Circulating markers of extracellular matrix remodelling in severe COVID-19 patients.

BACKGROUND: Abnormal remodelling of the extracellular matrix (ECM) has generally been linked to pulmonary inflammation and fibrosis and may also play a role in the pathogenesis of severe COVID-19. To further elucidate the role of ECM remodelling and excessive fibrogenesis in severe COVID-19, we examined circulating levels of mediators involved in various aspects of these processes in COVID-19 patients. METHODS: Serial blood samples were obtained from two cohorts of hospitalised COVID-19 patients (n = 414). Circulating levels of ECM remodelling mediators were quantified by enzyme immunoassays in samples collected during hospitalisation and at 3-month follow-up. Samples were related to disease severity (respiratory failure and/or treatment at the intensive care unit), 60-day total mortality and pulmonary pathology after 3-months. We also evaluated the direct effect of inactivated SARS-CoV-2 on the release of the different ECM mediators in relevant cell lines. RESULTS: Several of the measured markers were associated with adverse outcomes, notably osteopontin (OPN), S100 calcium-binding protein A12 and YKL-40 were associated with disease severity and mortality. High levels of ECM mediators during hospitalisation were associated with computed tomography thorax pathology after 3-months. Some markers (i.e. growth differential factor 15, galectin 3 and matrix metalloproteinase 9) were released from various relevant cell lines (i.e. macrophages and lung cell lines) in vitro after exposure to inactivated SARS-CoV-2 suggesting a direct link between these mediators and the causal agent of COVID-19. CONCLUSION: Our findings highlight changes to ECM remodelling and particularly a possible role of OPN, S100A12 and YKL-40 in the pathogenesis of severe COVID-19.

Gut microbiota composition during hospitalization is associated with 60-day mortality after severe COVID-19.

BACKGROUND: Gut microbiota alterations have been reported in hospitalized COVID-19 patients, with reduced alpha diversity and altered microbiota composition related to respiratory failure. However, data regarding gut microbiota and mortality are scarce. METHODS: Rectal swabs for gut microbiota analyses were collected within 48 h after hospital admission (baseline; n = 123) and three-month post-admission (n = 50) in a subset of patients included in the Norwegian SARS-CoV2 cohort study. Samples were analysed by sequencing the 16S rRNA gene. Gut microbiota diversity and composition at baseline were assessed in relation to need for intensive care unit (ICU) admission during hospitalization. The primary objective was to investigate whether the ICU-related gut microbiota was associated with 60-day mortality. RESULTS: Gut microbiota diversity (Shannon index) at baseline was lower in COVID-19 patients requiring ICU admission during hospitalization than in those managed in general wards. A dysbiosis index representing a balance of enriched and reduced taxa in ICU compared with ward patients, including decreased abundance of butyrate-producing microbes and enrichment of a partly oral bacterial flora, was associated with need of ICU admission independent of antibiotic use, dexamethasone use, chronic pulmonary disease, PO2/FiO2 ratio, C-reactive protein, neutrophil counts or creatinine levels (adjusted p < 0.001). The ICU-related dysbiosis index at baseline correlated with systemic inflammation and was associated with 60-day mortality in univariate analyses (Hazard ratio 3.70 [2.00-8.6], p < 0.001), as well as after separate adjustment for covariates. At the three-month follow-up, the dysbiosis index remained elevated in ICU patients compared with ward patients (adjusted p = 0.007). CONCLUSIONS: Although our data should be regarded as exploratory due to low number of clinical end points, they suggest that gut microbiota alterations during hospitalization could be related to poor prognosis after severe COVID-19. Larger studies of gut involvement during COVID-19 in relation to long-term clinical outcome are warranted. Trial registration NCT04381819 . Retrospectively registered May 11, 2020.

Efficacy and safety of baricitinib in hospitalized adults with severe or critical COVID-19 (Bari-SolidAct): a randomised, double-blind, placebo-controlled phase 3 trial.

