21 July 2016

Africa: HIV Vaccine Could Be Ready Before End of Year

Photo: International Aids Conference
The Inkosi Albert Luthuli International Convention Centre in Durban, venue of the 21st International AIDS Conference.

A new vaccine for HIV is set to be tested in South Africa this year.

The development was revealed during the ongoing 21st International AIDS Conference in Durban, South Africa, following results from immunology studies.

Interim immunology studies for the HVTN 100 conducted by US-based HIV Vaccine Trials Network (HVTN) and South African research sites showed that the vaccine tested the immune responses of South African volunteers to a modified version of the RV144 regimen, the only HIV vaccine regimen to show efficacy to date.

The original RV144 vaccine reduced the HIV infection rate among study participants in Thailand by 31 per cent over 3.5 years.

HVTN 100 Protocol Chair Linda-Gail Bekker, who is also Deputy Director of the Desmond Tutu HIV Centre in Cape Town and International AIDS Society President-Elect said that the HVTN 100 used the same vaccines that RV144 tested, but made them specific to the Clade C subtype of HIV, which is widespread in southern Africa.

"We also changed the adjuvant used with one of the vaccines, with the goal of eliciting a more powerful immune response, and added a booster injection to prolong the period of protection," she said.

Interim results from HVTN 100 provided the green light for a Phase III efficacy trial on the modified RV144 regimen although criteria for the go-ahead centred on the percentage of HVTN 100 vaccine-recipients who displayed a range of immune responses, and the strength of those responses.

"All the criteria were met unequivocally and, in many instances, the HVTN 100 outcomes exceeded both our own criteria and the immune responses seen in RV144," Bekker concluded.

Larry Corey, HVTN Principal Investigator, said that although these vaccines were previously designed for South Africa, they exceeded the criteria to provide ground for other trials.

"It is gratifying to see vaccines that were designed and manufactured specifically for South Africa meet and even exceed the criteria established to advance them into the large efficacy trial. HVTN 702 is a pivotal study that could lead to a licensed HIV vaccine in South Africa - the first preventive HIV vaccine worldwide," said Corey.

Launching vaccine tests

HVTN 702, a placebo-controlled study, is set to begin before the end of 2016. 5,400 HIV-negative men and women at 15 research sites across South Africa will be enrolled. Participants will receive five injections over the course of a year and will be followed-up for two years more to establish whether the vaccine elicits a sustained protective effect.

The trial will also seek to confirm earlier findings from HVTN 100 that the modified RV144 regimen is safe.

However, scientists pointed out that the major difficulty in the field of HIV vaccine development is the extraordinary capacity of HIV to mutate and evade the antibodies that might block it.

Fortunately, identification in a small minority of HIV-positive individuals of broadly neutralising antibodies (bNAbs), which can neutralise a wide range of HIV variants, led to a flourishing of vaccine-related research focused on how to manufacture bNAbs in the laboratory and how to harness bNAbs to prevent infection in HIV-negative individuals.

A landmark event in this field of research was the start of the first large-scale human trials to evaluate whether a bNAb called VRC01, given by infusion, is effective in preventing HIV acquisition.

Scientists are also exploring the design and development of antigens or immunogens that might stimulate the immune system of HIV-negative individuals.

The next major multi-site efficacy trial in the HIV vaccine field is likely to be a test of a vaccine regimen that includes a 'mosaic' immunogen, carrying fragments of HIV from different variants of the virus. Researchers believe that this complex immunogen might be fit for use globally, regardless of the predominant variants in different regions.

Other novel vaccine approaches in development include the exploration of improved vectors, safe viral 'vehicles' that are capable of delivering HIV genes that will trigger protection against HIV, or that may even be able to deliver bNAb genes directly.

The only available treatment approaches to HIV involve use of a combination of antiretroviral (ARV) drugs that suppress its HIV virus and stop the progression.

Unlike before when individuals would receive ARVS after their CD4 cells dropped to a certain threshold, new recommended approach adopted in Rwanda is to start treatment immediately after testing positive.

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