ORLANDO – Inotuzumab ozogamicin (InO), a CD22-targeted antibody approved for adults with relapsed/refractory B-cell acute lymphoblastic leukemia (R/R B-ALL), showed promising safety and efficacy in children and young adults with R/R B-ALL in a phase 2 trial.
Of 48 patients aged 1-21 years enrolled in the Children’s Oncology Group (COG) Protocol AALL1621 and evaluable for response and toxicity after treatment with the approved adult InO dose, 19 achieved a complete response (CR) and 9 achieved a complete response with incomplete count recovery (CRi) after the first treatment cycle, for an overall CR/CRi rate of 58.3%, Maureen M. O’Brien, MD, reported at the annual meeting of the American Society of Hematology.
Of those with CR/CRi, 19 (65.5%) achieved minimal residual disease less than 0.01%, said Dr. O’Brien, a pediatric hematologist and medical director of the Leukemia/Lymphoma Program at the Cancer and Blood Diseases Institute, Cincinnati Children’s Hospital Medical Center.
Three patients had a partial response (PR), nine had stable disease (SD), and eight had progressive disease (PD), and one of each with PR and SD achieved CR/CRi after a second treatment cycle.
“Of note, two patients who were characterized as [having] progressive disease actually had marrow complete response with incomplete count recovery, but had progressive CNS disease,” she said.
Patients included in the single-arm trial had CD22-positive B-ALL, defined as B-ALL with greater than 20% of blasts expressing CD22, and were in at least their second relapse, were refractory to two prior induction regimens, or had a relapse after hematopoietic stem cell transplantation (HSCT). One exception was that patients with Down syndrome were allowed inclusion after a first relapse, she noted.
Median patient age was 9 years, four patients had CNS 3 status, three had Down syndrome, and most were heavily pretreated, with 32 in at least their second relapse.
“Most patients had significant marrow disease burden, with a median marrow blast percentage of 81%,” Dr. O’Brien said. “In terms of prior therapy, 23% had prior transplant, 23% had prior CD19 [chimeric antigen receptor (CAR)] T-cell therapy – including two patients with prior CD22 CAR T, and 29% of patients had received prior blinatumomab.”
All patients received one cycle of InO at a dose of 1.8mg/m2, with .8mg/m2 given on day 1 and 0.5mg/m2 given on days 8 and 15. Intrathecal therapy was determined based on CNS status.
Patients with at least stable disease at day 28 were eligible for a second cycle; those with CR or CRi received InO at a dose of 0.5 mg/m2 on days 1, 8, and 15 in cycle 2, and those without CR/CRi received the same fractionated dose as in cycle 1. Patients with CR/CRi after two cycles were eligible for up to six total cycles at investigator discretion, Dr. O’Brien explained, adding that 26 of 40 patients eligible for cycle 2 proceeded, including 13 of 18 with MRD less than .01%, 6 of 10 with MRD of 0.01% or greater, and 7 of 12 with PR/SD.
After cycle 2, all 13 with MRD less than .01% maintained that MRD level, 3 of 6 with MRD of .01% or greater achieved MRD less than .01%, 2 of 7 with PR/SD achieved CRi with MRD of .01% or greater – and one of those 2 was MRD negative after a third cycle.
Seven patients received three or more cycles.
“Therapy was extremely well tolerated,” Dr. O’Brien said, noting that the most common nonhematological grade 3 or higher adverse events occurring in at least 5% of patients in cycle 1 were febrile neutropenia and infection, occurring in 27.1% and 16.7% of patients, respectively. “But toxicity was quite minimal.”
Hepatic toxicity included four cases of grade 3 alanine transaminase and one grade 3 bilirubin toxicity in cycle 1, and one grade 3 ALT in cycle 2.
“Importantly, there were no inotuzumab dose modifications or delays due to hepatic toxicity,” she said.
Nine patients experienced 11 dose-limiting toxicities in cycle 1, including 7 involving prolonged count recovery beyond day 42, which was not attributable to disease, and 4 nonhematologic events, including drug reaction with eosinophilia and systemic symptoms, bronchopulmonary hemorrhage, respiratory distress, and a postintrathecal methotrexate stroke.
Sinusoidal obstruction syndrome (SOS) developed in 5 of the 48 patients, all in patients who underwent transplant after InO treatment. Only one of the five had undergone a prior transplant. All SOS cases were grade 3 and were treated with defibrotide; four cases resolved quickly, and one was resolving at the time of death from other causes, she said.
“We found no evidence of association with age, conditioning regimen, SOS prophylaxis, cumulative InO exposure, or time from InO to transplant, bearing in mind that it is a small number of cases, so analysis is limited,” she added.
Central CD22 evaluation in 27 patients with pre– and post–cycle 1 samples showed that 11 of those patients had residual disease at the end of cycle 1.
“There is clearly a subset of patients for whom the resistance mechanism does not seem to have any bearing on CD22, as it was still highly expressed at the time of relapse, but there are a significant number of patients who have downregulation of CD22 expression or a subset of blasts that were CD22 negative at the time of relapse,” she said. “Notably, two of three patients with baseline partial CD22 expression – so less than 90% ... did not achieve a morphologic complete response, and both of these patients had KMT2A rearrangements.”
The findings are important, because 10%-20% of children and young adults with B-ALL will relapse, and therapies that can bridge patients to HSCT or CAR T-cell therapy are critical for improving outcomes, Dr. O’Brien said, explaining that InO, a humanized CD22 IgG4 antibody conjugated to calicheamicin, was approved in adults based on “the impressive results from thecompared with chemotherapy,” but prospective data on its efficacy and safety in pediatric patients are lacking.
Retrospectivefrom a compassionate use program in children demonstrated a response rate of 67% in a heavily pretreated population, and phase 1 data from the ITCC-059 trial presented in a at the ASH meeting also showed “quite impressive results,” but a major concern has been hepatic toxicity, including SOS, she said.
Given the observed safety and efficacy in the current phase 2 trial, investigation in children will continue, she said, explaining that “COG is now undertaking a phase 3 trial – AALL1732 – which will randomize patients to chemotherapy [with or without] inotuzumab for patients aged 1-25 with newly diagnosed high-risk B-ALL.”
COG AALL1621 was funded by NCTN grants, St. Baldrick’s Foundation, and Pfizer. Dr. O’Brien reported research funding from Pfizer, Celgene, AbbVie, Amgen, Bristol-Myers Squibb, and BTG.
SOURCE: O’Brien M et al. ASH 2019, .