Publications by authors named "John E Mittler"

Pathogens face a tradeoff with respect to virulence; while more virulent strains often have higher per-contact transmission rates, they are also more likely to kill their hosts earlier. Because virulence is a heritable trait, there is concern that a disease-modifying vaccine, which reduces the disease severity of an infected vaccinee without changing the underlying pathogen genotype, may result in the evolution of higher pathogen virulence. We explored the potential for such virulence evolution with a disease-modifying HIV-1 vaccine in an agent-based stochastic epidemic model of HIV in United States men who have sex with men (MSM).

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  • Policymakers face challenges in making decisions with limited information and conflicting predictions from different models, especially during crises like the COVID-19 pandemic.
  • A study brought together multiple modeling teams to assess reopening strategies in a mid-sized U.S. county, revealing consistent rankings for interventions despite variations in projection magnitudes.
  • The findings indicated that reopening workplaces could lead to a significant increase in infections, while restrictions could greatly reduce cumulative infections, highlighting the trade-offs between public health and economic activity with no optimal reopening strategy identified.
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  • Set-point viral load (SPVL) is found to correlate with the age of HIV acquisition, suggesting that older individuals may face a selection for more virulent strains due to decreasing risks of infection as they age.
  • The study utilized a model (EvoNetHIV) tailored for men who have sex with men (MSM) to simulate how various behavioral and clinical factors influence the relationship between age and SPVL.
  • Results indicated that while SPVL increases with age when not accounting for source partner SPVL, this effect diminishes significantly when it is included, highlighting behavioral factors like relationship duration and coital frequency as important influencers on SPVL outcomes.
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Pathogen populations can evolve in response to selective pressure from vaccine-induced immune responses. For HIV, models predict that viral adaptation, either via strain replacement or selection on de novo mutation, may rapidly reduce the effectiveness of an HIV vaccine. We hypothesized that behavioral risk compensation after vaccination may accelerate the transmission of vaccine resistant strains, increasing the rate of viral adaptation and leading to a more rapid decline in vaccine effectiveness.

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HIV set point viral load (SPVL), the viral load established shortly after initial infection, is a proxy for HIV virulence: higher SPVLs lead to higher risk of transmission and faster disease progression. Three models of test-and-treat scenarios, mainly in heterosexual populations, found that increasing treatment coverage selected for more virulent viruses. We modeled virulence evolution in a population of men who have sex with men (MSM) with increasing test-and-treat coverage.

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  • Predominantly heterosexual HIV-1 epidemics in sub-Saharan Africa are significantly affecting young people, leading to high rates of new infections.
  • The research used an agent-based model to explore how focusing on youth for antiretroviral therapy (ART) could improve treatment as prevention (TasP) efforts over 20-25 years.
  • Results showed that targeting individuals under age 30 could substantially reduce the number of people needing treatment and lower future AIDS-related deaths while maintaining broad treatment access.
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Pathogen evolution is a potential threat to the long-term benefits provided by public health vaccination campaigns. Mathematical modeling can be a powerful tool to examine the forces responsible for the development of vaccine resistance and to predict its public health implications. We conducted a systematic review of existing literature to understand the construction and application of vaccine resistance models.

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  • HIV viral load (VL) serves as a key indicator for both the likelihood of HIV transmission and the speed at which the disease progresses in individuals.
  • The study explores the concept of mean set point viral load (MSPVL), suggesting it's influenced by factors such as sexual network structures and concurrency, which differ across populations.
  • A dynamic network model was developed to analyze how various sexual network dynamics affect MSPVL evolution, revealing significant correlations between MSPVL, HIV prevalence, and other associated factors.
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Background: Development of an HIV vaccine might be essential to ending the HIV/AIDS pandemic. However, vaccines can result in the emergence and spread of vaccine-resistant strains. Indeed, analyses of breakthrough infections in the HIV phase 3 vaccine trial RV144 identified HIV genotypes with differential rates of transmission in vaccine and placebo recipients.

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There are global increases in the use of HIV antiretroviral therapy (ART), guided by clinical benefits of early ART initiation and the efficacy of treatment as prevention of transmission. Separately, it has been shown theoretically and empirically that HIV virulence can evolve over time; observed virulence levels may reflect an adaptive balance between infected lifespan and per-contact transmission rate. However, the potential effects of widespread ART usage on HIV virulence are unknown.

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  • HIV's rapid evolution allows it to escape treatments and immune responses, creating challenges in managing the pandemic.
  • Research highlights the effectiveness of structure-based computational models in identifying stable sites in the HIV-1 capsid protein that are less likely to mutate, which can inform drug and vaccine development.
  • A combined scoring system that merges sequence conservation with structural stability proves to be more effective in pinpointing harmful mutations than using either factor alone, suggesting a promising approach for future therapeutic targets.
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The innate immune response plays an important but unknown role in host defense against Mycobacterium tuberculosis. To define the function of innate immunity during tuberculosis, we evaluated M. tuberculosis replication dynamics during murine infection.