BACKGROUND: Baricitinib has shown efficacy in hospitalized patients with COVID-19, but no placebo-controlled trials have focused specifically on severe/critical COVID, including vaccinated participants. METHODS: Bari-SolidAct is a phase-3, multicentre, randomised, double-blind, placebo-controlled trial, enrolling participants from June 3, 2021 to March 7, 2022, stopped prematurely for external evidence. Patients with severe/critical COVID-19 were randomised to Baricitinib 4 mg once daily or placebo, added to standard of care. The primary endpoint was all-cause mortality within 60 days. Participants were remotely followed to day 90 for safety and patient related outcome measures. RESULTS: Two hundred ninety-nine patients were screened, 284 randomised, and 275 received study drug or placebo and were included in the modified intent-to-treat analyses (139 receiving baricitinib and 136 placebo). Median age was 60 (IQR 49-69) years, 77% were male and 35% had received at least one dose of SARS-CoV2 vaccine. There were 21 deaths at day 60 in each group, 15.1% in the baricitinib group and 15.4% in the placebo group (adjusted absolute difference and 95% CI - 0.1% [- 8·3 to 8·0]). In sensitivity analysis censoring observations after drug discontinuation or rescue therapy (tocilizumab/increased steroid dose), proportions of death were 5.8% versus 8.8% (- 3.2% [- 9.0 to 2.7]), respectively. There were 148 serious adverse events in 46 participants (33.1%) receiving baricitinib and 155 in 51 participants (37.5%) receiving placebo. In subgroup analyses, there was a potential interaction between vaccination status and treatment allocation on 60-day mortality. In a subsequent post hoc analysis there was a significant interaction between vaccination status and treatment allocation on the occurrence of serious adverse events, with more respiratory complications and severe infections in vaccinated participants treated with baricitinib. Vaccinated participants were on average 11 years older, with more comorbidities. CONCLUSION: This clinical trial was prematurely stopped for external evidence and therefore underpowered to conclude on a potential survival benefit of baricitinib in severe/critical COVID-19. We observed a possible safety signal in vaccinated participants, who were older with more comorbidities. Although based on a post-hoc analysis, these findings warrant further investigation in other trials and real-world studies. Trial registration Bari-SolidAct is registered at NCT04891133 (registered May 18, 2021) and EUClinicalTrials.eu ( 2022-500385-99-00 ).

COVID-19 patients treated with convalescent plasma. / Covid-19-pasienter behandlet med rekonvalesensplasma.

BACKGROUND: In Norway, treatment with COVID-19 convalescent plasma has been given through the NORPLASMA project. The treatment was initially offered to critically ill patients after an individual assessment, but from December 2020, the indication was limited to critically ill, immunocompromised patients. In this article we describe clinical characteristics, comorbidity and mortality in patients who received convalescent plasma in these two periods. MATERIAL AND METHOD: From 22 April 2020 to 30 March 2022, a total of 79 patients were included in the observational studies NORPLASMA MONITOR and the Norwegian SARS-CoV-2 study. The patients had received a total of 193 units of convalescent plasma at 15 Norwegian hospitals/nursing homes; 62 in South-Eastern Norway Regional Health Authority, 8 in Western Norway Regional Health Authority and 9 in Central Norway Regional Health Authority. Information on immune status, comorbidity and course of infection was retrieved from the patient records after informed written consent was obtained. RESULTS: Of 79 patients with a median age of 65 years (interquartile range 51-⁠73) who were treated with convalescent plasma, 31 (39 %) died during hospitalisation. A total of 59 patients were immunocompromised, and of these, 20 died in hospital compared to 11 of 20 who were assumed to be immunocompetent. Median number of comorbidities was 2 (interquartile range 1-4). The patients received a median of two plasma units (min.-max. 1-21). Two of the patients developed mild allergic skin reactions. INTERPRETATION: Convalescent plasma was well tolerated by patients with COVID-19. Immunocompromised patients may have benefitted from the treatment, with lower mortality than for those assumed to be immunocompetent.

High Circulating Levels of the Homeostatic Chemokines CCL19 and CCL21 Predict Mortality and Disease Severity in COVID-19.

