AIDSWEEKLY Plus; Monday, August 24 & 31, 1998
Daniel J. DeNoon, Senior Editor
The vaccine, dubbed TBC-3B by manufacturer Therion Biologics Corp., expresses the HIV env, gag, and pol genes. The trial enrolled 36 HIV negative volunteers who received the vaccine (or vaccinia placebo) either via scarification, intradermal injection, or subcutaneous injection.
"TBC-3B administered by [the various routes] to vaccinia-naive, HIV negative volunteers is well tolerated, even when given as a 100 times higher dose boost," reported Michael C. Keefer of the National Institutes of Health.
Keefer reported the findings in a presentation to the 12th World AIDS Conference, held June 28-July 3, 1998, in Geneva, Switzerland.
The TBC-3B prototype vaccine expresses antigens from the IIIB strain of HIV-1. Several safety features are built in to the genetically engineered vaccinia virus:
The HIV genes are coded in reverse order, interspersed with vaccinia sequences.
* The vaccine expresses the HIV antigens in the cytoplasm of infected cells and thus does not integrate HIV gene sequences into the host genome.
* HIV promoter sequences are absent.
The trial protocol calls for subjects to receive two doses of the vaccine (at a two-month interval). The second inoculation represents a 100-fold dose escalation. After receiving two doses of TBC-3B, subjects will be boosted with the VaxGen Env peptide vaccine at 8 and 12 months. Ten subjects received the TBC-3B via each of the three inoculation routes; two subjects received placebo via each route.
Vaccinia "takes" as defined by typical lesions at the site of inoculation occurred in all groups: 10 of 10 scarification subjects, nine of 10 intradermal subjects, and seven of 10 subcutaneous subjects.
Because inoculations were staggered to ensure safety, only 12 participants have thus far received their 12-month boost.
The TBC-3B vaccine strategy follows what is currently the most promising approach to HIV vaccines: elicitation of a priming cellular response with HIV DNA (encoded in a carrier virus or directly administered) followed by boosting with HIV peptides. This prime/boost approach is under evaluation in several different clinical studies.
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