What are International Units?

 

International Units (IU) represent units of functional or biological activity that indicate potency of biologically active substances when measured against international standards or reference materials. These biological substances may include a wide variety of substances such as recombinant proteins, hormones, or vaccines. IU values allow assessment of biological substances in a consistent, internationally accepted manner. Specifically, for recombinant proteins, IU values are determined by measuring functional activity against international standards provided by World Health Organization (WHO). These standards can be obtained from NIBSC.

 

Why are International Units important?

 

Recombinant proteins are manufactured by different laboratories using different protocols, making it difficult to assess and compare biological potency. The use of IU provides a standardized measurement of biological potency that simplifies comparison of recombinant proteins from different sources.

 

How are International Units measured for Cell-Vive GMP recombinant proteins?

 

At BioLegend, we assess biological potency using bioassays, during which we test our Cell-Vive™ GMP recombinant proteins side-by-side with a WHO international standard. Potency is expressed as IU/mg. In general, we follow these 4 steps to determine IU values for Cell-Vive GMP recombinant proteins:

 

1. Perform bioassay comparing WHO international standard versus Cell-Vive GMP recombinant protein.
2. Determine specific activity of WHO international standard.
3. Establish ED₅₀ ratio of WHO international standard versus Cell-Vive GMP recombinant protein.
4. Based on the ratio established, determine specific activity of Cell-Vive GMP recombinant protein.

 

Sample Method for IU Calculations using Cell-Vive GMP Recombinant Human G-CSF

 

1. Both the WHO international standard and Cell-Vive GMP Recombinant Human G-CSF were run in the same bioassay to induce proliferation of M-NFS-60 mouse myelogenous leukemia lymphoblast cells.
2. The specific activity of WHO International Standard Human G-CSF (09/136) was determined to be 95,000 IU/µg.
   • WHO assigned potency of international standard: 95,000 IU/mL
   • Concentration of Cell-Vive GMP Recombinant Human G-CSF in ampoule: 1 µg/mL
   • Specific activity of international standard: 95,000 IU/µg
3. From the bioassay performed, ED₅₀ in ng/mL was determined, thus establishing a ratio between the WHO international standard and Cell-Vive GMP Recombinant Human G-CSF.
   • WHO international standard ED₅₀: 0.027 ng/mL
   • Cell-Vive GMP Recombinant Human G-CSF ED₅₀: 0.08 ng/mL
   • Ratio: 0.338
4. The specific activity of Cell-Vive GMP Recombinant Human G-CSF was determined to be ≥ 3.2 x 10⁷ IU/mg.
   • Cell-Vive GMP Recombinant Human G-CSF specific activity = standard specific activity x ratio
   • International standard specific activity: 9.5x10⁷ IU/mg
   • Ratio: 0.338
   • Cell-Vive GMP Recombinant Human G-CSF specific activity: 3.2 x 10⁷ IU/mg

 

Cell-Vive GMP Recombinant Proteins IU Measurements Table

 

Cell-Vive GMP Recombinant Protein	Cat. No.	Reference Cytokine	NIBSC Code	Cell Line used for Bioassay	Type of Bioassay	IU measurement (IU/mg)
Human BDNF	788916	Human BDNF	96/534	N/A	Binding assay	≥ 5.5x105
Human BMP-2	767314, 767316	Human BMP-2	93/574	ATDC5	ALP induction	≥ 1.4x105
Human EGF	585514, 585516	Human EGF	91/530	A431	Proliferation	≥ 2.6x106
Human FGF-basic (146 aa)	792524, 792526	Human FGF basic (146 aa)	90/712	NIH/3T3	Proliferation	≥ 8.8x106
Human G-CSF	578614, 578616	Human G-CSF	09/136	M-NFS-60	Proliferation	≥ 3.2x107
Human GDNF	798425	Human GDNF	09/266	N/A	Binding assay	≥ 1.1x105
Human GM-CSF	572914, 572916	Human GM-CSF	88/646	TF-1	Proliferation	≥ 1.8x107
Human IL-1β	579414, 579416	Human IL-1β	86/680	D10.G4.1	Proliferation	≥ 4.5x107
Human IL-2	791925	Human IL-2	86/500	HT-2	Proliferation	≥ 2.4x106
Human IL-3	564314, 564316	Human IL-3	91/510	TF-1	Proliferation	≥ 1.6x105
Human IL-4	574014, 574016	Human IL-4	88/656	TF-1	Proliferation	≥ 7.7x107
Human IL-6	570814, 570816	Human IL-6	89/548	7TD1	Proliferation	≥ 3.5x107
Human IL-7	581914, 581916	Human IL-7	90/530	Peripheral Blood Lymphocytes	Proliferation	≥ 1x108
Human IL-10	571014, 571016	Human IL-10	93/722	PBMCs	IFNγ induction	≥ 1.3x106
Human IL-12	573014, 573016	Human IL-12	95/544	PBMCs	IFNγ induction	≥ 2.8x106
Human IL-13	571114, 571116	Human IL-13	94/622	TF-1	Proliferation	≥ 2.8x105
Human IL-15	570314, 570316	Human IL-15	95/554	MO7e	Proliferation	≥ 3.7x106
Human LIF	593924	Human LIF	93/562	TF-1	Proliferation	≥ 1.4x107
Human M-CSF	574814, 574816	Human M-CSF	89/512	M-NFS-60	Proliferation	≥ 9.4x107
Human TGF-β1	781816	Human TGF-β	89/514	HT-2	Proliferation	≥ 1x107
Human TNF-α	570114, 570116	Human TNFα	12/154	L929	Cytotoxicity	≥ 1.5x107
Human TPO	763714, 763716	Human TPO	03/124	MO7e	Proliferation	≥ 1.5x106
Human VEGF-165	583714, 583716	Human VEGF-165	19/246	HUVEC	Proliferation	≥ 1.4x106