High hydrostatic pressure treatment generates inactivated mammalian tumor cells with immunogeneic features

Most of the classical therapies for solid tumors have limitations in achieving long-lasting anti-tumor responses. Therefore, treatment of cancer requires additional and multimodal therapeutic strategies. One option is based on the vaccination of cancer patients with autologous inactivated intact tumor cells. The master requirements of cell-based therapeutic tumor vaccines are the: (a) complete inactivation of the tumor cells; (b) preservation of their immunogenicity; and (c) need to remain in accordance with statutory provisions. Physical treatments like freeze-thawing and chemotherapeutics are currently used to inactivate tumor cells for vaccination purposes, but these techniques have methodological, therapeutic, or legal restrictions. For this reason, we have proposed the use of a high hydrostatic pressure (HHP) treatment (p >= 100 MPa) as an alternative method for the inactivation of tumor cells. HHP is a technique that has been known for more than 100 years to successfully inactivate microorganisms and to alter biomolecules. In the studies here, we show that the treatment of MCF7, B16-F10, and CT26 tumor cells with HHP >= 300 MPa results in mainly necrotic tumor cell death forms displaying degraded DNA. Only CT26 cells yielded a notable amount of apoptotic cells after the application of HHP. All tumor cells treated with >= 200 MPa lost their ability to form colonies in vitro. Furthermore, the pressure-inactivated cells retained their immunogenicity, as tested in a xenogeneic as well as syngeneic mouse models. We conclude that the complete tumor cell inactivation, the degradation of the cell's nuclei, and the retention of the immunogeneic potential of these dead tumor cells induced by HHP favor the use of this technique as a powerful and low-cost technique for the inactivation of tumor cells to be used as a vaccine.