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 (C LA) 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 mu g/ ml, 2 h) reduced CLA by 59% when P511 cells were treated although this decrease was not drug dose dependent. Photofrin (1 mu g/ml, 2 h) foll owed by light (25 J/cm(2)) reduced CLA by 35% in a drug dose dependent manner. Longer incubation times led to reduced CLA inhibition (10% fo r 3 h incubation) after Photofrin followed by light. The light dose (2 5, 37, 50 J/cm(2)) did not influence CLA for a given Photofrin concent ration. Photofrin alone (0.5 mu g/ml, followed by light (25 J/cm(2) fo r 2 h) reduced CLA respectively by 8 and 45% only when lymphocytes wer e treated. When lymphocytes and P511 cells were treated with Photofrin alone or followed by light (25 J/cm(2)), CLA was also reduced (by 19 and 41% respectively). This type of damage can be evaluated in terms o f antigen expression on the target cells, on the lymphocyte T receptor , on H-2 (histocompatibility major complex), or on lymphocyte activity after PDT. (C) 1997 International Society for Immunopharmacology.