Weiss: Protection by Neutralizing Antibodies
What do HIV-infected women in Antwerp, genetically modified mice in Cambridge, and llamas in a field near Utrecht have in common? They have provided us with novel types on neutralizing monoclonal antibodies (mAbs) that will advance vaccine design to elicit protective immunity to HIV-1. The consortium on “Protection by Neutralizing Antibodies” led by Robin Weiss at University College London (UCL) has drawn Europe’s leading B-cell immunologists into AIDS vaccine discovery. Mike Neuberger, who elucidated how antibody diversity is generated, developed GM mice which make human antibodies when vaccinated and Quentin Sattentau in Oxford selected the anti-HIV mAbs from them; Antonio Lanzavecchia in Switzerland adapted his novel technique (first tested with blood samples from volunteers who had recovered from SARS) to the HIV-infected patients in Antwerp and London in order to immortalize human memory B-cells (antibody-producing cells) which then secrete HIV-neutralizing mAbs; Theo Verrips in Utrecht perfected the technique of high throughput screening for llama single-chain mAb fragments (VHH) to neutralize HIV by binding to clefts in the HIV envelope that other antibodies cannot always reach.
Using these mAbs, we can identify the epitopes on HIV that elicit these antibodies and exploit this knowledge in the design of novel vaccine candidates. The vaccine prototypes are based on recombinant envelope glycoproteins tested in small animals by Jonathan Heeney in Cambridge, on a rapid reshuffling technique for generating mutant, more immunogenic proteins pioneered by Ralf Wagner in Regensburg, and on synthetic peptides using a patented chemical method at Pepscan Inc in Lelystad. The crystal structure of mAb-immunogen complexes are analyzed by Winfried Weissenhorn’s team in Grenoble, France, and also in collaboration with Peter Kwong’s group in the Vaccine Research Center at NIH.
Carefully selected immunogens are being tested in Rhesus macaques for protection against challenge with a SHIV - a hybrid simian virus bearing an HIV envelope - by Willy Boger, David Davis and colleagues at the Biomedical Primate Research Centre in The Netherlands. Immunization will include novel combinations of adjuvants developed by Quentin Sattentau in Oxford in order to potentiate the humoral immune response. Passive protection by the new mAbs against SHIV challenge is being conducted by Ruth Ruprecht at Harvard Medical School with macaques at Yerkes Primate Research Center. The mAbs have been selected to target HIV-1 strains of clades C and A/CRF02_AG because they represent 55% and 27.5% respectively of currently circulating viruses. A vaccine against these clades will potentially protect individuals from ~80% of new HIV-1 infections, the majority in sub-Saharan Africa.
- Identify novel mAbs that potently cross-neutralize HIV-1 between clades.
- Direct the selection of novel immunogens recognized by these mAbs to serve as the basis for the design of HIV-1 vaccine candidates.
- Demonstrate the ability of these novel vaccine candidates to elicit anti-HIV-1 antibodies in animals and protection from SHIV challenge. The best candidate should progress to human clinical trial but not in this grant period.
- Test the capacity of mAbs to give protection from infection upon passive transfer in macaques.
At the start of the CAVD in 2006, only five neutralizing mAbs that broadly cross-neutralized multiple HIV-1 strains were known. Now, in 2012, that number has quintupled, thanks to the efforts of Dennis Burton with colleagues at IAVI, John Mascola and colleagues in the Vaccine Research Center, NIH, Michel Nussenzweig at Rockefeller University, and by our Vaccine Discovery Consortium within the CAVD. One important outcome from the findings of all these groups is that breadth of HIV-1 neutralization need not be at the expense of potency, as was originally feared. This means that, if the new insight into neutralizing mAbs can be translated into the design of effective immunogens, vaccines covering the vast majority of HIV-1 strains will be feasible.
Another important finding from this consortium is that immunization of animals (guinea-pigs rabbits, llamas) with HIV-1 envelope proteins can elicit potent and broad neutralizing antibodies, something not previously achieved by experimental immunization. If it works for llamas, small animals and macaques, the approach should be adaptable to humans. Thus, the group has gained proof of principle that envelope-based HIV vaccines can contribute to protective immunity.
One of the neutralizing human mAbs isolated by Davide Corti in Lanzavecchia’s laboratory was found by Ruth Ruprecht of Harvard to neutralize a SHIV. This mAb, HGN194, recognizes the crown of the V3 loop of gp120 and showed that protects juvenile Rhesus macaques from mucosal challenge infection with the Clade C SHIV. We have now determined protection by IgA.1 and IgA.2 versions of this nmAb. In the East End of London, Aine McKnight found that there is a greater diversity of HIV-1 strains and clades than even the Congo, because so many immigrants and asylum seekers settle there. So we do not need to scour the world for rare, long-term non-progressors or elite neutralizers; they are on our doorstep and they readily volunteer for follow-up studies.
The development of improved candidate vaccines is being pushed forward by Ralf Wagner’s gene-shuffling approach using an ingenious display system in cells in order to select better immunogens exploiting our novel mAbs as a screening system. In particular, we observed that our new mAb called HJ16 is surprisingly more effective at neutralizing HIV-1 “Tier 2” strains than “Tier 1” strains, as classified by the Duke VIMC (D Montefiori). HJ16 recognizes the CD4 binding site on HIV gp120, and the insight we are gaining from structure-function analysis with this mAb should help to design vaccines that successfully hit the less sensitive HIV strains, which unfortunately are the most prevalent ones.
The consortium's research has contributed to the understanding of some road-blocks to HIV vaccine development and therefore how to evade them. Ralf Wagner (Regensburg) and Jon Heeney (Cambridge) have established quality control of gene expression sequences for the HIV envelope as well as the glycoproteins themselves which has helped to resolve some of the generic problems in the HIV vaccine field in making native, immunogenic proteins. For example, we have provided an optimized ZM96 gene insert in a pox vector to Geppe Pantaleo’s CAVD consortium.
A beneficial knock-on effect beyond HIV/AIDS is that the team has also provided useful methods for assessing non-HIV vaccines affecting viral diseases in developing countries. They have adapted the rapid pseudovirus neutralization test devised for HIV to work for dangerous viral infections such as Rabies and highly pathogenic Avian Influenza without the need for high containment laboratories and therefore transportable to resource-poor settings in Africa and Asia.