Gene therapy and bone marrow transplantation

Retrovirus-mediated gene transfer into hematopoietic stem cells has been shown in mice, large animals, and humans. Transduction efficiency has been high in mice but has remained low in large animals and humans. Improved transduction efficiency into hematopoietic progenitor cells of large animals and humans has been achieved in vitro by enriching for CD34+ cells, adding growth factors to the transduction culture, extending the exposure time of hematopoietic cells to retrovirus particles, and by using retrovirus vectors pseudotyped with the gibbon ape leukemia virus envelope. Whether these modifications will also result in increased transduction of pluripotent hematopoietic stem cells has yet to be demonstrated by in vivo transplantation studies. Current transduction efficiency of hematopoietic stem cells in large animals and humans appears to be sufficiently high (0.1% to 1%) for gene marking studies. Efficiency needs to be further increased before gene transfer can be used for therapeutic applications.

Increased gene transfer into human hematopoietic progenitor cells by extended in vitro exposure to a pseudotyped retroviral vector

Retroviral-mediated gene transfer is the most attractive modality for gene transfer into hematopoietic stem cells. However, transduction efficiency has been low using amphotropic Moloney murine leukemia virus (MoMLV) vectors. In this study, we investigated modifications of gene transfer using amphotropic MoMLV vectors in cell-free supernatant for their ability to increase the currently low transduction of both committed hematopoietic progenitors, granulocyte-macrophage colony-forming units (CFU-GMs), and their precursors, long-term culture-initiating cells (LTC-IC). First, based on the observation that bone marrow cells express more gibbon ape leukemia virus (GALV) receptor (Glvr-1) than amphotropic receptor (Ram-1), PG13/LN, which is a MoMLV vector pseudotyped with the GALV envelope, was compared with the analogous amphotropic envelope vector (PA317/LN). Second, progenitor cell transduction efficiency was compared between CD34 enriched and nonenriched progenitor populations. Third, the duration of transduction in vitro was extended to increase the proportion of progenitor cells that entered cell cycle and could thereby integrate vector cDNA. In 20 experiments, 1 x 10(6) marrow or peripheral blood mononuclear cells (PBMCs)/mL were exposed to identical titers of pseudotyped PG13/LN vector or PA317/LN vector in the presence of recombinant human interleukin-1 (IL-1), IL-3, IL-6, and stem cell factor (SCF; c-kit ligand) for 5 days. 50% of fresh vector supernatant was refed daily. Hematopoietic progenitor cells as measured by G418-resistant granulomonocytic colony (CFU-GM) formation were transduced more effectively with PG13/LN (19.35%) than with PA317/LN (11.5%, P = .012). In 11 further experiments, enrichment of CD34 antigen positive cells significantly improved gene transfer from 13.9% G418-resistant CFU-GM in nonenriched to 24.9% in CD34-enriched progenitor cells (P < .01). To analyze gene transfer after extended growth factor-supported long-term culture, 1 x 10(6) marrow cells/mL were cultured with IL-1, IL-3, IL-6, and SCF (50 ng/mL each) for 1, 2, and 3 weeks. Fifty percent of PG13/LN supernatant with growth factors was refed on 5 days per week. Five percent of marrow CFU-GM and 67% of LTC-IC were G418 resistant at 1 week (n = 4), 60% of CFU-GM and 100% of LTC-IC were resistant at 2 weeks (n = 2) and 74% of CFU-GM (n = 4) and 82% of LTC-IC (n = 2) were resistant at three weeks.(ABSTRACT TRUNCATED AT 400 WORDS)

Retrovirus-mediated gene transduction into canine peripheral blood repopulating cells

Genetically marked peripheral blood progenitor cells were used to investigate their contribution to long-term hematopoietic reconstitution after autologous marrow and peripheral blood cell transplantation. After autologous marrow harvest and cryopreservation, canine peripheral blood progenitor cells were mobilized in three dogs by treatment with recombinant canine stem cell factor for 8 days. Peripheral blood mononuclear cells were collected and enriched for major histocompatibility complex (MHC) class II antigen-positive cells by avidin-biotin immunoadsorption, thereby enriching for repopulating cells. Subsequently, the cells were cocultivated for 24 hours on irradiated vector-producing packaging cells (PA317/LN), followed by an 11-day incubation in a vector containing long-term marrow culture system. On the day of transplantation, the animals were irradiated with 9.2 Gy total body irradiation (TBI), and transduced peripheral blood cells and untransduced cryopreserved marrow cells were infused within 2 hours of TBI. All three dogs engrafted. Two dogs are long-term survivors showing intermittently G418-resistant marrow-derived colony-forming unit granulocyte-macrophage colonies at a median of 1% and 2%, respectively (range, 1% to 10%), for now up to 48 weeks after transplantation. Neo-specific sequences were detected by polymerase chain reaction in peripheral blood granulocytes for now up to 65 weeks and in peripheral blood lymphocytes for up to 75 weeks after transplantation. Peripheral blood samples of the dogs were free of helper virus and no side effects from the transduction were observed. One of the three dogs died from chronic canine distemper sclerosing encephalitis on day 84, whereas the other two dogs are alive at 15 and 17 months. Our data show successful retroviral transduction of canine peripheral blood repopulating cells. Long-term persistence of marked myeloid and lymphoid cells after transplantation suggests that peripheral blood contains repopulating cells that contribute to long-term hematopoietic reconstitution after otherwise lethal TBI.

