Augmentation of vaccine efficacy by small amounts of helper antigen plasmid when codelivered with TCR-β plasmid. (A) Mice were immunized 5 times with gold particles carrying a fixed amount of TCR-β plasmid (1 μg/shot) and various amounts of β-gal plasmid (33 ng to 0.3 ng/shot) followed by subcutaneous challenge with MBL-2 tumor cells. (B) To test whether tumor protection is dependent on TCR-β cDNA or a nonspecific effect of β-gal DNA or any plasmid DNA, mice were immunized with TCR-β plasmid plus helper plasmid (), TCR-β plasmid plus empty vector (▲), empty vaccine vector (pVax) plus helper plasmid (6 ng β-gal/shot, △), or pcDNA-gag as a positive control (no symbol). (C) Survival of mice immunized with gold particles carrying coprecipitated TCR-β and β-gal (n = 8 mice/group) after challenge with subcutaneous MBL-2 cells. Similar data were obtained in 17 independent experiments in which TCR-β plus 6 ng β-gal was used as a positive control for other experimental lymphoma vaccines. Survival data from all experiments are summarized in Table S1. (D) To demonstrate that the “helper-effect” was not restricted to β-gal, gold particles carrying 1 μg TCR-β–encoding plasmid and 6 ng helper antigen-encoding plasmid (β-gal or fragment C of tetanus toxin) were used to immunize mice (n = 8/group) before subcutaneous challenge with MBL-2 tumor cells. As a control, mice were immunized with the TCR-β plasmid plus low-dose empty pcDNA vector or with empty pVax vector plus low-dose pVax plasmid. Representative data from 1 of 2 experiments are shown (mean ± SEM).