Patients with B-cell NHL that had returned after or failed to respond to a median of three prior therapies showed complete responses and durable remissions after being treated with an investigational drug called mosunetuzumab.

Among patients whose lymphoma progressed after treatment with CAR T-cell therapy, 22% had complete remissions when treated with mosunetuzumab.

This new drug targets two proteins, one on the surface of tumour cells and the other on the surface of the recipient’s Tcells.

“Unlike CAR T-cell therapy, mosunetuzumab is an off-the-shelf immunotherapy product that can be given to patients without having to genetically modify their T cells,” said lead author Stephen J. Schuster, MD, of Abramson Cancer Center at the University of Pennsylvania in Philadelphia. 

“Mosunetuzumab generates long-lasting responses with a very tolerable safety profile in patients with B-cell non-Hodgkin lymphomas for whom multiple prior treatments have failed and whose prognosis is poor. Of particular interest, we are seeing durable complete remissions in patients whose lymphomas progressed after CAR-T.” Many remissions continue after patients stop receiving the drug.

“I have stopped therapy in some patients after six months and they have remained in remission. Some patients have remained in remission without additional therapy for more than a year,” Dr. Schuster said.

New treatment options are needed not only for patients in whom CAR T-cell therapy has failed, but also for those patients whose lymphomas are getting worse so quickly that they cannot wait for CAR T cell manufacturing, which takes several weeks, Dr. Schuster said.

Mosunetuzumab is a synthetic antibody designed to bind to a specific marker on tumour cells.

It works by activating the patient’s own T cells, stimulating them to attack and kill cancerous B cells to which they have been introduced by the novel antibody.

The drug could potentially be given to patients before, after, or in combination with CAR-T, which needs to be further tested and explored, researchers explained.        

Data were presented for 270 patients (median age 62, 172 men) enrolled in the phase I trial in seven countries (the United States, Australia, Canada, Germany, South Korea, Spain, and the United Kingdom).

All had B-cell lymphomas that had come back or not responded to a median of three prior therapies.

Two-thirds of patients (67%) had fast-growing lymphomas; 85 (31%) patients had more slow-growing forms of the disease.

In 30 patients (11%), the cancer was resistant to or returned after an initial response to CAR T-cell therapy; in 77 patients (29%), the disease had progressed after a stem cell transplant.

All patients were treated with mosunetuzumab by intravenous infusion.

They had an imaging test at either six weeks or three months after starting therapy to assess the initial response to treatment, and responses continued to be followed every three months thereafter.

Forty-six of 124 patients with fast-growing lymphomas (37%) had measurable decreases in the extent of their cancer (objective response); 24 of 124 patients (19%) saw all detectable tumours disappear (complete response).

A higher response rate was observed in patients with higher exposure to mosunetuzumab.

Among patients with slow-growing lymphomas, 42 of 67 (63%) had objective responses and 29 of 67 (43%) had complete responses.

Both objective response rate and complete response rate were maintained in subgroups of patients at high risk for relapse.

Complete remissions appear to be long lasting, Dr. Schuster said.

With a median follow-up of six months since first complete remission, 24 of 29 patients (83%) who achieved complete remissions of their slow-growing lymphomas and 17 of 24 patients (71%) who achieved complete remissions of their fast-growing lymphomas remain free of disease.

In some patients whose cancers progressed after receiving CAR T-cell therapy, highly sensitive molecular testing showed that the previously administered CAR T cells increased in number.

This suggests that, in addition to its ability to kill cancerous B cells, mosunetuzumab may also help augment the effect of the prior CAR-T treatment, Dr. Schuster said.

In this study, 29% of patients treated with mosunetuzumab experienced cytokine-release syndrome that was mostly mild.

In 3% of patients, CRS was treated with tocilizumab.

Four percent of patients experienced moderately severe neurologic side effects.

Patients who received higher doses of mosunetuzumab were no more likely to have CRS or neurologic side effects than patients treated at lower doses.

A study of a higher dose of mosunetuzumab is now enrolling patients, Dr. Schuster said.

Long-term follow-up of these patients will ultimately help to better evaluate the durability of response data.

“Larger, randomised trials are needed to further confirm these promising data and determine whether the treatment benefit of mosunetuzumab is enhanced when it is used earlier in the course of lymphoma therapy or in combination with other agents,” Dr. Schuster said.

Source: American Society of Hematology

Watch ecancer's interview with Prof Schuster here. 

Watch the press conference here.