The flexible backbone of molecular biology
Joshua Lederberg first coined the term “plasmid” in 1952. At the time, Lederberg was describing genetic material in bacteria that is both independent of the endogenous chromosome and capable of being transferred between cells. In the 50s and 60s, plasmids were primarily used to study heredity and antibiotic resistance in bacteria. By the early 70s, technologies such as restriction enzymes and DNA ligase, which allowed biologists to “cut and paste” DNA fragments, enabled Stanley Cohen and Herbert Boyer to create the first transgenic organism. They inserted foreign DNA into a plasmid and introduced the plasmid into E. coli. The newly inserted DNA is called recombinant DNA, and the plasmid that carries it serves as a cloning vector. They demonstrated that the recombinant gene was replicated and expressed in the bacterial cells. Their experiments are considered to be the birth of genetic engineering. At this stage, plasmids took on a new role as one of the most important tools in molecular biology.
Plasmid vectors are highly versatile. Over the last 50 years, they have been enormously useful tools for cloning, protein expression, sequencing, drug delivery, GMOs, and countless other applications. Plasmid vectors are engineered for specific applications, but they generally share a basic structure: an origin of replication, a sequence which allows replication inside the host cell; an antibiotic resistance gene, which allows the infected host cells to be selected for in the presence of antibiotics; a multiple cloning site where the foreign DNA is inserted; and often a promoter driving expression of the recombinant gene.
Insulin was discovered in 1921 at the University of Toronto by Frederick Banting and Charles Best under the supervision of John Macleod. Because insulin is a small, endogenously produced protein, its production is relatively simple compared to that of many other drugs. The process consists of purifying insulin from a source that expresses the protein. Banting and Best did not know that insulin was a single protein; they injected crude pancreatic tissue into diabetic dogs and found that it lowered their blood sugar. A year later, a biochemist working with Banting and Best was the first to isolate insulin activity from tissue extract. In 1951, Frederick Sanger sequenced insulin, making it the first protein to be completely sequenced.
From the early 20s until the 70s, insulin was manufactured by purification from animal tissue. Although methods improved over time, the yield was very low—four tons of pig pancreas were required to produce a pound of insulin.
In the late 70s, the aforementioned Herbert Boyer played a key role in producing Humulin, the first human insulin produced by recombinant DNA (rDNA) technology. Broadly, this new process involved inserting the human insulin gene into a plasmid and introducing the plasmid into E. coli, which then produces the insulin protein. Due to the significantly higher yield and lower workload, rDNA technology dramatically reduced the cost of insulin manufacturing.
The animal-derived insulin is estimated to have cost hundreds of dollars per vial when adjusted for inflation. Since the 1980s, insulin has cost between $50 and $100 for a year’s supply, or less than $5 per vial. The cost of production has only decreased since then, making it increasingly laughable that the average price of a vial in the United States is around $100, reaching $300. This is one of countless examples of the private sector leeching off decades of publicly funded research to price-gouge a life-saving drug. That is all I will say about the issue, as insulin is relatively affordable in Canada.
Insulin is just one case. Plasmids have been key in synthetic biology, gene therapy, agriculture, and many other innovations. The plasmid story illustrates science’s inherently public nature. The discoveries of a handful of early molecular biologists could not have been put to use without the contributions of later scientists from a range of fields, and vice versa. Fairly distributing profits and credit among countless individuals is an impossible task. Instead, we should follow the example of the hard-working and democratic plasmid.