CCR5 and neoplasm: These alterations in monocyte-tumor cell co-culture depend on chemokine receptors, CCR2 and CCR5, since co-culture of tumor cells with monocytes derived from Ccr2- or Ccr5-deficient mice resulted in impaired activation of the monocytes, as observed by decreased CD86 expression, especially in Ccr5-deficient monocytes, and decreased tumor cell cluster formation (Fig. 4e).