Transgene Expression, but Not Gene Delivery, Is Improved by Adhesion-Assisted Lipofection of Hematopoietic Cells
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Gene Therapy (1999) 6, 931–938 1999 Stockton Press All rights reserved 0969-7128/99 $12.00 http://www.stockton-press.co.uk/gt Transgene expression, but not gene delivery, is improved by adhesion-assisted lipofection of hematopoietic cells H Keller1, C Yunxu2, G Marit2, M Pla3, J Reiffers2, J The`ze1 and P Froussard1 1Unite´ d’Immunoge´ne´tique Cellulaire, De´partement d’Immunologie, Institut Pasteur, Paris; 2Laboratoire de Greffe de Moelle, URA CNRS 5540, Universite´ Victor Segalen Bordeaux 2, Bordeaux; and 3Immunoge´ne´tique de la souris, U93 INSERM, Hoˆpital Saint- Louis, Paris France In contrast to adherent cells, cells growing in suspension in up to 30% of transfected human primary T lymphocytes. and particularly hematopoietic cells, are notoriously difficult Flow cytometry analysis performed on T lymphocyte sub- to transfect in vitro using nonviral approaches. In the sets revealed that 8 and 9%, respectively, of CD4 and CD8 present study, the effect of cell adhesion on gene transfer cells could be transfected with a plasmid carrying the green efficacy was investigated by allowing hematopoietic cells fluorescent protein gene. Other adherent cells, such as to bind to an adherent cell monolayer (ACM) before being MS5 murine stromal cells or HeLa epithelial cells, were subjected to cationic liposome-mediated DNA transfer. also a compatible matrix for AAL. Moreover, the pCMV Human CD34 and T CD4 cell lines were cultivated on an plasmid was present in similar amounts in the nuclei of TF1 ACM constituted of murine fibroblast NIH3T3 cells and cells transfected in suspension or with the AAL procedure. transfected with a plasmid carrying the -galactosidase These data raise the possibility that cell matrix/ gene. X-gal staining showed that up to 27% of the cells hematopoietic cell interactions might govern expression of expressed the transgene. In contrast, less than 0.1% of the transgene in hematopoietic cells growing usually in these cells were positively transfected in suspension. This suspension, but not endocytosis of liposome/DNA particles adhesion-assisted lipofection (AAL) procedure was also and plasmid migration to the cell nucleus. successfully tested on blood lymphocytes, since it resulted Keywords: liposomes; cationic liposomes; adhesion-assisted lipofection; gene transfer; hematopoietic cells Introduction obtained using adherent cells lines.5,6 However, many cell types, particularly primary cells, blood lymphocytes and At present, methods using viral vectors are the most more generally hematopoietic cells growing in suspen- promising for delivery and expression of foreign genes sion are largely resistant to this form of gene transfer,7 in vitro and in vivo. However, safety concerns and the though successful transfection has been reported in difficulty in obtaining large quantities of recombinant mouse bone marrow cells.8 viral vectors have prompted the search for efficient, non- The sequence of cellular and molecular events underly- immunogenic and easy-to-prepare nonviral vector sys- ing the complex phenomenon of DNA transfer remains tems. Among them, cationic liposome-mediated gene highly speculative,9 but it is commonly accepted that 1–3 delivery, which was pioneered by Felgner, has been endocytosis is the main mechanism of entry of demonstrated to be an effective approach presenting a liposome/DNA particles,10–13 and relatively high trans- 4 low risk of intrinsic toxicity and pathogenicity. Cationic fection efficiency is due to the intrinsic membrane-rup- liposomes, which are easy to prepare on a large scale, turing capability of cationic liposomes as a result of form complexes with DNA through charge interactions destabilizing the plasma and/or endosome membrane.14–16 in such a way that DNA is protected from degradative In contrast to adherent cells, liposome/DNA particles activities and virtually any size of plasmid molecule can have been reported to bind inefficiently to the cell surface be packaged. Liposome/DNA complexes bind to the of lymphocytes, suggesting that particles attach to mem- negatively charged cell surface due to the presence of brane components involved in cell anchoring to the extra- excess positive charges in the complex; the nature of non- cellular matrix and composed of cadherins or proteogly- specific interactions results in the ability to drive cans present on adherent cells only.6 This weak expression of a foreign gene in host cells, including non- interaction between particles and membrane lympho- dividing cells, with the greatest transfection efficiency cytes would prevent endocytosis of liposome/DNA par- ticles and release of DNA into the cytosol of nonadherent cells. Because the ability of target cultured cells to be Correspondence: P Froussard, Unite´ d’Immunoge´ne´tique Cellulaire, De´partement d’Immunologie, Institut Pasteur, 75724 Paris cedex 15, transfected with the liposome/DNA complex relies France essentially on their adhesion capacity, we investigated Received 8 May 1998; accepted 21 December 1998 