T-HA cells rescued from anti-CD3-induced death by IL-15 transgress from a semiactivated to a quiescent state.

T-HA cells were treated for 48 hours with IL-15 (1 ng/mL). On day 0, the cells were harvested, washed, and stimulated for 48 hours with immobilized anti-CD3 (solid lines) or with antigen/APC (dotted lines). On day 2, viable cells were recovered and 1 × 10⁴cells were incubated with the indicated doses of IL-2 (A) or IL-15 (B) for 96 hours. Proliferation was analyzed by measuring [³H]thymidine incorporation on day 6. In parallel, long-term cultures in IL-2 (10 ng/mL) or IL-15 (1 ng/mL) were set up with the T-HA cells recovered on day 2. On day 14, these cultures were harvested and 1 × 10⁴ cells were seeded and tested for proliferative responsiveness to IL-2 (C) or IL-15 (D) by pulsing with [³H]thymidine for the last 12 hours of the 72-hour assay period (day 17). All results are expressed as mean cpm from triplicate cultures ± SD.