Primary Cell Culture

Cell Culture

The cell is the building block of living organisms and holds the information that is highly representative of the whole organism. Cell culture is a technique by which the behavior of cells can be studied independent of whole organism. In this method cells are taken from an animal or plant and grown under controlled, favorable artificial conditions.

  • The process of cell culture includes the removal of cells from an animal or plant and their subsequent growth in a favorable artificial environmental condition. The cells may be removed from the tissue directly and disaggregated by enzymatic or mechanical means before cultivation, or may be derived from a cell line or cell strain that has already been established.
  • Sub culturing or passaging (or splitting) of cells refers to the processes that ensure the cells are alive and grow under cultured conditions for extended period of time.

Broadly, there are 3 types of cell culture procedures:

  • Primary cell culture: Primary cells are extracted straight from the tissue and processed to establish them under culture conditions.
  • Secondary cell culture: Sub-culture of primary cells results in secondary culture. Although it exhibits a few features of established cell line (below) it does not divide indefinitely.  
  • Cell Line: A cell culture developed from a single cell and having uniform genetic composition is called a cell line. On the basis of the life span, the cell lines are categorized into two types:
    • Finite cell lines – Finite cell lines have limited life span of about 20 – 80 population doublings. The growth is slow and the typical doubling time is 24 – 96 hours.
    • Continuous cell lines – Continuous cultures are comprised of a single cell type that can be serially propagated in culture for a limited number of cell divisions. To grow them indefinitely, continuous cell lines are transformed by viral oncogenes or by chemical treatments. They exhibit ploidy (aneuploidy or heteroploidy). The growth rate is rapid and the typical doubling time is 12 – 24 hours.

Primary Cell Culture

The source of primary cultures is excised animal tissue that is cultured either as an explant culture, suspension or as monolayer and maintained in vitro. The excised tissue is subjected to enzyme treatment and the dissociated cells are cultured under the appropriate conditions in culture medium until they reach adequate numbers. The isolated primary cells are of two types:

Adherent cells/ Anchorage Dependent cells - Cells that require attachment for growth are called anchorage dependent cells. The adherent cells are mostly derived from tissues of organs (such as kidney) where they are immobile and embedded in connective tissue.

Suspension cells/Anchorage Independent cells - Cells which do not require attachment for growth or do not attach to the surface of the culture vessels are called as anchorage independent cells/suspension cells. All suspension cultures are derived from cells of the blood system (as these cells are suspended in plasma in vitro e.g. lymphocytes).

The most popular primary cells used in research are epithelial cells, fibroblasts, keratinocytes, melanocytes, endothelial cells, muscle cells, hematopoietic and mesenchymal stem cells. The cultures are initially heterogeneous (represents a mixture of cell types present in the tissue) and can be maintained in vitro only for a limited period of time. Primary cells may be manipulated for indefinite subculture through an in vitro process called transformation. Transformation can occur spontaneously or can be chemically or virally induced. When a primary culture undergoes genetic transformation (provided with appropriate fresh medium and space), they divide indefinitely and become immortalized.

Comparison between Primary Cells and Continuous cell lines

Properties Primary cells Continuous cell lines
Life span and cell proliferation It is finite (i.e. limited to a less number of cell divisions)  It is infinite when handled properly (i.e. for a long period, approx. 30 cell divisions)
Consistency Variability exists between donors and preparations Minimal variability
Genetic Integrity Retains in vivo tissue genetic makeup through cell doublings Subject to genetic drift as cells divide (undefined set of mutations)
Biological relevance More closely mimics the physiology of cells in vivo Relevance can drift over time as cells divide (minimal biological relevance)
Ease of use (freeze-thaw & use) Needs optimized culture conditions and careful handling Well established conditions and robust protocols exist
Time & expense to use Needs more time and less abundance of cells Needs less time and more abundance of cells

Continuous Cell lines in Research

  • model systems for complex biological systems for the study of analysis of the biochemistry and cell biology of mammalian cells. The property of immortality renders them suitable for reproducibility in experiments
  • studies of toxicity of compounds and production of proteins in higher scale continuous cells are cost effective and easy to work with
  • isolation and identification of viruses for diagnostic, research, development as well as industrial purposes
  • gene expression studies as continuous cell lines are easier to clone, manipulate and maintain.

