Lack of Sufficient Data Sinks Atara in Mid-Phase MS Study

Immunotherapy-focused company Atara Biotherapeutics announced that it has completed an interim analysis of its Phase II EMBOLD trial for the use of  ATA188 in patients with progressive multiple sclerosis (MS).

Based on EMBOLD’s early safety, efficacy and biomarker data, the Independent Data and Safety Monitoring Committee (IDSMC) recommended that the study continues with no further need to adjust its sample size.

The IDSMC based its recommendations on data from just 34 and 15 patients who had evaluable follow-up information at 6 and 12 months, respectively, across both the ATA188 and placebo arms. Because of this lack of available data, the interim analysis was unable to determine whether or not the six-month change in EDSS could be used to predict disability improvements at 12 months. While no data have been made public regarding EMBOLD’s primary endpoints, Atara’s stocks dropped around 27% hours after the announcement.

EMBOLD is a randomized and placebo-controlled study that has currently enrolled 80 patients with progressive MS. Its primary endpoints include drug safety and improvements in the severity of the disability, as quantified by the expanded disability status scale (EDSS) scores at six months and beyond.

Atara’s candidate proved safe based on preliminary data, with no strong toxicity concerns detected during the interim analysis. Based on this encouraging safety profile and in line with IDSMC’s feedback, the company is pushing through with EMBOLD. Final results from the 12-month follow-up are expected to come in late next year.

“Following the EMBOLD IA [interim analysis], we are proceeding with the IDSMC’s recommendation that the study continue to completion without sample size adjustment,” Jakob Dupont, M.D., head of global research & development at Atara, said in a statement. “After reviewing the clinical and safety data available at the data cut-off, the IDSMC did not highlight any safety concerns in the ongoing study. We are pleased to have completed the target enrollment for the EMBOLD study and look forward to sharing the topline results as planned at an appropriate forum in October 2023.”

In an investor call Tuesday afternoon, company representatives declined to provide more specific details regarding the direction of treatment effect at both time points, nor did they reveal whether or not EMBOLD triggered its predefined futility thresholds.

“As part of the interim analysis, we did a full analysis covering all possibilities, including futility,” Dupont said. “We have not disclosed boundaries for futility in this particular study. As stated, to protect the integrity of the study, particularly the placebo-controlled nature of this, and to not introduce bias, because we really want to get to that final result on this study, when we have the primary endpoint data at the 12-month confirmed EDSS, we’re not able to disclose these aspects today.”

Also during the investor call, Atara's president and chief executive officer Pascal Touchon revealed that outside of a small R&D team, the company’s management had no access to the interim data.

Multiple sclerosis is an autoimmune condition of the central nervous system that arises when the immune system targets the protective myelin sheath around neurons, leading to their dysfunction. Though there is no singular cause of multiple sclerosis, infection with the Epstein-Barr virus (EBV) is known to dramatically increase disease risk. Atara hopes to take EBV out of the equation with ATA188, a T-cell-based off-the-shelf candidate that can target EBV-infected B cells and plasma cells.