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Summary A modified tetrazolium reduction assay (MTT) was used to assess the relation between HLA class I antigen expression on tumour cells and their susceptibility as a target for non-MHC restricted LAK/NK cytotoxicity using interleukin-2 activated peripheral blood mononuclear cells (MNC) from normal individuals. At 20/1 effector/target ratio this ranged from no killing to 77%. The efficiency of killing was dependent on duration of effector cell culture with IL-2, peaking at day 10 and declining thereafter. This killing could be enhanced by addition of other cytokines including interferons alpha, beta and gamma.Study of a panel of 15 tumour cell lines using a single effector showed that there was no statistically significant inverse correlation (using Spearman rank test) between the degree of tumour class I expression and LAK/NK killing at 20/1 (r = 0.23 P = 0.39) and 10/1 (r = 0.30, P = 0.27) and at 5/1 E/T ratio r = 0.47, P = 0.08) respectively. Lack of inverse correlation between these two parameters came from study of one bladder tumour line (FEN), whose absent class I antigens had been corrected by transfection with P2 microglobulin gene. At high E/T ratio (20/1) there was an increase in the susceptibility of target cells to lysis (36% parent cell, 45% transfected cell), whilst at lower E/T ratios (1/1) there was significantly more killing of the non-transfected cells (10% vs 31%). The addition of anti-class I antibody W6/32 increased killing by 18% but this was non-specific as the same increase occurred with a class II antibody.These data suggest that overall there was not an inverse correlation between class I expression and LAK/NK killing at high E/T ratios, whilst at low (5/1 or lower) E/T ratios this correlation nearly reached statistical significance suggesting that the conflicing literature reports may be due to a threshold levels of effector cells above which the masking effects of MHC antigens disappears.

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The pattern of expression of cell adhesion molecules, i.e., leucocyte function associated antigen 3 (LFA-3) and intercellular adhesion molecule 1 (ICAM-1) on human bladder tumour biopsy specimens was investigated. Attempts were also made to study the pattern of induction of these molecules by established human cell lines in response to cytokines. The results indicated that 15 of 25 tumour biopsy specimens were negative for ICAM-1, and amongst the remaining 10, only 1 showed strong positivity, whilst LFA-3 was expressed in 21 of 23 cases. Unlike LFA-3, the pattern of ICAM-1 expression on established tumour cell lines was different in that there were 7 of 21 cases showing positive staining. The parallel investigation of ICAM-1 and major histocompatibility complex class II antigen expression on bladder tumours showed that in 11 of 18 cases, there was a concomitant expression or complete absence of these molecules. In the remaining 7, there were 6 cases where only class II expression was observed. Exposure of cell lines to interferons alpha or gamma had no effects on LFA-3 expression. In contrast, interferon gamma induced ICAM-1 on all the eight lines with constitutive ICAM-1 expression, whereas interferon alpha upregulated only 2 of these 8 lines. The mean ± SD values for ICAM-1 expression on the eight inducible lines were 617 ± 406 cpm before and 943 ± 471 cpm (p = 0.001) after interferon gamma stimulation. The pattern of ICAM-1 inducibility of a bladder cell line Fen to interferon remained unchanged following transfection of a β₂-microglobulin gene and correction of cell surface HLA class I antigens. These results indicate that there was a significant minority of bladder tumours and tumour cell lines with abnormal cell adhesion molecule expression. In some cases, the abnormality in cell lines could not be corrected by cytokine stimulation. It is possible that these abnormalities may play a critical role in the overall tumour strategy for escape from immunological detection.

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