C3-Fc inhibits tumor growth in vivo. NOD/SCID mice (n=6/group) were engrafted subcutaneously with LS174T cells (1×106 per animal). When the tumor grew to 50 to 100 mm3, the mice were then grafted with freshly isolated human PBMCs (1×106 per animal) and treated intraperitoneally with vehicle PBS (gray line), trastuzumab (dashed line), or C3-Fc (solid line) every 2 days. The tumor volume was then measured. The data represent the average tumor volume of six mice. The error bars represent the standard deviation (*P<.05, t test, vehicle vs C3-Fc, vehicle vs trastuzumab).