Expression of interleukin 2 receptors and binding of interleukin 2 by gamma interferon-induced human leukemic and normal monocytic cells.

Gamma interferon induced surface expression of interleukin 2 (IL-2) receptors on normal human monocytes and the monocytoid cell lines U937 and HL60. These receptors were detected by anti-IL-2 receptor monoclonal antibodies, and U937 IL-2 receptors were indistinguishable from T lymphocyte IL-2 receptors by immunoprecipitation. Also, U937 IL-2 receptors bound biologically active IL-2. These results suggest a role for monocyte IL-2 receptors in T cell/monocyte interaction during an immune response.

A feasibility study of low-dose, prolonged oral topotecan in patients with advanced ovarian, fallopian tube, or primary peritoneal serous cancer who have attained a complete clinical response following platinum-based chemotherapy.

To determine the tolerability of oral maintenance topotecan when administered to patients with advanced ovarian, fallopian tube, and primary peritoneal serous cancers who have achieved a complete clinical response after first-line platinum-based therapy. Oral topotecan was given at a starting dose of 0.4 mg/m(2)/dose, twice a day (BID) for 21 consecutive days out of 28 days. The dose was subsequently increased to 0.5 mg/m(2)/dose, twice a day as tolerated. If the patient experienced toxicities during cycle 1 or subsequent cycles, doses were delayed and/or reduced. The lowest dose allowed on protocol was 0.3 mg/m(2)/dose twice daily. Thirteen patients were enrolled in the study, representing a total of fifty-nine cycles of oral topotecan. The starting dose of 0.4 mg/m(2) by mouth (PO) BID for 21 days was generally difficult for patients to tolerate, usually due to progressive anemia and fatigue, and a dose reduction to 0.3 mg/m(2) was necessary in 10/13 patients. A median of six cycles was administered, although 6 of 13 patients could not tolerate the planned 6 cycles due to toxicity. Hematologic toxicity was the most common side effect, although there were no episodes of febrile neutropenia. Diarrhea was the most common nonhematologic side effect, occurring in 8 of 13 patients. Six patients were removed from the study prior to completing the planned six cycles of therapy, after receiving a median number of 2.5 cycles of treatment. This dose and schedule of oral topotecan does not appear to be feasible in this patient population.

Relationship between HLA-DR expression by normal myeloid progenitor cells and inhibition of colony growth by prostaglandin E. Implications for prostaglandin E resistance in chronic myeloid leukemia.

The expression of HLA-DR antigens by normal myeloid progenitor cells (CFU-GM) has been linked to inhibition of colony growth by prostaglandin E (PGE), while resistance to the inhibitory effects of PGE in chronic myeloid leukemia (CML) has been attributed to a lower fraction of HLA-DR+ CFU-GM in this disease. However, we have previously shown that virtually all CFU-GM in normal bone marrow (NBM) as well as CML peripheral blood express HLA-DR antigens, which raises the possibility that these surface molecules may not be the sole determinants of a progenitor cell's sensitivity to PGE. In order to evaluate the relationship between HLA-DR expression and prostaglandin inhibition, we partially purified NBM progenitor cells using fluorescence-activated cell sorting to prepare cell fractions with high and low HLA-DR antigen density. Normal progenitor cells with high DR density tended to form monocyte colonies in agar culture, whereas the low DR density fraction was enriched for granulocyte colony-forming cells. Inhibition by PGE was greatest in the high DR+ fraction and was largely restricted to monocyte progenitor cells. Inhibition of CFU-GM by PGE was less in CML than in NBM, but this decreased inhibition correlated with a significantly lower number of monocyte-CFU in CML. These data suggest that high HLA-DR antigen density may select for normal progenitor cells that are committed to monocyte differentiation and are, therefore, more likely to be inhibited by PGE. The relative deficit of monocyte progenitor cells in CML may partially explain the phenomenon of PGE resistance in this disease.

Human granulocyte-macrophage colony-stimulating factor induces expression of the tumor necrosis factor gene by the U937 cell line and by normal human monocytes.

