2.2.1. Heat Shock

The induction of early necrosis using heat shock could be an alternative approach to obtaining TCLs (Figure 2D). A temperature of 42–43 ◦C could induce optimal cell death in antitumor immune outcomes, and maximum HSP production in the extracellular spaces of necrotic tumor cells, which could activate an adaptive antitumor immune response [41]. Mild hyperthermia (around 40 ◦C) induces thermotolerance [42], whereas high hyperthermia (over 45 ◦C) induces protein denaturation. In particular, HSP70 directly binds to CD40 receptors of DCs, and promotes the release of co-stimulatory signals [43]. Heat treatment of tumor cells also increases the expression of other DAMPs (such as HMGB-1 and ATP), and these molecules are recognized as danger signals by DCs.

For example, the heat shock treatment of three human melanoma cell lines at 42 ◦C for 1 h resulted in an allogeneic TCL mixture (TRIMEL) containing antigen components. The administration of TRIMEL significantly upregulated the release of the pro-inflammatory cytokine IFN-γ in DCs compared to the application of TCLs without heat shock treatment. Consequently, a previous study reported that TRIMEL showed clinical vaccination effects by developing a delayed type of hypersensitivity response in 64% of patients [31].
