Scientists at The Wistar Institute have developed an HIV vaccine candidate that induced detectable neutralizing antibodies after a single immunization in nonhuman primates, a breakthrough that could significantly shorten and simply HIV vaccinations. The research, published in Nature Immunology, details how the team engineered a protein that removes the N332-glycan completely to produce their candidate WIN332, an unprecedented approach to current vaccine efforts that have focused on preserving N332-glycan.
“By going against one commonly held belief in the field, we achieved low neutralization after a single immunization, which was further increased after one additional booster, something that has never been observed before,” said senior Amelia Escolano, PhD, an assistant professor in Wistar’s Vaccine and Immunotherapy Center. “Usually, HIV vaccination protocols require seven, eight, or even ten injections to start seeing any neutralization. For our immunogen, WIN332, we injected once and already saw some neutralization.”
The development of WIN332 potentially addresses one of the big challenges in HIV vaccine development, how to efficiently elicit broadly neutralizing antibodies (bNAbs) capable of working against diverse HIV strains. Sequential immunization strategies, which use a series of engineered envelope proteins (Env) to produce antibody maturation, have shown some promise, but the need for repeated injections over long periods would make them impractical in much of the developing world. Only a small number of these development attempts have consistently induced bNAbs in nonhuman primates. Even then, the responses have shown limited potency and breadth.
For their candidate, the Wistar team focused on one element of the HIV envelope protein, the V3-glycan epitope. Many prior attempts to target the V3-glycan epitope of Env have worked under the assumption that antibodies must interact with a specific sugar, the Asn332 glycan, to neutralize HIV. As a result, immunogens were designed to preserve this glycan. Escolano’s team, however, deliberately removed the Asn332 glycan completely to create WIN332, thinking that early antibody precursors may not require it and that glycan dependence could develop later through somatic hypermutation.
This line of thinking is supported by earlier studies in both humans and animal models showing that the Asn332 glycan is underrepresented in transmitted or founder viruses, and infection with Asn332-glycan-deficient viruses has been associated with the later development of Asn332-dependent bNAbs in humans. In addition, two human V3-glycan bNAbs, EPTC112 and 007, were found to neutralize HIV without contacting the Asn332 glycan. This provided evidence that Asn332-glycan-independent bNAbs could develop in humans.
To test their hypothesis, the Wistar team designed WIN332 as an Asn332-glycan-deficient priming immunogen and evaluated it in nonhuman primates. Their data showed that a single bolus immunization elicited serum antibodies with low but reproducible inhibitory activity displaying its potential of neutralization against fully glycosylated HIV-1 pseudoviruses, in some cases within three weeks. Although the activity did not reach IC50 levels—the amount of antibody needed to reduce viral infection by 50% in a lab assay—the team noted that high neutralization levels are not expected after a single immunization. A subsequent boost increased neutralization and drove affinity maturation of the antibody response.
Analysis of these responses showed that WIN332 elicited antibodies closely resembling potent human V3-glycan bNAbs. The data also found two distinct classes of antibodies: type-I antibodies that depend on the Asn332 glycan, and a new type-II class of antibodies that remain glycan independent. “This discovery potentially expands the toolkit available for developing HIV vaccines that provide broader protection against the diverse HIV strains circulating globally,” Escolano said.
By activating what the Wistar team describe as “premium” antibody lineages that require less complex maturation pathways, WIN332 may allow for shorter and simpler vaccination schedules. “If this approach proves successful, we could potentially achieve desired immunity with just three injections,” said first Ignacio Relano-Rodriguez, PhD, a postdoctoral fellow in the Escalano lab. “This would make vaccination protocols shorter and more affordable.”
Based on these findings the researchers are now conducting additional preclinical evaluations. The team is also hoping to design of subsequent immunogens that can be used in a significantly shorter sequential vaccine regimen that would enhance neutralization. Interest from global health organizations has also emerged to advance WIN332 toward human clinical trials.
