Inhibition of PKR expression or activity promotes DNA DSB repair in hematopoietic cells. Neutral Comet assays were used to measure DNA DSB repair following 5 Gy IR. (A) Inhibition of PKR by treatment with 0.5 μM PKRI prior to and following IR promoted faster kinetics of DNA DSB repair in primary CD34⁺ AML cells. SYBR gold-stained Comets were visualized by microscopy (×40). A representative Comet assay of 1 patient sample is shown. (B) The average Comet Olive Tail Moment from 50 randomly chosen CD34⁺ AML cells in each of 6 patient samples was determined. (C) Representative Comet assay, and (D) calculation of the average Comet Tail Moment of 50 randomly chosen REH cells demonstrates reduced PKR expression (sh-PKR) increases the rate of DNA DSB repair compared with control (sh-ctrl) cells. (E) Lin⁻ BM cells were collected from WT, TgPKR, and PKRKO mice, and treated with 5 Gy IR. Comet Tail Moments were calculated from 50 randomly chosen cells for each genotype. Lin⁻ BM cells from PKRKO mice displayed more rapid kinetics of DNA DSB repair than WT cells. Compared with WT, TgPKR cells exhibit delayed DNA DSB repair that can be restored by treatment with 0.5 μM PKRI. *P < .05; **P < .01.