Teachable moment in classrooms:

  1. immune system chapter – role of CD4 Helper T cells in adaptive immunity
  2. chemical basis of life – structural characteristics of DNA and RNA
  3. cellular basis of life chapter – transcription of DNA into RNA during protein synthesis
  4. microbiology – structure of the viral protein envelope of HIV (human immunodeficiency virus)

The news item:  Recently the following report appeared online:

U.S. FDA approves Gilead’s Descovy for HIV prevention

The approval does not include use of the drug by women to prevent HIV infection. Descovy, a combination drug, was approved in 2016 to treat people already infected with HIV. It contains a newer formulation of a drug used in Gilead’s older medication, Truvada, which has been used to treat people infected with HIV since 2004.

 

The article states that Descovy is a pharmaceutical approved for pre-exposure prophylaxis, the  prevention of HIV infection in men. Descovy was found to be less toxic to the kidneys and bones than  previous drugs used to treat HIV infected people.

So, Why Do I Care??  In the US alone there are over 1 million people living with HIV (human immunodeficiency virus) infection, and each year there are 30,000 – 40,000 new HIV infections. The new infections happen despite the already available preventative measures. Therefore, pharmaceutical prevention of new infections is still important.

Plain English, Please!!! First, let’s talk about how Descovy is expected to prevent infection by HIV in highly exposed individuals. The clinical definition of HIV infection is that the HIV virus should be detectable in human bodily fluids. For HIV virus to appear in the blood or in other bodily fluids, the infected cells must make a swarm of new HIV viruses to spread through the body and enter into the blood and other bodily fluids. The ingredients of Descovy promise to prevent the cells from making new viruses, so there will be no swarm of new HIV viruses, there will not be enough viruses to spread through the body, so HIV viruses never enter bodily fluids. Therefore, even in people frequently exposed to the HIV virus the blood testing doesn’t find any HIV, and the person remains clinically uninfected, remains HIV-negative. This prevention of infection is called “pre-exposure prophylaxis”. An HIV-negative person cannot spread the virus to other people, so the number of new HIV infections are reduced.

Second, let’s talk about the ingredients of Descovy. Both active ingredients (emtricitabine, and tenofovir alafenamide) are inhibitors of the enzyme called reverse transcriptase of the HIV virus. That enzyme is key to the infection, because once the HIV virus enters the main target, the CD4 Helper T cell, the RNA genetic information of the virus needs to be converted into freshly-made virus DNA. That conversion is accomplished by the reverse transcriptase enzyme of the virus. Without that conversion the virus cannot multiply, and, therefore, cannot spread throughout the body.

Third, let’s talk about the details of how Descovy prevents HIV reproduction. In order to make new HIV viruses, the infected cell must be hijacked to make new HIV proteins to form the outer shell of the new viruses.  If the virus cannot convert its RNA into DNA, the virus cannot make new viruses, because the DNA is needed to make new HIV virus proteins, and those, in turn, are needed to make new viruses. The DNA is the source of information just like the computer code of a messaging app on your phone. To use an app, you need to download the app information you’re your phone.  Once you delete the downloaded information, the app disappears, no longer useable. So, in order to make proteins to build new viruses, the viral DNA (the information source) needs to be made in the cell. Once you block formation of viral DNA you prevent the formation of infectious new viruses. Simply put, if there is no HIV DNA, there will be no HIV proteins, and there will be no new HIV viruses.