Contract Assay Services

Your CRO Partner

Contract Assay Services (CAS) is a contract research organization (CRO) established within STEMCELL Technologies that performs assay services based on in vitro and in vivo primary stem cell assays. Primary cells are thought to be more representative in terms of in vivo functionality than cell lines, when used in in vitro assays. We specialize in providing the in vitro hematopoietic colony-forming unit (CFU) assay (also known as the colony-forming cell (CFC) assay). In addition, we perform mesenchymal, immunological and custom cell-based assays for efficacy and toxicity studies.
Contract Assay Services at STEMCELL Technologies Inc.

About Contract Assay Services

Learn more about CAS at STEMCELL Technologies - how we began, what we’ve done and where we can go with you.

Contact us at to learn more about how we can help you meet your goals.

Our Assay Services Workflow

  1. One-on-one client consultation
  2. Preparation of a proposal that clearly defines project scope, timeline and cost
  3. Experimental execution and data analysis
  4. Preparation of final report

Contract Assay Services at STEMCELL Technologies

We combine the power of specialized STEMCELL Technologies media and reagents with the practical knowledge of our scientists to provide standardized and customized assay services. You can choose from a portfolio of characterized assays using pre-qualified primary stem cells or discuss your individual needs with our in-house experts. Since 2000, Contract Assay Services has performed such studies for over 120 pharmaceutical, biotechnology, government and academic life science organizations worldwide. We provide exceptional service through frequent communication, quality products and unparalleled expertise.

Why Use Contract Assay Services?

  • Our high standards for methods, materials, processes and customer communication are evident in the loyalty of our returning clientele.
  • As your eyes and ears in the lab, we place a priority on communication with our clients throughout the study process.
  • STEMCELL Technologies is a world leader in the development of industry-standard products for stem, progenitor and other primary cells.
  • We work directly with the scientists who develop the specialized STEMCELL products used in our assays.

Toxicity Testing

Toxicity is a major cause of attrition in therapeutic drug development and is a key factor in decision-making around the advancement of candidate drugs through the development pipeline. The expansion of preclinical testing to incorporate assays that better predict potential toxicities earlier in the drug development process has obvious advantages for the selection of successful lead candidates. In vitro testing on primary cells can allow investigators to preview in vivo responses, thus facilitating design of better dosing strategies and optimization of animal models in preclinical testing, as well as Phase I clinical trials.

We specialize in performing the in vitro colony-forming unit (CFU) assay on hematopoietic stem and progenitor cells to measure potential toxic effects of candidate therapeutics, including small molecule compounds and biologics. Mesenchymal stem and progenitor cells, which generate key components of bone, fat and cartilage, may also be tested in the colony-forming unit - fibroblast (CFU-F) assay to predict possible cytotoxic effects. In addition, potential immunomodulation caused by candidate therapeutics can be evaluated through in vitro and in vivo assays.

Contact us at for a more in-depth discussion on how each of the assays in the sections below can be modified to meet your specific goals.

Hematopoietic Toxicity Assessment

Human hematopoietic stem and progenitor cells (HSPCs) may be isolated from bone marrow, cord blood or peripheral blood. They have the capacity to differentiate into all mature hematopoietic cells including erythroid, myeloid and megakaryocyte lineages. One of the best examples of an in vitro assay used in hematotoxicity testing is the culture of primary human hematopoietic cells in the colony-forming unit (CFU) assay (also known as a colony-forming cell (CFC) assay). The in vitro CFU assay may be used to predict in vivo bone marrow toxicity and clinical cytopenia (anemia, neutropenia and thrombocytopenia).

Our scientists have the expertise to assess possible hematotoxicity due to the action of candidate therapeutics, alone or in combination, on erythroid, myeloid and megakaryocyte progenitors using standardized and custom-designed CFU assays. These in vitro studies can be performed using human, non-human primate, mouse, rat and dog cells, which can assist in the selection of appropriate animal models for pharmaceutical development. Clinically relevant results have been shown through the addition of candidate therapeutics directly to cells in a CFU assay, allowing the determination of the maximum tolerated dose (myeloid)1 or Cmax (megakaryocyte)2 using these in vitro assays.

