Low doses of rIL2 after autologous bone marrow transplantation induce a "prolonged" immunostimulation of NK compartment in high-grade non-Hodgkin's lymphomas.

Ten patients with high-grade non-Hodgkin's lymphoma (HG-NHL) entered a subcutaneous (s.c.) recombinant interleukin 2 (rIL2) trial within 2 months of undergoing autologous bone marrow transplantation (ABMT). Immunological studies, consisting in T- and natural killer (NK)-cell subset assessment, together with functional assays, such as NK activity and CD16-mediated redirected killing assay, were performed before therapy, after 2 weeks, and then monthly. Phenotypic analysis showed a significant increase (p = 0.01) of CD16 and CD56 NK cells, from 12% to 28% and from 17% to 37%, respectively. In particular, the CD56bright NK cell population showed a tenfold increase, while CD56dim NK cells remained unmodified compared with pretreatment values. The expression of IL2 receptors was also studied and a significant increase (p = 0.01) of CD122 (p75)-positive cells from 8% to 30% was found, while no significant increase was observed in CD25 (p55)-positive cells. Furthermore, rIL2 administration led to an increase of NK activity even at the lowest effectors:target ratio and to an increase of CD16-mediated redirected killing assay. These phenotypic and functional modifications lasted throughout the duration of rIL2 therapy and remained after completion of therapy. In addition, none of the ten patients relapsed, and two of them who started IL2 treatment while still showing residual disease experienced a complete disappearance of the disease after 10 and 7 months of therapy, respectively. Our data suggest that infusion of rIL2 s.c. after ABMT is safe, can selectively increase NK cell number and function, and may have a beneficial effect on the minimal residual disease.