Expression of A1 restores the ability of OX40 KO CD8 T cells to suppress tumor growth <i>in vivo</i>.

<p>Naive CD8<sup>+</sup> T cells from WT or OX40 KO OT-I TCR transgenic mice were stimulated with APCs/peptide. On day 2/3, T cells were transduced with retroviral vectors expressing GFP, or GFP with A1. On day 5 of primary culture, GFP<sup>+</sup> CD8<sup>+</sup> T cells were sorted and adoptively transferred into naive recipient mice that were subsequently injected with B16-OVA melanoma cells <i>s.c.</i> in the flank region. (a) Tumor growth was monitored over time. Tumor volume was calculated as follows: V = length×width<sup>2</sup>×0.52. Data are mean tumor size ± s.d from six individual mice and representative of three experiments (* <i>P</i><0.05, Student's unpaired <i>t</i>-test). (b) Mouse survival was assessed over 30 days. Kaplan–Meier survival analysis indicated significantly increased survival in mice (<i>n</i> = 6) receiving OX40 KO CD8<sup>+</sup> T cells transduced with A1 compared to mice receiving OX40 KO CD8 T cells with vector control (logrank test, <i>P</i><0.05).</p>