Answer:
Ionizing radiation.
Step-by-step explanation:
Mutation is the sudden change that is occur by exposing cells to the ionized radiation which change the genetic makeup of the cell. Due to mutation, the cell does not perform its normal function like before the mutation so when the mutation occurs in the cell, the genetic or DNA makeup is changed which make the environment unfavorable for the HIV virus and the virus can not cause any infection in the cell.