Step-in dosing of bosutinib in pts with chronic phase chronic myeloid leukemia (CML) after second-generation tyrosine kinase inhibitor (TKI) therapy: results of the Bosutinib Dose Optimization (BODO) Study

The approved dose of bosutinib in chronic phase CML is 400 mg QD in first-line and 500 mg QD in later-line treatment. However, given that gastrointestinal (GI) toxicity typically occurs early after treatment initiation, physicians often tend to start therapy with lower doses although this has never been tested systematically in prospective trials in the Western world. The Bosutinib Dose Optimization (BODO) Study, a multicenter phase II study, investigated the tolerability and efficacy of a step-in dosing concept of bosutinib (starting at 300 mg QD) in chronic phase CML patients in 2nd or 3rd line who were intolerant and/or refractory to previous TKI treatment. Of 57 patients included until premature closure of the study due to slow recruitment, 34 (60%) reached the targeted dose level of 500 mg QD following the 2-weekly step-in dosing regimen. While the dosing-in concept failed to reduce GI toxicity (grade II-IV, primary study endpoint) to < 40% (overall rate of 60%; 95% CI: 45-74%), bosutinib treatment (mean dosage: 403 mg/day) showed remarkable efficacy with a cumulative major molecular remission (MMR) rate of 79% (95% CI: 66 to 88%) at month 24. Of thirty patients refractory to previous therapy and not in MMR at baseline, 19 (64%) achieved an MMR during treatment. GI toxicity did not significantly impact on patient-reported outcomes (PRO) and led to treatment discontinuation in only one patient. Overall, the results of our trial support the efficacy and safety of bosutinib after failure of second-generation TKI pre-treatment. Trial registration: NCT02577926.

Nestin expression in osteocytes following myeloablation and during bone marrow metastasis

Nestin is an intermediate filament protein, which was originally detected in neuroepithelial stem cells. Besides its use as a phenotypic marker of mesenchymal stem cells in the hematopoeitic stem cell niche, the functional interpretation of nestin⁺ cells remains elusive. We investigated the cellular expression of nestin in bone marrow trephine biopsies of MPN patients, following myeloablation at a stage of hypocellularity during early regeneration. Here, nestin is highly expressed in mature osteocytes, arteriolar endothelial and perivascular cells and small capillaries within the bone marrow space, but not in sinusoid lining cells. This is in stark contrast to nestin expression pattern in myeloproliferative neoplasms that show hypercellularity due to oncogenic driver mutations. Here, nestin is expressed exclusively in endothelial cells of arterioles, but not in osteocytes or small capillaries. Thus, the pattern of nestin expression following myeloablation inversely correlates with cellularity in the bone marrow. This nestin expression pattern is mimicking early postnatal transcriptional programming during bone marrow development. We show that nestin expression in osteocytes occurs across different species following transplant and also in bone marrow metastasis.

Monocyte-derived macrophages aggravate pulmonary vasculitis via cGAS/STING/IFN-mediated nucleic acid sensing

Autoimmune vasculitis is a group of life-threatening diseases, whose underlying pathogenic mechanisms are incompletely understood, hampering development of targeted therapies. Here, we demonstrate that patients suffering from anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) showed increased levels of cGAMP and enhanced IFN-I signature. To identify disease mechanisms and potential therapeutic targets, we developed a mouse model for pulmonary AAV that mimics severe disease in patients. Immunogenic DNA accumulated during disease onset, triggering cGAS/STING/IRF3-dependent IFN-I release that promoted endothelial damage, pulmonary hemorrhages, and lung dysfunction. Macrophage subsets played dichotomic roles in disease. While recruited monocyte-derived macrophages were major disease drivers by producing most IFN-β, resident alveolar macrophages contributed to tissue homeostasis by clearing red blood cells and limiting infiltration of IFN-β-producing macrophages. Moreover, pharmacological inhibition of STING, IFNAR-I, or its downstream JAK/STAT signaling reduced disease severity and accelerated recovery. Our study unveils the importance of STING/IFN-I axis in promoting pulmonary AAV progression and identifies cellular and molecular targets to ameliorate disease outcomes.

