Impact of Pre-Exposure History and Host Genetics on Antibody Avidity Following Norovirus Vaccination

Background: Development of high avidity, broadly neutralizing antibodies (Abs) is a priority after vaccination against rapidly evolving, widely disseminated viruses like human norovirus. After vaccination with a multivalent GI.1 and GII.4c norovirus virus-like particle (VLP) vaccine candidate adjuvanted with alum and monophosphoryl lipid A (MPL), blockade Ab titers peaked early, with no increase in titer following a second vaccine dose. Methods: Blockade Ab relative avidity was evaluated by measuring the slope of blockade Ab neutralization curves. Results: Blockade Ab avidity to the GI.1 vaccine component peaked at day 35 (7 days after dose 2). Avidities to heterotypic genogroup I VLPs were not sustained at day 35 after vaccination or GI.1 infection, as measured from archived sera. Only secretor-positive participants maintained high avidity blockade Ab to GI.1 at day 180. Avidity to the GII.4c vaccine component peaked at day 7, remained elevated through day 180, and was not secretor dependent. Avidity to an immunologically novel GII.4 strain VLP correlated with preexisting Ab titer to an ancestral strain Epitope A. Conclusions: Host genetics and pre-exposure history shape norovirus vaccine Ab responses, including blockade Ab avidity. Avidity of potentially neutralizing Ab may be an important metric for evaluating vaccine responses to highly penetrant viruses with cross-reactive serotypes

Live, Attenuated Influenza A H5N1 Candidate Vaccines Provide Broad Cross-Protection in Mice and Ferrets

BACKGROUND: Recent outbreaks of highly pathogenic influenza A H5N1 viruses in humans and avian species that began in Asia and have spread to other continents underscore an urgent need to develop vaccines that would protect the human population in the event of a pandemic. METHODS AND FINDINGS: Live, attenuated candidate vaccines possessing genes encoding a modified H5 hemagglutinin (HA) and a wild-type (wt) N1 neuraminidase from influenza A H5N1 viruses isolated in Hong Kong and Vietnam in 1997, 2003, and 2004, and remaining gene segments derived from the cold-adapted (ca) influenza A vaccine donor strain, influenza A/Ann Arbor/6/60 ca (H2N2), were generated by reverse genetics. The H5N1 ca vaccine viruses required trypsin for efficient growth in vitro, as predicted by the modification engineered in the gene encoding the HA, and possessed the temperature-sensitive and attenuation phenotypes specified by the internal protein genes of the ca vaccine donor strain. More importantly, the candidate vaccines were immunogenic in mice. Four weeks after receiving a single dose of 10(6) 50% tissue culture infectious doses of intranasally administered vaccines, mice were fully protected from lethality following challenge with homologous and antigenically distinct heterologous wt H5N1 viruses from different genetic sublineages (clades 1, 2, and 3) that were isolated in Asia between 1997 and 2005. Four weeks after receiving two doses of the vaccines, mice and ferrets were fully protected against pulmonary replication of homologous and heterologous wt H5N1 viruses. CONCLUSIONS: The promising findings in these preclinical studies of safety, immunogenicity, and efficacy of the H5N1 ca vaccines against antigenically diverse H5N1 vaccines provide support for their careful evaluation in Phase 1 clinical trials in humans

Effect of Stalling after Mismatches on the Error Catastrophe in Nonenzymatic Nucleic Acid Replication

The frequency of errors during genome replication limits the amount of functionally important information that can be passed on from generation to generation. During the origin of life, mutation rates are thought to have been quite high, raising a classic chicken-and-egg paradox: could nonenzymatic replication propagate sequences accurately enough to allow for the emergence of heritable function? Here we show that the theoretical limit on genomic information content may increase substantially as a consequence of dramatically slowed polymerization after mismatches. As a result of postmismatch stalling, accurate copies of a template tend to be completed more rapidly than mutant copies and the accurate copies can therefore begin a second round of replication more quickly. To quantify this effect, we characterized an experimental model of nonenzymatic, template-directed nucleic acid polymerization. We found that most mismatches decrease the rate of primer extension by more than 2 orders of magnitude relative to a matched (Watson-Crick) control. A chemical replication system with this property would be able to propagate sequences long enough to have function. Our study suggests that the emergence of functional sequences during the origin of life would be possible even in the face of the high intrinsic error rates of chemical replication

Unusual Polymorphisms in Human Immunodeficiency Virus Type 1 Associated with Nonprogressive Infection

