Figure 6. tSC-CD80 Attenuates Cytotoxic T Cell Activities Both by Direct Engagement and Indirectly by Elevating Treg Numbers.

See also Figure S6.

(A) Primary CD8+ T cells were activated by incubation with CD3/CD28 Abs and labeled with CFSE, a dye that is only diluted with subsequent cell divisions. These T cells were then co-cultured to measure the effects of CD80(+) and CD80(−) SCC cells on their dye dilution as a proxy for T cell activity. Note that CD80(+) SCC cells robustly impaired T cell activity, and that this effect was abrogated by CTLA4 blocking Abs. This combined effect was comparable to that of SCC cells lacking CD80. n=15; data are mean ± SEM.

(B) Primary CD8+ T cells, activated as in (A), were exposed to IL2 and IL12 for 3d and then co­cultured to measure the effects of CD80(+) or CD80(−) SCC cells on their granzyme production as a proxy for CTL activity. Note that CD80(+) SCC cells robustly impaired T cell cytokine production, and that this effect was abrogated by silencing CD80 or CTLA4 blocking Abs. Data are mean ± SEM.

(C) CD80(+) or CD80(−) PDVC57 SCC cells were transplanted into C57/BL6 mice treated with either isotype control or CTLA4 blocking Abs, and tumor progression was analyzed at times indicated. Note that the effects of CD80 loss are as potent as CTLA4 Abs. n=15; data are mean ± SEM.

(D) Flow cytometry quantifications of the CD4⁺CD25^HiFoxp3⁺ Treg cells that infiltrated CD80(+) and CD80(−) tumors (Left, percentage of total CD4 T cells; Right, exact Treg number per 0.1 mg tumor).

(E) CD80(+) or CD80(−) SCC tumors grown on Foxp3^DTR mice treated with vehicle or with diphtheria toxin to eliminate Foxp3⁺ Treg cells. n=20; data are mean ± SEM.