Tumor glycolysis is differentially associated with each subset of immune cells
Using flow cytometry, tumor-infiltrating lymphoid cells and myeloid cells from lung ADC fresh tissues from 41 patients were comprehensively profiles. IHC was used to evaluate HK2 expression in tumor cells, as an indicator of tumor glycolysis, because HK2 is the first and the rate−limiting enzyme of glycolysis. The experimental scheme is described in Fig. 1A, and the correlations between individual immune cell subsets and tumor HK2 expression are summarized in Fig. 1B, C and Table 1.
Table 1
Correlations between tumor HK2 expression and immune cell subsets
Immune cell subsets
|
Correlation coefficient*
|
P value
|
Pan-immune cells (% of total cells)
|
0.030
|
0.855
|
CD3 + cells (% of ICs)
|
−0.283
|
0.077
|
CD4 + cells (% of CD3 + cells)
|
−0.225
|
0.162
|
CD4 + cells (% of ICs)
|
−0.326
|
0.040
|
CD8 + cells (% of CD3 + cells)
|
0.114
|
0.485
|
CD8 + cells (% of ICs)
|
−0.162
|
0.318
|
Treg (% of CD4 + cells)
|
0.480
|
0.003
|
Tregs (% of ICs)
|
0.239
|
0.161
|
CD8 + cells to Tregs ratio
|
−0.415
|
0.012
|
CD19 + cells (% of ICs)
|
−0.377
|
0.017
|
NK cells (% of ICs)
|
−0.134
|
0.411
|
Macrophages (% of ICs)
|
0.023
|
0.888
|
M0 (% of macrophages)
|
−0.116
|
0.477
|
M1 (% of macrophages)
|
0.089
|
0.584
|
M2 (% of macrophages)
|
−0.010
|
0.949
|
DCs (% of ICs)
|
0.091
|
0.604
|
MDSCs
|
0.028
|
0.901
|
*Spearman correlation analysis. |
Abbreviations: IC, immune cell; Tregs, regulatory T-cells; DC, dendritic cell; MDSC, myeloid-derived suppressor cell |
Total immune cell infiltration did not differ when quantified according to tumor HK2 expression. Tumor HK2 expression was more closely related to lymphoid cells compared with myeloid cells (Fig. 1B, C). The proportion of CD3 + cells to total immune cells and CD4 + T-cells to total immune cells tended to be inversely correlated with HK2 tumor expression (spearman rho = −0.283, P = 0.077; spearman rho = −0.326, P = 0.040, respectively). The proportion of CD19 + B-cells to total immune cells was also inversely correlated with HK2 tumor expression (spearman rho = −0.377, P = 0.017; Table 1). Although the proportion of Tregs to total immune cells did not significantly differ according to tumor HK2 expression, the proportion of Tregs to CD4 + T-cells showed a significant positive correlation with tumor HK2 expression (spearman rho = 0.480, P = 0.003). Of note, the ratio of CD8 + T-cell to Tregs was inversely correlated with tumor HK2 expression (spearman rho = −0.415, P = 0.012) (Fig. 1B). Proportions of tumor-infiltrating macrophages, dendritic cells, and MDSCs did not differ according HK2 tumor expression (Fig. 1C). In addition, HK2 tumor expression did not affect M1 versus M2 polarization of macrophages (Table 1). Among the above differentially infiltrating immune cells, we further validated the association between tumor HK2 expression and CD8 + T-cells, Tregs, and their ratio in additional larger cohorts.
Tumor HK2 expression was inversely correlated with the ratio of CD8+ T-cells to Tregs
To validate the above findings, we evaluated tumor HK2, CD8 + cells, and Tregs (FOXP3 + cells) using IHC in 375 lung ADC, 118 lung SqCC, and 338 colon ADC cases (Fig. 2), as schematically described in Fig. 3A. HK2 expression was not significantly different according to clinicopathologic parameters. The relationships of tumor HK2 expression with CD8 + T-cells, Tregs, and their ratio are summarized in Fig. 3B−D. Whereas CD8 + T-cell infiltration was not significantly correlated with tumor HK2 expression, Treg infiltration was positively correlated with HK2 tumor expression across the three cohorts (lung ADC, spearman rho = 0.489, P < 0.001; lung SqCC, spearman rho = 0.306, P = 0.001; colon ADC, spearman rho = 0.111, P = 0.054) (Fig. 3B-D). Of note, the ratio of CD8 + T-cells to Tregs was inversely correlated with HK2 tumor expression (lung ADC, spearman rho = −0.335, P < 0.001; lung SqCC, spearman rho = −0.236, P = 0.010; colon ADC, spearman rho = −0.175, P = 0.004) (Fig. 3B-D). These findings were consistent with the flow cytometry analyses and demonstrated that an increase in tumor glycolysis as represented by HK2 tumor expression was inversely correlated with the ratio of CD8 + T-cells to Tregs in patients with lung cancer and colon cancer.
A lower CD8 + T-cell to Treg ratio was associated with poor survival in patients with lung SqCC
Whereas high CD8 + T-cell infiltration generally predicts a favorable prognosis and good response to immunotherapy in cancer patients, high Treg infiltration was not consistent in predicting the prognosis of patients [29]. Treg recruitment partially depends on the presence of CD8 + T-cells [30]. A significant positive correlation between Treg and CD8 + T-cell infiltration in lung and colon cancer cohorts was consistently observed (all P < 0.001).
We also evaluated the prognostic significance of the CD8 + T-cell to Treg ratio as well as the numbers of CD8 + T-cells and Tregs. In lung SqCC, a lower number of CD8 + TILs was associated with poor progression-free survival (PFS) and overall survival (OS) (P = 0.008 and P = 0.004, respectively) (Fig. 4A). Of note, a lower ratio of CD8 + T-cells to Tregs was associated with poor PFS and OS (P = 0.005 and P < 0.001, respectively) (Fig. 4B). A lower number of CD8 + TILs was associated with poor OS in patients with advanced-stage (IIB−IIIB) (P = 0.003) rather than early-stage (I−IIA) (P = 0.075) cancer (Fig. 4A). In contrast, a decreased ratio of CD8 + T-cells to Tregs was associated with poor OS in patients with both early and advanced stages (P = 0.010 and 0.002, respectively). These findings suggest that the ratio of CD8 + T-cells to Tregs might be a more useful prognostic factor compared with CD8 + TILs. Together, these findings suggest that tumor HK2 expression influences patient survival indirectly via distinct immune profiling, specifically a low ratio of CD8 + T-cells to Tregs.
Implication of the CD8+ T-cell to Treg ratio in patients treated with immunotherapy
An additional validation cohort that included 78 non-small cell lung cancer patients with PD-1/PD-L1 blockade therapy was also investigated. Treg infiltration, but not CD8 + T-cell infiltration, was positively correlated with HK2 tumor expression (spearman rho = 0.247, P = 0.033). The CD8 + T-cell to Tregs ratio was also inversely correlated with HK2 tumor expression (spearman rho = −0.288, P = 0.013) (Fig. 5A). The CD8 + T-cell to Tregs ratio was a better discriminator for prognosis compared with CD8 + T-cells and Tregs individually. Additionally, patients with a high CD8 + T-cell to Treg ratio tended to show prolonged PFS and OS after immunotherapy (P = 0.113 and 0.049, respectively) (Fig. 5B).