Human granulocyte-macrophage colony-stimulating factor (GM-CSF) exerts profound effects on the proliferation, differentiation, and effector function of myeloid lineage cells. In contrast to its growth-promoting effects on normal myeloid progenitor cells, we found that GM-CSF unexpectedly inhibited the colony growth of U937 cells in agar culture. Furthermore, medium conditioned by recombinant GM-CSF(rGM-CSF)-treated U937 cells was found to exert an inhibitory effect on subsequent U937 colony growth that was partially due to the presence of tumor necrosis factor (TNF). By Northern blot analysis, rGM-CSF was shown to induce expression of the TNF gene in U937 cells and in T-lymphocyte-depleted, monocyte-enriched peripheral blood mononuclear cells. Furthermore, rGM-CSF was observed to significantly enhance TNF secretion by monocytes stimulated with endotoxin and phorbol myristate acetate (PMA). These data suggest that some of the biological effects of GM-CSF may be amplified through the release of monokines such as TNF.

In vivo inhibition of CD44 limits intra-abdominal spread of a human ovarian cancer xenograft in nude mice: a novel role for CD44 in the process of peritoneal implantation.

Ovarian cancer cells frequently metastasize by implanting onto the peritoneal mesothelial lining of the abdominal cavity. Data obtained from in vitro adhesion studies have suggested a possible role for the CD44 molecule in this process. The purpose of the present study was to determine the in vivo role of CD44 in ovarian cancer metastasis by using a nude mouse xenograft model of peritoneal implantation. Three groups of 10 athymic female nude mice each received an i.p. inoculum of 10 x 10(6) cells from a CD44-positive human ovarian cancer cell line (36M2) in the presence of either anti-D144 antibody (Ab; nonreactive IgG1), anti-DF3 Ab (reactive IgG1 Ab that does not inhibit in vitro binding), or neutralizing anti-CD44 Ab (IgG1). The number of peritoneal and diaphragmatic implants at 5 weeks for anti-D144 and anti-DF3-treated groups was 103 +/- 17 and 120 +/- 20, respectively (mean +/- SE; P > 0.2). In contrast, animals treated with anti-CD44 Ab experienced a significant reduction in the number of tumor implants (35 +/- 4; P < 0.002). Anti-CD44 Ab was not inhibitory to the growth of 36M2 cells in vitro and did not inhibit s.c. tumor growth in vivo, suggesting that the observed effect was related to inhibition of peritoneal implantation. These data suggest that the CD44 molecule plays an important in vivo role in ovarian cancer cell implantation and that strategies to inhibit CD44 function may represent a novel approach to limiting the intra-abdominal spread of this highly lethal tumor.

In vivo cytotoxicity of ovarian cancer cells through tumor-selective expression of the BAX gene.

The BAX proapoptotic protein is capable of inducing cell death either directly, through its effects on mitochondrial function, or indirectly, by lowering the apoptotic threshold in response to certain chemotherapy agents. In this study, we tested the hypothesis that selective expression of BAX in human ovarian cancer through adenoviral gene transfer might represent a novel approach to eradicating tumor cells in vivo. Two constructs were prepared using replication-deficient adenoviral vectors containing either the cDNA for beta-galactosidase (Ad.DF3.betaGAL) or hemagglutinin (HA)-tagged BAX (Ad.DF3.BAX) under the control of the DF3 promoter. The DF3 promoter was used to confer tumor-specific gene expression in view of its restricted pattern of expression in the majority of human ovarian cancers and its limited expression in normal peritoneal mesothelial cells. In vitro infection of up to seven different epithelial cancer cell lines with Ad.DF3.betaGAL or Ad.DF3.BAX resulted in expression of either beta-galactosidase activity or HA-BAX protein, respectively, which was highly correlated with DF3 levels. Furthermore, infection with Ad.DF3.BAX was capable of highly selective cytotoxicity of DF3-positive ovarian cancer clonogenic cells in vitro. The effect of i.p. administration of Ad.DF3.BAX was also assessed in nude mice inoculated with the DF3-positive 36M2 human ovarian cancer cell line. Expression of either beta-galactosidase activity (after Ad.DF3.betaGAL treatment) or HA-BAX transcripts (after Ad.DF3.BAX treatment) was restricted to tumor tissue in vivo. Importantly, administration of Ad.DF3.BAX on days 2 and 3 after tumor inoculation was capable of eradicating >99% of tumor implants. These results demonstrate the feasibility of tumor selective expression of a proapoptotic protein such as BAX through adenoviral gene transfer.

