Macrophages sense pathogens via DNA motifs: induction of tumor necrosis factor-alpha-mediated shock

Cell surface components of pathogens, such as lipopolysaccharide (LPS), are an important signal for receptor-mediated activation of immune cells. Here we demonstrate that DNA of gram-positive and gram-negative bacteria or certain synthetic oligonucleotides displaying unmethylated CpG-motifs can trigger macrophages in vitro to induce nuclear translocation of nuclear factor-kappa B, accumulate tumor necrosis factor (TNF)-alpha mRNA and release large amounts of TNF-alpha. In vivo these events culminate in acute cytokine-release syndrome which includes systemic but transient accumulation of TNF-alpha. D-Galactosamine (DGalN)-sensitized mice succumb to lethal toxic shock due to macrophage-derived TNF-alpha resulting in fulminant apoptosis of liver cells. LPS and a specific oligonucleotide synergized in vivo as measured by TNF-alpha-release, suggesting that macrophages integrate the respective signals. The ability of macrophages to discriminate and to respond to bacterial DNA with acute release of pro-inflammatory cytokines may point out an important and as yet unappreciated sensing mechanism for foreign DNA.

Induction of humoral and cellular immune responses by vaccination with M. tuberculosis antigen 85 DNA

DNA vaccines have been demonstrated to be effective in inducing protective cell-mediated immune responses in animal models of infectious disease. In order to investigate this approach for potential use as a vaccine for tuberculosis, DNA constructs encoding Mycobacterium tuberculosis antigen 85A (Ag85A) were prepared. Expression of Ag85A in mammalian cells was demonstrated by transient transfection of cells in vitro. Intramuscular injection of Ag85A DNA vaccines resulted in the generation of anti-Ag85A antibodies and robust cell-mediated immune responses, as measured by lymphoproliferation of spleen cells in vitro upon specific antigen restimulation, leading to protection in animal challenge models. Therefore, the technique of DNA vaccination is effective in inducing relevant immune responses for protection against tuberculosis and may be used to identify the protective antigens of M. tuberculosis.

Induction of NK activity in murine and human cells by CpG motifs in oligodeoxynucleotides and bacterial DNA

We have recently shown that oligodeoxynucleotides (ODN) containing unmethylated CpG dinucleotides (CpG motif) can induce B cells to proliferate, differentiate, and secrete cytokines. In this study we demonstrate that CpG motifs contained in ODN as short as 15 bases in length were quite effective at inducing NK cell lytic activity in vitro in both human and murine lymphocytes. Such ODN were also effective at inducing NK lytic activity, in vivo, in mice. Experiments designed to determine the cellular and cytokine requirements for NK cell induction revealed that B and T cells are not necessary, that the ODN do not augment the activity of highly purified NK cells, and that the ODN augment NK cell activity indirectly by inducing the secretion of IL-12, IFN-alpha beta, and TNF-alpha. Various ODN sequences were prepared to determine the optimal ODN length, motif, palindrome, backbone modification, and dose requirements. We found no requirement for a palindromic sequence but a definite requirement for an unmethylated CpG motif. While necessary, however, a CpG motif was not sufficient for NK cell induction. Instead, there appeared to be stringent requirements for the immediate flanking bases at the 5' and 3' ends as well as for flanking sequences outside the immediate 5' and 3' bases. In particular poly(G) ends seemed to exert a complex qualitative and quantitative effect which could be up- or down-modulating depending on whether the ODN backbone was phosphorothioate modified or not.

Vaccination against tuberculosis by DNA injection

There are 3 million deaths per annum worldwide due to tuberculosis, and AIDS is compounding the problem. A better vaccine than the live mycobacterium currently in use, bacillus Calmette-Guérin (BCG), is needed. When mice were injected with plasmid DNA encoding a single mycobacterial antigen (65-kDa heat shock protein, hsp65) they made specific cellular and humoral responses to the protein and became immune to subsequent challenge with Mycobacterium tuberculosis. Protection was equivalent to that obtained by vaccinating with live BCG, whereas immunizing with the protein was ineffective. Protection was also obtained with DNA encoding another mycobacterial antigen (36-kDa proline-rich antigen). These results suggest that DNA vaccination might yield improved vaccines to replace BCG.

