Emerging Paradigms in Type 2 Immunity.

A principal purpose of type 2 immunity was thought to be defense against large parasites, but it also functions in the restoration of homeostasis, such as toxin clearance following snake bites. In other cases, like allergy, the type 2 T helper (Th2) cytokines and cells present in the environment are detrimental and cause diseases. In recent years, the recognition of cell heterogeneity within Th2-associated cell populations has revealed specific functions of cells with a particular phenotype or gene signature. In addition, here we discuss the recent data regarding heterogeneity of type 2 immunity-related cells, as well as their newly identified role in a variety of processes ranging from involvement in respiratory viral infections [especially in the context of the recent COVID-19 (coronavirus disease 2019) pandemic] to control of cancer development or of metabolic homeostasis.

Lung epithelial cells: Upstream targets in type 2-high asthma.

Over the last years, technological advances in the field of asthma have led to the identification of two disease endotypes, namely, type 2-high and type 2-low asthma, characterized by different pathophysiologic mechanisms at a cellular and molecular level. Although specific immune cells are important contributors to each of the recognized asthma endotype, the lung epithelium is now regarded as a crucial player able to orchestrate responses to inhaled environmental triggers such as allergens and microbes. The impact of the epithelium goes beyond its physical barrier. It is nowadays considered as a part of the innate immune system that can actively respond to insults. Activated epithelial cells, by producing a specific set of cytokines, trigger innate and adaptive immune cells to cause pathology. Here, we review how the epithelium contributes to the development of Th2 sensitization to allergens and asthma with a "type 2-high" signature, in both murine models and human studies of this asthma endotype. We also discuss epithelial responses to respiratory viruses, such as rhinovirus, respiratory syncytial virus, and SARS-CoV-2, and how these triggers influence not only asthma development but also asthma exacerbation. Finally, we also summarize the results of promising clinical trials using biologicals targeting epithelial-derived cytokines in asthmatic patients.

Sterilizing Immunity against SARS-CoV-2 Infection in Mice by a Single-Shot and Lipid Amphiphile Imidazoquinoline TLR7/8 Agonist-Adjuvanted Recombinant Spike Protein Vaccine*.

The search for vaccines that protect from severe morbidity and mortality because of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19) is a race against the clock and the virus. Here we describe an amphiphilic imidazoquinoline (IMDQ-PEG-CHOL) TLR7/8 adjuvant, consisting of an imidazoquinoline conjugated to the chain end of a cholesterol-poly(ethylene glycol) macromolecular amphiphile. It is water-soluble and exhibits massive translocation to lymph nodes upon local administration through binding to albumin, affording localized innate immune activation and reduction in systemic inflammation. The adjuvanticity of IMDQ-PEG-CHOL was validated in a licensed vaccine setting (quadrivalent influenza vaccine) and an experimental trimeric recombinant SARS-CoV-2 spike protein vaccine, showing robust IgG2a and IgG1 antibody titers in mice that could neutralize viral infection in vitro and in vivo in a mouse model.

Sterilizing Immunity against SARS-CoV-2 Infection in Mice by a Single-Shot and Modified Imidazoquinoline TLR7/8 Agonist-Adjuvanted Recombinant Spike Protein Vaccine.

The search for vaccines that protect from severe morbidity and mortality as a result of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19) is a race against the clock and the virus. Several vaccine candidates are currently being tested in the clinic. Inactivated virus and recombinant protein vaccines can be safe options but may require adjuvants to induce robust immune responses efficiently. In this work we describe the use of a novel amphiphilic imidazoquinoline (IMDQ-PEG-CHOL) TLR7/8 adjuvant, consisting of an imidazoquinoline conjugated to the chain end of a cholesterol-poly(ethylene glycol) macromolecular amphiphile). This amphiphile is water soluble and exhibits massive translocation to lymph nodes upon local administration, likely through binding to albumin. IMDQ-PEG-CHOL is used to induce a protective immune response against SARS-CoV-2 after single vaccination with trimeric recombinant SARS-CoV-2 spike protein in the BALB/c mouse model. Inclusion of amphiphilic IMDQ-PEG-CHOL in the SARS-CoV-2 spike vaccine formulation resulted in enhanced immune cell recruitment and activation in the draining lymph node. IMDQ-PEG-CHOL has a better safety profile compared to native soluble IMDQ as the former induces a more localized immune response upon local injection, preventing systemic inflammation. Moreover, IMDQ-PEG-CHOL adjuvanted vaccine induced enhanced ELISA and in vitro microneutralization titers, and a more balanced IgG2a/IgG1 response. To correlate vaccine responses with control of virus replication in vivo, vaccinated mice were challenged with SARS-CoV-2 virus after being sensitized by intranasal adenovirus-mediated expression of the human angiotensin converting enzyme 2 (ACE2) gene. Animals vaccinated with trimeric recombinant spike protein vaccine without adjuvant had lung virus titers comparable to non-vaccinated control mice, whereas animals vaccinated with IMDQ-PEG-CHOL-adjuvanted vaccine controlled viral replication and infectious viruses could not be recovered from their lungs at day 4 post infection. In order to test whether IMDQ-PEG-CHOL could also be used to adjuvant vaccines currently licensed for use in humans, proof of concept was also provided by using the same IMDQ-PEG-CHOL to adjuvant human quadrivalent inactivated influenza virus split vaccine, which resulted in enhanced hemagglutination inhibition titers and a more balanced IgG2a/IgG1 antibody response. Enhanced influenza vaccine responses correlated with better virus control when mice were given a lethal influenza virus challenge. Our results underscore the potential use of IMDQ-PEG-CHOL as an adjuvant to achieve protection after single immunization with recombinant protein and inactivated virus vaccines against respiratory viruses, such as SARS-CoV-2 and influenza viruses.

Inflammatory Type 2 cDCs Acquire Features of cDC1s and Macrophages to Orchestrate Immunity to Respiratory Virus Infection.

The phenotypic and functional dichotomy between IRF8+ type 1 and IRF4+ type 2 conventional dendritic cells (cDC1s and cDC2s, respectively) is well accepted; it is unknown how robust this dichotomy is under inflammatory conditions, when additionally monocyte-derived cells (MCs) become competent antigen-presenting cells (APCs). Using single-cell technologies in models of respiratory viral infection, we found that lung cDC2s acquired expression of the Fc receptor CD64 shared with MCs and of IRF8 shared with cDC1s. These inflammatory cDC2s (inf-cDC2s) were superior in inducing CD4+ T helper (Th) cell polarization while simultaneously presenting antigen to CD8+ T cells. When carefully separated from inf-cDC2s, MCs lacked APC function. Inf-cDC2s matured in response to cell-intrinsic Toll-like receptor and type 1 interferon receptor signaling, upregulated an IRF8-dependent maturation module, and acquired antigens via convalescent serum and Fc receptors. Because hybrid inf-cDC2s are easily confused with monocyte-derived cells, their existence could explain why APC functions have been attributed to MCs.