One of the two men who developed effective vaccines againstpoliomyelitis 30 years ago declared Tuesday that effectivevaccination against human immunodeficiency virus (HIV) is"improbable."
Albert B. Sabin, whose oral, attenuated-virus polio vaccine hasbeen in worldwide use for three decades, made his declarationin writing in the Sept. 15 edition of the Proceedings of theNational Academy of Sciences (PNAS).
"In my judgment, the available data provide no basis for ...expecting that any HIV vaccine could be effective in humanbeings," Sabin stated.
He doubts the possibility of an AIDS vaccine because of HIV's"intracellular transmission and rectal port of entry." Sabincontends that anal transmission is critical because the virusenters the intestinal tract without exposure to immmunedefenses. Other researchers point out that more than 90percent of AIDS is contracted through heterosexual vaginalintercourse, particularly in Africa.
Sabin's contemporary and rival, vaccinologist Jonas E. Salk, alsoin the late 1950s and early '60s, created an injectable, killed-virus polio vaccine, credited with reducing the disease'sprevalence in the U.S. by 96 percent. At the Salk Institute ofBiological Studies in La Jolla, Calif., Salk now strives to developan AIDS vaccine based on cell-mediated rather than antibody-driven strategies.
Sabin denounced Salk's proposal, which Salk made to the AIDSconference in Amsterdam, of arresting the immune response atthe cell-mediated stage instead of inducing a virus-specificantibody response
"Cell-mediated immunity is toward viral antigens of the cellsurface, and has proved ineffective," Sabin told BioWorld. "Salkis wrong again."
Salk responded in a BioWorld interview, " KTime will tell' is myresponse."
In his PNAS article, Sabin contrasts the immune system'sresponse to HIV to the way antibodies respond to measles andpolio, for which effective vaccines have long existed. Polio andmeasles are viral diseases transmitted by free-floating virusesoutside infected cells, while most HIV infection is transmittednot by such cell-free virus, but by cells infected withincompletely expressed viral DNA.
Therefore, according to Sabin, antibodies against the AIDS-virus antigens and the separate, cell-directed defenses of theimmune system are both ineffective against viruses alreadyinfecting cells, which have no viral antigens on the cell surface.Optimistic reports on experimental AIDS vaccines in chimpsand monkeys measure their effectiveness by counting theantibodies produced and challenge the immunized animals withweak doses of free-floating HIV antibodies, not with infectedcells, according to Sabin. Such approaches, he contends, wouldnot be effective.
Sabin suggested that biotechnology researchers "determinewhether cells that only have suppressed HIV genetic materialin their chromosomes -- those without expression of viralantigens on the cell membrane -- produce a suppressor protein.If so, they should attempt to find a drug that would kill cellsinfected with chromosomally integrated HIV cDNA, but sparenormal cells.
"I have no problem with that as an interesting research lead,"observed Daniel F. Hoth, director of the division of AIDS of theNational Institute of Allergy and Infectious Disease, part of theNational Institutes of Health. "But what we're saying is: Don'tshift the entire vaccine field to focus on one idea. I thinkfinding a successful AIDS vaccine is just as probable as findinga highly selective, non-toxic chemotherapeutic. And we view anindustry-government collaboration in this area as absolutelycritical to success."
-- David N. Leff Science Editor
(c) 1997 American Health Consultants. All rights reserved.