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Why does the lack of proofreading by HIV reverse transcriptase make HIV difficult for the immune system to control?

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Diagram illustrating the process of retrovirus infection and reverse transcription, showing a retrovirus entering a host cell, releasing viral RNA, reverse transcriptase converting RNA to DNA, integration into the host genome, transcription of new viral RNA, assembly of new virions, and budding from the cell. — Reverse transcriptase After a retrovirus infects a cell, an enzyme known as reverse transcriptase converts viral RNA into proviral DNA in the cytoplasm. Proviral DNA then enters the nucleus, where it is incorporated into the host cell's DNA.

The lack of a "proofreading" function in the HIV reverse transcriptase enzyme is a primary reason the virus is difficult for the immune system to control.1

Most DNA-synthesizing enzymes possess mechanisms to correct errors during replication, but reverse transcriptase lacks this ability. Consequently, as the virus replicates, it accumulates mutations at a rate approximately one million times faster than the human genome evolves. This rapid evolution allows the virus to constantly change its surface proteins, a process known as antigenic drift.12

Because these mutations alter the viral antigens that the immune system uses to recognize and target the virus, HIV can effectively "escape" detection by antibodies and cytotoxic T lymphocytes. This continuous adaptation enables the virus to evade both natural immune responses and antiretroviral drugs, making it exceptionally challenging to eliminate from the body.314