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Granulocyte-colony stimulating factor (G-CSF) is a cornerstone of supportive care in oncology, widely used to prevent chemotherapy-induced neutropenia and maintain dose intensity and treatment schedule. While G-CSF has been shown to be safe and effective in the context of chemotherapy, its effects in patients receiving chemo-immunotherapy with immune checkpoint inhibitors (ICIs) are less clear. There is a growing body of preclinical data to suggest that G-CSF negatively impacts the tumor microenvironment in mice and may contribute to tumor growth and metastasis. Consequently, as chemo-immunotherapy regimens have become standard across solid malignancies, the immunologic consequences of G-CSF in this setting have come under renewed scrutiny. G-CSF is a pleiotropic cytokine, and one of its most prominent functions is to stimulate the proliferation and survival of neutrophils, which in the tumor microenvironment may exert both anti- and pro-tumorigenic roles. G-CSF stimulated neutrophils have been shown to contribute to the anti-tumor immune response via upregulation of unconventional T cells, maintenance of interferon gamma- based immunity, and direct tumor cell killing in some models. Other models, however, have shown that cytokine mixes containing G-CSF can polarize neutrophils towards a pro-tumorigenic state, promoting suppression of CD8+ T cells, creating an immunosuppressive cytokine milieu, and increasing metastatic potential. Ultimately, its effects appear to be dependent on the underlying immune state and composition of the tumor microenvironment. While preclinical data suggest that G-CSF may be blunting the efficacy of checkpoint blockade via its modulation of the neutrophil compartment in specific models, clinical data in the immunotherapy era remain limited and largely retrospective. Studies done primarily in lung cancer patients showed neither a clear survival benefit nor an increased mortality risk. In this review, we synthesize the preclinical and clinical literature examining G-CSF in solid tumor oncology, with a focus on its interaction with neutrophils and immune checkpoint inhibition. We highlight key mechanistic insights, emerging clinical signals, gaps in evidence, and ultimately emphasize the importance of adhering to strict, consensus guideline-based use of G-CSF during chemo-immunotherapy.

Diamond Blackfan anemia (DBA) is a rare inherited bone marrow failure syndrome caused by ribosomal protein haploinsufficiency. DBA exhibits marked phenotypic variability, commonly presenting with erythroid hypoplasia, less consistently with non-erythroid features. The p53 pathway, activated by abortive ribosome assembly, is hypothesized to contribute to the erythroid failure of DBA. We studied murine embryonic stem (ES) cell lines harboring a gene trap mutation in a ribosomal protein gene, either Rps19 or Rpl5. Both mutants exhibited ribosomal protein haploinsufficiency and polysome defects. Rps19 mutant ES cells showed significant increase in p53 protein expression, however, there was no similar increase in the Rpl5 mutant cells. Embryoid body formation was diminished in both mutants but nonspecifically rescued by knockdown of p53. When embryoid bodies were further differentiated to primitive erythroid colonies, both mutants exhibited a marked reduction in colony formation, which was again nonspecifically rescued by p53 inhibition. Cell cycle analyses were normal in Rps19 mutant ES cells, but there was a significant delay in the G2/M phase in the Rpl5 mutant cells, which was unaffected by p53 knockdown. Concordantly, Rpl5 mutant ES cells had a more pronounced growth defect in liquid culture compared to the Rps19 mutant cells. We conclude that the defects in our RPS19 and RPL5 haploinsufficient mouse ES cells are not adequately explained by p53 stabilization, as p53 knockdown appears to increase the growth and differentiation potential of both parental and mutant cells. Our studies demonstrate that gene trap mouse ES cells are useful tools to study the pathogenesis of DBA.

