Overview of the expression and mutation of different CCL family members.
To investigate the potential prognostic value of CCL family members, the mRNA levels of CCL family members (not including CCL6, CCL9, CCL10, CCL12) in tumor and normal tissues in different cancers were analyzed according to the Oncomine database (Figure.1A). Based on the data from Oncomine, the mRNA expression levels of CCL2, CCL3, CCL4, CCL5, CCL8, CCL11, CCL13, CCL18, CCL20 and CCL24 were significantly elevated in HNSCC tumor tissues, while the expression levels of CCL14, CCL15, CCL16, CCL19 and CCL21 were reduced (Table S1). Next we analyzed the data from TCGA HNSCC project. The genetic alternation status was shown in Figure.1B. Except CCL24 and CCL28, the mutation rate of other CCL family members was less than 10%. The expression level of CCL family members between tumor and normal tissues in TCGA HNSCC samples were compared and the results showed that CCL3, CCL4, CCL5, CCL7, CCL8, CCL11, CCL13, CCL18, CCL20, CCL22, CCL24, CCL26 were upregulated in tumor tissues, while CCL2, CCL14, CCL15, CCL16, CCL17, CCL19, CCL23, CCL28 were significantly reduced in tumor tissue (Figure.1C). The result from TCGA was basically consistent with the one from Oncomine. The expression status of CCL family members in pan-cancer from TCGA datasets was shown in Fig.S1 and Fig.S2. The expression and mutation overview of CCL family members indicated that CCL family members had different functions in HNSCC.
Prognostic role of CCL family members in TCGA HNSCC samples.
To evaluate the prognostic value of differentially expressed CCL family members in HNSCC, univariate Cox regression model was used to analyzed the correlation between the expression of CCL family members and overall survival in TCGA HNSCC samples. The results were showed in Figure.2. In the forest plot, the items with p value less than 0.1 were selected and bold-shown. Among CCL family members, CCL1, CCL5, CCL11, CCL14, CCL17, CCL20, CCL22, CCL25, CCL28 were associated with the prognosis. Further Kaplan-Meier curves were performed to verify the association between a high/ low expression of CCL family members and overall survival. The K-M curves of nine CCL family members mentioned above were shown in Figure.3A, while other members were shown in Fig.S3.
A strong co-expression relationship between CCL17 and CCL22 among CCL family members.
To further identify the key genes in nine CCL family members, we performed the correlation test to explore the co-expression relationship between each CCL family member. The correlation coefficient was clustered and visualized in the heat map (Figure.3B). In the heat map we found CCL17 was adjacent to CCL22, while CCL20 was adjacent to CCL25 (Blue and red boxes in heat map). The scatter plot of the expression of CCL17 and CCL22 as well as CCL20 and CCL25 was shown in Figure.3C and D. Based on the correlation test, CCL17 had a strong correlation with CCL22 (Spearman R = 0.620, p value < 0.001), while CCL20 had a weak correlation with CCL25 (Spearman R = 0.088, p value = 0.05). Considering the correlation with prognosis and co-expression relationship, we identified CCL17 and CCL22 as the key genes in HNSCC. We further analyzed the correlation between CCL17 and CCL22 expression levels with clinical parameters. The lower expression level of CCL22 was associated with the more advanced clinical stage of HNSCC, while there was no correlation between the expression of CCL17 and clinical stage (Figure.3E). A more detailed analysis of clinical parameters (including T stage, N stage, pathological gradie, and lympho Vascular invasion) was shown in Fig.S4. We also explored the diagnostic capability of CCL17 and CCL22. However, both of two genes had a poor capability in diagnosis (Figure.3F). The results above screened out CCL17 and CCL22 for a further analysis.
