Additionally, IL-21 injection in vivo could have off-target effects on mature lymphoid populations or even proliferative or survival effects in residual leukemic populations, such as in Waldenstrom macroglobulinemia, multiple myeloma, Hodgkin’s lymphoma, anaplastic large cell lymphoma, and adult T cell leukemia (100–106). Here, IL21 is linked to anaplastic large cell lymphoma.