Although graft survival following renal transplantation (RTx) has improved, outcomes following highrisk RTx are variable. Preexisting antibodies, including donor-specific antibodies (DSA), play an important role in graft dysfunction and survival. We have designed a study to investigate the safety and efficacy of anti-CD20 monoclonal antibodies (rituximab) in high-risk RTx recipients. Major eligibility criteria include: 1) major and minor ABO blood group mismatch, 2) positive DSA. Thirty-five patients will receive 200 mg/body of rituximab. The primary endpoint is the incidence of B cell depletion. This study will clarify whether rituximab is efficacious in improving graft survival in high-risk RTx recipients.