Inotuzumab Ozogamicin Compassionate Use for French Pediatric Patients with Relapsed or Refractory Acute Lymphoblastic Leukemia

Introduction: Inotuzumab ozogamicin (INO) is an anti-CD22-drug conjugate therapeutic agent, in which a cytotoxic agent, calicheamicin, is conjugated to a humanized IgG4 anti-CD22 mAb (de Vries et al., Leukemia, 2012). As CD22 expression is confined to the B-cell lineage and is largely expressed in mature and immature B-cell malignancies, INO represents an attractive drug to treat B-cell acute lymphoid leukemia (ALL). INO has been evaluated in clinical trials and its efficacy has been reported in adult and elderly patients (pts) with ALL (Kantarjian et al., NEJM, 2016; Lancet Oncol 2018 and Cancer 2018). Since half of the total number of cases of ALL occurs in children and teenagers and it is the most frequently diagnosed malignancy in children, with the vast majority arising from B-cell lineage (85%), INO is also a drug of interest for the 15% of pediatric pts who are not cured by current treatments. We here report French pediatric pts with refractory or relapsed (r/r) B-cell ALL who were treated by INO through a compassionate use access program.

Methods: French pediatric hematology centers provided retrospective clinical follow-up on pts' ≤ 18 years old affected by r/r B-cell ALL who received at least one dose of INO, provided by Pfizer through a compassionate use program following authorization by the French regulatory agency (ANSM) between 2015 and 2017. All pts were treated according to the adult phase 3 clinical trial dose of 1.8 mg/m² during the first course divided as followed: 0.8 mg/m² of body surface at day 1 and 0.5 mg/m² at day 8 and 15. A second course could be repeated at the same dosage if the response was not complete after the first course. Then the consolidation courses of treatment could be continued at the dose of 1.5 mg/m² divided as 0.5 mg/m² of body surface at day 1, 8 and 15, up to 3 total cycles.

Results: Eleven pts aged from 3 to 18 years old received INO; and were: 2 between 1 and 10 years old, 4 between 10 and 15 and 5 between 15 and 18. They received from 1 to 3 cycles of INO. They were heavily pretreated, as 6 of them received INO while refractory to the treatment of a first relapse, and 5 of them in treatment of second relapse or more. Prior to INO therapy, 4/11 pts had undergone allogenic hematopoietic stem cell transplantation (HSCT) and 7/11 pts had received anti-CD19 therapy with either Blinatumomab (6/7) or CAR-T cells (1/7). Pre-INO treatment medullary status was M3 (>25% blasts) for 8/11 pts, M2 (5-25%) for 2 pts and M1 (<5%) with positive minimal residual disease (MRD) and extra-medullary disease for 1 patient (pt).

Eight pts were in complete remission (CR) after one cycle (M2/M3 marrow prior to INO: 7, M1: 1), including 2 pts with an undetectable MRD (< 10-5). These 2 pts received a second cycle of INO and were brought to HSCT; both of them are alive (20 months (m)+, 27 m+). The 6 remaining pts in CR but MRD+ subsequently died: 1) 5 received a second cycle of INO without documentation of MRD negativity. All of them relapsed whatever the following treatment (time to disease progression ranged from 1 week to 17 months). 2) 1 pt was brought to HSCT but died of cardiac failure 3 months after the procedure.

As observed in adults, hepatic and hematologic adverse events were observed. All pts developed hematologic toxicities, 10/11 pts with grade 3/4 anemia, neutropenia or thrombocytopenia. Febrile neutropenia of grade 3/4 occurred for 5 pts. Cholestasis with grade 3/4 elevations of GGT or transaminases was noted in 4/11 pts. Sinusoidal obstruction syndrome (SOS) occurred in 1 pt who had previously undergone HSCT, during his first course of INO. Two pts who subsequently underwent HSCT developed SOS during transplant. All of these 3 pts recovered normal hepatic function. None of them died from INO direct toxicities.

Conclusion: Toxicities developed by these young patients were very similar to the ones reported in adults with hepatic and infectious toxicities. The incidence of SOS seems significant in patients that underwent HSCT either before or after INO treatment. INO showed promising results in pediatric compassionate use program in our French cohort, similarly to the one reported by Bhojwani D et al. (ASCO abstract, 2017). Its safety and efficacy in r/r B-cell ALL are to be further investigated in pediatric populations within prospective clinical trials currently underway in EU and US.