Immunogenicity and protective efficacy of a tuberculosis DNA vaccine

Tuberculosis is the most widespread and lethal infectious disease affecting humans. Immunization of mice with plasmid DNA constructs encoding one of the secreted components of Mycobacterium tuberculosis, antigen 85 (Ag85), induced substantial humoral and cell-mediated immune responses and conferred significant protection against challenge with live M. tuberculosis and M. bovis bacille Calmette-Guérin (BCG). These results indicate that immunization with DNA encoding a mycobacterial antigen provides an efficient and simple method for generating protective immunity and that this technique may be useful for defining the protective antigens of M. tuberculosis, leading to the development of a more effective vaccine.

Improved electro-transformation of highly DNA-restrictive corynebacteria with DNA extracted from starved Escherichia coli

Differences of up to 33 000-fold in electro-transformability of highly DNA restrictive corynebacteria are observed in the DNA of a shuttle plasmid extracted from Escherichia coli hosts propagated in different nutritional conditions. Growth of the host in minimal medium increases plasmid transformability, whereas growth on rich media decreases it. In the E. coli DH5 alpha host, the starvation-dependent increase DNA transformability is reverted by supplementing with methionine, an obligate 5-adenosyl-methionine (SAM) precursor. This suggests that an E. coli nutritionally modulated SAM-dependent DNA-methyltransferase may be involved in this phenomenon.

Bacterial DNA induces NK cells to produce IFN-gamma in vivo and increases the toxicity of lipopolysaccharides

Microbial products released during bacterial infection induce cytokine-mediated inflammatory responses that can be protective, but excessive release of inflammatory cytokines may promote development of the sepsis syndrome. We examined the ability of bacterial DNA to induce in vivo cytokine release and to potentiate the toxicity of LPS. Intravenous treatment of mice with Escherichia coli (EC) DNA, but not calf thymus (CT) DNA, induced a rapid (within 4 h) dose-dependent increase in serum IFN-gamma and splenic IFN-gamma-forming cells. Over 90% of splenic IFN-gamma-producing cells were identified by surface phenotype as NK cells. Mice also mounted an IFN-gamma response following challenge with 20-base oligonucleotide that contained an internal CG motif (but did not respond to a control oligonucleotide). Treatment of mice with EC DNA followed by a sublethal LPS challenge resulted in a 3-fold increase in the peak serum level of TNF-alpha and a 10-fold increase in the peak level of IL-6 compared with mice that received CT DNA followed by LPS. Mice treated with EC DNA followed by LPS showed 75% mortality, compared with no deaths in mice treated with CT DNA followed by LPS. EC DNA/LPS treatment of mice with disrupted IFN-gamma genes resulted in a 5% mortality while 59% of similarly treated +/+ mice died. Thus, bacterial DNA induces in vivo release of IFN-gamma which, in turn, is associated with an increase in LPS-induced TNF-alpha and IL-6 release, and with increased sensitivity to the toxic effects of LPS.

Depth-targeted efficient gene delivery and expression in the skin by pulsed electric fields: an approach to gene therapy of skin aging and other diseases

The ability to target genes to the various layers, cell types, and appendages of the skin could be used to correct disorders, including those of aging such as wrinkling, as well as utilize specific cell types for production molecules useful elsewhere in the body. However, the stratum corneum acts as a significant physical barrier to gene transfer into the skin. In this report we describe the ability to target and express the lacZ reporter gene to various depths of the dermis region in hairless mice. Skin-depth targeting is achieved by varying pulsed electrical fields and subsequent pressure from caliper-type electrodes on topically applied naked lacZ gene constructs. With electric pulses and extended pressure, the maximum depth of lacZ expression in the dermis and transfected cells was achieved at 370 micron and 457 cells/mm2, respectively. Gene expression was observed only the hair follicles in the case of the control.

