SAN DIEGO—Preliminary data on UCART19—the first off-the-shelf, anti-CD19, allogeneic chimeric antigen receptor (CAR) T-cell therapy—suggest it can produce complete responses (CRs) and minimal residual disease (MRD) negativity, and side effects are manageable.
Investigators pooled data from the phase 1 pediatric (PALL) and adult (CALM) trials of UCART19 in patients with relapsed or refractory acute lymphoblastic leukemia (ALL) and observed a 67% CR rate in the overall population and an 82% CR rate in patients who received a three-drug lymphodepleting regimen.
Additionally, investigators reported no instance of moderate or severe acute graft-versus-host disease (GVHD) with UCART19.
“We’ve been blessed with the new treatments that have emerged in recent years,” said Reuben Benjamin, MD, PhD, “that include BiTEs, antibody-drug conjugates, and most excitingly, the autologous CAR T-cell therapies.”
Nevertheless, some logistical issues with the autologous CAR T cells leave an unmet need in this group of patients, he noted.
“So an off-the-shelf approach using a product like UCART19 may potentially overcome some of these hurdles that we see in the autologous CAR T-cell therapy field,” he said.
Dr. Benjamin, of King’s College Hospital in London, U.K., presented the analysis of PALL and CALM data at the 2018 ASH Annual Meeting as abstract 896.*
UCART19 is an allogeneic, genetically modified, CAR T-cell product (anti-CD19 scFv- 41BB-CD3ζ) manufactured from healthy donor T cells.
It has a safety switch—RQR8, which is a CD20 mimotope—that allows the CAR T cells to be targeted by rituximab.
“And importantly,” Dr. Benjamin explained, “the T-cell alpha gene has been knocked out using TALEN® gene-editing technology to prevent T-cell receptor-mediated graft-versus-host disease.”
The CD52 gene is also knocked out, which permits an anti-CD52 monoclonal antibody, such as alemtuzumab, to be used in lymphodepletion.
The primary objective of both the adult (NCT02746952) and pediatric (NCT02808442) studies was to determine the safety and tolerability of UCART19. Also, the adult study was to determine the maximum tolerated dose of UCART19 and the optimal lymphodepleting regimen.
A secondary objective of both studies was to determine the remission rate at day 28.
Eligible patients received a lymphodepleting regimen for 7 days, followed by a single infusion of UCART19.
Lymphodepletion in the pediatric trial consisted of fludarabine (F) at 150 mg/m2 and cyclophosphamide (C) at 120 mg/kg, with or without alemtuzumab (A) at 1 mg/kg capped at 40 mg.
Adults received lower doses of each agent—90 mg/m2, 1,500 mg/m2, and (optionally) 1 mg/kg or 40 mg, respectively.
Investigators included alemtuzumab in the regimen to minimize viral infections.
The UCART19 dose was weight-banded in the pediatric trial and ranged from 1.1 to 2.3 x 106 cells/kg.
The adult trial included three UCART19 dose levels:
- 6 x 106 cells (≈1 x 105 cells/kg)
- 6 or 8 x 107 cells (≈1 x 106 cells/kg)
- 8 or 2.4 x 108 cells (≈3 x 106 cells/kg).
Patients were assessed for safety and response at day 28 and regularly thereafter for up to 12 months. Patients had the option during the follow-up period to receive a second dose if they did not respond or lost their response.
Twenty-one patients were enrolled in the trials—seven children and 14 adults. Median ages were 2.7 years (PALL; range, 0.8–16.4) and 29.5 years (CALM; range, 18–62).
Both studies included high-risk, heavily pretreated populations, Dr. Benjamin noted.
The pooled population had a median of 4 prior lines of therapy (range, 1–6), and nine patients had a high-risk cytogenetics, including complex karyotypes, MLL rearrangements, and Ph+ disease.
Thirteen patients had prior allogeneic stem cell transplants.
Nine patients had a bone marrow tumor burden of more than 25% blasts prior to lymphodepletion.
As of the cutoff date of October 23, all patients had been treated with UCART19.
