Stroma-free LTCs associated with repeated expansion-isolation procedures. Scheme of “fractionated” stroma-free LTCs with cytokines. At start of cultures, CB CD34⁺ cells were plated at 5 × 10⁴/mL as explained in “Patients, materials, and methods” in triplicate or quadruplicate tissue culture flasks. Every 4 weeks all cells were harvested and CD34⁺ cells isolated with miniMACS devices and recultured as described in “Patients, materials, and methods.”