BACKGROUND: Immune dysregulation is a major factor in the development of severe coronavirus disease 2019 (COVID-19). The homeostatic chemokines CCL19 and CCL21 have been implicated as mediators of tissue inflammation, but data on their regulation in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is limited. We thus investigated the levels of these chemokines in COVID-19 patients. METHODS: Serial blood samples were obtained from patients hospitalized with COVID-19 (n = 414). Circulating CCL19 and CCL21 levels during hospitalization and 3-month follow-up were analyzed. In vitro assays and analysis of RNAseq data from public repositories were performed to further explore possible regulatory mechanisms. RESULTS: A consistent increase in circulating levels of CCL19 and CCL21 was observed, with high levels correlating with disease severity measures, including respiratory failure, need for intensive care, and 60-day all-cause mortality. High levels of CCL21 at admission were associated with persisting impairment of pulmonary function at the 3-month follow-up. CONCLUSIONS: Our findings highlight CCL19 and CCL21 as markers of immune dysregulation in COVID-19. This may reflect aberrant regulation triggered by tissue inflammation, as observed in other chronic inflammatory and autoimmune conditions. Determination of the source and regulation of these chemokines and their effects on lung tissue is warranted to further clarify their role in COVID-19. CLINICAL TRIALS REGISTRATION: NCT04321616 and NCT04381819.

T-helper cell regulation of CD45 phosphatase activity by galectin-1 and CD43 governs chronic lymphocytic leukaemia proliferation.

Chronic lymphocytic leukaemia (CLL) is characterised by malignant mature-like B cells. Supportive to CLL cell survival is chronic B-cell receptor (BCR) signalling; however, emerging evidence demonstrates CLL cells proliferate in response to T-helper (Th) cells in a CD40L-dependent manner. We showed provision of Th stimulation via CD40L upregulated CD45 phosphatase activity and BCR signalling in non-malignant B cells. Consequently, we hypothesised Th cell upregulation of CLL cell CD45 activity may be an important regulator of CLL BCR signalling and proliferation. Using patient-derived CLL cells in a culture system with activated autologous Th cells, results revealed increases in both Th and CLL cell CD45 activity, which correlated with enhanced downstream antigen receptor signalling and proliferation. Concomitantly increased was the surface expression of Galectin-1, a CD45 ligand, and CD43, a CLL immunophenotypic marker. Galectin-1/CD43 double expression defined a proliferative CLL cell population with enhanced CD45 activity. Targeting either Galectin-1 or CD43 using silencing, pharmacology, or monoclonal antibody strategies dampened CD45 activity and CLL cell proliferation. These results highlight a mechanism where activated Th cells drive CLL cell BCR signalling and proliferation via Galectin-1 and CD43-mediated regulation of CD45 activity, identifying modulation of CD45 phosphatase activity as a potential therapeutic target in CLL.

Respiratory dysfunction three months after severe COVID-19 is associated with gut microbiota alterations.

BACKGROUND: Although coronavirus disease 2019 (COVID-19) is primarily a respiratory infection, mounting evidence suggests that the gastrointestinal tract is involved in the disease, with gut barrier dysfunction and gut microbiota alterations being related to disease severity. Whether these alterations persist and are related to long-term respiratory dysfunction remains unknown. METHODS: Plasma was collected during hospital admission and after 3 months from the NOR-Solidarity trial (n = 181) and analyzed for markers of gut barrier dysfunction and inflammation. At the 3-month follow-up, pulmonary function was assessed by measuring the diffusing capacity of the lungs for carbon monoxide (DLCO ). Rectal swabs for gut microbiota analyses were collected (n = 97) and analyzed by sequencing the 16S rRNA gene. RESULTS: Gut microbiota diversity was reduced in COVID-19 patients with respiratory dysfunction, defined as DLCO below the lower limit of normal 3 months after hospitalization. These patients also had an altered global gut microbiota composition, with reduced relative abundance of 20 bacterial taxa and increased abundance of five taxa, including Veillonella, potentially linked to fibrosis. During hospitalization, increased plasma levels of lipopolysaccharide-binding protein (LBP) were strongly associated with respiratory failure, defined as pO2 /fiO2 (P/F ratio) <26.6 kPa. LBP levels remained elevated during and after hospitalization and were associated with low-grade inflammation and respiratory dysfunction after 3 months. CONCLUSION: Respiratory dysfunction after COVID-19 is associated with altered gut microbiota and persistently elevated LBP levels. Our results should be regarded as hypothesis generating, pointing to a potential gut-lung axis that should be further investigated in relation to long-term pulmonary dysfunction and long COVID.

