Influenza virus contributes substantially to the global human and animal disease burden. To protect individuals against disease, strategies are needed to minimize the time an individual is at risk of developing disease symptoms. Passive immunization using avian IgY antibodies can protect individuals against a variety of pathogens, including influenza virus. Yet the effect of IgY administration on generation of protective immunity is largely unknown. To address the effect of passive immunization on the host immune response development, adult or aged, male and female C57BL/6NCrl mice received chicken IgY anti-H5N1, normal IgY or PBS intranasally four hours before, and 20 hours after intranasal infection with H1N1 influenza A virus (PR8). The mice receiving cross-reactive IgY anti-H5N1 were protected from disease and developed influenza virus-specific memory T cells similar to control-treated mice. When re-challenged with PR8 35 days post primary infection IgY anti-H5N1-treated mice were fully protected. Moreover, when challenged with heterologous H3N2 influenza A virus (X-31) or with PR8 three months post infection the mice were protected against severe disease and death, albeit a slight transient weight loss was noted. The results show that passive immunization with IgY anti-H5N1 is safe and protects mice against disease induced by influenza virus without inhibiting development of protective immunity after virus exposure. This indicate that passive immunization can be used as prophylactic therapy in combination with immunization to prevent disease.

The immune mechanism underlying hepatitis B surface antigen (HBsAg) loss, particularly type I inflammatory response, during pegylated interferon-α (PEG-IFN) therapy remains unclear. In this study, we aimed to elucidate such immune mechanisms. Overall, 82 patients with chronic hepatitis B (CHB), including 41 with HBsAg loss (cured group) and 41 uncured patients, received nucleos(t)ide analogue and PEG-IFN treatments. Blood samples from all patients, liver tissues from 14 patients with CHB, and hepatic perfusate from 8 liver donors were collected for immune analysis. Jurkat, THP-1 and HepG2.2.15 cell lines were used in cell experiments. The proportion of IFN-γ+ Th1 cells was higher in the cured group than in the uncured group, which was linearly correlated with HBsAg decline and alanine aminotransferase (ALT) levels during treatment. However, CD8+ T cells were weakly associated with HBsAg loss. Serum and intrahepatic levels of Th1 cell-associated chemokines (C-X-C motif chemokine ligand [CXCL] 9, CXCL10, CXCL11, IFN-γ) were significantly lower in the cured patients than in patients with a higher HBsAg quantification during therapy. Serum from cured patients induced more M1 (CD68+CD86+ macrophage) cells than that from uncured patients. Patients with chronic HBV infection had significantly lower proportions of CD86+ M1 and CD206+ M2 macrophages in their livers than healthy controls. M1 polarization of intrahepatic Kupffer cells promoted HBsAg loss by upregulating the effector function of tissue-resident memory T cells with increased ALT levels. IFN-γ+ Th1 activates intrahepatic resident memory T cells to promote HBsAg loss by inducing M1 macrophage polarization.

Resident memory T cells (TRMs), which are memory T cells that are retained locally within tissues, have recently been described as antigen-specific frontline defenders against pathogens in barrier and nonbarrier epithelial tissues. They have also been noted for perpetuating chronic inflammation. The conditions responsible for TRM differentiation are still poorly understood, and their contributions, if any, to sterile models of chronic kidney disease (CKD) remain a mystery. In this study, we subjected male C57BL/6J mice and OT-1 transgenic mice to five consecutive days of 2 mg/kg aristolochic acid (AA) injections intraperitoneally to induce CKD or saline injections as a control. We evaluated their kidney immune profiles at 2 wk, 6 wk, and 6 mo after treatment. We identified a substantial population of TRMs in the kidneys of mice with AA-induced CKD. Flow cytometry of injured kidneys showed T cells bearing TRM surface markers and single-cell (sc) RNA sequencing revealed these cells as expressing well-known TRM transcription factors and receptors responsible for TRM differentiation and maintenance. Although kidney TRMs expressed Cd44, a marker of antigen experience and T cell activation, their derivation was independent of cognate antigen-T cell receptor interactions, as the kidneys of transgenic OT-1 mice still harbored considerable proportions of TRMs after injury. Our results suggest a nonantigen-specific or antigen-independent mechanism capable of generating TRMs in the kidney and highlight the need to better understand TRMs and their involvement in CKD.NEW & NOTEWORTHY Resident memory T cells (TRMs) differentiate and are retained within the kidneys of mice with aristolochic acid (AA)-induced chronic kidney disease (CKD). Here, we characterized this kidney TRM population and demonstrated TRM derivation in the kidneys of OT-1 transgenic mice with AA-induced CKD. A better understanding of TRMs and the processes by which they can differentiate independent of antigen may help our understanding of the interactions between the immune system and kidneys.