Use of a SCID mouse/human lymphoma model to evaluate cytokine-induced killer cells with potent antitumor cell activity

C.B-17 severe combined immune deficient (SCID) mice, which lack functional B and T lymphocytes, allow xenografts and, therefore, can be used to study the biology of human malignancies. Two different human B cell lymphoma cell lines, SU-DHL-4 and OCI-Ly8, which both harbor the t(14;18) chromosomal translocation, were injected into C.B-17 SCID mice. Mice injected intravenously or intraperitoneally developed tumors and died in a dose-dependent manner. The presence of tumor cells in various murine tissues could be demonstrated by a clonogenic tumor assay, staining of frozen sections with a monoclonal antibody (mAb) against a human B cell antigen (CD19), and with the polymerase chain reaction technique. A protocol using cytotoxic effector cells was developed and used to selectively deplete the tumor cells from bone marrow. These cells were developed by growing peripheral blood mononuclear cells in the presence of interferon gamma (IFN-gamma), anti-CD3 mAb, and interleukin 2 (IL-2). The timing of IFN-gamma treatment was critical and optimal if IFN-gamma was added before IL-2 treatment. The cells that were stimulated by IFN-gamma, followed by IL-2, could be expanded by treatment with a mAb directed against CD3. These cells could be further activated by IL-1, but not by tumor necrosis factor alpha. With this protocol, a tumor cell kill of 3 logs was obtained as measured by a clonogenic assay. Interestingly, despite their high cytotoxic activity against lymphoma cells, these cells had little toxicity against a subset of normal human hematopoietic precursor cells (granulocyte/macrophage colony-forming units). These cells were further tested by treating murine bone marrow contaminated with the human lymphoma cell line SU-DHL-4, and injecting these cells into SCID mice to assay for tumor growth in vivo. The animals injected with bone marrow contaminated with SU-DHL-4 cells had enhanced survival if the bone marrow was treated with the cytokine-induced killer cells before infusion. The SCID mouse provides a useful in vivo model for evaluation of new therapeutic approaches for lymphoma treatment. The cytokine-induced killer cells generated as described here could have an important impact on bone marrow purging for autologous bone marrow transplantation as well as for adoptive immunotherapy.

Use of the polymerase chain reaction to monitor the effectiveness of ex vivo tumor cell purging

The polymerase chain reaction (PCR) was used to detect residual malignant disease before and after ex vivo purging with monoclonal antibodies and complement or immunomagnetic treatment of BM samples contaminated with known numbers of t(14;18)-carrying tumor cells. Sensitivity of the PCR was demonstrated by detecting a specific t(14;18) amplification product in DNA extracted from a preparation consisting of one tumor cell among 10(5) normal cells. When BM contaminated with 1% to 5% t(14;18)-carrying cells from the B-cell lymphoma line SU-DHL-4 was subjected to two rounds of anti-B-cell pool of antibodies and complement (Ab-C) treatment a 3- to 4-log reduction of the pretreatment PCR signal was observed. A similar log-cell kill was detected using an independent clonogenic assay confirming the utility of the PCR approach. BM contaminated with a second B-cell lymphoma cell line, OCI-Ly8, was more resistant because a third cycle of Ab-C treatment was required to obtain a similar reduction in the PCR signal. A similar 4 logs of tumor cell removal was obtained using anti-B-cell antibodies conjugated to magnetic beads. These studies demonstrate that the t(14;18) PCR can be used to detect levels of tumor cells as low as 0.001%. This approach can be used to determine the effectiveness of BM purging in patients undergoing autologous BM transplantation as well as to assess the biologic role of minimal marrow disease.

Concurrent activation of c-myc and inactivation of bcl-2 by chromosomal translocation in a lymphoblastic lymphoma cell line

We have characterized a chromosomal translocation in a cell line (SU-DUL5) established from a patient with lymphoblastic lymphoma in which the c-myc gene on chromosome 8 was juxtaposed to a t(14;18). Cytogenetic analysis of this cell line showed 14q+, 18q-, and 8p+q+ marker chromosomes in the absence of t(14;18). Genomic Southern blot analysis showed juxtaposition of the immunoglobulin heavy chain joining region (JH) with chromosome 18 near the minor breakpoint cluster region (mcr) of the bcl-2 gene. There was also a rearranged c-myc gene detectable with a 5' c-myc probe. Molecular cloning studies showed that the c-myc gene was joined to chromosome 18 DNA. Nucleotide sequence analysis of cloned breakpoint DNA revealed that the crossover between chromosomes 8 and 18 occurred at the 3' end of the bcl-2 gene resulting in replacement of the bcl-2 gene on the 14q+ chromosome with the c-myc gene. As a result of this translocation the SU-DUL5 cell line contains no detectable bcl-2 mRNA or protein but has abundant levels of c-myc mRNA. Our data suggest that bcl-2 inactivation occurred simultaneously with c-myc translocation in a B cell lymphoblastic lymphoma.