In addition to the CFU assay, we also offer higher-throughput assays for liquid culture-based hematotoxicity testing in a 96-well plate format. Small molecule compounds or biologics may be assessed for their effects on the expansion and lineage-specific differentiation of CD34+ cells into erythroid, myeloid and megakaryocyte progenitor cells. The readout for this assay includes viability phenotyping using flow cytometry but it may be customized depending on your needs. The toxicity levels of molecular entities observed in this assay generally correlate with those observed in the CFU assay, with the added benefit of increased screening capacity in addition to flexibility in treatment schedules.

1. Pessina A et al. (2003) Toxicol Sci 75:355-367
2. Pessina A et al. (2009) Toxicol In Vitro 23(1):194-200

The Hematopoietic CFU Assay as Performed by Contract Assay Services:

  • Yields clinically predictive information, allowing for better planning and a reduction in in vivo studies
  • Uses physiologically relevant primary cells from human, non-human primate, mouse, rat and dog (Table 1)
  • Assesses both the proliferation and differentiation of erythroid (BFU-E), myeloid (CFU-GM) and megakaryocyte (CFU-Mk) progenitors
    (Figure 1)
  • Provides both quantitative (colony number) and qualitative (cell and colony morphology) data
  • Can be used to determine dose response curves, including IC50 and IC90 values (Figure 2)

Table 1. Comparison of Myelotoxicity (CFU-GM) Response to Different Compounds in Human, Mouse, Canine and Rat Models to Drive Selection of Relevant In Vivo Model

Figure 1. Dose Response Curves and IC50 values for Human BM-Derived Erythroid and Myeloid Progenitors Incubated with 5-Fluorouracil

Figure 2. Dose Response Curves and IC50 and IC90 Values Showing Effect of Test Article 1 (TA1) Alone and in Combination with Chemotherapeutics Cisplatin (Cis), Temozolomide (TMZ) and Small Molecule (SN38) on Human BM Myeloid (CFU-GM) Progenitor Growth

Liquid Culture-Based Hematotoxicity Assays as Performed by Contract Assay Services:

  • Uses physiologically relevant primary stem cells from human cord blood or bone marrow
  • Assesses both the proliferation and differentiation of erythroid, myeloid and megakaryocyte progenitors
  • Generally correlative with the CFU assay (Figure 3)
  • Provides a higher-throughput capacity for toxicity screening
  • Can be used to determine dose-response curves, including IC50 and IC90 values (Figure 4)
  • Offers flexibility as test compounds may be added to the culture or cells may be collected from it at different points during culture, allowing effects on progenitor cells at different stages of differentiation to be examined.

Figure 3. Correlation Between IC50 Values for Six Drugs Measured Using the CFU-GM Assay and the 96-Well Plate Liquid Culture-Based Myeloid Cell Hematotoxicity Assay
Human BM CD34+ cells were cultured in colony-forming unit - granulocyte/macrophage (CFU-GM) assays and in liquid culture-based hematotoxicity assays for myeloid cells (HemaTox™ Myeloid Kit). IC50 values generated using each assay were plotted on the X and Y axes and shown to be highly correlated with a correlation coefficient, R2, of 0.91.

Figure 4. Reproducibility of Liquid Culture-Based Hematotoxicity Assay Results Between Experiments and Using Different CD34+ Cell Preparations
Dose-response curves were generated from titrations of 5-FU added to human CB CD34+ cells isolated from 3 donors and cultured with the liquid culture-based hematotoxicity assays for (A,D) erythroid and (B,E) myeloid cells, as well as (C,F) megakaryocytes. Three to five separate experiments were performed with cells from each donor. In each assay similar IC50 values were obtained with cells from different donors and in different experiments with cells from the same donor. Shown are values normalized to the percentages (%) of maximum cell growth without drug. Despite differences in absolute cell counts, curves are reproducible when normalized within each experiment. (D, E, F) Tables showing IC50 values generated for 5-FU in culture with each kit including standard deviation (SD) and the coefficient of variation (% CV) across experiments.

