Biology subjects

Pauly, M. D.

Publications and source records attributed to Pauly, M. D..

4 recordsLinked to original sources

bioRxiv2026

Within-host adaptive evolution is limited by genetic drift in experimental human influenza A virus infections

Selection of advantageous mutations drives the emergence of dominant variants during seasonal influenza epidemics. However, within-host detection of such variants remains rare, limiting our understanding of how selection operates at the scale of individual hosts. In this study, we used a controlled human infection model to examine the within-host evolutionary dynamics in thirteen participants intranasally infected with a seasonal H3N2 influenza A virus. Although this clinical trial is ongoing, our work represents a pre-planned, interim, exploratory analysis. Results in this system were contrasted with those observed in a ferret model of infection. The inoculum, used in both humans and ferrets, carried standing diversity that enabled evaluation of variant trajectories during infection. Although the dynamics were variable among participants, in humans, the minor variants in the PA and NP gene segments tended to increase in frequency as infection progressed. Variant dynamics were more consistent among ferrets but showed differences from humans in the fate of the minor NP allele. Based on these observations, we fit a population genetic model to longitudinal measurements of variant frequencies. Estimates of variant selection coefficients and effective viral population sizes indicated that in humans the two minor variants had a selective advantage over the major variants, but genetic drift was strong, limiting the efficiency of selection. In ferrets, the PA minor variant also was estimated to have a selective advantage, while the NP minor variant was estimated to have a selective disadvantage. Moreover, effective viral population sizes were estimated to be considerably higher in ferrets than in humans, indicating that genetic drift was weaker in ferrets. Our analyses reveal differing selective environments acting on influenza viruses in human and ferret hosts and indicate that selection at the within-host level is weakened by genetic drift.

microbiology↗

bioRxiv2025

Innate antiviral readiness drives the expansion of protective T stem cell memory against influenza

The development of T-cell-based influenza vaccines relies on eliciting broad CD8+ T-cell immunity, wherein T stem cell-like memory (TSCM) cells serve as the ultimate long-lived reservoir for immune memory, thereby unlocking the potential for durable protection against viral drift and shift. However, the specific immunological cues that drive the robust expansion and functional preservation of this self-renewing, multipotent subset remain unknown. Here, utilizing multi-omic systems immunology in a pediatric cohort immunized with live attenuated influenza vaccine, we identified the determinants governing the expansion of influenza virus-reactive TSCM cells. We show that a pre-existing state of innate antiviral readiness, defined by a plasmacytoid dendritic cell-associated type I interferon signature, is the requisite condition for a robust TSCM expansion. Mechanistically, this baseline innate state enhances antigen priming and enforces a qualitative divergence in T-cell fate, driving responders toward a functionally poised, Th1-dominant phenotype while non-responders default to a dysfunctional, hyper-proliferative state. To determine the clinical relevance of this cellular subset, we analyzed an independent controlled human influenza challenge study. This validation revealed a critical functional division of labor in host defense: whereas pre-existing antibodies primarily mitigated symptom severity, the baseline frequency of influenza virus-reactive TSCM cells was the strongest predictor of rapid viral load clearance. These findings establish that the expansion of durable cellular memory is not stochastic but is predetermined by the innate cytokine environment, providing a predictive biomarker for patient stratification and a validated target for adjuvants designed to expand the TSCM reservoir deliberately.

immunology↗

bioRxiv2017

Epistatic interactions within the influenza virus polymerase complex mediate mutagen resistance and replication fidelity

