Peripheral blood mononuclear cell pellets, or PBMC pellets, are an important part of immunological research and molecular biology. PBMC pellets consist of innate and adaptive immune cells, including T cells, B cells, NK cells, dendritic cells and monocytes. Due to their ease-of-use and ability to provide a dynamic immunological model, PBMC pellets remain a favorite tool among biomedical researchers.
PBMC pellets are an easily accessible source for protein and nucleic acids isolation (DNA and RNA). They are typically the starting material for quantitative mRNA analysis, western blot analysis and cell culture.
Protein quantification from PBMCs can be performed using conventional techniques such as enzyme-linked immunosorbent assay (ELISA), multiplex bead array assay (Luminex) and flow cytometry. Using these techniques enables the quantification of extracellular or intracellular molecules either by using PBMC supernatants or cell lysates, respectively. In recent years, PBMCs have increasingly become a useful tool in metabolomics and proteomics using mass-spectroscopy.
In this article, we provide an overview of how PBMC pellets are currently used in research and their potential to transform disease modeling and drug discovery.
Overview of PBMC Pellets
PBMC pellets are typically derived from whole blood in FDA-licensed donor centers and further processed using Ficoll gradient and several washes to remove platelets. All donors are tested for HIV, Hepatitis B and C, WNV, CMV, and other blood-borne pathogens.
The cells are centrifuged and concentrated into a packed pellet. The resulting PBMC pellet is subsequently snap frozen in liquid nitrogen if the cells will be ultimately lysed in downstream applications. If a researcher needs viable PBMCs (e.g., for use in cell culture), then the cells are resuspended in a cryoprotectant media, such as CryoStor CS-10, and stored in liquid nitrogen vapor phase.
The frequency of various immune cell types in PBMC pellets fluctuates across individuals. However, T cells typically account for roughly 70% of the PBMC pellet. Other cells like natural killer cells contribute 10%, B lymphocytes – 15%, monocytes – 5%, and dendritic cells – 1%, approximately. 
What Are the Uses of PBMC Pellets in Biomedical Research?
Peripheral blood mononuclear cells are considered a crucial tool in biomedical research due to their wide applications. Their use in biotechnology has increased substantially in recent years, as described below.
PBMC pellets can serve as a crucial source of biomarkers associated with different diseases, including cancers, allergies, autoimmune diseases, schizophrenia, diabetes, etc. Their analysis in disease states shows dysregulation of microRNAs, change in methylation profile and mRNA level of different genes. Studies show a strong probability that PBMCs can portray the condition of affected tissues that interact with them, such as tumor tissue or cells. PBMC pellets are a non-invasive and suitable biomarker analysis tool, that may easily be used in clinical trials. 
Drug Research and Immunotoxicology
PBMC culturing can be used as model to evaluate an individual’s immune system. This approach has been improved and modified over a period of time through continuous experimentation and validation. Recent research studies have suggested PBMCs as a tool for investigating the effects of drugs and xenobiotics on the human immune system. (3)
PBMCs enable the in-vitro assessment of potential adverse effects on the immune system. They can be used for new compound toxicity screening, comparative studies, measuring occupational exposure, chemotherapy toxicity, immunotherapy toxicity and pharmacogenomics studies. 
PBMCs are a significant source of T cells with several immunotherapeutic applications such as CAR-T cell therapy. These cancer therapies consist of T cells which are genetically manipulated to represent a chimeric antigen receptor. The CAR-T cells then recognize specific antigens independent of the MHC proteins and kill tumor cells. T cells are the largest component of PBMCs and are mainly obtained from an unfractionated population before it gives rise to cell populations comprising T cells and other mononuclear cells. 
OMICS and Disease Modeling
Omics techniques are powerful tools in molecular biology, as they enable high-throughput measurements of many genes, proteins, and metabolites in samples. PBMCs can generate omics data that can be used to understand health and disease states, including:
- Regenerative medicine ⤵
PBMCs have several constructive applications in regenerative medicine. PBMCs contain a small percentage of adult stem cells, and upon culturing in a particular microenvironment these cells have the potential to differentiate into other cell types. Transplantation of these PBMC-derived stem cells can help tissue regeneration and tissue restoration after injury. 
Interestingly, PBMCs can release biologically active paracrine factors with regenerative properties. Several research studies have successfully used the apoptotic PBMC secretome (released paracrine factors, i.e., proteins) to treat chronic heart disease, spinal cord injury, myocardial infarction, and healing of wounds. Considering this evidence, PBMC secretome can be referred to as an alternative approach to cell-based therapies. 
