CP-690,550 inhibited ATL and HAM/TSP PBMC 6-day culture supernatant–mediated NK92-cell proliferation. After cytokine starvation for 24 hours, NK92 cells were stimulated with a 6-day ex vivo culture supernatant of PBMCs from an ATL patient (A) or a HAM/TSP patient (B) for 48 hours. Antibodies directed against the cytokines IL-2, IL-9, or IL-15 or CP-690,550 were added to the plates 1 hour prior to cell seeding. ³H-thymidine was added during the last 6 hours of the cultures. Cells were then harvested and analyzed for ³H-thymidine incorporation. The percentage of inhibition of proliferation with CP-690,550 was determined for 11 ATL culture supernatants (C) or 8 HAM/TSP culture supernatants (D). Black bars indicate the mean percentage of inhibition.