BAX expression is associated with enhanced intracellular accumulation of paclitaxel: a novel role for BAX during chemotherapy-induced cell death.

SW626 cells that overexpress BAX are sensitized to the cytotoxic effects of paclitaxel and vincristine. It has been assumed that BAX mediates these effects through its ability to alter mitochondrial function, specifically by promoting the release of cytochrome c and facilitating the mitochondrial permeability transition. However, we have found that several early paclitaxel-mediated events are enhanced in SW626 transfectants that overexpress BAX, including G2-M-phase arrest, tubulin polymerization, and BCL-2 phosphorylation. We now demonstrate that these seemingly disparate effects are explained by an enhanced accumulation of paclitaxel in BAX-overexpressing cells, an effect due to diminished drug efflux. In contrast, drug efflux is increased in cells that do not overexpress BAX, resulting in low intracellular paclitaxel levels and relative resistance to the effects of this drug. Drug efflux in SW626 cells is mediated by a verapamil-inhibitable, non-MDR-1, non-MRP-1 transporter whose function or expression may be inhibited by BAX. These data suggest that stable transfectants that overexpress BAX may be sensitized to apoptotic cell death through a novel mechanism involving the enhancement of intracellular levels of naturally occurring toxins such as alkaloid derivatives.

Binding of ovarian cancer cells to peritoneal mesothelium in vitro is partly mediated by CD44H.

Epithelial cancer of the ovary spreads by implantation of tumor cells onto the mesothelial lining of the peritoneal cavity. We have developed an in vitro binding assay using confluent monolayers of normal peritoneal mesothelial cells in order to assess the role of known adhesion proteins in this process. Cells from normal ovarian surface epithelium and the ovarian cancer cell lines CAOV-3 and SKOV-3 exhibited significant adhesion to mesothelium in vitro (range 33-56% specific binding). Although these cells expressed several adhesion molecules, including CD44 and integrins such as alpha 4 beta 1, alpha 5 beta 1, and alpha v beta 3, only anti-CD44 antibody was capable of inhibiting mesothelial binding (range 42-44% inhibition). Adhesion molecule expression was also determined for fresh ovarian specimens, with CD44 being expressed in 2 of 2 cases of normal ovarian epithelium, 15 of 16 (94%) cases of tissue-derived tumor (from primary sites or peritoneal implants), and only 2 of 8 (25%) cases of free-floating tumor cells from ascites. Three of three CD44-positive cases derived from peritoneal implants exhibited significant mesothelial binding which was partly blocked by anti-CD44 antibody, whereas 2 of 2 CD44-negative cases derived from ascites showed minimal binding. CD44-mediated binding of ovarian cancer cells was determined to be due to recognition of mesothelium-associated hyaluronate, suggesting that the CD44H isoform was involved in this process. Immunoprecipitation of the CD44 species expressed by ovarian cancer cells revealed 2 major bands at 85-90 and 180 kDa, consistent with the known molecular masses of CD44H. These results suggest that CD44H may be an important mediator of ovarian cancer cell implantation and that decreased CD44H expression may be associated with release of cells into the peritoneal space during ascites formation. It is possible that strategies to interfere with CD44H function may result in decreased intraabdominal spread of this highly lethal neoplasm.

Radiation-induced apoptosis is not enhanced by expression of either p53 or BAX in SW626 ovarian cancer cells.

