Haploidentical Donor Transplantation Using a Novel Clofarabine-containing Conditioning Regimen for Very High-risk Hematologic Malignant Neoplasms

The combination of clofarabine, etoposide, and cyclophosphamide shows limited efficacy as a bridge to transplant for children with refractory acute leukemia: results of a monitored prospective study

Clofarabine has been shown to effectively induce remission in children with refractory leukemia. We conducted a prospective trial (clinicval.trials.gov NCT01025778) to explore the use of clofarabine-based chemotherapy as a bridge-to-transplant approach. Children with refractory acute leukemia were enrolled to receive two induction courses of clofarabine, etoposide, and cyclophosphamide (CloEC). Responding patients were scheduled for T-cell depleted haploidentical hematopoietic stem cell transplantation (HSCT). The primary objective was to improve survival by achieving sufficient disease control to enable stem cell transplantation. Secondary objectives were to evaluate safety and toxicity. Seven children with active disease entered the study. Two children responded to induction courses and underwent transplantation. Five children did not respond to induction: one died in progression after the first course; two received off-protocol chemotherapy and were transplanted; and two succumbed to progressive leukemia. All transplanted children engrafted and no acute skin graft-versus-host disease > grade I was observed. One child is alive and well 7.5 years after the first CloEC course. One child developed fulminant adenovirus hepatitis and died in continuous complete remission 7 months after start of induction. Two children relapsed and died 6.5 and 7.5 months after enrollment. Infection was the most common toxicity. CloEC can induce responses in some patients with refractory acute leukemia but is highly immunosuppressive, resulting in substantial risk of life-threatening infections. In our study, haploidentical HSCT was feasible with sustained engraftment. No clinically significant organ toxicity was observed. Also, repeating CloEC probably does not increase the chance of achieving remission.

Phase I/II multisite trial of optimally dosed clofarabine and low-dose TBI for hematopoietic cell transplantation in acute myeloid leukemia

Clofarabine is an immunosuppressive purine nucleoside analog that may have better anti-leukemic activity than fludarabine. We performed a prospective phase I/II multisite trial of clofarabine with 2 Gy total body irradiation as non-myeloablative conditioning for allogeneic hematopoietic cell transplantation in adults with acute myeloid leukemia who were unfit for more intense regimens. Our main objective was to improve the 6-month relapse rate following non-myeloablative conditioning, while maintaining historic rates of non-relapse mortality (NRM) and engraftment. Forty-four patients, 53 to 74 (median: 69) years, were treated with clofarabine at 150 to 250 mg/m² , of whom 36 were treated at the maximum protocol-specified dose. One patient developed multifactorial acute kidney injury and another developed multiorgan failure, but no other grade 3 to 5 non-hematologic toxicities were observed. All patients fully engrafted. The 6-month relapse rate was 16% (95% CI, 5%-27%) among all patients and 14% (95% CI, 3%-26%) among high-risk patients treated at the maximum dose, meeting the pre-specified primary efficacy endpoint. Overall survival was 55% (95% CI, 40%-70%) and leukemia-free survival was 52% (95% CI, 37%-67%) at 2 years. Compared to a historical high-risk cohort treated with the combination of fludarabine at 90 mg/m² and 2 Gy TBI, protocol patients treated with the clofarabine-TBI regimen had lower rates of overall mortality (HR of 0.50, 95% CI, 0.28-0.91), disease progression or death (HR 0.48, 95% CI, 0.27-0.85), and morphologic relapse (HR 0.30, 95% CI, 0.13-0.69), and comparable NRM (HR 0.85, 95% CI 0.36-2.00). The combination of clofarabine with TBI warrants further investigation in patients with high-risk AML.