“…These models typically place tumor spheroids in microwells to image the infiltration and cytotoxicity of lymphocytes [ 41 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 ]. Other studies encapsulate tumor spheroids in hydrogels such as collagen or Matrigel, either embedding the lymphocytes or applying them to the surface of the hydrogel [ 29 , 48 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 ]. The advantage of performing these studies in 3D is that lymphocytes must actively migrate through the ECM toward and into the tumor spheroids in order to exert cytotoxic effects, rather than the passive interactions that occur in traditional cytotoxicity assays in which lymphocytes settle onto a 2D cancer cell monolayer.…”