Generation of a small cell lung cancer variant resistant to lymphokine-activated killer (LAK) cells: association with resistance to a LAK cell-derived, cytostatic factor.

Cells of OS2-RA, a human small cell lung cancer line sensitive to lymphokine-activated killer (LAK) cells, were repeatedly cocultured with human LAK cells. Fourteen cycles of the coculture produced a variant, termed OS2-RA-R, capable of growing successfully in the presence of LAK cells. OS2-RA-R showed a moderate resistance to lysis by LAK cells in 4-h 51Cr release assays. OS2-RA-R acted positively as a cold target for lysis of OS2-RA by LAK cells, suggesting no loss of the binding site for LAK cells on the cell surface of the variant. On the other hand, LAK cells were shown to produce a factor capable of suppressing the proliferation of OS2-RA and certain other cell lines but not lymphocytes. Interestingly, OS2-RA-R exhibited a substantial resistance to the cytostatic activity of LAK cell supernatants. The cytostatic factor, eluted at the 57-kDa fraction in gel filtration, showed no activity of interleukin 1, gamma-interferon, transforming growth factor beta, or tumor necrosis factor. These results suggest that LAK cells exhibit antitumor activity through not only rapid cytolysis but also slow-acting cytokine production, and the successful growth of OS2-RA-R in a coculture with LAK cells is the result of acquiring resistance to these two different LAK cell phenomena.

Two monoclonal antibodies against small-cell lung cancer show existence of synergism in binding.

Murine IgG1 monoclonal antibodies (mAbs), ITK-2 and ITK-3, were generated against a small-cell lung cancer (SCLC) cell line. Enzyme-linked immunosorbent assay using a variety of established cell lines as substrates, immunoperoxidase staining of freshly frozen tissue sections, and fluorescence-activated cell sorter analysis of peripheral blood leukocytes showed that these mAbs recognize a part of the SCLC-associated cluster 1 antigen. In immunoprecipitation studies, both ITK-2 and ITK-3 bound to a 145-kDa glycoprotein of SCLC cell membrane extracts, as did MOC-1 and NKH-1, which both recognize the cluster 1 antigen. However, because the binding of 125I-labeled ITK-2 to SCLC cells was not inhibited by MOC-1 or NKH-1, the binding site of ITK-2 on SCLC cells appeared to be different from that of either MOC-1 or NKH-1. Unexpectedly, binding of 125I-labeled ITK-2 to SCLC cells increased in the presence of ITK-3. This ITK-3-induced increase in ITK-2 binding was due partly to an increase in the number of binding sites for ITK-2 on SCLC cells. Addition of ITK-3 may, therefore, improve the effectiveness of ITK-2-based tumor detection or therapy.