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  • * Researchers created a model to analyze how HIV virulence changes over time, using set point viral load (SPVL) to draw comparisons with real-world data from longitudinal studies.
  • * The findings indicate that HIV evolves to a balanced level of virulence for better transmission and longer infectious periods, and variations in SPVL trends can be influenced by the epidemic's specific context and improvements in testing, rather than being solely predictive of HIV incidence rates.
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  • Purified silymarin from milk thistle is effective in blocking hepatitis C virus (HCV) and inhibiting T cell proliferation in lab settings.
  • An intravenous version of silibinin, a key component of silymarin, shows anti-HCV effects and reduces T-cell activity in human studies.
  • Silibinin also significantly reduces the replication of HIV-1 and affects the expression of various activation markers on T cells, suggesting it might help manage infections and inflammation in both HIV and HCV patients.
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Many Proteobacteria use acyl-homoserine lactone (AHL)-mediated quorum sensing to activate the production of antibiotics at high cell density. Extracellular factors like antibiotics can be considered public goods shared by individuals within a group. Quorum-sensing control of antibiotic production may be important for protecting a niche or competing for limited resources in mixed bacterial communities.

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The inference of regulatory and biochemical networks from large-scale genomics data is a basic problem in molecular biology. The goal is to generate testable hypotheses of gene-to-gene influences and subsequently to design bench experiments to confirm these network predictions. Coexpression of genes in large-scale gene-expression data implies coregulation and potential gene-gene interactions, but provide little information about the direction of influences.

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  • Computer simulation models can help study the effectiveness of HIV therapies in stopping drug-resistant viruses, but current tools are complicated for users without a background in computational biology.
  • The newly developed HIV Therapy Simulator (HIVSIM) is a user-friendly program that allows non-technical users to easily assess different therapeutic strategies for HIV treatment.
  • HIVSIM is freely available for both Mac and Windows users, and it aims to support clinical research and educational efforts related to HIV therapy.
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  • HIV-1 is commonly found in the lungs of infected individuals, which may play a role in the development of lung infections due to unique immune responses in this area.
  • The study involved sequencing HIV-1 from lung samples and blood to assess differences and compartmentalization; it was found that in 10 out of 18 subjects, there was some evidence of compartmentalization, although sequences between lung and blood were intermingled overall.
  • The findings suggest that while HIV-1 continuously migrates between blood and lung tissue, there may be limited localized evolution or clonal replication occurring in the lung.
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Conjugative plasmids of Gram-negative bacteria have both vertical and horizontal modes of transmission: they are segregated to daughter cells during division, and transferred between hosts by plasmid-encoded conjugative machinery. Despite maintaining horizontal mobility, many plasmids carry fertility inhibition (fin) systems that repress their own conjugative transfer. To assess the ecological basis of self-transfer repression, we compared the invasion of bacterial populations by fin(+) and fin(-) variants of the plasmid R1 using a computational model and co-culture competitions.

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  • Researchers have developed a new method to assess how the tuberculosis bacteria (Mycobacterium tuberculosis) replicate during chronic infection, which is important for understanding latent tuberculosis.
  • They use an unstable plasmid that is lost at a consistent rate to track bacterial replication in mice, applying mathematical models to estimate growth and death rates.
  • Their findings reveal that M. tuberculosis continues to replicate throughout chronic infection in mice and that its growth is controlled by the host's immune response, challenging previous assumptions about its inactivity during latency.
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Background: In HIV-1 evolution, a 100-100,000 fold discrepancy between census size and effective population size (Ne) has been noted. Although it is well known that selection can reduce Ne, high in vivo mutation and recombination rates complicate attempts to quantify the effects of selection on HIV-1 effective size.

Results: We use the inbreeding coefficient and the variance in allele frequency at a linked neutral locus to estimate the reduction in Ne due to selection in the presence of mutation and recombination.

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The tradeoff between the need to suppress drug-resistant viruses and the problem of treatment toxicity has led to the development of various drug-sparing HIV-1 treatment strategies. Here we use a stochastic simulation model for viral dynamics to investigate how the timing and duration of the induction phase of induction-maintenance therapies might be optimized. Our model suggests that under a variety of biologically plausible conditions, 6-10 mo of induction therapy are needed to achieve durable suppression and maximize the probability of eradicating viruses resistant to the maintenance regimen.

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The effects that granulocyte-monocyte colony-stimulating factor (GM-CSF) has on HIV-1 replication in monocyte-derived macrophage are controversial. We noted that groups reporting that GM-CSF inhibits HIV-1 replication performed their experiments at relatively high cell densities. To address this issue, we performed experiments at different macrophage densities.

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A biologically explicit simulation model of resource competition between two species of seed-eating heteromyid rodent indicates that stable coexistence is possible on a homogeneous resource if harvested food is stored and consumers steal each other's caches. Here we explore the coexistence mechanisms involved by analyzing how consumer phenotypes and presence of a noncaching consumer affect the competitive outcome. Without cache exchange, the winning consumer is better at harvesting seeds and produces more offspring per gram of stored food.

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