THBS4 and B-cell chronic lymphocytic leukemia: Third, TSP-4 participates in both CTL-mediated direct killing and SMAP-mediated latent killing, like TSP-1, but only TSP-4 expression was down-regulated by chronic lymphocytic leukemia (CLL) culture supernatants that suppress both direct killing by CTLs and latent killing by released SMAPs.