AIDS:
This is a STI caused by the retrovirus, names as HIV.
After getting into the body of the person, the HIV enters into macrophages where it's RNA genome replicates to form viral DNA with the help of the enzyme reverse transcriptase.
Simultaneously, HIV enters into helper T-lymphocytes (TH), replicates and produce progeny viruses.
The progeny viruses released in the blood attack other helper T-lymphocytes.