Photofrin, but not benzoporphyrin derivative, stimulates hematopoiesis in the mouse

This report describes the effects of the porphyrin photosensitizers, Photofrin and benzoporphyrin derivative (BPD) on the immunohematopoietic system of normal and immunosuppressed DBA/2 mice in the absence of activating light. Photofrin (10 and 25 mg/kg) significantly increased in vitro colony formation by cells of the granulocyte-macrophage lineage in the spleen and bone marrow. Splenic hypercellularity, splenomegaly and elevated levels of blood leukocytes were observed in these mice 7 days following Photofrin injection. Evidence that Photofrin influenced the lymphohematopoietic compartment was suggested by a significant increase in blood lymphocytes and a population of spleen cells identified by a monoclonal antibody (LR-1) reactive with mouse splenic B lymphocytes. Proliferative responses of spleen cells from Photofrin-treated mice to sub-optimal concentrations of Con A were greater than that observed for controls. However, spleen cell responses to LPS were unaltered by Photofrin administration. In contrast, BPD (10 mg/kg) did not alter any of the immunohematopoietic parameters studied. When Photofrin was administered to mice treated with the myeloablative agent 5-FU there was a significant acceleration in the recovery of total blood leukocyte and spleen cell numbers, relative to the controls. These studies demonstrate that, in addition to its previously documented activities as a photosensitizer, Photofrin can exert stimulatory effects upon murine hematopoiesis.