Drawbacks of Continuous Cell lines in Research

Despite the ease of handling continuous cell lines, there are distinct drawbacks that restrict the extrapolation of experimental results to in vivo conditions.

  • gross mutations and chromosomal abnormalities that increase as cells divide
  • poor indicators of normal cell phenotype and progression of early-stage disease
  • no direct correlation of function of cell lines in relation to that of other cells, healthy or diseased

Relevance of primary cell culture over continuous cell lines

Primary cell culture increasingly being used as a  major tool in cellular and molecular biology, providing excellent model systems for studying the normal physiology and biochemistry of cells (e.g., metabolic studies, aging, signaling studies), the effects of drugs and toxic compounds on the cells and mutagenesis and carcinogenesis. It is also used in drug screening as well as for the development of biological compounds (such as: vaccines, therapeutic proteins) on a large scale.

  • Model system: Since primary cells are non-transformed, non-immortalized they closely simulates a living model and yield more physiologically significant results. These cells can act as a model system to study cell biology and biochemistry, to study the interaction between cell and disease causing agents (like bacteria, virus), to study the effect of drugs, to study the process of aging, to study cell signaling and metabolic regulations. In many cases the use of primary cells allows the researchers to avoid the complications (availability, cost and ethics) involved in using animal models
  • Cancer Research: Primary cells can be exposed to radiation, chemicals and viruses to make them cancerous. Thus, the mechanism and cause of cancer and the altered signaling pathways can be studied. It can also be used for determination of effective drugs for cancer cells. The side effects of cancer treatments (chemotherapy and irradiation) on normal cells can also be studied in this context.
  • Virology: Detection, isolation, growth and development cycles of viruses can be studied. Primary cells are also useful to study the mode of infection.
  • Drug Screening and Toxicity Testing: Primary cell cultures are used to study the cytotoxicity of new drug (to study the effect and safe dosage) and/or drug carriers (nanoparticles). It is useful for the synthesis or production of a variety of biomolecules at an industrial scale. This is particularly useful in the pharmaceutical industry. Various research projects on  cell-based therapeutic products, using primary cells are being developed.6 Primary (animal cell) culture is used in the place of animal models to test the effects of new drugs, cosmetics and chemicals. They are also used to determine the maximum permissible dosage of new drugs.
  • Vaccine Production: Primary animal cells are used in the production of viruses and these viruses are used to produce vaccines (such as vaccines, for deadly diseases like polio, rabies, chicken pox, measles and hepatitis B are produced using animal cell culture) thus avoiding the use of animal models.
  • Genetic Engineering: Primary (animal) cell cultures are used to produce commercially important genetically engineered proteins such as monoclonal antibodies, insulin, hormones, and much more.
  • Tissue or Organ Replacement: Primary (animal) cell culture can be used as replacement tissue or organs. Research is on-going on utilizing primary cells in the reconstruction of damaged tissue or replacement of non-functional cells or tissues. Organ culture techniques and research are being conducted on both embryonic and adult stem cell culture. These cells have the capacity to differentiate into many different types of cells and organs. By controlling the development and differentiation of these cells, we may be able to treat variety of medical conditions.
  • Prenatal diagnosis: Amniotic fluid from pregnant women is extracted and cells are cultured for the study of chromosomes abnormalities, genes using karyotyping, and used in early detection of fetal disorders.
  • Stem Cell Therapy: Stem cells isolated from bone marrow, blood or embryo involve primary cell culture. Patient’s own stem cells or those from a donor are grown in vitro for generating enough cells that may be used to regenerate tissue or replace functionally deficient cells. This is an area that is being explored to design therapies for genetic disorders, spinal cord injuries, degenerative diseases and cancer.

