Constitutive expression of IL-15 in T-25 lymphoma cells increases survival of mice and is associated with clinical CNS symptoms. (A) Kaplan-Meier survival curve of 7-day-old BALB/C mice injected with either T-25-IL15 (n = 27) or T-25 cells (n = 28) (P < .0001, log-rank test). (B) Kaplan-Meier curve depicting the accumulated rate of CNS symptoms. Mice were monitored every day for clinical symptoms for CNS involvement including spin when held by tail, ataxia, and side-walk. These symptoms were present only in the T-25-IL15 group. (C) Representative picture of a T-25-IL15-injected mouse with ocular involvement. Note the opacity of the left eye (arrow) caused by accumulation of lymphoma cells in the left anterior chamber. (D) IL-15 secretion was measured by enzyme-linked immunosorbent assay in cells derived from the eyes of T-25-IL15-injected mice (n = 2). The T-25-injected mouse served as a control. (E-F) Hematoxylin and eosin staining of brain sections derived from T-25- (upper) and T-25-IL15-injected mice (lower), showing infiltration of lymphoma cells in the subarachnoid space. Histopathology analysis revealed that there was no difference in the number of mice with CNS involvement between both groups. (G) T-25-IL15-injected mice exhibited a significant increase in peripheral blood NK cells. Values presented as means ± SE (P = .01, t test).