TRANSDUCTION OF THE IL2 GENE INTO HUMAN ACUTE-LEUKEMIA CELLS - INDUCTION OF TUMOR REJECTION WITHOUT MODIFYING CELL-PROLIFERATION AND IL2 RECEPTOR EXPRESSION

Background: Previous studies have suggested that some of the limitatio ns associated with the administration of high-dose exogenous interleuk in 2 (IL2) may be overcome, at least partly, by cytokine gene transfer modalities. These findings have prompted investigations into whether human tumor cells may be transduced with the IL2 gene and whether tumo r cell lines could be engineered to release IL2. Purpose: The purpose of this study was to evaluate the possibility of inducing a productive transfer of the IL2 gene into human acute leukemia cells and to asses s the phenotypic and proliferative changes generated in the engineered cells, as well as their tumorigenic potential in nude mice. Methods: Three retroviral vectors (DC/TK/IL2, DC/AD/R/IL2, and N2/CMV/IL2) carr ying the IL2 gene were used to transduce three human leukemic cell lin es: K562 and U937 (myeloid) and ST4 (lymphoid). Messenger RNA expressi on of the IL2 gene was analyzed by reverse transcriptase-polymerase ch ain reaction (RT-PCR) and productive IL2 release using a human IL2 ass ay and an enzyme-linked immunosorbent assay kit. The expression of the p55 (alpha) and p75 (beta) chains of the IL2 receptor were determined by RT-PCR and indirect immunofluorescence. The kinetics of in vitro g rowth and proliferation of parental and engineered cells were also mea sured. Parental and IL2 gene-transduced ST4 lymphoblasts were injected into immunosuppressed nude mice that had their tumors measured twice weekly. Results: The productive insertion of the IL2 gene was achieved in all three cell lines studied. The amounts of IL2 constitutively re leased by the engineered neoplastic cells ranged between 1 and 11 U/mL of IL2 produced from 10(6) cells in 72 hours. A fivefold increase in IL2 production was obtained in ST4 cells by further limiting dilution cloning of the bulk-infected cells. The stable integration of the IL2 gene did not modify the phenotype of the leukemic cells, the expressio n of the IL2 receptor a and p chains and of several cytokine genes, or the kinetics of in vitro growth and proliferation. In nude mice injec ted with various IL2-producing ST4 clones, tumor growth associated inv ersely with the amounts of IL2 secreted by the leukemic cells. Conclus ions: The results of this study demonstrate that the IL2 gene can be p roductively transduced into human myeloid and lymphoid leukemic cells without modifying their phenotypic and proliferative properties and th at this transduction leads to a reduced or abrogated in vivo tumorigen ic potential.