The answer to the billion dollar question – Does the chimeric antigen receptor T-cell (CAR T) construct CTL019 (tisagenlecleucel-T) have a favorable risk-benefit profile for the treatment of children and young adults with relapsed/refractory B-cell precursor acute lymphoblastic leukemia? – was a unanimous “yes” at a July 12 meeting of the Food and Drug Administration’s Oncologic Drugs Advisory Committee.

“This is the most exciting thing I have seen in my lifetime, and probably since the introduction of ‘multiagent total cancer care,’ as it was called then, for treatment of childhood leukemia,” remarked Timothy P. Cripe, MD, PhD , from Nationwide Children’s Hospital in Columbus, Ohio, and a temporary voting member of the ODAC.

Catherine M. Bollard, MD, MBChB, from the Children’s National Medical Center in Washington, also a temporary ODAC member, said that she voted “yes” because “this is a very poor-risk patient population, this is an unmet need in the pediatric population, and as you saw in the data [presented to ODAC] today, the clinical responses are remarkable. I think Novartis [the maker of CTL019] has done a great job putting together a plan for mitigating risk going forward.”

CTL019 was shown in a pivotal phase 2 clinical trial to induce an overall remission rate of 83% in children and young adults with relapsed/refractory ALL for whom at least two prior lines of therapy had failed. Based on these results, the FDA accepted a biologics license application for the agent from Novartis.

At the meeting, panel members initially seemed favorably disposed toward recommending approval but heard concerns from FDA scientists about the potential for severe or fatal adverse events such as the cytokine release syndrome (CRS); the possible generation of replication competent retrovirus (RCR); and the potential for secondary malignancies from insertional mutagenesis, the incorporation of portions of the lentiviral vector into the patient’s genome.

In his opening remarks, Wilson W. Bryan, MD, from the FDA’s Office of Tissue and Advanced Therapies and Center for Biologics Evaluation and Drug Research, commented that “the clinical development of tisagenlecleucel suggests that this is a life-saving product.”

He went on, however, to frame the FDA’s concerns: “Clinical trials are not always a good predictor of the effectiveness and safety of a marketed product,” he said. “In particular, we are concerned that the same benefit and safety seen in clinical trials may not carry over to routine clinical use.”

The purpose of the hearing was to focus on manufacturing issues related to product quality, including replicability of the product for commercial use and safety issues such as prevention of CRS and neurotoxicities.

“We are also concerned about the hypothetical risk of secondary malignancies. Therefore, we are asking for the committee’s recommendations regarding the nature and duration of follow-up of patients who would receive this product,” Dr. Bryan said.

“CTL019 is a living drug, which demonstrates activity after a single infusion,” said Samit Hirawat, MD , head of oncology global development for Novartis.

But the nature of CTL019 as a living drug also means that it is subject to variations in the ability of autologous T cells harvested via leukapheresis to be infected with the lentiviral vector and expanded into a population of CAR T cells large enough to have therapeutic value, said Xiaobin Victor Lu, PhD, a chemistry, manufacturing, and controls reviewer for the FDA.

Mitigation plan

Novartis’ proposed plan includes specific, long-term steps for mitigating the risk of CRS and neurologic events, such as cerebral edema, the latter of which caused the FDA to call for a clinical hold of the phase 2 ROCKET trial for a different CAR T-cell construct.

Among the proposed elements of the mitigation plan are a 15-year minimum pharmacovigilance program and long-term safety follow-up for adverse events related to the therapy, efficacy, immunogenicity, transgene persistence of CD19 CAR, and the incidence of second malignancies possibly related to insertional mutagenesis.

Novartis also will train treatment center staff on processes for cell collection, cryopreservation, transport, chain of identity, safety management, and logistics for handling the CAR T-cell product. The company proposes to provide on-site training of personnel on CRS and neurotoxicity risk and management, as well as to offer information to patients and caregivers about the signs and symptoms of adverse events of concern.

Dr. Cripe expressed his concerns that Novartis’ proposal to initially limit the mitigation plan to 30 or 35 treatment sites would create problems of access and economic disparities among patients, and could cause inequities among treatment centers even with the same city.

David Lebwohl, MD, head of the CAR T global program for Novartis, said that the planned number of sites for the mitigation program would be expanded after 6 to 12 months if the CAR T construct receives final approval and clinical implementation goes well.

There was nearly unanimous agreement among the panel members that the planned 15-year follow-up and other mitigation measures would be adequate for detecting serious short- and long-term consequences of CAR T-cell therapy.

Patient/advocate perspective

In the public comment section of the proceedings, panel members were urged to vote in favor of CTL019 by parents of children with ALL, including Don McMahon, whose son Connor received the therapy after multiple relapses, and Tom Whitehead, father of Emily Whitehead, the first patient to receive CAR T cells for ALL.

Both children are alive and doing well.

CTL019 is produced by Novartis.