Respiratory syncytial virus infection of primary human mast cells induces the selective production of type I interferons, CXCL10, and CCL4.

BACKGROUND: Respiratory syncytial virus (RSV) causes severe respiratory tract infections, which might have a role in the development of airway hyperreactivity. Mast cells are important effector cells in allergy, with sentinel cell roles in host defense. However, the role of mast cells in response to RSV infection is unknown. OBJECTIVE: Human mast cell responses to RSV were investigated with a view to better understanding the role of mast cells in RSV-induced disease. METHODS: Human cord blood-derived mast cells and the HMC-1 mast cell line were exposed to RSV or UV-inactivated RSV. Viral gene and protein expression were evaluated by using PCR and flow cytometry. The expression of interferon-stimulated genes and selected mediators were evaluated by using quantitative PCR and ELISA. RESULTS: Human mast cells expressed multiple RSV genes after exposure to RSV, and a small percentage of mast cells supported RSV antigen protein expression. RSV induced mast cells to upregulate production of chemokines, including CCL4, CCL5, and CXCL10, as well as type I interferons, and interferon-stimulated gene expression. However, production of the granulocyte chemoattractants CXCL8 and CCL11 was not induced. Antibody blockade of the type I interferon receptor on human cord blood-derived mast cells reduced the RSV-mediated induction of CXCL10 and CCL4 but not CCL5. Leukotriene C4 production by mast cells was not enhanced by exposure to RSV. CONCLUSION: Despite low levels of infection, human mast cells produce multiple chemokines in response to RSV through mechanisms that include responses to type I interferons. Such mast cell responses might enhance effector cell recruitment during RSV-induced disease.

Dynamics of virological and immunological markers of HIV persistence after allogeneic haematopoietic stem-cell transplantation in the IciStem cohort: a prospective observational cohort study.

BACKGROUND: Allogeneic haematopoietic stem-cell transplantation (allo-HSCT) markedly reduces HIV reservoirs, but the mechanisms by which this occurs are only partly understood. In this study, we aimed to describe the dynamics of virological and immunological markers of HIV persistence after allo-HSCT. METHODS: In this prospective observational cohort study, we analysed the viral reservoir and serological dynamics in IciStem cohort participants with HIV who had undergone allo-HSCT and were receiving antiretroviral therapy, ten of whom had received cells from donors with the CCR5Δ32 mutation. Participants from Belgium, Canada, Germany, Italy, the Netherlands, Spain, Switzerland, and the UK were included in the cohort both prospectively and retrospectively between June 1, 2014 and April 30, 2019. In the first 6 months after allo-HSCT, participants had monthly assessments, with annual assessments thereafter, with the protocol tailored to accommodate for the individual health status of each participant. HIV reservoirs were measured in blood and tissues and HIV-specific antibodies were measured in plasma. We used the Wilcoxon signed-rank test to compare data collected before and after allo-HSCT in participants for whom longitudinal data were available. When the paired test was not possible, we used the Mann-Whitney U test. We developed a mathematical model to study the factors influencing HIV reservoir reduction in people with HIV after allo-HSCT. FINDINGS: We included 30 people with HIV with haematological malignancies who received a transplant between Sept 1, 2009 and April 30, 2019 and were enrolled within the IciStem cohort and included in this analysis. HIV reservoirs in peripheral blood were reduced immediately after full donor chimerism was achieved, generally accompanied by undetectable HIV-DNA in bone marrow, ileum, lymph nodes, and cerebrospinal fluid, regardless of donor CCR5 genotype. HIV-specific antibody levels and functionality values declined more slowly than direct HIV reservoir values, decaying significantly only months after full donor chimerism. Mathematical modelling suggests that allogeneic immunity mediated by donor cells is the main viral reservoir depletion mechanism after massive reservoir reduction during conditioning chemotherapy before allo-HSCT (half-life of latently infected replication-competent cells decreased from 44 months to 1·5 months). INTERPRETATION: Our work provides, for the first time, data on the effects of allo-HSCT in the context of HIV infection. Additionally, we raise the question of which marker can serve as the last reporter of the residual viraemia, postulating that the absence of T-cell immune responses might be a more reliable marker than antibody decline after allo-HSCT. FUNDING: amfAR (American Foundation for AIDS Research; ARCHE Program), National Institutes of Health, National Institute of Allergy and Infectious Diseases, and Dutch Aidsfonds.

