PTGES2 and cancer: Off-target Cas9 nuclease activity can be a concern (e.g., Frock et al., 2015), but because we have used multiple sgRNAs to ablate Ptges1, Ptges2, and/or Pges1/2 in four different cancer cell lines that, in all cases, become susceptible to immune-mediated control, we believe that on-target ablation of the ability of the tumor cells to produce PGE2 accounts for our findings.