Since there was no difference in the protective abilities between the two hybrid antibodies, the researchers used 8AH8AL to determine the minimum effective dose. Groups of mice were given decreasing doses--90, 45 and 22.5 micrograms per mouse--of 8AH8AL or a single 5-mg dose of human VIG (two and a half times the recommended human dose on a weight basis) as a point of comparison. All five mice in the control group died or were sacrificed when their weight fell to 70 percent of their starting weight. All of the mice that were injected with 8AH8AL (even at the lowest dose) or with VIG were protected from death.
Further, mice that received a single 90-microgram dose of 8AH8AL two days after virus exposure experienced only slight weight loss followed by rapid recovery. Conversely, all five of the mice that received 5 mg of VIG 48 hours after virus exposure experienced much greater weight loss than those that received the hybrid antibody.
"This study demonstrated that the hybrid antibodies provide instant protection against the vaccinia virus and likely smallpox and are potentially more potent and more specific than the treatment we currently have available," says Dr. Purcell. The hybrid antibodies also offer a potentially significant advantage over VIG as a treatment for smallpox vaccination complications not only because VIG is in limited supply but because VIG lots may have different potencies and carry the potential to transmit other infectious agents, he adds.
According to Dr. Purcell, the hybrid antibodies should be tested in another animal model for effectiveness against the monkeypox virus, which closely mirrors smallpox but is less virulent in humans.
Currently, the smallpox virus exists in only two laboratories found in Atlanta, Georgia, and in Russia.