Efficacy of selective CD28 blockade in controlling donor-reactive CD8⁺ T cell expansion is independent of its ability to inhibit ICOS expression.

<p>Naïve B6 animals were adoptively transferred with 10⁶ congenically labeled ICOSrg Thy1.1⁺ OT-I T cells (or pMY Thy1.1⁺ OT-I controls) along with 10⁶ Thy1.1⁺ CD4⁺ WT OT-II T cells and then challenged with an OVA-expressing skin graft. Groups of animals were left untreated or treated with anti-CD28 dAb. Animals were sacrificed at day 10 post transplant, and graft-draining LN T cells were analyzed for the expression of the magnitude of the CD8⁺ Thy1.1⁺ response. A, Representative flow cytometry plots depicting frequencies of CD44^hi Thy1.1⁺ CD8⁺ T cells in the treatment groups indicated. B, Summary data of the frequencies of CD44^hi Thy1.1⁺ CD8⁺ T cells (three independent experiments with a total of n = 6–9 animals/group). C, Summary data of the absolute numbers of CD44^hi Thy1.1⁺ CD8⁺ T cells (three independent experiments with a total of n = 6–9 animals/group). D, Summary data of the frequencies of CD44^hi Thy1.1⁺ CD4⁺ T cells (three independent experiments with a total of n = 6–9 animals/group). C, Summary data of the absolute numbers of CD44^hi Thy1.1⁺ CD4⁺ T cells (three independent experiments with a total of n = 6–9 animals/group). *p<0.05, **p<0.01.