Intercellular cGAMP transmission induces innate immune activation and tissue inflammation in Trex1 deficiency

Intercellular transmission of the second messenger 2′,3′-cGAMP, synthesized by the viral DNA sensor cGAMP synthase (cGAS), is a potent mode of bystander activation during host defense. However, whether this mechanism also contributes to cGAS-dependent autoimmunity remains unknown. Here, using a murine bone marrow transplantation strategy, we demonstrate that, in Trex1^−/−-associated autoimmunity, cGAMP shuttling from radioresistant to immune cells induces NF-κB activation, interferon regulatory factor 3 (IRF3) phosphorylation, and subsequent interferon signaling. cGAMP travel prevented myeloid cell and lymphocyte death, promoting their accumulation in secondary lymphoid tissue. Nonetheless, it did not stimulate B cell differentiation into autoantibody-producing plasmablasts or aberrant T cell priming. Although cGAMP-mediated bystander activation did not induce spontaneous organ disease, it did trigger interface dermatitis after UV light exposure, similar to cutaneous lupus erythematosus. These findings reveal that, in Trex1-deficiency, intercellular cGAMP transfer propagates cGAS signaling and, under conducive conditions, causes tissue inflammation.

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In Trex1^−/−-associated autoimmunity radioresistant cells transfer cGAMP to immune cells

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cGAMP shuttling induces NF-κB activation, IRF3 and IFN signaling in vivo

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Intercellular cGAMP transmission is sufficient to cause UV skin inflammation

Macrophage frequency in the bone marrow correlates with morphologic subtype of myeloproliferative neoplasm

Bone marrow (BM) fibrosis in myeloproliferative neoplasms (MPNs) is associated with a poor prognosis. The development of myelofibrosis and differentiation of mesenchymal stromal cells to profibrotic myofibroblasts depends on macrophages. Here, we compared macrophage frequencies in BM biopsies of MPN patients and controls (patients with non-neoplastic processes), including primary myelofibrosis (PMF, n = 18), essential thrombocythemia (ET, n = 14), polycythemia vera (PV, n = 12), and Philadelphia chromosome-positive chronic myeloid leukemia (CML, n = 9). In PMF, CD68-positive macrophages were greatly increased compared to CML (p = 0.017) and control BM (p < 0.001). Similar findings were observed by CD163 staining (PMF vs. CML: p = 0.017; PMF vs. control: p < 0.001). Moreover, CD68-positive macrophages were increased in PV compared with ET (p = 0.009) and reactive cases (p < 0.001). PMF had higher frequencies of macrophages than PV (CD68: p < 0.001; CD163: p < 0.001) and ET (CD68: p < 0.001; CD163: p < 0.001). CD163 and CD68 were often co-expressed in macrophages with stellate morphology in Philadelphia chromosome-negative MPN, resulting in a sponge-like reticular network that may be a key regulator of unbalanced hematopoiesis in the BM space and may explain differences in cellularity and clinical course.

Development and function of human innate immune cells in a humanized mouse model

Mice repopulated with human hematopoietic cells are a powerful tool for the study of human hematopoiesis and immune function in vivo. However, existing humanized mouse models are unable to support development of human innate immune cells, including myeloid cells and NK cells. Here we describe a mouse strain, called MI(S)TRG, in which human versions of four genes encoding cytokines important for innate immune cell development are knocked in to their respective mouse loci. The human cytokines support the development and function of monocytes/macrophages and natural killer cells derived from human fetal liver or adult CD34⁺ progenitor cells injected into the mice. Human macrophages infiltrated a human tumor xenograft in MI(S)TRG mice in a manner resembling that observed in tumors obtained from human patients. This humanized mouse model may be used to model the human immune system in scenarios of health and pathology, and may enable evaluation of therapeutic candidates in an in vivo setting relevant to human physiology.

B cell-derived IL-10 does not regulate spontaneous systemic autoimmunity in MRL.Fas(lpr) mice

