Forced expression of A1 restores the ability of OX40 KO CD8 T cells to accumulate and survive over time <i>in vivo</i>.

<p>Naive CD8 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 T cells were sorted and adoptively transferred into naive C57BL/6 recipient mice that were subsequently challenged <i>i.p.</i> with whole OVA protein in PBS (filled bars) or PBS alone (open bars). (a) On days 5, 10, and 15, GFP<sup>+</sup>Vβ5<sup>+</sup>CD8<sup>+</sup> T cells were enumerated from pooled lymph nodes and spleen. Data are mean number of GFP<sup>+</sup>Vβ5<sup>+</sup>CD8<sup>+</sup> cells ± s.d from four individual mice and representative of three experiments (* <i>P</i><0.05, ** <i>P</i><0.01, Student's unpaired <i>t</i>-test). (b) At day 15, percentage of GFP<sup>+</sup>CD44<sup>+</sup> T cells was analyzed by flow cytometry, after gating on live CD8<sup>+</sup> T cells in the spleen. Results are representative of three experiments.</p>