The present invention concers a ligand-toxin conjugate (LTC) comprising a photosensitizer (Ps) and a ligand linked thereto, for use in combination with a chemiluminiscent agent which reacts with an oxygen species present in situ and produces chemiluminescent light, wherein said Ps transfers energy to molecular oxygen and produces reactive oxygen species when light-activated by said chemiluminescent agent, in the treatment of a disorder associated with undesired activity of a cell population.