CD-34 Stem Cell Mimics as reliable controls for Cell Therapy:

Addressing challenges in CD-34 expression in Stem Cells and Lot-to-Lot Consistency

Subhanip Biswas, Martina de Geus, Kanwal Palla

Slingshot Biosciences, Inc. 

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The use of CD34 stem cells in cell therapy is evolving, and ongoing research is continuously expanding our understanding of their potential applications and therapeutic benefits. Control cells are often needed throughout the cell therapy development process for phenotypic characterization of starting material or for quality control of downstream processing steps such as pre and post isolation. Commercially available stem cell controls are limited in their percentage of CD-34 expressing cells, have inconsistent supply, and poor closed-vial shelf life stability requiring more frequent bridging studies. These commercial controls also require specific gating which may deviate from in-house protocols. The current alternative requires the use of mobilized peripheral blood in order to get high CD34-positive expression for use as a control which adds significant costs to the process. To address these challenges, Slingshot Biosciences has developed synthetic CD34 Stem cell mimics with CD45 dim+ CD34+ (90%) mixed with CD45 dim+ (10%) and CD45 dim+ CD34+ (1%) mixed with CD45 dim+ (99%). These can be complemented with cell mimics that contain a biologically relevant, heterogeneous mix of immune cell types, and therefore are a complete blood control without the drawbacks of do- nor-derived biologics. We show that these CD34+ stem cell mimics match the scatter optics of donor-derived and commercially available controls on conventional and spectral flow cytometry instruments. These cell mimics also show superior lot-to-lot consistency compared to donor-derived mobilized peripheral blood. This is the only non- biohazardous high CD34-expressing control that mimics biological samples such as mobilized blood, allowing confidence and standardization for downstream cell therapy manufacturing. These CD34-cell mimics are also representative of pre and post CD34-enrichment samples without having to perform time-consuming enrichment processes. With our superior closed-vial stability, customers can secure a single lot for the entire duration of the study without worrying about inconsistent results or changing supplies.


A robust, competitive CD34 based product has been successfully developed and shows superior and consistent performance compared to relevant biological samples. The CD34 low and CD34 high product is compatible with multiple fluorophores across three sets of antibodies for CD45 and four sets of antibodies for CD34. Intralot variability in MFI and % populations is <6%, and interlot variability between three lots in MFI and % populations is <6%. The TruCytesTM CD34 product is compatible with both conventional and spectral flow cytometers and is developed as a kit containing one vial of the CD34 low and one vial of the CD34 high sample, and serves as a positive reference control for stem cell therapies at both the pre-and post-enrichment stages.

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