Vaccine development is a crucial, time consuming and pretty expensive process that relies on animal model-based studies. Despite successful animal experiments, many vaccines failed clinical trials doubting the prognostic value of animal models. Herein, for efficient and reproducible vaccine screening, unfractionated PBMC pellets isolated from healthy individuals are cultured in-vitro to evaluate T cell responses to vaccine candidates. This will help assess the functional properties of vaccine candidates in the human context before boarding on to expensive clinical trials. 
Diagnosis of Autoimmune Diseases
PBMCs are utilized to diagnose and elucidate the mechanisms behind the various autoimmune diseases based on intracellular regulatory pathways in the cells. These signaling pathways are either common to many autoimmune disorders or specific to some of them. PBMC pellets obtained from diseases patients’ blood can be used for gene expression and protein-protein interactions studies to diagnose and understand autoimmune diseases. 
PBMCs can be easily collected from patients and cultured in the lab to monitor physiological distresses caused by disease. They have been an attractive tissue source in molecular, immunological and pharmacogenomic investigations. Research has been conducted on PBMC cellular models to study infectious parasites such as Toxoplasma gondii and other apicomplexan parasites. These models may help investigate new vaccines and anti-parasitic therapies. 
PBMC pellets are used in hematological lymphoid and myeloid malignancies research. They are valuable in understanding the molecular mechanisms underlying these diseases, optimization of diagnosis and validation of treatment responses. 
PBMC pellets enable the assessment of particular cell populations and proteins, such as cellular markers, cytokines, chemokines, intracellular proteins, transcription factors and expressed genes. In addition, they can easily be cryopreserved in liquid nitrogen and then thawed or lysed later for immunology studies.
As the field of immunology research continues to expand, scientists will require increased access to quality PBMC products to evaluate the potential of new therapeutic concepts.
At Cytologics, we are proud to supply pharmaceutical, biotech and academic customers with quality PBMCs, frozen PBMC pellets and other lymphocytes to support their research.
. Sen P, Kemppainen E, Orešič M. Perspectives on systems modeling of human peripheral blood mononuclear cells. Frontiers in molecular biosciences. 2018;4:96. . Mosallaei M, Ehtesham N, Rahimirad S, Saghi M, Vatandoost N, Khosravi S. PBMCs: A new source of diagnostic and prognostic biomarkers. Archives of Physiology and Biochemistry. 2020:1-7. . Kasten‐Jolly J, Lawrence DA. In Vitro Evaluation of Toxicant Influences on the Immune System. Current Protocols in Toxicology. 2020;84(1):e95. . Pourahmad J, Salimi A. Isolated human peripheral blood mononuclear cell (PBMC), a cost effective tool for predicting immunosuppressive effects of drugs and xenobiotics. Iranian journal of pharmaceutical research: IJPR. 2015;14(4):979. . Hartmann J, Schüßler‐Lenz M, Bondanza A, Buchholz CJ. Clinical development of CAR T cells—challenges and opportunities in translating innovative treatment concepts. EMBO molecular medicine. 2017;9(9):1183-97. . Zhang M, Huang B. The multi-differentiation potential of peripheral blood mononuclear cells. Stem cell research & therapy. 2012;3(6):1-10. . Beer L, Mildner M, Gyöngyösi M, Ankersmit HJ. Peripheral blood mononuclear cell secretome for tissue repair. Apoptosis. 2016;21(12):1336-53. . Tapia-Calle G, Born PA, Koutsoumpli G, Gonzalez-Rodriguez MI, Hinrichs WL, Huckriede AL. A PBMC-based system to assess human T cell responses to influenza vaccine candidates in vitro. Vaccines. 2019;7(4):181. . Tuller T, Atar S, Ruppin E, Gurevich M, Achiron A. Common and specific signatures of gene expression and protein–protein interactions in autoimmune diseases. Genes & Immunity. 2013;14(2):67-82. . Davila JAA, De Los Rios AH. An overview of peripheral blood mononuclear cells as a model for immunological research of Toxoplasma gondii and other apicomplexan parasites. Frontiers in cellular and infection microbiology. 2019;9. . Sioud, M., Pettersen, S., Ailte, I., & Fløisand, Y. Targeted Killing of Monocytes/Macrophages and Myeloid Leukemia Cells with Pro-Apoptotic Peptides. Cancers. 2019, 11(8), 1088.