Abstract 857: Calcium enhances synthetic HPV long peptide vaccination-mediated anti-tumor immunity and improves tumor control

Abstract Introduction: Transfection efficiency is a critical factor in the successful delivery of tumor vaccines. Intramuscular (IM) injection followed by electroporation is considered a superior approach compared to conventional IM injection alone. However, electroporation’s clinical unavailability and feasibility present significant limitations. Calcium, a ubiquitous second messenger, plays a crucial role in regulating various cellular processes, including transcription and cell death. Calcium overload can increase cell membrane permeability, promote reactive oxygen species accumulation, and trigger cell necrosis, leading to the release of intracellular contents such as antigens and damage-associated molecular pattern molecules (DAMPs). Our hypothesis is that calcium administration, by effectively priming immune responses, could serve as a feasible therapeutic strategy to overcome these limitations in cancer vaccine delivery. Method: The synthetic long-peptide vaccine utilized in this study, E7aa 43-62, comprises a synthetic peptide that mimics the 43-62 amino acid sequence of the HPV-16 E7 antigen. The long-peptide vaccines (20 µg) were administered to evaluate their anti-tumor effects in buccal TC-1 tumor-bearing C57BL/6 mice, with a total of three doses given at 7-day intervals. Vaccination was followed immediately by calcium administration or calcium electroporation. Calcium chloride solution (168 mM) was administered either subcutaneously or intratumorally. Electrical pulses were delivered using Tweezertrodes electrodes connected to a BTX electroporation generator (ECM830; BTX Harvard Apparatus). Eight pulses at 72 V were applied, each lasting 20 ms, with 200-ms intervals between pulses. Results: In the current study, calcium administration was shown to enhance HPV long-peptide vaccination-mediated anti-tumor immunity. Specifically, calcium administration achieved tumor control and prolonged survival comparable to calcium electroporation, accompanied by elevated levels of serum E7-specific tetramer formation. Additionally, mice receiving calcium injections, either subcutaneously or intratumorally, exhibited improved tumor control and superior survival compared to vaccination alone. Cellular analysis revealed that calcium injection significantly increased the systemic E7-tetramer population. This robust and sustained immunological activation was not only effective against contralateral buccal tumors but also provided protection against TC-1 tumor re-challenge. Conclusion: Our data demonstrate that calcium administration, either subcutaneously or intratumorally, enhances the anti-tumor immunity elicited by HPV long-peptide vaccination. This treatment effect is evidenced by controlled tumor growth and prolonged survival, accompanied by increased E7-specific tetramer formation. Citation Format: Ming-Hung Hu. Calcium enhances synthetic HPV long peptide vaccination-mediated anti-tumor immunity and improves tumor control [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 857.