CDO1 and acute lymphoblastic leukemia: In line with a critical and selective role for stromal cysteine in ALL support, treatment of co-cultures with recombinant cysteine dioxygenase (CDO1), which catalyzes conversion of cysteine into cysteine sulfinic acid and bypasses GSH synthesis [28], reduced the survival of xc−-dependent ALL cells, while xc−-independent ALL cells did not respond to this treatment (Fig. 4I).