Seasonal influenza causes 290,000-650,000 deaths annually, with vaccination efficacy ranging from 10 to 60%. The emergence of drug-resistant and highly pathogenic avian influenza viruses underscores the urgent need for novel protective strategies. Epidemiological observations have long suggested that certain vaccines, such as Bacillus Calmette-Guérin (BCG), can provide protection against diverse pathogens (S. Biering-Sørensen, P. Aaby, N. Lund, et al., Clin Infect Dis 65:1183-1190, 2017, https://doi.org/10.1093/cid/cix525; M.-L. Garly, C. L. Martins, C. Balé, et al., Vaccine 21:2782-2790, 2003, https://doi.org/10.1016/s0264-410x(03)00181-6; C. A. G. Timmermann, S. Biering-Sørensen, P. Aaby, et al., Trop Med Int Health 20:1733-1744, 2015, https://doi.org/10.1111/tmi.12614). While the cellular and molecular mechanisms underlying such protection remain incompletely understood, emerging research offers critical insights into innate immune system modulation (B. Cirovic, L. C. J. de Bree, L. Groh, et al., Cell Host Microbe 28:322-334, 2020, https://doi.org/10.1016/j.chom.2020.05.014; L. Kong, S. J. C. F. M. Moorlag, A. Lefkovith, et al., Cell Rep 37:110028, 2021, https://doi.org/10.1016/j.celrep.2021.110028; H. Mohammadi, N. Sharafkandi, M. Hemmatzadeh, et al., J Cell Physiol 233:4512-4529, 2018, https://doi.org/10.1002/jcp.26250; S. J. C. F. M. Moorlag, Y. A. Rodriguez-Rosales, J. Gillard, et al., Cell Rep 33:108387, 2021, https://doi.org/10.1016/j.celrep.2020.108387). We investigated whether a trained innate immune system with non-replicating adenoviruses could provide protection against diverse influenza virus strains. We demonstrated that replication-defective human adenoviruses can effectively train the innate immune system, conferring protective immunity in mice against multiple influenza virus strains, including H1N1, H3N2, H5N2, H7N9, and H9N2. In addition, bovine and chimpanzee adenoviruses can also activate human innate lymphoid cells (ILCs) and confer protection against challenge with influenza H3N2 virus in mice. Remarkably, this protection occurs in the complete absence of influenza-specific adaptive immune responses (influenza virus-specific hemagglutination-inhibiting antibodies, neutralizing antibodies, and influenza nucleoprotein-specific CD8 T cells). Key protective mechanisms include increased activation of ILC1, ILC2, and ILC3 populations, enhanced expression of interferon-stimulated genes (ISGs), upregulation of antiviral signaling pathways, and metabolic reprogramming of ILC subsets. Adoptive transfer experiments demonstrated that trained ILCs were sufficient to protect against influenza H1N1 infection in ILC-deficient mice. This research establishes a novel strategy for enhancing innate antiviral immunity, offering broad-spectrum protection against diverse influenza strains, a promising approach for not only pandemic preparedness but also against emerging infectious diseases. Training innate lymphoid cells through non-replicating adenoviral vectors represents a promising approach to enhancing broad-spectrum antiviral immunity, complementing traditional vaccination strategies.IMPORTANCEThe findings represent a potential game-changer for fighting influenza, which kills hundreds of thousands of people worldwide each year despite our best vaccination efforts. Current flu vaccines often provide limited protection because they must be reformulated annually to match circulating strains, and their effectiveness varies dramatically from year to year. The scientists discovered something remarkable: common adenoviruses (which typically cause mild cold-like symptoms) can essentially "train" our immune system's first line of defense to recognize and fight off multiple types of flu viruses simultaneously. This protection works through a completely different mechanism than traditional vaccines-it does not rely on creating specific antibodies against flu proteins. Instead, the treatment activates special immune cells called innate lymphoid cells (ILCs), which act like the body's rapid response team. These trained cells provide broad protection against various flu strains, including dangerous bird flu variants that could cause future pandemics. The significance lies in potentially creating a universal flu protection strategy that could work against unknown future flu strains, offering hope for better pandemic preparedness and reducing seasonal flu's devastating global impact.