Mesenchymal Toxicity Assessment

Mesenchymal stem cells (MSCs), under the appropriate conditions, can differentiate into cells that make up adipose tissue, cartilage, bone and muscle. Drug candidates destined for the tissue engineering market can be assessed for effects on the differentiation potential, as well as stimulatory or inhibitory effects on mesenchymal stem and progenitor cells, using the colony-forming cell - fibroblast (CFU-F) assay (Figure 3). The effects of compounds on the size and density of the colony can also be evaluated.

The CFU-F Assay as Performed by Contract Assay Services:

  • Measures the effects of a test article on progenitor frequency
  • Assesses proliferative or expansion potential of progenitors (size and morphology of colonies)
  • Quantitates mesenchymal progenitors in bone marrow

Figure 5. The Presence of an Inhibitory Compound Changes the Morphology of Human Bone Marrow-Derived CFU-F Colonies

Shown are Colony-Forming Unit - Fibroblast (CFU-F) assays containing MSCs plated (A) in the absence (B) in the presence of an inhibitory compound. Notable differences in morphology include fewer cells and a more scattered distribution in the culture containing (B) the inhibitory compound. Colony numbers are also reduced in the presence of an inhibitory compound (data not shown).

Immunotoxicity and Immune Profiling

The immune system can be the target of many chemicals, including environmental contaminants and therapeutic drugs, leading to potentially adverse effects. Although evaluation of immune function following in vivo exposure is the most relevant model to predict patient response, it is increasingly desirable to limit the use of animals and use human cells to maximize the relevance of testing. Recommendations from the ECVAM workshop on “The Use of In Vitro Systems for Evaluating Immunotoxicity” suggests that in vitro testing for direct immunotoxicity can be done in a tiered approach, the first tier measuring myelotoxicity using the CFU-GM assay.1

In addition to performing the CFU-GM assay with test articles of interest, CAS can assist in designing and optimizing experiments to evaluate aspects of immunotoxicity that result from altered activity of the immune system. Flow cytometry and immune profiling may be used to assess for various immunological effects, where cells from primary human or mouse sources are isolated, enriched and used in the appropriate in vitro assay to assess effects of test articles on immune pathways, such as pro- or anti-inflammatory responses. Custom assays can be designed and optimized to answer your particular question regarding the immunomodulation of your test articles.

1. Gennari A et al. (2005) J Immunotoxicol 2(2):61-83

Contract Assay Services can customize:

  • Flow cytometric analysis and immune profiling of B cells, various T cell subsets, NK cells, dendritic cells and macrophages/monocytes
  • ELISA assays to quantify immune effector molecules (e.g. cytokines and immunoglobulins)
  • Cytometric bead analysis (for simultaneous analysis of multiple analytes)
  • Chemotactic assays
  • Cell proliferation assays, including T cell proliferation assays (mitogen or Anti-CD3-stimulated)

Intestinal Organoid Models for Toxicity Assessment

3D culture systems have the potential to increase the physiological relevance of basic research into biological mechanisms, bridging the gap between high-throughput in vitro screening methods and large in vivo studies during drug development.1,2 Organoids generated from the intestinal epithelium are thought to recapitulate numerous features of the adult intestine in vivo, including self-renewal and differentiation pathways, cell types present and cellular organization within the epithelium. Together these characteristics create a culture system that is a powerful tool for investigating potential toxicity to the intestinal epithelium due to the action of candidate therapeutics.

Contract Assay Services offers an in vitro mouse intestinal organoid-based assay to assess the effect of candidate therapeutics on cell viability via measurement of intracellular ATP.

1. Ranga et al. Drug Discovery Through Stem Cell-Based Organoid Models. Adv Drug Deliv Rev 69-70C: 19-28, 2014
2. Sato T & Clevers H. Growing Self-Organizing Mini-Guts from a Single Intestinal Stem Cell: Mechanism and Applications. Science 340(6137):1190-94, 2013

Biopharmaceutical and Biosimilar Assessment

Biopharmaceutical drugs, also known as biologics, have become an essential part of modern pharmacotherapy and include examples such as biological proteins, cytokines, hormones, monoclonal antibodies, vaccines, and cell- and tissue-based therapies. Biopharmaceuticals may include compounds such as biosimilars, molecules meant to be an improved version of a previously developed drug on which the patent has expired.

