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In this study, we assessed the efficiency of T lymphocyte transduction with a retroviral vector carrying the herpes simplex virus thymidine kinase (HSV-tk) and neomycin phosphotransferase (neo) genes by four different protocols: standard supernatant infection, supernatant infection plus centrifugation steps, supernatant infection on fibronectin fragment-coated wells, and cocultivation. After retrovirus-mediated gene transfer of tk-neo in PHA/IL-2-stimulated primary T lymphocytes and G418 selection, T cells retained their proliferative activity, alloresponsiveness, ability to produce and to respond to IL-2, and ganciclovir (gcv)-specific sensitivity. When the four different transduction techniques were compared, no significant differences were seen in terms of cellular viability, proliferation capacity, and immunophenotyping. tk gene expression was the same in all transduced selected populations, as indicated by gcv sensitivity. Transduction efficiency was evaluated by semiquantitative PCR. Using the standard supernatant infection method, the rate of infection was extremely low (

High-dose chemotherapy (HDC) supported by autologous transplantation of blood stem cells (BSC) is used increasingly for patients with poor-risk malignancies. We report our experience with 93 consecutive patients who were mobilized with recombinant human granulocyte colony-stimulating factor (rhG-CSF) alone. They received a fixed dose of G-CSF for 5 or 6 days, and BSC were collected by leukapheresis. Aphereses were evaluated for MNC, CD34+ cells, and CFU-GM counts and cryopreserved. All patients received a conditioning regimen without TBI. Engraftment was assessed as the first of 2 consecutive days on which patients achieved 0.5 and 1 x 10(9)/L neutrophils and an unsupported platelet count of 25 x 10(9)/L. Multivariate analysis was performed to study patients and graft characteristics that could influence reconstitution. The G-CSF priming regimen was well tolerated and allowed collection of BSC for all patients, 66% of them achieving >3 x 10(6)/kg CD34+ cells, and 86% achieving >10 x 10(4) CFU-GM/kg. The numbers of collected CD34 and CFU-GM cells were highly correlated. The number of courses of chemotherapy prior to collection, a diagnosis of breast cancer, the use of rhG-CSF posttransplant, and the numbers of CFU-GM and CD34+ cells reinfused were correlated with hematologic recovery. In a multivariate analysis, however, the number of CD34+ cells was the only factor independently influencing both granulocyte and platelet recovery. Patients who received at least 3 x 10(6)/kg CD34+ cells achieved granulocyte reconstitution on day 11 after reinfusion (range 8-15) and an unsupported platelet count of 25 x 10(9)/l on day 14 (range 12-180), significantly earlier than patients who received fewer cells (p < 0.001). In addition, G-CSF administration postreinfusion independently enhanced granulocyte reconstitution but not platelet recovery. In conclusion, CD34+ cell number appears to be the only factor predicting both granulocyte and platelet reconstitution. Based on this study, the collection of a minimal number of 3 x 10(6)/kg CD34+ cells appears desirable.

Prostate cancer is the second cause of cancer mortality in men in Western countries. To study new therapeutic approaches such as gene therapy, animal models of human prostate cancer with metastatic behavior are mandatory. We used the Nod Scid mouse strain to develop an orthotopic animal model. Two androgen-independent cell lines (PC-3 and DU 145) were used. Local tumor growth and metastases were analyzed. The tumor take rates were close to those reported in the literature. However, a high frequency of various metastatic sites has been observed (liver, lung, spleen, adrenal, kidney, lymph node, and diaphragm). It can be concluded that the Nod Scid mouse is a relevant preclinical animal model to study human prostate cancer. Metastatic sites seem more numerous in comparison to other orthotopic mice models described.