Protection against mycoplasma infection using expression-library immunization

As is evident from the human immunodeficiency virus epidemic, there is no systematic method for producing a vaccine. Genetic immunization is a new approach to vaccine production that has many of the advantages of live/attenuated pathogens but no risk of infection. It involves introducing DNA encoding a pathogen protein into host cells and has shown promise in several disease models. Here we describe a new method for vaccine development, expression-library immunization, which makes use of the technique of genetic immunization and the fact that all the antigens of a pathogen are encoded in its DNA. An expression library of pathogen DNA is used to immunize a host thereby producing the effects of antigen presentation of a live vaccine without the risk. We show that even partial expression libraries made from the DNA of Mycoplasma pulmonis, a natural pathogen in rodents, provide protection against challenge from the pathogen. Expression library immunization may prove to be a general method for vaccination against any pathogen.

Gene delivery into the central nervous system by nasal instillation in rats

Replication-deficient adenoviruses have been used successfully to transfer foreign DNA into postmitotic cells. This article demonstrates that it is possible to transfer the Escherichia coli lacZ gene in vivo into the central nervous system structures of rats after nasal instillation of replication-defective adenoviral vector AdRSV beta gal. Mitral cells from the olfactory bulb, neurons from the anterior olfactory nucleus, locus coeruleus and area postrema expressed beta-galactosidase for at least 12 days. No cytopathic effect was observed in the CNS structures studied at the viral titer used (1-3 x 10(9) plaque-forming units (p.f.u.)). This method could be useful for the gene therapy of diseases affecting different CNS structures.

The feasibility of targeted selective gene therapy of the hair follicle

Loss of hair and hair colour is associated with ageing, and when it involves the scalp hair, it can be distressing to both sexes. Hair loss resulting from cancer chemotherapy is particularly distressing. However, safe, effective therapies directed to hair have only just started to be developed. The hair follicle is a complex skin appendage composed of epidermal and dermal tissue, with specialized keratinocytes, the hair matrix cells, forming the hair shaft. Specific therapy of the hair follicle depends on selective targeting of specific cells of the hair follicle. We have developed the histoculture of intact hair-growing skin on sponge-gel matrices. We have recently found in histocultured skin that liposomes can selectively target hair follicles to deliver both small and large molecules. That liposomes can target the hair follicle for delivery has been confirmed independently. Two decades ago we introduced the technique of entrapping DNA in liposomes for use in gene therapy. In this report we describe the selective targeting of the lacZ reporter gene to the hair follicles in mice after topical application of the gene entrapped in liposomes. These results demonstrate that highly selective, safe gene therapy for the hair process is feasible.

Delivery of plasmid DNA to glial cells using pH-sensitive immunoliposomes

Immunoliposomes were constructed with an antibody specific to glial cells. They were used to examine the specificity and efficacy of cell type plasmid transfection. Liposomes contained a beta-galactosidase gene under control of an SV-40 promotor. Two different monoclonal antibodies of a different subclass, IgM and IgG, were examined for their targeting ability using immunoliposomes. Cultured C6 glioma (specific target cell type) and NIH 3T3 (control cell type, fibroblast) cells were transfected using these immunoliposomes. Results indicate a three-fold increase in transfection by the glial specific immunoliposomes, "gliasomes", in glial cell culture over control liposomes. Gliasomes were exposed to NIH 3T3 cells and showed no enhanced transfection over control liposomes. Gliasomes were tested for their specificity by the addition of excess antibody to the cell culture in order to saturate specific receptors on C6 glioma cells. Results indicate a reduced transfection, nearly three-fold, in cells that were saturated with excess antibody prior to exposure to the immunoliposomes.

