Transient CDK4/6 inhibition protects hematopoietic stem cells from chemotherapy-induced exhaustion.

Conventional cytotoxic chemotherapy is highly effective in certain cancers but causes dose-limiting damage to normal proliferating cells, especially hematopoietic stem and progenitor cells (HSPCs). Serial exposure to cytotoxics causes a long-term hematopoietic compromise ("exhaustion"), which limits the use of chemotherapy and success of cancer therapy. We show that the coadministration of G1T28 (trilaciclib), which is a small-molecule inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6), contemporaneously with cytotoxic chemotherapy protects murine hematopoietic stem cells (HSCs) from chemotherapy-induced exhaustion in a serial 5-fluorouracil treatment model. Consistent with a cell-intrinsic effect, we show directly preserved HSC function resulting in a more rapid recovery of peripheral blood counts, enhanced serial transplantation capacity, and reduced myeloid skewing. When administered to healthy human volunteers, G1T28 demonstrated excellent in vivo pharmacology and transiently inhibited bone marrow (BM) HSPC proliferation. These findings suggest that the combination of CDK4/6 inhibitors with cytotoxic chemotherapy should provide a means to attenuate therapy-induced BM exhaustion in patients with cancer.

Increased frequency of circulating IL-21 producing Th-cells in patients with granulomatosis with polyangiitis (GPA).

INTRODUCTION: The present study aimed to explore a possible role for IL-21 producing Th-cells in the immunopathogenesis of granulomatosis with polyangiitis (GPA). METHODS: Peripheral blood from 42 GPA patients in remission and 29 age-matched healthy controls (HCs) were stimulated in vitro, and the frequencies of IL-21 producing Th-cells were determined by flow cytometry. Since Th17-cells produce a low level of IL-21, IL-17 was also included in the analysis. Given that IL-21 is a hallmark cytokine for T follicular helper cells (T(FH)), we next evaluated the expression of their key transcription factor BCL-6 by RT-PCR and flow cytometry. To investigate the effect of IL-21 on autoantibody-production, PBMCs from GPA patients were stimulated in vitro with BAFF/IL-21 and total IgG and ANCA levels were measured in supernatants. In addition, the expression of IL-21-receptor on B-cells was analyzed. RESULTS: Percentages of IL-21 producing Th-cells were significantly elevated in GPA-patients compared to HCs, and were restricted to ANCA-positive patients. The expression of BCL-6 was significantly higher in ANCA-positive GPA-patients, as compared with ANCA-negative patients and HCs. IL-21 enhanced the production of IgG and ANCA in vitro in stimulated PBMCs from GPA patients. No difference was found in the expression of the IL-21-receptor on B-cells between ANCA-negative patients, ANCA-positive patients, and HCs. CONCLUSION: The increased frequency of circulating IL-21 producing Th-cells in ANCA-positive GPA patients and the stimulating capacity of IL-21 on ANCA-production suggest a role for these cells in the immunopathogenesis of GPA. Blockade of IL-21 could constitute a new therapeutic strategy for GPA.

Increased expression of Toll-like receptors by monocytes and natural killer cells in ANCA-associated vasculitis.

INTRODUCTION: Toll-like receptors (TLRs) are a family of receptors that sense pathogen associated patterns such as bacterial cell wall proteins. Bacterial infections are associated with anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV). Here, we assessed the expression of TLRs 2, 4, and 9 by peripheral blood leukocytes from patients with AAV, and investigated TLR mediated responses ex vivo. METHODS: Expression of TLRs was determined in 38 AAV patients (32 remission, 6 active disease), and 20 healthy controls (HC). Membrane expression of TLRs 2, 4, and 9, and intracellular expression of TLR9 by B lymphocytes, T lymphocytes, NK cells, monocytes and granulocytes was assessed using 9-color flowcytometry. Whole blood from 13 patients and 7 HC was stimulated ex vivo with TLR 2, 4 and 9 ligands and production of cytokines was analyzed. RESULTS: In patients, we observed increased proportions of TLR expressing NK cells. Furthermore, patient monocytes expressed higher levels of TLR2 compared to HC, and in a subset of patients an increased proportion of TLR4(+) monocytes was observed. Monocytes from nasal carriers of Staphylococcus aureus expressed increased levels of intracellular TLR9. Membrane expression of TLRs by B lymphocytes, T lymphocytes, and granulocytes was comparable between AAV patients and HC. Patients with active disease did not show differential TLR expression compared to patients in remission. Ex vivo responses to TLR ligands did not differ significantly between patients and HC. CONCLUSIONS: In AAV, monocytes and NK cells display increased TLR expression. Increased TLR expression by these leukocytes, probably resulting from increased activation, could play a role in disease (re)activation.

Bacterial infections in Wegener's granulomatosis: mechanisms potentially involved in autoimmune pathogenesis.

