Peripheral Blood Mononuclear Cells: A Brief Review
Tera Muir, PhD., Laboratory Operations Manager
What are PBMCs
Peripheral Blood Mononuclear Cells (PBMCs) are a diverse mixture of highly specialized immune cells that play key roles in keeping our bodies healthy. This brief review tells a short story about PBMCs starting with their origin, the different immune cells within the PBMC fraction, isolation of these cells and how to characterize them, and once isolated and characterized, how these cells benefit medical research.
Origin of Peripheral Blood Mononuclear Cells
Peripheral blood mononuclear cells originate from hematopoietic stem cells (HSCs) that reside in the bone marrow. HSCs give rise to all blood cells of the immune system through a process called hematopoiesis. As hematopoietic stem cells progress through hematopoiesis they generate the myeloid (monocytes, macrophages, granulocytes, megakaryocytes, dendritic cells, erythrocytes) and lymphoid (T cells, B cells, NK cells) lineages (Figure 1).
Within both lineages are cells that make up the PBMCs. PBMCs are blood cells with round nuclei that encompass a heterogeneous cell population comprising various frequencies of lymphocytes (T cells, B cells, and NK cells), dendritic cells, and monocytes (Table 1). These cells are critical components of the innate and adaptive immune system which defends the body against viral, bacterial, and parasitic infection and destroys tumor cells and foreign substances.
Figure 1. Overview of the different cells that arise from hematopoietic stem cells through the process of hematopoiesis.
The Frequency of Different Cell Populations within the PBMC Fraction
Human cell frequencies vary across individuals, but on average, most PBMCs are lymphocytes (70-90%). Lymphocytes play an essential role in cell-mediated and humoral immune responses, primarily associated with the activation of T and B cells.
Within the lymphocyte population, CD3+ T cells contribute to the most significant portion of cells (45-70%). Most T cells exist as resting, naïve T cells, which are T cells that have not been activated by an antigen, or as memory T cells. Activation of naïve T cells occurs through antigen recognition and accounts for a small population of T cells within healthy individuals. Once active, T cells launch a cell-mediated immune response that targets antigens within an infected or diseased cell.
Similarly, CD19+ B cells exist as naïve or memory cells that are awaiting activation by an antigen, and comprise only 5-15% of the total lymphocyte population. Once activated, B cells differentiate into plasma cells capable of secreting antibodies that specifically target free antigens circulating in the bloodstream. The ability to target free antigens by secreted antibodies within the extracellular space is defined as the humoral immune response.
NK cells account for a smaller portion of the lymphocyte population (5-10%) and, from a historical perspective, are part of the innate immune system, our bodies’ front-line defense system. These cells perform their effector function without requiring an antigen and defend the body against tumor activity.
A small portion of white blood cells include dendritic cells (1-2%) that form a critical interface between the innate and adaptive immune system. Dendritic cells, a highly specialized antigen-presenting cell, engulf antigens and present fragments of the antigen to cells of the adaptive immune system eliciting activation of T and B cells.
Varying in complexity and size as compared to lymphocytes, monocytes (10-30%) circulate within the bloodstream to the peripheral tissue where, when stimulated, mature and differentiate into either dendritic cells or macrophages that mediate both the innate and adaptive immune responses by acting as phagocytic and antigen-presenting cells.
Table 1. Average cell frequencies from enriched PBMC fractions.
Last, but of great importance, are the hematopoietic stem cells. HSCs within the blood and bone marrow give rise to all the cells within the blood, including red blood cells, platelets, lymphocytes, monocytes, and granulocytes. Although desirable for stem cell transplants, this rare cell population accounts for only 0.1-0.2% of the PBMC fraction, making them difficult to isolate from whole blood samples. Injection of mobilizations agents, such as granulocyte-colony stimulating factor (G-CSF) or Plerixafor, can increase the frequency of circulating CD34+ stem cells to o.5-1.5%, allowing for greater quantities of these rare cells from a donor.
Isolation of Peripheral Blood Mononuclear Cells
Two primary techniques that separate peripheral blood mononuclear cells from whole peripheral blood are through the use of a density gradient centrifugation process or by leukapheresis.
Since cells have a specific density, the use of a density gradient centrifugation process separates the main cell populations, such as lymphocytes, monocytes, granulocytes, and red blood cells, throughout a density gradient medium. For human cells, the medium will have a density of 1.077 g/ml to allow sufficient separation of PBMCs (density < 1.077 g/ml) from red blood cells and granulocytes (density > 1.077 g/ml).1 Layering of whole blood over or under a density medium without mixing of the two layers followed by centrifugation will disperse the cells according to their densities (Figure 2). After centrifugation, the PBMC fraction will appear as a thin white layer at the interface between the plasma and the density gradient medium making it easy to remove the PBMC fraction.
A leukapheresis machine is an automated device that separates the inflow of whole blood from the target PBMC fraction using high-speed centrifugation while returning the outflow material, such as plasma, red blood cells, and granulocytes, back to the donor. On average, leukapheresis provides 14x more PBMCs from a single donor than the density gradient centrifugation process of whole blood (Figure 3). The sheer number of PBMCs within a Leukopak, the product of leukapheresis, makes them ideal for large-scale research studies or pre-clinical trials. Depending on the quality of the leukapheresis machine and the downstream research applications, further processing of a Leukopak may be necessary to remove residual red blood cells (RBC lysis) and granulocytes (density gradient centrifugation).
