Purification of coated vesicles by agarose gel electrophoresis.

We have applied agarose gel electrophoresis as a novel step in the purification of clathrin-coated vesicles. Preparations of coated vesicles obtained by sedimentation velocity and isopycnic centrifugation are resolved into two distinct fractions upon electrophoresis. The slower migrating fraction contains smooth vesicles, whereas the faster contains only coated vesicles and empty clathrin coats. The faster mobility of the coated vesicles is primarily caused by the acidic nature of clathrin. Coated vesicles from three different cell types have different mobilities. In each case, however, all of the major polypeptides previously attributed to coated vesicles comigrate with the now homogeneous particles, even though a powerful ATPase activity is completely removed.

Mitoguazone therapy in patients with refractory or relapsed AIDS-related lymphoma: results from a multicenter phase II trial.

PURPOSE: Patients with AIDS-related lymphoma usually have extensive lymphomatous disease, with relatively frequent involvement of the CNS. Approximately half may achieve complete remission after chemotherapy. Mitoguazone, an inhibitor of polyamine biosynthesis, has demonstrated efficacy in patients with de novo recurrent lymphoma. The drug is relatively nonmyelotoxic and may cross the blood-brain barrier. The current study was designed to assess the safety and potential efficacy of mitoguazone in patients with relapsed or refractory AIDS-lymphoma. PATIENTS AND METHODS: Thirty-five patients were accrued, all of whom had failed one (51%) or multiple (two to six) prior regimens. Mitoguazone (600 mg/m2) was given intravenously on days 1 and 8, and then every 2 weeks, until best response, progression, or toxicity. RESULTS: The median age was 39 years. High-grade lymphoma was diagnosed in 29 patients (83%). Extranodal disease was present in 30 patients (86%), with multiple extranodal sites (two to seven) in 18 (51%). The median CD4 cell count at study entry was 66/dL (range, zero to 549). Twenty-six patients were assessable for response. The objective response rate was 23% (95% confidence interval [CI], 6.9 to 39.3), with complete remission in three patients (11.5%), and partial remission (PR) in three patients (11.5%). Six patients experienced stable disease. Median survival from study entry was 2.6 months for the group as a whole; 21.5 months (range, 3.8 to 29.1) in complete responders, 5.6 months (range, 3.8 to 34.8) in partial responders. The most common toxicities occurred solely during drug infusion and included vasodilation (63%), paresthesia (86%), and somnolence (17%). Fourteen patients (40%) experienced nausea and 16 (46%) vomiting (grade 3 in one). Ten patients (29%) developed stomatitis, including grade 3 in two and grade 4 in one. Seven patients (20%) developed neutropenia, with grade 4 in one. Thrombocytopenia occurred in nine patients (26%). While on study, three patients developed sepsis, four had pneumonia, and two developed opportunistic infections. CONCLUSION: Mitoguazone is an effective agent in patients with multiply relapsed or refractory AIDS-related lymphoma, with acceptable toxicity. Further study in patients with newly diagnosed disease is warranted.

Gene transfer into murine hematopoietic stem cells and bone marrow stromal cells.

The use of recombinant retroviral vectors to transfer genetic sequences into hematopoietic stem cells (HSC) is one approach to somatic gene therapy. Two limitations of such retroviral vectors are the degree of efficiency of transfer into the reconstituting hematopoietic stem cells and the loss of reconstituting ability of hematopoietic stem cells when manipulated in vitro during infection and selection. We have investigated the effects on the efficiency of gene transfer of prestimulation of hematopoietic stem cells by growth factors prior to infection. Prestimulation of bone marrow cells in WEHI-3b-conditioned media improved the efficiency of gene transfer into CFU-S stem cells. The majority of animals transplanted with bone marrow infected after prestimulation with a simplified retrovirus, Zip PGK ADA, demonstrated long-term and stable expression of human adenosine deaminase (ADA) after full hematopoietic reconstitution. In separate experiments, retroviral vectors have been used to transfer the SV40 large T antigen sequences into stromal cells making up the hematopoietic microenvironment. Stromal cells expressing large T antigen are immortalized, and some support the maintenance of day 12 CFU-S (CFU-S12) and reconstituting hematopoietic stem cells in vitro for up to 4 weeks. Such immortalized stromal cell lines provide an in vitro hematopoietic microenvironment which may allow prolonged in vitro manipulations during infection and selection of hematopoietic stem cells without loss of reconstituting ability. We are using immortalized stromal cell lines resistant to deoxycoformycin (dCF) to select transduced murine HSC containing human ADA in vitro. The use of recombinant retroviral vectors provides a promising approach to correction of human diseases involving bone marrow cells.

