Laser-photosensitizer assisted immunotherapy: a novel modality for cancer treatment

Photosensitizer-enhanced laser treatment, where dyes are activated in situ by lasers of appropriate wavelengths, provides highly selective tissue destruction, both spatially and temporally, through photophysical reactions. Although laser-sensitizer treatment for cancer can achieve a controlled local tumor cell destruction on a large scale, total tumor eradication may not be accomplished because of the incomplete local tumor killing or the presence of tumor metastases, or both. The long-term control of cancer depends on the host immune surveillance and defense systems in which both cell-mediated and humoral responses are critical. In this study we report a novel minimally invasive cancer treatment combining the laser photophysical effects with the photobiological effects. Irradiation of a rat mammary tumor by an 805 nm diode laser, after an intratumor administration of a specific photosensitizer, indocyanine green in a glycated chitosan gel, caused immediate photothermal destruction of neoplastic cells. Concomitantly this treatment stimulated the immunological defense system against residual and metastatic tumor cells. Increases in survival rate and in the eradication of tumor burden, both primary and metastatic, were observed after this treatment. Furthermore, the resistance of successfully treated rats to tumor rechallenge demonstrated a long-lasting systemic effect of the treatment. These findings indicate that our treatment has triggered a specific humoral immune response in the tumor-bearing rats.