Immune Checkpoint Inhibitors: Fundamental Mechanisms, Current Status and Future Directions

Prognostic Significance of B7H3 Expression in Solid Tumors: A Systematic Review and Meta-Analysis

B7H3 (CD276), an immunoregulatory molecule known for its role in immune evasion by transmitting inhibitory signals to T lymphocytes, has garnered significant attention in recent years as a promising target for cancer immunotherapy. This interest is largely due to its high expression in various types of solid tumors, coupled with low protein levels in normal tissues. However, studies examining the impact of B7H3 on survival outcomes have shown inconsistent results, leaving its prognostic significance not fully clarified. Therefore, this meta-analysis aimed to assess the relationship between B7H3 expression and various prognostic parameters in patients with solid malignancies. PubMed, Web of Science (WOS), Cochrane, SCOPUS, and Embase databases were searched for eligible articles published until November 2024. Statistical analysis was performed using R studio (version 4.3.2). The analysis included a total of 51 eligible studies comprising 11,135 patients. Results showed that overexpression of B7H3 is a negative predictor for all examined survival outcomes: OS (HR = 1.71, 95% CI = 1.44-2.03, p < 0.0001), DFS (HR = 2.02, 95% CI = 1.49-2.73, p < 0.0001), PFS (HR = 2.10, 95% CI = 1.44-3.06, p < 0.0001), RFS (HR = 1.66, 95% CI = 1.11-2.48, p = 0.01), and DSS (HR = 1.70, 95% CI = 1.24-2.32, p < 0.01). Despite the high heterogeneity observed across the studies, the sensitivity analysis confirmed the robustness of these results. This research suggests that B7H3 may serve as an effective biomarker for prognosis in solid tumors.

Spontaneous Necrosis of a High-Risk Bladder Tumor Under Immunotherapy for Concurrent Malignant Melanoma: Role of BRAF Mutations and PD-L1 Expression

Background: Bladder cancer (BC) is a heterogeneous malignancy, and predicting response to immune checkpoint inhibitors (ICIs) remains a challenge. Herein, we investigate a high-risk bladder tumor, which developed during anti-BRAF/MEK therapy for a concurrent advanced BRAF-V600E-positive malignant melanoma (MM) and subsequently underwent complete spontaneous necrosis following Nivolumab immunotherapy, only to recur thereafter while still under the same treatment. This unique scenario provided an opportunity to investigate the roles of BRAF gene mutations in BC pathogenesis, respectively, of PD-L1 expression in immunotherapy response prediction. Methods: We retrospectively analyzed BC specimens obtained via transurethral resection at two critical time-points: prior to the complete spontaneous necrosis under Nivolumab (prenecrosis) and after tumor recurrence postnecrosis (postnecrosis). The BRAF gene mutation status was evaluated using quantitative polymerase chain reaction (qPCR). PD-L1 expression was assessed by immunohistochemistry (IHC), quantified using the combined positive score (CPS), and a cutoff of ≥10 for positivity. Results: Neither pre- nor postnecrosis BC samples harbored BRAF gene mutations. Prenecrosis PD-L1 expression (CPS = 5) indicated a minimal likelihood of response to immunotherapy. However, complete spontaneous necrosis occurred under Nivolumab, followed by recurrence with further reduced PD-L1 expression (CPS = 1). Conclusions: The complete BC regression challenges the conventional role of PD-L1 as a sole predictive biomarker for immunotherapy. This study also highlights the potential role of BRAF/MEK inhibitors in BC oncogenesis and underscores the need for alternative biomarkers, such as tumor mutation burden (TMB) and circulating tumor DNA (ctDNA), to guide treatment selection in BC better.

The gut microbiome and cancer response to immune checkpoint inhibitors

Immune checkpoint inhibitors (ICIs) are widely used for cancer immunotherapy, yet only a fraction of patients respond. Remarkably, gut bacteria impact the efficacy of ICIs in fighting tumors outside of the gut. Certain strains of commensal gut bacteria promote antitumor responses to ICIs in a variety of preclinical mouse tumor models. Patients with cancer who respond to ICIs have a different microbiome compared with that of patients who don't respond. Fecal microbiota transplants (FMTs) from patients into mice phenocopy the patient tumor responses: FMTs from responders promote response to ICIs, whereas FMTs from nonresponders do not promote a response. In patients, FMTs from patients who have had a complete response to ICIs can overcome resistance in patients who progress on treatment. However, the responses to FMTs are variable. Though emerging studies indicate that gut bacteria can promote antitumor immunity in the absence of ICIs, this Review will focus on studies that demonstrate relationships between the gut microbiome and response to ICIs. We will explore studies investigating which bacteria promote response to ICIs in preclinical models, which bacteria are associated with response in patients with cancer receiving ICIs, the mechanisms by which gut bacteria promote antitumor immunity, and how microbiome-based therapies can be translated to the clinic.