Egg-free influenza vaccines, specifically cell culture-based inactivated influenza vaccine (ccIIV) and recombinant influenza vaccine (RIV), represent a significant advancement over traditional egg-based inactivated influenza vaccines (IIV), particularly for populations with extensive vaccination histories. This comprehensive immunological study investigated the comparative efficacy of ccIIV, IIV, and RIV in healthcare personnel (HCP) with repeated vaccination histories, examining both cellular and humoral immune responses through multiple analytical approaches. Our investigation employed a multi-faceted analytical framework, combining serological assessments via hemagglutination inhibition (HI) and microneutralization (MN) assays with detailed cellular immune response analysis. We utilized advanced flow cytometry techniques with recombinant hemagglutinin (HA) probes to evaluate both circulating T follicular helper cells (cTfh) and HA-specific B cells, providing a comprehensive view of vaccine-induced immune responses. The results revealed RIV's superior immunogenicity profile, demonstrating significantly elevated levels of both cTfh and HA-specific B cells compared to ccIIV and IIV. RIV's enhanced performance was particularly evident in its response to influenza A components, with notably higher immunogenicity against both A(H3N2) and A(H1N1) strains. This superiority was reflected in elevated HI titers and markedly increased HA-specific B cell induction. While RIV also demonstrated enhanced HA-specific B cell responses against influenza B components compared to ccIIV, interestingly, HI titers remained comparable across all vaccine groups for these strains. These findings underscore the critical importance of comprehensive immune response evaluation in vaccine assessment. The disparity between cellular and serological responses, particularly for influenza HA-specific B cells, highlights that traditional serological measures alone may not fully capture the breadth and depth of vaccine-induced immunity. This study provides compelling evidence for the inclusion of cellular immunity assessments in vaccine evaluation protocols, offering crucial insights into vaccine immunogenicity that may be missed by conventional serological analysis alone.

Cytotoxic T lymphocytes (CTLs) mediate host defense against viral and intracellular bacterial infections and tumors. However, the magnitude of CTL response and their function needed to confer heterosubtypic immunity against influenza virus infection are unknown. We addressed the role of CD8(+) T cells in the absence of any cross-reactive antibody responses to influenza viral proteins using an adenoviral vector expressing a 9mer amino acid sequence recognized by CD8(+) T cells. Our results indicate that both CD8(+) T cell frequency and function are crucial for heterosubtypic immunity. Low morbidity, lower viral lung titers, low to minimal lung pathology, and better survival upon heterosubtypic virus challenge correlated with the increased frequency of NP-specific CTLs. NP-CD8(+) T cells induced by differential infection doses displayed distinct RNA transcriptome profiles and functional properties. CD8(+) T cells induced by a high dose of influenza virus secreted significantly higher levels of IFN-γ and exhibited higher levels of cytotoxic function. The mice that received NP-CD8(+) T cells from the high-dose virus recipients through adoptive transfer had lower viral titers following viral challenge than those induced by the low dose of virus, suggesting differential cellular programming by antigen dose. Enhanced NP-CD8(+) T-cell functions induced by a higher dose of influenza virus strongly correlated with the increased expression of cellular and metabolic genes, indicating a shift to a more glycolytic metabolic phenotype. These findings have implications for developing effective T cell vaccines against infectious diseases and cancer. IMPORTANCE: Cytotoxic T lymphocytes (CTLs) are an important component of the adaptive immune system that clears virus-infected cells or tumor cells. Hence, developing next-generation vaccines that induce or recall CTL responses against cancer and infectious diseases is crucial. However, it is not clear if the frequency, function, or both are essential in conferring protection, as in the case of influenza. In this study, we demonstrate that both CTL frequency and function are crucial for providing heterosubtypic immunity to influenza by utilizing an Ad-viral vector expressing a CD8 epitope only to rule out the role of antibodies, single-cell RNA-seq analysis, as well as adoptive transfer experiments. Our findings have implications for developing T cell vaccines against infectious diseases and cancer.

