B-Cell Analysis for Monitoring Patients Undergoing B-Cell Depletion for the Treatment of Autoimmune Diseases

B-cell depleting therapy is increasingly used in the treatment of many distinct autoimmune diseases. This not only involves remission induction therapy, but also maintenance therapy. In this respect, it is of importance to monitor composition of the B-cell compartment in the peripheral blood. This can be performed at the time of initiation of the therapy, especially in those cases in which the expected clinical effect is not achieved. If B-cells are absent, B-cell depletion may not be the best treatment option; if B-cells are present, the efficacy may be hampered by neutralizing antibodies. For monitoring B-cell recovery it is important not to just enumerate B-cells, but to also phenotype the B-cells. A phenotype of IgD-CD27++CD38++ indicates the presence of circulating plasmablasts that lack CD20 and which are therefore not sensitive for B-cell depletion with anti-CD20 biologicals. A phenotype of IgD+CD27-CD38++ on the other hand, indicates recovery from the bone marrow with transitional B-cells. This chapter will focus on B-cell analyses by flow cytometry.