CTLA-4 in mesothelioma patients: tissue expression, body fluid levels and possible relevance as a prognostic factor

Abstract

CTLA-4 function as a negative regulator of T cell-mediated immune response is well established, whereas much less is known about the immunoregulatory role of its soluble isoform (sCTLA-4). No data are available on CTLA-4 expression and prognostic impact in malignant pleural mesothelioma (MPM). We investigated, by immunohistochemistry, CTLA-4 expression in tumor tissues and, by ELISA, sCTLA-4 levels in sera and matched pleural effusions from 45 MPM patients. Prognostic effect of CTLA-4 expression on overall survival (OS) was assessed through Cox regression and prognostic significance expressed as death rate ratio (HR). We found that 56.0 % of MPM tissues expressed CTLA-4 with variable intensity and percentage of positive cells estimated by the immunoreactive score. sCTLA-4 levels were significantly higher in sera (S-sCTLA-4) than in pleural effusions (PE-sCTLA-4) (geometric mean ratio = 2.70, P value = 0.020). CTLA-4 expression at the tissue level was higher in the epithelioid histological subtype than in the sarcomatoid, whereas at the serum level, it was higher in the sarcomatoid subtype. A homogeneous favorable prognostic effect was found for CTLA-4 overexpression in tissue, serum and pleural effusion. Interestingly, only the PE-sCTLA-4 was found to be a statistically significant positive prognostic factor (HR = 0.37, 95 % CI = 0.18-0.77, P value = 0.007). Indeed, PE-sCTLA-4 correlated with CTLA-4 expression in tissues, whereas this latter expression showed a weak association with OS. To confirm our findings, further experimental evidences obtained from a larger cohort of MPM patients are required. However, our results would indicate a positive correlation of PE-sCTLA-4 levels and OS in MPM patients.

Keywords: CTLA-4; Mesothelioma; Overall survival; Pleural effusion; Prognostic factor.

Fig. 1

Immunohistochemical (IHC) staining patterns of CTLA-4 in representative malignant pleural mesothelioma (MPM) tissue sections (panels a–d). All CTLA-4-positive tissues showed cytoplasmic staining with some samples showing also a membrane staining (panel a) or a perinuclear staining (panel b) and others showing only a cytoplasmic staining (panel c). A representative MPM tissue section with negative CTLA-4 staining is also shown (panel d). IHC images were taken at 400× magnification. A further magnification of the small black square insert in each panel is shown. H&E stainings (panels e–h) are shown for each MPM tissue. Scale bars 100.00 µm

Fig. 2

Scatter plot of sCTLA-4 levels in PE and serum of MPM and BNG patients. The concentration of sCTLA-4 was evaluated by ELISA testing in duplicate wells. Results were expressed as log-transformed concentrations (pg/ml); the horizontal lines in each column represent median values. P value: significance level of the non parametric median test. A P value < 0.05 was regarded as statistically significant. PE pleural effusion

Fig. 3

Overall survival analysis results based on Cox regression modeling according to CTLA-4 expression levels in malignant pleural mesothelioma (MPM) tissues (panel a: IRS positives vs. IRS negatives; No. = 38 male patients; sera (panel b: S-sCTLA-4 > 66.0 pg/ml vs. S-sCTLA-4 ≤ 66.0 pg/ml; No. = 45 patients, both sexes) and pleural effusion (panel c: PE-sCTLA-4 > 67.0 pg/ml vs. PE-sCTLA-4 ≤ 67.0 pg/ml; No. = 45 patients, both sexes) of MPM patients. Results are expressed in terms of cumulative death rates adjusted for age at diagnosis, tumor stage and histological type, therapy and gender. IRS immunoreactive score; S serum-sCTLA-4; PE pleural effusion-sCTLA-4