The hematopoietic colony-forming cell (CFC) or colony-forming unit (CFU) assay can be used to test the biosimilar activity of biopharmaceutical cytokines, such as erythropoietin (EPO) both in vitro (Figure 1, Table 1) and in vivo (Figure 2, Table 2), or granulocyte-stimulating factor (G-CSF) (Figure 3). Hematopoietic progenitors are isolated from human bone marrow, and plated in a CFU assay to observe the direct stimulatory effects of test articles on progenitor growth and morphology. The effects of these cytokines can also be evaluated in animal models.

Contact us at to learn more about how we can help you and your organization reach your goals.

Example Data from Previous Studies

Figure 1. The Effect of EPO on Erythroid Colony Growth in CFU Assays of Human Bone Marrow Cells

Human bone marrow mononuclear cells were isolated from three individual patients and plated in CFU assays using MethoCult™ medium, in the presence of decreasing concentrations of Control erythropoietin (EPO). The percentage of erythroid colonies in samples treated with decreasing concentrations of EPO-based biosimilars can be compared to the number of colonies supported by an optimal concentration of Control EPO, as determined by this graph.

Table 1. EC50 Values for the Effect of EPO on Erythroid Colony Growth in CFU Assays of Human Bone Marrow Cells

Figure 2. Mobilization of Erythroid Progenitors and Increased Erythropoiesis in Mice Treated with EPO

Wild type BDF1 mice were treated with EPO on days 0 and 1. On day 4 the mice were sacrificed and the progenitor content of the spleens was assessed by plating cells in a CFU assay and counting the number of erythroid (BFU-E) progenitors per spleen. The percentage of reticulocytes were also measured by flow cytometry (Table 2).

Table 2. The Number of BFU-E Measured by a CFU Assay and Percentage of Reticulocytes as Measured by Flow Cytometry per Spleen Isolated from Mice Treated with EPO

Figure 3. The Number of Total CFU Observed in the PB of Mice Following Treatment With G-CSF

C3H/HeN mice were treated with 5 µg rhG-CSF per day on days 0 - 2. Eighteen hours after the last G-CSF injection mice were sacrificed and the peripheral blood (PB) was collected. The progenitor content of in the PB of each mouse was then assessed in a CFU assay. Mice treated with G-CSF showed a 10-fold increase in the number of CFUs per mL of PB when compared to vehicle control.

Stem Cell Characterization

Stem cells are rare cells which may be phenotypically identified by the expression of cell surface markers. The identification of hematopoietic stem and progenitor cells (HSPCs) and mesenchymal stem cells (MSCs) is the result of years of scientific research showing that phenotypically-identified populations of cells maintain corresponding functions. Functional assays are the most stringent test of a stem cell’s identity and are key in understanding the effect of genes, biochemical pathways and candidate therapeutics.

Contract Assay Services can provide both phenotypic and functional assessments of your stem cell population of interest. Our scientists are experienced in designing and performing studies to evaluate the effects of novel test articles on the expansion and differentiation capacity of stem cells.

Contact us at if you are interested in our stem cell characterization services and assays.

Hematopoietic Stem and Progenitor Cell Characterization

To measure the effects of test articles on hematopoietic stem and progenitor cell (HSPC) numbers and function, in vivo and in vitro assays have been developed. We can evaluate HSC renewal, expansion and ability to differentiate to various mature cell types. These assays include:

  • Engraftment Assays
    Complex in vivo assay that allows the determination of the true hematopoietic stem cell (HSC) frequency and effects of test articles on this frequency by transplanting human stem cells into the NOD/SCID mouse model1

  • Long-Term Cultures - Initiating Cell (LTC-IC) Assays
    Assay to determine the effect of test articles on the in vitro growth of primitive HSPCs using co-culture with stromal cells2
  • Mobilization Assays
    Evaluation of the movement in vivo of HSCs out of bone marrow into peripheral blood following treatment with agents such as Mozobil and cytokines such as G-CSF (Figure 1)

  • Hematopoietic Lineage-Specific Expansion Cultures
    Ex vivo expansion of HSPCs (CD34+ cells) isolated from human cord blood or bone marrow and differentiation into erythroid, megakaryocyte or myeloid progenitor cells.

