Ebolavirus delta-peptide immunoadhesins inhibit marburgvirus and ebolavirus cell entry.

With the exception of Reston and Lloviu viruses, filoviruses (marburgviruses, ebolaviruses, and "cuevaviruses") cause severe viral hemorrhagic fevers in humans. Filoviruses use a class I fusion protein, GP(1,2), to bind to an unknown, but shared, cell surface receptor to initiate virus-cell fusion. In addition to GP(1,2), ebolaviruses and cuevaviruses, but not marburgviruses, express two secreted glycoproteins, soluble GP (sGP) and small soluble GP (ssGP). All three glycoproteins have identical N termini that include the receptor-binding region (RBR) but differ in their C termini. We evaluated the effect of the secreted ebolavirus glycoproteins on marburgvirus and ebolavirus cell entry, using Fc-tagged recombinant proteins. Neither sGP-Fc nor ssGP-Fc bound to filovirus-permissive cells or inhibited GP(1,2)-mediated cell entry of pseudotyped retroviruses. Surprisingly, several Fc-tagged Δ-peptides, which are small C-terminal cleavage products of sGP secreted by ebolavirus-infected cells, inhibited entry of retroviruses pseudotyped with Marburg virus GP(1,2), as well as Marburg virus and Ebola virus infection in a dose-dependent manner and at low molarity despite absence of sequence similarity to filovirus RBRs. Fc-tagged Δ-peptides from three ebolaviruses (Ebola virus, Sudan virus, and Taï Forest virus) inhibited GP(1,2)-mediated entry and infection of viruses comparably to or better than the Fc-tagged RBRs, whereas the Δ-peptide-Fc of an ebolavirus nonpathogenic for humans (Reston virus) and that of an ebolavirus with lower lethality for humans (Bundibugyo virus) had little effect. These data indicate that Δ-peptides are functional components of ebolavirus proteomes. They join cathepsins and integrins as novel modulators of filovirus cell entry, might play important roles in pathogenesis, and could be exploited for the synthesis of powerful new antivirals.

Booster of mRNA-1273 Strengthens SARS-CoV-2 Omicron Neutralization.

The Omicron variant of SARS-CoV-2 is raising concerns because of its increased transmissibility and potential for reduced susceptibility to antibody neutralization. To assess the potential risk of this variant to existing vaccines, serum samples from mRNA-1273 vaccine recipients were tested for neutralizing activity against Omicron and compared to neutralization titers against D614G and Beta in live virus and pseudovirus assays. Omicron was 41-84-fold less sensitive to neutralization than D614G and 5.3-7.4-fold less sensitive than Beta when assayed with serum samples obtained 4 weeks after 2 standard inoculations with 100 µg mRNA-1273. A 50 µg boost increased Omicron neutralization titers and may substantially reduce the risk of symptomatic vaccine breakthrough infections.

Hammerhead ribozymes designed to cleave all human rod opsin mRNAs which cause autosomal dominant retinitis pigmentosa.

PURPOSE: Knockdown hammerhead ribozymes were designed to cleave at a sterically accessible site in long expression-competent mutant and normal human rod opsin mRNAs. Ribozyme suppression of mutant mRNA is expected to rescue autosomal dominant retinitis pigmentosa (adRP) caused by rod opsin mutations. METHODS: Energy minimization algorithms predicted regions in human rod opsin mRNA accessible to ribozyme cleavage. Opsin and ribozyme RNAs were generated by in vitro transcription. Ribozyme cleavage reactions were performed in vitro at various enzyme:substrate ratios with appropriate controls and analyzed on denaturing polyacrylamide gels. RESULTS: A GUC triplet in a predicted unhybridized loop was selected as the target cleavage site. Ribozymes were designed to stabilize catalytic core folding. Ribozyme reactions with normal and representative mutant (C187Y) opsin mRNAs demonstrated a decrease of long and short RNA targets and proportional appearance of cleavage products. Site-specific targeting was proved by lack of cleavage of a normal mRNA engineered with a silently altered cleavage motif. CONCLUSIONS: Knockdown ribozymes, targeting all known adRP mutants, cleaved human rod opsin mRNAs at the intended target site in vitro. These ribozymes may reduce total opsin mRNA and protein in rod photoreceptors as a gene therapy strategy. A beneficial outcome on rod survival in adRP is expected although normal rhodopsin levels, already in excess, would also decrease. Knockdown ribozymes attack an accessible site common to all mutant mRNAs to avoid redesign and optimization for each new dominant mutation. This strategy can be extended to any dominant disease affecting genes normally expressed in excess.