Inhibition of self-renewal of GBM tumor sphere cells. A, The GC4 but not other GBM tumor sphere cell-binding scFvs significantly inhibited GBM sphere cell proliferation. Cloning efficiencies were calculated from tumor spheres formed per 1,000 GBM cells seeded. Control, untreated sphere cells. N3M2, a non-binding scFv control. Experiments were done in triplicates with standard deviations indicated by error bars. *, P < 0.05 for pairs indicated. B, Production of recombinant GC4 IgG. H: heavy chain. L: light chain. MW: molecular weight. C, Quality control study confirming that the GC4 scFv-derived IgG1 retains the ability to bind GBM sphere cells. Ctr: a non-binding human IgG1. D, GC4 IgG1 inhibits colony formation of GBM cells in the soft agar assay. Both microscopic and digital photographic images of the GC4 and control IgG1-treated wells are shown. Scale bar, 250 μm.