Optimized Rabbit Antithymocyte Globulin Protocol Plus Sequential Cyclosporine and Levamisole Regimen for Newly Diagnosed Severe Aplastic Anemia: A Single-Arm, Single-Centre, Prospective, Phase 2 Trial

Background The inferior effect of rATG is due to the early fatal blow caused by the more potent immunosuppression. In order to retain its sustainable immunosuppression while weakening the early fatal blow. We explored a modifying schedule of administration of rATG by prolonging the course of rATG administration based on the equality of total dose, and then reported the better response and survival in severe aplastic anemia (SAA). And previously, we reported the encouraging effectiveness of cyclosporine alternately combined with levamisole (CSA and LMS regimen) in moderate AA, refractory or relapsed SAA, and SAA. We aim to establish whether the optimized rATG protocol plus sequential CSA and LMS regimen could improve SAA outcomes.

Methods We conducted a single-arm, prospective, phase 2 trial at The Institute of Hematology & Blood Diseases Hospital, Chinese Academy of Medical Science & Peking Union Medical College (CAMS & PUMC). Patients aged 6 years or older with confirmed, newly diagnosed SAA were eligible. Patients received optimized rATG administration (1.97 mg/kg/d for 9 days) based on the equality of total does with standard protocol (3.55 mg/kg/d for 5 days). And then CSA and LMS were alternatively administrated every other day from day 14. The initial dose of CSA was 3mg/kg/day in adults and 5mg/kg/day in children (6-18 years old). Oral LMS was alternatively administrated at a dose of 150 mg per day in adults and 2.5 mg/kg per day in children (< 40 kg) in three divided doses. The primary endpoint was overall response rate at 6 months. The trial is registered at www.clinicaltrials.gov as NCT02203396.

Results: Between Aug 1, 2014 and Sep 30, 2017, 40 patients with newly diagnosed SAA were treated (median age 24 years [range 7-57 years]; 19 [47.5%] male; 18 [45%] VSAA; 1[2.5%] post-hepatitis). All of these patients were transfusion dependent. Demographic data and clinical characteristics of these patients are outlined in Table 1.

The 3-month overall response rates (ORRs) was 40.0%, including 2.5% CR and 37.5% PR. The ORRs increased to 60% (15% CR and 45% PR) at 6 months and 72.5% (42.5% CR and 30% PR) at 12 months. With a median follow-up of 77 months (range 0.1-97 months), estimated 8-year OS rate and event-free survival rate were 84.9% (95% CI, 69.35-92.9%) and 66.5 (95%CI, 49.1-79.1%), respectively.

No patient discontinued therapy because of treatment-related toxicity. There were two deaths-one due to infection and another due to cerebral hemorrhage. In this cohort, 4/40 patients (5.7%) evolved to clonal disorders. Of the 4 patients, 1 patients progressed to overt PNH, 2 MDS and 1 acute myeloid leukemia (AML). Cytogenetic abnormalities involved chromosome 7 occurred in one cases with AML. A total of 2 (7.1%) patients relapsed at 33 and 79 months after initial response. Both of the 2 relapsed patients acquired response again with the administration of CSA.

Conclusions: Front-line sequential optimized rATG protocol with CSA and LMS regimen resulted in encouraging long-term survival. Future randomized studies should evaluate the optimized IST regimen in the treatment of patients with SAA.