Stephen M. Wiesner

Expression of MHC I and NK ligands on human CD133+ glioma cells: possible targets of immunotherapy

Mounting evidence suggests that gliomas are comprised of differentiated tumor cells and brain tumor stem cells (BTSCs). BTSCs account for a fraction of total tumor cells, yet are apparently the sole cells capable of tumor initiation and tumor renewal. BTSCs have been identified as the CD133-positive fraction of human glioma, whereas their CD133-negative daughter cells have limited proliferative ability and are not tumorogenic. It is well established that the bulk tumor mass escapes immune surveillance by multiple mechanisms, yet little is known about the immunogenicity of the CD133-positive fraction of the tumor mass. We investigated the immunogenicity of CD133-positive cells in two human astrocytoma and two glioblastoma multiforme samples. Flow cytometry analyses revealed that the majority of CD133-positive cells do not express detectable MHC I or natural killer (NK) cell activating ligands, which may render them resistant to adaptive and innate immune surveillance. Incubating CD133-positive cells in interferon gamma (INF-γ) significantly increased the percentage of CD133-positive cells that expressed MHC I and NK cell ligands. Furthermore, pretreatment of CD133-positive cells with INF-γ rendered them sensitive to NK cell-mediated lysis in vitro. There were no consistent differences in immunogenicity between the CD133-positive and CD133-negative cells in these experiments. We conclude that CD133-posistive and CD133-negative glioma cells may be similarly resistant to immune surveillance, but that INF-γ may partially restore their immunogenicity and potentiate their lysis by NK cells.

Clostridium difficile toxins A and B can alter epithelial permeability and promote bacterial paracellular migration through HT-29 enterocytes.

Clostridium difficile toxins A and B are the widely recognized etiologic agents of antibiotic-associated diseases ranging from diarrhea to pseudomembranous colitis. We hypothesized that C. difficile toxins may alter intestinal epithelial permeability and facilitate bacterial penetration of the intestinal epithelial barrier. Experiments were designed to clarify the effects of C. difficile toxins A and B on the flux of inert particles across HT-29 enterocyte monolayers, and to correlate these results with bacteria-enterocyte interactions. In all experiments, mature, confluent HT-29 cultures were preincubated 16 h with toxin A or B (1-100 ng/mL). To study alterations in epithelial permeability, toxin-treated enterocytes were incubated with 5 pM solutions of 10- and 40-kD inert dextran particles. Toxin A, but not toxin B, was associated with increased dextran flux through enterocyte monolayers. To study bacteria-enterocyte interactions, toxin-treated enterocytes were incubated with 10(8) Salmonella typhimurium, Proteus mirabilis, or Escherichia coli. Although numbers of internalized bacteria were generally unaffected, both toxins were associated with increased bacterial adherence, as well as increased bacterial transmigration through enterocyte monolayers. Bacterial transmigration was significantly greater using toxin A- compared to toxin B-treated enterocytes, consistent with the observation that dextran flux was significantly greater using toxin A- compared to toxin B-treated enterocytes. Thus intestinal colonization with toxigenic C. difficile may facilitate bacterial penetration of the intestinal epithelium by a mechanism involving increased permeability of the intestinal epithelial barrier.

Cecal Colonization and Systemic Spread of Candida albicans in Mice Treated with Antibiotics and Dexamethasone

Infections with Candida albicans have become a significant problem among very low birth weight infants in the neonatal intensive care unit. Risk factors are multiple and include administration of antibiotics and glucocorticoids, such as dexamethasone. Experiments were designed to study the combined effect of oral broad-spectrum antibiotics and parenteral dexamethasone on cecal colonization and extraintestinal dissemination of C. albicans in separate groups of mice that were orally inoculated with one of four C. albicans strains that were either wild-type INT1/INT1 or had one or more disruptions of the INT1 gene. Intestinal colonization was monitored by quantitative culture of the mouse cecum, and extraintestinal invasion was monitored by quantitative culture of the draining mesenteric lymph nodes and kidneys. At sacrifice, the average numbers of cecal C. albicans differed from 7.7 log10/g to 6.7 log10/g (p < 0.01) in mice orally inoculated with C. albicans containing two functional copies of INT1 and no functional copies of INT1, respectively. The incidence of extraintestinal dissemination to mesenteric lymph nodes and kidneys correspondingly varied from 57 to 13% (p < 0.01) and 83 to 4% (p < 0.01) in mice inoculated with these two C. albicans strains. Mice orally inoculated with C. albicans containing one functional copy of INT1 had intermediate levels of cecal colonization and extraintestinal dissemination. Thus, cecal colonization and extraintestinal dissemination of C. albicans was facilitated in antibiotic-treated mice given dexamethasone. In addition, the presence of two functional copies of the INT1 gene was associated with the greatest levels of cecal colonization and extraintestinal dissemination of C. albicans.

Gastrointestinal colonization by Candida albicans mutant strains in antibiotic-treated mice.

ABSTRACT Antibiotic-treated mice orally inoculated with one of threeCandida albicans strains (including two mutant strains) or indigenous Candida pelliculosa showed levels of candidal gastrointestinal colonization that were strain specific. However, regardless of strain, the numbers of viable candida were intermediate to high in the stomach, were consistently lowest in the upper small intestine, and increased progressively down the intestinal tract.

