To determine whether anti‐miR223 PCs could change the phenotype of leukocytes in the tumor within the vicinity of the injection area, we injected tailfin melanomas of Ras‐expressing adult fish (Tg(kita:HRASG12V‐GFP)) with PCs loaded with either scrambled‐anti‐miR (control) or anti‐miR223 cargo, dissected the tumor, and immunostained sections of these tumors with anti‐L‐plastin and anti‐IL1β antibodies at several timepoints post injection. The gene discussed is IL1B; the disease is melanoma.