Advances in Photodynamic Therapy Dosimetry*

The upregulation of immune checkpoints after photodynamic therapy reducing immune effect for treating breast cancer

The immune effect induced by photodynamic therapy (PDT) has a limited effect on breast tumor. This study hypothesized that suppressive immune checkpoints on T cells might upregulate after PDT, which may reduce the antitumor effect of PDT for treating breast tumor. This study explored the alteration of immune checkpoint for the first time. A bilateral subcutaneous transplanted breast tumor mice model was established, and right tumors imitated primary tumors, and left tumors imitated distant tumors. Primary tumors were treated with PDT mediated by hematoporphyrin derivatives (HpD-PDT). Costimulatory molecules (ICOS, OX40, and 4-1BB) and immune checkpoints (PD1, LAG-3, CTLA-4, TIM-3, TIGIT) on tumor infiltrating T cells after HpD-PDT were analyzed by flow cytometry. Antitumor and immune effects were also assessed after HpD-PDT combined with anti-PD1 and LAG-3 antibodies. Primary tumors were suppressed, but distant tumors could not be inhibited after HpD-PDT. The number of T cells was increased, but function did not enhance after HpD-PDT. Additionally, costimulatory molecules (ICOS, OX40, and 4-1BB) were not elevated, but the suppressive immune checkpoints on tumor infiltrating T cells were upregulated after HpD-PDT. Notably, PD1+ LAG-3+ CD4+ T and PD1+ LAG-3+ CD8+ T cells were significantly increased. When PD1 and LAG-3 blockade combined with HpD-PDT, both primary and distant tumors were significantly suppressed, and antitumor immune effects were significantly enhanced. HpD-PDT could upregulate the PD1+ LAG-3+ CD4+ T and PD1+ LAG-3+ CD8+ T cells. Dual blockade of PD1 and LAG-3 immune checkpoints can enhance the antitumor effect of HpD-PDT.

Rhodamine B as an optical thermometer in cells focally exposed to infrared laser light or nanosecond pulsed electric fields

The temperature-dependent fluorescence property of Rhodamine B was used to measure changes in temperature at the cellular level induced by either infrared laser light exposure or high intensity, ultrashort pulsed electric fields. The thermal impact of these stimuli were demonstrated at the cellular level in time and contrasted with the change in temperature observed in the extracellular bath. The method takes advantage of the temperature sensitivity of the fluorescent dye Rhodamine B which has a quantum yield linearly dependent on temperature. The thermal effects of different temporal pulse applications of infrared laser light exposure and of nanosecond pulsed electric fields were investigated. The temperature increase due to the application of nanosecond pulsed electric fields was demonstrated at the cellular level.