The Rise of Immuno-Oncology Biomarkers in IHC

IHC’s Critical Role in Immuno-Oncology
Immuno-oncology (IO) has transformed cancer therapy by harnessing the body’s immune system to identify and eliminate tumor cells. As checkpoint inhibitors and other immunotherapies have reshaped treatment landscapes, there is a growing need to better understand tumor-immune interactions at the tissue level. Immunohistochemistry (IHC) remains an essential tool for this purpose, enabling the visualization and quantification of key immune biomarkers within the tumor microenvironment (TME). IHC supports patient selection and disease characterization by detecting specific protein biomarkers within tissue, offering spatial insights that helps guide diagnosis, assess tumor behavior, and inform therapeutic strategies.

Key Biomarkers Shaping the Field
PD-L1
Programmed death-ligand 1 (PD-L1) expression has become a pivotal biomarker for predicting response to immune checkpoint inhibitors such as pembrolizumab and nivolumab. PD-L1 testing helps identify patients more likely to benefit from these therapies, though expression thresholds and scoring systems can vary significantly between assays and tumor types. This variability remains a critical challenge for consistent clinical interpretation and underscores the need for assay standardization.

PD-L1’s value lies in its ability to inform first-line treatment decisions and stratify patients for immunotherapy, particularly when other targeted options are limited.

CD8
CD8 is a well-established marker for cytotoxic T lymphocytes (CTLs), which plays a direct role in recognizing and eliminating tumor cells. These cells exert their antitumor effects through granule-mediated cytotoxicity (e.g., perforin and granzymes) and death receptor pathways (e.g., Fas/FasL, TRAIL/TRAIL-R) and can also influence other immune cells to enhance tumor elimination.

Assessing CD8+ T cell presence, localization, and functional status within the tumor microenvironment offers valuable insight into the immune landscape of tumors. High CD8+ infiltration often correlates with more favorable immune activation and can support prognosis, therapeutic decision-making, and trial stratification.

As a biomarker, CD8 helps define the presence of active cytotoxic immune responses and supports the development and evaluation of immunotherapeutic strategies.

FOXP3
FOXP3 is a transcription factor marking regulatory T cells (Tregs), which are central to maintaining immune tolerance but can also suppress anti-tumor immunity within the tumor microenvironment. Elevated FOXP3 expression in tumor-infiltrating lymphocytes is often associated with a more immunosuppressive environment, contributing to poor prognosis and resistance to immunotherapy in several cancer types.

Recent studies also highlight the complex role of FOXP3 in breast cancer, where high FOXP3 expression—both in immune cells and occasionally in tumor cells themselves—has shown diagnostic value and may be associated with improved prognosis under specific conditions¹. These dual roles suggest FOXP3’s function may depend on cellular context and tumor type, underscoring the need for careful interpretation in translational research.

As a biomarker, FOXP3 helps characterize the immune regulatory landscape of tumors and informs therapeutic strategies aimed at restoring immune balance.

Complementary and Emerging Immune Markers Expanding the IHC Toolkit

• CD4 (Helper T Cells) helps identify the balance between pro-inflammatory (e.g., Th1, Th17) and immunosuppressive subsets (e.g., Tregs) within the tumor microenvironment. CD4 profiling supports spatial analysis of immune architecture and may inform strategies for combination immunotherapies that modulate helper T cell function or amplify downstream immune signaling.
• CD68 (Macrophages) serves as a marker for tumor-associated macrophages (TAMs), enabling evaluation of their spatial distribution. CD68 is increasingly used in multiplex IHC and spatial biology platforms to correlate macrophage infiltration patterns with response or resistance to therapies such as anti-PD-1 and CSF1R inhibitors.
• Granzyme B indicates the cytolytic activity of CD8+ T cells and NK cells. Measuring Granzyme B levels within the tumor or at the tumor–stroma interface provides functional insights into immune cell killing potential. It is a useful biomarker for assessing immunotherapy efficacy, particularly in trials evaluating checkpoint blockade or bispecific T cell engagers (BiTEs).

These complementary markers are increasingly leveraged in multiplex IHC and spatial profiling platforms to map immune cell interactions, assess functional activity, and refine biomarker strategies across diverse immuno-oncology applications.

Translational Research Applications
These immune biomarkers play a critical role in translational oncology, particularly during early-stage and preclinical research, where understanding the tumor-immune interface is essential. For academic researchers, biotech teams, and drug developers alike, immune marker analysis supports the discovery of novel targets, evaluation of therapeutic mechanisms, and development of predictive models. By characterizing immune cell composition, spatial dynamics, and functional activity, these tools help generate robust data to inform trial design, preclinical modeling, and hypothesis-driven research. These insights help bridge the gap between discovery science and patient-centered immunotherapy development.

Next-Generation Immune Profiling in IHC
IHC-based immune biomarkers are driving innovation in cancer research and immunotherapy development, and the field is rapidly evolving toward multiplexed and quantitative approaches that provide richer, more actionable immune profiling. Advances in spatial biology technologies—including digital pathology platforms and spatial transcriptomics—are expanding abilities to map immune cell interactions and distributions in situ with unprecedented precision.

At the same time, efforts to standardize and harmonize IHC assays are essential to ensure reproducibility, enable cross-study comparisons, and support broader clinical adoption. Looking ahead, the development of novel biomarkers and customized panels for next-generation immunotherapies will continue to push the boundaries of precision oncology, helping researchers translate complex immune landscapes into targeted, patient-centered treatments.

Interested in exploring advanced IHC assays or designing custom immune marker panels? Connect with HistoSpring to learn how we can support your immuno-oncology research. Contact us at 413-794-0523 / info@histospring.com.