Biolistic transformation of conidia of Botryotinia fuckeliana

Botryotinia fuckeliana, the causal agent of grey mould, was biolistically transformed to hygromycin B resistance using a plasmid (pOHT) containing a bacterial hygromycin phosphotransferase gene fused to regulatory sequences from Aspergillus nidulans. Multiple copies of the plasmid, precipitated onto tungsten particles, were delivered into the conidia by a helium-driven gene gun. Southern analysis showed that the plasmid was integrated into the fungal genome at one single locus. After five subsequent transfers on selective medium, all transformants were mitotically stable. When propagated on non-selective medium, four out of eight transformants retained their resistance to hygromycin B. Southern analysis of the fifth generation of transformants showed that no genetic rearrangements occurred during vegetative growth of stable transformants.

Introduction of exogenous DNA into somatic and germ cells of chickens by microinjection into the germinal disc of fertilized ova

The plasmid DNA, pAcZ, containing Escherichia coli beta-galactosidase (lacZ) gene under the control of chicken beta-actin gene promoter was injected in a linearized form into the germinal disc of fertilized chick ova at the single-cell stage. The manipulated embryos were cultured by the method of Naito et al. (1990) until hatching. The rate of hatching was 11.8% (31/263), and 19 males and 6 females were matured. DNA from blood and semen samples of the 25 matured chickens was analyzed for the presence of the injected DNA by Southern blot hybridization. The injected DNA was detected in the blood DNA of one male and in the sperm DNA of another male up to 13 months after hatching, indicating that the injected DNA was stably maintained in these chickens. Restriction digestion analysis of the injected DNA suggested that it was not rearranged and was organized as head-to-tail multimers. The copy numbers of the DNA were 0.07-0.02 in the blood DNA of one male per diploid genome, and 0.02-0.015 in the sperm DNA of another male, indicating that the exogenous DNA was present in limited populations of blood and sperm cells.

Quantitative determination of adenovirus-mediated gene delivery to rat cardiac myocytes in vitro and in vivo

To optimize the use of modified adenoviruses as vectors for gene delivery to the myocardium, we have characterized infection of cultured fetal and adult rat cardiac myocytes in vitro and of adult cardiac myocytes in vivo by using a replication-defective adenovirus carrying the chloramphenicol acetyltransferase (CAT) reporter gene driven by the cytomegalovirus promoter (AdCMVCATgD). In vitro, virtually all fetal or adult cardiocytes express the CAT gene when infected with 1 plaque-forming unit of virus per cell. CAT enzymatic activity can be detected in these cells as early as 4 hr after infection, reaching near-maximal levels at 48 hr. In fetal cells, CAT expression was maintained without a loss in activity for at least 1 week. Using in vitro studies as a guide, we introduced the AdCMVCATgD virus directly into adult rat myocardium and compared the expression results obtained from virus injection with those obtained by direct injection of pAdCMVCATgD plasmid DNA. The amount of CAT activity resulting from adenovirus infection of the myocardium was orders of magnitude higher than that seen from DNA injection and was proportional to the amount of input virus. Immunostaining for CAT protein in cardiac tissue sections following adenovirus injection demonstrated large numbers of positive cells, reaching nearly 100% of the myocytes in many regions of the heart. Expression of genes introduced by adenovirus peaked at 5 days but was still detectable 55 days following infection. Adenoviruses are therefore a very useful tool for high-efficiency gene transfer into the cardiovascular system.

