Correction of age-associated defects in dendritic cells enables CD4+ T cells to eradicate tumors.

Defective host defenses later in life are associated with changes in immune cell activities, suggesting that age-specific considerations are needed in immunotherapy approaches. In this study, we found that PD-1 and CTLA4-based cancer immunotherapies are unable to eradicate tumors in elderly mice. This defect in anti-tumor activity correlated with two known age-associated immune defects: diminished abundance of systemic naive CD8+ T cells and weak migratory activities of dendritic cells (DCs). We identified a vaccine adjuvant, referred to as a DC hyperactivator, which corrects DC migratory defects in the elderly. Vaccines containing tumor antigens and DC hyperactivators induced T helper type 1 (TH1) CD4+ T cells with cytolytic activity that drive anti-tumor immunity in elderly mice. When administered early in life, DC hyperactivators were the only adjuvant identified that elicited anti-tumor CD4+ T cells that persisted into old age. These results raise the possibility of correcting age-associated immune defects through DC manipulation.

Respiratory Syncytial Virus Infects Regulatory B Cells in Human Neonates via Chemokine Receptor CX3CR1 and Promotes Lung Disease Severity.

Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract infections in infants and is characterized by pulmonary infiltration of B cells in fatal cases. We analyzed the B cell compartment in human newborns and identified a population of neonatal regulatory B lymphocytes (nBreg cells) that produced interleukin 10 (IL-10) in response to RSV infection. The polyreactive B cell receptor of nBreg cells interacted with RSV protein F and induced upregulation of chemokine receptor CX3CR1. CX3CR1 interacted with RSV glycoprotein G, leading to nBreg cell infection and IL-10 production that dampened T helper 1 (Th1) cytokine production. In the respiratory tract of neonates with severe RSV-induced acute bronchiolitis, RSV-infected nBreg cell frequencies correlated with increased viral load and decreased blood memory Th1 cell frequencies. Thus, the frequency of nBreg cells is predictive of the severity of acute bronchiolitis disease and nBreg cell activity may constitute an early-life host response that favors microbial pathogenesis.

NLRP3 inflammasomes that induce antitumor immunity.

Inflammasomes have emerged as context-dependent regulators of inflammation and protective immunity in vertebrates. Depending on the cell type and stimulus, inflammasome activities lead to interleukin (IL)-1 release from living (hyperactive) or dead (pyroptotic) cells. Herein, we review the mechanisms by which inflammasomes can impact CD8+ T cell-mediated antitumor immunity. We describe recent work demonstrating the differential impact of pyroptosis in cancer cells and dendritic cells (DCs) on antitumor immunity. We further highlight the surprising ability of inflammasomes within hyperactive DCs to facilitate the use of tumor lysates as immunogens, promoting CD8+ T cell-mediated antitumor responses. These context-dependent roles of inflammasomes in living and dead cells offer much opportunity for future research and should inform discussions of next-generation immunotherapy development.

Dectin-1 activation unlocks IL12A expression and reveals the TH1 potency of neonatal dendritic cells.

BACKGROUND: Early life is characterized by a high susceptibility to infection and a TH2-biased CD4 T-cell response to vaccines. Toll-like receptor (TLR) agonists are currently being implemented as new vaccine adjuvants for TH1 activation, but their translation to the field of pediatric vaccines is facing the impairment of neonatal innate TLR responses. OBJECTIVE: We sought to analyze C-type lectin receptor pathways as an alternative or a coactivator to TLRs for neonatal dendritic cell activation for TH1 polarization. METHODS: Neonatal monocyte-derived dendritic cells (moDCs) were exposed to various combinations of TLR agonists with or without Dectin-1 agonist. IL-12 and IL-23 responses were analyzed at the transcriptional and protein levels after stimulation. The intracellular pathways triggered by combined TLR plus Dectin-1 stimulation was determined by using pharmacologic inhibitors. The capacity of neonatal moDCs to differentiate naive CD4 TH cells was evaluated in cocultures with heterologous neonatal naive T cells. Curdlan was finally tested as an adjuvant within a subunit tuberculosis vaccine in neonatal mice. RESULTS: Simultaneous coactivation through Dectin-1 and TLRs induced robust secretion of IL-12p70 by neonatal moDCs by unlocking transcriptional control on the p35 subunit of IL-12. Both the spleen tyrosine kinase and Raf-1 pathways were involved in this process, allowing differentiation of neonatal naive T cells toward IFN-γ-producing TH1 cells. In vivo a Dectin-1 agonist as adjuvant was sufficient to induce TH1 responses after vaccination of neonatal mice. CONCLUSION: Coactivation of neonatal moDCs through Dectin-1 allows TLR-mediated IL-12p70 secretion and TH1 polarization of neonatal T cells. Dectin-1 agonists represent a promising TH1 adjuvant for pediatric vaccination.

