Methods for treating cancer, e.g., in conjunction with anti-cancer therapy, like immunotherapy, and for identifying candidate therapeutic agents, by targeting ICAM4. While MDSCs in mice have been extensively characterized, their human counterparts are not well defined, and cell markers present in mice are not always usable in humans. MDSCs have been described as a heterogenous population of myeloid derived cells with immune suppressive capacity (5, 9, 40, 41). Recent renewed interest in the role of MDSC accumulation in human tumors has resulted in the increased need to define these cells better in order to target them for therapeutic intervention.