5. Female subject is either post-menopausal for one year prior to screening or surgically sterilized. Women of childbearing potential (WOCBP) must not become pregnant and so must be sexually inactive by abstinence (starting 2 weeks prior to the 1st belimumab and/or bortezomib dose) or use contraceptive methods with a failure rate of < 1% (starting 1 month prior to the 1st belimumab and/or bortezomib dose) for the duration of the study through 16 weeks after the last belimumab and/or bortezomib dose. WOCBP must have a negative urine or serum pregnancy test at screening and < 7 days prior to the first belimumab and/or bortezomib dose.