AbataCept for the Treatment of Immune-cHeckpoint Inhibitors Induced mYocarditiS

Abatacept will be administered by intravenous injection over 1h15 to 2h30 on D1, D5+/-2 and D14+/-2 at 10mg/kg (arm A), or 20mg/kg (arm B) or 25mg/kg (arm C) depending on the randomization (max 3 000 mg per administration). Starting Day 21 (after evaluation of the primary outcome), other injection of abatacept may be given (D22 at D90) with dosage (10 or 20mg/kg max) decided by the treating physician (max 2 500 mg per administration) as a function of the relapse or not of the ICI myocarditis after immunosuppressant therapeutics tapering. After day 21, the administrations will be carried out in open but the blind administration 1 to 3 (D1 to D21) will be kept.