ANALYSIS OF IL-2 RECEPTOR EXPRESSION AND OF THE BIOLOGICAL EFFECTS OFIL-2 GENE TRANSFECTION IN SMALL-CELL LUNG-CANCER

We have analysed the expression of interleukin-2 receptor (IL-2R) on a panel of small-cell lung cancer (SCLC) cell lines. None of the 11 SCL C cell lines studied expressed detectable surface IL-2R alpha or beta chains by indirect immunofluorescence. Reverse transcriptase-polymeras e chain reaction (RT-PCR) analyses indicated that only one out of 11 c ell lines expressed detectable IL-2R beta mRNA while two expressed a w eak positivity for IL-2R gamma. Five SCLC cell lines were transfected with the plasmid vector RSV.5 neo containing IL-2 cDNA coding. sequenc e. Stable transfectants secreted biologically active IL-2 (ranging Fro m 25 to 100 U ml(-1) in the culture supernatant). IL-2, transfection d id not product significant modifications in the expression of surface molecules such as IL-2R alpha and beta chains, intercellular adhesion molecule-1 (ICAM-1), CD44, HLA class I and II or in IL-2R beta or gamm a mRNA. More importantly, IL-2-transfected N592 and NCI H69 cell lines completely lost their tumorigenic potential in nude mice after subcut aneous injection, whereas experimental controls transfected with RSV.5 neo vector only, displayed an in vivo growth pattern identical to tha t of untransfected cells. In addition, in the N592 model. IL-2-produci ng N592 inhibited the growth of wild-type N592 injected at the same si te, while injection of parental cells on the opposite side did not sig nificantly affect the growth of wild-type tumour cells. Histopathologi cal analysis of the rejection process of IL-2-transfected cells demons trated the presence of MAC-1(+), MAC-3(+) macrophages and of RB68C5(+) granulocytes, whereas T cells were undetectable and NK cells were sca rcely represented. In addition, a reduction of the tumour blood vessel s was observed. The possible relevance of these data for the developme nt of vaccination strategies using cytokine-engineered tumour cells in SCLC is discussed.