Intestinal newborn regulatory B cell antibodies modulate microbiota communities.

The role of immunoglobulins produced by IL-10-producing regulatory B cells remains unknown. We found that a particular newborn regulatory B cell population (nBreg) negatively regulates the production of immunoglobulin M (IgM) via IL-10 in an autocrine manner, limiting the intensity of the polyreactive antibody response following innate activation. Based on nBreg scRNA-seq signature, we identify these cells and their repertoire in fetal and neonatal intestinal tissues. By characterizing 205 monoclonal antibodies cloned from intestinal nBreg, we show that newborn germline-encoded antibodies display reactivity against bacteria representing six different phyla of the early microbiota. nBreg-derived antibodies can influence the diversity and the cooperation between members of early microbial communities, at least in part by modulating energy metabolism. These results collectively suggest that nBreg populations help facilitate early-life microbiome establishment and shed light on the paradoxical activities of regulatory B cells in early life.

mRNAs encoding self-DNA reactive cGAS enhance the immunogenicity of lipid nanoparticle vaccines.

Lipid nanoparticle (LNP)-encapsulated mRNAs have emerged as effective vaccination tools to stimulate immunity. The most common application of this technology is to deliver mRNAs that encode antigenic proteins to dendritic cells (DCs), which then stimulate antigen-specific lymphocyte responses. It is unclear whether other immunostimulatory DC activities necessary for vaccine efficacy, beyond antigen presentation, can be induced via mRNA-encoded proteins. Herein, we report an mRNA encoding a self-DNA reactive variant of the enzyme cyclic GMP-AMP synthase (cGAS), known as cGAS∆N. cGAS∆N produces the cyclic dinucleotide cGAMP upon binding intra-mitochondrial DNA. cGAMP binds the protein STING, which activates innate immune responses that stimulate T cells. We found that when delivered to DCs via LNPs, mRNA-encoded cGAS∆N induced the upregulation of chemokine receptors, T cell costimulatory molecules, major histocompatibility complex proteins, pro-inflammatory cytokines and type I interferons from murine and human DCs. These activities exceeded the immunostimulatory activities of mRNA-encoded antigens delivered via LNPs. Co-immunization of mice with antigen-LNPs and cGAS∆N-LNPs led to the robust production of antigen-specific IFNγ-producing T cells. These T cell responses were durable and circulated through the lymphatics, blood, and lungs. Immunizations with antigen-LNPs alone, akin to what are used in the clinic, stimulated weak and transient T cell responses. Antibody responses to antigen-LNPs were biased towards type I isotypes when co-injected with cGAS∆N-LNPs, as compared to immunizations with antigen-LNPs alone. These findings establish the enzyme cGAS∆N as a catalytic adjuvant, which may prove useful in enhancing the immunogenicity of nucleic acid-based vaccines. IMPORTANCE Nucleic acid-based vaccines hold promise in preventing infections and treating cancer. The most common use of this technology is to encode antigenic proteins on mRNAs that are delivered to cells via lipid nanoparticle (LNP) formulations. In this study, we discovered that immunostimulatory proteins can also be encoded on mRNAs in LNPs. We found that an active mutant of the enzyme cGAS, referred to as cGAS∆N, acts as a catalytic adjuvant in LNP-encapsulated mRNA vaccines. The delivery of cGAS∆N mRNA via LNPs in combination with antigen mRNA-LNPs led to durable antigen-specific IFNγ-producing T cells that exceeded the efficiency of antigen-LNPs similar to those currently used in the clinic. This strategy did not compromise B cell responses; rather it induced Th1-biased antibody isotypes. This work unveils new vaccine design strategies using mRNA-encoded catalytic adjuvants that could be ideal for generating CD8+ T cell and B cell responses for immunotherapies.

Innate immune detection of lipid oxidation as a threat assessment strategy.

Oxidized phospholipids that result from tissue injury operate as immunomodulatory signals that, depending on the context, lead to proinflammatory or anti-inflammatory responses. In this Perspective, we posit that cells of the innate immune system use the presence of oxidized lipids as a generic indicator of threat to the host. Similarly to how pathogen-associated molecular patterns represent general indicators of microbial encounters, oxidized lipids may be the most common molecular feature of an injured tissue. Therefore, microbial detection in the absence of oxidized lipids may indicate encounters with avirulent microorganisms. By contrast, microbial detection and detection of oxidized lipids would indicate encounters with replicating microorganisms, thereby inducing a heightened inflammatory and defensive response. Here we review recent studies supporting this idea. We focus on the biology of oxidized phosphocholines, which have emerged as context-dependent regulators of immunity. We highlight emerging functions of oxidized phosphocholines in dendritic cells and macrophages that drive unique inflammasome and migratory activities and hypermetabolic states. We describe how these lipids hyperactivate dendritic cells to stimulate antitumour CD8+ T cell immunity and discuss the potential implications of the newly described activities of oxidized phosphocholines in host defence.