Induction of T-cell-mediated immunity against MethA fibrosarcoma by intratumoral injections of a bacillus Calmette-Guérin nucleic acid fraction

MY-1, which consists of DNA and RNA extracted and purified from bacillus Calmette-Guérin (BCG), has been shown to have strong antitumor activity against various experimental tumors. To examine the role of T cells in the antitumor mechanism of MY-1, the effect of MY-1 injection on the development of tumor-specific immunity against MethA fibrosarcoma was investigated. MY-1 injections inhibited tumor growth less effectively in T-cell-deficient nude mice than in normal BALB/c mice. MethA tumor growth was suppressed after inoculation with L3T4-positive lymphocytes from tumor-bearing mice treated with MY-1. MethA-specific delayed-type hypersensitivity was also detected in tumor-bearing mice treated with MY-1. Immunohistochemical analyses showed that many L3T4-positive and a few Lyt2-positive cells infiltrated the regressing tumors. These results indicate that intratumoral MY-1 injections induce a MethA-specific, L3T4-positive cell-mediated, delayed-type hypersensitivity, which is necessary for the tumor regression.

Characterization of recombination intermediates from DNA injected into Xenopus laevis oocytes: evidence for a nonconservative mechanism of homologous recombination

Homologous recombination between DNA molecules injected into Xenopus laevis oocyte nuclei is extremely efficient if injected molecules have overlapping homologous ends. Earlier work demonstrated that ends of linear molecules are degraded by a 5'----3' exonuclease activity, yielding 3' tails that participate in recombination. Here, we have characterized intermediates further advanced along the recombination pathway. The intermediates were identified by their unique electrophoretic and kinetic properties. Two-dimensional gel electrophoresis and hybridization with oligonucleotide probes showed that the intermediates had heteroduplex junctions within their homologous overlaps in which strands ending 3' were full length and those ending 5' were shortened. Additional characterization suggested that these intermediates had formed by the annealing of complementary 3' tails. Annealed junctions made in vitro were rapidly processed to products, indicating that they are on the normal recombination pathway. These results support a nonconservative, single-strand annealing mode of recombination. This recombination mechanism appears to be shared by many organisms, including bacteria, fungi, plants, and mammals.

Delivery systems for gene therapy

Introduction of foreign genes into mammalian cells in vitro has been accomplished previously by a variety of methods. The few techniques that have been developed for transfection of mammalian cells in vivo, are technically difficult or lack cell specificity. We have developed a soluble, targetable DNA carrier system consisting of an asialoglycoprotein covalently coupled to a polycation. The strategy was based on: 1) the presence of unique receptors on hepatocytes which internalize galactose-terminal (asialo-)glycoproteins; 2) polycations can bind DNA in a non-covalent, non-damaging interaction. Using chloramphenicol acetyltransferase (CAT) as a marker gene, specific delivery and expression of CAT was demonstrated in vitro using asialoglycoprotein receptor (+) and (-) cell lines. Intravenous injection of conjugate-DNA complexes in rats resulted in detection of CAT DNA sequences in liver 10 min later by dot blots with a CAT cDNA probe. CAT enzyme activity 24 hrs later was found specifically in liver but no other tissues or control livers. Targeted hepatic CAT expression was transient, maximal at 24 hrs but declined to barely detectable levels by 96 hrs. Persistent foreign gene expression was achieved by injection of DNA complex followed by 67% partial hepatectomy. High levels of hepatic CAT activity were detected through 11 weeks post-hepatectomy. The data indicate that a targetable gene delivery system can permit in vivo expression of an exogenous gene after simple intravenous injection. The foreign gene expression can be enhanced and made to persist by induction of hepatocyte replication.

Immunotherapeutic potential in guinea-pig tumor model of deoxyribonucleic acid from Mycobacterium bovis BCG complexed with poly-L-lysine and carboxymethylcellulose

In vivo antitumor activity of a deoxyribonucleic acid fraction obtained from Mycobacterium bovis BCG (named MY-1) increased when it was complexed with poly-L-lysine (poly LL) solubilized by addition of carboxymethylcellulose (CMC). The complex of MY-1 and poly LL/CMC induced interferon in vivo at a low dose of MY-1 which alone exerted no IFN induction. With Line 10 hepatoma (L10) which is syngeneic with strain 2 guinea pigs, it was demonstrated that repeated intralesional injections of the complex resulted in delay of tumor growth and complete cure of animals from L10 tumor inoculated. Similar treatment of the animals with the same amount of MY-1 or poly LL/CMC alone had little therapeutic effect on the tumor growth.