B cells contribute to the pathogenesis of chronic autoimmune disorders, like systemic lupus erythematosus (SLE), via multiple effector functions. However, B cells are also implicated in regulating SLE and other autoimmune syndromes via release of IL-10. B cells secreting IL-10 were termed "Bregs" and were proposed as a separate subset of cells, a concept that remains controversial. The balance between pro- and anti-inflammatory effects could determine the success of B cell-targeted therapies for autoimmune disorders; therefore, it is pivotal to understand the significance of B cell-secreted IL-10 in spontaneous autoimmunity. By lineage-specific deletion of Il10 from B cells, we demonstrated that B cell-derived IL-10 is ineffective in suppressing the spontaneous activation of self-reactive B and T cells during lupus. Correspondingly, severity of organ disease and survival rates in mice harboring Il10-deficient B cells are unaltered. Genetic marking of cells that transcribe Il10 illustrated that the pool of IL-10-competent cells is dominated by CD4 T cells and macrophages. IL-10-competent cells of the B lineage are rare in vivo and, among them, short-lived plasmablasts have the highest frequency, suggesting an activation-driven, rather than lineage-driven, phenotype. Putative Breg phenotypic subsets, such as CD1d(hi)CD5(+) and CD21(hi)CD23(hi) B cells, are not enriched in Il10 transcription. These genetic studies demonstrated that, in a spontaneous model of murine lupus, IL-10-dependent B cell regulation does not restrain disease and, thus, the pathogenic effects of B cells are not detectably counterbalanced by their IL-10-dependent regulatory functions.

An acquired defect in IgG-dependent phagocytosis explains the impairment in antibody-mediated cellular depletion in Lupus

B cells play important roles in autoimmune diseases ranging from multiple sclerosis to rheumatoid arthritis. B cells have also long been considered central players in systemic lupus erythematosus. However, anti-CD20-mediated B cell depletion was not effective in two clinical lupus studies, whereas anti-B lymphocyte stimulator, which inhibits B cell survival, was effective. Others and we previously found that anti-CD20-based depletion was surprisingly ineffective in tissues of lupus-prone mice, but that persistent high doses eventually led to depletion and ameliorated lupus. Lupus patients might also have incomplete depletion, as suggested in several studies, and which could have led to therapeutic failure. In this study, we investigated the mechanism of resistance to Ab-mediated cellular depletion in murine lupus. B cells from lupus-prone mice were easily depleted when transferred into normal environments or in lupus-prone mice that lacked serum Ig. Serum from lupus-prone mice transferred depletion resistance, with the active component being IgG. Because depletion is FcγR-dependent, we assayed macrophages and neutrophils exposed to lupus mouse serum, showing that they are impaired in IgG-mediated phagocytosis. We conclude that depletion resistance is an acquired, reversible phagocytic defect depending on exposure to lupus serum IgG. These results have implications for optimizing and monitoring cellular depletion therapy.

Dendritic cells in lupus are not required for activation of T and B cells but promote their expansion, resulting in tissue damage

Dendritic cells (DCs) initiate and control the adaptive immune response against infections. However, their contributions to the anti-self adaptive immune response in autoimmune disorders like systemic lupus erythematosus are uncertain. By constitutively deleting DCs in MRL.Fas(lpr) mice, we show that they have complex roles in murine lupus. The net effect of DC deletion was to ameliorate disease. DCs were crucial for the expansion and differentiation of T cells but, surprisingly, not required for their initial activation. Correspondingly, kidney interstitial infiltrates developed in the absence of DCs, but failed to progress. DC deletion concomitantly decreased inflammatory and regulatory T cell numbers. Unexpectedly, plasmablast numbers and autoantibody concentrations depended on DCs, in contrast to total serum immunoglobulin concentrations, suggesting an effect of DCs on extrafollicular humoral responses. These findings reveal that DCs operate in unanticipated ways in murine lupus and validate them as a potential therapeutic target in autoimmunity.

[Current views on lipid metabolism: statin-induced myopathy]

Cardiovascular diseases are the most common causes of death in Germany and the prevalence is increased in patients with inflammatory rheumatic diseases. Statins are often employed for primary and secondary prophylaxis of cardiovascular events but can potentially induce myopathy as a side-effect. In addition to an asymptomatic elevation of muscle enzymes, myalgia and myositis as well as rhabdomyolysis, the most severe side-effect, have been observed, which are mostly manifested within 6 months after initiation of therapy. Statin-induced myopathy is rare but if risk factors are present, the individual risk can be much higher. Such factors are in particular interaction with other medications, statin dosage, the characteristics of the statin preparation used, comorbidities, age and sex of the patient. Regular testing of muscle enzymes after induction of statin therapy is not generally recommended for asymptomatic patients, but is indispensable when muscle symptoms appear. Statin therapy must be immediately terminated and a diagnostic evaluation must be carried out at the latest when creatine kinase values show a more than 10-fold increase.