Rhodamine derivatives for photodynamic diagnosis and treatment

A method of reducing or preventing graft-versus-host disease associated with allogeneic stem cell transplantation, which comprises the steps of:

• a) harvesting hernatopoietic cells from a patient with an immunologic disorder;
• b) harvesting hematopoietic cells from a donor;
• c) mixing the cells of step a) with the cells of step b) ex vivo for a period of time sufficient to activate lymphocytes within the hematopoietic cells harvested from said donor such that an immune reaction occurs, wherein an activated portion and an unactivated portion is produced;
• d) adding to the mixture of cells of step c) ex vivo a therapeutic amount of a rhodamine derivative according to formula (i):
• e) irradiating the mixture of cells of step d) ex vivo with a suitable wavelength and intensity for the selective destruction and/or inactivation of the activated portion without substantially affecting the unactivated portion or causing systemic toxicity in said patient;
• and
• f) infusing the mixture of cells of step e) into the patient.