Patient deaths, FDA hold cloud Unum’s $86M IPO bid

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Unum's immunotherapies are designed to pack a double punch against cancer when administered alongside antibodies like rituximab. (Unum Therapeutics)

Cancer immunotherapy company, Unum Therapeutics, filed with the SEC Friday to raise up to $86 million in its IPO. But the biotech revealed more than its desire for capital in its filing: It revealed a clinical hold on, and two patient deaths in, a phase 1 trial in non-Hodgkin's lymphoma.

The candidate, ACTR087, was being tested in combination with rituximab in patients with CD20+ B cell-relapsed or refractory non-Hodgkin's lymphoma. The company observed “ACTR087-related serious adverse events, including two patient deaths” in the trial, which led to the FDA halting the trial pending certain information, Unum said in its form S-1.

The FDA lifted the hold last month, Unum said, but the Cambridge, Massachusetts-based biotech kept mum on the hold and patient deaths while prepping for the IPO. It filed confidentially in November.

Unum’s pipeline is based on its Antibody-Coupled T-cell Receptor, or ACTR, platform. T cells, are modified to express ACTR, a chimeric protein that gives them the ability to bind to tumor-targeting antibodies. When the engineered T cells are reinfused into the patient alongside antibodies like rituximab, they are expected to unleash a heightened tumor-fighting response.

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Its lead candidate, ACTR087, was given to patients in two doses in the phase 1 trial. Of the six patients in the lower-dose arm with evaluable data, two had complete responses to the treatment and one had a partial response. No adverse events were reported.

But in the nine-patient, higher-dose group, there were “dose-limiting toxicities in three patients.” Two deaths were directly tied to ACTR087—the patients developed severe cytokine release syndrome, a frequent side effect of CAR-T therapies that can be fatal. The third patient died from ACTR087-related neurotoxicity.

“[No] conclusions regarding the efficacy of ACTR087 can yet be drawn and no head-to-head trials have been conducted that would enable us to make a direct safety and efficacy comparison,” Unum said in the SEC filing. But it is already comparing the treatment with Yescarta and Kymriah, the CAR-T therapies that scored FDA approval last year for blood cancers. The response rate in the lower-dose group are similar to those reported for Yescarta and Kymriah, at 39% and 32% complete response rates, respectively.