HIV causes immunodeficiency diseases (AIDS). The first case was reported in 1959 in Congo. However, the cure, prevention, and its exact origin remained to be hand-waving. There had been hypotheses regarding the origin circulating within our scientific community. One of them is the administration of polio vaccine introduced by a virologist Hilary Koprowski. The administration of the polio vaccine in Congo coincided with the place and the time of the initial case of HIV. This hypothesis is commonly known as the oral polio vaccine theory. The other hypothesis, which is agreed by most scientists, is the cut hunter hypothesis.
Polio vaccine is an attenuated vaccine, which a chemical reagent, formaldehyde, was added to a pool of poliovirus to kill the virus. But before killing the virus, scientists need to obtain the pool of polioviruses. In order to produce virus, the cultivation procedure is dependent on monkey kidney cells. In the 1960s, polyomavirus SV40 was found to be integrated in the genome of monkey kidney cells. Like papillomavirus, polyomavirus SV40 can induce S phase progression. As a result of SV40 genome integration, cells can grow without control. Consequently, malignant tumor is developed in the host organism. Because monkey kidney cells are used to cultivate poliovirus, the researchers then asked if the polio vaccine contains any SV40 genome. The answer was yes. This finding put anyone who received the oral polio vaccination from 1955 to 1963 at risk for cancers.
So how does this have anything to do with the debate on the origin of HIV? HIV is classified under the family of lentiviruses. HIV is a virus that contains a dimer of positive strand RNA. After entering the cell, HIV reverse transcribes RNA into double stranded DNA. With an enzyme called integrase, the HIV double stranded DNA is integrated into the host genome. As SV40 is found inside the monkey kidney cells, scientists speculated that the polio vaccine contains SIV (the monkey version of HIV). It is a good hypothesis, as HIV and SIV DNAs can be integrated into our genome (as provirus). This hypothesis is known as the oral polio vaccine hypothesis. However, the SIV genome was not found in any stocks of polio vaccines. With this piece of information, the oral polio vaccine theory was discarded.
The other hypothesis, which everyone believes in, is the cut hunter hypothesis. This hypothesis believes that a hunter in Congo who had a cut when butchering a chimpanzee. This results in a cross-species transmission of SIV, and leads to the HIV-1 epidemic that circulates worldwide.