Persistent T-cell exhaustion in relation to prolonged pulmonary pathology and death after severe COVID-19: Results from two Norwegian cohort studies.

BACKGROUND: T-cell activation is associated with an adverse outcome in COVID-19, but whether T-cell activation and exhaustion relate to persistent respiratory dysfunction and death is unknown. OBJECTIVES: To investigate whether T-cell activation and exhaustion persist and are associated with prolonged respiratory dysfunction and death after hospitalization for COVID-19. METHODS: Plasma and serum from two Norwegian cohorts of hospitalized patients with COVID-19 (n = 414) were analyzed for soluble (s) markers of T-cell activation (sCD25) and exhaustion (sTim-3) during hospitalization and follow-up. RESULTS: Both markers were strongly associated with acute respiratory failure, but only sTim-3 was independently associated with 60-day mortality. Levels of sTim-3 remained elevated 3 and 12 months after hospitalization and were associated with pulmonary radiological pathology after 3 months. CONCLUSION: Our findings suggest prolonged T-cell exhaustion is an important immunological sequela, potentially related to long-term outcomes after severe COVID-19.

B cell receptor ligation induces display of V-region peptides on MHC class II molecules to T cells.

The B cell receptors (BCRs) for antigen express variable (V) regions that are enormously diverse, thus serving as markers on individual B cells. V region-derived idiotypic (Id) peptides can be displayed as pId:MHCII complexes on B cells for recognition by CD4+ T cells. It is not known if naive B cells spontaneously display pId:MHCII in vivo or if BCR ligation is required for expression, thereby enabling collaboration between Id+ B cells and Id-specific T cells. Here, using a mouse model, we show that naive B cells do not express readily detectable levels of pId:MHCII. However, BCR ligation by Ag dramatically increases physical display of pId:MHCII, leading to activation of Id-specific CD4+ T cells, extrafollicular T-B cell collaboration and some germinal center formation, and production of Id+ IgG. Besides having implications for immune regulation, the results may explain how persistent activation of self-reactive B cells induces the development of autoimmune diseases and B cell lymphomas.

Evaluation of the Effects of Remdesivir and Hydroxychloroquine on Viral Clearance in COVID-19 : A Randomized Trial.

BACKGROUND: New treatment modalities are urgently needed for patients with COVID-19. The World Health Organization (WHO) Solidarity trial showed no effect of remdesivir or hydroxychloroquine (HCQ) on mortality, but the antiviral effects of these drugs are not known. OBJECTIVE: To evaluate the effects of remdesivir and HCQ on all-cause, in-hospital mortality; the degree of respiratory failure and inflammation; and viral clearance in the oropharynx. DESIGN: NOR-Solidarity is an independent, add-on, randomized controlled trial to the WHO Solidarity trial that included biobanking and 3 months of clinical follow-up (ClinicalTrials.gov: NCT04321616). SETTING: 23 hospitals in Norway. PATIENTS: Eligible patients were adults hospitalized with confirmed SARS-CoV-2 infection. INTERVENTION: Between 28 March and 4 October 2020, a total of 185 patients were randomly assigned and 181 were included in the full analysis set. Patients received remdesivir (n = 42), HCQ (n = 52), or standard of care (SoC) (n = 87). MEASUREMENTS: In addition to the primary end point of WHO Solidarity, study-specific outcomes were viral clearance in oropharyngeal specimens, the degree of respiratory failure, and inflammatory variables. RESULTS: No significant differences were seen between treatment groups in mortality during hospitalization. There was a marked decrease in SARS-CoV-2 load in the oropharynx during the first week overall, with similar decreases and 10-day viral loads among the remdesivir, HCQ, and SoC groups. Remdesivir and HCQ did not affect the degree of respiratory failure or inflammatory variables in plasma or serum. The lack of antiviral effect was not associated with symptom duration, level of viral load, degree of inflammation, or presence of antibodies against SARS-CoV-2 at hospital admittance. LIMITATION: The trial had no placebo group. CONCLUSION: Neither remdesivir nor HCQ affected viral clearance in hospitalized patients with COVID-19. PRIMARY FUNDING SOURCE: National Clinical Therapy Research in the Specialist Health Services, Norway.

