In order to reduce the effects of CCL5-CCR5 mediated immune cell recruitment to the tumor microenvironment that would influence tumor proliferation, we harvested tumors from MMTV-PyMT.CCR5+/+ and MMTV-PyMT.CCR5−/− mice, prepared tumor cell suspensions, then injected these cell suspensions into mammary fat pads of NSG mice, as described in the Methods section. The gene discussed is CCR5; the disease is neoplasm.