The CD161⁺⁺ CD8αα population emerges on expansion of the CD161⁺⁺CD8αβ subset with age. (A) CD161⁺⁺ CD8αα cells are not found in cord or infant blood. (B) Comparison of CD161⁺⁺CD8α⁺ and CD161⁺⁺CD8αα populations in cord, infant, and adult blood. **P < .001, ***P < .0001 (1-way ANOVA). (C) Comparison of TCR Vβ and Vα usage between CD161⁺⁺ CD8αβ and CD161⁺⁺CD8αα subsets in adult blood.