AnaptysBio Stock Jumps On Promising Rheumatoid Arthritis Drug Readout; Retail Traders Brace For Potential Offering

AnaptysBio Inc.’s shares rose to a six-month high on Tuesday following the announcement of successful Phase 2b results from testing their experimental rheumatoid arthritis medication rosnilimab.

The stock closed 7.6% higher at $23.52 on Tuesday, extending gains by another 5.1% to $24.71 in after-hours trading.

A trial involving 424 patients proved that rosnilimab, a PD-1+ T cell depleter and agonist, delivered similar effectiveness to JAK inhibitors when administered monthly. 

Patients saw significant disease activity improvements through reductions in the Clinical Disease Activity Index (CDAI) and ACR70 response rates, which lasted for six months.

The treatment-free period of up to two months showed sustained patient responses, which signals the possibility for longer dosing intervals. 

According to the company, no serious treatment-related adverse events appeared during the study, and the drug demonstrated superior tolerability compared to existing biologics and JAK inhibitors.

On Stocktwits, retail sentiment was ‘bearish’ amid ‘extremely high’ message volume.

One user suggested the stock was being "pumped" and speculated that a direct offering might follow. 

Another user said they expected the updated data to disappoint and anticipated a potential offering.

The stock has risen 76.1% so far in 2025.

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