Factors accounting for long-term nonprogression may include infection with an attenuated strain of human immunodeficiency virus type 1 (HIV-1), genetic polymorphisms in the host, and virus-specific immune responses. In this study, we examined eight individuals with nonprogressing or slowly progressing HIV-1 infection, none of whom were homozygous for host-specific polymorphisms (CCR5-Δ32, CCR2-64I, and SDF-1-3\u27A) which have been associated with slower disease progression. HIV-1 was recovered from seven of the eight, and recovered virus was used for sequencing the full-length HIV-1 genome; full-length HIV-1 genome sequences from the eighth were determined following amplification of viral sequences directly from peripheral blood mononuclear cells (PBMC). Longitudinal studies of one individual with HIV-1 that consistently exhibited a slow/low growth phenotype revealed a single amino acid deletion in a conserved region of the gp41 transmembrane protein that was not seen in any of 131 envelope sequences in the Los Alamos HIV-1 sequence database. Genetic analysis also revealed that five of the eight individuals harbored HIV-1 with unusual 1- or 2-amino-acid deletions in the Gag sequence compared to subgroup B Gag consensus sequences. These deletions in Gag have either never been observed previously or are extremely rare in the database. Three individuals had deletions in Nef, and one had a 4-amino-acid insertion in Vpu. The unusual polymorphisms in Gag, Env, and Nef described here were also found in stored PBMC samples taken 3 to 11 years prior to, or in one case 4 years subsequent to, the time of sampling for the original sequencing. In all, seven of the eight individuals exhibited one or more unusual polymorphisms; a total of 13 unusual polymorphisms were documented in these seven individuals. These polymorphisms may have been present from the time of initial infection or may have appeared in response to immune surveillance or other selective pressures. Our results indicate that unusual, difficult-to-revert polymorphisms in HIV-1 can be found associated with slow progression or nonprogression in a majority of such cases

Mutational Specificity of γ-Radiation-Induced Guanine−Thymine and Thymine−Guanine Intrastrand Cross-Links in Mammalian Cells and Translesion Synthesis Past the Guanine−Thymine Lesion by Human DNA Polymerase η†

ABSTRACT: Comparative mutagenesis of γ- or X-ray-induced tandem DNA lesions G[8,5-Me]T and T[5-Me,8]G intrastrand cross-links was investigated in simian (COS-7) and human embryonic (293T) kidney cells. For G[8,5-Me]T in 293T cells, 5.8 % of progeny contained targeted base substitutions, whereas 10.0 % showed semitargeted single-base substitutions. Of the targeted mutations, the G f T mutation occurred with the highest frequency. The semitargeted mutations were detected up to two bases 5 ′ and three bases 3 ′ to the cross-link. The most prevalent semitargeted mutation was a C f T transition immediately 5 ′ to the G[8,5-Me]T cross-link. Frameshifts (4.6%) (mostly small deletions) and multiple-base substitutions (2.7%) also were detected. For the T[5-Me,8]G cross-link, a similar pattern of mutations was noted, but the mutational frequency was significantly higher than that of G[8,5-Me]T. Both targeted and semitargeted mutations occurred with a frequency of ∼16%, and both included a dominant G f T transversion. As in 293T cells, more than twice as many targeted mutations in COS cells occurred in T[5-Me,8]G (11.4%) as in G[8,5-Me]T (4.7%). Also, the level of semitargeted single-base substitutions 5 ′ to the lesion was increased and 3 ′ to the lesion decreased in T[5-Me,8]G relative to G[8,5-Me]T in COS cells. It appeared that the majority of the base substitutions at or near the cross-links resulted from incorporation of dAMP opposite the template base, in agreement with the so-called “A-rule”. To determin

Transfer of penicillin resistance between Neisseriae in microcosm

Horizontal gene transfer between commensal and pathogenic Neisseriae is the mechanism proposed to explain how pathogenic species acquire altered portions of the penA gene, which encodes penicillin binding protein 2. These changes resulted in a moderately penicillin-resistant phenotype in the meningococci, whose frequency of isolation in Spain increased at the end of the 1980s. Little has been published about the possibility of this gene transfer in nature or about its simulation in the laboratory. We designed a simple microcosm, formed by solid and liquid media, that partially mimics the upper human respiratory tract. In this microcosm, penicillin-resistant commensal strains and the fully susceptible meningococcus were co-cultivated. The efficiency of gene transfer between the strains depended on the phase of bacterial growth and the conditions of culture. Resistance of penicillin was acquired in different steps irrespective of the source of the DNA. The presence of DNase in the medium had no effect on gene transfer, but it was near zero when nicked DNA was used. Cell-to-cell contact or membrane blebs could explain these results. The analysis of sequences of the transpeptidase domain of PBP2 from transformants, and from donor and recipient strains demonstrated that the emergence of moderately resistant transformants was due to genetic exchange between the co-cultivated strains. Finally, mechanisms other than penA modification could be invoked to explain decreased susceptibilit