Noninvasive bioluminescence imaging as a measure of therapeutic potential of OPG variants as compared with WT OPG. Groups of SCID mice were challenged with 5 × 10⁵ CAG^Hep cells via tail vein followed by noninvasive imaging for establishment of tumor cells around day 14. Cohorts of mice were then left untreated or administered with hMSCs modified to express WT OPG (OPG^wt), or OPG variants: OPG^Y49R/OPG^F107A. Tumor growth following therapy was monitored by noninvasive imaging on day 7 (day 21 after tumor challenge), and day 14 (day 28 after tumor challenge) after initiation of therapy.