Enhancing cell culture with MACS® Premium-Grade Cytokines

Only correctly expressed and properly folded cytokines are biologically active and thus will impact the cellular response. Consequently, the total protein amount (protein weight) does not equal the amount of active cytokine (biological activity given in units). 

To receive a reproducible response in cell culture experiments, recombinant cytokines are best applied based on their biological activity instead of the protein weight.

The amount of correctly expressed and folded recombinant proteins depends on the production process. Therefore, the specific biological activity of a cytokine varies between vendors and even between production lots, as shown in the figure below.

To facilitate convenient cytokine dosing according to the biological activity, we provide the lot-specific activity with our MACS Premium-Grade Cytokines. Knowing the exact biological activity, you can always apply the same amount of active cytokine and create reproducible cell culture conditions.

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To determine a cytokine’s biological activity, the response of cultured cells to different cytokine doses is measured with bioassays. But as the results in bioassays are influenced by many factors, e.g., by applied cells or assay conditions, resulting activity values are relative. Consequently, given (minimal) biological activity values for recombinant cytokines are difficult to compare between different manufactures or even between different production batches from one supplier.

To be able to compare cytokine activity values with each other, bioassays need to be calibrated with a standard with known biological activity. The National Institute for Biological Standards and Control (NIBSC) provides such standards for a large number of cytokines to enable uniformity for calibration. 

When a common cytokine standard is used for assay calibration and the same bioassay is applied to determine the biological activity, cytokine activity becomes comparable between different experiment runs, suppliers, and production batches. This increases the comparability of results from different laboratories as shown in the bar graph below.

With our MACS Premium-Grade Cytokines we provide the lot-specific activity calibrated with NIBSC standards whenever available. This maximizes comparability of your results with other laboratories and other publications. 

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Dose-response experiments show how the cellular response in a certain bioassay depends on the amount of active cytokine applied. If cytokine levels are not saturated, small variations in cytokine concentrations can result in notable variations of the measured cellular response. Once cytokine levels are saturated, the dose-response curve reaches a plateau and the maximum cellular response in the respective cell type and culture setting is reached. 

To avoid variable results or artificial effects due to inconsistent or too high cytokine concentrations, optimal cytokine doses are usually titrated for each cell culture assay.

In cell culture assays, cytokine levels are usually saturated in order to achieve the maximum cellular response. Without knowing the exact cytokine activity, one option to reach saturation is to deliberately add more cytokine than actually needed, creating a state of oversaturation.

However, evidence has increased over the years that artificially high cytokine levels in oversaturated experiments can be harmful for cells. And even if oversaturation is not directly detrimental, it can influence the experimental outcome. The following examples illustrate that the cytokine concentration may determine the cell fate:

• IL-2 in CAR T cell expansion:
  Kaartinen et al. showed that low IL-2 concentrations favor differentiation of early memory over effector T cells. As memory T cells multiply faster than effector T cells in vivo, excessive IL-2 concentrations can significantly reduce the efficacy of CAR T cell production.
• GM-CSF in myeloid differentiation:  
  Rautela et al. demonstrated that GM-CSF quantities orchestrate cell fate during myeloid differentiation. Low GM-CSF levels promote the granulocytic lineage, moderate quantities drive moDC differentiation, and high levels stimulate the monocytic lineage. Moreover, monocytes/macrophages generated with different doses of GM-CSF differ in their function.
• FGF-2 (FGFb) in ESC differentiation:
  Ameri et al. found that differentiation of hESC-derived definitive endoderm into foregut/midgut cell lineage is dependent on the FGF-2 concentration: High FGF-2 levels inhibit hepatocyte differentiation and promote pulmonary cell fate, whereas moderate levels promote pancreatic differentiation.

Moreover, inefficient reagent usage by deliberate overdosing causes a significant cost increase. Knowing the exact cytokine activity, you can refrain from oversaturation, use the optimal amount of active cytokine for your experiment, and save up to 10-fold reagent expenses.

With the given lot-specific activity of MACS Premium Grade Cytokines, you can precisely apply cytokines according to their biological activity. In this way, you can generate reproducible cell culture conditions and aim for natural cytokine concentrations. You can avoid possibly harmful oversaturation, artificial experimental results, and at the same time reduce costs.

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As only correctly expressed and properly folded proteins are biologically active, the biological activity of recombinant cytokines varies between production batches. However, manufactures often only provide the minimal biological activity specifications rather than the exact biological activity of a cytokine batch. 

Consequently, the biological activity of each cytokine batch has to be determined by the end-user with a suitable bioassay and standard. Only then the cytokine activity can be compared to previous lots and the cytokine dosing can be adjusted accordingly.

The exact expenses of lot-to-lot testing will depend on the respective assay; they include material costs such as cell culture dishes, filter tips and pipettes, cultivation and coating reagents, media and supplements, as well as time to run the assay and manpower conducting and evaluating the assay. 

With MACS Premium-Grade Cytokines you can skip lot-to-lot testing. We assess the biological activity for each finally filled cytokine batch, calibrate the biological activity whenever possible to NIBSC standards, and provide this calibrated lot-specific activity value to you. Thus, you will save time and reagent expenses and can directly get started with your experiments.