Assessing the Clinical Relevance of Soluble PD-1 and PD-L1: A Multi-Cohort Study Across Diverse Tumor Types and Prognostic Implications

Background/Objectives: Immune checkpoint inhibitors targeting the PD-1/PD-L1 pathway have revolutionized cancer immunotherapy, however the clinical relevance of their soluble forms (sPD-1 and sPD-L1) remains less studied. Soluble PD-1 and PD-L1 have been implicated in tumor progression, prognosis, and treatment response across various malignancies. This study aims to provide a comprehensive analysis of sPD-1 and sPD-L1 levels in serum across diverse tumor types, including rare malignancies, and to evaluate their associations with clinicopathological characteristics and prognostic significance. Methods: In this study we analyzed sPD-1 and sPD-L1 levels in serum samples from 675 cancer patients representing a range of malignancies, including ovarian cancer, breast cancer, gastric cancer, colorectal cancer, renal cell carcinoma, and bone tumors. sPD-1 and sPD-L1 concentrations were measured using ELISA. Statistical analyses were performed to evaluate associations between soluble marker concentrations and clinicopathological factors, including tumor stage, size, histological subtype, and survival outcomes. Results: Elevated sPD-L1 levels were observed in several tumor types, including ovarian cancer, renal cell carcinoma, and gastric cancer, where they were associated with features of advanced disease, such as tumor size, stage, and metastases. In contrast, sPD-1 levels showed limited associations, with significant findings solely in gastric cancer and bone tumors, where levels correlated with histological subtype and differentiation. Prognostic analyses identified sPD-L1 as a marker of poor survival outcomes in ovarian cancer and bone tumors, while sPD-1 displayed no consistent prognostic significance. Conclusions: This study identifies the potential of sPD-L1 as a biomarker for tumor progression and prognosis across multiple malignancies. In contrast, sPD-1 showed limited clinical relevance, suggesting the importance of further investigation. These findings contribute to our understanding of soluble immune checkpoint proteins and their integration into personalized oncology strategies.

Clinical Relevance of Soluble Forms of Immune Checkpoint Molecules sPD-1, sPD-L1, and sCTLA-4 in the Diagnosis and Prognosis of Ovarian Cancer

It is crucial to find new diagnostic and prognostic biomarkers. A total of 80 patients were enrolled in the study. The study group consisted of 37 patients with epithelial ovarian cancer, and the control group consisted of 43 patients with benign ovarian cystic lesions. Three proteins involved in the immune response were studied: PD-1, PD-L1, and CTLA-4. The study material was serum and peritoneal fluid. The ROC curve was plotted, and the area under the curve was calculated to characterize the sensitivity and specificity of the studied parameters. Univariate and multivariate analyses were performed simultaneously using the Cox regression model. The cut-off level of CTLA-4 was 0.595 pg/mL, with the sensitivity and specificity of 70.3% and 90.7% (p = 0.000004). Unfavorable prognostic factors determined in serum were: PD-L1 (for PFS: HR 1.18, 95% CI 1.11–1.21, p = 0.016; for OS: HR 1.17, 95% CI 1.14–1.19, p = 0.048) and PD-1 (for PFS: HR 1.01, 95% CI 0.91–1.06, p = 0.035). Unfavorable prognostic factors determined in peritoneal fluid were: PD-L1 (for PFS: HR 1.08, 95% CI 1.01–1.11, p = 0.049; for OS: HR 1.14, 95% CI 1.10–1.17, p = 0.045) and PD-1 (for PFS: HR 1.21, 95% CI 1.19–1.26, p = 0.044). We conclude that CTLA-4 should be considered as a potential biomarker in the diagnosis of ovarian cancer. PD-L1 and PD-1 concentrations are unfavorable prognostic factors for ovarian cancer.

