Combination of CD80 and granulocyte-macrophage colony-stimulating factor coexpression by a leukemia cell vaccine: preclinical studies in a murine model recapitulating Philadelphia chromosome-positive acute lymphoblastic leukemia.

Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL) is a highly aggressive malignancy caused by the bcr-abl translocation oncogene. To explore alternative treatments for Ph+ ALL we tested gene-modified cell vaccines in the BALB/c-derived BM185 leukemia model. We compared the efficacy of BM185 cell vaccine expressing CD80 alone or in combination with IL-2 or GM-CSF. Mice injected with viable BM185 leukemia cells modified to express CD80 and GM-CSF (BM185/CD80+GM-CSF) showed the highest leukemia rejection rates. Cell vaccines consisting of irradiated BM185/CD80+GM-CSF cells administered subcutaneously stimulated a potent cytotoxic T lymphocyte (CTL) response against parental BM185. Histological examination of the vaccination site showed a large concentration of immune cells. Administration of the BM185/CD80+GM-CSF cell vaccine before intravenous challenge with parental cells caused strong inhibition of leukemia development. Vaccination after subcutaneous challenge with BM185 cells caused efficient elimination of leukemia promoting 40-60% long-term survival rates. The immunization efficacy of the BM185/CD80+ GM-CSF cell vaccine was directly correlated with the percentage of cells expressing the transgenes. In all, this preclinical study shows that leukemia cell vaccines coexpressing CD80 and GM-CSF can potentially be explored for immunotherapy in Ph+ ALL patients.

Immune response to Philadelphia chromosome-positive acute lymphoblastic leukemia induced by expression of CD80, interleukin 2, and granulocyte-macrophage colony-stimulating factor.

We examined the potential of generating an immune response against Philadelphia chromosome-positive acute lymphoblastic leukemia. The immunostimulatory molecules chosen for this study were the cytokines IL-2 and GM-CSF and the costimulatory ligand CD80 (B7.1). We used a murine model based on a BALB/c pre-B cell line, BM185wt, in which leukemia is induced by the p185 BCR-ABL oncogenic product, which reproduces Philadelphia chromosome-positive ALL. BM185wt cells were transduced with retroviral vectors and the transduced clones expressing mIL-2, mGM-CSF, or mCD80 were used for challenge. Expression of the immunomodulators by BM185 cells was correlated with delay in leukemia development in immunocompetent mice, but not in immunodeficient mice, indicating an immune response against the modified leukemia cells. Expression of CD80 caused leukemia rejection in 50% of the cohort, which was associated with the CD4+ and CD8+ T cell-dependent development of anti-leukemia cytotoxic T lymphocytes. Furthermore, mice surviving the BM185/CD80 challenge or preimmunized with irradiated BM185/CD80 cells developed an immune response against subsequent challenge with the parental leukemia. These studies provide evidence that immunotherapeutic approaches can be developed for the treatment of ALL.

Protection of alveolar macrophages from hyperoxia by gamma-glutamyl transpeptidase.

Exposure to hyperoxia causes loss of alveolar macrophage cell function. Toxicity was measured as suppression of the respiratory burst stimulated by phorbol myristate acetate subsequent to exposure (43.5% depression by 2-h exposure to 5 atm absolute O2 vs. controls). The presence of extracellular glutathione significantly protected these cells (7% loss). gamma-Glutamyl transpeptidase, a membrane enzyme with its active site directed outward, was necessary for use of extracellular glutathione. This was demonstrated using the gamma-glutamyl transpeptidase inhibitor, serine-borate complex, which significantly blocked both protection of cells by extracellular glutathione and extracellular glutathione-dependent synthesis of glutathione. The principal use of glutathione in antioxidant defense is as a substrate for glutathione peroxidase. The apparent Km for glutathione of glutathione peroxidase of rat alveolar macrophages was determined to be 2 mM; however, rat alveolar macrophages have approximately 1.3 mM intracellular glutathione, which is insufficient for maximal enzymatic activity. During hyperoxic exposure, this deficit would probably be more significant. Thus the ability of extracellular glutathione along with gamma-glutamyl transpeptidase activity to provide amino acids for de novo glutathione synthesis appears to be a potentially important component of antioxidant defense.

