[Plasma cells]

Plasma cells are specialized terminally differentiated B cells that synthesize and secrete antibodies to maintain humoral immunity. By the production of pathogenic antibodies, plasma cells contribute to the development of many conditions, such as autoimmune disorders, transplant rejection and allergies. Two different plasma cell compartments can independently generate different types of pathogenic antibodies: (1) short-lived plasmablasts (proliferating precursors of mature plasma cells) and plasma cells, which live only as long as B cells are activated. Consequently, these cells cause disease flares that respond to immunosuppressive drugs and B cell targeting therapies. (2) Long-lived non-proliferating memory plasma cells, which survive in niches in bone marrow and inflamed tissues for months, years or a lifetime independent of B or T cell help or antigen contact. Because they do not respond to immunosuppressants or treatment targeting B cells, they are responsible for refractory chronic conditions. Therefore, long-lived memory plasma cells in particular have emerged as important therapeutic targets and strategies to target these cells are discussed in this article. So far long-lived plasma cells can only be depleted by immunoablative therapy with antithymocyte globulin in the setting of stem cell transplantation or by treatment with proteasome inhibitors approved for multiple myeloma. These strategies provide options for treating refractory autoantibody-mediated diseases. One interesting approach aims at an antigen-specific elimination of target plasma cells without depleting the protective plasma cells responsible for maintaining humoral immunity.