Phase 2 clinical trial design of ex vivo and in vivo Sirolimus for low-intensity allogeneic HCT. Donors underwent steady-state apheresis #1, whereby CD4⁺ T cells were purified by positive selection; costimulated with anti-CD3 and anti-CD28; and exposed to IL-4, IL-2, and rapamycin in culture for 12 days. The resultant “T-Rapa” cell product was cryopreserved and administered as a preemptive DLI at day 14 post-HCT. Donors underwent apheresis #2 after granulocyte–colony-stimulating factor (G-CSF) mobilization; the peripheral blood stem cell (PBSC) product was unmanipulated (T-cell replete). The recipient was treated for 4 consecutive days (days −6 through −3) with concomitant fludarabine (Flu, 30 mg/m² per day) and cyclophosphamide (Cy, 300 mg/m² per day). GVHD prophylaxis consisted of short-course Sirolimus (from day −2 until day +14 post-HCT) and cyclosporine A (from day −1 until day +100 post-HCT).