The main objective is to assess the safety and tolerability of inebilizumab in adult participants with active and refractory systemic lupus erythematosus (SLE) with nephritis (Subprotocol A) and to assess the safety and tolerability of subcutaneous (SC) blinatumomab in adult participants with active and refractory SLE with and without nephritis (Subprotocol B Part A) and in adult participants with active refractory rheumatoid arthritis (RA) (Subprotocol C Part A). The trial will also assess the efficacy of SC blinatumomab in adult participants with active and refractory SLE with and without nephritis (Subprotocol B Part B and Subprotocol C Part B).