SLAMF6 and neoplasm: Here we used Pdcd1 expression (which encodes for PD-1) as a surrogate marker of tumor specificity (14) and observed that indeed, Pdcd1+ Havcr2– Slamf6+ cells were enriched in Tcf7+ cells compared to bulk Pdcd1+ or Pdcd1+ Havcr2– cells (Figure 1B).