Role of selenium-dependent glutathione peroxidase in antioxidant defenses in rat alveolar macrophages.

Glutathione peroxidase is a crucial component of cellular antioxidant defenses. Using tertiary butyl hydroperoxide (tBOOH) as a model for oxidant stress in alveolar macrophages, we determined the effectiveness of glutathione peroxidase in preventing both cell "death" (lactate dehydrogenase release) and more subtle alterations in cell function. The KM of glutathione peroxidase for tBOOH was 54 microM, and the Vmax was 26 nmol/min/10(6) cells in alveolar macrophages. Concentrations of tBOOH greater than 100 microM caused lactate dehydrogenase release; however, a lag greater than 30 min was observed when with 10 mM tBOOH. With 200 microM tBOOH, the rate of decrease in membrane potential, measured by 3,3'-dipentyloxacarbocyanine iodide fluorescence, inversely correlated with glutathione peroxidase. Computer-enhanced microscopy showed that this fluorescence predominately was in mitochondria. NADPH fluorescence was altered in selenium-deficient alveolar macrophages; the tBOOH-dependent rate of NADPH oxidation was slowed, and higher concentrations of tBOOH were required to disturb the steady state NADPH/NADP+ ratio. Although alteration in NADPH or glutathione oxidation can reflect oxidant stress and can adversely affect cell function, such a change does not dictate irreversible injury. Nevertheless, irreversible injury by oxidants appears to involve an overwhelming of the glutathione-NADPH antioxidant system.

Consistent, persistent expression from modified retroviral vectors in murine hematopoietic stem cells.

Retroviral vectors based on the Moloney murine leukemia virus (MoMuLV) have shown inconsistent levels and duration of expression as well as a propensity for the acquisition of de novo methylation in vivo. MoMuLV-based vectors are known to contain sequences that are capable of suppressing or preventing expression from the long terminal repeat. Previously, we constructed a series of modified retroviral vectors and showed that they function significantly better than MoMuLV-based vectors in vitro. To test the efficacy of the modified vectors in hematopoietic stem cells in vivo, we examined gene expression and proviral methylation in differentiated hematopoietic colonies formed in the spleens of mice after serial transplantation with transduced bone marrow (2 degreesCFU-S). We found a significant increase in the frequency of expression with our modified vectors (>90% expression in vector DNA containing 2 degreesCFU-S) over the frequency observed with the standard MoMuLV-based vector (28% expression in vector containing 2 degreesCFU-S). Expression from the modified vectors was highly consistent, with expression in >50% of the vector-containing 2 degreesCFU-S from all 20 transplant recipients analyzed, whereas expression from the standard MoMuLV-based vector was inconsistent, with expression in 0-10% of the vector containing 2 degreesCFU-S from 8 recipients and expression in >50% of the vector-containing 2 degreesCFU-S from 4 other recipients. In addition, we established that the modified vectors had a lower level of DNA methylation than the control vector. These findings represent significant advances in the development and evaluation of effective retroviral vectors for application in vivo.

Cells expressing human glucocerebrosidase from a retroviral vector repopulate macrophages and central nervous system microglia after murine bone marrow transplantation.

Gaucher disease is an inherited lysosomal storage disease in which the loss in functional activity of glucocerebrosidase (GC) results in the storage of its lipid substrate in cells of the macrophage lineage. A gene therapy approach involving retroviral transduction of autologous bone marrow (BM) followed by transplantation has been recently approved for clinical trial. Amelioration of the disease symptoms may depend on the replacement of diseased macrophages with incoming cells expressing human GC; however, the processes of donor cell engraftment and vector gene expression have not been addressed at the cellular level in relevant tissues. Therefore, we undertook a comprehensive immunohistologic study of macrophage and microglia replacement after murine BM transplantation with retrovirus-marked BM. Serial quantitative PCR analyses were employed to provide an overview of the time course of engraftment of vector-marked cells in a panel of tissues. Following reconstitution of hematopoietic tissues with vector-marked donor cells at early stages, GC+ cells began to infiltrate the liver, lung, brain, and spinal cord by 3 months after transplant. Immunohistochemical analyses of PCR+ tissues using the 8E4 monoclonal antibody specific for human GC revealed that macrophages expressing human GC had partially reconstituted the Mac-1+ population in all tissues in a manner characteristic to each tissue type. In the brain, 20% of the total microglia had been replaced with donor cells expressing GC by 3 to 4 months after transplant. The finding that significant numbers of donor cells expressing a retroviral gene product immigrate to the central nervous system suggests that gene therapy for neuronopathic forms of lysosomal storage diseases as well as antiviral gene therapy for AIDS may be feasible.

