Antigenicity and immunogenicity of a trimeric envelope protein from an Indian clade C HIV-1 isolate

Optimizing the Production of gp145, an HIV-1 Envelope Glycoprotein Vaccine Candidate and Its Encapsulation in Guanosine Microparticles

We have developed a pipeline to express, purify, and characterize HIV envelope protein (Env) gp145 from Chinese hamster ovary cells, to accelerate the production of a promising vaccine candidate. First in shake flasks, then in bioreactors, we optimized the growth conditions. By adjusting the pH to 6.8, we increased expression levels to 101 mg/L in a 50 L bioreactor, nearly twice the previously reported titer value. A battery of analytical methods was developed in accordance with current good manufacturing practices to ensure a quality biopharmaceutical. Imaged capillary isoelectric focusing verified proper glycosylation of gp145; dynamic light scattering confirmed the trimeric arrangement; and bio-layer interferometry and circular dichroism analysis demonstrated native-like properties (i.e., antibody binding and secondary structure). MALDI-TOF mass spectrometry was used as a multi-attribute platform for accurate mass determination, glycans analysis, and protein identification. Our robust analysis demonstrates that our gp145 product is very similar to a reference standard and emphasizes the importance of accurate characterization of a highly heterogeneous immunogen for the development of an effective vaccine. Finally, we present a novel guanosine microparticle with gp145 encapsulated and displayed on its surface. The unique properties of our gp145 microparticle make it amenable to use in future preclinical and clinical trials.

The adjuvant AlhydroGel elicits higher antibody titres than AddaVax when combined with HIV-1 subtype C gp140 from CAP256

With the HIV-1 epidemic in southern Africa still rising, a prophylactic vaccine against the region’s most prolific subtype (subtype C) would be a significant step forward. In this paper we report on the effect of 2 different adjuvants, AddaVax and AlhydroGel, formulated with HIV-1 subtype C gp140, on the development of binding and neutralising antibody titres in rabbits. AddaVax is a squalene-based oil-in-water nano-emulsion (similar to MF59) which can enhance both cellular and humoral immune responses, whilst AlhydroGel (aluminium hydroxide gel) mainly drives a Th2 response. The gp140 gene tested was derived from the superinfecting virus (SU) from participant CAP256 in the CAPRISA 002 Acute infection cohort. The furin cleavage site of the Env protein was replaced with a flexible linker and an I559P mutation introduced. Lectin affinity purified soluble Env protein was mainly trimeric as judged by molecular weight using BN-PAGE and contained intact broadly neutralising epitopes for the V3-glycan supersite (monoclonal antibodies PGT128 and PGT135), the CD4 binding site (VRC01) and the V2-glycan (PG9) but not for the trimer-specific monoclonal antibodies PG16, PGT145 and CAP256-VRC26_08. When this soluble Env protein was tested in rabbits, AlhydroGel significantly enhanced soluble Env and V1V2 binding antibodies when compared to AddaVax. Finally, AlhydroGel resulted in significantly higher neutralization titres for a subtype C Tier 1A virus (MW965.26) and increased neutralization breadth to Tier 1A and 1B viruses. However, no autologous Tier 2 neutralisation was observed. These data suggest that adjuvant selection is critical for developing a successful vaccine and AlhydroGel should be further investigated. Additional purification of trimeric native-like CAP256 Env and/or priming with DNA or MVA might enhance the induction of neutralizing antibodies and possible Tier 2 HIV-1 neutralisation.

Cross Type Neutralizing Antibodies Detected in a Unique HIV-2 Infected Individual From India

Background: Infection with HIV-2, a retrovirus that is closely related to HIV-1, is characterized by slower disease progression and transmission, longer latency period and low or undetectable viremia. Host immunity, including production of potent neutralizing antibodies, may be one of the possible contributors to the distinction between the two infections. In an attempt to understand whether HIV-2 infection results in production of neutralizing antibodies and to characterize the nature of the neutralization response we screened plasma of 37 HIV-2 infected individuals for the presence of broadly neutralizing antibodies. Materials and Methods: Thirty seven asymptomatic, ART-naïve, HIV-2 infected individuals were recruited for the study. Plasma obtained from these individuals were screened for the presence of broadly cross reactive neutralizing antibodies (BCNabs) using the standard neutralization screening protocol with a panel of HIV-1 and HIV-2 pseudoviruses. Plasma exhibiting broad neutralization activity were assessed for their potency employing a titration assay. Further, an attempt was made to characterize the neutralization specificity of the plasma exhibiting broad and potent neutralization activity. Result: While majority of the samples tested were capable of neutralizing HIV-2 pseudoviruses with high to moderate potency, one unique sample demonstrated broad cross clade and cross type neutralization with ability to strongly neutralize the vast majority of both HIV-1 and HIV-2 viruses tested (19/20). Preliminary analyses indicate the possible presence of antibodies with multiple glycan epitope binding specificities. Conclusion: The study identified a unique HIV-2 sample with exceptional ability to neutralize HIV-2 viruses and cross-neutralize HIV-1 viruses with great breadth and potency. This sample holds promise for isolation of novel monoclonal antibodies that may exploited as potential therapeutic tools for HIV infection.

