CD8A and lymphopenia: The relative improvement in total T‐cell numbers, from Days 10 to 14, including an overall increase in WNV‐specific CD8 precursors on Day 13 following IL‐7C treatment suggested that functional immunity could be improved within this temporal window, because lymphopenia in old mice was measurably reduced and residual IL‐7C (if any) did not cause further T‐cell proliferation in secondary lymphoid tissues.