A critical role for mast cells and mast cell-derived IL-6 in TLR2-mediated inhibition of tumor growth.

Several TLR agonists are effective in tumor immunotherapy, but their early innate mechanisms of action, particularly those of TLR2 agonists, are unclear. Mast cells are abundant surrounding solid tumors where they are often protumorigenic and enhance tumor angiogenesis. However, antitumor roles for mast cells have also been documented. The impact of mast cells may be dependent on their activation status and mediator release in different tumors. Using an orthotopic melanoma model in wild-type C57BL/6 and mast cell-deficient Kit(W-sh/W-sh) mice and a complementary Matrigel-tumor model in C57BL/6 mice, mast cells were shown to be crucial for TLR2 agonist (Pam(3)CSK(4))-induced tumor inhibition. Activation of TLR2 on mast cells reversed their well-documented protumorigenic role. Tumor growth inhibition after peritumoral administration of Pam(3)CSK(4) was restored in Kit(W-sh/W-sh) mice by local reconstitution with wild-type, but not TLR2-deficient, mast cells. Mast cells secrete multiple mediators after Pam(3)CSK(4) activation, and in vivo mast cell reconstitution studies also revealed that tumor growth inhibition required mast cell-derived IL-6, but not TNF. Mast cell-mediated anticancer properties were multifaceted. Direct antitumor effects in vitro and decreased angiogenesis and recruitment of NK and T cells in vivo were observed. TLR2-activated mast cells also inhibited the growth of lung cancer cells in vivo. Unlike other immune cells, mast cells are relatively radioresistant making them attractive candidates for combined treatment modalities. This study has important implications for the design of immunotherapeutic strategies and reveals, to our knowledge, a novel mechanism of action for TLR2 agonists in vivo.

Histamine receptor 2 blockade selectively impacts B and T cells in healthy subjects.

Histamine receptor 2 (H2R) blockade is commonly used in patients with gastric, duodenal ulcers or gastroesophageal reflux disease. Beyond the gastrointestinal tract, H2R is expressed by multiple immune cells, yet little is known about the immunomodulatory effects of such treatment. Clinical reports have associated H2R blockade with leukopenia, neutropenia, and myelosuppression, and has been shown to provide clinical benefit in certain cancer settings. To systematically assess effects of H2R blockade on key immune parameters, a single-center, single-arm clinical study was conducted in 29 healthy subjects. Subjects received daily high dose ranitidine for 6 weeks. Peripheral blood immunophenotyping and mediator analysis were performed at baseline, 3 and 6 weeks into treatment, and 12 weeks after treatment cessation. Ranitidine was well-tolerated, and no drug related adverse events were observed. Ranitidine had no effect on number of neutrophils, basophils or eosinophils. However, ranitidine decreased numbers of B cells and IL-2Rα (CD25) expressing T cells that remained lower even after treatment cessation. Reduced serum levels of IL-2 were also observed and remained low after treatment. These observations highlight a previously unrecognised immunomodulatory sustained impact of H2R blockade. Therefore, the immune impacts of H2R blockade may require greater consideration in the context of vaccination and immunotherapy.

Centenarians and extremely old people living with frailty can elicit durable SARS-CoV-2 spike specific IgG antibodies with virus neutralization functions following virus infection as determined by serological study.

