A pilot phase II study of the safety and immunogenicity of HIV p17/p24:VLP (p24-VLP) in asymptomatic HIV seropositive subjects.

The aim of this phase II study was to evaluate the safety, immunogenicity and tolerability of the yeast-derived virus-like particle immunogen, Ty.p24.VLP (p24-VLP), in HIV-antibody-positive asymptomatic volunteers. Fifteen informed and consented volunteers, with p24 Antibody titres >1/100, p24 Antigen <20 pg/l, and CD4>350 x 10(9)/l were enrolled. Five were immunized with aluminium hydroxide placebo, five with 25 microg, and five with 100 microg p24-VLP in Alum adjuvant at weeks 0 and 4 by the intramuscular route. Patients were followed for 16 weeks post vaccination and the main outcome assessments were CD4 and CD8 lymphocyte counts, p24 antigen and antibody, Ty antibody and quantitative viral cultures. No serious adverse events were observed in any of the groups. There were increases in CD4 counts in the treated groups but not in the controls, although these changes were not statistically significant. There were no significant intrasubject or intergroup changes in the other parameters, such as p24 antigen and antibody. No pattern of change in plasma viraemia was detected, and most cultures were negative. Therefore we conclude that p24-VLP immunizations of 25 microg and 100 microg are well tolerated, and the CD4 changes are encouraging, but higher doses and larger numbers are required to see if there are significant humoral or cellular responses, and extended phase II studies are now in progress.