Evolution of Neutralization Response in HIV-1 Subtype C-Infected Individuals Exhibiting Broad Cross-Clade Neutralization of HIV-1 Strains

Strain-specific neutralizing antibodies develop in all human immunodeficiency virus type 1 (HIV-1)-infected individuals. However, only 10–30% of infected individuals produce broadly neutralizing antibodies (bNAbs). Identification and characterization of these bNAbs and understanding their evolution dynamics are critical for obtaining useful clues for the development of an effective HIV vaccine. Very recently, we published a study in which we identified 12 HIV-1 subtype C-infected individuals from India whose plasma showed potent and broad cross-clade neutralization (BCN) ability (1). In the present study, we report our findings on the evolution of host bNAb response over a period of 4 years in a subset of these individuals. Three of the five individuals (NAB033, NAB059, and NAB065) demonstrated a significant increase (p < 0.05) in potency. Interestingly, two of the three samples also showed a significant increase in CD4 binding site-specific antibody response, maintained stable CD4+ T cell counts (>350 cells/mm³) and continued to remain ART-naïve for more than 10 years after initial diagnosis, implying a strong clinical correlation with the development and evolution of broadly neutralizing antibody response against HIV-1.

DNA prime/protein boost vaccination elicits robust humoral response in rhesus macaques using oligomeric simian immunodeficiency virus envelope and Advax delta inulin adjuvant

The partial success of the RV144 trial underscores the importance of envelope-specific antibody responses for an effective HIV-1 vaccine. Oligomeric HIV-1 envelope proteins delivered with a potent adjuvant are expected to elicit strong antibody responses with broad neutralization specificity. To test this hypothesis, two SIV envelope proteins were formulated with delta inulin-based adjuvant (Advax) and used to immunize nonhuman primates. Oligomeric gp140-gp145 from SIVmac251 and SIVsmE660 was purified to homogeneity. Oligomers showed high-affinity interaction with CD4 and were highly immunogenic in rabbits, inducing Tier 2 SIV-neutralizing antibodies. The immunogenicity of an oligomeric Env DNA prime and protein boost together with Advax was evaluated in Chinese rhesus macaques. DNA administration elicited antibodies to both envelopes, and titres were markedly enhanced following homologous protein boosts via intranasal and intramuscular routes. Strong antibody responses were detected against the V1 and V2 domains of gp120. During peak immune responses, a low to moderate level of neutralizing activity was detected against Tier 1A/1B SIV isolates, with a moderate level noted against a Tier 2 isolate. Increased serum antibody affinity to SIVmac251 gp140 and generation of Env-specific memory B cells were observed in the immunized macaques. Animals were subjected to low-dose intravaginal challenge with SIVmac251 one week after the last protein boost. One out of three immunized animals was protected from infection. Although performed with a small number of macaques, this study demonstrates the utility of oligomeric envelopes formulated with Advax in eliciting broad antibody responses with the potential to provide protection against SIV transmission.

Broad and potent cross clade neutralizing antibodies with multiple specificities in the plasma of HIV-1 subtype C infected individuals

Broadly Cross clade Neutralizing (BCN) antibodies are recognized as potential therapeutic tools and leads for the design of a vaccine that can protect human beings against various clades of Human Immunodeficiency Virus (HIV). In the present study, we screened plasma of 88 HIV-1 infected ART naïve individuals for their neutralization potential using a standard panel of 18 pseudoviruses belonging to different subtypes and different levels of neutralization. We identified 12 samples with good breadth of neutralization (neutralized >90% of the viruses). Four of these samples neutralized even the difficult-to-neutralize tier-3 pseudoviruses with great potency (GMT > 600). Analysis of neutralization specificities indicated that four samples had antibodies with multiple epitope binding specificities, viz. CD4-binding site (CD4BS), glycans in the V1/V2 and V3 regions and membrane proximal external region (MPER). Our findings indicate the strong possibility of identifying highly potent bNAbs with known or novel specificities from HIV-1 subtype C infected individuals from India that can be exploited as therapeutic tools or lead molecules for the identification of potential epitopes for design of a protective HIV-1 vaccine.

