Antiviral susceptibility of clade 2.3.4.4b highly pathogenic avian influenza A(H5N1) viruses isolated from birds and mammals in the United States, 2022

Clade 2.3.4.4b highly pathogenic avian influenza (HPAI) A(H5N1) viruses that are responsible for devastating outbreaks in birds and mammals pose a potential threat to public health. Here, we evaluated their susceptibility to influenza antivirals. Of 1,015 sequences of HPAI A(H5N1) viruses collected in the United States during 2022, eight viruses (∼0.8%) had a molecular marker of drug resistance to an FDA-approved antiviral: three adamantane-resistant (M2-V27A), four oseltamivir-resistant (NA-H275Y), and one baloxavir-resistant (PA-I38T). Additionally, 31 viruses contained mutations that may reduce susceptibility to inhibitors of neuraminidase (NA) (n = 20) or cap-dependent endonuclease (CEN) (n = 11). A panel of 22 representative viruses was tested phenotypically. Overall, clade 2.3.4.4b A(H5N1) viruses lacking recognized resistance mutations were susceptible to FDA-approved antivirals. Oseltamivir was least potent at inhibiting NA activity, while the investigational NA inhibitor AV5080 was most potent, including against NA mutants. A novel NA substitution T438N conferred 12-fold reduced inhibition by zanamivir, and in combination with the known marker N295S, synergistically affected susceptibility to all five NA inhibitors. In cell culture-based assays HINT and IRINA, the PA-I38T virus displayed 75- to 108-fold and 37- to 78-fold reduced susceptibility to CEN inhibitors, baloxavir and the investigational AV5116, respectively. Viruses with PA-I38M or PA-A37T showed 5- to 10-fold reduced susceptibilities. As HPAI A(H5N1) viruses continue to circulate and evolve, close monitoring of drug susceptibility is needed for risk assessment and to inform decisions regarding antiviral stockpiling.

Biomarkers of Early Liver Graft Damage in Circulatory Death and Brain Death Donors: A Propensity Score Matching Analysis

BACKGROUND

Donation after circulatory death (DCD) is related to a warm ischemia time and more complications compared with traditional donors (donation after brain death [DBD]).

METHODS

This study included biopsy samples retrospectively collected from November 2014 to December 2018 to compare histologic and biological markers of DCD and DBD liver grafts. The analysis includes marker of early apoptosis (p21), senescence (telomerase reverse transcriptase [TERT]), cell damage (caspase-3 active), endothelial damage (vascular endothelial growth factor), stem cell (CD90), hypoxia (HIF1A), inflammatory activation (COX-2), and cross-organ allograft rejection (CD44). A propensity score matching (PSM) was used to match patients receiving DCD livers to those receiving DBD livers. We analyzed the immunohistochemical initial liver damage-related warm ischemia time.

RESULTS

Positive staining expression of liver damage biomarkers (COX-2, CD44, TERT, HIF1A, and CD90) was found, but no significant differences were found between DCD and DBD and with ischemic cholangiopathy. After PSM, there was a significant relationship between CD90 and male donors (odds ratio [OR], 0.26; 95% confidence interval [CI], 0.07-0.91), TERT with donor sodium (OR, 1.11; 95% CI, 1.02-1.2), HIF1A with steatosis (OR, 0.33; 95% CI, 0.13-0.83), and CD44 with donor vasoactive drugs (OR, 0.36; 95% CI, 0.13-1) and glutamic oxaloacetic transaminase 1 week increase (OR, 1.01; 95% CI, 1-1.03).

CONCLUSIONS

DCD immunohistochemical initial liver damage was found to behave similarly to DBD. The increase in complications and cholangiopathy associated with warm ischemia could be related to a different later phenomenon.

Susceptibility of Influenza A, B, C, and D Viruses to Baloxavir1

Baloxavir showed broad-spectrum in vitro replication inhibition of 4 types of influenza viruses (90% effective concentration range 1.2-98.3 nmol/L); susceptibility pattern was influenza A ˃ B ˃ C ˃ D. This drug also inhibited influenza A viruses of avian and swine origin, including viruses that have pandemic potential and those resistant to neuraminidase inhibitors.

Insights into the antigenic advancement of influenza A(H3N2) viruses, 2011-2018

Influenza A(H3N2) viruses evade human immunity primarily by acquiring antigenic changes in the haemagglutinin (HA). HA receptor-binding features of contemporary A(H3N2) viruses hinder traditional antigenic characterization using haemagglutination inhibition and promote selection of HA mutants. Thus, alternative approaches are needed to reliably assess antigenic relatedness between circulating viruses and vaccines. We developed a high content imaging-based neutralization test (HINT) to reduce antigenic mischaracterization resulting from virus adaptation to cell culture. Ferret reference antisera were raised using clinical specimens containing viruses representing recent vaccine strains. Analysis of viruses circulating during 2011–2018 showed that gain of an N158-linked glycosylation in HA was a molecular determinant of antigenic distancing between A/Hong Kong/4801/2014-like (clade 3C.2a) and A/Texas/50/2012-like viruses (clade 3C.1), while multiple evolutionary HA F193S substitution were linked to antigenic distancing from A/Switzerland/97152963/2013-like (clade 3C.3a) and further antigenic distancing from A/Texas/50/2012-like viruses. Additionally, a few viruses carrying HA T135K and/or I192T showed reduced neutralization by A/Hong Kong/4801/2014-like antiserum. Notably, this technique elucidated the antigenic characteristics of clinical specimens, enabling direct characterization of viruses produced in vivo, and eliminating in vitro culture, which rapidly alters the genotype/phenotype. HINT is a valuable new antigenic analysis tool for vaccine strain selection.