BACKGROUND: The SARS-CoV-2 (Severe Acute Respiratory Syndrome coronavirus 2) has led to more than 165 million COVID-19 cases and >3.4 million deaths worldwide. Epidemiological analysis has revealed that the risk of developing severe COVID-19 increases with age. Despite a disproportionate number of older individuals and long-term care facilities being affected by SARS-CoV-2 and COVID-19, very little is understood about the immune responses and development of humoral immunity in the extremely old person after SARS-CoV-2 infection. Here we conducted a serological study to investigate the development of humoral immunity in centenarians following a SARS-CoV-2 outbreak in a long-term care facility. METHODS: Extreme aged individuals and centenarians who were residents in a long-term care facility and infected with or exposed to SARS-CoV-2 were investigated between April and June 2020 for the development of antibodies to SARS-CoV-2. Blood samples were collected from positive and bystander individuals 30 and 60 days after original diagnosis of SARS-CoV-2 infection. Plasma was used to quantify IgG, IgA, and IgM isotypes and subsequent subclasses of antibodies specific for SARS-CoV-2 spike protein. The function of anti-spike was then assessed by virus neutralization assays against the native SARS-CoV-2 virus. FINDINGS: Fifteen long-term care residents were investigated for SARS-CoV-2 infection. All individuals had a Clinical Frailty scale score ≥5 and were of extreme older age or were centenarians. Six women with a median age of 98.8 years tested positive for SARS-CoV-2. Anti-spike IgG antibody titers were the highest titers observed in our cohort with all IgG positive individuals having virus neutralization ability. Additionally, 5 out of the 6 positive participants had a robust IgA anti-SARS-CoV-2 response. In all 5, antibodies were detected after 60 days from initial diagnosis.

Ranitidine Inhibition of Breast Tumor Growth Is B Cell Dependent and Associated With an Enhanced Antitumor Antibody Response.

Background: The histamine receptor 2 antagonist ranitidine is a commonly used, non-prescription, medication. It limits the development, growth, and metastasis of breast cancers in mouse models of disease. In this study, we examined the role of B cells in this response, the impact of ranitidine on the development of antitumor antibodies and subpopulations of natural killer cells using murine breast cancer models. Methods: Peripheral blood granulocyte populations were assessed in both E0771-GFP and 4T1 orthotopic tumor-bearing mice by evaluation of stained blood smears. Antibody responses were assessed both in terms of the levels of anti-GFP antibodies detected by enzyme-linked immunosorbent assay and also by antibody binding to the surface of tumor cells evaluated by flow cytometry. B cell and NK cell populations were examined in the draining lymph nodes and spleens of tumor-bearing animals, by flow cytometry with and without ranitidine treatment. Results: Oral ranitidine treatment was not associated with changes in peripheral blood granulocyte populations in tumor-bearing mice. However, ranitidine treatment was associated with the development of enhanced antitumor antibody responses. This was not limited to the tumor setting since ranitidine-treated mice immunized with ovalbumin also demonstrated increased IgG antibody responses. Analysis of B cell populations indicated that while B1 cell populations remained unchanged there was a significant decrease in B2 cells in the tumor-draining inguinal lymph nodes. Notably, ranitidine did not significantly inhibit primary tumor growth in B cell-deficient animals. Examination of NK cell populations revealed a significant decrease in the proportion of intermediately functionally mature NK cells populations (CD27+CD11b-) in ranitidine-treated tumor-bearing mice compared with untreated tumor-bearing controls. Conclusion: These data demonstrate an important role for B cells in the enhanced antitumor immune response that occurs in response to ranitidine treatment. Our findings are consistent with a model, whereby ranitidine reduces tumor-associated immune suppression allowing for the development of more effective antitumor responses mediated by B cells which may include the participation of NK cells. These data underline the importance of considering widely used histamine receptor antagonists as modulators of antitumor immunity to breast cancer.

Interferon α2 and interferon γ induce the degranulation independent production of VEGF-A and IL-1 receptor antagonist and other mediators from human mast cells.