Structure-based Design of Cyclically Permuted HIV-1 gp120 Trimers That Elicit Neutralizing Antibodies

A major goal for HIV-1 vaccine development is an ability to elicit strong and durable broadly neutralizing antibody (bNAb) responses. The trimeric envelope glycoprotein (Env) spikes on HIV-1 are known to contain multiple epitopes that are susceptible to bNAbs isolated from infected individuals. Nonetheless, all trimeric and monomeric Env immunogens designed to date have failed to elicit such antibodies. We report the structure-guided design of HIV-1 cyclically permuted gp120 that forms homogeneous, stable trimers, and displays enhanced binding to multiple bNAbs, including VRC01, VRC03, VRC-PG04, PGT128, and the quaternary epitope-specific bNAbs PGT145 and PGDM1400. Constructs that were cyclically permuted in the V1 loop region and contained an N-terminal trimerization domain to stabilize V1V2-mediated quaternary interactions, showed the highest homogeneity and the best antigenic characteristics. In guinea pigs, a DNA prime-protein boost regimen with these new gp120 trimer immunogens elicited potent neutralizing antibody responses against highly sensitive Tier 1A isolates and weaker neutralizing antibody responses with an average titer of about 115 against a panel of heterologous Tier 2 isolates. A modest fraction of the Tier 2 virus neutralizing activity appeared to target the CD4 binding site on gp120. These results suggest that cyclically permuted HIV-1 gp120 trimers represent a viable platform in which further modifications may be made to eventually achieve protective bNAb responses.

Membrane bound Indian clade C HIV-1 envelope antigen induces antibodies to diverse and conserved epitopes upon DNA prime/protein boost in rabbits

The partial success of RV144 human clinical trial demonstrated that ALVAC prime/envelope protein boost vaccine regimen may represent a promising strategy for the development of an effective HIV-1 vaccine. Our earlier study demonstrated that a trimeric HIV-1 envelope gp145 from an Indian clade C isolate elicited cross clade neutralizing antibodies primarily towards Tier 1 isolates. In the present study, we examined the immunogenicity of DNA prime/envelope protein boost vaccine in rabbits using gp160 DNA of the Indian clade C isolate with various cytoplasmic tail truncations and trimeric gp145 protein. Cytoplasmic tail mutants of gp160 exposed epitopes that reacted strongly with a number of broadly neutralizing human monoclonal antibodies against HIV-1. Overall, envelope specific titers were found to be similar in all rabbit groups with higher pseudovirus neutralization in protein only immunized rabbits. The complete linear epitope mapping of rabbit immune sera revealed strong binding to C1, C2, V3, C3 and C4 domains of gp145. Importantly, reactivity of gp41 ecto-domain peptides was observed in DNA prime/protein boost sera but not in the sera of rabbits immunized with protein alone. Moreover, membrane anchored but not soluble envelope encoding DNA immunization elicited antibodies against linear epitopes on the conserved gp41 ecto-domain. Together, these results suggest that priming with DNA encoding cytoplasmic domains of Env alters the quality of antibodies elicited following protein boost and hence may be utilized to generate protective immunity by HIV-1 vaccine.

Enhanced Immune Responses to HIV-1 Envelope Elicited by a Vaccine Regimen Consisting of Priming with Newcastle Disease Virus Expressing HIV gp160 and Boosting with gp120 and SOSIP gp140 Proteins

Newcastle disease virus (NDV) expressing HIV-1 BaL gp160 was evaluated either alone or with monomeric BaL gp120 and BaL SOSIP gp140 protein in a prime-boost combination in guinea pigs to enhance envelope (Env)-specific humoral and mucosal immune responses. We showed that a regimen consisting of an NDV prime followed by a protein boost elicited stronger serum and mucosal Th-1-biased IgG responses and neutralizing antibody responses than NDV-only immunizations. Additionally, these responses were higher after the gp120 than after the SOSIP gp140 protein boost.

Characterization of protective immune response elicited by a trimeric envelope protein from an Indian clade C HIV-1 isolate in rhesus macaques

BACKGROUND

Recent preclinical studies have demonstrated the use of properly folded trimeric HIV-1 envelope proteins as immunogen for eliciting protecting immune response in macaques.

METHODS

Trimeric gp145 protein of Indian clade C HIV-1 (93IN101) was characterized for antigenicity by evaluating its binding to sCD4, and several monoclonal antibodies to HIV-1 by bio-layer interferometry. Ten macaques were immunized four times with purified gp145 in adjuplex adjuvant, and serum antibodies were characterized for binding to gp145 and neutralization. Immunized macaques were subjected to weekly low-dose vaginal challenge with SHIV1157-ipEL-p for 8 weeks.

RESULTS

Env protein elicited strong antibody response in macaques. Following challenge, seven of ten immunized macaques resisted challenge, while six of eight control animals were infected.

CONCLUSIONS

Env proteins from a clade C Indian isolate can elicit protective immune response and therefore may be a candidate for inclusion in a multiclade-based HIV-1 vaccine.