Three waves of COVID-19 in a Norwegian local hospital. / Tre bølger med covid-19 på et norsk lokalsykehus.

BACKGROUND: The objective of this article is to summarise the course of illness and treatment for patients with COVID-19 admitted to Bærum Hospital since the start of the pandemic. MATERIAL AND METHOD: We present data from a prospective observational study with the aim of systematising knowledge about patients admitted because of COVID-19. All patients admitted to Bærum Hospital up to and including 28 June 2021 were included. The results are presented for three waves of admissions: 9 March-23 June 2020, 21 September 2020-28 February 2021 and 1 March-28 June 2021. RESULTS: A total of 300 patients, divided into 77, 101 and 122 in the three waves respectively, were admitted because of COVID-19. The number of hospital deaths during the three waves was 14 (18 %), 11 (11 %) and 5 (4 %) respectively. The average age of the patients was 67.6 years in the first wave and 53.3 years in the third wave. Altogether 204 patients (68 %) received medical oxygen or ventilation support, and 31 of these (10 % of all the patients) received invasive ventilation support. Non-invasive ventilation support was used as the highest level of treatment in 4 (8 %), 9 (13 %) and 17 (20 %) patients with respiratory failure in the three waves respectively. In the second and third wave, 125 out of 152 patients with respiratory failure (82 %) were treated with dexamethasone. INTERPRETATION: Differences in patient characteristics and changes to treatment methods, such as the use of dexamethasone and non-invasive ventilation support, may have contributed to the apparent fall in mortality from the first to the third wave. Conditions that are not registered in the study, such as vaccination status, may also have impacted on mortality.

An immunosuppressed woman in her seventies with night sweats and weight loss. / En immunsupprimert kvinne i 70-årene med nattesvette og vekttap.

BACKGROUND: Candidatus Neoehrlichia mikurensis is an emerging tick-borne pathogen with widespread distribution in Ixodes ricinus ticks in Europe and Asia. It has been found to cause chronic infections, particularly in immunosuppressed individuals. Common symptoms include relapsing fever, night sweats and thromboembolic episodes, likely due to endovascular infection. CASE PRESENTATION: A patient in her seventies developed persistent night sweats and moderate weight loss that persisted for four months prior to evaluation. There was no history of fever or organ-specific symptoms. Prior diseases included a ten-year history of rheumatoid arthritis treated with rituximab. Initial workup revealed moderately increased acute phase reactants, but no evidence of malignant disease or endocrine abnormalities. Night sweats persisted, and after eight months moderate splenic enlargement was observed. PCR revealed presence of Candidatus Neoehrlichia mikurensis DNA, and symptoms resolved promptly after initiation of oral doxycycline treatment. INTERPRETATION: Infection with anaplasmataceae such as Candidatus Neoehrlichia mikurensis can present with non-specific constitutive symptoms. In this case, persistent night sweats and moderate weight loss were the only manifestations over an eight-month period. Diagnosis is readily established by PCR analysis of whole blood, but a high degree of suspicion and careful assessment of potential exposure is required for timely diagnosis.

Complications and mortality among patients hospitalised with COVID-19. / Komplikasjoner og dødelighet blant pasienter innlagt med covid-19.

