Complement-dependent mpox-virus-neutralizing antibodies in infected and vaccinated individuals.

Mpox virus (MPXV) caused a multi-country outbreak in non-endemic areas in 2022. Following historic success of smallpox vaccination with vaccinia virus (VACV)-based vaccines, the third generation modified vaccinia Ankara (MVA)-based vaccine was used as prophylaxis for MPXV, but its effectiveness remains poorly characterized. Here, we applied two assays to quantify neutralizing antibodies (NAbs) in sera from control, MPXV-infected, or MVA-vaccinated individuals. Various levels of MVA NAbs were detected after infection, historic smallpox, or recent MVA vaccination. MPXV was minimally sensitive to neutralization. However, addition of complement enhanced detection of responsive individuals and NAb levels. Anti-MVA and -MPXV NAbs were observed in 94% and 82% of infected individuals, respectively, and 92% and 56% of MVA vaccinees, respectively. NAb titers were higher in individuals born before 1980, highlighting the impact of historic smallpox vaccination on humoral immunity. Altogether, our results indicate that MPXV neutralization is complement dependent and uncover mechanisms underlying vaccine effectiveness.

Identification of a postendocytic sorting sequence in CCR5.

The chemokine receptor 5 (CCR5), a member of the G protein-coupled receptor family (GPCR), is used by human immunodeficiency virus type 1 (HIV-1) with a R5 tropism as an entry receptor in addition to CD4. It is a key target for an antiviral action aiming at inhibiting the HIV-1 entry process. Only few data are available today regarding the mechanism involved in the intracellular trafficking process of CCR5. Understanding how CCR5 cell surface expression is regulated is particularly important with regard to HIV-1 entry inhibition. We set out to investigate whether CCR5 molecular determinants were involved in the postendocytic recycling and degradative pathways. We constructed progressive deletion mutants of the C-terminal domain of CCR5 that we stably expressed in HEK293 cells. All of the deletion mutants were expressed at the cell surface and were functional HIV-1 receptors. The deletion mutants were internalized after stimulation, but they lost their ability to recycle to the plasma membrane. They were rerouted toward a lysosomal degradative pathway. We identified here a sequence of four amino acids, present at the extreme C terminus of CCR5, that is necessary for the recycling of the internalized receptor, independently of its phosphorylation. A detailed analysis of this sequence indicated that the four amino acids acted as a postsynaptic density 95/discs-large/zona occludens (PDZ) interacting sequence. These results show that the CCR5 cytoplasmic domain bears a sequence similar to the "recycling signals" previously identified in other GPCRs. Drugs able to disrupt the recycling pathway of CCR5 may constitute promising tools for therapeutic treatment.