PVR and acute lymphoblastic leukemia: Specifically, ligands to all CRs, particularly CD155, were detectable on most AML cell lines, whereas most (all but two) B-ALL cell lines (one of them being Nalm-6 which is related and similar to Nalm-16 [30]) expressed ligands at low levels and lacked any CD155 expression (Fig. 3A, Suppl. Table 1 and Table 2).