We have investigated the value of a gene therapy approach for neuroblastoma (NB), based on retroviral transduction of the IL-1beta or TNF-alpha cytokine genes into human NB lines. Secretion of the corresponding cytokine, was demonstrated in all lines, although with considerable quantitative variations. Cytokine gene expression significantly reduced the proliferation index (p = 0.0001); this effect was associated with either terminal neuronal (one TNF-alpha line) or fibroblast-like differentiation (two IL-1beta lines), leading to growth arrest after a few weeks. Cell surface levels of CD54 and HLA class II remained unaffected, but HLA class I (p0.001) and CD58 expression (p = 0.01) increased on SKNSH after TNF-alpha gene transfer. Mononuclear cells from normal allogeneic donors cocultured with both IL-1beta (p0.001) and TNF-alpha lines (p0.01), showed a significant increase in the proportion of activated T cells (CD3+DR+); however, their cytotoxicity and proliferation rate remained unchanged. Immunotherapy of neuroblastoma will require identification of transduced lines in which cytokine secretion induces phenotypic changes in such a way as to augment their likely immunomodulatory properties without impeding cell growth. Because of the limited efficacy of IL-1beta or TNF-alpha gene transfer alone, further studies should focus on combination with other immunomodulatory agents, to improve their potential efficacy in neuroblastoma.

Mobilized peripheral blood stem cells characterized by sustained re-populating ability could be optimal target cells for ex-vivo gene transfer. In spite of very attractive preliminary results obtained in the murine studies, therapeutically efficient gene transfer and expression in human targeted cells must be proven. In recent years, effort has been spent on the identification of factors limiting gene transfer efficiency of haematopoietic stem cells. Increasing knowledge concerning haematopoiesis and gene transfer has helped in identifying a number of limiting factors. These factors as well as the strategies that showed increased retroviral infection of haematopoietic stem cells will be discussed. Finally, the results of the clinical trials will be reported.

Gene transfer and expression of exogenous genetic information coding for an immunogenic protein in antigen presenting cells (APCs) can promote an immune response. This was investigated by retroviral transfer of a marker gene into CD34+ derived APCs.To achieve long term expression of a specific transgene in APCs, G-CSF mobilized peripheral blood CD34+ cell populations were retrovirally transduced with the bacterial nlsLacZ, a marker gene used here as a model, in the presence of IL-3, IL-6, GM-CSF and SCF prior to being induced to differentiate into dendritic and macrophage cells by GM-CSF and TNF-a.Addition of IL-4 was found to induce dendritic differentiation preferentially by inhibiting proliferation and differentiation of the macrophage lineage. As assessed by X-Gal staining, LacZ gene expression was observed in cells from both the dendritic lineage (CD1a+/CD14-) which still exhibits the highest immunostimulatory activity in mixed lymphocyte reaction and from the macrophage lineage (CD1a-/ CD14+).This study sets out the possibility of transducing dendritic and macrophage progenitors present in the CD34+ cell population and in using a marker gene such as nlsLacZ to study gene expression in antigen presenting cell compartments.

Relative transduction efficiency with retroviral vector-producing clones was assayed by cocultivating TF-1, a human CD34+ hematopoietic cell line and YR-2, a sheep B-lymphoid cell line, with LacZ containing vector-producing cells, and then by scoring the percentage of X-Gal+ cells. At the same time, viral titer was estimated by titration assay with murine fibroblasts. Results clearly demonstrated a lack of correlation between viral titer and efficiency of transduction into hematopoietic cells, which depends neither on the type of packaging cell line, PG-13 and GP-envAM12 in this study, nor on the type of LacZ containing retroviral vector. These results strongly favor consideration of interactions between producers and target cells of the study for the screening of producing cell lines.

