CD28 and rheumatoid arthritis: The most common biotherapies used in RA included biotherapies targeting cytokines, such as Infliximab, a monoclonal antibody which blocks TNF or Tocilizumab, a monoclonal antibody which blocks the IL-6 receptor, and biotherapies targeting cells, such as Abatacept, a fusion protein (CTLA-4-Ig) which interacts with B7 (ligand of CD28) or Rituximab, a monoclonal antibody against CD20.