Research Stories

--by Richard Harth

In the annals of medicine, Edward Jenner’s 1796 vaccination of a young boy against smallpox remains a landmark case. Jenner used fluid from cowpox blisters for his vaccine. In a new study, Kathryn Sykes and her colleagues at Arizona State University’s Biodesign Institute are taking a fresh look at cowpox.

Sykes says that poxviruses are important for human health. Why? Because they provide an ideal framework for investigating protective antigens, she says. Antigens are the parts of the virus that can be used to develop a vaccine by means of modern genomic and proteomic screening technologies.

Findings of a study by Sykes and the ASU research team appeared in the advanced online issue of the journal Virology. Sykes says the findings demonstrate that this ancient pathogen still has much to teach us. It may help to hasten development of novel vaccines against smallpox and other pox-like diseases.

The genomes for viruses such as Ebola or HIV contain a small number of genes—maybe just three to nine, Sykes explains. A genome is the full complement of genetic information that an organism inherits from its parents. In the case of a virus, it is all the genetic information passed on to new viruses as they replicate themselves.

The ASU scientist notes that the number of genes is too small for the purposes of demonstrating a capacity for modern screen techniques. Other pathogens such as malaria, which boasts tens of millions of nucleotides, are much too large.

“We wanted something in the middle that could demonstrate our high-throughput technologies, but not blow us away before we had a few protocols in place,” she says. “Poxviruses are the Goldilocks case. At around 220 genes in size, they are just right.”

The ASU team used functional screening of cowpox to identify new vaccine candidates against similar viruses. These were compared with 4-pox—a vaccine comprised of four protective genes from a close genetic relative of cowpox called the vaccinia virus.

Sykes says that her team found that the identified antigens offered superior protection in a cowpox challenge compared with the 4-pox vaccine. The 4-pox vaccine was developed by the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID). It was meant to be an alternative to the licensed vaccine against smallpox, known as Dryvax. Dryvax is made from live vaccinia. It presents significant risk for people with suppressed immune systems.

By rapidly screening the entire viral genome, Sykes’ group attempts to isolate genes necessary for an effective vaccine. The result is called a subunit vaccine. The approach is different from traditional vaccine methods where scientists use a weakened form of a live, whole-virus strain.

“You want to make a vaccine that recreates the immune responses that happens upon natural infection. That was the dogma among old-fashioned vaccinologists,” Sykes says. But pathogens like poxviruses also contain elements that can help the virus evade or in some cases, subvert the host’s immune system. Subunit vaccines make use of only those genomic segments known to be immunogenic. Those segments provoke a robust immune response without the danger of initiating disease.

Sykes explains that the tricky part is identifying the effective subunits. Using a process known as expression library immunization, the entire cowpox genetic library was separated into pools. They were then tested in comparison with the 4-pox vaccine for protective effect using laboratory mice. In all, the team identified nine new protective components.

Sykes stresses that the majority of new candidates would not have been identified through traditional methods. Using those methods, scientists focus only on a viral gene because of its function or surface exposed location.

“The power of this technology is that it’s assumption-free with respect to what should be a vaccine candidate,” the ASU scientist says.

To further boost the immune response, Sykes recommends using a gene gun to deliver the subunit vaccines. This is a process in which protective antigens are shot directly into the cytoplasm of immunogenic skin cells. Traditional vaccines are injected by needle into muscle cells, which are not immunogenically active. Gene gun delivery provides a highly effective mechanism for delivering antigens to the immune system.

Sykes emphasizes that a single viral subunit will likely not offer comprehensive protection. Rather, suites of antigens must work together synergistically. Further high-throughput, rapid vaccine development research will focus on identifying such cooperative antigen groups.

“We need to come up with empirical ways of determining which antigens are working together,” Sykes says. “There’s your highly effective subunit vaccine.”

Scientists are studying the application of subunit component vaccine strategies for other diseases, including tularemia, African swine fever virus, and even cancer.

“Think of a tumor cell as a pathogen. We want to take that tumor cell and treat it the same way we treated cowpox. We want to screen all of its potential antigens and then test each one,” Sykes adds.