|autoantigens & type I diabetes | antibodies and HIV | antibodies and cancer|
» recombinant antibodies:
» autoantigens and type I diabetes:
» antibodies and HIV:
» antibodies and cancer treatment:
antibodies and HIV treatmentHIV and Antibodies in Transgenic Plants
Human immunodeficiency virus (HIV) is one of the leading causes of death in the world. In 2003 alone, there were approximately 37 million adults and 2.5 million children under the age of 15 who were infected, while approximately 4.2 million adults and 700,000 children were newly infected. The only treatment currently available against HIV is HAART (highly active antiretroviral therapy), which requires greater than 90% adherence for the rest of the infected individual's life as well as costs of around $1500 per month. Several new treatments are currently in research, however. These include treatments in which plant-produced pokeweed antiviral protein (PAP), gp120, Tat, and Cyanovirin-N are used to inhibit HIV infection. This review will focus on PAP since it is the most relevant to antibodies and immunotherapy.
Pokeweed antiviral protein inhibits protein translation
PAP is a protein that is found naturally in the roots and leaves of the pokeweed plant, Phytolacca americana [2,3]. It functions to inactivate prokaryotic and eukaryotic ribosomes by removing a specific adenine residue from the larger rRNA to generate a depurinated ribosome no longer capable of binding to the elongation factor 2 (EF-2)-GTP complex. This step is crucial to protein synthesis by allowing the translocation of the nascent protein polypeptide from one site in the ribosome to another[2,3]. The current hypothesis is that PAP is released into the plant cell cytoplasm during mechanical disruption of the plant cell wall, such as during vector innoculation or viral infection, and thereafter inhibits viral growth. In the animal cell, however, evidence suggests that the inhibition of viral growth by PAP is through some mechanism other than that of protein synthesis: PAP's inhibition of viral growth far surpasses its ability to inhibit protein synthesis.
PAP inhibits many viruses when conjugated with monoclonal antibodies
PAP has been made in transgenic potato and tobacco plants[2,3]. In these plants, PAP has been shown to be an effective antiviral compound against poliovirus, herpes simplex virus, cytomegalovirus, influenza virus and HIV-1. This broad-spectrum effect of PAP makes it a particularly strong candidate for the production of a microbicide that can protect individuals against the more common sexually transmitted diseases (STDs). Rajamohan et al. found that PAP conjugation to monoclonal antibodies that recognize CD4, CD5 or CD7 antigens on the surface of lymphocytes was crucial to its inhibition of HIV-1 development in CD4+ cells infected with HIB-1. They found the same result in activated T-cells from asymptomatic HIV-1-seropositive donors as well.
Animal models and human epithelial cell systems show that PAP is relatively safe
Research within the last five years has shown some tentative evidence for the safety of PAP use inside the body: PAP can protect against HIV infection without affecting the motility or function of sperm in mice and humans[4,5]; it does not cause cytotoxicity or the development of lesions in mouse, human and rabbit vaginal epithelium [4,5,6], but there was mild to moderate vaginal irritation in rabbits. Therefore current research suggests that PAP is a good candidate for use as a microbicide, but requires careful monitoring to prevent irritation.
There have been several advancements in HIV research within the last decade. In particular, the production of PAP in transgenic potatoes and tobacco plants represents a promising alternative in HIV anti-viral therapy. Key to PAP's activity, however, seems to be its function in relation to its presentation on antibodies. However, there are several other developments in anti-HIV therapy that were not covered in this report. For example, Cyanovirin-N molecule is another potentially useful microbicide that inhibits HIV entry into epithelial cells by binding to the viral gp120 cell surface protein and preventing its interaction with epithelial cell receptors. As well, Tat protein and gp120 that are produced in transgenic spinach and gp120, respectively, have been used as antigens in vaccines to induce host immune response against the virus. It can be seen that there are many potential HIV treatments in development along with PAP.
references1) Cochrane A. Personal Communication. February 2006.
2) Rajamohan F, Engstrom CR, Denton TJ, Engen LA, Kourinov I, Uckun FM. High-level expression and purification of biologically active recombinant pokeweed antiviral protein. Protein Expression and Purification 1999, 16: 359-368.
3) Tumer NE, Hwang DJ, Bonness M. C-terminal deletion mutant of pokeweed antiviral protein synthesis inhibits viral infection but does not depurinate host ribosomes. Proc Natl Acad Sci USA 1997, 94: 3866-3871.
4) D'Cruz OJ, Uckun FM. Pokeweed antiviral protein: a potential nonspermicidal prophylactice antiviral agent. Fertility and Sterility 2001, 75:106-14.
5) D'Cruz OJ, Waurzyniakt B, Uckun FM. A 13-week subchronic intravaginal toxicity study of pokeweed antiviral protein in mice. Phytomedicine 2004, 11:342-51.
6) D'Cruz OJ, Waurzyniakt B, Uckun FM. Mucosal toxicity studies of a gel formulation of native pokeweed antiviral protein. Toxicol Pathol 2004, 32: 212-21.
7) Sexton A, Drake PM, Mahmood N, Harman SJ, Shattock RJ, Ma JK-C. Transgenic plant production of Cyanovirin-N, an HIV microbicide. The FASEB Journal 2006, 20: 356-8.
8) Karasev AV, Foulke S, Wellens C, Rich A, Shon KJ, Zwierzynski I, Hone D, Koprowski H, Reitz M. Plant based HIV-1 vaccine candidate: Tat protein produced in spinach. Vaccine 2005, 23: 1875-80.
9) Kim T-G, Gruber A, Langridge WHR. HIV-1 gp120 V3 cholera toxin B subunit fusion gene expression in transgenic potato. Protein Expression & Purification 2004, 37: 196-202.