NGFR and neoplasm: Importantly, while exposing NGFR-enriched CD44v6 CAR-T cells to CD44v6+ MM.1S cells induced secondary proliferation, adding soluble NGF at concentrations capable of forcing neuronal tumor-cell differentiation had no effect (Figure 3), ruling out a potential proliferative advantage of NGFR-enriched CD44v6 CAR-T cells upon encounter with its natural ligand NGF.