Researchers at the Spanish Superior Scientific Research Council (CSIC) have successfully completed Phase I human clinical trials of a HIV vaccine that came out with top marks after 90% of volunteers developed an immunological response against the virus. The MVA-B vaccine draws on the natural capabilities of the human immune system and "has proven to be as powerful as any other vaccine currently being studied, or even more", says Mariano Esteban, head researcher from CSIC's National Biotech Centre.

The MVA-B vaccine first showed promising signs back in 2008 when clinical trials involving mice and macaque monkeys demonstrated a very high efficiency against Simian immunodeficiency virus (SIV). The recent human trials involved 30 healthy volunteers, where 24 were treated with MVA-B, while the other 6 were treated with a placebo, carried out over a 48 week period.

Development of MVA-B is based on the insertion of four HIV genes in a previously used vaccine (MVA) for smallpox. When injected with the vaccine, a healthy immune system can react against the MVA, whilst the HIV genes are incapable of self-replicating. This guarantees a safe clinical trial for HIV free volunteers. Furthermore by trialing the vaccine on healthy patients, the immune system can learn how to detect and combat the HIV virus components. "It is like showing a picture of the HIV so that it is able to recognize it if it sees it again in the future", says Esteban.

"Our body is full of lymphocytes, each of them programmed to fight against a different pathogen" continued Esteban. "Training is needed when it involves a pathogen, like the HIV one, which cannot be naturally defeated".

Three-dimensional model of a HIV virus particle (Image: CSIC)

The trial demonstrated how the vaccine stimulates the production of lymphocytes B, which produces HIV attacking antibodies that block the virus from infecting healthy cells. Blood tests during the 48th week revealed that 72.7% of the treated volunteers had developed these HIV fighting antibodies. However generating a long lasting response against future attacks truly renders the vaccine effective. This is achieved when the body maintains a basic memory level of T lymphocytes, which are generated after the first attack and can circulate the body for years. The T lymphocytes are responsible for stimulating the attacked cell's immune response, which can then identify and destroy the HIV virus. Blood tests during the 48th week revealed that the 85% of the patients maintained the memory T lymphocytes immune response.

"MVA-B immune profile meets, initially, the requirements for a promising HIV vaccine," says Esteban. Although it does not remove the virus from the body, the immune response induced by the vaccine could keep the virus under control by destroying the infected cell.

According to CSIC, "if this genetic cocktail passes Phase II and Phase III future clinic trials, and makes it into production, in the future HIV could be compared to herpes virus nowadays".

Phase I clinic trials will also commence with HIV infected volunteers to test its efficiency as a therapeutic vaccine.

Source: Spanish Superior Scientific Research Council (Spanish).