Inflammasomes within Hyperactive Murine Dendritic Cells Stimulate Long-Lived T Cell-Mediated Anti-tumor Immunity.

Central to anti-tumor immunity are dendritic cells (DCs), which stimulate long-lived protective T cell responses. Recent studies have demonstrated that DCs can achieve a state of hyperactivation, which is associated with inflammasome activities within living cells. Herein, we report that hyperactive DCs have an enhanced ability to migrate to draining lymph nodes and stimulate potent cytotoxic T lymphocyte (CTL) responses. This enhanced migratory activity is dependent on the chemokine receptor CCR7 and is associated with a unique transcriptional program that is not observed in conventionally activated or pyroptotic DCs. We show that hyperactivating stimuli are uniquely capable of inducing durable CTL-mediated anti-tumor immunity against tumors that are sensitive or resistant to PD-1 inhibition. These protective responses are intrinsic to the cDC1 subset of DCs, depend on the inflammasome-dependent cytokine IL-1ß, and enable tumor lysates to serve as immunogens. If these activities are verified in humans, hyperactive DCs may impact immunotherapy.

Unique aspects of the perinatal immune system.

The early stages of life are associated with increased susceptibility to infection, which is in part due to an ineffective immune system. In the context of infection, the immune system must be stimulated to provide efficient protection while avoiding insufficient or excessive activation. Yet, in early life, age-dependent immune regulation at molecular and cellular levels contributes to a reduced immunological fitness in terms of pathogen clearance and response to vaccines. To enable microbial colonization to be tolerated at birth, epigenetic immune cell programming and early life-specific immune regulatory and effector mechanisms ensure that vital functions and organ development are supported and that tissue damage is avoided. Advancement in our understanding of age-related remodelling of immune networks and the consequent tuning of immune responsiveness will open up new possibilities for immune intervention and vaccine strategies that are designed specifically for early life.

In utero development of memory T cells.

Pathogen-specific immune memory develops subsequent to primary exposure to antigen, mainly in the context of infection or vaccination to provide protection. Although a safe fetal life requires a tolerogenic environment in order to circumvent unnecessary inflammatory responses, it needs to be prepared in utero to face the microbial environment outside the womb. The possibility of immune memory generation in the fetus would help such transition providing protection in early life. This requires fetal T cell exposure to foreign antigens presented by dendritic cells. There are evidences of fetal T cell priming in several cases of congenital infections or in uninfected children born of infected mothers. Fetal T cell memory seems to arise also without any reported infection during pregnancy. Such memory T cells display various effector functions, including Th1, Th2, or Th17 profiles, raising the issue of benefits and risks for postnatal life when considering maternal vaccination, susceptibility to infection, or environmental allergen sensitization.

CD4 T cells with effector memory phenotype and function develop in the sterile environment of the fetus.

The T cell compartment is considered to be naïve and dedicated to the development of tolerance during fetal development. We have identified and characterized a population of fetally developed CD4 T cells with an effector memory phenotype (TEM), which are present in cord blood. This population is polyclonal and has phenotypic features similar to those of conventional adult memory T cells, such as CD45RO expression. These cells express low levels of CD25 but are distinct from regulatory T cells because they lack Foxp3 expression. After T cell receptor activation, neonatal TEM cells readily produced tumor necrosis factor-α (TNF-α) and granulocyte-macrophage colony-stimulating factor (GM-CSF). We also detected interferon-γ (IFN-γ)-producing T helper 1 (TH1) cells and interleukin-4 (IL-4)/IL-13-producing TH2-like cells, but not IL-17-producing cells. We used chemokine receptor expression patterns to divide this TEM population into different subsets and identified distinct transcriptional programs using whole-genome microarray analysis. IFN-γ was found in CXCR3(+) TEM cells, whereas IL-4 was found in both CXCR3(+) TEM cells and CCR4(+) TEM cells. CCR6(+) TEM cells displayed a genetic signature that corresponded to TH17 cells but failed to produce IL-17A. However, the TH17 function of TEM cells was observed in the presence of IL-1ß and IL-23. In summary, in the absence of reported pathology or any major infectious history, T cells with a memory-like phenotype develop in an environment thought to be sterile during fetal development and display a large variety of inflammatory effector functions associated with CD4 TH cells at birth.