HIV Replication Cycle: 7 stages of HIV Life Cycle

HIV Replication or Cycle refers to how the HIV virus reproduces using the genetic makeup of the Host cell (Human cell). There are seven (7) stages HIV Virus replication cycle. Each of these steps is used as a target to make HIV drugs inhibit the progress of the infection. This means that there are drugs that have been made to destroy the HIV virus at each of the stages of the HIV life cycle and these drugs are classified based on each stage that they inhibit; they however do not cure HIV infection but can greatly reduce the HIV viral load in the body making the infected individual live a normal life.

The 7 stages of HIV Replication

  1. Binding or Attachment stage
  2. Fusion stage
  3. Reverse transcription
  4. Replication
  5. Integration
  6. Assembly
  7. Budding
HIV Life cycle diagram showing all the steps of HIV Replication with associated HIV drugs used for inhibiting each step
A diagram showing all the steps of HIV Replication with associated drugs used for inhibiting each step

Binding stage of HIV Life Cycle

In the binding or attachment stage of the HIV Life cycle, the HIV virus attaches itself to the surface of CD4 cells by using its receptor known as gp120 (a glycoprotein) to attach to some receptors on the CD4 cells such as CCR5 receptors and CXCR4. The HIV virus only infects CD4 cells because these cells express the receptors that help the HIV virus to enter the cells. It is due to this infection that HIV brings down the immune system of the body because the CD4 cells maintain the immunity of the body. This stage of HIV replication is inhibited by CCR5 drugs used for the treatment of HIV infection.

Fusion stage of HIV Replication Cycle

After binding to the CD4 cell, the HIV virus then fuses its envelope (which serves as the covering of the virus) with the cell membrane of the CD4 cell. This enables the Virus to gain entry into the CD4 cell. This stage of HIV Replication is blocked by Fusion inhibitors which are drugs used for the treatment of HIV infection.

Reverse transcription stage of HIV Replication

For an HIV virus to replicate, it must change from RNA (RiboNucleic Acid) to DNA (DeoxyriboNucleic Acid); for HIV to effect this change, it uses a protein (enzyme) called Reverse Transcriptase. This enzyme then changes the HIV RNA to HIV DNA. Once the HIV DNA is produced, it can then enter the nucleus of the CD4 cell now (remember that it fused with the CD4 membrane to enter the cytoplasm; in the cytoplasm is another compartment (or organelle) called the nucleus where the genetic materials are stored to enable reproduction and transfer of genes for animals to give birth to their kind). This stage is blocked by two classes of HIV drugs: Nucleoside Reverse Transcriptase Inhibitors and Non-Nucleoside Reverse Transcriptase Inhibitors.

HIV Replication cycle picture diagram
HIV Replication cycle picture diagram

Integration 

Inside the CD4 nucleus, HIV then uses an enzyme known as Integrase to integrate (or insert) its vital DNA into the DNA of the CD4 cell. This stage is blocked using Integrase Inhibitors drugs.

Replication of HIV 

In the Nucleus of the CD4 cell, the HIV DNA combines with the CD4 DNA so that anytime the CD4 cell wants to produce, it uses the proteins of the cells to produce more HIV long chains Proteins thereby multiplying the HIV protein copies. This stage of the HIV Life Cycle is called Replication and not Reproduction as in animals. There is currently no drug that blocks this stage.

Assembly stage 

Once the HIV long chains proteins are produced, they move out of the Nucleus to the surface of the CD4 membrane to assemble into immature noninfectious HIV.

Budding stage 

After moving to the surface of the CD4 membrane, HIV releases another enzyme called Protease that helps to cleave or break up the long chains of HIV proteins into short chains of proteins. These short chains of HIV proteins then combine to form the Mature HIV virus that is infectious and can then infect another new CD4 cell. By this repeated replication and infection, it reduces the CD4 cells count in the body and the immunity of the HIV patient goes down. Protease Inhibitors are the HIV Drugs that block this stage.

These are the 7 stages of HIV Replication and their associated classes of drugs used for blocking the steps.