Lentiviral vectors for efficient delivery of CD80 and granulocyte-macrophage- colony-stimulating factor in human acute lymphoblastic leukemia and acute myeloid leukemia cells to induce antileukemic immune responses.

Cell vaccines engineered to express immunomodulators have shown feasibility in eliminating leukemia in murine models. Vectors for efficient gene delivery to primary human leukemia cells are required to translate this approach to clinical trials. In this study, second-generation lentiviral vectors derived from human immunodeficiency virus 1 were evaluated, with the cytomegalovirus (CMV) promoter driving expression of granulocyte-macrophage-colony-stimulating factor (GM-CSF) and CD80 in separate vectors or in a bicistronic vector. The vectors were pseudotyped with vesicular stomatitis virus G glycoprotein and concentrated to high titers (10(8)-10(9) infective particles/mL). Human acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), and chronic myeloid leukemia cell lines transduced with the monocistronic pHR-CD80 vector or the bicistronic pHR-GM/CD vector became 75% to 95% CD80 positive (CD80(+)). More important, transduction of primary human ALL and AML blasts with high-titer lentiviral vectors was consistently successful (40%-95% CD80(+)). The average amount of GM-CSF secretion by the leukemia cell lines transduced with the pHR-GM-CSF monocistronic vector was 2182.9 pg/10(6) cells per 24 hours. Secretion was markedly lower with the bicistronic pHR-GM/CD vector (average, 225.7 pg/10(6) cells per 24 hours). Lower amounts of CMV-driven messenger RNA were detected with the bicistronic vector, which may account for its poor expression of GM-CSF. Primary ALL cells transduced to express CD80 stimulated T-cell proliferation in an autologous mixed lymphocyte reaction. This stimulation was specifically blocked with monoclonal antibodies reactive against CD80 or by recombinant cytotoxic T-lymphocyte antigen 4-immunoglobulin fusion protein. These results show the feasibility of efficiently transducing primary leukemia cells with lentiviral vectors to express immunomodulators to elicit antileukemic immune responses. (Blood. 2000;96:1317-1326)

Increased levels of spliced RNA account for augmented expression from the MFG retroviral vector in hematopoietic cells.

A persistent obstacle in the use of vector systems for gene therapy has been the inability to attain high-level expression of the target gene in primary cells in vivo. The MFG retroviral vector was designed to yield improved expression over the widely used N2 or LN vectors; however, the molecular basis for this effect has not been examined. Using the human glucocerebrosidase (GC) enzyme as a reporter, we compared expression from the MFG and N2 vector backbones in transduced murine hematopoietic cells after syngeneic bone marrow transplantation. Reporter enzyme activities in primary spleen colonies of transplanted mice were seven-fold higher per vector copy in cells transduced with the (MFG-based) MGC vector than in cells bearing the (N2-based) G2 vector. In spleen colonies harboring the MGC vector, the ratio of spliced to unspliced vector RNA was increased four-fold relative to the G2 vector transcripts in Northern blot analyses. Further analyses indicated that MGC-transduced cells contained five-fold higher levels of spliced RNA per vector copy. Since translation of spliced RNA species (in which the complex secondary structure of the packaging signal has been excised) is likely to proceed with enhanced efficiency, the augmented levels of spliced RNA produced by MFG may represent the key element of increased protein expression from this vector. These findings suggest that the MFG retroviral vector may provide higher level expression of target genes used in human gene therapy.