Efficacy of Retreatment After Failed Direct-acting Antiviral Therapy in Patients With HCV Genotype 1-3 Infections

Hepatitis C virus infection is causing chronic liver disease, cirrhosis, and hepatocellular carcinoma. By combining direct-acting antivirals (DAAs), high sustained virologic response rates (SVRs) can be achieved. Resistance-associated substitutions (RASs) are commonly observed after DAA failure, and especially nonstructural protein 5A (NS5A) RASs may impact retreatment options.^1-3 Data on retreatment of DAA failure patients using first-generation DAAs are limited.^4-7 Recently, a second-generation protease- and NS5A-inhibitor plus sofosbuvir (voxilaprevir/velpatasvir/sofosbuvir [VOX/VEL/SOF]) was approved for retreatment after DAA failure.⁸ However, this and other second-generation regimens are not available in many resource-limited countries or are not reimbursed by regular insurance, and recommendations regarding the selection of retreatment regimens using first-generation DAAs are very important. This study aimed to analyze patients who were re-treated with first-generation DAAs after failure of a DAA combination therapy.

Transmembrane beta-barrel of staphylococcal alpha-toxin forms in sensitive but not in resistant cells

Staphylococcal alpha-toxin is a 293-residue, single-chain polypeptide that spontaneously assembles into a heptameric pore in target cell membranes. To identify the pore-forming domain, substitution mutants have been produced in which single cysteine residues were introduced throughout the toxin molecule. By attaching the environmentally sensitive dye acrylodan to the sulfhydryl groups, the environment of individual amino acid side chains could be probed. In liposomes, a single 23-amino acid sequence (residues 118-140) was found to move from a polar to a nonpolar environment, indicating that this sequence forms the walls of the pore. However, periodicity in side chain environmental polarity could not be detected in the liposomal system. In the present study, the fluorimetric analyses were extended to physiological target cells. With susceptible cells such as rabbit erythrocytes and human lymphocytes, the 23 central amino acids 118-140 were again found to insert into the membrane; in contrast to the previous study with liposomes, the expected periodicity was now detected. Thus, every other residue in the sequence 126-140 entered a nonpolar environment in a striking display of an amphipathic transmembrane beta-barrel. In contrast, human granulocytes were found to bind alpha-toxin to a similar extent as lymphocytes, but the heptamers forming on these cells failed to insert their pore-forming domain into the membrane. As a consequence, nonfunctional heptamers assembled and the cells remained viable. The data resolve the molecular organization of a pore-forming toxin domain in living cells and reveal that resistant cells can prevent insertion of the functional domain into the bilayer.