Blood levels of human Ig, soluble IL-6R, and soluble gp130 in mice grafted with XG-1 cells. Ten mice received IP 100 μg of B-S12 + B-P8 MoAbs (50 μg each) 2 days before graft of 50 × 10⁶ XG-1 cells in matrigel. They then received IP 50 μg of B-S12 + B-P8 MoAbs (25 μg each) every fortnight. Tumors were detected by palpation at the site of inoculation in all mice 4 to 5 weeks after the graft. Blood was collected every 2 weeks and assayed for human Ig, human sIL-6R, and human sgp130. The limit of sensitivity of the ELISA was 1 μg/mL for human Ig, 20 ng/mL for human sIL-6R, and 5 ng/mL for human sgp130. Results are the mean ± SD of the determinations. For some points, the error bars were too small to be visible on the graphs.