Figure 2. Whole blood layered onto a density gradient medium. After centrifugation, the PBMC fraction is defined by the white layer at the interface between the plasma and the density gradient medium.
Peripheral Blood Mononuclear Cells in Research
PBMCs are critical components of the immune system since they can elicit a response to intruders entering the human body and existing cells that have undergone a transformation into a cancerous cell type. Therefore, researchers and clinicians use PBMCs in areas relating to immunology, infectious disease, hematological malignancies, vaccine development, transplant therapy, personalized medicine, and toxicology. Predominately, in vitro PBMC studies provide the most information regarding cell function6, biomarker identification7, and disease modeling8, just to name a few. But the research also expands into in vivo analysis through the use of humanized mice. Reconstitution of immunocompromised mice with human PBMCs allows the study of the human immune system and its response to pathogens, toxins, or cancer in an in vivo model.9
But studies using PBMCs are advancing into more precise human medicine. The generation of induced pluripotent stem cells (iPSCs) from single donors PBMC fraction has great implications in personalized medicine regarding disease modeling, drug toxicity screening, drug discovery, and cell replacement therapy.10 And of recent, the use of genome editing technology, such as CRISPR/Cas9, can transform immune cells (T cells from PBMCs) into off-the-shelf CAR-T cells making it possible to treat human cancers without a donor match.11
Market Growth and Trends
The global market for PBMCs has witnessed substantial growth, driven by their expanding applications in research and therapy.
- Market Size and Projections: In 2022, the global PBMC market was valued at approximately USD 235.68 million and is projected to grow at a CAGR of 10.39% from 2023 to 2028 .
- Regional Insights: North America currently leads the market, accounting for 45% of total revenue in 2023, followed by Europe at 30%, and Asia Pacific at 15%. Notably, Asia Pacific is the fastest-growing region, attributed to increased healthcare expenditures and a surge in biotechnological innovations. Verified Market Reports
- Application Segmentation: PBMCs are extensively used in immunology, hematology, infectious disease research, and increasingly in cell therapy applications. The immunology segment dominated the market with a 49.25% share in 2022. TechSci Research
Advancements in Research and Therapeutic Applications
PBMCs have become indispensable in various research domains and therapeutic strategies:
- Toxicology Research: PBMCs are utilized to assess the immunotoxic effects of new drugs and chemicals, providing insights into potential adverse immune responses. Research and Markets
- Cell and Gene Therapy: The role of PBMCs in adoptive cell transfer therapies, including CAR-T cell therapy, has been pivotal. Their ability to be genetically modified and expanded ex vivo makes them suitable candidates for personalized medicine approaches .
- Vaccine Development: PBMCs serve as a model to study immune responses to vaccines, aiding in the evaluation of vaccine efficacy and safety.
- Single-Cell Multi-Omics: The integration of PBMCs in single-cell multi-omics studies has enhanced the understanding of cellular heterogeneity and disease mechanisms, contributing to the growth of this market segment projected to reach USD 11.5 billion by 2034. GlobeNewswire
The Rise of AI in PBMC Research
Artificial intelligence is not just a buzzword in biotech anymore—it’s rapidly becoming a cornerstone in PBMC research. From cell-type identification to predictive diagnostics, AI is unlocking unprecedented possibilities.
One standout example is the integration of chromatin imaging with machine learning. A study published in Nature Communications showed that this approach could classify healthy individuals versus tumor patients by identifying robust chromatin biomarkers from PBMC samples. The model used high-content imaging data fed into neural networks to distinguish disease states, opening the door for AI-assisted diagnostics in oncology and beyond (Nature, 2023).
Another innovation comes from the development of ScType, a fully automated cell-type identification platform using single-cell RNA sequencing data. ScType not only improves the speed and scalability of PBMC analysis but also enhances the accuracy of results—especially crucial for translational research and immunotherapy development (Nature Communications, 2022).
AI is also playing a pivotal role in biomarker discovery. A 2023 study in Genomics, Proteomics & Bioinformatics used explainable AI (XAI) techniques like XGBoost to identify novel diagnostic biomarkers from PBMC gene expression profiles in breast cancer patients. The transparent nature of XAI provides both accuracy and interpretability—key for regulatory approval and clinical adoption (ScienceDirect, 2023).
AI’s footprint extends to digital hematopathology as well. Machine learning algorithms are increasingly used for automated classification of blood cells, identification of acute leukemia, and diagnosis of hematopoietic stem cell disorders. These applications reduce manual labor, minimize error rates, and accelerate time to diagnosis in clinical labs (PMC, 2022).
Finally, in a comprehensive review in Annual Review of Immunology, researchers emphasized AI’s role in systems immunology. By analyzing large, complex immune datasets—often generated from PBMCs—AI models can predict immune responses to vaccines, therapies, or infections. These models enhance personalized medicine approaches, particularly in immuno-oncology and infectious disease (Annual Reviews, 2023).
TL;DR: AI is no longer an experimental add-on in PBMC workflows—it’s a validated, scalable asset in modern research. Whether you’re profiling T cells, searching for biomarkers, or building predictive disease models, AI-driven platforms are becoming indispensable tools in cell and gene therapy R&D.
Conclusion
PBMCs are an important element and a powerful tool for research and clinical studies relating to human health and disease. Through efficient and successful processing and analysis of PBMCs, researchers and clinicians can test immune responses, gain a deeper understanding of the immune system, and apply their findings to treatments and cures for human diseases.
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