The EasySep™ Mouse TIL (CD45) Positive Selection Kit is designed to isolate highly purified CD45+ tumor infiltrating leukocytes (TILs) by immunomagnetic positive selection. This kit has been optimized for use on single-cell suspensions of solid mouse tumors with a low CD45+ start cell frequency, including tumors induced by implantation of 4T1, B16-F10, and CT26.WT cell lines into syngeneic mice. Due to the heterogeneity of mouse tumors, this kit may require optimization. This kit targets CD45+ cells for positive selection with antibodies recognizing the CD45 surface marker. Desired cells are labeled with antibodies and magnetic particles, and separated without columns using an EasySep™ magnet. Unwanted cells are simply poured off, while desired cells remain in the tube. Isolated cells are immediately available for downstream applications such as flow cytometry, culture, and cell-based experiments.