Primary Cells from Cell Applications

Sigma-Aldrich introduces a range of human and animal primary cells and media from Cell Applications. From Adipogenesis to Zoonotic Enteric Disease, your research can benefit from human primary cells and animal primary cells. For neuron, pluripotent stem cell, fibroblast, lymphocyte (T Cell, B Cell), osteoblast and more. The following features of our primary cells make them ideal for your research:

  • High purity and low passage
  • Rigorous and strict quality control
  • Cells from wide variety of tissue & species
  • Matched sets from the same donor
  • Maximum flexibility
  • Ready to use total kits

Pre-screened Primary Cells

The variability induced in primary cells acquired from donors and during subculture practices is a major challenge faced by the researchers who study cell signaling pathways. Researchers prefer to screen the cells for sensitivity to common stimuli before embarking on signaling studies. Pre-screened cells from Cell Applications save your valuable resources as they are stimulated for activation of major signaling pathways.

  • Endothelial Cells: Pre-screened for Angiogenesis & VEGF signaling
    We offer the most commonly used human endothelial cells such as Human Umbilical Vein Endothelial Cells, (HUVEC), Human Microvascular Endothelial Cells (HMVEC) and Human Aortic Endothelial Cells (HAOEC). All these cells have been pre-screened to demonstrate stimulation-dependent angiogenesis and key endothelial cell signaling pathways (phosphorylation of VEGFR, Akt, MAPK, and expression of Tie2, eNOS, Axl and Etk/Bmx).
  • Preadipocytes: Pre-Screened for Adipogenesis Signaling
    Primary cultures of adipocytes are prepared by inducing differentiation of human primary pre-adipocytes and are prescreened for the expression of the major adipocyte markers, such as PPARg (Peroxisome proliferator-activated receptor gamma), C/EBPa (CCAAT/enhancer binding protein alpha), IR (Insulin receptor), ACCa (Acetyl-CoA carboxylase alpha), GSK-3b (Glycogen synthase kinase-3-beta) and Adiponectin.
  • Skeletal Muscle Cells: Pre-Screened for Insulin & AMPK signaling
    The pre-screened Human Skeletal Muscle Cells (HSkMC) are isolated from the skeletal muscle of hamstrings. It retains morphological, biochemical and metabolic characteristics of skeletal muscle.  These cells can undergo differentiation to exhibit actin and myosin myofilaments. It is specially tested for functional AMPK & Insulin Signaling Pathways.

Why Choose Cell Applications?

Reproducibility

  • Primary cells, isolated directly from fresh tissue are physiologically relevant, but notoriously finicky to isolate and culture. Mass-produced, multi-purpose media like DMEM and RPMI, and immortalized cell lines (HeLa, HEK 293, MCF-7, CACO-2, JURKAT, U937, CHO, COS-7, etc.) though important in life science research can be associated with false-positives and -negatives, sub-optimal cell/media pairing, poor cell growth, and erroneous data due to genetic alterations inherent to cell lines. Take advantage of the skills of our PhD staff who have honed the craft for each unique tissue, species and cell type.
  • Non-standardized protocols differ substantially, depending on the person, protocol, laboratory, materials, reagents, cell culture plastic, even lab/water bath temperature, humidity, time of year and HVAC system. Avoid these variables that result in data inconsistencies, unexpected costs, repeats and project delays by choosing our primary cells and media products.
  • Primary cell isolation techniques are riddled with not-so-uncommon phenotypic inconsistencies, contamination, poor growth, unwanted cell types in the isolate and cell death due to improper technique and non-optimized media. Physiologically-relevant primary cells meticulously isolated by us and small-batch specialty media are more cost-effective compared to do-it-yourself primary cell isolation.

