High hydrostatic pressure inactivated human tumour cells preserve their immunogenicity

High hydrostatic pressure (HHP) is an established method to inactivate biomolecules and microoganisms. It is routinely used for the sterilization of foodstuff. Recently, new applications as inactivation of microorganisms and tumour cells for bone transplants or for cancer vaccines have emerged. Characterization of the HHP-induced cellular responses are a prerequisite for its clinical use. To this end, we investigated the fate of human cells after HHP by cytofluorometry. We observed that the induction by HHP of cell death is time- and pressure-dependent. Surprisingly, an HHP-treatment of 100 MPa did not reduce viability at any time point. Pressures from 150 to 250 MPa-induced programmed cell death in most cells. However, survivors were observed in long term culture experiments under these conditions. Pressures above 300 MPa immediately induced cell death by necrosis and completely inactivated the cells. In contrast to inactivation by other necrosis inducing treatments like heat, freeze/thaw, or chemical agents, HHP avoids generation of Maillard products and disintegration and lysis of the cells. Instead HHP generates a gelatinised mixture of antigens captured in a distinct and robust particle and maintains their humoral immunogenicity. The high viscosity of the internal matrix of a pressurised cell is reflected by the slow penetration of the low molecular compound propidium iodide and limits the bleeding of antigen before uptake by antigen presenting cells. Taken together, HHP is an alternative method for the inactivation of mammalian cells in clinical settings.