PDCD1LG2 and osteosarcoma: Interestingly, osteosarcoma Saos-2 cells, which are unable to undergo senescence (because of the absence of RB1 (ref. 40)), did not upregulate PD-L2 in response to palbociclib, in contrast to TIS-competent osteosarcoma U2OS cells (Fig. 1k).