The t(8;21) translocation between two genes known as AML1 and ETO is seen in approximately 12-15% of all acute myeloid leukemia (AML) and is the second-most-frequently observed nonrandom genetic alteration associated with AML. AML1 up-regulates a number of target genes critical to normal hematopoiesis, whereas the AML1/ETO fusion interferes with this trans-activation. We discovered that the fusion partner ETO binds to the human homolog of the murine nuclear receptor corepressor (N-CoR). The interaction is mediated by two unusual zinc finger motifs present at the carboxyl terminus of ETO. Human N-CoR (HuN-CoR), which we cloned and sequenced in its entirety, encodes a 2,440-amino acid polypeptide and has a central domain that binds ETO. N-CoR, mammalian Sin3 (mSin3A and B), and histone deacetylase 1 (HDAC1) form a complex that alters chromatin structure and mediates transcriptional repression by nuclear receptors and by a number of oncoregulatory proteins. We found that ETO, through its interaction with the N-CoR/mSin3/HDAC1 complex, is also a potent repressor of transcription. This observation provides a mechanism for how the AML1/ETO fusion may inhibit expression of AML1-responsive target genes and disturb normal hematopoiesis.

We present evidence that both corepressors SMRT and N‐CoR exist in large protein complexes with estimated sizes of 1.5–2 MDa in HeLa nuclear extracts. Using a combination of conventional and immunoaffinity chromatography, we have successfully isolated a SMRT complex and identified histone deacetylase 3 (HDAC3) and transducin (β)‐like I (TBL1), a WD‐40 repeat‐containing protein, as the subunits of the purified SMRT complex. We show that the HDAC3‐containing SMRT and N‐CoR complexes can bind to unliganded thyroid hormone receptors (TRs) in vitro . We demonstrate further that in Xenopus oocytes, both SMRT and N‐CoR also associate with HDAC3 in large protein complexes and that injection of antibodies against HDAC3 or SMRT/N‐CoR led to a partial relief of repression by unliganded TR/RXR. These findings thus establish both SMRT and N‐CoR complexes as bona fide HDAC‐containing complexes and shed new light on the molecular pathways by which N‐CoR and SMRT function in transcriptional repression.

A 67-year-old right-handed woman presented with dysarthria, left upper extremity weakness and right-sided neglect of 3 hours duration. Imaging of the brain revealed acute right middle cerebral artery stroke; however, tissue plasminogen activator could not be administered due to severe thrombocytopenia. A peripheral smear revealed schistocytes and the patient was treated empirically for thrombotic thrombocytopenic purpura (TTP) with therapeutic plasma exchange. An extensive workup revealed no embolic source or other cause for stroke, and a diagnosis of large vessel infarct secondary to TTP was made. After a prolonged hospital course, the patient had partial neurological recovery and was discharged to a rehabilitation facility. Although transient neurologic deficits due to small vessel occlusions are well described in TTP, large vessel infarct can occur as well. This diagnosis should be considered in patients presenting with concomitant stroke and thrombocytopenia, as untreated TTP is nearly always fatal.

Shwachman-Diamond syndrome (SDS) is an autosomal recessive disease caused by mutations in the SBDS gene in approximately 90% of cases. SDS is characterized by exocrine pancreatic insufficiency and bone marrow failure, which predisposes to the development of myelodysplastic syndrome and/or acute myeloid leukemia. In a new report, the French national cohort studied 102 SDS patients with a median follow-up of 11.6 years, focusing on the natural history of severe cytopenias. The authors concluded that SDS patients with a young age (<3 months) at first symptomatic presentation or cytopenia at diagnosis were at a high risk of subsequent severe hematological complications (either malignant or nonmalignant). Their findings raise the possibility that a clinical algorithm may predict the subsequent development of hematological complications in SDS.

Human mesenchymal stem cells form the supportive structure in which the functional cells of a differentiated tissue reside. We describe the creation of ectopic niches within polyurethane scaffolds coated with human mesenchymal stem cells. When implanted subcutaneously in NOD/SCID mice, these niches supported engraftment of primary human acute myeloid leukemia cells. The scaffolds showed vascularization and presence of osteoclasts and adipocytes, suggestive of an organizing human bone marrow microenvironment in the murine host. The chemokine stromal-derived factor-1 (SDF-1 or CXCL12) and its receptor CXCR4 are critical for homing and migration of acute myeloid leukemia. We found that a CXCR4 antagonist could disrupt homing to the ectopic niches, possibly by modulation of the mesenchymal stroma. We believe that these scaffold niches provide a new and powerful tool to study the leukemia stem cell microenvironment and may be useful for identification of novel drug targets.