Intranasal vaccines, unlike injectable vaccines, boost immunity along the respiratory tract; this can significantly limit respiratory virus replication and shedding. There remains a need to develop mucosal adjuvants and vaccine delivery systems that are both safe and effective following intranasal administration. Here, biopolymer particles (BP) densely coated with repeats of MHC class I restricted immunodominant epitopes derived from influenza A virus namely NP366, a nucleoprotein-derived epitope and PA224, a polymerase acidic subunit derived epitope, are bioengineered. These BP-NP366/PA224 can be manufactured at a high yield and are obtained at ≈93% purity, exhibiting ambient-temperature stability. Immunological characterization includes comparing systemic and mucosal immune responses mounted following intramuscular or intranasal immunization. Immunization with BP-NP366/PA224 without adjuvant triggers influenza-specific CD8+ T cell priming and memory CD8+ T cell development. Co-delivery with the adjuvant poly(I:C) significantly boosts the size and functionality of the influenza-specific pulmonary resident memory CD8+ T cell pool. Intranasal, but not intramuscular delivery of BP-NP366/PA224 with poly(I:C), provides protection against influenza virus challenge. Overall, the BP approach demonstrates as a suitable antigen formulation for intranasal delivery toward induction of systemic protective T cell responses against influenza virus.

Activin A strongly influences immune responses; yet, few studies have examined its role in infectious diseases. We measured serum activin A levels in two independent tuberculosis (TB) patient cohorts and in patients with pneumonia and sarcoidosis. Serum activin A levels were increased in TB patients compared to healthy controls, including those with positive tuberculin skin tests, and paralleled severity of disease, assessed by X-ray scores. In pneumonia patients, serum activin A levels were also raised, but in sarcoidosis patients, levels were lower. To determine whether blockade of the activin A signaling axis could play a functional role in TB, we harnessed a soluble activin type IIB receptor fused to human IgG1 Fc, ActRIIB-Fc, as a ligand trap in a murine TB model. The administration of ActRIIB-Fc to Mycobacterium tuberculosis-infected mice resulted in decreased bacterial loads and increased numbers of CD4 effector T cells and tissue-resident memory T cells in the lung. Increased frequencies of tissue-resident memory T cells corresponded with downregulated T-bet expression in lung CD4 and CD8 T cells. Altogether, the results suggest a disease-exacerbating role of ActRIIB signaling pathways. Serum activin A may be useful as a biomarker for diagnostic triage of active TB or monitoring of anti-tuberculosis therapy.
OBJECTIVE: Tuberculosis remains the leading cause of death by a bacterial pathogen. The etiologic agent of tuberculosis, Mycobacterium tuberculosis, can remain dormant in the infected host for years before causing disease. Significant effort has been made to identify biomarkers that can discriminate between latently infected and actively diseased individuals. We found that serum levels of the cytokine activin A were associated with increased lung pathology and could discriminate between active tuberculosis and tuberculin skin-test-positive healthy controls. Activin A signals through the ActRIIB receptor, which can be blocked by administration of the ligand trap ActRIIB-Fc, a soluble activin type IIB receptor fused to human IgG1 Fc. In a murine model of tuberculosis, we found that ActRIIB-Fc treatment reduced mycobacterial loads. Strikingly, ActRIIB-Fc treatment significantly increased the number of tissue-resident memory T cells. These results suggest a role for ActRIIB signaling pathways in host responses to Mycobacterium tuberculosis and activin A as a biomarker of ongoing disease.

Local immune memory develops at the site of antigen exposure and facilitates a rapid and strong local adaptive defense upon re-exposure. Resident memory T (TRM) cells play a role in local immune memory, and their cell-surface molecules CD69 and CD103 promote their tissue residency. However, the contribution of these molecules to skin immune memory remains unclear. In this study, by inducing contact hypersensitivity (CHS) in CD69KO (CD69-deficient) and CD103-deficient mice, where different degrees of TRM cell contribution are observed by repeated challenges on the right ear and a single challenge on the left ear, we found that the deficiency of CD69 but not CD103 leads to impaired CHS upon repeated antigen challenges, even although TRM cells-like CD8 T cells developed at the challenged site of CD69KO. CHS responses in both ears were diminished in CD69KO by FTY720 or CD8 neutralization, suggesting that CHS in CD69KO is ascribed to circulating CD8 T cells and that the developed TRM cell-like CD8 T cells do not behave as TRM cells. The infiltration of macrophages was reduced in the rechallenged site of CD69KO, along with the downregulation of Cxcl1 and Cxcl2. Thus, CD69 is considered essential for an effective recall response, involving the development of functional TRM cells and the recruitment of macrophages.

