04 April 2013

Antibody roadmap to Aids vaccine

Scientists on a quest for an antibody-based Aids vaccine say they've found promising clues in the uncommonly "robust" natural immune response of a patient in Africa.

Studying blood samples over a three-year period after the person was infected, researchers were witness to a microscopic battle between the virus and antibodies - both evolving as they sought to gain the upper hand.

For the first time, scientists were able to follow the full chain of events leading to the patient naturally producing broadly neutralising antibodies (BnAbs -- so called because they attack different strains of the human immunodeficiency virus (HIV) that causes Aids.

"The current research... fills gaps in knowledge that have impeded development of an effective vaccine for a virus that has killed more than 30 million people worldwide," said a statement from Duke Medicine, which participated in the study by a team of researchers in the United States and Malawi.

"We learned from this individual how the antibodies get induced with the hope that this information can be a map for how to induce these antibodies as a preventive vaccine," added team leader Barton Haynes, director of Duke University's Human Vaccine Institute.

How the antibodies 'work'

Antibodies are the foot soldiers of the immune system, latching onto viruses or microbial intruders and tagging them for destruction by specialised "killer" cells.

Most antiviral vaccines are made by priming antibodies to recognise germs, but the method has not yet been successful in AIDS control.

One of vaccine developers' fiercest foes, the HIV virus typically evolves too fast to ever be left open to antibody attack.

The individual in the study, from an African country that is not specified, is one of about 20% of HIV-infected people whose immune systems naturally produce BnAbs.

Unfortunately, this generally only happens two to four years after infection and is of no help to the host who will still develop AIDS if not treated with anti-retroviral drugs.

"When broad neutralising antibodies are made they are no help to the person already infected. The notion is however; if they are present before infection, then they can prevent infection and prevent insertion of the virus genetic material into the host genetic material," Haynes told AFP of the research published in the journal Nature.

Vaccine keenly pursued

In monkeys, BnAbs have shown to prevent infection.

A BnAbs-based vaccine is being keenly pursued in the battle against Aids, an immune system-wrecking disease first recognised in 1981.

Almost 1% of the world's population today is infected with HIV, according to the United Nations.

In this study, researchers isolated an antibody named CH103, and found that it was triggered by a specific protein envelope found on an early, little-mutated form of the HIV virus.

This meant the antibodies may only be stimulated to respond in the presence of this protein or other similar ones on the virus.

While most antibodies require about 10 to 15 mutations to be able to attack their target, potent BnAbs show 40 to 100, said a comment on the study also published by Nature, which described the findings as a possible "roadmap" to an HIV vaccine.

The CH103 antibody had a much lower number of mutations, which may explain how it developed so quickly in this patient.

The scientists said they had gained a "critical insight" for developing a potential vaccine.

"We are now making recombinant forms of the (protein) envelopes from this patient as a vaccine to immunise animals to recreate the induction of a similar type of antibody," said Haynes.

A Nature statement said it remained to be seen whether or not the finding could be used to develop an effective vaccine.

"But it presents a strong and testable rationale that can be used to address the major challenges of creating an antibody-based HIV-1 vaccine," it said.


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Dr Sindisiwe van Zyl qualified at the University of Pretoria in 2005. She is a patients' rights activist and loves using social media to teach about HIV. She is in private practice in Johannesburg.

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