PDCD1 and melanoma: In transwell experiments, B16 melanoma tumor cells cocultured in transwell plates with ILCs induced PD-1 with an increase in frequency in PD-1+ ILCs observed at the 1:1 ratio at 6 h, with a trend noted at 1:10 ratio which was completely abrogated at a 1:100 ratio (Fig. 4C and SI Appendix, Fig. S5A).