CSF2 and neoplasm: The reduction in tumor cell proliferation upon GM-CSF expression was confirmed in surface transplants of the respective cell line, where tumor cells precultured on a collagen-1 gel are grafted onto the back muscle fascia of nude mice 24, The proliferation rate of GM-CSF negative control transplants as determined by immunofluorescent staining against BrdU incorporation was high at day 7 and remained constant throughout the experiment.