The increase in total body lymphocytes is not measured accurately in blood, because hetIL-15—as well as other formulations of IL-15 administration—induces relocation of lymphocytes to the tissues, as shown in macaques and humans.20 34 This rapid and massive relocation of lymphocytes to effector sites creates the impression of lymphopenia in peripheral blood. The gene discussed is IL15; the disease is lymphopenia.