Four of the pediatric patients are still on the trial. Two are in remission, one has relapsed, and one is refractory.
Eight adult patients are still on trial. Three are in remission, three are relapsed, and two are refractory.
“UCART19 appears to show an acceptable safety profile based on the adverse events reported so far,” Dr. Benjamin said.
Nineteen patients experienced cytokine release syndrome (CRS), primarily grades 1 and 2. Eight patients had grade 1 and 2 neurotoxicity events, and two patients had grade 1 acute skin GVHD.
“In keeping with what is seen in some of the autologous CAR T-cell trials,” Dr. Benjamin explained, “prolonged cytopenias were seen, which we defined in these studies as grade 4 neutropenia or thrombocytopenia occurring at 42 days post-UCART infusion.”
Six of 21 patients developed prolonged cytopenia.
There was also an increased incidence of viral infections occurring in eight patients, including cytomegalovirus, adenovirus, BK virus, and metapneumovirus.
“Most of these infections, however, were manageable,” Dr. Benjamin said.
Two patients developed neutropenic sepsis, one grade 5, which was one of the treatment-related deaths in the CALM trial.
No treatment-related deaths occurred in the PALL study, but there were two in the CALM study—one from pulmonary hemorrhage and the other from neutropenic sepsis and grade 4 CRS.
Twelve patients are still alive, five of whom are in CR.
Of the patients who received FCA lymphodepletion, 82% (14/17) achieved CR/CR with incomplete hematologic recovery (CRi), and 71% (10/14) achieved MRD negativity.
An additional patient gained MRD-negative status after the second dose of UCART19.
Of the 14 patients who achieved a CR/CRi, 78% (n=11) went on to receive an allogeneic transplant.
In the entire pooled population, 67% (14/21) achieved CR/CRi.
Three patients received a second UCART19 dose, and five patients remain in CR/CRi.
UCART19 expansion, as measured by quantitative polymerase chain reaction in PALL and flow-based methods in CALM, occurred primarily in the first 28 days in the FCA-treated population.
Investigators observed expansion in 15 of 17 patients treated with FCA. None of the patients who received FC alone (n=4) had expansion detectable in blood or bone marrow, Dr. Benjamin noted.
“The response we’ve seen in the study so far,” Dr. Benjamin clarified, “is linked to the expansion observed within the first 28-day period.”
UCART cells persisted in three patients beyond day 42. In one patient, they persisted up to day 120.
“Of interest is the T-cell recovery seen in the study,” Dr. Benjamin elaborated. “We only have data from the adult study here—14 patients. And you’ll see that, in the FCA-treated arm (n=11), you have a deeper and more sustained lymphodepletion compared to the FC-treated patients (n=3). And this may play a role in the subsequent UCART19 expansion and disease response.”
Of the three patients who were re-dosed, two achieved MRD negativity.
One patient achieved MRD-negative status at day 28 but relapsed and received a second infusion 3 months after the first dose. The second expansion was not as deep as the first, but the patient nevertheless achieved MRD negativity after the second dose.
The second patient received FC lymphodepletion and was refractory at day 28.
“The second time around, he received FCA, had a slightly better expansion, and achieved molecular remission,” Dr. Benjamin said.
And the third patient had FCA lymphodepletion but was refractory at day 28.
“We elected to give a second dose at 2.4 months later, but unfortunately, there wasn’t very much expansion, even the second time around, and the patient progressed,” Dr. Benjamin said.
FCA lymphodepletion appears to be required for UCART19 expansion. There was no UCART19 expansion and no response in all four patients lymphodepleted with FC.
The evaluation of UCART19 is ongoing in pediatric and adult B-cell ALL, and “there is a plan for moving into the lymphoma space as well,” Dr. Benjamin added.
Dr. Benjamin disclosed honoraria from Amgen, Takeda, Novartis, Gilead, and Celgene, and research funding from Servier and Pfizer.
Servier and Allogene are supporting the UCART19 trials.
*Data in the abstract differ from the presentation.