BACKGROUND: Mast cells are resident immune effector cells, often studied in the context of allergic disease. Found in substantial numbers at sites of potential infection they are increased at sites of angiogenesis and can be pivotal for the sensing and clearance of a variety of pathogens. Interferons (IFNs) are cytokines that are critical for host defence against intracellular pathogens. Increased levels of IFNs are observed during viral infection and in autoimmune diseases. IFNs are also widely used therapeutically and have been examined in the therapy of severe asthma. OBJECTIVE: To define the selective human mast cell cytokine and chemokine response following activation with type I or type II IFN's. METHODS: The ability of both IFNα2 and IFNγ to induce cytokine production by human cord blood-derived mast cells was examined in vitro. Cytokine and chemokine production at 6 and 24 h was assessed by multiplex protein analysis. Degranulation was assessed by ß-hexosaminidase release. Mast cells were also treated with reovirus or respiratory syncytial virus and their production of CXCL10, IL-1 receptor antagonist (IL-1Ra), and vascular endothelial growth factor (VEGF) examined after 24 h. RESULTS: In addition to increased expression of classical IFN response genes, such as CXCL10, small but significant increases in CCL5 and IL-17 production were observed following IFN activation. Notably, human mast cells produced both VEGF and IL-1Ra in a dose dependent manner. These responses occurred in the absence of mast cell degranulation by a mechanism consistent with classical IFN signaling. Both reovirus and respiratory syncytial virus infection of mast cells, were also associated with IFN-dependent IL-1Ra expression. CONCLUSION AND CLINICAL RELEVANCE: Our findings demonstrate that IFNs have profound impact on cytokine and chemokine expression by human mast cells, alone or in the context of viral infection. Mast cell VEGF and IL-1Ra responses to IFNs could impact the regulation of local inflammatory responses and subsequent tissue remodeling.

Ranitidine modifies myeloid cell populations and inhibits breast tumor development and spread in mice.

Histamine receptor 2 (H2) antagonists are widely used clinically for the control of gastrointestinal symptoms, but also impact immune function. They have been reported to reduce tumor growth in established colon and lung cancer models. Histamine has also been reported to modify populations of myeloid-derived suppressor cells (MDSCs). We have examined the impact of the widely used H2 antagonist ranitidine, on both myeloid cell populations and tumor development and spread, in three distinct models of breast cancer that highlight different stages of cancer progression. Oral ranitidine treatment significantly decreased the monocytic MDSC population in the spleen and bone marrow both alone and in the context of an orthotopic breast tumor model. H2 antagonists ranitidine and famotidine, but not H1 or H4 antagonists, significantly inhibited lung metastasis in the 4T1 model. In the E0771 model, ranitidine decreased primary tumor growth while omeprazole treatment had no impact on tumor development. Gemcitabine treatment prevented the tumor growth inhibition associated with ranitidine treatment. In keeping with ranitidine-induced changes in myeloid cell populations in non-tumor-bearing mice, ranitidine also delayed the onset of spontaneous tumor development, and decreased the number of tumors that developed in LKB1(-/-)/NIC mice. These results indicate that ranitidine alters monocyte populations associated with MDSC activity, and subsequently impacts breast tumor development and outcome. Ranitidine has potential as an adjuvant therapy or preventative agent in breast cancer and provides a novel and safe approach to the long-term reduction of tumor-associated immune suppression.

Mast cells as targets for immunotherapy of solid tumors.

Mast cells have historically been studied mainly in the context of allergic disease. In recent years, we have come to understand the critical importance of mast cells in tissue remodeling events and their role as sentinel cells in the induction and development of effective immune responses to infection. Studies of the role of mast cells in tumor immunity are more limited. The pro-tumorigenic role of mast cells has been widely reported. However, mast cell infiltration predicts improved prognosis in some cancers, suggesting that their prognostic value may be dependent on other variables. Such factors may include the nature of local mast cell subsets and the various activation stimuli present within the tumor microenvironment. Experimental models have highlighted the importance of mast cells in orchestrating the anti-tumor events that follow immunotherapies that target innate immunity. Mast cells are long-lived tissue resident cells that are abundant around many solid tumors and are radiation resistant making them unique candidates for combined treatment modalities. This review will examine some of the key roles of mast cells in tumor immunity, with a focus on potential immunotherapeutic interventions that harness the sentinel role of mast cells.

Discordant expression of HLA class II-associated co-chaperones and HLA-DRB alleles in cultured fibroblast-like synoviocytes.

