Phase 1 studies of the safety and immunogenicity of electroporated HER2/CEA DNA vaccine followed by adenoviral boost immunization in patients with solid tumors

Abstract

Background: DNA electroporation has been demonstrated in preclinical models to be a promising strategy to improve cancer immunity, especially when combined with other genetic vaccines in heterologous prime-boost protocols. We report the results of 2 multicenter phase 1 trials involving adult cancer patients (n=33) with stage II-IV disease.

Methods: Patients were vaccinated with V930 alone, a DNA vaccine containing equal amounts of plasmids expressing the extracellular and trans-membrane domains of human HER2, and a plasmid expressing CEA fused to the B subunit of Escherichia coli heat labile toxin (Study 1), or a heterologous prime-boost vaccination approach with V930 followed by V932, a dicistronic adenovirus subtype-6 viral vector vaccine coding for the same antigens (Study 2).

Results: The use of the V930 vaccination with electroporation alone or in combination with V932 was well-tolerated without any serious adverse events. In both studies, the most common vaccine-related side effects were injection site reactions and arthralgias. No measurable cell-mediated immune response (CMI) to CEA or HER2 was detected in patients by ELISPOT; however, a significant increase of both cell-mediated immunity and antibody titer against the bacterial heat labile toxin were observed upon vaccination.

Conclusion: V930 vaccination alone or in combination with V932 was well tolerated without any vaccine-related serious adverse effects, and was able to induce measurable immune responses against bacterial antigen. However, the prime-boost strategy did not appear to augment any detectable CMI responses against either CEA or HER2.

Trial registration: Study 1 - ClinicalTrials.gov, NCT00250419; Study 2 - ClinicalTrials.gov, NCT00647114.

Figures

Figure 1

V930 DNA plasmids (a) and V932 adenoviral vector (b) encoding for HER2/neu and CEA. V930 is a bivalent DNA plasmid vaccine consisting of a plasmid expressing the ECD and TM domains of HER2 and a plasmid expressing CEA fused to the B subunit of E coli LTB. V932 Ad encodes human CEA fused to LTB and the truncated version of human HER2 tumor antigen (HER2-ECDTM). The CEA-LTB expression is driven by the human CMV IE promoter, whereas mouse CMV IE promoter drives the expression of HER2-ECDTM.

Figure 2

Vaccination schedule with V930 DNA-EP alone (Study 1) and combined V930 DNA-EP→ V932Ad (Study 2). Patients who safely tolerated the highest dose of V930 DNA-EP (2.5 mg/injection) in Study 1 were allowed to enroll directly into Study 2, provided they had completed all 5 V930 vaccinations at least 4 weeks and no more than 24 weeks prior to entry and met all other eligibility criteria.

Figure 3

Frequencies of CEA and HER2/neu specific IFN-γ producing T cells following high-dose V930 DNA-EP vaccination. Longitudinal frequencies were determined from evaluable subjects (n=14); the threshold for CMI response was ≥35 SFC/106 PBMC and ≥3.5-fold above mock (i.e., control well levels [red line]). Differences between time points or between CEA and HER2 and mock were not significant (P>0.05 by Wilcoxon rank sum test). Arrow shows day of last V930-DNA-EP vaccination.

Figure 4

Longitudinal cell-mediated and antibody responses to LTB. a) Frequencies of LTB-specific IFN-γ producing T cells from evaluable subjects in both Studies 1 and 2, who had received low- or high-dose V930 DNA-EP vaccination. Arrow shows day of last V930-DNA-EP vaccination. Differences in peak values (day 87) from baseline levels were statistically significant for anti-LTB antibody responses (*P=0.03 by Wilcoxon rank sum test). b) Anti-LTB antibody responses. Differences in peak values (day 87) from baseline levels were statistically significant for the high-dose cohort (P<0.007 by Wilcoxon rank sum test). Peak levels (day 72) for the low-dose cohort were not significantly different from baseline levels (P>0.05).

Figure 5

Correlation between anti-LTB antibody response, and BMI or weight. A bivariate analysis was performed to determine if BMI or weight were inversely correlated with an LTB response. No effect of weight or BMI was seen on the ratio of post-vaccination to pre-vaccination anti-LTB titers (P>0.20 in each case). LTB, Escherichia coli heat labile enterotoxin, B subunit; BMI, body mass index.