A distinctive feature of HIV is that during the process of virus replication to produce offspring, its genetic material is highly altered. This feature is not only the basis for HIV to survive under the pressure of immunity and drugs, but also the main reason why the virus is difficult to eliminate and the main obstacle to vaccine development. Some scientists estimate that “the rate of evolution of HIV is about 1 million times that of human genes.” One of the reasons is that the error rate of DNA polymerase in eukaryotic cells is between 10-10 and 10-9. HIV- 1 The average error rate per site of reverse transcriptase is as high as 10-4～10-3; another reason is that base mutations can also occur in many links in the HIV replication process. With the rapid replication of the HIV genome, a large number of progeny virus particles are produced, these mutations are rapidly accumulated and gradually amplified, and finally differentiated into different biological functions.
How HIV variants generated
causes high variability in the HIV genome comprises: (1) replication of HIV is the most important reverse transcriptase lacks corrective function, the average may be introduced in an HIV genome in a replication cycle 1 Base errors; (2) HIV has a high replication rate. In an infected person, 1010 new virus particles can be produced every day. The high replication rate enables rapid accumulation and amplification of HIV genome mutations; (3) HIV high recombination rate. One or more HIV can undergo genomic recombination in the body, and the recombination rate per replication cycle is about 2%. Based on the above reasons, after HIV infects the human body and begins to replicate, it can quickly produce a complex virus population in the host. The variation of the virus in an HIV-infected person is even greater than that of all influenza viruses.
What is the result
of the high variability of HIV? The high variability of HIV can help HIV quickly adapt to the new environment, evade drugs and host immunity, and ultimately survive in the host and spread among the population.
Due to the large number of mutations in the HIV replication process, the evolution of antibodies in the body often fails to keep up with the mutation speed of the virus, and eventually the immune system loses resistance and collapses. Secondly, with the popularity of HAART, under the dual selective pressure of antiviral drugs and antibodies, some viruses that produce resistance genes due to random mutations will reoccupy the high ground, especially for patients with poor medication compliance. Third, the design and development of HIV vaccines need to be able to produce high-titer neutralizing antibodies and effective memory. The high variation of HIV results in different subtypes, recombinant types and idiotypes, as well as huge differences between different strains. The difference in antigenicity of HIV can reach 35%, so the development of HIV vaccines has become extremely difficult. To this day, there is no vaccine that can produce effective broad-spectrum protection.
