Patient characteristics
The patients’ characteristics are summarized in Table 1. The population comprised 31 men (43.7%) and 40 women (56.3%); the overall median age was 64 years (range, 29–86 years). The tumors in our cohort comprised 44 glioblastomas, IDH-wildtype, WHO grade 4 (62.0%), 4 astrocytomas, IDH-mutant, WHO grade 4 (5.6%), 20 glioblastomas, not otherwise specified (NOS; 28.2%), 2 oligodendrogliomas, IDH-mutant and 1p19q co-deleted, WHO grade 3 (2.8%); and 1 high-grade astrocytoma, NOS (1.4%). In 20 (28.2%) and 35 (49.3%) tumors, the MGMT promoter status was hypermethylated and hypomethylated, respectively.
Among the 44 patients with glioblastomas, IDH-wildtype, WHO grade 4 , 34 patients (77.3%) received combined radiotherapy and temozolomide (TMZ)-based chemotherapy, 7 (15.9%) received combined radiotherapy and nimustine hydrochloride (ACNU)-based chemotherapy, and 3 (6.8%) received radiotherapy alone. Furthermore, 29 patients (65.9%) underwent total or subtotal resection, while 15 patients (34.1%) underwent biopsy or partial resection. Finally, 27 (61.4%) and 17 (38.6%) patients had a postoperative KPS score of ≥70 and <70, respectively.
Correlation of PD-L1 expression with TIICs densities, IDH1/2 mutation, and MGMT promoter methylation status
PD-L1 staining was diffusely and focally positive in eight (Fig. 1A) and seven (Fig. 1B) tumors, respectively. Therefore, these 15 tumors (21.1%) were defined as PD-L1+ tumors; the remaining 56 tumors (78.9%) that showed no PD-L1 staining (Fig. 1C) were defined as PD-L1- tumors.
Immunohistochemical findings for CD4, CD8, and CD204 are shown in Fig. 2A, B, C, and D, respectively. The median number of CD4+ and CD8+ cell densities was significantly higher in PD-L1+ tumors than in PD-L1- tumors (PD-L1+ vs. PD-LI-: 24.5 vs. 5.3 cells/mm2 for CD4+ cells [p = 0.025, Fig. 2A]; 19.8 vs. 6.3 cells/mm2 for CD8+ cell densities [p = 0.0098, Fig. 2B]). There was no significant difference in the median number of CD204+ cell densities between PD-L1+ and PD-L1- tumors (332.7 vs. 512.6 cells/mm2; p = 0.19; Fig. 2C). The frequencies of PD-L1+ tumors were 16.7% and 27.3% in IDH-mutant tumors (n =6) and IDH-wildtype tumors (n =44), respectively; however, this difference was not statistically significant (p = 0.58; Fig. 2D). Furthermore, 30.0% and 20.0% of the PD-L1+ tumors were MGMT hypermethylated (n = 20) and hypomethylated (n =35), respectively; this difference was not statistically significant (p = 0.40; Fig. 2E).
Imaging characteristics
We evaluated the imaging characteristics of 62 patients who showed a single enhanced lesion. The contrast enhancement and FLAIR hyperintensity areas did not differ between the PD-L1- and PD-L1+ tumors (p = 0.18 and p = 0.84, respectively) and among tumors with low and high of CD4+ T cell densities (p = 1.00 and p = 0.86, respectively), CD8+ T cell densities (p = 0.33, and p = 0.17, respectively), and CD204+ macrophage densities (p = 0.23, and p = 0.39, respectively). The FLAIR-to-enhancement ratio was significantly higher in PD-L1+ tumors than in PD-L1- tumors (p = 0.0037), but not in tumors with low and high tumors of CD4+ T cell densities, CD8+ T cell densities, and CD204+ macrophage densities (p = 0.14, 0.44, and 0.85, respectively; Table 2).
The optimal cutoff value of the FLAIR-to-enhancement ratio for differentiating between tumors with and without PD-L1 expression was 1.83, as calculated by an ROC curve (area under the curve: 0.75). Tumors with FLAIR to enhancement ratio above the cutoff value were observed in 78.6% (11/14) of PD-L1+ tumors, whereas those with FLAIR to enhancement ratio below the cutoff value were in 27.1% (13/48) of PD-L1- tumors (p = 0.0011) (Fig. 3B).
Prognostic impact in patients with IDH-wildtype glioblastomas
Next, we focused on the 44 patients with IDH-wildtype glioblastomas to evaluate the prognostic impact of PD-L1 and TIICs. Kaplan–Meier analysis did not show a significant association of PD-L1 expression with the OS or PFS (median survival time [MST]: PD-L1+ vs. PD-LI-, 19.2 vs. 14.9 months [p = 0.39]; median PFS (mPFS): PD-L1+ vs. PD-L1-1-, 9.6 vs. 8.1 months [p = 0.46]). Tumor-infiltrating CD4, CD8, and CD204 cells densities and the ratio of CD8/CD204 cells densities were not significantly associated with patient outcomes (Supplementary Table 1). Moreover, 44 patients with IDH-wildtype glioblastomas were categorized into the PD-L1+/CD8 high (five patients, 11.4%), PD-L1+/CD8 low (seven patients, 15.9%), PD-L1–/CD8 high (five patients, 11.4%), and PD-L1–/CD8 low (27 patients, 61.4%) groups. The MST and mPFS did not differ significantly among these groups (Supplementary Table 1).