Fusion-mediated microinjection of liposome-enclosed DNA into cultured cells with the aid of influenza virus glycoproteins

Influenza viruses were able to mediate fusion of DNA-loaded liposomes with living cultured cells such as monkey COS-7 cells. This was inferred from the appearance of CAT activity in recipient cells incubated with the combination of influenza viruses and liposomes loaded with the plasmid pSV2CAT. Influenza virions were found to be as efficient as intact Sendai virions in mediating microinjection of foreign DNA into living cells. Also, reconstituted envelopes bearing either influenza glycoproteins or the combination of Sendai and influenza glycoproteins were highly efficient in promoting fusion of loaded liposomes with recipient cells. Introduction of DNA into cultured cells required the presence of an active influenza fusion protein; namely, an active HA glycoprotein. Very little or no CAT activity was observed in cells incubated with loaded liposomes and unfusogenic influenza viruses. The virus-induced fusion event probably occurs within intracellular organelles such as endosomes following receptor-mediated endocytosis of virus-liposome complexes. This is due to the fact that the viral fusion glycoprotein is activated only at acidic pH values such as those which characterize the intraendosomal environment. Results of the present work demonstrate for the first time microinjection of foreign DNA via fusion with membranes of intracellular organelles. The potential of the present system to serve as a biological carrier for in vivo use is discussed.

Rapid and apparently error-prone excision repair of nonreplicating UV-irradiated plasmids in Xenopus laevis oocytes

Repair of UV-irradiated plasmid DNA microinjected into frog oocytes was measured by two techniques: transformation of repair-deficient (delta uvrB delta recA delta phr) bacteria, and removal of UV endonuclease-sensitive sites (ESS). Transformation efficiencies relative to unirradiated plasmids were used to estimate the number of lethal lesions; the latter were assumed to be Poisson distributed. These estimates were in good agreement with measurements of ESS. By both criteria, plasmid DNA was efficiently repaired, mostly during the first 2 h, when as many as 2 x 10(10) lethal lesions were removed per oocyte. This rate is about 10(6) times the average for removal of ESS from repair-proficient human cells. Repair was slower but still significant after 2 h, but some lethal lesions usually remained after overnight incubation. Most repair occurred in the absence of light, in marked contrast to differentiated frog cells, previously shown to possess photoreactivating but no excision repair activity. There was no increase in the resistance to DpnI restriction of plasmids (methylated in Escherichia coli at GATC sites) incubated in oocytes; this implies no increase in hemimethylated GATC sites, and hence no semiconservative DNA replication. Plasmid substrates capable of either intramolecular or intermolecular homologous recombination were not recombined, whether UV-irradiated or not. Repair of Lac+ plasmids was accompanied by a significant UV-dependent increase in the frequency of Lac- mutants, corresponding to a repair synthesis error frequency on the order of 10(-4) per nucleotide.

The antibody response of normal mice to immunization with single-stranded DNA of various species origin

To further assess the mechanism for the induction of anti-DNA antibodies, the response of BALB/c mice to immunization with single-stranded DNA of various species origin was determined. Anti-DNA levels of mice immunized with Escherichia coli DNA as complexes with methylated BSA in adjuvant were significantly greater by ELISA than those from mice immunized similarly with calf thymus DNA. Furthermore, comparison of the responses of mice immunized with complexes of DNA from calf thymus, chicken blood, Clostridium perfringens, E. coli, human placenta, or salmon testes indicated that the bacterial DNAs induced the highest antibody levels. The antibody response to E. coli DNA was shown by inhibition ELISA to have two populations, one binding unique determinants in E. coli DNA and the other cross-reactive with determinants expressed on all DNAs tested. These results indicate that DNA molecules, when complexed to a protein carrier, differ in their immunogenic potential, likely because of the presence of unique sequences or structures rarely presented by mammalian host DNA.

