INDUCIBLE KNOCKOUT OF THE INTERLEUKIN-2 RECEPTOR-ALPHA CHAIN - EXPRESSION OF THE HIGH-AFFINITY IL-2 RECEPTOR IS NOT REQUIRED FOR THE IN-VITRO GROWTH OF HTLV-I-TRANSFORMED CELL-LINES

Adult T cell leukemia (ATL) is an aggressive malignancy that is associ ated with HTLV-I infection and characterized by constitutive expressio n of the high-affinity interleukin-2 receptor. The cu subunit of the h igh-affinity receptor (IL-2R alpha), which is normally present only on activated T cells, is specifically upregulated by HTLV-I and constitu tively expressed on fresh leukemic cells from ATL patients as well as cell lines transformed by HTLV-I in vitro. Here we directly address th e functional significance of IL-2R alpha expression in HTLV-I transfor med cell lines by using an endoplasmic reticulum-targeted single-chain antibody to inhibit the cell surface expression of IL-2 alpha. Using constitutive and tetracycline-repressible systems to express the ER-ta rgeted antibody against IL-2R alpha, we have reduced cell surface expr ession of IL-2R alpha by more that 2 logs of mean fluorescence intensi ty to virtually undetectable levels in the IL-2-independent HTLV-I-tra nsformed cell lines C8166-45 and HUT102. No toxicity was associated wi th the intracellular retention of IL-2R alpha, and the growth rate of the IL-2R alpha-negative cells was in each case comparable to that of the parental cell line. We conclude that cell surface expression of IL -2R alpha is dispensable for the in vitro growth of these HTLV-l-trans formed cells. (C) 1997 Academic Press.