BACKGROUND: The course of disease, complications and hospital mortality among patients with COVID-19 admitted to Norwegian hospitals has not been widely described. The purpose of this study was to survey patients with COVID-19 admitted to a local hospital. MATERIAL AND METHOD: The data were retrieved from a prospective observational study of all patients admitted with COVID-19 to Bærum Hospital since the start of the coronavirus outbreak. RESULTS: A total of 73 patients with COVID-19 admitted in the period 9 March 2020-7 May 2020 were included. The mean age was 67.9 years, and 43 patients (59 %) were men. The average number of days hospitalised was 10.1. Altogether 19 patients (26 %) had a very severe course of disease, and 14 (19 %) died during their stay in hospital. The mean age among the patients who died was 79.5 years. A total of 49 patients (67 %) had hypoxaemia and required oxygen therapy for an average of 10.1 days. Of these, 9 patients were given invasive respiratory support for a median 18 days. Symptoms of delirium occurred in 26 patients (36 %) and was the most frequent non-respiratory complication. INTERPRETATION: The majority of the patients hospitalised with COVID-19 needed prolonged oxygen therapy, and there was a high incidence of severe complications.

COVID-19: Symptoms, course of illness and use of clinical scoring systems for the first 42 patients admitted to a Norwegian local hospital. / Covid-19: Symptomer, forløp og bruk av kliniske skåringsverktøy hos de 42 første pasientene innlagt på et norsk lokalsykehus.

BACKGROUND: The COVID-19 outbreak is presenting the health system with new challenges, and there is a great need for knowledge about symptoms, clinical findings and course of illness in patients admitted to Norwegian hospitals with COVID-19. MATERIAL AND METHOD: In this observational qualitative study, all patients admitted to a Norwegian local hospital (Bærum Hospital) with proven COVID-19 infection were included consecutively from the start of the outbreak. We present here patient characteristics, symptoms, clinical findings, experience of using clinical scoring systems and course of illness based on data in medical records. RESULTS: In the period 9-31 March 2020, 42 patients, of whom 28 (67 %) were men, were admitted to hospital with COVID-19 infection. The median age was 72.5 years (range 30-95). Fever (79 %), reduced general condition (79 %), dyspnoea (69 %) and cough (67 %) were the most common symptoms. A total of nine patients (21 %) had a critical course of illness with treatment in the Intensive Care Department and/or death during their stay in hospital. Patients with a critical course had a higher average score on National Early Warning Score 2 (NEWS2) on admission (7.6 vs 3.3). Only one of the most severely ill patients scored ≥ 2 on the quick Sepsis-related Organ Failure Assessment (qSOFA) on admission. INTERPRETATION: Most patients admitted to our hospital with COVID-19 had a fever and respiratory tract symptoms. A high percentage of patients had a critical course of illness. A NEWS2 score of ≥ 5 on admission may be a useful aid in identifying patients at risk of a critical course of illness, while CRB-65 and qSOFA score ≥ 2 proved to be of little usefulness for this purpose in our material.

Pulmonary embolism in cases of COVID-19. / Lungeembolisme ved covid-19.

BACKGROUND: Emerging reports indicate a high incidence of venous thromboembolism in patients hospitalised for SARS-CoV-2 pneumonia during the spring 2020 pandemic. The pronounced pulmonary and systemic inflammatory responses observed in these patients may contribute to a transient hypercoagulable state. In this setting, pulmonary embolism may cause further respiratory distress and clinical deterioration. CASE PRESENTATION: We describe the clinical course of three patients admitted with SARS-CoV-2 infection and respiratory distress, where pulmonary embolism was detected during the course of the hospitalisation. Two of the cases occurred despite early institution of standard dosage of low molecular weight heparin thromboprophylaxis, and in one case, pulmonary embolism was diagnosed during the convalescent phase of an otherwise benign COVID-19 disease course. INTERPRETATION: These cases highlight the importance of awareness of the potentially increased incidence of venous thromboembolism in COVID-19 disease. Further research is required to establish appropriate clinical management guidelines for prevention of thromboembolic complications in COVID-19.

CD4+ T cells indirectly kill tumor cells via induction of cytotoxic macrophages in mouse models.

