Option 1: Monoclonal antibodies are not the same as vaccines. Monoclonal antibodies are laboratory-produced molecules that can mimic the immune system`s ability to fight off harmful pathogens, while vaccines are substances that stimulate the body`s immune system to produce an immune response against specific diseases.

Option 2: This option correctly states that treated bacteria or viruses, or one of their proteins, are used in vaccines. Vaccines are designed to introduce weakened or inactivated forms of pathogens or their proteins into the body to stimulate an immune response. This helps the body develop immunity to a specific disease, without causing the actual disease.

Option 3: MHC (Major Histocompatibility Complex) proteins are responsible for presenting antigens to the immune system. They play a crucial role in recognizing and responding to foreign substances. However, MHC proteins are not directly involved in the composition of vaccines.

Option 4: Strands of nucleic acids, such as DNA or RNA, are used in some types of vaccines. These vaccines are known as nucleic acid vaccines and work by introducing the genetic material of a pathogen into the body to trigger an immune response.

In conclusion, the correct answer is option 2, as treated bacteria or viruses, or one of their proteins,