3.1 Association between PD-1, PD-L1, p-S6 and combined PD-1 and PD-L1 expression and clinicopathological features in NPC cases
The expression and subcellular localization of PD-L1, PD-1 and p-S6 proteins in NPC and non-cancerous control nasopharyngeal epithelia were marked by IHC. PD-L1 protein staining was located in the membrane of NPC (Figure-1A), while PD-1 protein staining was in the cytoplasm of NPC (Figure-1B). Staining of p-S6 protein was discovered in the cytoplasm in both NPC (Figure-1C) and the control normal nasopharyngeal epithelia (Figure-1D). No staining of PD-L1 protein was found in the normal nasopharyngeal epithelia (Figure-1E). No staining showed up in negative control in the NPC (Figure-1F) (IHC, DAB staining, X200).
The positive expression of PD-1, PD-L1, p-S6 and co-expression of PD-1 and PD-L1 in NPC was 22.1% (62/281), 62.3% (175/281), 87.2% (245/281), and 17.8% (50/281), respectively. However, the positive expression of these proteins in non-cancerous nasopharyngeal epithelia was dramatically lower ( 7.8% (4/51), 33.3% (17/51), 51.0% (26/51) and 3.9(2/51), respectively ) (Fig. 2A).
We further investigated PD-L1, PD-1, p-S6 and combined PD-1 and PD-L1 expression in the primary NPC and their matched lymph node metastases. Results in Fig. 2B showed that the positive expression percentage of PD-1 in the primary lesions (25.0%, 6/24) was significantly lower than that in matched metastasis (62.5%, 15/24) (P = 0.009), as well as the co-expression of PD-1 and PD-L1 (P = 0.009) (Fig. 2B). It's worth noting that in these primary and matched metastatic samples, all samples with PD-1 positive also acquired PD-L1 positive. No obvious difference in the expression of PD-L1 and p-S6 protein between primary NPC and their matched metastasis yet (P > 0.05).
We then explored the relationship between PD-1, PD-L1, p-S6 or the co-expression of PD-L1/PD-1 proteins and clinicopathological features of NPC patients including gender, age, T/N/M stage category, clinical stages, histological type and lymph node metastasis status. These results were displayed in Table 1. The positive percentage of PD-L1 (P = 0.002) was statistically lower in NPC patients with clinic T1 than those in T2, T3 and T4, but the patients with N0, N1 and N2 stage category was evidently higher than that N3 (P = 0.015). However, the positive percentages of PD-1 and co-expression of PD-L1 and PD-1, and p-S6 were not associated with gender, N or M stage category, clinical stage, histological type and lymph node status (all P > 0.05).
Table 1
Association between expression of PD-L1、PD-1 and p-S6 proteins and NPC clinicopathological features (n = 281)
Parameter(n) | PD-L1 P (%) N (%) | P-values | PD-1 P (%) N (%) | P-values | p-S6 P (%) N (%) | P-values | PD-1/PD-L1# H (%) L (%) | P-values |
Gender | | | | | | | | | | | | |
Male (203) | 130(64.0) | 73(36.0) | 0.326 | 46(22.7) | 157(77.3) | 0.697 | 181(89.2) | 22(10.8) | 0.110 | 38(18.7) | 165(81.3) | 0.513 |
Female (78) | 45(57.7) | 33(42.3) | | 16(20.5) | 62(79.5) | | 64(82.1) | 14(17.9) | | 12(15.4) | 66(84.6) | |
Age (yr)## | | | | | | | | | | | | |
༜50 (146) | 100(62.1) | 61(37.9) | 0.947 | 29(18.0) | 120(82.0) | 0.058 | 136(84.5) | 25(15.5) | 0.115 | 25(15.5) | 136(84.5) | 0.250 |
≥ 50 (135) | 75(62.5) | 45(37.5) | | 33(27.5) | 99(72.5) | | 109(90.8) | 11(9.2) | | 25(20.8) | 95(79.2) | |
Histological type | | | | | | | | | | | | |
