Browsing by Author "Fouda, Genevieve G"

Background

Methods

Results

Conclusions

Since its outbreak in the 1980s, the Human Immunodeficiency Virus (HIV) has become a major threat to global health. According to UNAIDS 2021 epidemiological estimates (2, 3), at the end of 2020 around 37.7 million people were living with HIV worldwide and 1.5 million new HIV infections occurred. Among those HIV-positive individuals, 10.5 million including 800,000 children did not have access to treatment, resulting in 680,000 AIDS-related deaths. Currently, different preventative measures are implemented including condom use, and pre- and post-exposure prophylaxis (4). However, these measures are not feasible for scaling up to population level because they require constant use of medication, and their efficacy depends on adherence to the treatment regimen. Vaccines are among the most cost-effective approaches to prevent infectious diseases (5). Yet, after 40 years of pandemic HIV, no vaccine has been able to provide enough protection against HIV acquisition, reflecting the formidable challenge of developing an efficacious HIV vaccine. These difficulties come from the two sides of the battle: the virus and the immune system. Virologically, HIV represents one of the most genetically diverse viruses in human history (6). Therefore, an effective vaccine will need to provide protection against an enormous set of viral strains. Moreover, the extensive glycosylation of the HIV Envelop glycoproteins (Env) protects the sites of vulnerability in the Env against antibody recognition (7), resulting in delayed emergence of neutralizing antibodies following infection (8, 9). Immunologically, antibodies with extensive neutralizing ability (known as broadly neutralizing antibodies, bnAbs) have features that disfavor their generation, such as high frequency of somatic hypermutation (SHM) (10), long complementarity determining region 3 (CDR3) (11), and high frequency of immunologically disfavored mutations (known as improbable mutations) (1). Because traditional vaccination strategies have failed to elicit broad protective immune responses, novel approaches are required for a universal HIV vaccine. The success of passive immunization with bnAbs in protecting non-human primates from the Chimeric Simian-human Immunodeficiency virus (SHIV) infection (12-17), has highlighted bnAbs as critical for protection; and elicitation of bnAbs is the ultimate goal for most current HIV vaccine designs. The features of bnAbs indicate that several rounds of SHM are required for B cells to produce bnAbs, and it is thought that the first event to drive B cells toward bnAb formation is when Env engages the B cell precursors that express the unmutated form of a bnAb, known as germline or unmutated common ancestor (UCA) (10). Different strategies have been used to engage the germline B cells such as using Env antigen of the transmitted/founder (T/F) virus that first establishes infection (18). Moreover, the use of native-like Env trimers instead of monomeric glycoproteins may enhance the immunogenicity of epitopes important for broad neutralization. To induce neutralizing antibodies against HIV, one of the vaccine candidates we tested (CH505T/F SOSIP) is a native-like trimer Env antigen designed based on the T/F virus isolated in a patient who developed the anti-CD4 binding site (CD4bs) bnAb CH103 (18). This antigen was chosen because it has demonstrated the ability to engage the CH103 UCA (19). While the mechanism of elicitation of bnAbs during natural infection are not completely elucidated, several recent studies have reported that HIV infected children develop neutralization breadth earlier and more frequently than adults (20, 21). Moreover, the few pediatric bnAbs described in the literature feature lower SHM frequency and fewer improbable mutations than adult bnAbs with similar neutralizing breath (1, 22, 23). Overall, these observations suggest that immunization in early life could present advantages for inducing bnAbs. Therefore, in one of the studies presented in this dissertation, we tested our immunization strategy in infant non-human primates. To date, only one HIV vaccine trial has demonstrated any evidence of efficacy. In the HIV vaccine trial RV144, the vaccine was correlated with a 31% reduction of HIV acquisition in the vaccinees (24). Importantly, only very limited neutralizing antibody response was induced in RV144 vaccinees, suggesting that non-neutralizing antibody functions can provide some degree of protection. Indeed, post-hoc analyses indicate that antibody-dependent cellular cytotoxicity (ADCC) was associated with reduced HIV acquisition in RV144 vaccinees (24, 25). Unlike neutralization, which is mainly regulated by the Fab region of an antibody, non-neutralizing antibody effector functions (such as ADCC and antibody-dependent cellular phagocytosis, ADCP) are regulated both by Fab and Fc regions (26, 27). Antibodies with a certain Fc phenotype exert non-neutralizing functions via selectively engaging different Fc receptors. (26, 27). As an ideal vaccine would probably need to induce antibodies that mediate neutralization as well as non-neutralizing Fc effector functions, it is important to further explore how vaccine strategies can modulate the Fc portion of the antibodies in order to enhance desired Fc functions. As traditional immunization strategies have failed to induce protective immunity against HIV, various classes of nanomaterials have been applied to HIV vaccine development in the past decade (28). That is because certain properties of nanomaterials can be harnessed to improve specific immune responses. Notably, self-assembling peptide nanomaterial such as the synthetic peptide Q11 which can self-assemble into fibrillar structure upon transition from pure water to aqueous solution with physiological salt concentration (29) are self-adjuvanting (30). Moreover, Q11 allows control of valency of the conjugated antigens (31). Thus far, Q11 has been used in immune therapy for different disease models such as malaria (32), influenza virus (33-35), psoriasis (36), and bacterial endotoxin-induced anaphylactic shock (37). Because of Q11’s engineerability and self-adjuvanting nature, it may present advantages for tailoring immune response against diseases with unknown immune correlates for protection such as HIV. The overarching goal of this dissertation project is to construct a next-generation HIV vaccine capable of inducing a broad protection against different HIV strains. We hypothesized that presenting HIV Env on Q11 improves the humoral response elicited by the Env vaccine. To test this hypothesis, we utilized Q11 to formulate different HIV vaccines, and we defined the humoral responses induced by Q11-based HIV vaccines in animal models including mice, rabbits, and infant rhesus macaques. We first conjugated gp120 from the T/F clade C virus 1086.C (38) to Q11 nanofiber and immunized wildtype mice with either the Q11-conjugated gp120 (gp120-Q11) or with soluble gp120. We demonstrated that gp120-Q11 induced higher magnitude of antibody response than gp120. More importantly, by testing the antibody binding to Envs from heterologous HIV strains, we demonstrated that gp120-Q11 also induced higher binding breadth. This enhancement in antibody binding magnitude and breadth was found to be associated with the gp120 valency on Q11 nanofiber, as diminished response was observed in mice immunized with lower valency gp120-Q11 vaccine. We then immunized rabbits with a gp120-Q11 and the corresponding gp120 to assess the function of the vaccine-elicited antibodies. The gp120-Q11 vaccine induced higher levels of tier 1 autologous virus (CH505 w4.3) neutralization, ADCC, and ADCP to heterologous Env antigen in rabbits than the gp120 vaccine. Since Fc-mediated functions such as ADCC and ADCP can be modulated by the glycosylation of the IgG Fc region, we analyzed the Fc glycan in gp120-specific IgG in the immunized rabbits and found that the gp120-Q11 vaccine induced an IgG response with higher levels of fucosylation, bisection, and mono-galactosylation. Similar glycosylation profile was also observed in gp120-Q11 immunized mice. These results suggest that Q11 nanofiber’s ability to modulate Fc glycosylation may be applicable across different mammalian species. Finally, we assess the immunogenicity of a Q11-conjugated trimeric Env construct (SOSIP) in infant rhesus macaques. Although slightly lower antibody magnitude was induced by the Q11-conjugated SOSIP vaccine as compared to SOSIP only, we found higher titers of neutralizing antibody against the autologous tier 1 HIV CH505 w4.3 in infant macaques immunized with the SOSIP-Q11 vaccine. Yet, SOSIP-Q11 and soluble SOSIP vaccine groups demonstrated similar frequency of neutralization of the autologous tier 2 virus (CH505T/F). These results may reflect differences in the animal models or on how neonatal and adult B cells respond to multivalent vaccines. Future studies should investigate the mechanism of this difference in order to define if construct optimization can improve the response to HIV Env-Q11 multivalent vaccines in pediatric settings. Taken together, in this dissertation we described a self-assembling nanomaterial as a versatile vaccine platform for HIV. This vaccine platform did not only improve the overall binding antibody response and breadth; antibodies induced by Q11 vaccine also demonstrated superior functional capacity (ADCC, ADCP and tier 1 virus neutralization). Moreover, Q11 appears to modulate the Fc glycosylation across species and these changes in glycosylation profile were associated with increased ADCC in rabbits. This finding implies an opportunity to further explore the possibility of using Q11 or other similar nanomaterials to tailor Fc-mediated antibody functions via modulating the glycan moiety.