The p53 protein is known to play a central role in mediating G1 arrest or apoptosis in response to ionizing radiation in some cell types. It has been proposed that the link between p53 and induction of apoptosis is provided in part by p53-mediated upregulation of BAX. In this study, we used the human SW626 ovarian cancer cell line, which lacks functional p53, to further investigate the relationship between wildtype p53, BAX, and apoptosis. SW626 cells expressing a temperature sensitive (ts) p53 mutant did not undergo G1 arrest or apoptosis and did not exhibit enhanced sensitivity to radiation at the permissive temperature of 32 degrees C. The tsp53 protein was functional in these cells as evidenced by rapid induction of p21 at 32 degrees C, but not at 37 degrees C. Interestingly, restoration of wildtype p53 function at 32 degrees C was not associated with BAX upregulation. In addition, stable overexpression of BAX in SW626 cells was not capable of enhancing apoptotic cell death in response to radiation. Thus, failure of p53 to upregulate BAX is not the sole reason for its inability to promote radiation-induced apoptosis in SW626 cells. Taken together, our data suggest that neither p53 nor BAX upregulation is sufficient for the induction of apoptosis in response to genotoxic damage in some cell types.

BAD partly reverses paclitaxel resistance in human ovarian cancer cells.

Although paclitaxel is an important chemotherapy agent for the treatment of patients with epithelial ovarian cancer, its utility is significantly limited by the frequent development of drug resistance. Recent evidence suggests that resistance to chemotherapy may be partly related to defects in the apoptotic pathway. In this study we have investigated whether enhancement of apoptotic pathway function through stable expression of the BAD protein is capable of sensitizing human epithelial ovarian cancer cells to the effects of chemotherapy. Expression of HA-BAD in six separate clonal transfectants from two different ovarian cancer cell lines was found to significantly enhance the cytotoxic effects of paclitaxel, vincristine, and, to a lesser extent, etoposide. Enhancement of paclitaxel-induced apoptosis in HA-BAD-expressing clones was demonstrated by trypan blue exclusion, clonogenic cell assay, and flow cytometric evaluation. Importantly, this effect was associated with binding of HA-BAD to BCL-xL and concomitant disruption of BAX:BCL-xL interaction. Taken together, these data suggest that the development of small molecules which mimic the effects of BAD may represent a new class of drugs capable of preventing or reversing resistance to chemotherapy agents such as paclitaxel.

CD44 variant expression is a common feature of epithelial ovarian cancer: lack of association with standard prognostic factors.

PURPOSE: CD44 is a hyaluronic acid receptor that exists as a standard 90-kd form (CD44S) as well as several CD44 variant isoforms produced through alternative splicing. Expression of CD44 variants is associated with clinically aggressive behavior in some human tumors. The purpose of the present study is to define the expression of CD44 variant isoforms in ovarian cancer and to investigate whether the expression of these molecules is associated with adverse prognosis. MATERIALS AND METHODS: Six specimens of normal ovarian surface epithelium (NOSE) and 31 separate cases of newly diagnosed ovarian cancer were studied by a combination of reverse-transcription polymerase chain reaction (RT-PCR) and immunoperoxidase staining. Clinical correlation was made between CD44 variant expression and stage (I/II v III/IV), residual disease (< or = 2.0- v > 2.0-cm mass), age (< or = 65 v > 65 years), histology (papillary serous v other), grade, and survival. RESULTS: RT-PCR analysis revealed that NOSE predominantly expressed transcripts for CD44S, as well as a restricted pattern of transcripts characteristic of CD44 splice variants. CD44S and CD44 variant exon nine sequences (CD44-9v) were focally expressed in one of two NOSE specimens examined by immunoperoxidase staining. In comparison, the majority (71%) of ovarian cancer specimens expressed a complex pattern of CD44 splice variants by RT-PCR analysis. Immunoperoxidase studies revealed that the majority of ovarian cancer specimens expressed both CD44S and CD44-9v, whereas expression of sequences from variant exons 3, 4, and 6 was uncommon. There was no association between CD44 variant expression (transcript or protein) and stage, residual disease, age, histology, grade, or survival. CONCLUSION: Expression of CD44S and CD44-9v is a common feature of epithelial ovarian cancer cells. The lack of a significant association between CD44 variant expression and prognosis suggests that other factors may be more important in determining the clinical behavior of this disease.

BAX protein expression and clinical outcome in epithelial ovarian cancer.