DNC (12) | 7(58.3) | 6(41.7) | 0.773 | 2(16.7) | 10(83.3) | 0.645 | 9(75.0) | 3(25.0) | 0.197 | 2(16.7) | 10(83.3) | 0.917 |
UDNC (269) | 168(62.5) | 101(37.5) | | 60(22.3) | 209(77.7) | | 236(87.7) | 33(12.3) | | 48(17.8) | 221(82.2) | |
T-classification | | | | | | | | | | | | |
T1 (25) | 7(28.0) | 18(72.0) | 0.002** | 5(20.0) | 20(80.0) | 0.921 | 19(76.0) | 6(24.0) | 0.357 | 2(8.0) | 23(92.0) | 0.317 |
T2 (103) | 65(63.1) | 38(36.9) | | 23(22.3) | 80(77.7) | | 91(88.3) | 12(11.7) | | 16(15.5) | 87(84.5) | |
T3 (78) | 51(65.4) | 27(34.6) | | 19(24.4) | 59(75.6) | | 68(87.2) | 10(12.8) | | 18(23.1) | 60(76.9) | |
T4 (75) | 52(69.3) | 23(30.7) | | 15(20.0) | 60(80.0) | | 67(89.3) | 8(10.7) | | 14(18.7) | 61(81.3) | |
N-classification | | | | | | | | | | | | |
N0 (46) | 29(63.0) | 17(37.0) | 0.015* | 14(30.4) | 32(60.6) | 0.416 | 43(93.5) | 3(6.5) | 0.180 | 10(21.7) | 36(78.3) | 0.729 |
N1 (82) | 49(59.8) | 33(40.2) | | 16(19.5) | 66(80.5) | | 72(87.8) | 10(12.2) | | 13(15.9) | 69(84.1) | |
N2 (122) | 85(69.7) | 37(30.3) | | 24(19.7) | 98(80.3) | | 101(82.8) | 21(17.2) | | 23(18.9) | 99(81.1) | |
N3 (31) | 12(38.7) | 19(61.3) | | 8(25.8) | 23(74.2) | | 29(93.5) | 2(6.5) | | 4(12.9) | 27(87.1) | |
M-classification | | | | | | | | | | | | |
M0 (272) | 171(62.9) | 101(37.1) | 0.262 | 59(21.7) | 213(78.3) | 0.407 | 237(87.1) | 35(12.9) | 0.887 | 48(17.6) | 224(82.4) | 0.7249 |
M1 (9) | 4(44.4) | 5(55.6) | | 3(33.3) | 6(66.7) | | 8(88.9) | 1(11.1) | | 2(22.2) | 7(77.8) | |
Clinical stage | | | | | | | | | | | | |
Ⅰ and Ⅱ (n = 57) | 34(59.6) | 23 (40.4) | 0.647 | 10(17.5) | 47(82.5) | 0.357 | 52(91.2) | 5(8.8) | 0.307 | 7(12.3) | 50(87.7) | 0.223 |
Ⅲ and Ⅳ (224) | 141(62.9) | 83(37.1) | | 52(23.2) | 172(76.8) | | 193(86.2) | 31(13.8) | | 43(19.2) | 181(80.8) | |
Lymph node status | | | | | | | | | | | | |
LNM (235) | 146(62.1) | 89(37.9) | 0.907 | 48(20.4) | 187(79.6) | 0.134 | 202(86.0) | 33(14.0) | 0.163 | 40(17.0) | 195(83.0) | 0.444 |
No LNM (46) | 29(63.0) | 17(37.0) | | 14(30.4) | 32(69.6) | | 43(93.5) | 3(6.5) | | 10(21.7) | 36(78.3) | |
Abbreviations: NPC nasopharyngeal carcinoma; DNPC differentiated non-keratinizing nasopharyngeal carcinoma; UDNPC undifferentiated non-keratinizing nasopharyngeal carcinoma; LNM lymph node metastasis; N negative; P positive. # Co-expression of PD-1 and PD-L1; ## the average age of all subjects was 49.8 years; *Correlation is significant at the p < 0.05 level (two tailed). **Correlation is significant at the p < 0.01 level (two tailed). |
3.2 Correlations of PD-1, PD-L1, p-S6 and co-expression of PD-L1 and PD-1 proteins expression in NPC
There was a notable phenomenon that in primary and matched metastatic NPC tissues, samples with positive PD-1 expression were accompanied by positive PD-L1, which attracted our attentions (Fig. 2B). Therefore, we investigated whether there were some correlations among these proteins. The relationship between PD-1, PD-L1, p-S6 and co-expression of PD-L1/PD-1 proteins in 281 NPC patients was shown in Table 2. PD-L1 expression was positively associated with PD-1 (r = 0.219, P < 0.001), p-S6 (r = 0.273, P < 0.001) or co-expression of PD-L1 and PD-1 (r = 0.366, P < 0.001) in NPC. In addition, p-S6 was also positively related to PD-1 (r = 0.127, P = 0.033) and co-expression of PD-L1 and PD-1 in NPC (r = 0.153, P = 0.01). Consistent with the notable phenomenon, expression of PD-1 was strongly related to combined PD-L1 and PD-1 expression (r = 0.885, P < 0.001).
