To test the hypothesis that leukemic cell-derived IL-9 contributes to the assembly of dysfunctional ISs by modulating PD-1 expression in CTLs, healthy CD8+ cells were cultured with healthy B cell or CLL cell-conditioned media in the presence of either isotype control or anti-IL-9 neutralizing antibodies prior to conjugate formation. The gene discussed is IL9; the disease is B-cell chronic lymphocytic leukemia.