PURPOSE: Expression of the pro-apoptotic protein BAX sensitizes ovarian cancer cell lines to paclitaxel in vitro by enhancing the pathway of programmed cell death. The present study was performed to determine the relationship between BAX expression and clinical outcome in 45 patients with newly diagnosed ovarian cancer. METHODS: BAX protein expression was analyzed by immunohistochemistry, and its relationship with clinical outcome was determined. Assessment of BAX mRNA transcript levels and mutational analysis of the BAX coding region were also performed. RESULTS: BAX protein was expressed at high levels (defined as > or = 50% of tumor cells positive) in tumor tissue from 60% of newly diagnosed patients. All patients whose tumors expressed high levels of BAX achieved a complete response (CR) to first-line chemotherapy that contained paclitaxel plus a platinum analogue, compared with 57% of patients in the low-BAX group (P = .036). After a median follow-up of 1.9 years, the median disease-free survival (DFS) of patients in the high-BAX group has not been reached, compared with a median DFS of 1.1 years for low-BAX expressors (P = .0061). BAX retained independent prognostic significance in multivariate analysis when corrected for stage and histology. BAX mRNA transcripts were easily detected in samples with low BAX protein expression, and no BAX mutations were identified. CONCLUSION: The correlation between high BAX levels and improved clinical outcome suggests that an intact apoptotic pathway is an important determinant of chemoresponsiveness in ovarian cancer patients who receive paclitaxel.

Use of peripheral-blood progenitor cells abrogates the myelotoxicity of repetitive outpatient high-dose carboplatin and cyclophosphamide chemotherapy.

PURPOSE: Attempts to increase dose-intensity in clinical practice have been limited by cumulative hematologic toxicity despite the use of hematopoietic growth factors. To address this problem, we designed a study to determine whether four cycles of dose-intensive chemotherapy with carboplatin could be administered in the outpatient setting using granulocyte-macrophage colony-stimulating factor (GM-CSF) and peripheral-blood progenitor cells (PBPCs) that had been harvested before initiation of treatment. PATIENTS AND METHODS: An initial cycle (cycle no. 0) of cyclophosphamide 4 g/m2 followed by GM-CSF was used to mobilize PBPCs harvested by leukapheresis for 6 consecutive days. Cycles no. 1 through 4 consisted of outpatient carboplatin 600 mg/m2 and cyclophosphamide 600 mg/m2 followed by GM-CSF 5 micrograms/kg subcutaneously (SC) twice per day every 28 days. In cycle no. 1, PBPC were not reinfused to assess the effects of GM-CSF alone. In cycles no. 2 through 4, PBPCs were reinfused on day 3 in an outpatient setting. RESULTS: In eight assessable patients, the addition of PBPCs in cycle no. 2 resulted in a significant reduction in the median duration of thrombocytopenia less than 20,000/microL (6.5 v 1 day; P = .016), days to platelets more than 50,000/microL (20.5 v 15 days; P = .020), number of platelet transfusions (five v 1.5; P = .016), and duration of neutropenia (absolute neutrophil count [ANC] < 1,000/microL (7 v 2.5 days; P = .008) when compared with cycle no. 1. Dose-limiting hematologic toxicity, defined as more than 7 days of platelets less than 20,000/microL or ANC less than 500/microL, was observed in four of eight patients during cycle no. 1, but not during cycles no. 2, 3, and 4 of chemotherapy supported by PBPCs (a total of 19 cycles in eight patients). Five of eight patients completed all four cycles of high-dose therapy. Three patients did not complete four cycles due to late thrombocytopenia (n = 2) or tumor progression (n = 1). CONCLUSION: These results indicate a benefit of PBPCs in addition to GM-CSF in alleviating myelosuppression of dose-intensive chemotherapy. Initial collection of PBPCs may allow administration of repetitive cycles of high-dose chemotherapy with acceptable toxicity to outpatients at disease onset.

Granulocyte-macrophage colony-stimulating factor enhances the cytotoxic effects of cytosine arabinoside in acute myeloblastic leukemia and in the myeloid blast crisis phase of chronic myeloid leukemia.

