Although a fraction of the KO DP cells silenced CD4 expression after activation, the ratio of SP/DP cells in each enriched population remained constant thereafter, and we did not observe any major differences between these two populations throughout the culture period, indicating that in terms of effector CTL differentiation and under our culture conditions, Runx3−/− CD8+ T cells that also coexpress CD4 are indistinguishable from those that do not.