HIV-1 superinfection results in broad polyclonal neutralizing antibodies

<div><p>HIV-1 vaccines designed to date have failed to elicit neutralizing antibodies (Nabs) that are capable of protecting against globally diverse HIV-1 subtypes. One relevant setting to study the development of a strong, cross-reactive Nab response is HIV-1 superinfection (SI), defined as sequential infections from different source partners. SI has previously been shown to lead to a broader and more potent Nab response when compared to single infection, but it is unclear whether SI also impacts epitope specificity and if the epitopes targeted after SI differ from those targeted after single infection. Here the post-SI Nab responses were examined from 21 Kenyan women collectively exposed to subtypes A, C, and D and superinfected after a median time of ~1.07 years following initial infection. Plasma samples chosen for analysis were collected at a median time point ~2.72 years post-SI. Because previous studies of singly infected populations with broad and potent Nab responses have shown that the majority of their neutralizing activity can be mapped to 4 main epitopes on the HIV-1 Envelope, we focused on these targets, which include the CD4-binding site, a V1/V2 glycan, the N332 supersite in V3, and the membrane proximal external region of gp41. Using standard epitope mapping techniques that were applied to the previous cohorts, the present study demonstrates that SI did not induce a dominant Nab response to any one of these epitopes in the 21 women. Computational sera delineation analyses also suggested that 20 of the 21 superinfected women’s Nab responses could not be ascribed a single specificity with high confidence. These data are consistent with a model in which SI with diverse subtypes promotes the development of a broad polyclonal Nab response, and thus would provide support for vaccine designs using multivalent HIV immunogens to elicit a diverse repertoire of Nabs.</p></div

Structural rearrangements maintain the Glycan Shield of an HIV-1 envelope trimer after the loss of a glycan

The HIV-1 envelope (Env) glycoprotein is the primary target of the humoral immune response and a critical vaccine candidate. However, Env is densely glycosylated and thereby substantially protected from neutralisation. Importantly, glycan N301 shields V3 loop and CD4 binding site epitopes from neutralising antibodies. Here, we use molecular dynamics techniques to evaluate the structural rearrangements that maintain the protective qualities of the glycan shield after the loss of glycan N301. We examined a naturally occurring subtype C isolate and its N301A mutant; the mutant not only remained protected against neutralising antibodies targeting underlying epitopes, but also exhibited an increased resistance to the VRC01 class of broadly neutralising antibodies. Analysis of this mutant revealed several glycans that were responsible, independently or through synergy, for the neutralisation resistance of the mutant. These data provide detailed insight into the glycan shield’s ability to compensate for the loss of a glycan, as well as the cascade of glycan movements on a protomer, starting at the point mutation, that affects the integrity of an antibody epitope located at the edge of the diminishing effect. These results present key, previously overlooked, considerations for HIV-1 Env glycan research and related vaccine studies.IS

Prime-boost immunization of rabbits with HIV-1 gp120 elicits potent neutralization activity against a primary viral isolate

<div><p>Development of a vaccine for HIV-1 requires a detailed understanding of the neutralizing antibody responses that can be experimentally elicited to difficult-to-neutralize primary isolates. Rabbits were immunized with the gp120 subunit of HIV-1 JR-CSF envelope (Env) using a DNA-prime protein-boost regimen. We analyzed five sera that showed potent autologous neutralizing activity (IC50s at ∼10³ to 10⁴ serum dilution) against pseudoviruses containing Env from the primary isolate JR-CSF but not from the related isolate JR-FL. Pseudoviruses were created by exchanging each variable and constant domain of JR-CSF gp120 with that of JR-FL or with mutations in putative N-glycosylation sites. The sera contained different neutralizing activities dependent on C3 and V5, C3 and V4, or V4 regions located on the glycan-rich outer domain of gp120. All sera showed enhanced neutralizing activity toward an Env variant that lacked a glycosylation site in V4. The JR-CSF gp120 epitopes recognized by the sera are generally distinct from those of several well characterized mAbs (targeting conserved sites on Env) or other type-specific responses (targeting V1, V2, or V3 variable regions). The activity of one serum requires specific glycans that are also important for 2G12 neutralization and this serum blocked the binding of 2G12 to gp120. Our findings show that different fine specificities can achieve potent neutralization of HIV-1, yet this strong activity does not result in improved breadth.</p> </div