CD3ζ− CD8 T cells are not activated by CD3ε/CD28 cross-linking to express the high-affinity IL-2 receptor.

Cell surface expression of the early activation markers CD69 and CD25 was measured on gated CD8 T cells after overnight culture without activation (left) or with activation by either low concentration anti-CD3ε and anti-CD28 (middle) or with high concentration anti-CD3ε and PMA (right). Samples shown were obtained from (A) a normal donor, (B) subject AI-1 on day 19 and day 54, and (C) subject AI-2 on day 11 and day 100. The level of cell surface expression of CD69 in the induced patient samples was also somewhat reduced in the CD3ζ− down-modulated population.