  • Flow Cytometry and profiling of various cell populations
    Including megakaryocytes, myeloid, erythroid, T, B and NK cells

Example Data from Previous Studies

Figure 1. Mobilization of Hematopoietic Progenitors Induced by rhG-CSF and AMD3100

C3H/HeN mice were treated with 5 µg rhG-CSF per day on days 0 - 2. Sixteen hours after the last G-CSF injection, one group of 5 mice was treated with 5 mg/mL of AMD3100 (also know as Mozobil or Plerixafor). Ninety minutes after treatment with AMD3100, mice were sacrificed and peripheral blood (PB) was collected. The progenitor content in the PB of each mouse was then assessed using the CFU assay. Mice treated with rhG-CSF alone showed a 10-fold increase in the number of CFUs per mL of PB, and mice treated with rhG-CSF and AMD3100 showed a 50-fold increase in the number of CFUs per mL of PB, when compared with vehicle control.


1. Szilvassy SJ et al. Quantitation of Murine and Human Hematopoietic Stem Cells by Limiting-Dilution Analysis in Competitively Repopulated Hosts. Chapter 12 Methods in Molecular Medicine Vol 63: Stem Cell Protocols. Edited by Klug CA and Jordon CT Humana Press Inck Totowa NJ Pages 167-187.
2. Miller CL and Eaves CJ. Long-Term Culture-Initiating Cell Assays for Human and Murine Cultures. Chapter 8 Methods in Molecular Medicine Vol 63: Stem Cell Protocols. Edited by Klug CA and Jordon CT Humana Press Inc. Totowa NJ Pages 123--141.

Mesenchymal Stem Cell Characterization

Mesenchymal stem cells (MSCs) are a heterogeneous population of plastic-adherent, fibroblast-like cells, which are able to self-renew and differentiate into bone, adipose and cartilage tissue. In recent years there has been increased interest in MSCs and their potential utility in both tissue engineering and repair. MSCs also exhibit immunomodulatory and anti-proliferative effects on T cells, an attractive feature for cell therapy. Contract Assay Services can assess your MSC cell populations and provide assays for:

  • MSC expansion
    • Culture media that allows expansion using high quality media options including xeno- and animal component-free formulations

  • Characterization of surface markers
    • Including CD90, CD105, CD73, CD34 and CD45

  • In vitro differentiation into adipocytes, osteocytes and chondrocytes

  • Evaluation of the ability of MSC to suppress T cells (Figure 2)

Figure 2. MSC Suppression of T Cell Proliferation

Using co-culture experiments and the CFSE dye dilution assay, we can show that passage 2 MSCs can suppress division of activated T cells at both day 3 and day 7 of culture.

Custom Stem Cell Assays

STEMCELL Technologies is a world leader in providing products for stem cell research. We offer products and services for hematopoietic, mesenchymal and neural stem cell culture as well as embryonic stem (ES) cells and induced pluripotent stem (iPS) cells.

Clinical Trial Support

Contract Assay Services can design and perform custom experiments to support preclinical studies and ongoing clinical trials. We use the colony-forming unit (CFU) assay (also known as the colony-forming cell (CFC) assay) to evaluate the functionality of hematopoietic progenitors. These assays leverage the quality of STEMCELL Technologies products and the extensive expertise of the scientists in our Contract Assay Services team. We also offer services to help determine the suitability of clinical samples for transplantation.

Samples That Can Be Assessed:

  • Peripheral blood samples from clinical trials and preclinical studies, pre- and post-drug treatment
  • Mobilized peripheral blood patient samples for transplantation
  • Cord blood samples for banking and/or transplantation

Parameters Assessed Include:

  • Total cell count and viability
  • Frequency of hematopoietic stem and progenitor cells for erythroid, myeloid and megakaryocyte progenitors
  • Percentage of CD34+ cells quantified by the ISHAGE1 protocol
  • Flow cytometric analysis of hematopoietic and immune cells

1. Sutherland et al. (1996). J of Hematoth. 5(3):213-226.

Contact us at for a more in-depth discussion on how these assays may be modified to meet your goals.
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