Lethal mutagenesis is a broad-spectrum antiviral strategy that employs mutagenic nucleoside analogs to exploit the high mutation rate and low mutational tolerance of many RNA viruses. Studies of mutagen-resistant viruses have identified determinants of replicative fidelity and the importance of mutation rate to viral population dynamics. We have previously demonstrated the effective lethal mutagenesis of influenza virus using three nucleoside analogs as well as the viruss high genetic barrier to mutagen resistance. Here, we investigate the mutagen-resistant phenotypes of mutations that were enriched in drug-treated populations. We find that PB1 T123A has higher replicative fitness than the wild type, PR8, and maintains its level of genome production during 5-fluorouracil treatment. Surprisingly, this mutagen-resistant variant also has an increased baseline rate of C to U and G to A mutations. A second drug-selected mutation, PA T97I, interacts epistatically with PB T123A to mediate high-level mutagen resistance, predominantly by limiting the inhibitory effect of nucleosides on polymerase activity. Consistent with the importance of epistatic interactions in the influenza polymerase, we find that nucleoside analog resistance and replication fidelity are strain dependent. Two previously identified ribavirin-resistance mutations, PB1 V43I and PB1 D27N, do not confer drug resistance in the PR8 background, and the PR8-PB1 V43I polymerase exhibits a normal baseline mutation rate. Our results highlight the genetic complexity of the influenza virus polymerase and demonstrate that increased replicative capacity is a mechanism by which an RNA virus can counter the negative effects of elevated mutation rates.\n\nImportanceRNA viruses exist as genetically diverse populations. This standing genetic diversity gives them the potential to adapt rapidly, evolve resistance to antiviral therapeutics, and evade immune responses. Viral mutants with altered mutation rates or mutational tolerance have provided insights into how genetic diversity arises and how it affects the behavior of RNA viruses. To this end, we identified variants within the polymerase complex of influenza virus that are able tolerate drug-mediated increases in viral mutation rates. We find that drug resistance is highly dependent on interactions among mutations in the polymerase complex. In contrast to other viruses, influenza virus counters the effect of higher mutation rates primarily by maintaining high levels of genome replication. These findings suggest the importance of maintaining large population sizes for viruses with high mutation rates and show that multiple proteins can affect both mutation rate and genome synthesis.

microbiology↗

bioRxiv2017

The mutation rates and mutational bias of influenza A virus

Influenza virus has a high mutation rate, and this low replicative fidelity contributes to its capacity for rapid evolution. Clonal sequencing and fluctuation tests have suggested that the mutation rate of influenza A virus is 7.1 x 10-6 - 4.5 x 10-5 substitutions per nucleotide per cell infection cycle and 2.7 x 10-6 - 3.0 x 10-5 substitutions per nucleotide per strand copied (s/n/r). However, sequencing assays are biased toward mutations with minimal impacts on viral fitness and fluctuation tests typically investigate only a subset of the twelve mutational classes. We developed a fluctuation test based on reversion to fluorescence in a set of virally encoded mutant green fluorescent proteins. This method allowed us to measure the rates of selectively neutral mutations representative of all 12 mutational classes in the context of an unstructured RNA. We measured an overall mutation rate of 1.8 x 10-4 s/n/r for PR8 (H1N1) and 2.5 x 10-4 s/n/r for Hong Kong 2014 (H3N2). The replication mode was linear. The mutation rates of these divergent strains are significantly higher than previous estimates and suggest that each replicated genome will have an average of 2-3 mutations. The viral mutational spectrum is heavily biased toward A to G and U to C transitions, resulting in a transition to transversion bias of 2.7 and 3.6 for the two strains. These mutation rates were relatively constant over a range of physiological temperatures. Our high-resolution analysis of influenza virus mutation rates will enable more refined models of its molecular evolution.\n\nSignificanceThe rapid evolution of influenza virus is a major problem in public health. A key factor driving this rapid evolution is the virus very high mutation rate. We developed a new method for measuring the rates of all 12 mutational classes in influenza virus, which eliminates some of the biases of existing assays. We find that the influenza virus mutation rate is much higher than previously reported and is consistent across two distinct strains and a range of temperatures. Our data suggest that influenza viruses replicate at their maximally tolerable mutation rates, highlighting both the virus evolutionary potential and its significant constraints.

microbiology↗