and protect against lethal challenge in mice. While CpG recoding is an emerging and promising vaccine approach, little is known about infection phenotypes caused by recoded viruses in vivo, particularly in non-rodent species. Here, we used well-established mouse and porcine models to study infection phenotypes of the CpG-enriched neurotropic and congenital virus—Zika virus, directly in the target tissues—the brain and placenta. Specifically, we used the uttermost challenge and directly injected mice intracerebrally to compare infection phenotypes caused by wild-type and two CpG-recoded Zika variants and model the scenario where vaccine strains breach the blood-brain barrier. Also, we directly injected porcine fetuses to compare in utero infection phenotypes and model the scenario where recoded vaccine strains breach the placental barrier. While overall infection kinetics were comparable between wild-type and recoded virus variants, we found convergent phenotypical differences characterized by reduced pathology in the mouse brain and reduced replication of CpG-enriched variants in fetal lymph nodes. Next, using next-generation sequencing for the whole virus genome, we compared the stability of de novo introduced CpG dinucleotides during prolonged virus infection in the brain and placenta. Most de novo introduced CpG dinucleotides were preserved in sequences of recoded Zika viruses showing the stability of vaccine variants. Altogether, our study emphasized further directions to fine-tune the CpG recoding vaccine approach for better safety and can inform future immunization strategies.