Bristol Myers Squibb drops Prothena's PRX019 after internal review

Bristol Myers Squibb told Prothena Corporation plc on October 28, 2026 that following an internal strategic review, it had decided not to advance PRX019 further in the clinic.¹

The PRX019 program stemmed from a research and development collaboration between the two companies that began in 2018, covering both PRX019 and moponetug as clinical-stage programs.¹ The PRX019-specific license came later: in May 2024, a Prothena subsidiary signed an exclusive global license agreement with Bristol Myers Squibb to develop, manufacture and commercialize antibody products targeting a specified target, including PRX019, and received an $80 million upfront payment.¹ That agreement will terminate on January 28, 2027.¹

Prothena said the drug had cleared early testing. In the first half of 2026, the company completed the Phase 1 trial for PRX019, which showed a benign safety and tolerability profile, no immunogenicity, and dose-dependent pharmacokinetic and pharmacodynamic effects, meeting the company's prespecified pharmacodynamic targets.¹

Financially, the termination closes off further payments tied to PRX019. Beyond the upfront payment, Prothena had been eligible for development, regulatory and sales milestones up to $617.5 million, plus tiered royalties on worldwide net sales of licensed products.¹ With the agreement ending, Bristol Myers Squibb will not owe any of those amounts.¹

The broader 2018 collaboration continues through moponetug. Bristol Myers Squibb is still developing moponetug, formerly PRX005, an antibody targeting a tau epitope for Alzheimer's disease, in the ongoing Phase 2 "TargetTau-1" trial in early Alzheimer's patients (NCT06268886).¹ Bristol Myers Squibb has paid Prothena $135 million in licensing payments for moponetug so far, with up to $562.5 million more in potential regulatory and sales milestones plus tiered royalties.¹