Prognostic significance of soluble forms of immune checkpoint PD-1/PDL1 receptor and ligand in blood plasma of gastric cancer patients

Analysis of long-term treatment results of 101 primary gastric cancer patients at various stages of the tumor process followed during 1 - 41 months (median - 6,4 months) from the onset of specific treatment are presented depending on the levels of soluble forms (s) of PD-1 receptor and its ligand PD-L1 in blood plasma. Overall survival assessed by Kaplan-Meyer analysis and with the help of Cox multiparametric regression model was applied as the criterion of prognostic value. It was found that at high (≥ 35 pg/ml) sPD-L1 levels in blood plasma, the overall survival of patients with gastric cancer was statistically significantly lower than at the marker's levels below 35 pg / ml (p <0.045): 1-year survival comprised 78 and 96%, 2-year - 52 and 78%; 3-year - 40 and 61% at high and low sPD-L1 respectively. Median survival of patients with high plasma sPD-L1 comprised 29 months, of those with low sPD-L1 was not achieved during the whole follow-up period. This trend was observed not only in the total group of stage I-IV gastric cancer patients, but also in patients at the early stages of the disease, though sPD-L1 did not show an independent prognostic value in multiparametric model. At the same time, the overall survival of patients with gastric cancer did not depend on the baseline levels sPD-1 in blood plasma. Thus, soluble ligand sPD-L1 can be considered as a potentially valuable factor for prognosis of gastric cancer patients' survival, and, probably, of anti-PD-1/PD-L1 treatment efficiency, but further studies and patients' monitoring are required to prove this statement.

Key Immune Checkpoint PD-1/PD-L1 Signaling Pathway Components in the Blood Serum from Patients with Bone Tumors

The levels of sPD-1 and sPD-L1 were analyzed in blood serum of 132 patients (age 14-70 years) with primary bone tumors: osteosarcoma (N=39), chondrosarcoma (N=42), Ewing sarcoma (N=9), chordoma (N=12), giant-cell bone tumor (GCBT) (N=16), benign neoplasms (N=14) and in and practically healthy subjects (age 19-58 years; N=27). sPD-L1 levels in all studied bone neoplasms were significantly higher than in the control. Serum sPD-1 level in GCBT patients was significantly higher than in the control, benign neoplasms, chondrosarcoma, and chordoma patients, but did not differ from osteosarcoma group. sPD-1 concentration in Ewing sarcoma was significantly higher than in chordoma and chondrosarcoma, but did not differ from the control. sPD-1 level in chondrosarcoma patients was also lower than in osteosarcoma, Ewing sarcoma, and in the control. Both sPD-1 and sPD-L1 concentrations were not significantly associated with the type of affected bone, process localization, disease stage, tumor histological grade, patients' age and sex. These results suggest the possibility of using these biological markers for preliminary assessment of the character of the process in the bone.

[The content of the soluble forms PD-1 and PD-L1 in blood serum of patients with gastric cancer and their relationship with clinical and morphological characteristics of the disease.]

Results of comparative ELISA investigation of pretreatment sPD-1 and sPD-L1 content in blood plasma of 100 gastric cancer patients at various disease stages aged 25 to 81 years are presented. Control group included 60 practically healthy donors aged 18 - 68 years. Plasma sPD-L1 concentrations did not differ between gastric cancer patients and control group, and sPD-1 levels were statistically significantly lower in patients than in healthy donors (p<0.0001). Positive correlation (R=0.38; p=0.003) was revealed between plasma sPD-1 и sPD-L1 levels in control group and negative (R= -0.26; p=0,009) - in gastric cancer patients. ROC curve revealed the best sPD-1 cut-off level (< 21 pg/ml) with 77% sensitivity and 63.3% specificity, which is not sufficient for its application as diagnostic marker. Statistically significant increase of plasma sPD-L1 from stage I to stage IIIC (R=0.50; p=0.000011) was found. Analysis of associations between the evaluated markers' levels and indices of gastric cancer expansion according to TNM system revealed statistically significant positive associations of plasma sPD -L1 levels with T (tumor invasiondepth) and N (number of affected lymph nodes) indices: R=0.33; p=0.00093, and R=0.27; p=0.0099 respectively. sPD-L1 level was significantly increased in patients with low differentiated adenocarcinoma and cricoid-cell cancer as compared to highly differentiated adenocarcinoma (p=0.02 and p=0.004 respectively); in patients with cricoid-cell cancer it was also higher than in those with moderately differentiated adenocarcinoma (p=0.043) and undifferentiated cancer (p=0.049). Plasma sPD-1 level did not depend on disease stage, TNM system indices and tumor histological structure. Thus, soluble ligand sPD-L1, but not its receptor sPD-1, plasma level is increased in patients with unfavorable clinical and morphological characteristics, may be regarded as potentially valuable prognostic factor for gastric cancer patients' survival, and probably as a predictor of anti - PD-1/PD-L1 treatment efficiency.