Cancer Gene Ther 1997 May;4(3):167-175

Transmissibility of murine stem cell virus-based retroviral vectors carrying both interleukin-12 cDNAs and a third gene: implications for immune gene therapy.

Lieu FH, Hawley TS, Fong AZ, Hawley RG

The combination of immunotherapy with conventional treatments such as radio- and chemotherapy may be necessary to eradicate minimal residual disease. Interleukin 12 (IL-12) is a heterodimeric cytokine composed of two subunits, p40 and p35. Coordinate expression of the IL-12 p40 and p35 genes in several solid tumor models has been found to induce strong and specific antitumor immune responses. In the interest of obtaining high level IL-12 expression in leukemia/lymphoma cells for use as vaccines in cancer immunotherapy, we evaluated three IL-12 retroviral vector designs based on the murine stem cell virus (MSCV) vector which efficiently transduces functional genes into normal hematopoietic cells. MSCVpac-mlL-12 and MIPV-mIL-12 contain an encephalomyocarditis virus internal ribosome entry site for internal translation of bicistronic mRNA transcripts, while MDCVpac-mIL-12 carries an expression cassette in the U3 region of the 3' long terminal repeat. We found that the MSCVpac-mIL-12 vector directed robust expression of both p40 and p35 genes in several murine tumor cell lines of hematopoietic origin, including a T-cell lymphoma, a B-cell lymphoma, and a plasmacytoma/myeloma. In contrast, genomic instability or promoter interference hampered p40 gene expression in cells transduced with the MIPV-mIL-12 and MDCVpac-mIL-12 vectors, respectively. These findings provide the basis for the design of IL-12 retroviral vectors for the treatment of hematologic malignancies in humans.

PMID: 9171935, UI: 97315943 Ann N Y Acad Sci 1996 Oct 31;795:341-345

Retroviral vectors for production of interleukin-12 in the bone marrow to induce a graft-versus-leukemia effect.

Hawley RG, Lieu FH, Fong AZ, Goldman SJ, Leonard JP, Hawley TS

PMID: 8958949, UI: 97118066

Proc Natl Acad Sci U S A 1996 Sep 17;93(19):10297-10302

Thrombopoietic potential and serial repopulating ability of murine hematopoietic stem cells constitutively expressing interleukin 11.

Hawley RG, Hawley TS, Fong AZ, Quinto C, Collins M, Leonard JP, Goldman SJ

Based on transplantation studies with bone marrow cultured under various conditions, a role of interleukin 11 (IL-11) in the self-renewal and/or the differentiation commitment of hematopoietic stem cells has been indicated. To better evaluate the in vivo effects of IL-11 on stem/progenitor cell biology, lethally irradiated mice were serially transplanted with bone marrow cells transduced with a defective retrovirus, termed MSCV-mIL-11, carrying the murine IL-11 (mIL-11) cDNA and the bacterial neomycin phosphotransferase (neo) gene. High serum levels (i.e., > 1 ng/ml) of mIL-11 in all (20/20) primary and 86% (12/14) of secondary long-term reconstituted mice, as well as 86% (12/14) of tertiary recipients examined at 6 weeks posttransplant, demonstrated persistence of vector expression subsequent to transduction of bone marrow precursors functionally definable as totipotent hematopoietic stem cells. In agreement with results obtained with human IL-11 in other myeloablation models, ectopic mIL-11 expression accelerated recovery of platelets, neutrophils, and, to some extent, total leukocytes while preferentially increasing peripheral platelet counts in fully reconstituted mice. When analyzed 5 months posttransplant, tertiary MSCV-mIL-11 recipients had a significantly greater percentage of G418-resistant colony-forming cells in their bone marrow compared with control MSCV animals. Collectively, these data show that persistent stimulation of platelet production by IL-11 is not detrimental to stem cell repopulating ability; rather, they suggest that IL-11 expression in vivo may have resulted in enhanced maintenance of the most primitive hematopoietic stem cell compartment. The prolonged expression achieved by the MSCV retroviral vector, despite the presence of a selectable marker, contrasts with the frequent transcriptional extinction observed with other retroviral vectors carrying two genes. These findings have potentially important implications for clinical bone marrow transplantation and gene therapy of the hematopoietic system.

PMID: 8816794, UI: 96413640
Oncogene 1996 Apr 4;12(7):1405-1415

Activation of the erythropoietin gene in the majority of F-MuLV-induced erythroleukemias results in growth factor independence and enhanced tumorigenicity.

Howard JC, Berger L, Bani MR, Hawley RG, Ben-David Y

Retroviral insertional activation of Fli-1 is the first detectable genetic alteration associated with F-MuLV-induced primary erythroleukemias, while mutations within p53 are only observed in Epo-dependent (ED) cell lines derived from syngeneic mice serially transplanted with F-MuLV-induced primary erythroleukemias. In this study we have determined the mechanism of growth factor independence in several Epo-independent (EI) cell lines established from adult mice previously injected with ED-erythroleukemia cell lines or serially transplanted primary tumor cells. Here we have shown constitutive expression of the Epo gene in 12 of 15 (80%) EI-erythroleukemia cell lines. Among these 12 cell lines, eight were shown to possess clonal rearrangement of the Epo gene which could be detected in the tumors used to establish the majority of these EI-cell lines. Analysis of the pattern of proviral integration revealed that the activation of the Epo gene in these cell lines is independent of retroviral insertional mutagenesis, but apparently the result of genomic rearrangements. Furthermore, the acquisition of growth factor independence by these leukemic cells confers a selective growth advantage in vivo and is associated with enhanced tumorigenicity. Together these observations suggest that the activation of the Epo gene in the large majority of these F-MuLV-induced erythroleukemic cell lines establishes an autocrine loop resulting in the constitutive activation of the Epo receptor signal transduction pathway, thereby conferring a growth and survival advantage in vito and in vitro.

PMID: 8622856, UI: 96203995