Generation of an effective anti-lung cancer vaccine by DTPP-mediated photodynamic therapy and mechanistic studies

The objective of this study was to generate an effective vaccine against lung cancer using photosensitizing drug-mediated photodynamic therapy (PDT) and to study the mechanism. The efficiency of a photosensitizing drug (DTPP) was investigated by singlet oxygen yield determination, killing effect analysis, and cell apoptosis induction effect assessment. DTPP-based PDT tumor cell lysates and cell surface antigens obtained from acid-eluted adherent cells were then used as vaccines to prevent lung cancer using LA795 murine lung cells. The optimal protocol for PDT vaccine preparation was selected based on the tumor growth retardation effect of the vaccines, DTPP concentration, illumination dose, and numbers of DTPP-based PDT cells. To study the mechanism of the anti-tumor effect of vaccines, host anti-tumor immune responses were studied, including CD4⁺/CD8⁺ ratios and percentage of NK cells and serum cytokine levels. A comparison of cytokine (IFN-γ and IL-1) secretion from splenocytes and tumor pathologic features from mice immunized with vaccines were compared with controls and showed that the optimal protocol for PDT vaccine preparation was LA795 cells exposed to 10 μg/ml DTPP photosensitizer for 24 h, illuminated with 7.2 J/cm² at 20 mW/cm² (630 nm) and 2 × 10⁷ PDT cell lysates injected per mouse. DTPP-based PDT cell lysate vaccination had a significant inhibitory effect on tumor growth based on increased CD4⁺/CD8⁺ ratios, NK cell percentages, elevated serum IFN-γ and IL-1 levels, and lymphocyte aggregation at the edge of tumors. Thus, DTPP-based PDT can induce LA795 cell apoptosis that can generate anti-tumor effects without use of an adjuvant.