Infusion of “off-the-shelf” Third Party Ex Vivo Expanded Cord Blood Progenitor Cells As Supportive Care Following Clofarabine with High Dose Cytarabine and Granulocyte Colony-Stimulating Factor Priming for the Treatment of AML,

Abstract 3640

Regardless of patient age, prolonged neutropenia and infectious complications are common side effects of AML induction and salvage chemotherapy, requiring intensive supportive care and contributing to treatment failure. Thus, novel therapies that can abrogate prolonged pancytopenia and facilitate more rapid hematopoietic recovery are needed. Previously, we have demonstrated that the absolute number of repopulating cord blood (CB) hematopoietic stem/progenitor cells (HSPC) can be increased by culture with Notch ligand; recent data from a Phase I double CB transplant trial utilizing ex vivo expanded CB HSPC has suggested more rapid neutrophil recovery (Delaney et al, Nat med). We hypothesize that this expanded cell product, which is devoid of T cells, could be cryopreserved and then infused as an off-the-shelf non-HLA matched product to provide rapid but temporary donor myeloid engraftment and might also facilitate autologous hematopoietic recovery following AML therapy, thus reducing the infectious complications associated with therapy.

In a cohort of 50 patients, Becker et al at the Fred Hutchinson Cancer Research Center have reported on the use of clofarabine and high dose ara-c, in combination with G-CSF (GCLAC) in a phase I/II trial for the treatment of relapsed/refractory AML (Becker et al, Br. J. Haematol, in press). GCLAC is profoundly immunosuppressive and myelosuppressive, with periods of prolonged neutropenia post-GCLAC ranging from 17 to 35 days (median time to ANC >500 is 21 days) in this cohort. Infection was the most frequent adverse event, with ≥ grade 3 bacterial and fungal infections seen in 40% of patients (including 1^st and ≥ 2^nd salvage patients). We now herein report the preliminary results of a phase I safety trial investigating the use of GCLAC plus infusion of off-the-shelf expanded and cryopreserved CB HSPC for patients with AML.

To date, 12 adult patients with relapsed (n=8), primary refractory (n=2) or de novo high risk (n=2) AML have been enrolled and received GCLAC as their first salvage or initial induction therapy. The median age and weight was 55 years (range, 38 to 59 years) and 79.5 kg (range, 63.8 to 126) respectively. Patients received cycle 1 of GCLAC followed by infusion of off-the-shelf expanded CB HSPC 24 hours after completion of chemotherapy. Patients who achieved a complete morphologic remission and did not experience any toxicities associated with the expanded cell product were eligible to receive a 2^nd cycle of GCLAC with cells if not proceeding directly to stem cell transplant. A total of 15 products have been infused in 12 patients. Five of the 12 patients were refractory to GCLAC and therefore non-evaluable for neutrophil recovery. The median time to achieve an ANC > 500 in the evaluable patients was 19 days (range 18 to 27) after cycle 1, as compared to 21 days (range 17 to 35) in the historical cohort of patients receiving GCLAC only without expanded cells. Importantly, in this phase I study, there have been no infusional toxicities from the expanded cells or adverse events attributed to the expanded cell product. Alloimmunization has not been observed as monitored by pre- and post-infusion panel reactive antibody assays to determine the presence of donor directed antibodies.

Four of the 12 enrolled patients have experienced clinically significant infections (e.g., bacteremia, fungal infections) compared to 40% in the comparison cohort, and no infectious deaths have been observed. Finally, in contrast to the first cycle of chemotherapy where donor cells were detected in only one patient, 4 out of 4 patients who received a 2^nd cycle of GCLAC with expanded cells were found to have transient donor contribution to myeloid recovery (by peripheral blood cell sorted DNA chimerism assay) one week after infusion of the cells ranging from 85 to 100% donor in the CD33/CD14 cell lineages. Expanded cells were also able to home to the marrow as evidenced by transient donor engraftment (range, 3 to 15%) in recipient marrows one week after expanded cell infusion. It is unclear whether this is related to increased marrow “space” or increased host immunosuppression following cycle 2. With this encouraging data, we are continuing accrual of newly-diagnosed patients. This approach may decrease complications of pancytopenia and allow delivery of more dose-intense therapy, particularly in patients with intermediate/favorable cytogenetics who are already relatively sensitive to GCLAC.