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[SANET-MG] tobacco with a transgene to control AIDS



August 11, 2006

Prof. Joe Cummins

Tobacco modified with a transgene to control AIDS

There are currently 20 anti-human immune deficiency virus (HIV) drugs licensed for clinical use. The licensed drugs fall into five catagories: nucleoside reverse transcription inhibitors, non-nucleoside reverse transcription inhibitors, protease inhibitors and fusion inhibitors (such inhibitors prevent fusion of vial and cell membranes preventing viral entry into the cell). There are at least thirty drugs in clinical trials (I,II or III). Among these is compound cyanovirin-N a topical anti HIV microbiocide applied as a cream to vagina or anus(1,2). Results of a phase I clinical tial of cyanovirin-N was reported in 2006., 36 sexually abstaining women were tested in a double blind study showing that cyanovirin-N gels did not have undesirable side effects and retained protective levels of the biocide for at least 12 hours (3). Cyanovirin-N was first isolated from the from the cyanobacterium, Nostoc, it is a peptide of 101 amino acids it is resistant to degradation. It binds to N-linked mannose glycans such as those found on the HIV gp120 surface protein (4,5). Cyanovirin-R also prevents hepatitis C virus entry into cells (6).

Intravaginal and intrarectal biocides provide a relatively inexpensive way of preventing AIDS transmission . Condom use prevents spread of AIDS but use of such devices is erratic and not well suited for poor counties. Microbiocides such as cyanovirin-R may be widely distributed at relatively little cost and effectively control spread of AIDS (7,8).

Production of cyanovirin-N has required recombinant technology , first by production in recombinant microbes and later using recombinant plants. Before describing the recombinant microbes used to produce cyanovirin-N , the plant system will be discussed. The patent for a DNA sequence producing a glycosylation resistant form of cynaovirin-N protein (created by deleting 3 amino acid codons from the native gene was assigned to the USA Deaprtment of Health and Human Services)(9). That patented sequence was used to modify tobacco plants. The modified tobacco contained a cauliflower mosaic virus 35S promoter , a short mouse antibody (IgG) leader sequence to direct the recombinant protein to endomembrane system and genes for resistance to the antibiotics spectomycin and kanomycin, along with a nopaline transcription terminator seuqence. Recombinant tobacco plants grown in hydroponic solutions excreted cyanovirin-N into the culture medium. The tobacco plants produced up to 130ng cyanovirin-N/mg of leaf tissue (1.3g/Kg). The transgenic plants are expected to provide a high level of microbiocide production at a relatively low cost (10).

It is worth pointing out that the tropical plant Dorstenia contrajera a tropical plant used in traditional medicine was found to produce a strong anti-HIV peptide as did the tropical plant Treculia obovoidae (related to African breadfruit) (11). Such indigenous plants can be used to produce anti-HIV biocides immediately and in doing so can provide work for indigenous farmers. Lectins (sugar binding proteins) from Hippeastrum hybrid (Amaryllis) and Galanthus nivalis (snowdrop) were also found to potently inhibit HIV infection (12). Such wild plants could provide a source of livelihood for indigenous farmers while serving to alleviate the AIDS epidemic in developing countries.

Turning to the use of recombinant bacteria to produce cyanovirin-N , the recombinant bacterium Escherichia coli (E coli) provides a means of mass producing cyanovirin-N in liquid culture (13). Recombinant vaginal Lactobacilli for mucosal delivery of cyanovirin-N have been developed. A human isolate of Lactobacillus jenenii was modified with the cyanovirin-N gene to produce a biocide capable of colonizing the human vagina. The live microbiocide is capapble of producing a very inexpensive and stable protection against HIV infection in women (14,15). A commensal bacterium Streptococcus gordonii was modified with a cyanovirin-N gene and provided a system to deliver and maintain an HIV biocide to the vaginal mucosa (16). As an alternative approach, a portion of the HIV envelope glycoprotein (Env) protein known to neutralize the activity of HIV was introduced into a colonizing strain of E. coli. It blocks HIV entry by interfering with the conformational changes that drive the membrane fusion mechanism for HIV entry (17). Colonizing bacteria modified to become virus specific microbiocides provide a possible long term protection from HIV infection

Inexpensive microbiocides offer a global solution to the spread of HIV-AIDS to both men and women. Recombinant micro biocides , though appealing, are not yet tested adequately . In contrast , biocide containing tropical plants have been used as folk remedies for ages. A global strategy for implementing use of microbiocides to limit spread of HIV is likely to fail unless it is based on diverse biocides. Medicinal tropical plants shown to contain effective biocides can be cultivated by indigenous farmers and the product distributed through a local community at little cost and compelling immediacy. Once tested adequately the colonizing microbial biocides may prove effective provided that diversity to cope with viral mutation is respected. The tobacco based recombinant cyanovirin-N based biocide is being promoted to be a way of revitalizing the flagging tobacco industry. However, the system is not yet tested adequately and lacks the diversity required for long term AIDS protection. Implementing the use and global distribution of microbiocides should be based on common sense , not on corporate greed and public relations alone.

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