Recruitment of myeloid cells in oHSV-injected tumors. A673 xenograft tumors were injected with rRp450 or PBS control. (a) The relative numbers of CD11b+ myeloid cells in the spleen (n = 4–5, t-test) and infected flank tumors (n = 6, t-test) were determined 3 days after virus injection by flow cytometry. In a separate experiment, (b,c) spleens and (d,e) tumors were collected 24 hours after virus injection and analyzed by hematoxylin and eosin (H&E) and by Ly6G immunohistochemistry staining (4X objective). The spleen served as a control, and brown staining is restricted to the red pulp and absent from the white pulp. oHSV, oncolytic herpes simplex virus; PBS, phosphate-buffered saline.