This Phase 1/2a clinical trial involves patients diagnosed with refractory polymyositis or dermatomyositis.~The initial safety assessment is conducted, including development of DLT in subjects up to Week 2 after the investigational product administration.~[DLT assessment criteria and method]~Low dose or intermediate dose level~No DLT developing in the initially enrolled 3 subjects (0/3): Increase the dose to the next dose group~DLT developing 1 of 3 subjects (1/3): Enroll 3 additional subjects at the same dose group and then assess DLT, and ① DLT developing in 1 out of total 6 subjects (1/3+0/3; 1/6): Increase the dose to the next dose group ② DLT developing in ≥ 2 out of total 6 subjects (≥ 2/6): In case of the low dose level, the trial is discontinued without MTD determination. In case of the intermediate dose level, MTD is assessed at the low dose which is a one lower dose level~High dose level~No DLT developing in the initially enrolled 3 subjects (0/3): Declare as the MTD~DLT developing 1 of 3 subjects (1/3): Enroll 3 additional subjects at the same dose group and then assess DLT, and ① DLT developing in 1 out of total 6 subjects (1/3+0/3; 1/6): Declare as the MTD ② DLT developing in ≥ 2 out of total 6 subjects (≥ 2/6): Assess MTD at the intermediate dose which is the one lower dose level
To determine the maximum tolerated dose (MTD) based on the safety and tolerability after single-dose administration of PN-101 in patients with refractory polymyositis or dermatomyositis. To explore the efficacy after single-dose administration of PN-101 in patients with refractory polymyositis or dermatomyositis.