The hematopoietic stem cell has long been considered an ideal target for the introduction of therapeutic genes to treat human disorders such as Fanconi anemia (FA). Although recent progress in large animal models is encouraging, application to nonmalignant conditions is limited by the perceived necessity of myeloablative conditioning. We and others have shown that very low irradiation doses are sufficient to allow significant hematopoietic engraftment in murine hosts even after the introduction of xenogeneic genes. To determine the degree of engraftment of genetically modified cells attainable with very low irradiation doses in larger animals, we employed the rhesus macaque competitive repopulation model. Four animals underwent mobilization with stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF) followed by apheresis. The apheresis product was enriched for the CD34-positive fraction by immunomagnetic selection and split equally for transduction with either G1FC26, a retroviral vector carrying the Fanconi anemia complementation group C gene, or PLII, a nonexpression control retroviral vector carrying both neomycin and β-galactosidase gene sequences modified to prevent translation. Transductions were performed daily in the presence of fresh IL-3, IL-6, SCF, and Flt-3 ligand on fibronectin-coated plates over 96 h. Animals were conditioned with a single dose of either 100 (n = 2) or 200 (n = 2) cGy and received the combined products of transduction on the following day. None of the animals experienced clinically significant neutropenia nor required the use of central line placement, transfusional support with blood products, or intravenous antibiotics. Using real-time PCR, circulating levels of genetically modified cells as high as 1% were initially detected. Stable, albeit, significantly lower levels from both vector-transduced aliquots (<0.1%) persisted beyond 12 months posttransplant in all four animals. Although not sufficient to correct the phenotype in many human disorders, stable low-level engraftment by genetically modified cells following low-intensity conditioning may prove adequate in disorders such as FA due to the selective advantage conferred upon corrected cells.

Diamond Blackfan anemia (DBA) is a rare inherited bone marrow failure syndrome caused by ribosomal protein haploinsufficiency. DBA exhibits marked phenotypic variability, commonly presenting with erythroid hypoplasia, less consistently with non-erythroid features. The p53 pathway, activated by abortive ribosome assembly, is hypothesized to contribute to the erythroid failure of DBA. We studied murine embryonic stem (ES) cell lines harboring a gene trap mutation in a ribosomal protein gene, either Rps19 or Rpl5. Both mutants exhibited ribosomal protein haploinsufficiency and polysome defects. Rps19 mutant ES cells showed significant increase in p53 protein expression, however, there was no similar increase in the Rpl5 mutant cells. Embryoid body formation was diminished in both mutants but nonspecifically rescued by knockdown of p53. When embryoid bodies were further differentiated to primitive erythroid colonies, both mutants exhibited a marked reduction in colony formation, which was again nonspecifically rescued by p53 inhibition. Cell cycle analyses were normal in Rps19 mutant ES cells, but there was a significant delay in the G2/M phase in the Rpl5 mutant cells, which was unaffected by p53 knockdown. Concordantly, Rpl5 mutant ES cells had a more pronounced growth defect in liquid culture compared to the Rps19 mutant cells. We conclude that the defects in our RPS19 and RPL5 haploinsufficient mouse ES cells are not adequately explained by p53 stabilization, as p53 knockdown appears to increase the growth and differentiation potential of both parental and mutant cells. Our studies demonstrate that gene trap mouse ES cells are useful tools to study the pathogenesis of DBA.

Gene therapy of severe hemoglobinopathies will require high-level expression of a transferred globin gene in erythroid cells. Distant regulatory elements flanking the β-globin gene cluster, the locus control region, are needed for appropriate expression. We have explored the use of a human parvovirus, the adeno-associated virus (AAV), for globin gene transfer. The human Aγ-globin gene, linked to hypersensitivity site 2 from the locus control region of the β-globin gene cluster, was subcloned into a plasmid (psub201) containing the AAV inverted terminal repeats. This construct was cotransfected with a helper plasmid containing trans-acting AAV genes into human 293 cells that had been infected with adenovirus. The recombinant AAV vector containing hypersensitivity site 2 stably introduced on average one or two unrearranged proviral copies into human K562 erythroleukemia cells. The transferred globin gene exhibited normal regulation upon hemin induction of erythroid maturation and was expressed at a level equivalent to a native chromosomal Aγ-globin gene.