Retroviral-mediated gene transfer stably introduces exogenous genes into normal and neoplastic cells of the hematopoietic system.We used two retroviral vectors [the first, FLac, expresses a chimeric protein (Sh-ble::LacZ) between the product of the phleomycin resistance gene (Sh-ble) and the bacterial beta-galactosidase encoded by the LacZ gene; the second, NuNL vector, contains a fusion sequence (LacZ::Neo) that expresses the LacZ and the neomycin resistance genes] to transduce T lymphocytes derived from the peripheral blood of healthy human donors. Two lymphocyte activation procedures were employed: a) phytohemagglutinin/interleukin-2 (PHA/IL-2) polyclonal stimulation; b) allogeneic stimulation in a mixed irradiated or non irradiated lymphocyte reaction, both supplemented with IL-2 (MLR/IL-2). Infection was achieved by co-cultivating activated T cells with the producing amphotropic cell line pretreated with mitomycin C for 96 hours. Infection and transduction efficiency were assayed by LacZ gene expression, which is detected as indigo blue staining with the chromogenic substrate 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X..Gal).The highest percentage of transduced T cells was reached on the 3rd PHA/IL-2 and on 9th MLR/IL-2 activation days. In these conditions with FLac vector we obtained up to 80% X-Gal+ cells after PHA/IL-2 activation and 66% and 44%, respectively, with non irradiated and irradiated MLR/IL-2, respectively. Up to 40% X-Gal+ cells were obtained with NuNL vector after PHA/IL-2 stimulation, 40% with irradiated and 48% with non irradiated MLR/IL-2 activated cells. In term of transduction efficiency, large variability was observed among patients. There were no immunophenotypical differences between FLac or NuNL vector-transduced cells activated by either of the two techniques and the control cells.Our results indicate that: a) the use of FLac or NuNL vector retroviral-mediated gene transfer into T-lymphocytes derived from peripheral blood and stimulated by either PHA/IL-2 or a MLR produces a high percentage of transduced T cells; b) MLR is a good system for generating a transduced alloreactive lymphocyte population. The combination of high transduction efficiency and the capacity to obtain alloreactive transduced lymphocytes should open up the possibility of generating new in vitro and in vivo studies with selectable genes for in vivo therapeutic use.

To insert a new genetic information by gene transfer into haemopoietic stem cells would result in expression of the transgene in progenitors and progeny of cell blood lineages. If successfull, such an approach would open interesting prospectives in the field of experimental research and in the possibility to treat genetic defects affecting blood lineages such as immune deficiencies (ADA, SCID, AIDS) or enzymes defects. Moreover progenitors could be engineered to become more resistant to chemotherapy or oncogenic process. Many parameters and technical problems are still involved in this issue, including identification, isolation and selection of the most primitive progenitors, and search for the most efficient vectors to insert new genes into the target cells. So far retroviral vectors have been shown to be the most effective but search for better vectors are still underway. Peripheral blood stem cells isolated from patients stimulated by cytokines and/or chemotherapy appear interesting target cells for genetic manipulations aimed to correct an acquired or genetic defect.

Culture of human hematopoietic progenitors on a large scale could lead to several clinical applications within the near future, including the production of differentiated and functional cells, the increase in the number of early progenitors, especially stem cells, with such use as gene transfer, or the improvement of grafts used to limit the hematological toxicity associated with high-dose chemotherapy. In this case, one can still distinguish different objectives: improvement of grafts that contain low numbers of progenitors because of prior chemotherapies or because of marrow involvement for example, and qualitative changes in the graft content that would allow to envision the disappearance, or the further reduction, in the duration of absolute neutropenia that follows delivery of high dose chemotherapy ("nadir rescue"), despite substitution of mobilized blood cells to marrow cells and the in vivo use of hematopoietic growth factors. Additional advantages may be related to tumor purging in autologous expanded cells, and to the change in the ratio between hematopoietic progenitors and immunocompetent cells in allogeneic expanded populations. Therefore it appears that in vitro expansion currently raises two types of questions: the first ones are related to the definition of clinical or biological endpoints to be achieved, the second ones are related to "bioengineering", and deal with the efficiency and safety of progenitor cell cultures to be used for clinical applications. We here present preliminary results preparing future pilot clinical studies with ex vivo cultured human hematopoietic cells.