PURPOSE OF REVIEW: Wegener's granulomatosis is associated with bacterial infection, in particular nasal carriage of Staphylococcus aureus. Infection may play a role in the induction of autoimmunity as well as in the effector phase of the disease. Here, the current hypotheses aiming to explain the link between infections and Wegener's granulomatosis immunopathogenesis are reviewed and discussed. RECENT FINDINGS: In recent years, studies suggested that molecular mimicry could play a role in antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitides (AAV), either via direct mimicry between human lysosome-associated membrane protein-2 and bacterial FimH or indirectly via the development of antibodies against a peptide complementary to proteinase 3 (cPr3). More recent work has focused on Toll-like receptors (TLRs), a family of receptors specialized in the recognition of pathogen-associated molecular patterns. In animal models, it has been shown that TLR ligands can aggravate anti-MPO antibody-mediated disease. Furthermore, it was shown that a TLR9 ligand can trigger the production of ANCA in vitro by peripheral blood-derived B lymphocytes from AAV patients. The newly described process of ANCA-mediated neutrophil extracellular trap formation may provide an endogenous TLR9 ligand. Finally, TLR2 signaling is involved in the development of a Th17-driven immune response, consistent with skewing towards a Th17 T cell phenotype that has been observed in Wegener's granulomatosis. SUMMARY: Although Wegener's granulomatosis pathophysiology is becoming better understood, the specific events leading to autoimmunity are not clear. Recent studies show that several mechanisms may be involved in linking infection to autoimmunity. Molecular mimicry may be involved, and a role for TLR signaling is suggested.

Vasculitis and infections: contribution to the issue of autoimmunity reviews devoted to "autoimmunity and infection".

Infections are associated with secondary forms of vasculitis. However, there is increasing evidence that microbial agents play a role also in primary systemic vasculitides. For a long time it has been noted that Hepatitis B virus (HBV) is involved in polyarteritis nodosa (PAN) although the incidence of HBV-associated PAN seems to decline. Cryoglobulinemic vasculitis has been shown to be strongly associated with Hepatitis C Virus (HCV) infection, but this is most striking in Southern Europe and less in Northern Europe. Different microbial agents have been suggested to influence disease expression in other primary vasculitides but no specific association has been established. In Wegener's Granulomatosis (WG) chronic carriage of Staphylococcus aureus (S. aureus) is associated with a strongly increased risk for relapsing disease. Various pathogenic pathways for this association have been suggested by clinical and experimental observations. Recent studies even suggest that S. aureus derived peptides, amongst others, may induce proteinase 3-ANCA via idiotypic-anti-idiotypic interactions. Treatment with co-trimoxazole in WG localized to the upper airways may result in (temporary) remission of the disease.

Mucin1 expression is enriched in the human stem cell fraction of cord blood and is upregulated in majority of the AML cases.

OBJECTIVE: Mucin1 is a membrane glycoprotein that is overexpressed in a variety of human cancers. Here, we analyzed the role of Mucin1 in human hematopoietic stem/progenitor cells as well as in acute myeloid leukemia (AML) cells. MATERIALS AND METHODS: Mucin1 expression was determined within the normal stem cell and progenitor compartment, as well as in the AML CD34+ and CD34- subfractions of patient samples. Stem cells were enumerated in long-term culture-initiating cell (LTC-IC) assays in limiting dilution and progenitor frequencies in colony-forming cell (CFC) assays in methylcellulose, and consequences of elevated Mucin1 expression were studied using retroviral overexpression systems in cord blood (CB) CD34+ cells. RESULTS: Ten percent of CB and 5% of peripheral blood CD34+ cells expressed Mucin1. Retroviral overexpression of Mucin1 in CB CD34+ cells resulted in elevated stem cell and progenitor frequencies as determined in LTC-IC and CFC assays without affecting differentiation, which coincided with increased proliferation. Overexpression of intercellular adhesion molecule-1, a ligand for Mucin1, in MS5 stromal cells further increased LTC-IC frequencies. Mucin1 overexpression was associated with increased nuclear factor-kappaB p50 nuclear translocation, suggesting that Mucin1-induced phenotypes involve increased cell survival mechanisms. Finally, we observed increased Mucin1 expression in 70% of the AML cases (n=24), suggesting that elevated Mucin1 levels might be involved in regulating the proliferative potential of the immature leukemic compartment as well. CONCLUSIONS: Our data indicate that hematopoietic stem cells as well as CD34+ AML subfractions are enriched for Mucin1 expression, and that overexpression of Mucin1 in CB cells is sufficient to increase both progenitor and LTC-IC frequencies.

Dependence of neovascularization mechanisms on the molecular microenvironment.

In vivo vascularization of implanted (bio)artificial constructs is essential for their proper function. Vascularization may rely on sprouting angiogenesis, vascular incorporation of bone marrow-derived endothelial cells (BMDECs), or both. Here we investigated the relative contribution of these 2 mechanisms to neovascularization in a mouse model of a foreign body reaction (FBR) to subcutaneously implanted Dacron and in hind limb ischemia (HLI) in relation to the molecular microenvironment at these neovascularization sites. Neovascularization was studied in C57Bl/6 mice reconstituted with enhanced green fluorescent protein (EGFP) transgenic bone marrow. Sprouting angiogenesis, detected using nuclear incorporation of bromodeoxyuridine in endothelial cells was present in both models, whereas vascular incorporation of EGFP(+) BMDECs was restricted to HLI. In HLI, the presence of a pro-angiogenic molecular microenvironment comprising vascular endothelial growth factor, fibroblast growth factor 2, and granulocyte colony-stimulating factor corroborated the importance of these factors for vascular BMDEC incorporation, whereas this microenvironment was absent in FBR. Enhanced mobilization of BMDECs by granulocyte-macrophage colony-stimulating factor administration or by combining HLI and FBR with Dacron did not induce incorporation of BMDECs in FBR neovessels. We conclude that the efficacy of BMDEC-based therapy is not generally warranted, but it depends on the molecular microenvironment in the targeted tissue.