Photodynamic effect on the specific antitumor immune activity

Photofrin is a potent sensitizer which localizes, among other sites in membranes of malignant cells. To evaluate the effect of photodymanic therapy (PDT) on specific antitumoral immunological response, we used a chromium release assay to compare the specific cytolytic activity (CLA) of primed mouse spleen T lymphocytes sensitized against syngeneic mastocytoma P511 cells. P511 cells or lymphocytes or both were treated or not with Photofrin and/or light (514 nm). Photofrin alone (1 microg/ml, 2 h) reduced CLA by 59% when P511 cells were treated although this decrease was not drug dose dependent. Photofrin (1 microg/ml, 2 h) followed by light (25 J/cm2) reduced CLA by 35% in a drug dose dependent manner. Longer incubation times led to reduced CLA inhibition (10% for 3 h incubation) after Photofrin followed by light. The light dose (25, 37, 50 J/cm2) did not influence CLA for a given Photofrin concentration. Photofrin alone (0.5 microg/ml, followed by light (25 J/cm2 for 2 h) reduced CLA respectively by 8 and 45% only when lymphocytes were treated. When lymphocytes and P511 cells were treated with Photofrin alone or followed by light (25 J/cm2), CLA was also reduced (by 19 and 41% respectively). This type of damage can be evaluated in terms of antigen expression on the target cells, on the lymphocyte T receptor, on H-2 (histocompatibility major complex), or on lymphocyte activity after PDT.