Panel to Review GP160 Vaccine Candidate: Report of the Meeting

York University Medical Center in New York, New York. If an
effective product could be developed, it might very well become
"a practical and cheaper therapy" than many of the other
approaches now being pursued or already in use, Dr. Hoth said.
Animal model experiments. For most categories of
therapeutics, testing of the concept in animal models usually
provides in vivo evidence that it is feasible. In the area of
therapeutic vaccines, there is, at present, no animal model data
that have demonstrated a positive effect. For example, macaques
can be infected with simian immunodeficiency virus (SIV)--a
lentivirus that causes an infection in such animals that is
comparable to HIV infection in humans. When SIV-infected animals
are subsequently inoculated with an appropriate experimental
vaccine, there is an added immune response, but no reduction of
the viral load from the SIV infection, and no extension of the
infected animals' life spans, Hoth said, summarizing information
from independent research efforts. In contrast, animal model
studies of prophylactic vaccines do show evidence that some
vaccines are effective in preventing infection.
Therapeutic HIV vaccine candidates in clinical trials.
Among the HIV vaccine candidates being evaluated in clinical
trials, at least eight HIV envelope-based vaccines are being
developed by five different manufacturers for therapeutic use.
Of these, six have been tested in limited clinical trials so far,
but data on only two of these vaccines had been made public by
the time of the panel's first meeting in early November.
The candidate HIV envelope vaccines include: two gpl60
vaccines (based on different strains of HIV) that are being
produced by MicroGeneSys in baculovirus-infected insect cells;
two other versions of gpl60 being produced in mammalian cells by
Immuno AG. In addition, several candidates made from a component
of the HIV envelope, called gpl20, are also being tested in HIVinfected (seropositive) individuals. Two candidates (based on
different clinical isolates of the virus) of gpl20 are being
produced in mammalian cells by Genentech (South San Francisco,
CA), and two other gpl20 vaccine candidates--one in yeast cells,
the other in mammalian cells--are being developed by the Biocine
Group (Chiron of Emeryville, California and Ciba-Geigy).
Beyond these HIV envelope-based vaccine candidates, Phase I
clinical studies are underway or close to beginning for several
other types of vaccine products for therapeutic application,
including: a viral core protein-based vaccine (being developed
in the United Kingdom); synthetic peptides being developed by a
team at Duke University and a second group at UBI (New York);
and, an whole-inactivated virus vaccine, depleted of envelope
protein, being developed by Dr. Jonas Salk and his collaborators
at the Immune Response Corporation in California.
At least two Phase II trials of therapeutic vaccine
candidate trials are underway: one involving a MicroGeneSys
product being tested by the group at the Walter Reed Army