AIDSWEEKLY Plus; Monday, August 24 & 31, 1998
Daniel J. DeNoon, Senior Editor
The vaccine is a canarypox virus engineered to express HIV genes. The virus is capable only of a single round of expression in human cells and has proven safe in earlier human tests.
"We are having very good, durable CTL," said Thomas Evans of the AIDS Vaccine Evaluation Group (AVEG). "At two years it looks like 50 percent [of subjects] will be positive for [CTL specific for] HIV-1 Env or Gag."
Evans presented the data to the 12th World AIDS Conference, held June 28-July 3, 1998, in Geneva, Switzerland.
Data came from trials of several candidate HIV vaccines based on the canarypox virus: vCP125 (encoding the HIV-1 gp160 envelope precursor), vCP205 (encoding the gp120 and gp41 transmembrane portion of Env, Gag, and protease), and vCP300 (encoding the vCP205 sequences plus CTL epitopes in the viral Nef and Pol proteins). All are manufactured by Virogenetics Inc. in cooperation with Pasteur-Merieux- Connaught.
He said that CTL isolated from 14 of 18 of the positive subjects could lyse HIV infected target cells, even those infected with HIV from a different clade than that used in the vaccine.
Exactly why the vaccine elicited anti-HIV cellular immunity in only half of the subjects remains a mystery. Response could not be positively or negatively correlated with any specific human leukocyte antigen (HLA) types.
"We think if we had a broader vaccine we would increase the percentage of responders," Evans said.
He drew several conclusions from the studies:
* Increasing the complexity of the ALVAC vector will increase the breadth as well as the rate of responses.
* Anti-HIV vaccines can elicit memory CTLs of long duration.
* HIV vaccines can only be evaluated in clinical trials.
Evans noted that Phase I evaluation of more complex ALVAC vaccines are currently planned.
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