Quality & Reliability

  • Primary cells & media offerings from Cell Applications are produced via tight SOPs and go through rigorous QC, testing and certification, so the procedures remain consistent. We are certified with regard to FDA 21 CFR Part 820, Current Good Manufacturing Practice for Medical Devices, pertaining to the manufacturing and packaging of human and animal cell culture media. Also CAI's administration systems have been assessed and approved to the ISO 9001:2008 management systems, standards and guidelines, applying to the manufacture and supply of human and animal cells and related products for research use. Certifications demonstrate our commitment to product quality and customer requirements, with increased emphasis in supporting R&D programs in pharmaceutical, biotechnology and consumer product industries, in addition to academic, government and research institutes.
  • Independent third parties conduct regular audits at the Cell Applications headquarters in San Diego, CA to assess conformance to numerous standards, including records, statistical techniques, and controls for process, design, production, labelling, packaging, documentation and purchasing. They assess our activities for product identification, trace-ability, acceptance, handling, storage, and distribution. Corrective and preventive actions for nonconforming products are also examined.

Culture of Primary Cells

Growth requirements

Primary cells can be grown either in suspension or adherent cultures. Some cells naturally live in suspension, without being attached to a surface (for example those derived from peripheral blood). There are also cell lines that have been modified to be able to survive in suspension cultures, they grow to a higher density than adherent conditions would allow. For the primary cells that are anchorage-dependent, adherent cells (such as solid tissues) require a surface to grow properly in vitro. These cells are mostly cultured in a flat un-coated plastic vessel, but sometimes a micro-carrier, which may be coated with extracellular matrix (such as collagen and laminin) components to increase adhesion properties and provide other signals needed for growth and differentiation. The cell culture media is composed of a basal medium supplemented with appropriate growth factors and cytokines. Cells are grown and maintained at an appropriate temperature and gas mixture (typically, 37 °C, 5% CO2 for mammalian cells) in a cell incubator. The culture conditions widely vary depending up on the cell type. Growth media can vary in pH, glucose concentration, growth factors, and the presence of other nutrients depending up on the cell types.

During establishment of primary cultures, it is essential to include an antibiotic in the growth medium to inhibit contamination introduced from the host tissue. Antibiotics used may include a mixture of gentamicin, penicillin, streptomycin and amphotericin B. However, long-term use of antibiotics is not recommended, since some reagents (such as amphotericin B) may be toxic to cells on a long run.

It is very important to retain the viability of primary cells after isolation as most of them undergo the process of senescence and stop dividing after a certain number of population doublings. For long-term viability of the cells excellent cell-culture handling skills along with appropriate culture condition (i.e. growth medium, temperature, gas mixture, pH, growth factors concentration, presence of nutrients and glucose) are essential. Growth factors used to supplement media are often derived from animal blood (the blood-derived ingredients possess the potential for contamination) it is recommended to minimize or eliminate the use of these ingredients wherever possible. Use of aseptic technique is also necessary.

Cellular confluence

Cellular confluence generally refers to the percentage of the culture vessel inhabited by attached cells. For example, 100% cellular confluence means the surface area is completely covered by cells, whereas 50% confluence means roughly half of the surface is covered. It is an important and essential parameter to track and assess in primary cell culture as various cell types require different confluence end points, at which point they need to be sub-cultured.

Maintenance and Subculture

The maintenance phase of cells begins when isolated cells are attached to the surface of the culture dish. Usually attachment takes about 24 hours after initiation of the culture. When cells reaches to a desired percent of cellular confluence and are actively proliferating, it is time to subculture. It is the best time to subculture primary cell cultures before reaching 100% confluence, since post-confluent cells may undergo differentiation and exhibit slower proliferation after passaging.

Anchorage-dependent cells grow in monolayers and need to be sub-cultured at regular intervals with appropriate culture medium to maintain exponential growth. Sub-cultivation of monolayers involves the breakage of both inter- and intracellular cell-to-surface bonds. Most adherent primary cells require the digestion of their protein attachment bonds or separation from the monolayer or relevant tissue with a low concentration of a proteolytic enzyme such as trypsin/EDTA. After the cells dissociation and dispersion into a single-cell suspension, they are counted and diluted to the appropriate concentration and transferred to fresh culture vessels (the composition of the media varies depending up on the cell types) where they will reattach and divide.