A strategy designed to stimulate myeloid leukemic blasts into active cell cycle may increase the effectiveness of S phase-specific agents such as cytosine arabinoside (ARA-C). Since recombinant human granulocyte-macrophage colony stimulating factor (GM-CSF) is known to stimulate the growth of myeloid leukemic cells in vitro, we have evaluated the ability of this growth factor to enhance leukemic clonogenic cell kill in the presence of ARA-C. In seven patients studied, GM-CSF increased the fraction of myeloid leukemic blasts in S phase as measured by propidium iodide DNA staining, bromodeoxyuridine incorporation, or ARA-C suicide techniques. Six of these seven patients demonstrated clonogenic cell growth in agar in response to GM-CSF. In five of these six patients, the combination of GM-CSF and ARA-C treatment in vitro resulted in a significant increase in leukemic clonogenic cell kill when compared to treatment with ARA-C in the absence of GM-CSF. Similar results were observed with the combination of GM-CSF and hydroxyurea, another S phase specific agent, further suggesting that the observed enhancement of cytotoxicity was due to the ability of GM-CSF to increase the number of leukemic cells in S phase. These data provide a rationale for investigating the toxicity and efficacy of combined GM-CSF and ARA-C therapy in patients with high-risk myeloid leukemia.

Simultaneous administration of granulocyte-macrophage colony-stimulating factor and cytosine arabinoside for the treatment of relapsed acute myeloid leukemia.

The treatment of patients with relapsed or refractory acute myeloid leukemia (AML) with high dose cytosine arabinoside (ara-C) results in short-lived complete response rates of 30-50%. We have previously shown that entry of myeloid leukemic cells into S phase can be accelerated in vitro through the use of recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF), resulting in enhancement of ara-C-mediated cytotoxicity. In order to evaluate the in vivo biological and clinical effects of this strategy in patients with high risk AML, we treated three patients with either refractory or relapsed disease with a continuous infusion of rhGM-CSF (0.45 micrograms/kg/h aglycoprotein) for 18 h, followed by the institution of high dose ara-C and continuation of rhGM-CSF throughout the 4 day duration of ara-C treatment. Prior to therapy, no patient had detectable levels of circulating rhGM-CSF, and there was no evidence of GM-CSF receptor occupancy in leukemic myeloblasts. After 18 h of rhGM-CSF therapy, all patients had biologically active levels of circulating rhGM-CSF (7.9-12.0 ng/ml), and two patients showed a significant degree of leukemic GM-CSF receptor occupancy without evidence of GM-CSF receptor down-regulation. A significant rise in the S phase fraction of leukemic myeloblasts was observed at 18 h of rhGM-CSF treatment in all three patients (29-56% increment). The toxicity of combined rhGM-CSF/ara-C therapy included pericarditis and cerebellar degeneration in one patient, fever and mild renal dysfunction in two patients, and mild hepatic dysfunction in all three patients. Each patient showed a transient rise in the absolute neutrophil and blast count during rhGM-CSF/ara-C administration, followed by profound, but clinically tolerable, myelosuppression. No patient developed clinical evidence of leukostasis. There was one death related to pericardial tamponade, one death related to refractory disease, and one clinical and cytogenetic remission. These results suggest that exogenously administered rhGM-CSF is capable of rapidly mobilizing leukemic cells into S phase in vivo and theoretically should be useful in overcoming kinetic resistance to ara-C. Clinical trials of this regimen in patients with high risk AML who are not already pharmacologically resistant to ara-C are warranted.

Functional heterogeneity of CD44 molecules in ovarian cancer cell lines.