BACKGROUND: Understanding the immune response kinetics to SARS-CoV-2 infection and COVID-19 vaccination is important in nursing home (NH) residents, a high-risk population. METHODS: An observational longitudinal evaluation of 37 consenting vaccinated NH residents with/without SARS-CoV-2 infection from October 2020 to July 2022 was conducted to characterize the immune response to spike protein due to infection and/or mRNA COVID-19 vaccine. Antibodies (IgG) to SARS-CoV-2 full-length spike, nucleocapsid, and receptor binding domain protein antigens were measured, and surrogate virus neutralization capacity was assessed using Meso Scale Discovery immunoassays. The participant's spike exposure status varied depending on the acquisition of infection or receipt of a vaccine dose. Longitudinal linear mixed effects modeling was used to describe trajectories based on the participant's last infection or vaccination; the primary series mRNA COVID-19 vaccine was considered two spike exposures. Mean antibody titer values from participants who developed an infection post receipt of mRNA COVID-19 vaccine were compared with those who did not. In a subset of participants (n = 15), memory B cell (MBC) S-specific IgG (%S IgG) responses were assessed using an ELISPOT assay. RESULTS: The median age of the 37 participants at enrollment was 70.5 years; 30 (81%) had prior SARS-CoV-2 infection, and 76% received Pfizer-BioNTech and 24% Moderna homologous vaccines. After an observed augmented effect with each spike exposure, a decline in the immune response, including %S IgG MBCs, was observed over time; the percent decline decreased with increasing spike exposures. Participants who developed an infection at least two weeks post-receipt of a vaccine were observed to have lower humoral antibody levels than those who did not develop an infection post-receipt. CONCLUSIONS: These findings suggest that understanding the durability of immune responses in this vulnerable NH population can help inform public health policy regarding the timing of booster vaccinations as new variants display immune escape.

We evaluated the performance of self-collected anterior nasal swab (ANS) and saliva samples compared with healthcare worker-collected nasopharyngeal swab specimens used to test for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We used the same PCR diagnostic panel to test all self-collected and healthcare worker-collected samples from participants at a public hospital in Atlanta, Georgia, USA. Among 1,076 participants, 51.9% were men, 57.1% were >50 years of age, 81.2% were Black (non-Hispanic), and 74.9% reported >1 chronic medical condition. In total, 8.0% tested positive for SARS-CoV-2. Compared with nasopharyngeal swab samples, ANS samples had a sensitivity of 59% and saliva samples a sensitivity of 68%. Among participants tested 3-7 days after symptom onset, ANS samples had a sensitivity of 80% and saliva samples a sensitivity of 85%. Sensitivity varied by specimen type and patient characteristics. These findings can help physicians interpret PCR results for SARS-CoV-2.

Influenza infections cause several million cases of severe respiratory illness, hospitalizations, and hundreds of thousands of deaths globally. Secondary infections are a leading cause of influenza's high morbidity and mortality, and significantly factored into the severity of the 1918, 1968, and 2009 pandemics. Furthermore, there is an increased incidence of other respiratory infections even in vaccinated individuals during influenza season. Putative mechanisms responsible for vaccine failures against influenza as well as other respiratory infections during influenza season are investigated. Peripheral blood mononuclear cells (PBMCs) are used from influenza vaccinated individuals to assess antigen-specific responses to influenza, measles, and varicella. The observations made in humans to a mouse model to unravel the mechanism is confirmed and extended. Infection with influenza virus suppresses an ongoing adaptive response to vaccination against influenza as well as other respiratory pathogens, i.e., Adenovirus and Streptococcus pneumoniae by preferentially infecting and killing activated lymphocytes which express elevated levels of sialic acid receptors. These findings propose a new mechanism for the high incidence of secondary respiratory infections due to bacteria and other viruses as well as vaccine failures to influenza and other respiratory pathogens even in immune individuals due to influenza viral infections.

AIMS: PD-1 inhibitors facilitate immune response against certain tumour types, including melanoma. These drugs have led to prolonged survival but can also result in autoimmune-type side effects, including gastrointestinal inflammation. The histopathological effects of this medication class have not been well studied. METHODS AND RESULTS: We identified 37 gastrointestinal tract biopsies from 20 patients taking a PD-1 or PD-L1 inhibitor and evaluated clinicopathological findings. Diarrhoea was the most common symptom, and endoscopic findings ranged from mild erythema to erosion/ulceration. Common histological findings included lamina propria expansion, villous blunting (if applicable), intra-epithelial neutrophils and increased crypt/gland apoptosis, although intra-epithelial lymphocytes were rarely prominent. A few cases showed crypt rupture with resultant histiocytic/granulomatous response. Most patients responded to drug cessation and/or steroids, but follow-up endoscopies were not performed. CONCLUSIONS: PD-1/PD-L1 inhibitors can cause gastritis, enteritis and colitis, similar to other immunomodulatory antibodies (such as CTLA-4 inhibitors and PI3Kdelta inhibitors), but the histological findings vary somewhat among drug classes. Clinical history, lack of prominent intra-epithelial lymphocytes and crypt rupture may help to distinguish PD-1 inhibitor gastroenterocolitis from mimics, which include other medication effect, inflammatory bowel disease, graft-versus-host disease, cytomegalovirus infection and autoimmune enteropathy.