Functional Enrichment Analysis of CCL17 and CCL22 correlated genes in TCGA HNSCC samples
Neighboring genes correlated with CCL17 and CCL22 were first selected according to the cBioPortal database. The correlated neighboring genes of CCL17 and CCL22 were shown in Table S2 and Table S3. GO and KEGG functional analysis was performed by clusterProfiler in R and the results were shown in Figure.4A and C. The detailed items of functional analysis were displayed in Table S4 and Table S5. We also used GeneMANIA to construct molecular regulatory networks between correlated genes (Figure.4B and D). The functional analysis results indicated that the correlated genes were mostly associated with the immune cell activation but not cancer-associated pathways. To further identify the upstream and downstream molecules of CCL17 and CCL22, TRRUST database was used to explore the upstream factors while STRING database was used to identify the downstream molecules. Several transcriptional factors targets CCL family members were predicted by TRRUST (Table 1). Among them, NFKB1 and RELA were predicted to target CCL22, while STAT6 was predicted to target CCL17. The downstream receptors including CCR1, CCR2, CCR3, CCR4, CCR5, CCR7, CCR8 and CXCR3 were predicted by STRING database as the interaction score was set as 0.70. CCR2, CCR4, CCR7, CCR8 and CXCR3 were the targets for both CCL17 and CCL22. The regulation network of CCL17 and CCL22 was shown in Figure.4E. The scatter plot between CCL17 or CCL22 and CCR2, CCR4, CCR7, CCR8 and CXCR3 were shown in Fig.S5. The results of functional analysis suggested that CCL17 and CCL22 might mainly function in immune cells rather than cancer cells.
Table.1
Key regulated transcriptional factor of CCL chemokines in HNSC (TRRUST)
Key TF
|
Description
|
Regulate gene
|
P value
|
Q value
|
RELA
|
v-rel reticuloendotheliosis viral oncogene homolog A (avian)
|
CCL4,CCL19,CCL20,CCL22,CCL2,
CCL3,CCL11,CCL5,CCL13
|
6.25E-11
|
3.32E-10
|
NFKB1
|
nuclear factor of kappa light polypeptide gene enhancer in B-cells 1
|
CCL5,CCL3,CCL20,CCL11,CCL13,
CCL4,CCL22,CCL19,CCL2
|
6.63E-11
|
3.32E-10
|
STAT6
|
signal transducer and activator of transcription 6, interleukin-4 induced
|
CCL11,CCL17,CCL26
|
1.26E-05
|
4.18E-05
|
IRF3
|
interferon regulatory factor 3
|
CCL2,CCL5
|
0.000161
|
0.000403
|
REL
|
v-rel reticuloendotheliosis viral oncogene homolog (avian)
|
CCL2,CCL5
|
0.000353
|
0.000705
|
SPI1
|
spleen focus forming virus (SFFV) proviral integration oncogene spi1
|
CCL2,CCL5
|
0.0028
|
0.00466
|
STAT1
|
signal transducer and activator of transcription 1, 91kDa
|
CCL2,CCL3
|
0.00507
|
0.00725
|
STAT3
|
signal transducer and activator of transcription 3 (acute-phase response factor)
|
CCL11,CCL2
|
0.0139
|
0.017
|
JUN
|
jun proto-oncogene
|
CCL5,CCL2
|
0.0153
|
0.017
|
SP1
|
Sp1 transcription factor
|
CCL2,CCL5
|
0.12
|
0.12
|
CCL17 and CCL22 expression correlated with immune infiltration levels in HNSCC
As mentioned above, CCL17 and CCL2 might affect immune cells in HNSCC patients. Therefore, we used TIMER database and ESITMATE algorithm to focus on the relationship between CCL17 or CCL22 and immune infiltration cells in HNSCC samples. First, tumor purity of samples in TCGA HNSCC project was calculated by using ESTIMATE algorithm in R. The ESTIMATE scores and purity scores were displayed in Table S6. Correlation test between CCL17 or CCL22 expression and tumor purity scores were performed using Spearman correlation test. As shown in Figure.5A and B, the expression of CCL17 and CCL22 had a negative correlation with the tumor purity in TCGA HNSCC samples (Spearman R=-0.34, p value < 0.001 for CCL17 and Spearman R=-0.52, p value < 0.001 for CCL22). The results validated the functions of CCL17 and CCL22 as the chemokines that can recruit the immune cells, which caused the reduction of the tumor purity in tumor. Then the immune infiltration levels of each sample were calculated by TIMER database (Table S7). Spearman correlation test was performed between the expression of CCL17 or CCL22 and each immune cells infiltration score. The correlation R was displayed in Figure.5C and D. At the same time, we performed the Spearman correlation test between the expression of CCL17 or CCL22 and the expression of PD1 (PDCD1) and PD-L1 (CD274). As shown in the Figure.5E and F, CCL17 expression was positively correlated with PD1 (PDCD1) expression, but had not correlation with PD-L1 (CD274). The expression of CCL22 was both positively correlated with PD1 (PDCD1) and PD-L1 (CD274) in TCGA HNSCC samples (Spearman R=-0.38, p value < 0.001 for PD1 and Spearman R=-0.19, p value < 0.001 for PD-L1) (Figure.5G and H).