Cell counting

Hemocytometers is mostly commonly used for estimation of cell number and determination of cell viability (exclusion dye such as Trypan Blue or Erythrosin B may be used). A hemocytometer is a fairly thick glass microscope slide with a rectangular indentation that creates a chamber.  The chamber is engraved with a laser-etched grid of perpendicular lines and the device is carefully crafted. The area bounded by the lines and the depth of the chamber is known. Therefore it is possible to count the number of cells in a specific volume of fluid, and thereby calculate the concentration of cells in the fluid overall.

Automated cell counters that provide accurate and fast viable cell count are also available.

Cryopreservation and recovery

Cryopreservation is the process to preserve structurally intact living cells using low temperatures. It is essential to cryopreserve and thaw primary cells in order to minimize cell damage and death during each process. In case of human cells it is achieved with the use of a cryoprotectant, such as DMSO or glycerol (at correct temperature and with a controlled rate of freezing). Cryopreservation can be achieved in a mixture of 80% complete growth medium supplemented with 10% FBS and 10% DMSO for most primary cells. The freezing process needs to be slow, at a rate of -1°C per minute, to minimize the formation of ice crystals within the cells. The frozen culture needs to be stored in the vapor phase of liquid nitrogen (-196°C), or below -130°C.

Thawing cryopreserved cells is a rapid process accomplished by immersing frozen cells in a 37°C water bath for about 1 to 2 minutes. Precaution should be taken not to centrifuge primary cells upon thaw (as they are extremely sensitive to damage during recovery from cryopreservation). It is good to plate cells directly upon thaw, and allows cultures to attach for the first 24 hours.1

When initiating a culture of cryopreserved primary cells, it is essential to remove the spent media once the cells are attached (as DMSO is harmful to primary cells and may cause a drop in post-thaw viability).

Challenges faced during primary cell culture:

  • Contamination: Contamination of primary tissue when carried over to culture.
  • Shifts in pH: This may be caused sue to incorrect salt in the culture medium, bacterial or fungal contamination, insufficient bicarbonate buffering, incorrect carbon dioxide tension etc.
  • Optimum adherence: Insufficient or absence of attachment factors in the medium or contamination or overly trypsinized cells.
  • Slow growth: Reasons include change in pH of the medium, depletion of essential growth-promoting components/factors, low contamination, improper storage of reagents etc.
  • Cell death: Temperature fluctuation, absence of CO2, cell damage during thawing and/or cryopreservation, increase concentration of toxic metabolite, imbalanced osmotic pressure in culture medium result in decrease in the survival of cells.
  • Precipitation: (no change in pH): Precipitates in the medium without change in the pH may appear due to use of frozen medium, residual phosphate leftover while washing with detergent, which may precipitate powdered medium components.
  • Cell clumping: Suspension cell may clump due to presence of calcium, magnesium ions or due to cell lysis and release of DNA (over digestion with proteolytic enzymes).
  • Induced variability: Use of a variety of reagents and media induces variability in data acquired using primary cells. The handling methodology between the users may also contribute to the variability.

Lists of Products

Primary Cells

Media

Reagents

Advantages and Drawbacks of Primary Cells

Advantages Drawbacks
Use of primary culture avoids many ethical objections raised against animal experiments Allows experiments on human tissues which otherwise could not have been done in vivo. Primary cells takes more time to grow than other cell lines, it possess limited growth potential even under optimal growth conditions and eventually senesce and die.
 The use of primary cells provides more relevant results than cell lines. Pre-screened primary cells are good models to represent the signaling in vivo very closely. The cells taken from different donors behave differently in response to pro-inflammatory cytokines (unless they are pre-screened).2 The growth of metabolic regulatory mechanism that exist under in vivo conditions are absent in culture condition.
Primary cells are cost-effective as they help reduce the expenditure on animal models required for in vivo studies The cost of isolation and culture is often high and prohibitive though cheaper that animal models. The tissue culture may not be always possible. The characteristics of primary cells may change with each subsequent passage if optimum culture conditions are not maintained.