Panel to Review GP160 Vaccine Candidate: Report of the Meeting

Institute of Research in collaboration with NIAID's Community
Programs for Clinical Research on AIDS (CPCRA); and, the other
being conducted on a smaller scale by a clinical research group
at McGill University in Canada. Another Phase II trial,
involving the Genentech gpl20 product, is expected to begin soon.
This is not meant to be an exhaustive list of these
products, since there may be other candidate HIV vaccines that
are also being considered for evaluation in seropositives.
Therapeutic HIV vaccines in clinical trials: difficulties
in analysis. At this time, data is available only from Phase I
trials. Since most results have not been published, the summary
presented here is based largely on presentations at meetings.
Furthermore, some studies are still ongoing, and the analyses for
most studies that have been released are not considered final.
The Phase I trials evaluated safety and immunogenicity, and thus
none in that group was designed to demonstrate efficacy. As
another caution, none of the Phase I trials is usually designed
to make comparisons between candidates about safety and
immunogenicity.
Even as trials have expanded into greater complexity and
sophistication at the Phase II level, they are nonetheless being
conducted mainly in individuals who are in the early stages of
their HIV infection, a period when few clinical signs are present
with which to gauge efficacy. Several additional HIV vaccine
clinical trials are scheduled to begin soon, with at least one of
them designed to determine whether a gpl20 product can generate
useful immune responses in HIV-infected individuals whose CD4
cell counts have dropped to a relatively low level as their
disease has progressed, according to Dr. Valentine. Vaccine
recipients in that study will also be receiving therapeutic drug
treatments (AZT), an added complication when it comes time to
interpret the study findings, he noted.
Demographic analysis is another important factor to consider
when judging the safety and efficacy of new therapeutic products.
Studies must include HIV infected women and minorities. A number
of trials in HIV-infected children and pregnant women will soon
begin.
Meeting participants acknowledged the considerable
uncertainty about the possible effects that candidate vaccines
may have on a variety of minority population groups of HIVinfected individuals. Explicit efforts are being made to ensure
that diverse population groups are adequately represented in
clinical trials to assess both safety and efficacy. However,
many meeting participants also agreed that the life-threatening
urgency of the epidemic should be continually and realistically
weighed against the perceived needs in any particular product
development program to acquire fully satisfactory scientific
data.