Background: Non-surgical treatments for cervical intraepithelial neoplasia 2/3 (CIN2/3) are needed as surgical treatments have been shown to double preterm delivery rate. An investigational human papillomavirus (HPV) therapeutic vaccine, PepCan, consists of four current good manufacturing production-grade peptides covering the HPV type 16 E6 protein and Candida skin test reagent as a novel adjuvant. Methods: The study was a single-arm, single-institution, dose-escalation Phase I clinical trial, and patients with biopsy-proven CIN2/3 were eligible for vaccination. Four injections were administered intradermally every 3 weeks in limbs, and loop electrical excision procedure (LEEP) was performed 12 weeks after the last injection for treatment and histological analysis. Six subjects were enrolled at each dose level, and dose escalation was allowed as long as less than two subjects demonstrated dose-limiting toxicities. Results: Six subjects at each of four dose levels (50, 100, 250, and 500 mcg per peptide) were accrued, and none of the subjects experienced any dose-limiting toxicities. The most common adverse events were injection site reactions. Vaccine-induced immune responses to E6 were detected in 65% of recipients (significantly in 43%), and systemic T-helper type 1 (Th1) cells were significantly increased after 4 vaccinations (p= 0.02). The best histological response was seen at the 50 mcg dose level with a regression rate of 83% (n = 6), and the overall rate was 52% (n = 23). Conclusions: PepCan has been shown to be safe, and able to induce HPV-specific immune responses and Th1 cells. Candida, which has been shown in vitro to induce interleukin-12 secretion, is likely responsible for the increased Th1 cells, and should be considered as a candidate adjuvant for other vaccines. A Phase II clinical trial to assess the full effect of PepCan is warranted using the 50 mcg per peptide dose. Clinical trial information: NCT00569231