Retroviral gene transfer of human adenosine deaminase in murine hematopoietic cells: effect of selectable marker sequences on long-term expression.

Retroviral-mediated gene transfer of human adenosine deaminase (hADA) provides a model system for the development of somatic gene therapy as a therapy for diseases of bone marrow-derived cells. We have previously demonstrated that hADA can be observed in all hematopoietic lineages in a minority of mice transplanted with bone marrow cells infected with a simplified retroviral vector, ZipPGK-ADA. Here we report a majority of mice (six of eight) demonstrate expression of hADA in the peripheral blood at least 6 months after transplantation with bone marrow infected with this simplified retroviral vector, which contains no selectable marker. The failure to express hADA in two of eight mice was associated with the absence of the recombinant retroviral provirus in DNA prepared from bone marrow cells of these mice apparently due to failure to efficiently infect the reconstituting hematopoietic stem cell. In an effort to preselect bone marrow stem cells containing proviral integrations, we incorporated the selectable marker neo phosphotransferase (NEO) into a retroviral vector encoding hADA, N2/ZipPGK-ADATKNEO, and used G418 selection of infected bone marrow cells before transplantation. In contrast to the simplified retroviral vector, hADA expression in these recipients was short lived (less than 8 weeks), despite the continued presence of intact provirus in DNA prepared from bone marrow of these mice. To determine whether the preselection of bone marrow using G418 was responsible for the lack of sustained hADA expression, we repeated the infection with the N2/ZipPGK-ADATKNEO vector but omitted the G418 selection step. Again, the majority of recipient mice failed to express hADA long term, although the continued presence of provirus in DNA prepared from peripheral blood cell mononuclear cells was clearly demonstrated. Finally, we demonstrate clonal fluctuation of infected stem cells, and observe a temporal correlation between cessation of expression of hADA and the emergence of a dominant stem cell clone between 14 and 20 weeks posttransplantation in one recipient. These data suggest that inclusion of a second transcriptional unit that includes neo phosphotransferase sequences in this simplified vector is associated with decreased expression of the nonselectable ADA sequences.

Stem cell factor, interleukin-3, and interleukin-6 promote retroviral-mediated gene transfer into murine hematopoietic stem cells.