We have previously shown that CD44 partly mediates ovarian cancer cell attachment to peritoneal mesothelium through recognition of mesothelial-associated hyaluronate. CD44 is a major receptor for hyaluronate and exists as a standard 90-180-kDa form (CD44H), as well as several higher molecular mass variant forms produced by alternative splicing. To determine whether functional differences exist between CD44H and its variants we have investigated the relationship between CD44 isoform expression and mesothelial adhesion in 12 ovarian cancer cell lines. Eight lines were CD44 positive (range, 83-94%) and demonstrated significant binding to mesothelium and hyaluronate, whereas two lines showed reduced CD44 levels (3-13%) and demonstrated decreased binding. Interestingly, two other lines (OVC-3 and SW626) expressed CD44 in the majority of cells (>93%) and yet bound weakly to mesothelium. Mean linear fluorescence intensity of CD44 expressed by OVC-3 and SW626 cells was approximately one-half that of strongly binding cell lines, suggesting that the ability to adhere may be partly related to CD44 surface density. However, immunoprecipitation and immunoblot analyses revealed that standard CD44H represented only 23-31% of total CD44 in weakly binding cells, with the majority of species being comprised of CD44 variants. Indirect immunofluorescence of OVC-3 and SW626 cells confirmed the presence of CD44 variants containing exons v3, v6, and v9. In contrast, CD44H represented the majority (75-86%) of total CD44 expressed by strongly binding cell lines such as CAOV-3 and UPN36T. Transfection of CD44H cDNA into weakly binding OVC-3 cells restored significant mesothelial binding which was partly blocked by anti-CD44 antibody. These data suggest that the expression of CD44 is necessary but not sufficient for mediating attachment of ovarian cancer cells to mesothelium. Although CD44 variants may constitute the major CD44 species in certain ovarian cancer cell lines, it appears that these CD44 species are not always capable of mediating significant binding to mesothelium or hyaluronate. Rather, an adequate level of CD44H is the critical determinant of binding in this system. The role of CD44 variants in the process of ovarian cancer metastasis will require further investigation.

Monocytes enhance gamma-interferon-induced inhibition of myeloid progenitor cell growth through secretion of tumor necrosis factor.

In this study, we have examined the effects of autologous monocytes and T-lymphocytes on gamma-interferon (gamma-IFN)-induced inhibition of granulocyte-monocyte progenitor cells (CFU-GM) in vitro. Depletion of adherent cells from the mononuclear fraction of normal bone marrow (NBM) resulted in a significant reduction in the inhibitory effects of gamma-IFN on CFU-GM growth, whereas T-lymphocyte depletion had no effect. Adding back autologous monocytes to the underlayer fraction of agar culture resulted in a concentration-dependent enhancement of gamma-IFN-induced CFU-GM inhibition that did not require cell-cell contact. Adding back autologous T-lymphocytes had no effect and did not synergize with monocytes in enhancing gamma-IFN-induced inhibition. Based on the use of indomethacin and the pattern of CFU-GM subset growth, it was determined that prostaglandin E was unlikely to be the humoral inhibitory factor involved in this process. However, the effects of monocytes were completely reversed in the presence of a neutralizing monoclonal antibody to tumor necrosis factor (TNF), suggesting that monocyte-derived TNF was responsible for the enhancement of gamma-IFN-induced CFU-GM inhibition. This observation was further supported by the ability of gamma-IFN to induce an eightfold increase of baseline monocyte TNF secretion in agar culture. These data suggest that gamma-IFN may inhibit progenitor cell growth in vitro through indirect humoral mechanisms involving monocyte-derived TNF, as well as through direct inhibitory effects on CFU-GM proliferation. Because monocytes are a component of the bone marrow microenvironment, the ability of gamma-IFN to induce biologically relevant levels of monocyte-derived TNF may play an important role in the negative regulation of hematopoiesis.

Vascular cell adhesion molecule-1 expressed by peritoneal mesothelium partly mediates the binding of activated human T lymphocytes.

