Recombinant Human TPO Protein

What it means: This TPO is produced in Human cells rather than in E. coli or insect cells. The manufacturer states the host as human cells and does not name a specific cell line for this product.

Why it matters:

• TPO is a heavily glycosylated cytokine, and expression in human cells supports glycosylation of the full-length protein.
• A human host avoids bacterial host-cell contaminants that can affect sensitive stem/progenitor cultures.
• Together with the animal-free, xeno-free format, it fits fully human culture systems.

How to interpret here: An expression system of Human cells means the TPO was made by a human cell line. It is intended for megakaryocyte, platelet-development and HSPC research.

Tip: When switching from a TPO made in another host, re-titrate the working concentration.

What it means: The protein is Tag-free: no His, Fc, GST or other affinity tag is fused to the TPO sequence, and no tag needs to be removed before use.

Why it matters:

• A tag adds extra amino acids that can change folding, receptor binding, stability or the apparent molecular weight of a signaling protein.
• In defined hematopoietic stem/progenitor cultures every added component is a variable; a tag-free protein keeps the ligand close to the native sequence.
• Tag-free proteins are also easier to compare with published protocols that used untagged factors.

How to interpret here: Tag-free here means the vial contains only the TPO protein. It cannot be captured or detected with anti-His, anti-GST or Protein A reagents, so plan detection with an antibody against TPO itself.

What it means: Purity of >95% by SDS-PAGE means that when the protein is run on a denaturing gel and stained, at least 95% of the stained protein is the TPO band.

Why it matters:

• High purity limits other proteins in the vial that could act on cells or interfere with downstream readouts.
• Dosing is done by protein mass, so a pure preparation makes the amount of active ligand added more accurate and comparable between experiments.
• Endotoxin is specified separately at <0.5 EU/µg, so purity and endotoxin together describe how clean the preparation is.

How to interpret here: A specification of >95% by SDS-PAGE is a minimum value. The exact result for the lot received is on the Certificate of Analysis (CoA), available from BioHippo on request.

Tip: SDS-PAGE purity shows how clean the preparation is, not how active it is; check the activity data separately.

What it means: The species is Human: the amino-acid sequence is that of human TPO (thrombopoietin). The protein is also produced in human cells, so both the sequence and the expression host are human.

Why it matters:

• Matching the species of the factor to the species of the cells avoids differences in receptor affinity between species.
• Human sequence is the usual choice for human CD34+ HSPC, megakaryocyte and iPSC-derived hematopoietic work.
• Recording the species in protocols matters because the same protein is sold from several species by many suppliers.

How to interpret here: Human here refers to the protein sequence. When reproducing a published protocol, check that it also used Human TPO; if it used a protein from another species, the working concentration may need adjusting.

What it means: The protein is supplied Lyophilized (freeze-dried) from a 0.2 µm-filtered PBS solution, without carrier protein.

Why it matters:

• Lyophilized protein is more stable during storage than a solution, which gives a long shelf life when stored correctly.
• The stock concentration is chosen at reconstitution, so it can be matched to the volumes used in each protocol.
• As supplied, store at −20°C to −80°C for up to 12 months from receipt; after reconstitution keep it at 2°C to 8°C for up to 1 month or at −20°C to −80°C for up to 3 months under sterile conditions.

How to interpret here: Lyophilized means the vial must be reconstituted before use: briefly centrifuge the vial before opening, then reconstitute in sterile PBS containing 0.1% endotoxin-free recombinant human serum albumin, mix gently and prepare single-use aliquots.

Tip: Avoid repeated freeze–thaw cycles of the reconstituted protein; a manual-defrost freezer is recommended.

What it means: The molecular weight stated by the manufacturer is 80–85 kDa. Separately, the manufacturer describes the structure of TPO as a glycosylated monomer.

Why it matters:

• Molecular weight is the first check of identity when the protein is run on a gel or analysed by other methods.
• Band position can differ between reducing and non-reducing gels and between methods, so note the conditions used when comparing results with the stated value.
• The manufacturer gives a nominal value and refers to lot-level data for the exact profile.

How to interpret here: 80–85 kDa is a nominal value. Refer to the lot-specific Certificate of Analysis (CoA), available from BioHippo on request, for the data that apply to the lot received.

Tip: If a gel band differs slightly from the stated value, compare it with the CoA for that lot before drawing conclusions.

What it means: Activity is tested as proliferation of human Mo7e cells in response to TPO. The manufacturer reports EC50 0.36–0.53 ng/mL, the concentration that gives half of the maximal response in this assay.

Why it matters:

• A cell-based activity test confirms that the protein is functionally active, which purity alone cannot show.
• Proliferation of the human Mo7e line is a direct functional readout of TPO activity.
• An EC50 range gives a reference point for comparing lots and other TPO preparations tested in the same assay.

How to interpret here: EC50 0.36–0.53 ng/mL describes potency in the Mo7e assay. It is not a working dose for HSPC or megakaryocyte protocols, which should be optimized for each system.

Tip: Check the lot-specific Certificate of Analysis for the release values of the lot received.