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

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⁺ CD8⁺ T cells were sorted and adoptively transferred into naive recipient mice that were subsequently injected with B16-OVA melanoma cells s.c. in the flank region. (a) Tumor growth was monitored over time. Tumor volume was calculated as follows: V = length×width²×0.52. Data are mean tumor size ± s.d from six individual mice and representative of three experiments (* P<0.05, Student's unpaired t-test). (b) Mouse survival was assessed over 30 days. Kaplan–Meier survival analysis indicated significantly increased survival in mice (n = 6) receiving OX40 KO CD8⁺ T cells transduced with A1 compared to mice receiving OX40 KO CD8 T cells with vector control (logrank test, P<0.05).