Maoli Yuan

A Novel, Live-Attenuated Vesicular Stomatitis Virus Vector Displaying Conformationally Intact, Functional HIV-1 Envelope Trimers That Elicits Potent Cellular and Humoral Responses in Mice

Though vaccination with live-attenuated SIV provides the greatest protection from progressive disease caused by SIV challenge in rhesus macaques, attenuated HIV presents safety concerns as a vaccine; therefore, live viral vectors carrying HIV immunogens must be considered. We have designed a replication-competent vesicular stomatitis virus (VSV) displaying immunogenic HIV-1 Env trimers and attenuating quantities of the native surface glycoprotein (G). The clade B Env immunogen is an Env-VSV G hybrid (EnvG) in which the transmembrane and cytoplasmic tail regions are derived from G. Relocation of the G gene to the 5′terminus of the genome and insertion of EnvG into the natural G position induced a ∼1 log reduction in surface G, significant growth attenuation compared to wild-type, and incorporation of abundant EnvG. Western blot analysis indicated that ∼75% of incorporated EnvG was a mature proteolytically processed form. Flow cytometry showed that surface EnvG bound various conformationally- and trimer-specific antibodies (Abs), and in-vitro growth assays on CD4+CCR5+ cells demonstrated EnvG functionality. Neither intranasal (IN) or intramuscular (IM) administration in mice induced any observable pathology and all regimens tested generated potent Env-specific ELISA titers of 104–105, with an IM VSV prime/IN VSV boost regimen eliciting the highest binding and neutralizing Ab titers. Significant quantities of Env-specific CD4+ T cells were also detected, which were augmented as much as 70-fold by priming with IM electroporated plasmids encoding EnvG and IL-12. These data suggest that our novel vector can achieve balanced safety and immunogenicity and should be considered as an HIV vaccine platform.

Vaccine-induced immune responses against both Gag and Env improve control of simian immunodeficiency virus replication in rectally challenged rhesus macaques

The ability to control lentivirus replication may be determined, in part, by the extent to which individual viral proteins are targeted by the immune system. Consequently, defining the antigens that elicit the most protective immune responses may facilitate the design of effective HIV-1 vaccines. Here we vaccinated four groups of rhesus macaques with a heterologous vector prime/boost/boost/boost (PBBB) regimen expressing the following simian immunodeficiency virus (SIV) genes: env, gag, vif, rev, tat, and nef (Group 1); env, vif, rev, tat, and nef (Group 2); gag, vif, rev, tat, and nef (Group 3); or vif, rev, tat, and nef (Group 4). Following repeated intrarectal challenges with a marginal dose of the neutralization-resistant SIVmac239 clone, vaccinees in Groups 1–3 became infected at similar rates compared to control animals. Unexpectedly, vaccinees in Group 4 became infected at a slower pace than the other animals, although this difference was not statistically significant. Group 1 exhibited the best post-acquisition virologic control of SIV infection, with significant reductions in both peak and chronic phase viremia. Indeed, 5/8 Group 1 vaccinees had viral loads of less than 2,000 vRNA copies/mL of plasma in the chronic phase. Vaccine regimens that did not contain gag (Group 2), env (Group 3), or both of these inserts (Group 4) were largely ineffective at decreasing viremia. Thus, vaccine-induced immune responses against both Gag and Env appeared to maximize control of immunodeficiency virus replication. Collectively, these findings are relevant for HIV-1 vaccine design as they provide additional insights into which of the lentiviral proteins might serve as the best vaccine immunogens.

Evaluation of a replication-competent VSV-SIV vaccine candidate

Background Immunity elicited by live attenuated vaccines confers protection against viral pathogens causing measles, yellow fever, smallpox and others, but this approach is not well suited to HIV vaccine development. Accordingly, to develop a vaccine that incorporates features of a live virus that make it immunogenic without the inherent safety issues associated with attenuated lentiviruses, we are developing replication-competent, recombinant vesicular stomatitis virus (rVSV) vectors for delivery of SIV and HIV vaccines.

Viral vector delivery of Env trimer immunogens

Methods We are using vesicular stomatitis virus (VSV) as a vector platform for delivery of Env immunogens as transmembrane glycoproteins. We have investigated a variety of vector designs and Env modifications to identify combinations that balance the practical requirement for vector genetic stability with factors influencing antibody responses including immunogen abundance, efficient post-translational processing, and presentation of antigenic determinants representative of a functional trimeric spike.

Optimizing expression of functional HIV envelopes in rVSV-ΔG vaccine vectors.

Methods Using a combination of nucleotide sequence optimization and protein domain swapping, we have generated a panel of novel gene inserts for VSV vectors that encode chimeric HIV-1 and VSV glycoprotein immunogens (EnvG). A stable VERO cell line engineered to express human CD4 and CCR5 was used to rescue rVSV vectors in which the G gene was replaced with coding sequence for several different EnvG proteins.

Development of candidate HIV vaccines using VSV vectors to express membrane-anchored MPER immunogen

Background The HIV-neutralizing activity of monoclonal antibodies 2F5, 4E10, and Z13 have shown that the membrane-proximal external region (MPER) of HIV Env is an important vaccine target, but development of an immunogen that elicits similar virus-neutralizing antibody responses against the MPER from a wide range of subtypes has been difficult to achieve. It has been proposed that a MPER immunogen must be membrane-associated to adopt the conformation needed to elicit broadly neutralizing antibodies, and accordingly, we have developed Vesicular Stomatitis Virus (VSV) Vectors that express membrane-anchored MPER epitopes.