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Background: The innovative light-activated drug therapy LitxTM is a cytoreductive treatment that uses light-emitting diodes to activate talaporfin sodium (LS 11(R)), a water-soluble drug, resulting in the production of singlet oxygen.Tumor destruction involves direct and indirect tumor kill through apoptosis, vascular occlusion, and potentially anti-tumor immunologic effects.To provide evidence for the potential anti-tumor immunologic effects, we have used Litx to treat primary tumors and examine effects on untreated lesions in Colon-38 (colon carcinoma) and 4T1 (metastatic breast cancer) models.Methods: To confirm tumor kill, primary 4T1 tumors grown in mice were treated and animal survival was followed.To determine whether Litx could enhance anti-tumor immunity and reduce metastases, lymph-node (LN) cells from treated and control mice were transferred to naive recipient mice.Recipients were challenged with a tumorigenic dose of 4T1 cells 3 days after adoptive transfer, and primary and secondary tumor growth in the recipients was examined.To test immune memory, additional recipients were challenged with tumor 40 days after lymphocyte transfer.In another experiment, one of two subcutaneous Colon-38 tumors was treated with Litx in C57BL/6 mice and the untreated tumor was followed.Results: Treatment of primary 4T1 tumors significantly increased survival (P≤0.01) when compared to control animals.LN cells isolated from treated mice, but not control mice, significantly inhibited primary tumor growth in recipients (P≤0.0001) and dramatically reduced the number of lung metastases present 40d after tumor challenge (P≤0.02).The ability to inhibit primary and secondary tumor growth in recipients depended on the presence of CD8+ T cells; depletion of CD8+ T cells from the LN abolished the effect.Lymphocytes from Litx-treated animals provided lasting immune protection when recipients were challenged with tumor 40 days post transfer.In mice bearing contralateral Colon-38 tumors, treatment of one tumor caused significant reduction of volume in untreated tumors.Preliminary evidence for such effect on untreated tumors has been observed in human trials of Litx.Conclusions: These results indicated that Litx not only destroyed treated tumors directly but also controlled growth of untreated tumors through induction of a specific host anti-tumor immune response mediated by CD8+ T cells.