Johnson & Johnson halted patient recruitment in a mid‑stage trial of an Alzheimer’s candidate being developed with partner AC Immune. The pause prompted an approximately 10% decline in AC Immune’s stock and signals a safety, operational or endpoint‑related issue under evaluation. J&J and AC Immune did not disclose details but said enrollment has been suspended while the companies and investigators review trial conduct and data. Sponsors commonly pause recruitment to preserve participant safety and data integrity while assessing next steps with regulators and investigators.