In vitro and in vivo growth of IL-6-dependent INA-6 MM cells. (A) In vitro growth of INA-6 cells in the absence or presence of increasing doses of exogenous huIL-6. (B) In vitro coculture of INA-6 cells and BMSCs in the absence of exogenous IL-6. ^*P < .05. (C) Levels of shuIL-6R in sera of mice injected with INA-6 cells into human bone implant (SCID-hu, n = 45) or subcutaneously (SCID, n = 8). (D) Clustering of a cohort of 45 SCID-hu mice on the day of first detection of serum shuIL-6R. (E) The kinetics of appearance and evolution of shuIL-6R in SCID-hu mice (n = 16) following engraftment of INA-6 cells (2.5 × 10⁶ cells) injected directly into human bone implant. Each symbol represents a different SCID-hu mouse. (F) Overall survival of SCID-hu (•; n = 16) and SCID mice (○; n = 8) after INA-6 injection (2.5 × 10⁶ cells/mouse). (G) Levels of huIL-6 in sera of SCID or SCID-hu mice given injections of INA-6 cells either subcutaneously or directly into the human bone implant, respectively. Sera were obtained from tail vein in SCID mice (n = 4), or from both tail vein and fetal bone aspirate in SCID-hu mice (n = 6). (H) H&E staining of a human fetal bone section implanted in a SCID-hu mouse and engrafted with INA-6 cells (original magnification ×100). Error bars in panels A-C and G indicate standard error.