Biotechnology Terms Starting With H
Biotechnology Glossary: H
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HEK293 Cell
/ HECK-too-nine-tee-three SEL / · Acronym from Human Embryonic Kidney 293, numbered as 293rd experiment
HEK293 Cell is a widely used immortalized human cell line derived from embryonic kidney tissue and transformed with sheared adenovirus 5 DNA by Frank Graham at McMaster University in 1973.
HEK293 cells have become one of the most common mammalian expression systems in biotechnology, cited in over 17,000 published studies. These cells double approximately every 24 hours in suspension culture and can reach densities exceeding 6 million cells per milliliter in bioreactors, making them well suited for large-scale recombinant protein production. Major applications include manufacturing viral vectors for gene therapy, propagating viruses for vaccine development, and studying protein-protein interactions.
Several COVID-19 vaccine candidates, including the AstraZeneca formulation, used HEK293-derived cells during development and quality testing, though not as an ingredient in the final injected product.
Genomic analysis published in 2014 revealed that HEK293 cells express gene patterns more consistent with neurons than with kidney cells, suggesting the original embryonic tissue may have contained adrenal or neuronal precursor cells rather than pure kidney epithelium, a finding that has implications for interpreting decades of receptor pharmacology data generated in this line.
HEK293 cells are embryonic stem cells. They are immortalized somatic cells that cannot differentiate into other tissue types and were not derived from an embryo destroyed specifically for research; the original tissue was obtained from a routine legal abortion in the Netherlands.
Researchers at the University of British Columbia used HEK293 cells grown in 10-liter bioreactors to produce the SARS-CoV-2 spike protein for structural studies, harvesting more than 50 milligrams of purified protein per liter of culture medium. That yield was sufficient to supply crystallography and cryo-electron microscopy teams working to characterize the protein's receptor-binding domain within weeks of the sequence being published.
High Throughput Screening
/ HY THROO-poot SKREE-ning / · Old English heah; Old English thurh; Old English screnian
High throughput screening is a drug discovery method that uses robotic automation and miniaturized assays to test thousands to millions of chemical compounds rapidly for biological activity against a defined molecular target.
HTS campaigns typically run in 384-well or 1536-well microplate formats, with robotic liquid handlers dispensing nanoliter volumes and automated plate readers measuring fluorescence, luminescence, or absorbance signals in seconds per well. A primary screen against a large compound library can generate hundreds of thousands of data points within days, far exceeding what manual testing could accomplish. Hit compounds identified in primary screens advance to counter-screens that distinguish true inhibitors from assay artifacts before medicinal chemists begin structural optimization.
The integration of HTS with machine learning-based virtual screening has shortened the time from target identification to lead compound selection in several recent drug discovery programs, including efforts targeting SARS-CoV-2 proteases in 2020.
The Broad Institute's Drug Repurposing Hub, launched in 2017, assembled a library of approximately 6,000 approved drugs and clinical candidates specifically so that HTS campaigns could identify new uses for compounds already proven safe in humans, a strategy that identified several antiviral leads during the COVID-19 pandemic.
Are Enzymes Proteins? →Screening thousands of compounds immediately produces a medicine. Hits from a primary screen are starting points that typically require years of medicinal chemistry, pharmacokinetic optimization, and safety testing before any candidate enters clinical trials.
A research team at the National Institutes of Health screened roughly 300,000 compounds from the Molecular Libraries Small Molecule Repository against an enzyme linked to antibiotic-resistant Staphylococcus aureus, completing the primary screen in under two weeks using a 1536-well format. Only 0.1% of tested compounds showed reproducible inhibition after counter-screening, illustrating how large an initial library must be to yield even a handful of viable leads.
Humanized Antibody
/ HYOO-muh-nized AN-tih-bod-ee / · From humanize, to make human-like, plus antibody from anti- against and body
Humanized antibody is a monoclonal antibody engineered by grafting the antigen-binding regions from a non-human antibody onto a human immunoglobulin framework to reduce the immune response patients mount against foreign protein sequences.
The process identifies the complementarity-determining regions of a mouse antibody and transplants them into human IgG constant and variable region frameworks, typically producing a protein that is 90 to 95 percent human sequence. Retaining only the CDRs rather than the entire mouse variable domain dramatically reduces the human anti-mouse antibody response that caused rapid clearance and allergic reactions with earlier fully murine therapeutics. Trastuzumab, a humanized antibody targeting HER2 receptors in breast cancer, received FDA approval in 1998 and has generated over 100 billion dollars in cumulative sales.
Modern computational tools predict which mouse framework residues must be kept alongside the CDRs to preserve binding affinity, a step called back-mutation that is often necessary when initial humanization weakens target recognition. More than 40 humanized antibodies have received FDA approval, representing roughly half of all therapeutic monoclonal antibodies currently on the market.
The first humanized antibody approved for clinical use, daclizumab for transplant rejection in 1997, took nearly a decade to develop partly because researchers had to solve the problem of human immune systems destroying fully murine antibodies within days of infusion, sometimes triggering dangerous serum sickness reactions.
Humanized antibodies are completely safe because they are mostly human in sequence. They can still trigger infusion reactions, anti-drug antibody formation, and long-term immunosuppression in some patients, and their safety profile must be evaluated individually for each molecule.
Genentech humanized a mouse anti-VEGF antibody by grafting its CDRs onto a human IgG1 framework to create bevacizumab, which inhibits the formation of new blood vessels that tumors need to grow beyond a few millimeters in diameter. Bevacizumab reached peak annual sales exceeding 7 billion dollars and is approved for multiple cancer types including colorectal, lung, and cervical cancers.
Hybridoma
/ hy-brih-DOH-muh / · Latin hybrida, crossbreed; Greek oma, tumor
Hybridoma is an immortal cell line created by fusing an antibody-producing B lymphocyte with a myeloma tumor cell, producing unlimited quantities of a single monoclonal antibody directed against one specific epitope.
Georges Köhler and César Milstein developed the hybridoma technique in 1975 at the MRC Laboratory of Molecular Biology in Cambridge, work that earned them the Nobel Prize in Physiology or Medicine in 1984. The procedure fuses spleen cells from an immunized mouse with immortal myeloma cells using polyethylene glycol, then selects fused cells in HAT medium, which kills unfused myeloma cells and allows only hybridomas to survive. Each surviving clone secretes a single antibody recognizing one epitope on the target antigen, providing a renewable and chemically consistent reagent that polyclonal antisera cannot match.
Monoclonal antibodies produced by hybridomas now represent the largest category of approved biopharmaceuticals by revenue, with global sales exceeding 150 billion dollars annually.
Köhler and Milstein did not patent the hybridoma technique, a decision that allowed laboratories worldwide to adopt it freely and accelerated the development of thousands of research and diagnostic antibodies within a decade of the original publication in Nature in 1975.
Monoclonal antibodies come directly from one animal indefinitely. Hybridoma technology creates a stable, immortal cell line that researchers grow in culture to produce the antibody continuously without returning to the original animal.
When researchers needed a consistent reagent to detect the HER2 protein in breast tumor biopsies, they immunized mice with purified HER2 extracellular domain and fused the responding B cells with myeloma cells to generate hybridoma clones. Screening identified clones secreting antibodies that bound HER2 with dissociation constants in the low nanomolar range, providing the diagnostic tool that later guided trastuzumab therapy selection.
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