Phase 1b/2a in SLE With Budoputug

This is a Phase 1b/2a, multicenter, open-label study designed to evaluate the safety, tolerability, PK, and PD of budoprutug in adult participants with SLE. In Phase 1b, participants who fulfill the 2012 Systemic Lupus International Collaborating Clinics(SLICC) classification criteria for SLE, and who have active SLE (as defined by a SLEDAI ≥ 4 at Screening and Day 1),have failed at least 1 line of treatment, and who are assessed as appropriate for the study by the Eligibility Adjudicator, will be enrolled in sequential escalating dose cohorts. Three dose cohorts are planned. The Phase 2a expansion cohort will include approximately 16 to 20 participants with active SLE, at least one-half of whom will have renal involvement. Participants will continue to be followed through Week 52 for safety, PK, and PD assessmentsParticipants will also be monitored during this time for ongoing clinical response, safety parameters, and kinetics of re-population of B-cell subsets after the return of B cells to baseline values.