Tumor relapses after suicide gene therapy in animals that received transplants of either uncloned or cloned MO3TIN cells occur with variable kinetics. The tumor size (y-axis, diameter of the hind leg in mm) was determined in mice (n = 5 per group) at regular intervals (days after inoculation, x-axis). m.c. indicates mass culture; all clones are transduced with a single copy of the MO3TIN vector.