Photodynamic therapy(PDT)is a promising approach to treat cancer.1 It involves the use of three individually nontoxic substances to produce a toxic effect.A photosensitizer,when illuminated with light of an appropriate wavelength,will be activated and convert molecular oxygen into reactive oxygen species(ROS),which can then kill tumor cells.The success of PDT depends on its potency as well as the targeting of the photosensitizer to the tumor site.2 For example,in photoimmunotherapy,the photosensitizer is conjugated to monoclonal antibodies that direct the photosensitizer to tumor cells that express the specific antigen recognized by the antibodies,and the tumor cells are killed upon light irradiation of the tumor site.3 This direct cytotoxicity is useful in treating localized tumor;however,it has limited applicability when metastasis occurs.In this regard,the activation of antitumor immunity appears to be more promising because most cancer patients die,not from localized tumor,but from cancer metastasis and relapse.
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