Conference Coverage

Pembrolizumab + rituximab boost response rates in relapsed follicular lymphoma



– A novel combination of the anti-programmed death 1 (PD-1) checkpoint inhibitor pembrolizumab (Keytruda) and the anti-CD20 monoclonal antibody rituximab was associated with a high overall response rate (ORR) in patients with relapsed follicular lymphoma in a phase II clinical trial.

“Follicular lymphoma is probably one of the best examples of targeting the immune system and also one of the earliest examples. Over the last few years we’ve learned a great deal about the different mechanisms of not only negative impact on infiltrating T cells, but also immune escape and T-cell exhaustion,” she said at the International Conference on Malignant Lymphoma.

Although biopsies of follicular lymphoma tumors have demonstrated infiltration of anti-tumor T cells, these cells are typically impeded by immune checkpoints, including PD-1 and its ligand (PD-L1).

The use of anti-PD-1 checkpoint inhibitors such as pembrolizumab has been shown to enhance the function of antitumor T cells in follicular lymphoma, and blocking PD-1 on natural killer cells enhances the antibody-dependent cell-mediated cytotoxicity of the natural killer cells, she said.

Because rituximab, a mainstay of therapy for non-Hodgkin lymphomas, induces antibody-dependent cell-mediated cytotoxicity, the investigators reasoned that combining it with pembrolizumab would simultaneously and synergistically stimulate activation of innate and adaptive immunity.

They designed a phase II, single-arm study in 30 patients with relapsed follicular lymphoma following one or more prior lines of therapy. The patients also had to have rituximab-sensitive disease, defined as a complete response (CR) or partial response lasting for at least 6 months following the most recent rituximab-containing therapy.

The patients were treated with rituximab 375 mg/m2 IV on days 1, 8, 15, and 22 of cycle 1, and pembrolizumab 200 mg IV every 3 weeks for up to 16 cycles starting on day 2 of cycle 1.

The investigators expected that the combination would improve ORR, the primary endpoint, to at least 60%, compared with 40% for historical controls treated with repeat courses of rituximab.

At the data cutoff for the interim analysis, 32 patients had been enrolled, 30 were evaluable for safety, and 20 for efficacy after a median follow-up of 8.2 months.

Among the 20 patients (median age 64) in the efficacy analysis, 10 (50%) had a CR, and 3 (15%) had a partial response, for an ORR of 65%. Three additional patients had stable disease, and four had disease progression as best responses.

Among the patients with CRs, the duration of response ranged from nearly 275 days to more than 600 days.

“This does appear to be durable, and it is time dependent in terms of response. We did see early response, and we also saw deepening of response over time,” Dr. Nastoupil said.

Four patients were discontinued from the study because of immune-related adverse events. All four patients had achieved a CR at the time of study removal, and all four have ongoing CRs.

Among the 30 patients evaluable for safety, there were no grade 4 adverse events, no deaths, and few grade 3 events. Most events were grade 1 or 2, and included fatigue, eye pain/blurred vision/watery eye, nausea and vomiting, diarrhea dyspnea, rash, cough, and lymphopenia.

The investigators also looked at potential biomarkers for response, including PD-L1 expression in tumors prior to treatment. They found in samples from three patients who went on to achieve CRs that PD-L1 expression in tumor cells was low, ranging from 0% to 8%, suggesting that PD-L1 expression may not be necessary to generate a response with the combination.

They then looked at the association between CD8-positive T effector cells and responses in 12 patients, and found that patients with higher levels of expression had better ORR and CR rates.

“These interim results warrant further investigation of this combination in follicular lymphoma, and an expansion to include patients with refractory follicular lymphoma is planned,” Dr. Nastoupil concluded.

The Leukemia & Lymphoma Society supported the study. Dr Nastoupil has disclosed consulting fees from Celgene and contracted research for Abbvie, Janssen, and TG Therapeutics.

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