Potential mechanisms of human natural killer cell expansion in vivo during low-dose IL-2 therapy
Todd A. Fehniger, … , Wendy Stock, Michael A. Caligiuri
Todd A. Fehniger, … , Wendy Stock, Michael A. Caligiuri
Published January 1, 2000
Citation Information: J Clin Invest. 2000;106(1):117-124. https://doi.org/10.1172/JCI6218.
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Article

Potential mechanisms of human natural killer cell expansion in vivo during low-dose IL-2 therapy

Abstract

The continuous, in vivo infusion of low-dose IL-2 selectively expands the absolute number of human natural killer (NK) cells after 4–6 weeks of therapy. The mechanism responsible for this expansion is unknown and was examined in this study. NK cells cultured at low concentrations of IL-2, comparable to those found during in vivo therapy, proliferate for 6 days and then exit the cell cycle. However, NK cells in vivo did not traverse the S/G2/M phase of the cell cycle during low-dose IL-2 therapy. Low concentrations of IL-2 delay programmed cell death of NK cells but have the same effect on resting T cells that do not expand in vivo. When CD34+ bone marrow hematopoietic progenitor cells are cultured for 21 days with low concentrations of IL-2, they differentiate into CD56+CD3− NK cells, not T cells. Thus, the selective expansion of human NK cells during continuous in vivo infusion of low-dose IL-2 likely results from enhanced NK-cell differentiation from bone marrow progenitors, combined with an IL-2–dependent delay in NK-cell death, rather than proliferation of mature NK cells in the periphery.

Authors

Todd A. Fehniger, Eric M. Bluman, Michelle M. Porter, Ewa Mrózek, Megan A. Cooper, Jeffrey B. VanDeusen, Stanley R. Frankel, Wendy Stock, Michael A. Caligiuri

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Figure 1

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(a) 12-day 3H-TdR incorporation of CD56bright NK cells cultured in 100 p...
(a) 12-day 3H-TdR incorporation of CD56bright NK cells cultured in 100 pM rIL-2. Freshly isolated CD56bright NK cells (>97% pure) were plated in 96-well plates and cultured in medium containing 100 pM rIL-2, as described in Methods. Cells were assayed for 3H-TdR incorporation every 48 hours. Each time point represents the mean cpm ± SEM of triplicate wells. Inset: Histogram of Hoechst-stained CD56bright NK cells cultured for 4 days with medium containing 100 pM rIL-2. Cell number is measured along the ordinate, DNA content along the abscissa. Five thousand events were collected and analyzed. Number above the region marker (22%) indicates the percentage of cells in the G2/M phase of the cell cycle. Approximately 45% of cells were found in the hypodiploid region of the histogram, usually indicative of apoptosis. (b) Enumeration of CD56bright NK cells by vital dye exclusion during 12-day culture in medium supplemented with or without 100 pM rIL-2. Values shown represent the mean ± SEM of readings done in triplicate wells. This figure is representative of four independent experiments performed on sorted CD56bright cells from four normal individuals.