Current status of melanoma treatment with interferon, cytokines and other biologic response modifiers in Japan

This paper introduces the current status of melanoma treatment with various biologic response modifiers (BRMs) in Japan, with an emphasis on the clinical results of Interferon therapies. The authors also refer briefly to the current situation of interleukin-2 (IL-2) and tumor necrosis factor (TNF) in Japan. Many BRMs have been used in treatment of melanoma, e.g., IFN, IL-2, TNFs, BCG, MY-1 (DNA extracted from BCG), WPG (CWs of Bifidobacterium infantis, ATCC 15697), OK-432 (Picibanil, Streptococcus pyogenes preparation), bestatin, and forphenicinol. Some of these have completed clinical trials, while others are still undergoing clinical testing. Among IFN-alpha, beta, and gamma, intralesional administration of natural IFN-beta was found to be more effective than IFN-alpha for metastatic skin melanoma, the survival time of patients being prolonged by the administration of IFN-beta. IFN-gamma appeared to have lower efficacy than IFN-alpha and beta. The frequency of BRM application to melanoma treatment will increase. The authors foresee that combinations with radio- and/or other chemotherapy will be more common than the single use of a BRM, especially in the case of IFN.

Induction of anti-double stranded DNA antibodies in normal mice by immunization with bacterial DNA

Because of recent observations suggesting that bacterial DNA is immunogenic, the induction in normal mice of antibodies to Escherichia coli (EC) dsDNA was investigated. BALB/c and C57BL/6 mice were immunized with dsEC or ds calf thymus (CT) DNA complexed to methylated BSA in adjuvant; antibody responses were measured by ELISA. In both strains, dsEC DNA immunization induced a much higher anti-dsDNA response to dsEC DNA than did dsCT DNA immunization. Neither immunized group showed an appreciable antibody response when tested on dsCT DNA. Anti-dsDNA antibodies were also demonstrated by ELISA using synthetic DNA duplexes as well as a filter binding assay using 3H-labeled dsEC DNA as Ag. These results suggest that bacterial dsDNA is immunogenic and that at least some anti-dsDNA specificities can arise by immunization.

Optimal parameters for the polybrene-induced DNA transfection of diploid human fibroblasts

Recently it has been shown that Polybrene, in conjunction with dimethyl sulfoxide (DMSO) shock, can markedly increase frequency of DNA transfection of chicken embryo fibroblasts as compared with the frequency obtained with the standard calcium phosphate protocol. We have adapted this procedure for use with diploid human fibroblasts. Using plasmid DNA containing a dominant selectable marker gene (resistance to Geneticin), we have determined that treatment of the cells for 6 h in culture medium containing Polybrene at a concentration of 2 to 5 micrograms/ml, followed by a 4-min shock with 30% DMSO, resulted in the highest yield of transfectants, ca. 400/10(6) cells treated with as little as 100 ng of plasmid DNA. The selective agent could be added immediately after the DMSO shock. This allows transfection and selection to be carried out in the same dishes and ensures that each clone represents a unique event.

Factors affecting the efficiency of introducing foreign DNA into mice by microinjecting eggs

Microinjection of foreign DNA into fertilized mammalian eggs is a convenient means of introducing genes into the germ line. Some of the more important parameters that influence successful integration of foreign DNA into mouse chromosomes are described. The effects of DNA concentration, size, and form (supercoiled vs. linear with a variety of different ends) are considered as well as the site of injection (male pronucleus, female pronucleus, or cytoplasm) and buffer composition. The optimal conditions for integration entail injection of a few hundred linear molecules into the male pronucleus of fertilized one-cell eggs. Under these conditions about 25% of the mice that develop inherit one or more copies of the microinjected DNA. The overall efficiency also depends on the choice of mouse strains; for example, generating transgenic mice that express foreign growth hormone genes is about eight times easier with C57/BL6 X SJL hybrid mice than with inbred C57/BL6 mice.