Hyper-CVAD Plus Epratuzumab As Salvage Regimen for Younger Relapsed/Refractory CD22+ B Acute Lymphoblastic Leukemia (ALL) Patients: Results of the Phase 2 Prospective Cheprall Study

Purpose: Hyper-CVAD developed by the MD Anderson group a few years ago, is one of the standard salvage regimen used for younger relapsed/refractory ALL patients. Recently, targeted therapies using monoclonal antibodies directed against such surface antigens as CD19, CD20 or CD22 have allowed to obtain complete remission (CR) in B ALL expressing these markers. We hypothesized that combining Hyper-CVAD and an anti-CD22 monoclonal antibody could improve the response of such patients.

Materials and Methods: This study evaluated the Cheprall salvage regimen, where epratuzumab, a humanized therapeutic monoclonal antibody against CD22 with mainly ADCC property, was associated to Hyper-CVAD, in younger patients (18-59 years old) with relapsed/refractory CD22+ (>30% of expression) B-ALL. Cheprall consisted of epratuzumab 360 mg/m²/d iv on days 1, 8, 15 and 22, cyclophosphamide 300 mg/m²/12h iv on days 1 to 3, vincristine 2 mg iv on days +4 and +11, doxorubicin 50 mg/m² iv on day +4 and dexamethasone 40 mg po on days 1 to 4 and 11 to 14. The main objective of the study was the overall response rate (CR + CR with incomplete platelets recovery (<100 000/mm³, CRp) + partial response (PR, >=50% of bone marrow (BM) blasts decrease or CR with persistent extramedulladory disease) evaluated between 4 and 6 weeks from day+1. Secondary objectives were overall (OS) and leukemia free (LFS) survivals and minimal residual disease (MRD) evaluated by flow cytometry.

Results: Between January 2011 and April 2016, 31 patients from 11 French centres were enrolled in the study. A combination of epratuzumab + vincristine and dexamethasone (EVD) only was given to one patient subsequently excluded from the analysis. Among the 30 patients ultimately considered for analyses, 19 were males and the median age was 35 years (range: 21-59). The median time between diagnosis and Cheprall was 14.5 months (range: 4-130) and 13 patients had been allotransplanted. Disease status at time of Cheprall was as follows: primary refractory n=3; first relapse non treated n=13; refractory first relapse n=6, second relapse non treated n=7 and fourth relapse n=1. Median percentage of white blood cells and BM blasts were 4525/mm³(range: 90-86790) and 60% (range: 15-100), respectively. The median CD22 expression of BM blasts was 100% (range: 36-100). Four patients had extramedullary disease: breast n=2, parotid n=1, nervous central system n=1 (deviation). Cheprall was overall well tolerated including mostly pancytopenia as grade ¾ toxicities. Three patients died during aplasia (septis n=1; cerebral haemorrhage n=1, fusariosis n=1) and were not evaluable for response.

The overall response rate was 50% (n=15) including 9 CR (30%), 1 CRp (3%) and 5 PR (17%). The number of CR/CRp was higher for patients in first non-treated relapse (54% vs 18%) with an age below 36 years (50% vs 14%), with <=50% of BM blasts (57% vs 26%) and with a delay between diagnosis and Cheprall > 18 months (54% vs 17%). Four out of 9 evaluated CR/CRp patients (45%) were documented with negative MRD. All patients in CR/CRp and 1 patient in PR received a consolidation consisting of a second cycle of Cheprall n=5, EVD n=5 or blinatumomab n=1. At the time of analysis (July 2016), all patients have died (during aplasia n=3, progression n=23, multiple organ failure n=1), except three responders still in CR, but yet recently enrolled (2015 n=1, 2016 n=2). Six patients received allogeneic transplant after Cheprall: 4 in CR2, 1 as salvage treatment and 1 in CR3. The last patient included and who achieved CR2 should be allografted in August 2016. Median OS was 3 months (range: 0.2-34.8). Median LFS for those achieving CR/CRp was 4.5 months (range: 1-12).

Conclusion: Hyper-CVAD + epratuzumab allowed to obtain 50% of response in this cohort of patients at high risk of failure with refractory/relapsed younger CD22+ B-ALL. Disease improvement was however short-lived, which could be explained either by an insufficient disease load decrease and/or by escape of the blast cells to epratuzumab. This partial efficacy in a population of poor prognosis may suggest that epratuzumab should be tested within first-line chemotherapies as it may participate to decrease MRD level, especially before transplantation. The trial was registered at http://clinicaltrials.gov/ct no.NCT01219816. This study was supported by a grant from the French National Cancer Institute (PHRC 2010).