The efficiency of retroviral-mediated gene transfer into hematopoietic stem cells (HSC) is dependent on the survival and self-renewal of HSC in vitro during retroviral infection. We have examined the effect of prestimulation of bone marrow with various cytokines, including the product of the Steel gene, Steel factor or stem cell factor (SCF) (the ligand for the c-kit receptor) on the efficiency of retroviral transduction of the human adenosine deaminase (hADA) cDNA into murine HSC. Bone marrow cells were prestimulated for 48 hours with hematopoietic growth factors, then cocultivated with the packaging cell line producing the ZipPGK-ADA simplified retrovirus for an additional 48 hours with continued growth factor exposure. Nonadherant cells from these cocultures were injected into lethally irradiated recipients. The content of day 12 colony-forming unit-spleen (CFU-S12) in SCF/interleukin 6 (IL-6)-prestimulated and cocultured bone marrow was more than threefold greater than that of IL-3/IL-6-prestimulated bone marrow cells. All mice receiving bone marrow cells infected with the PGK-ADA virus after prestimulation with IL-3/IL-6 or SCF/IL-6 demonstrated hADA expression in the peripheral blood after full hematopoietic reconstitution. While all recipients of IL-3/IL-6-prestimulated bone marrow expressed hADA at 4 months posttransplant, in three independent experiments examining a total of 33 mice, in most recipients of SCF/IL-6-prestimulated and infected bone marrow cells, the expression of human enzyme was higher than IL-3/IL-6 mice. Southern blot analysis of DNA from hematopoietic tissues from these same mice prepared at least 4 months posttransplantation also demonstrated a higher infection efficiency of HSC as measured by proviral integration patterns and genome copy number analysis. These results suggest that the higher level of hADA expression seen in mice receiving marrow prestimulated with SCF/IL-6 before retroviral infection is due to more efficient infection of reconstituting HSC. Other growth factor combinations were also studied; however, prestimulation with SCF/IL-6 or IL-3/IL-6 appeared optimal. Using retroviral-mediated gene transfer and viral integration patterns, Steel factor (SCF) in combination with IL-6 appears to increase the survival and self-renewal of reconstituting hematopoietic stem cells and proves useful in effecting expression of foreign genes in transplant recipients. Such pretreatment may also be useful in the application of retroviral transfer methods to human cells.

Functional expression of human CD8 in fully reconstituted mice after retroviral-mediated gene transfer of hemopoietic stem cells.

Retroviral-mediated gene transfer has been used in an attempt to efficiently and stably express functional cell-surface molecules in lymphoid and myeloid cells. The human CD8 molecule is a T cell-specific surface receptor that is intimately involved in class I MHC-restricted Ag recognition and subsequent T cell activation. After infection with a recombinant, replication-defective retrovirus containing the human CD8 alpha cDNA, bone marrow cells were transplanted into lethally irradiated recipients. The majority of lymphoid and myeloid cells of reconstituted animals expressed high levels of human CD8 for at least 8 months after transplantation. Transfer of bone marrow and spleen cells from these recipients 100 days after transplantation into secondary recipients also resulted in long term expression of CD8 in lymphoid and myeloid cells. CD8 expressed in splenic T cells associated with the lymphoid-specific tyrosine protein kinase p56lck, participated in T cell activation and conferred an increased xenogeneic response to human MHC class I Ag. Thus, retroviral-mediated gene transfer allows the long term, functional expression of cell-surface molecules in normal murine lymphoid and myeloid cells.

Long-term in vivo expression of a murine adenosine deaminase gene in rhesus monkey hematopoietic cells of multiple lineages after retroviral mediated gene transfer into CD34+ bone marrow cells.

Retroviral mediated gene transfer into stem cells has been proposed as therapy for many inherited hematopoietic diseases. Deficiency of the enzyme adenosine deaminase (ADA) results in depletion of T lymphocytes, causing severe combined immunodeficiency syndrome (SCIDS). In this report, we describe retroviral mediated gene transfer of a murine ADA cDNA into Rhesus monkey hematopoietic stem cells. Immunoselected CD34+ bone marrow cells were exposed to medium containing the ADA retrovirus during culture on a stromal cell line engineered to express the transmembrane form of stem cell factor. After infusion of autologous, transduced cells into irradiated recipients, gene transfer was observed in all three monkeys. The ADA provirus was detected in 2% of circulating granulocytes and T cells from 100 days post-transplantation to longer than 1 year and in B cells from 250 days post-transplantation and beyond. Mouse ADA activity was detected in peripheral blood cells at approximately 3% the activity of monkey ADA. Thus, we have shown gene transfer into repopulating cells that contribute to all hematopoietic lineages with persistent gene expression. These data provide support for the use of stem cell targeted gene transfer for therapy of ADA deficiency.