Rather than try to repair defects through genetic therapy,scientist David Weiner of the University of Pennsylvania Schoolof Medicine has provoked a protective immune response inmice by injecting them with genes encoding the HIV coat.
This "genoculation," described in an article in Saturday's issueof The Proceedings of the National Academy of Sciences, maypresent an advantage over protein vaccines because injectingDNA stimulates production of killer T cells, which destroyinfected cells.
Recent studies indicate that HIV lurks hidden within cells ofthe lymph system during "latent" infection, outside the reach ofanti-viral agents.
Weiner has started a collaboration with a 1-year-oldbiotechnology start-up, Apollon, formed with funding fromminority shareholder Centocor Inc. of Malvern, Pa., and venturecapitalists DSV Partners of Princeton, N.J., and ChancellorCapital Management of New York.
Apollon, a private company in Malvern, is evaluating aprototype HIV vaccine in cynomolgus monkeys to check thekiller T cell response, said Vince Zuraski, president and chiefexecutive officer, and a former senior vice president and chiefscientific officer of Centocor.
The team will later examine how well a vaccine using SIV, thesimian AIDS virus, protects rhesus monkeys from SIV infection.Weiner said he hopes to move toward clinical trials of a humanvaccine.
In mice, Weiner's group made eight of 10 animals take up theDNA when it was injected into their muscles, which had beenprimed to absorb the rings of genetic material by priorinjection with the drug bupivacaine.
Genes for HIV coat proteins were placed in a circular plasmidfor transport into the muscle tissue, Weiner said, because theplasmid is not believed to incorporate into chromosomes,where it might accidentally initiate cancer, and because musclecells don't divide, which also decreases the chance ofpermanently incorporating the plasmid.
The mice received three booster shots two weeks apart, andtheir muscle cells briefly made HIV coat proteins based on thegenetic code carried by the plasmid.
The cells might process this long gp160 protein into pieces thatinclude gp120, responsible for HIV adhering to the CD4+ T cellsit infects. Because the muscle cells made the proteinsthemselves, the class I immune pathway was activated,creating killer T cells.
Weiner's group compared this approach to injection with therecombinant protein, which generates a class II immuneresponse that creates no killer T cells.
Genoculation elicited a very diverse immune response.
The mice made antibodies to specific envelope proteins and tomultiple determinants, which implies genoculation might beeffective against a rapidly changing pathogen. The mice'sbloodstreams neutralized free virus from infected cells andprevented transmission to uninfected cells. Sera from treatedmice inhibited gp120 binding to CD4 cells by 22 percent.
Immune globulins switched from IgM to IgG duringmaturation, implying a strong helper T cell response, whilepreliminary data showed 33 percent of cells creating envelopeprotein were destroyed by cytotoxic T cells.
The "rapid and specific" immunization could provide a quickstrategy against HIV and other contagions, Weiner said. Themethod appears to combine the effectiveness and diversity of alive, weakened viral vaccine with the safety and malleability ofa recombinant protein vaccine.
In fact, combined "cocktails" directed against multipleinfectious agents are already being considered, he said, whilethe concept of mixing DNA with different HIV characteristics isalso attractive.
In April, Vical Inc. of San Diego and collaborators at MerckResearch Laboratories in West Point, Pa., reported in thejournal Science that naked DNA encoding an influenza viruscoat protein protected 90 percent of immunized mice fromcatching a strain that surfaced 34 years later.
Meanwhile, a group attempting to transfer the human growthhormone gene reported in Nature last summer that the effortelicited an antibody-based immune response.
Without knowing anyone was working in this area, Weiner'steam decided to mimic an infection with retrovirus using DNA,he said, then "worked very hard on enhancing it."
While the usefulness of stimulating killer T cells remains to beshown, the humoral and cellular immune responsesgenoculation generates would all be valuable in a vaccine to avirus such as HIV, he said.
-- Nancy Garcia Associate Editor
(c) 1997 American Health Consultants. All rights reserved.