Adhesion molecules such as selectins and integrins are known to mediate leukocyte attachment and transmigration through activated vascular endothelium. However, the molecules that mediate subsequent leukocyte entry into nonvascular spaces such as the abdominal cavity during states of peritoneal inflammation have not been identified. Because the peritoneal mesothelial lining represents the final barrier to leukocyte migration into the abdomen, it is likely that adhesion molecules expressed by mesothelial cells are involved in this process. We have developed an in vitro binding assay using confluent layers of normal human mesothelial cells to determine which adhesion molecules might be involved in T lymphocyte-mesothelial recognition. Normal peripheral blood T lymphocytes exhibit low-level specific binding to mesothelium (mean 13% specific binding, n = 4), which is enhanced by phorbol myristate acetate (PMA) treatment (mean 38% specific binding, n = 4). This binding is significantly inhibited in the combined presence of antibodies reactive with CD29 and CD18, suggesting a role for beta 1 and beta 2 integrins, respectively, in this interaction. Interestingly, cultured human mesothelial cells were shown to express vascular cell adhesion molecule-1 (VCAM-1), suggesting that this molecule might function as a counter-receptor for alpha 4 beta 1 expressed by T lymphocytes. Mesothelial cells were also noted to express ICAM-1, CD29, and CD44, but not CD18 or selectins. VCAM-1 expression was not a constitutive property of freshly obtained mesothelial cells but was inducible upon culture in the presence of either interleukin-1 (IL-1), tumor necrosis factor (TNF), or PMA. Neutralizing antibodies reactive with either alpha 4, VCAM-1, or CD29 were all equally capable of inhibiting the binding of activated leukocytes to mesothelial cells (in the presence of anti-CD18 antibody). Mesothelial VCAM-1 was found to have a molecular mass of 110 kD and an mRNA transcript of approximately 3.2 kb, consistent with the predominant VCAM-1 species found in activated endothelium. These data suggest that functional VCAM-1 is expressed on activated mesothelial cells and may play a role in the distal arm of leukocyte trafficking to the abdominal cavity.

In vitro expression of colony-stimulating factor genes by human acute myeloblastic leukemia cells.

Cells from most cases of acute myeloblastic leukemia (AML) proliferate in vitro in response to one or more colony-stimulating factor (CSF). Previous studies have suggested that some AML cells can produce their own CSFs, but the frequency of this phenomenon is unclear. In this study, Northern blot hybridization was used to detect mRNA transcripts for granulocyte-monocyte CSF (GM-CSF), granulocyte-CSF (G-CSF), and macrophage-CSF (M-CSF) in 22 randomly selected cases of AML. Ten cases expressed one CSF transcript (generally M-CSF), one case expressed two CSF transcripts, and six cases expressed all three. The expression of CSF transcripts did not significantly correlate with the French-American-British classification, with the possible exception that four of the five cases expressing all three CSF mRNAs were FAB M1. Six cases had autonomous growth of clonogenic cells in agar, and all six cases expressed one or more type of CSF transcript. None of the five evaluated cases lacking all three CSF transcripts had autonomous growth. However, there were many cases in which CSF transcripts were present and no autonomous growth was observed. In response to exogenously added human recombinant CSFs, 11 of 18 cases proliferated in response to GM-CSF, 8 of 18 cases in response to G-CSF, and 0 of 10 cases in response to M-CSF. Response to a CSF was not significantly correlated with the presence or absence of CSF transcripts, particularly for M-CSF. These results show that CSF transcripts are frequently detected in AML, although with a substantial degree of heterogeneity. It is possible that CSF production contributes to unregulated growth in some cases of AML.

Regulation of the production and function of granulocytes and monocytes.

The bone marrow responds to infection by rapidly producing mature granulocytes and monocytes from a small pool of committed progenitor cells under the influence of a heterogeneous family of glycoproteins termed colony-stimulating factors (CSFs). There are at least four major CSFs (IL-3, GM-, G-, and M-CSF) which are structurally distinct but have a great deal of functional overlap. The humoral signals which regulate the production of CSFs are generated at peripheral sites of infection through the activation of local macrophages and T lymphocytes by the invading pathogen. The monokines IL-1 and TNF are most likely the major humoral factors involved in stimulating CSF secretion by accessory cells in peripheral tissue sites as well as in the bone marrow microenvironment, although the functions of CSFs produced in these two organ compartments is distinct. CSFs secreted by bone marrow endothelial cells and fibroblasts serve to stimulate the proliferation and differentiation of myeloid progenitor cells, while CSFs present in areas of local infection are most likely involved in the activation of mature myeloid cell function. The dual ability of CSFs to both regulate bone marrow proliferation and to stimulate mature myeloid cell function represents a novel mechanism for producing a coordinated host response to infection.