Assessing baloxavir susceptibility of influenza viruses circulating in the United States during the 2016/17 and 2017/18 seasons

The anti-influenza therapeutic baloxavir targets cap-dependent endonuclease activity of polymerase acidic (PA) protein. We monitored baloxavir susceptibility in the United States with next generation sequencing analysis supplemented by phenotypic one-cycle infection assay. Analysis of PA sequences of 6,891 influenza A and B viruses collected during 2016/17 and 2017/18 seasons showed amino acid substitutions: I38L (two A(H1N1)pdm09 viruses), E23G (two A(H1N1)pdm09 viruses) and I38M (one A(H3N2) virus); conferring 4-10-fold reduced susceptibility to baloxavir.

Adverse role of influenza A virus-induced Nox1 in neutralizing antibody responses and survival against lethal viral challenge in mice. (P1407)

Highly pathogenic influenza viruses can elicit a severe cytokine storm, leading to acute lung injury (ALI), or in its more severe form, acute respiratory distress syndrome (ARDS). Reactive oxygen species (ROS) produced by NADPH Oxidase (Nox) enzymes of both the lung infiltrating cells and the lung epithelial tissue can contribute to lung injury directly or via inflammatory signaling pathways. Here, we present evidence that Nox1 expression is enhanced in vitro (A549 lung epithelial cells, 33-fold; THP-1 monocytic cells, 633-fold; HULEC lung endothelial cells, 27-fold) and in vivo (mouse lung tissue, 17-fold) in response to infection with influenza A virus. Notably, in A549 cells, Nox1 expression levels were enhanced by laboratory strains A/X31 (H3N2) and A/WSN/33 (H1N1), as well as A(H1N1)pdm09 clinical isolates (A/California/08/2009, A/Mexico/4108/2009, and A/Texas/15/2009) of influenza A virus. Nox1 induction was virus dose- and replication-dependent. However, Nox1-deficient mice had a higher survival rate (p=0.008) compared to wild-type controls in response to a lethal dose of A/PR8/1934 influenza. Improved survival of Nox1-deficient mice corresponded with increased (p=0.0006) flu-specific neutralizing antibody responses. These results suggest that therapeutic blockade of Nox1 deserves further attention as a possible adjunct therapy for influenza A-associated ALI/ARDS.

A novel quinazolin-derived reactive oxygen species-inhibitor suppresses influenza A virus-induced inflammatory mediators and leads to enhanced survival in mice (P4214)

Acute lung injury (ALI) and its more severe form acute respiratory distress (ARD) can result from infectious agents, including several strains of influenza A virus. Recent evidence suggests that excessive production of reactive oxygen species (ROS) is a major contributor to ALI caused by influenza. We evaluated the effects of TG6-44, a novel inhibitor of ROS production, in in vitro and in vivo models of influenza A virus infection. In vitro, using the monocytic cells (THP-1) and human PBMC infected with influenza A virus (X31), we found that TG6-44 treatment decreased virus-induced ROS and inflammatory markers in THP1 (IL6, IFNγ , MCP1, TNFα , MIP1β) and in PBMC (IL6, IL8, TNFα , MCP1). Also, in influenza A virus-infected THP1 cells, TG6-44 treatment led to a reduction in virus-induced cell death as evidenced by decreased Caspase3 activation, decreased proportion of Annexin V+/PI+ cells, and increased Bcl2 phosphorylation. Notably, TG6-44-treatment decreased the proportion of THP1 cells expressing viral nucleoprotein and delayed its translocation into the nucleus. Moreover, mice infected with a lethal dose of influenza A virus (PR8) and given TG6-44 had both reduced levels of virus-induced inflammatory markers in lungs and a higher survival rate compared to controls. Taken together, our results demonstrate anti-inflammatory and anti-infective effects of TG6-44, and suggest ROS-inhibitors as valuable adjunct therapeutics to reduce ALI/ARD caused by influenza A virus infection.

Protein energy malnutrition decreases immunity and increases susceptibility to influenza infection in mice

BACKGROUND

Protein energy malnutrition (PEM), a common cause of secondary immune deficiency in children, is associated with an increased risk of infections. Very few studies have addressed the relevance of PEM as a risk factor for influenza.

METHODS

We investigated the influence of PEM on susceptibility to, and immune responses following, influenza virus infection using isocaloric diets providing either adequate protein (AP; 18%) or very low protein (VLP; 2%) in a mouse model.

RESULTS

We found that mice maintained on the VLP diet, when compared to mice fed with the AP diet, exhibited more severe disease following influenza infection based on virus persistence, trafficking of inflammatory cell types to the lung tissue, and virus-induced mortality. Furthermore, groups of mice maintained on the VLP diet showed significantly lower virus-specific antibody response and a reduction in influenza nuclear protein-specific CD8(+) T cells compared with mice fed on the AP diet. Importantly, switching diets for the group maintained on the VLP diet to the AP diet improved virus clearance, as well as protective immunity to viral challenge.

CONCLUSIONS

Our results highlight the impact of protein energy on immunity to influenza infection and suggest that balanced protein energy replenishment may be one strategy to boost immunity against influenza viral infections.