It is well recognized that CD4+ T cells may play an important role in immunosurveillance and immunotherapy against cancer. However, the details of how these cells recognize and eliminate the tumor cells remain incompletely understood. For the past 25 years, we have focused on how CD4+ T cells reject multiple myeloma cells in a murine model (MOPC315). In our experimental system, the secreted tumor-specific antigen is taken up by tumor-infiltrating macrophages that process it and present a neoepitope [a V region-derived idiotypic (Id) peptide] on MHC class II molecules to Th1 cells. Stimulated Th1 cells produce IFNγ, which activates macrophages in a manner that elicits an M1-like, tumoricidal phenotype. Through an inducible nitric oxide synthetase (iNOS)-dependent mechanism, the M1 macrophages secrete nitric oxide (NO) that diffuses into neighboring tumor cells. Inside the tumor cells, NO-derived reactive nitrogen species, including peroxynitrite, causes nitrosylation of proteins and triggers apoptosis by the intrinsic apoptotic pathway. This mode of indirect tumor recognition by CD4+ T cells operates independently of MHC class II expression on cancer cells. However, secretion of the tumor-specific antigen, and uptake and MHCII presentation on macrophages, is required for rejection. Similar mechanisms can also be observed in a B-lymphoma model and in the unrelated B16 melanoma model. Our findings reveal a novel mechanism by which CD4+ T cells kill tumor cells indirectly via induction of intratumoral cytotoxic macrophages. The data suggest that induction of M1 polarization of tumor-infiltrating macrophages, by CD4+ T cells or through other means, could serve as an immunotherapeutic strategy.

Vaccine molecules targeting Xcr1 on cross-presenting DCs induce protective CD8+ T-cell responses against influenza virus.

Targeting antigens to cross-presenting dendritic cells (DCs) is a promising method for enhancing CD8(+) T-cell responses. However, expression patterns of surface receptors often vary between species, making it difficult to relate observations in mice to other animals. Recent studies have indicated that the chemokine receptor Xcr1 is selectively expressed on cross-presenting murine CD8α(+) DCs, and that the expression is conserved on homologous DC subsets in humans (CD141(+) DCs), sheep (CD26(+) DCs), and macaques (CADM1(+) DCs). We therefore tested if targeting antigens to Xcr1 on cross-presenting DCs using antigen fused to Xcl1, the only known ligand for Xcr1, could enhance immune responses. Bivalent Xcl1 fused to model antigens specifically bound CD8α(+) DCs and increased proliferation of antigen-specific T cells. DNA vaccines encoding dimeric Xcl1-hemagglutinin (HA) fusion proteins induced cytotoxic CD8(+) T-cell responses, and mediated full protection against a lethal challenge with influenza A virus. In addition to enhanced CD8(+) T-cell responses, targeting of antigen to Xcr1 induced CD4(+) Th1 responses and highly selective production of IgG2a antibodies. In conclusion, targeting of dimeric fusion vaccine molecules to CD8α(+) DCs using Xcl1 represents a novel and promising method for induction of protective CD8(+) T-cell responses.

Naive idiotope-specific B and T cells collaborate efficiently in the absence of dendritic cells.

Anti-idiotope (anti-Id) Abs have a role in therapy against B cell lymphomas, as inhibitors of pathogenic autoantibodies, and as surrogate Ags for immunization. Despite these observations, the mechanism by which Id(+) Ig generates anti-Id Abs is essentially unknown. To address this issue, we generated a double knock-in mouse that expresses V regions of a somatically mutated anti-Id mAb with intermediate affinity (affinity constant [Ka] = 0.77 × 10(7) M(-1)) for the myeloma protein M315. The anti-Id mice have normal peripheral B cell populations, and allelic exclusion is efficient. Anti-Id B cells from BCR knock-in mice, together with Id-specific CD4(+) T cells from previously established TCR-transgenic mice, enabled us to study Id-specific T cell-B cell collaboration by dilution of transferred cells into syngeneic BALB/c recipients. We show that previously unstimulated (naive) Id-specific B and T cells collaborate efficiently in vivo, even at low frequencies and in the presence of low amounts of Id(+) Ig, resulting in germinal center formation, plasma cell development, and secretion of isotype-switched anti-Id Abs. We further demonstrate that Id-specific T cell-B cell collaboration occurs readily in the absence of adjuvant and is not dependent on Id-presentation by dendritic cells. The results underscore the potency of anti-Id B cells in MHC class II-restricted presentation of Id(+) Ig and suggest that Id-specific T cell-B cell collaboration is of physiological relevance.