The success of mRNA-based vaccines during the Covid-19 pandemic has highlighted the value of this new platform for vaccine development against infectious disease. However, the CD8+ T cell response remains modest with mRNA vaccines, and these do not induce mucosal immunity, which would be needed to prevent viral spread in the healthy population. To address this drawback, we developed a dendritic cell targeting mucosal vaccination vector, the homopentameric STxB. Here, we describe the highly efficient chemical synthesis of the protein, and its in vitro folding. This straightforward preparation led to a synthetic delivery tool whose biophysical and intracellular trafficking characteristics were largely indistinguishable from recombinant STxB. The chemical approach allowed for the generation of new variants with bioorthogonal handles. Selected variants were chemically coupled to several types of antigens derived from the mucosal viruses SARS-CoV-2 and type 16 human papillomavirus. Upon intranasal administration in mice, mucosal immunity, including resident memory CD8+ T cells and IgA antibodies was induced against these antigens. Our study thereby identifies a novel synthetic antigen delivery tool for mucosal vaccination with an unmatched potential to respond to an urgent medical need.

Recent studies have suggested that CD8+ liver-resident memory T (TRM) cells are crucial in the protection against liver-stage malaria. We used liver-directed mRNA-containing lipid nanoparticles (mRNA-LNPs) to induce liver TRM cells in a murine model. Single-dose intravenous injections of ovalbumin mRNA-LNPs effectively induced antigen-specific cytotoxic T lymphocytes in a dose-dependent manner in the liver on day 7. TRM cells (CD8+ CD44hi CD62Llo CD69+ KLRG1-) were induced 5 weeks after immunization. To examine the protective efficacy, mice were intramuscularly immunized with two doses of circumsporozoite protein mRNA-LNPs at 3-week intervals and challenged with sporozoites of Plasmodium berghei ANKA. Sterile immunity was observed in some of the mice, and the other mice showed a delay in blood-stage development when compared with the control mice. mRNA-LNPs therefore induce memory CD8+ T cells that can protect against sporozoites during liver-stage malaria and may provide a basis for vaccines against the disease.

Tissue-resident memory CD8+ T cells (TRM) reside at sites of previous infection, providing protection against reinfection with the same pathogen. In the skin, TRM patrol the epidermis, where keratinocytes are the entry site for many viral infections. Epidermal TRM react rapidly to cognate antigen encounter with the secretion of cytokines and differentiation into cytotoxic effector cells, constituting a first line of defense against skin reinfection. Despite the important protective role of skin TRM, it has remained unclear, whether their reactivation requires a professional antigen-presenting cell (APC). We show here, using a model system that allows antigen targeting selectively to keratinocytes in a defined area of the skin, that limited antigen expression by keratinocytes results in rapid, antigen-specific reactivation of skin TRM. Our data identify epidermal Langerhans cells that cross-present keratinocyte-derived antigens, as the professional APC indispensable for the early reactivation of TRM in the epidermal layer of the skin.

Tissue-resident memory T (TRM ) cells are detrimental in allergic contact dermatitis (ACD), in which they contribute to the chronicity and severity of the disease.
We assessed the impact of a standard topical corticosteroid (TCS) treatment, triamcinolone acetonide (TA), on the formation, maintenance and reactivation of epidermal TRM cells in a preclinical model of ACD to 2,4-dinitrofluorobenzene. TA 0.01% was applied at different time points of ACD response and we monitored skin inflammation and tracked CD8+ CD69+ CD103+ TRM by flow cytometry and RNA sequencing.
The impact of TA on TRM formation depended on treatment regimen: (i) in a preventive mode, that is, in sensitized mice before challenge, TA transiently inhibited the infiltration of effector T cells and the accumulation of TRM upon hapten challenge. In contrast, (ii) in a curative mode, that is, at the peak of the ACD response, TA blocked skin inflammation but failed to prevent the formation of TRM . Finally, (iii) in a proactive mode, that is, on previous eczema lesions, TA had no effect on the survival of skin TRM , but transiently inhibited their reactivation program upon allergen reexposure. Indeed, specific TRM progressively regained proliferative functions upon TA discontinuation and expanded in the tissue, leading to exaggerated iterative responses. Interestingly, TRM re-expansion correlated with the decreased clearance of hapten moieties from the skin induced by repeated TA applications.
Our results demonstrate that TCS successfully treat ACD inflammation, but are mostly ineffective in impeding the formation and expansion of allergen-specific TRM , which certainly restricts the induction of lasting tolerance in patients with chronic dermatitis.