Expert: Selective inhibition of active C1s, the catalytic serine protease subunit of the C1 complex in the classical complement pathway. Blocks C1s cleavage of C4 and C2, preventing formation of the C3 convertase (C4b2a) and all downstream events (C3 amplification, C5a/C3a anaphylatoxin generation, MAC/C5b-9 formation). Targets ONLY the enzymatically active form of C1s (not the abundant zymogen precursor, avoiding target-mediated drug disposition). Preserves lectin pathway (MASP-2 mediated) and alternative pathway (Factor B/D mediated) fully intact, maintaining MAC-mediated bacterial defense — no meningococcal vaccination required. More targeted than C2 inhibition (blocks only classical) or C5 inhibition (blocks terminal pathway from all three routes).

Everyday: Blocks one specific step in the immune system's "demolition cascade." When autoantibodies trigger the classical complement cascade (a chain reaction of proteins that ultimately punches holes in cells), C1s is an early enzyme that relays the demolition order. By blocking active C1s, the demolition crew never gets mobilized through this pathway. Importantly, this leaves two other immune defense pathways fully intact — the "always-on" alternative pathway can still kill bacteria normally, so patients don't need meningococcal vaccination (unlike C5 inhibitors). Think of it as disconnecting one specific alarm system (the one producing false alarms in autoimmune disease) while leaving the 24/7 security cameras running.

Targets: ["C1S"]

Primary EP: [{"id":"captivate-incat-relapse","name":"Time to INCAT Relapse During Randomized Withdrawal","type":"PRIMARY","unit":"time-to-event","results":[],"timepoint":"Variable (randomized withdrawal period)",

Claseprubart - gMG - Ph3 - Trial Initiation 2026

Claseprubart - CIDP - Ph3 - Interim Responder Analysis (CAPTIVATE Part A, n=40) Q2 2026

Claseprubart - MMN - Ph2 - Topline Data (MoMeNtum) H2 2026

MOLECULE PROFILE: - Format: IgG4 monoclonal antibody (naturally effector-silent) - Target: Active C1s only (not zymogen — avoids TMDD from abundant inactive C1s pool) - Half-life: ~21 days (standard IgG4) - Route: All SC (subcutaneous injection, pre-filled syringe) - Dosing: SC Q2W (every 2 weeks) - Self-administration: Yes, all doses at home DIFFERENTIATION vs RILIPRUBART (SNY): - ALL-SC regimen (no IV loading) = simpler treatment initiation - Q2W dosing (vs riliprubart Q4W) = more frequent maintenance - IgG4 format (natural) vs riliprubart IgG1-LALA-PG-YTE (engineered) - Shorter half-life means faster washout if adverse event occurs CLINICAL PROGRAM: - CAPTIVATE: Phase 3 CIDP (randomized withdrawal, INCAT, PCD Sep 2026) - Phase 2 gMG, Phase 2 MMN ongoing - Company also developing DNTH212 (earlier-stage C1s asset) MECHANISM ADVANTAGE (C1s over C2): - More targeted: blocks only classical pathway vs classical + lectin for C2 - In antibody-driven diseases (MG, CIDP), lectin blockade likely unnecessary - Same safety advantage as C2: alternative pathway preserved, no meningococcal vaccination needed