Rapid and Massive Expansion of Cord Blood Derived Cytokine Induced Killer (CIK) Cells: An Innovative Proposal for the Treatment of Leukemia Relapse after Cord Blood Transplantation.

Cytokine induced killer cells (CIK) are CD3+/CD56+ T/NK cells with cytotoxic potential against leukemic and other tumor cells but not normal bone marrow in vitro and in vivo. They are expanded in vitro with rhIL-2 after stimulation of peripheral blood mononuclear cells with OKT3 and IFN-γ. We have shown in a recent phase I study that 10⁷/kg allogeneic CIK cells can be safely given to patients relapsing after allogeneic bone marrow transplantation and show evidence of anti-leukemic activity in vivo with very little GVHD. Cord blood (CB) transplantation is progressively becoming an extensively used treatment for patients with malignant disorders. One major limitation of this procedure is the lack of donor derived cells to perform donor lymphocyte infusions in case of relapse. In order to be able therefore to extend the use of CIK cells to the CB transplantation setting, we have standardised a 21 days expansion protocol to produce CIK cells starting from very small amounts of nucleated cells isolated from cord blood. Using this protocol, 15x10⁶ mononuclear cells (MNC) from CB containing a mean 0.3x10⁶ CD3+/CD56+ yielded on average 805 x 10⁶ MNC (50 fold expansion) containing 630 x10⁶ CD3+/CD56+ cells (corresponding to a fold expansion of 1860 for CIK). In order to transfer the method to a clinical setting, we explored the possibility of expanding the residual cells recovered from the empty bags after CB transplantion. Three used CB bags were returned to the laboratory after transplantation and repeatedly washed. An average of 22 x10⁶ nucleated cells could be recovered, yielding a mean 473 x10⁶ CD3/CD56+ cells at the end of the culture period (1485 fold expansion of CIK cells). CIK cells generated from CB showed strong cytotoxic activity against a variety of tumor target cell lines including B and T lymphomas and myeloid leukemias (42–72% killing at a 30:1 E:T ratio). More importantly, they were cytotoxic against AML blasts isolated from 2 patients (41% lysis). During expansion CB derived CIK cells upregulated the NKG2D marker from a mean fluorescence intensity of 49 to 209. Furthermore they expressed perforin and granzyme molecules in >90% of cells. These observations open up the possibility of a future clinical application of this protocol, performed in GMP conditions. Patients relapsing following cord blood transplantation may be treated with CIK cells expanded from the same cord blood unit, where donors would not be anymore available for cell mediated immunotherapy.