Monocytes prevent chemotherapy-induced cell death and promote tumor engraftment in a human xenograft model. (A) HuT 78 cells were cultured in serum-free media alone, in B cell–conditioned media, T cell–conditioned media, patient mono-CM (Mp), or mono-CM obtained from 3 normal donors (Mnd), and thymidine incorporation was determined 72 hours later (mean ± SD). (B) HuT 78 cells in SF or mono-CM were stained with annexin V/PI and viability was determined 48 hours later. (C) HuT 78 cells were cultured in media alone or in media supplemented with mono-CM, and doxorubicin was added at the concentration (80 ng/mL) that inhibited thymidine incorporation at 72 hours by approximately 50%. Data shown are representative of at least 3 independently performed experiments (mean ± SD). (D) MyLa cells, alone or combined with purified monocytes (ratio 1:1), were injected subcutaneously into the flanks of NOD-SCID mice (each group n = 10). Tumors were considered established when the average tumor diameter reached at least 3 mm. Data shown are representative of 4 similarly performed experiments. (E) Tumors were harvested from both groups of mice and immunohistochemistry was performed for markers (CD11c, CD68) expressed by monocyte-derived cells (×200).