 This is a single-center, non-randomized, phase 2A, proof-of-concept study to evaluate the effects of a combination treatment with rituximab and belimumab. This combination therapy is designed to induce long-term B-cell depletion to achieve significant reduction of autoantibody-mediated immune complexes. In addition to standard therapy, SLE patients will receive 2 infusions of rituximab 1000 mg on day 0 and 14 week 2 and belimumab on day 28 week 4 , 42 week 6 and 56 week 8, then every 28 days. The primary endpoint is at 24 weeks after which an extended follow-up will take place, for subjects continuing belimumab, until 104 weeks after treatment start. 