Consistent with these findings, recombinant IL-9 added to healthy B cell-conditioned media impaired IS formation, an effect that was not observed in the presence of neutralizing anti-IL-9 antibodies (Fig. 6A-D), Consistent with the IS defects (Fig. 6A–D), the suppressive activity of the CLL supernatants on CTL-mediated killing and degranulation were neutralized by anti-IL-9 antibodies (Fig. 6E, F). Here, IL9 is linked to B-cell chronic lymphocytic leukemia.