Impact of Neoadjuvant Therapy on PD-L1 Expression in Triple-Negative Breast Cancer and Correlation with Clinicopathological Factors

BACKGROUND

This study aims to deliver more insights on the impact of neoadjuvant treatment on Pd-L1 expression and to evaluate its correlation with clinicopathological factors.

METHODS

We reviewed 88 TNBC cases for the period 2021-2023. Data on age, tumor size, stage, and treatment were collected. Histological slides were assessed for subtype, grade, and TILs. A total of 48 received neoadjuvant treatment. HER2 and Ki67 were evaluated via immunohistochemistry. PD-L1 expression was tested on primary and residual tumors. Statistical analysis was performed using IBM SPSS (p < 0.05).

RESULTS

In this study, PD-L1 positive expression was found in 44.3% of primary tumors, with 52.9% of initially positive cases losing expression post-treatment. TILs were significantly higher in PD-L1-positive tumors (mean 41.79% vs. 27.55%, p = 0.001). A notable correlation was found between PD-L1 expression and Ki-67 proliferation index, with PD-L1-positive tumors having a median Ki-67 of 64.49 compared to 52.86 in negative cases (p = 0.015). Neoadjuvant immunotherapy led to a lower mean residual cancer burden (0.95 vs. 2.55, p = 0.002) compared to chemotherapy alone. Higher Ki-67 levels (≥50%) were associated with better treatment outcomes, showing a mean RCB score of 1.60 versus 3.16 for lower levels (p = 0.022). HER2-negative cases had a higher prevalence of favorable pathological response (54.5%) compared to HER2-low tumors (25%, p = 0.048), because of the strong correlation to high proliferative index.

CONCLUSIONS

In conclusion, PD-L1 expression in TNBC shows significant discordance post-treatment, highlighting the need for routine testing and further research on predictive biomarkers.

Predictive Biomarkers and Resistance Mechanisms of Checkpoint Inhibitors in Malignant Solid Tumors

Predictive biomarkers for immune checkpoint inhibitors (ICIs) in solid tumors such as melanoma, hepatocellular carcinoma (HCC), colorectal cancer (CRC), non-small cell lung cancer (NSCLC), endometrial carcinoma, renal cell carcinoma (RCC), or urothelial carcinoma (UC) include programmed cell death ligand 1 (PD-L1) expression, tumor mutational burden (TMB), defective deoxyribonucleic acid (DNA) mismatch repair (dMMR), microsatellite instability (MSI), and the tumor microenvironment (TME). Over the past decade, several types of ICIs, including cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) inhibitors, anti-programmed cell death 1 (PD-1) antibodies, anti-programmed cell death ligand 1 (PD-L1) antibodies, and anti-lymphocyte activation gene-3 (LAG-3) antibodies have been studied and approved by the Food and Drug Administration (FDA), with ongoing research on others. Recent studies highlight the critical role of the gut microbiome in influencing a positive therapeutic response to ICIs, emphasizing the importance of modeling factors that can maintain a healthy microbiome. However, resistance mechanisms can emerge, such as increased expression of alternative immune checkpoints, T-cell immunoglobulin (Ig), mucin domain-containing protein 3 (TIM-3), LAG-3, impaired antigen presentation, and alterations in the TME. This review aims to synthesize the data regarding the interactions between microbiota and immunotherapy (IT). Understanding these mechanisms is essential for optimizing ICI therapy and developing effective combination strategies.

Combined cancer immunotherapy based on targeting adenosine pathway and PD-1/PDL-1 axis

INTRODUCTION

Cancer immunotherapy has revolutionized the field of oncology, offering new hope to patients with advanced malignancies. Tumor-induced immunosuppression limits the effectiveness of current immunotherapeutic strategies, such as PD-1/PDL-1 checkpoint inhibitors. Adenosine, a purine nucleoside molecule, is crucial to this immunosuppression because it stops T cells from activating and helps regulatory T cells grow. Targeting the adenosine pathway and blocking PD-1/PDL-1 is a potential way to boost the immune system's response to tumors.

AREAS COVERED

This review discusses the current understanding of the adenosine pathway in tumor immunology and the preclinical and clinical data supporting the combination of adenosine pathway inhibitors with PD-1/PDL-1 blockade. We also discuss the challenges and future directions for developing combination immunotherapy targeting the adenosine pathway and the PD-1/PDL-1 axis for cancer treatment.

EXPERT OPINION

The fact that the adenosine signaling pathway controls many immune system processes suggests that it has a wide range of therapeutic uses. Within the next five years, there will be tremendous progress in this area, and the standard of care for treating malignant tumors will have switched from point-to-point therapy to the integration of immunological networks comprised of multiple signaling pathways, like the adenosine axis.