CSF2 and prostate cancer: Effects on circulating leukocyte subsets were observed, and transient reductions in serum PSA levels were observed in two prostate cancer patients.35 We have also developed the GM-CSF-neutralising monoclonal antibodies 4D4 and 4A12 that block human GM-CSF activity in vitro.36, 37 Thus, E21R and the neutralising monoclonal antibodies 4D4 and 4A12 may be able to interfere with GM-CSF-dependent generation of MDSC.