This study will evaluate the safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and efficacy of KP104 in participants with systemic lupus erythematosus (SLE)-Thrombotic microangiopathy (TMA). The study consists of 2 parts: Part 1 (Dose Optimization) and Part 2 (Proof of Concept). All participants will receive KP104 in combination with standard of care (SOC) for SLE-TMA.
Meets criteria for SLE per the 2019 European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) criteria.
Decrease in platelet count to less than (<)150,000/microliters (mcL).
Abnormal renal function.
Females of childbearing potential with negative pregnancy test and males must agree to practice effective contraception from Screening until 28 days after the End of study (EOS) visit.
Diagnosis of other TMA syndromes.
A renal biopsy within 7 days of screening that shows exclusively chronic changes of TMA.
Positive Coombs test at the time of TMA diagnosis.
Active or unresolved Neisseria meningitidis infection at screening.