Human leukocyte antigen (HLA)-DR-positive synovial fibroblasts are frequently observed in rheumatoid arthritis (RA) and may be implicated in the autoimmune reaction because RA is associated with certain HLA-DRB1* alleles. The question of whether components of the class II antigen presentation pathway and specific DRB alleles are efficiently expressed by synovial fibroblasts is germane to this hypothesis. To address this, cultured fibroblast-like synoviocytes (cFLS) were analyzed for constitutive and interferon (IFN)-gamma-induced expression of specific DRB alleles and class II-associated cochaperones. IFN-gamma induction of invariant chain, DM, and DR molecules was observed in all cFLS, but expression of specific DR allotypes was variable. Interestingly, DM-modulated epitopes on RA-associated DR molecules were either absent or delayed, despite strong DM expression and a paucity of major histocompatibility complex/class II-associated invariant chain peptide complexes. Altered expression of specific peptide-dependent epitopes on RA-associated HLA-DR molecules suggests differences in antigen presentation by cFLS, which may have implications for the immunopathogenesis of RA.

Tumor cell expression of HLA-DM associates with a Th1 profile and predicts improved survival in breast carcinoma patients.

Studies aimed at elucidating the immunological and prognostic significance of HLA-DR expression on breast carcinoma cells have yielded contradictory results. To expand on previous studies, we have investigated the associations of tumor cell expression of HLA-DR and its related co-chaperones, invariant chain (Ii) and HLA-DM, with infiltrating inflammatory cells, in situ cytokine mRNA levels and prognosis and outcome in 112 breast carcinoma patients with a median follow-up of 59 months. While the majority of HLA-DR+ tumors co-express Ii, only a minority express HLA-DM. Tumor cell expression of HLA-DR and co-chaperones positively associated with both infiltrating CD4+ and CD8+ T-cell subsets (P < 0.01). Expression of HLA-DR and Ii associated with decreased estrogen receptor alpha levels and younger age at diagnosis, suggesting a role for hormones in the control of HLA class II expression in breast carcinoma. Patients with DR+Ii+DM- tumors had markedly decreased recurrence-free and disease-specific survival as compared with patients with DR+Ii+DM+ tumors (P < 0.05) and HLA-DR/co-chaperone expression was an independent predictor of survival by multivariate Cox regression analysis, controlling for standard prognostic indicators. Tumors that co-express HLA-DR, Ii and HLA-DM have increased levels of IFN-gamma, IL-2 and IL-12 mRNA, suggesting improved survival of patients with DR+Ii+DM+ tumors may be attributable to Th1-dominated immunity. We conclude that expression of determinants of the immune response by tumor cells may influence breast tumor progression and patient outcome.

HLA-DRB alleles are differentially expressed by tumor cells in breast carcinoma.

The biologic and prognostic significance of HLA-DR expression and T-cell infiltration in breast carcinoma are presently controversial. To test the hypothesis that these factors are influenced by particular HLA-DRB alleles, 52 breast tumor samples, composed of 26 DRB1*04 and 26 non-DRB1*04 tumors, were assessed using immunohistochemistry for expression of DR and its associated invariant chain (Ii) and for infiltrating CD3+ T cells. While DR expression by tumor cells was significantly associated with T-cell infiltration, DRB1*04 tumors were more frequently DR+ Ii+ and contained smaller CD3+ infiltrates than non-DRB1*04 tumors. This difference was largely attributable to DRB1*07 tumors, which were typically DR- Ii-, although they contained similar numbers of T cells to DR+ Ii+ tumors. Further analysis of DR+ tumors using allotype discriminating antibodies revealed that DRB1*04 alleles were always expressed, while non-DRB1*04 alleles were inconsistently expressed. The results of this study provide the first reported evidence that DRB alleles influence DR expression and T-cell infiltration in breast carcinoma and suggest that multiple factors contribute to DR expression. Ongoing studies aimed at elucidating the molecular and immunologic mechanisms controlling differential DR expression and implications for prognosis and outcome should further our understanding of the antitumor immune response and evasion strategies employed by tumor cells.