Tumor MHC class I expression improves the prognostic value of T-cell density in resected colorectal liver metastases

Abstract

Tumor-infiltrating lymphocytes (TIL) in colorectal cancer liver metastases (CLM) have been associated with more favorable patient outcomes, but whether MHC class I (MHC-I) expression on cancer cells affects prognosis is uncertain. Immunohistochemistry was performed on a tissue microarray of 158 patients with CLM, who underwent partial hepatectomy with curative intent. Using the antibody HC-10, which detects HLA-B and HLA-C antigens and a minority of HLA-A antigens, MHC-I expression was correlated with β-2 microglobulin (β2m; r = 0.7; P < 0.001), but not with T-cell density (r < 0.32). The median follow-up for survivors was 9.7 years. High levels of MHC-I expression in tumors concomitant with high T-cell infiltration (CD3, CD4, or CD8) best identified patients with favorable outcomes, compared with patients with one or none of these immune features. The median overall survival (OS) of patients with MHC-I(hi)CD3(hi) tumors (n = 31) was 116 months compared with 40 months for the others (P = 0.001), and the median time to recurrence (TTR) was not reached compared with 17 months (P = 0.008). By multivariate analysis, MHC(hi)CD3(hi) was associated with OS and TTR independent of the standard clinicopathologic variables. An immune score that combines MHC-I expression and TIL density may be a valuable prognostic tool in the treatment of patients with CLM.

Figure 1. Quantification of MHC class I, Beta-2 microglobulin, and T-cell subsets

A. Representative staining in triplicate of MHC class I (MHC-I) expression in 5 colorectal liver metastases, with calculated mean percent surface expression ±standard error. For the same tumors, example of Beta-2 microglobulin (β2m) staining of one of the triplicate core is shown. Correlation of MHC-I and β2m expression is shown. Solid and dotted lines represent median and terciles, respectively (MHC-I, 32%, 48%, and 65%; β2m, 13%, 21%, and 33%). B. Quantification of intratumoral CD3 (n=154), CD4 (n=155), and CD8 (n=155) T cells. One dot represents one metastasis (cells/core, mean of replicates). Bars represent medians (109, 9, and 52 cells/core, respectively). One value is out of scale (CD8=502). C. Within the 52 tumors found to express the highest level of MHC-I (upper tercile), 31 displayed high CD3 infiltration, 80.6% of which represented tumors detected to have high CD4 and/or CD8 infiltration (25 of 31, medians used as cut-off points). D. Dot plot representing the absence of correlation between MHC-I expression and CD3 infiltration. Using the highest tercile as cut-off for high MHC-I expression (broken Y axis, 65%) and the median count for high CD3 infiltration (broken X axis, 109 cells/core), 4 groups are defined: MHC-I^hiCD3^hi (n=31, red); MHC-I^loCD3^hi (n=46, blue); MHC-I^hiCD3^lo (n=19, yellow); MHC-I^loCD3^lo (n=58, black). Spearman r used for correlation analysis.

Figure 2. Prognostic impact of MHC class I expression and CD3 T-cell infiltration

A. Association between MHC-I expression and CD3 infiltration alone and combined with overall survival (upper) and time to recurrence (lower) in the entire patient cohort. For MHC-I alone, outcomes are displayed for groups trichotomized based on tercile. For CD3, outcomes are displayed using the median count as cutoff. For the combination of MHC-I and CD3, 4 groups are displayed and color-coded: MHC-I^hiCD3^hi (red); MHC-I^loCD3^hi (blue); MHC-I^hiCD3^lo (yellow); MHC-I^loCD3^lo (black). B. Impact of favorable tumor immune features (MHC-I^hiCD3^hi, red) on overall survival in patient subgroups according to clinicopathologic features associated with better prognosis (see supplementary Fig. S2 for recurrence). Log-rank (Mantel Cox). CEA, carcinoembryonic antigen; DFI, disease-free interval, i.e. time between resection of primary tumor and liver recurrence; Met, metastasis; N0 primary, absence of cancer cells in mesenteric lymph nodes draining the primary tumor.