4-1BB-mediated memory formation of CD8⁺ T cells in the absence of IL-2/IL-2R signaling.

<p>(A-C) C57BL/6 mice were injected i.v. with Thy1.1^<b>+</b> OT-1 CD8^<b>+</b> T cells (2 × 10^<b>6</b> cells/mice) and immunized s.c. with 20 μg of whole OVA-emulsified in IFA. Anti-rat IgG or anti-4-1BB mAb were administered to the immunized mice at day 0, 7, and 14, and anti-CD25 F(ab’)₂ was given at days 0, 5, 10, and 15 via i.p. route. The mice were re-challenged with 20 μg of whole OVA-emulsified in IFA at days 21 to boost memory T cells. Inguinal LN cells were prepared from each group of mice at 7, 14, 21 or 26 days, stained with anti-CD8 and anti-Thy1.1 mAb, and subsequently analyzed by FACSCalibur (A). Absolute numbers of Thy1.1^<b>+</b> CD8^<b>+</b> T cells in inguinal LNs at the indicated days (B). Serum IL-2 and IFN-γ were assessed using BD Cytometric Bead Array Mouse IL-2 & IFN-γ Flex Set (BD Bioscience) (C). Arrows indicate the days of immunization. Results in B and C are mean ± SD (n = 3; *, p< 0.05; **, p< 0.01). LN: lymph node.