Adherence of yeast and filamentous forms of Candida albicans to cultured enterocytes

OBJECTIVE Systemic candidiasis is a major cause of complicating infections in intensive care units. Morbidity and mortality are high, even in those who receive appropriate antifungal therapy. Because the intestinal tract is considered a major portal of entry for systemic candidiasis, experiments were designed to clarify the ability of yeast and filamentous forms, as well as the INT1 gene product, to influence adherence of Candida albicans to the intestinal epithelium. DESIGN Controlled. SETTING University teaching hospital research laboratory. SUBJECTS Mature Caco-2 and HT-29 cultured enterocytes. INTERVENTIONS C. albicans INT1 mutant strains, defective in filament production, were used to observe the ultrastructural surface interactions of C. albicans with cultured intestinal epithelial cells, namely Caco-2 and HT-29 cells. These mutant strains also were used to quantify the effect of the INT1 gene product on C. albicans adherence (yeast and filamentous forms) to cultured enterocytes. Ultrastructural surface interactions of C. albicans with cultured enterocytes were observed with high resolution scanning electron microscopy. C. albicans adherence to cultured enterocytes was quantified by using a colorimetric enzyme-linked immunosorbent assay. MEASUREMENTS AND MAIN RESULTS Both yeast and filamentous forms of C. albicans appeared tightly adherent to the apical surface of cultured enterocytes, and INT1 appeared to have little, if any, effect on these ultrastructural surface interactions. The distal ends of C. albicans filaments appeared to mediate adherence to enterocyte apical microvilli, and thigmotropism (contact guidance) appeared to play a role in C. albicans adherence. The absence of functional INT1 was associated with decreased adherence of C. albicans yeast forms to cultured enterocytes. CONCLUSIONS Although functional INT1 appeared to facilitate adherence of C. albicans yeast forms to cultured enterocytes, the role of INT1 in adherence of filamentous forms was unclear, and both yeast and filamentous forms could adhere to, and perhaps invade, the apical surface of cultured enterocytes.

Stat5 is critical for the development and maintenance of myeloproliferative neoplasm initiated by Nf1 deficiency

Juvenile myelomonocytic leukemia is a rare myeloproliferative neoplasm characterized by hyperactive RAS signaling. Neurofibromin1 (encoded by the NF1 gene) is a negative regulator of RAS activation. Patients with neurofibromatosis type 1 harbor loss-of-function mutations in NF1 and have a 200- to 500-fold increased risk of juvenile myelomonocytic leukemia. Leukemia cells from patients with juvenile myelomonocytic leukemia display hypersensitivity to certain cytokines, such as granulocyte-macrophage colony-stimulating factor. The granulocyte-macrophage colony-stimulating factor receptor utilizes pre-associated JAK2 to initiate signals after ligand binding. JAK2 subsequently activates STAT5, among other downstream effectors. Although STAT5 is gaining recognition as an important mediator of growth factor signaling in myeloid leukemias, the contribution of STAT5 to the development of hyperactive RAS-initiated myeloproliferative disease has not been well described. In this study, we investigated the consequence of STAT5 attenuation via genetic and pharmacological approaches in Nf1-deficient murine models of juvenile myelomonocytic leukemia. We found that homozygous Stat5 deficiency extended the lifespan of Nf1-deficient mice and eliminated the development of myeloproliferative neoplasm associated with Nf1 gene loss. Likewise, we found that JAK inhibition with ruxolitinib attenuated myeloproliferative neoplasm in Nf1-deficient mice. Finally, we found that primary cells from a patient with KRAS-mutant juvenile myelomonocytic leukemia displayed reduced colony formation in response to JAK2 inhibition. Our findings establish a central role for STAT5 activation in the pathogenesis of juvenile myelomonocytic leukemia and suggest that targeting this pathway may be of clinical utility in these patients.

Nf1 mutant mice with p19ARF gene loss develop accelerated hematopoietic disease resembling acute leukemia with a variable phenotype

Juvenile Myelomonocytic Leukemia (JMML) is a relentlessly progressive myeloproliferative/myelodysplastic (MPD/MDS) hematopoietic disorder more common in patients with any one of at least three distinct genetic lesions, specifically NF1 gene loss and PTPN11 and NRAS mutations. NF1 and PTPN11 are molecular lesions associated with Neurofibromatosis Syndrome Type I (NF1 Syndrome) and Noonans Syndrome, respectively. The occurrence of JMML is rare; even among those predisposed with these syndromes to development of disease, and secondary genetic events likely contribute to the development and progression of disease. In NF1 syndrome, loss of p53 function is a common event in solid tumors, but uncommon in JMML, suggesting that the p53 pathway may be modified by other events in this hematopoietic disorder. The work presented here investigates the possible role of the p19Arf (p19) tumor suppressor in development of MPD associated with Nf1 gene loss in mice. We find that Nf1 mutant hematopoietic cells with loss of p19 develop accelerated hematopoietic disease similar to acute leukemia with a variable phenotype. This suggests that p19 may play a role in development of JMML and evaluation of the human p19 homolog (p14ARF) in JMML may be informative. Am. J. Hematol. 86:579–585, 2011.