In the presence of increased ROS, STAT3 can be oxidized to formmultimers.34 An alternative oxidative modification ofSTAT3 by S-glutathionylation has also been observed.35Complex I-associated STAT3 of CLL-BC may thus limit ROS production by decreasing electron leak ofcomplex I and/or by serving as a critical electron scavenger, as previouslysuggested.28, 29, 30. Here, STAT3 is linked to B-cell chronic lymphocytic leukemia.