Zag Bio

Zag Bio is a Cambridge, Massachusetts biotechnology startup pioneering thymus-targeted medicines for autoimmune disease. Founded and incubated by Polaris Partners and launched in October 2025 with an $80M Series A, the company designs bifunctional antibodies that ferry self-antigens directly into the thymus - the organ that trains immune cells - to re-teach the body to tolerate its own tissue rather than attack it. Its lead program, ZAG-101, aims to prevent or delay Type 1 diabetes by inducing durable, antigen-specific central tolerance instead of broad immunosuppression.