Serum-free Media

Our Serum-free Medias have been optimized for all kind of cellular based immune assays, giving you a high signal and a low background ratio in your assays.

CTL Anti-Aggregate Wash™
20x Solution

Stabilizes PBMC during thawing and prevents cell loss due to aggregation


Our CTL-Test™ Medium can be used for all ex vivo cellular cytokine experiments (like ELISPOT or ELISA) which require functional PBMC.

PLUS Medium

The CTL-Test™ PLUS Medium is specialized for the functional detection of the different subpopulations of memory T-Cells (TH1, TH2, and TH17) in an ELISPOT assay.

Supplement 10x

Replacing media after thawing is required. Hence, washing steps are necessary in your protocol. With the CTL-Wash™ Supplement, we offer our customers a product which maintain functions and survival of their PBMC.

ABC Media Kit

Serum-free freezing media kit for cryopreservation of freshly-isolated PBMC

Scientific Background

Serum, like fetal calf serum (FCS) is routinely used as a supplement for any kind of cell culture condition as a source of nutrients. But serum is particularly unsuitable for assays like ELISPOT for the following reasons

  1. Every batch of serum can differ enormous in their nutrient composition. This high variability in the biological properties of different serum batches makes it necessary to pre-screen every batch in order to obtain a batch which is suited for a single experiment. Serum-free cell culture media allows users to standardize their cell culture conditions, providing the same results in all of your experiments.
  2. Mitogenic contaminated serum batches can induce immune cell activity resulting in a high negative background and a false positive signal in your sample conditions.
  3. Toxic or inhibitory serum batches will jeopardize the assay results.
  4. Furthermore, contaminated serum can be infectious, resulting in tighter restrictions for international shipment.
  5. The unique performance of each serum batch necessitates the purchase of large lots to assure consistency of assay conditions, if possible. This results in enormous amount of costs.

For all these reasons, there is a serious interest in replacing serum and using well defined serum substitutes. Using a substitute is challenging, because serum itself is rich of nutrients like growth factors and hormones and the exact composition of a substitute has to be defined very well, especially for primary cells and for PBMC. For example most of the available serum free media contain inhibitors for tumor growth but freshly-isolated PBMC need a more stringent condition in order to maintain functions and viability.

Our supplier, C.T.L has been working for years with US governmental-, industrial-, and academic partners to standardize ELISPOT and other direct ex vivo cytokine assays performed on freshly-isolated or cryopreserved PBMC. We have incorporated all of our knowledge into the C.T.L. Serum-free Media Platform, which consists of three product lines that have been carefully designed to cover the four critical steps of working with human PBMC: washing, testing, freezing, and thawing.

Performance of our Media

We investigated the advantages of our media with an IFN-γ ELISPOT assay with serum-containing complete RPMI medium vs. the Serum-free CTL-Test™ Medium. Freshly-isolated PBMC of three healthy donors were tested in parallel under both conditions. The number of spots obtained (Y axis) or in serum (X axis) after stimulation of CD4+ T helper cells, is represented by the dots. We used an antigen pool of Mumps, PPD and Candida. The black line indicates equal performance. The medium background was zero for all conditions. We observed that several recall responses that were not detectable in serum became clearly positive in CTL Test™ Medium.

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Comparison of different sera in laboratories

Cryopreserved PBMC of the same batch were thawn and tested in an IFN-γ ELISPOT assay in eight different laboratories, using either CTL-Test™ (gray), or, in parallel in the media that the respective laboratory has selected for their T-Cell work (blue). Panel A illustrates the number of counted spots in a well. Panel B provides the number of spots thought CEF-peptides T-Cell activation. The stimulation index (St: antigen-induced spots/medium background) defining the strength of signal measured is also shown for each of the laboratories for the results, obtained with CTL-Test™ (SI: CTL- Test™) and with the respective laboratory's serum (SI: Serum). In all cases, the maximal spot counts with CTL-Test™ were equal to better than the sera. Four of the eight sera induced an elevated background, which reduces significantly the Stimulation Index. Read more here: (Zhang et al., J. immunotoxicology, 2009, 6:227).