the role of cell adhesion in gene delivery to hematopoietic Adhesion-assisted lipofection in hematopoietic cells H Keller et al 932 cells. We primarily observed that hematopoietic cells could be transfected when cultured on an adherent cell matrix before being subjected to liposome-mediated DNA delivery. We then studied the usefulness of this new gene transfer approach in more detail using several types of established hematopoietic cell lines and primary lymphocytes of human origin, as well as different cell matrices. The role of cell adhesion in gene transfer optim- ization was also investigated. Results Coculture with adherent cells makes TF1 cells competent for gene transfer Figure 2 Analysis of -galactosidase transcripts in cells transfected with  Human TF1 cells, which grow in suspension, were liposome/pCMV complexes. Cells were transfected using the AAL pro- cedure or a standard lipofection (SdL) assay. Total RNA was purified from loaded on to an NIH3T3 ACM as described in Materials 5 × 105 transfected cells, subjected to DNase I and amplified by RT-PCR. and methods. The whole mixed cell population was then PCR products encoding -galactosidase DNA sequences were then elec- subjected to liposome-mediated DNA transfer using trophoresed, transferred to nitrocellulose and hybridized with a 32P-labeled lipofectamine/pCMV  complexes. Two days after trans- specific DNA probe. RNAs from untransfected cells and RNAs subjected fection, adherent cells were eliminated by adhesion on to both DNase 1 and RNase A did not show any RT-PCR products. plastic flasks and expression of the bacterial -galacto- sidase gene was assessed in purified TF1 cells and in pure by the anti-mouse mAb. In other respects, respectively TF1 cells transfected in suspension. Counting of dark 97.1% and 91.9% of purified transfected cells were blue-stained cells revealed that up to 26% of TF1 purified detected with anti-HLA class I and anti-CD34 mAbs, cells expressed -galactosidase activity transferred with compared with 99.5% and 94.6% for pure TF1 cells. The the pCMV vector. In contrast, less than 0.1% of blue same transfection study performed using MS5 stromal cells was observed when TF1 cells were transfected in cells as a matrix showed that virtually 100% of recovered suspension (Figure 1). Total RNA was purified from cells suspension cells were recognized with both anti-HLA harvested 48 h after transfection and -galactosidase class I and anti-CD34 mAbs (Figure 3b). Taken together, transcripts were subjected to a non-quantitative RT-PCR. these representative experiments show that NIH3T3 and Bacterial -galactosidase mRNA level in TF1 cells trans- MS5 contaminant cells are barely detectable in purified fected with AAL was 50 to 80% of what was found in suspension cells and that essentially pure TF1 cells can NIH3T3 cells; transgene transcripts were poorly detected be recovered after the three 2-h adhesion steps. in TF1 cells transfected in suspension (Figure 2). Thus, it is obvious that culture of TF1 cells on a NIH3T3 mono- AAL, but not adhesion, is optimized by prolonged layer authorizes a substantial improvement in liposome- coculture of TF1 cells with the cell matrix mediated gene transfer. In the interest of optimizing the AAL procedure, TF1 cells and NIH3T3 ACM were cocultured for increasing per- Purified TF1 cells transfected with AAL are essentially iods of time before being subjected to transfection. Pur- free of contaminating adherent cells ified TF1 cells were then assessed for bacterial -galacto- The purpose of these experiments was to assess the sidase gene expression. As shown in Figure 4, the efficiency of the three 2-h adhesion steps used at the end percentage of TF1 blue cells increased linearly for the first of the AAL procedure. In practice, the purity of the cell 6 to 8 h of coculture before reaching a plateau, but acqui- suspension was evaluated by detection of specific cell sition of the full competent state by TF1 cells required surface markers. As shown in Figure 3a, less than 1.1% overnight coculture with the ACM before transfection. of the purified AAL transfected cells could be recognized The ability of TF1 cells to bind to the ACM was studied as a function of the time to link the gene transfer efficiency to the adhesion/suspension state of TF1 cells. Surprisingly, 72% of TF1 cells were already bound to the cell matrix less than 2 h after being loaded on to the ACM. This indicates that prolonged coculture with the ACM is necessary for optimized liposome-mediated gene delivery and that adhesion of TF1 cells to the ACM pre- cedes the acquisition of the features rendering TF1 cells competent. CD34 and CD4 cell lines are efficiently transfected with AAL As a step towards examining primary cells, we examined  the ability of the AAL procedure to mediate gene deliv- Figure 1 Analysis of -galactosidase expression in purified TF1 cells after ery in three different CD34 cell lines (TF1, KG1a, K562 transfection with lipofectamine/pCMV complexes. TF1 cells were trans- fected in suspension (a) or using the adhesion-assisted lipofection pro- cells) and in Jurkat CD4 T lymphocytes using NIH3T3, cedure on to a NIH3T3 cell matrix (b).