Table 2
The pairwise correlation between expression of PD-L1, PD-1 and p-S6 proteins in the 281 cases of NPC
| PD-L1 | PD-1 | p-S6 | PD-1/PD-L1# |
PD-L1 | | | | |
Values | - | 0.219 | 0.273 | 0.366 |
Significant | | 0.000** | 0.000** | 0.000** |
PD-1 | | | | |
Values | - | - | 0.127 | 0.885 |
Significant | | | 0.033* | 0.000** |
p-S6 | | | | |
Values | - | - | - | 0.153 |
Significant | | | | 0.010* |
Values are Spearman's rank correlation coefficient. # Co-expression of PD-1 and PD-1; *Correlation is significant at the p < 0.05 level (two tailed); **Correlation is significant at the p < 0.05 level (two tailed). |
3.3 The impact of PD-L1, PD-1, p-S6 and combined PD-1and PD-L1 proteins expression on prognosis in NPC patients.
Survival status of NPC patients with differentially expressed PD-L1, PD-1, p-S6 and combined PD-L1 and PD-1 proteins was studied through Kaplan-Meier survival curves (Fig. 3). As to NPC patients, overall survival rate was significantly higher in cases with positive expression of PD-L1, compared to ones with negative PD-L1 expression (P = 0.035, Fig. 3A). On the contrary, NPC patients with positive expression of PD-1 (P = 0.031, Fig. 3B), p-S6 (P = 0.044, Fig. 3C) or combined PD-1 and PD-L1 (P = 0.042, Fig. 3D) had shorter survival time than others by univariate analysis.
Furthermore, we investigated whether PD-1, PD-L1, p-S6 and combined PD-L1 and PD-1 proteins expression could be used as independent prognostic factors for NPC patients. Data in Table 3 revealed that positive expression of PD-L1 protein was identified as an independent good prognostic factor (P = 0.002), while positive expression of p-S6 protein (P = 0.003), lymph node metastasis (LNM) status (P = 0.004), N-stage category (P < 0.001), M-stage category (P < 0.001) and clinical stage (P = 0.005) were identified as independent poor prognostic factors for overall survival of NPC patients. However, patients with positive PD-1 expression and co-expression of PD-L1 and PD-1 had no significant impact on the overall survival of NPC patients (P > 0.05, respectively). Other factors including gender, age, histological type and T/N stage category also have no obvious impacts on the prognosis in NPC (all P > 0.05).
Table 3
Summary of multivariate Cox proportional hazard regression analysis used to evaluate overall survival in 281 cases of NPC patients.
Parameter | SE | Wald | Significance | Exp(B) | 95.0% CI for Exp(B) Lower Upper |
Gender | 0.305 | 0.626 | 0.429 | 0.785 | 0.432 | 1.429 |
Age | 0.251 | 2.736 | 0.098 | 1.516 | 0.926 | 2.481 |
Histological type | 1.017 | 0.759 | 0.384 | 0.412 | 0.056 | 3.024 |
LNM status | 0.412 | 8.504 | 0.004** | 3.329 | 1.483 | 7.470 |
T-classification | 0.169 | 1.090 | 0.297 | 1.193 | 0.856 | 1.662 |
N-classification | 0.167 | 12.792 | 0.000** | 1.817 | 1.310 | 2.521 |
M-classification | 0.452 | 16.961 | 0.000** | 6.426 | 2.651 | 15.575 |
Clinical stages | 0.176 | 7.830 | 0.005** | 1.637 | 1.159 | 2.312 |
PD-L1 | 0.301 | 9.434 | 0.002** | 0.397 | 0.220 | 0.716 |
PD-1 | 0.501 | 1.626 | 0.202 | 1.895 | 0.709 | 5.064 |
p-S6 | 0.481 | 8.665 | 0.003** | 4.115 | 1.604 | 10.556 |
PD-L1/PD-1 | 0.607 | 0.170 | 0.680 | 1.284 | 0.391 | 4.217 |
Abbreviations: SE, standard error (SE); Exp (B), exponentiation of the B coefficient; CI, confidence interval.; LNM lymph node metastasis; NPC nasopharyngeal carcinoma.
Note: multivariate analysis of Cox proportional hazard regression, *Correlation is significant at the p<0.05 level (two tailed). **Correlation is significant at the p<0.01 level (two tailed).
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