To monitor CTL lytic granule polarization towards target cells with the dynamics of melanoma LLE on cognate cell–cell interaction in T cell/melanoma cell conjugates, we took advantage of the observation that pretreatment of CTL with either Av-SRho or Av-Alexa488 allows to stain lytic granules (as shown by Av-SRho and perforin co-localization in fixed and permeabilized CTL, Supplementary Fig. 5). Here, PRF1 is linked to melanoma.