c-MPL expression in polyclonal human T cells produces agonist-dependent proliferation and increased persistence in vivo. (A) c-MPL expression in polyclonal CD4⁺ and CD8⁺ T cells 7 days after retroviral transduction, representative FACS plots (left) and summary (right, n = 5). NT, green circles; c-MPL-transduced (c-MPL⁺), orange squares, mean± SD. (B) Expansion of NT (left) or c-MPL⁺ (right) T cells cultured in noCK (gray circles, solid lines), TPO 50 ng/mL (red squares, solid lines), or IL-2 50 U/mL (purple triangles, dashed lines) for 7 days. Replicates for n = 4 donors. (C) CFSE dilution of c-MPL-transduced cells cultured in noCK (gray), TPO50 ng/mL (red), or IL-2 50 U/mL (purple) for 7 days, gated on c-MPL⁻ (left) or c-MPL⁺ (right) cells. One representative of 3 donors. (D) c-MPL ligand induced STAT5 phosphorylation in c-MPL⁺ T cells after treatment of 1 or 24 hours with noCK (gray), TPO 5 ng/mL (red), TPO 50 ng/mL (blue) or eltrombopag (EP 0.1 μg/mL, green). (E) Mouse model experimental set up. (F) Transduction efficiency of T cells transduced with GFP-ffLuc alone (top) or cotransduced with GFP-ffLuc and c-MPL (lower) and injected IV into unconditioned hTPOtg-RAG2^−/−γc^−/− mice. (G) Summary of bioluminescent imaging data of control T cells (GFP-ffLuc⁺, blue circles and lines; n = 10) or c-MPL⁺ T cells (GFP-ffLuc⁺c-MPL⁺, red squares and lines; n = 8). *P = .0003, GFP-ffLuc⁺ vs GFP-ffLuc⁺c-MPL⁺, Student t test on log area under the curve for second T-cell infusion. Combined results from 2 independent experiments. (H) Three representative mice/group imaged over time by BLI; color scale 5 × 10³ to 5 × 10⁴ p/sec/cm²/sr (radiance).