High expression of CCL22 recruited more CD4 + T cells according to scRNA-seq data
We downloaded the scRNA-seq data of GSE103322 from GEO database. Cancer cells were first excluded and rest of cells were re-clustered into 9 groups (Figure.6A, B and C). The expression and distribution of CCL17 and CCL22 were explored in each cell type The t-SNE plots indicated that CCL17 and CCL22 were mainly expressed in the endothelial cells (Figure.6D and E). Then we calculated the sum of CCL17 and CCL22 expression of each sample. The samples were divided into CCL17/CCL22 high expression group and low expression group according to the median expression. Then we counted the cell numbers of each type of T cells including CD4 + T cells, Tregs, CD8 + T cells and CD8 + dysfunction T cells. Finally, only CD4 + T cells had a different expression between high and low CCL22 expression group (p < 0.05) (Figure.6F and Table S8). The results were consistent with the analysis of TCGA samples which confirmed that CCL22 can increase the CD4 + T cells infiltration in HNSCC patients.
High expression of CCR7 activated the mTORC1 signaling in CD4 + T cells
The expression and distribution of receptors of CCL17 and CCL22 (including CCR2, CCR4, CCR7, CCR8 and CXCR3) were shown in Fig. 7A, which suggested that CCR7 and CCR8 were the main receptors in HNSCC. These two receptors were mainly located in T cells. Besides, since CCR7 and CCR8 were the major receptors in HNSCC, we further investigate the potential signaling pathway of CCR7 and CCR8 in CD4 + T cells and Treg cells, respectively. As shown in Fig. 7B and C, CCR7 was mainly expressed in CD4 + T cells and CD8 + T cells, while CCR8 was expressed in Treg cells. In CD4 + T cells, we divided cells into high or low CCR7 expression group, while in Treg cells, we divided cells into high or low CCR7 expression group. Differentially expressed genes (DEGs) were analyzed in two cell types and were visualized using volcano plot (Fig. 7D and E). The detailed information of DEGs was shown in Table S9. GO analysis was performed on the DEGs (Fig. 7F and G). To identify the different pathways, GSEA analysis showed in CD4 + T cells, high CCR7 expression cells were mainly enriched in MYC-targets and MTORC1 signaling (Fig. 7H). In Treg cells, high CCR8 expression cells were mainly enriched in IL6-JAK-STAT3 signaling and KRAS signaling DN (Fig. 7I). The detailed items of GSEA were shown in Table S10
Prediction of clinical response to immune checkpoint blockade (ICB) through CCL17/CCL22 expression
Immune checkpoint blockade therapy has exhibited a great improvement in the treatments of a variety of cancers. Since we have found that CCL17 and CCL22 had a recruitment effect on T cells, we next explored whether CCL17 and CCL22 could be used to predict the response of ICB therapy. TIDE database was used to investigate the role of CCL17 and CCL22 played in cancer ICB therapy. The results suggested that in different type of cancer, CCL17 and CCL22 had a different effect on the T cell dysfunction phenotype (Figure.8A left panel). The high expression of CCL17 and CCL22 was associated with a good prognosis in most cancer ICB therapies (Figure.8A second to left panel. The red color means a poor ICB response and prognosis, while blue means a good ICB response and prognosis). In clinical studies of blocking specific immune checkpoints, the relationship between gene expression of CCL17/CCL22 and treatment outcomes is shown in Table S11. A Risk scores calculated by TIDE algorithms based on a variety of datasets were shown in Figure.8B and Table S12. We then extracted the part of HNSCC datasets and found that based on TCGA datasets, high CCL17 and CCL22 expression had a lower risk scores which means a better response to ICB therapy. However, the role of CCL17 and CCL22 in other datasets were conflicted with TCGA datasets (Figure.8C). Finally, we used the function of “Biomarker Evaluation” in TIDE to see the prediction power of CCL17 and CCL22. This function can calculated the AUC value of biomarkers based on the data from a study of immunotherapy (PD1) on a mouse oral squamous cell carcinoma model[28]. Compared with several biomarkers currently used, we found a combination of CCL17, CCL22, PD-L1 (CD274) and PD1 (PDCD1) had a better prediction power than other biomarkers in pre-surgical groups (Figure.8D. The AUC of combination was 0.69). Therefore, according to the analysis results, CCL17 and CCL22 might be selected as potential biomarkers for prediction of HNSCC ICB therapy.