Accumulation of single- or double-stranded DNA breaks. (A) Alkaline single cell gel electrophoresis (Comet assay) of CD4⁺CD8⁻ (ISP) and CD4⁺CD8⁺ (DP) subpopulations for control, SCID P1, P2, and OS P3 cells. DNA was visualized by SYBR Gold. The scale bar corresponds to 100 μm. Tail lengths were measured and summarized in (B). ****P < .0001; **P < .01.