Tumour regression in mice inoculated with Zera® separately. Mice received 0.5 × 106 C3 tumour cells s.c. and when the tumours were clearly palpable they were immunized with 100 μg DNA vaccine or 2.5 μg 16E7SH +/- 2.5 μg Zera® PBs +/- 100 μl IFA per animal and surface tumour size was measured. Experiments were repeated (Exp. I and Exp. II) and both results are shown. The experiment was terminated at day 39 due to the size of tumours in the control groups (empty vectors). Data gives the mean ± SEM. of the indicated group at day 39 but in the second exp: on day 43 (n = 10). pTH-ZERA-16E7SH DNA compared to pTH-16E7SH (Exp. I - p < 0.05, Exp. II p = 0.2). 16E7SH protein compared to 16E7SH protein plus Zera® PBs (Exp. I - p < 0.005, Exp. II p < 0.0005).