Self-Awareness: Nucleic Acid-Driven Inflammation and the Type I Interferonopathies.

Recognition of foreign nucleic acids is the primary mechanism by which a type I interferon-mediated antiviral response is triggered. Given that human cells are replete with DNA and RNA, this evolutionary strategy poses an inherent biological challenge, i.e., the fundamental requirement to reliably differentiate self-nucleic acids from nonself nucleic acids. We suggest that the group of Mendelian inborn errors of immunity referred to as the type I interferonopathies relate to a breakdown of self/nonself discrimination, with the associated mutant genotypes involving molecules playing direct or indirect roles in nucleic acid signaling. This perspective begs the question as to the sources of self-derived nucleic acids that drive an inappropriate immune response. Resolving this question will provide fundamental insights into immune tolerance, antiviral signaling, and complex autoinflammatory disease states. Here we develop these ideas, discussing type I interferonopathies within the broader framework of nucleic acid-driven inflammation.

Immune imprinting, breadth of variant recognition, and germinal center response in human SARS-CoV-2 infection and vaccination.

During the SARS-CoV-2 pandemic, novel and traditional vaccine strategies have been deployed globally. We investigated whether antibodies stimulated by mRNA vaccination (BNT162b2), including third-dose boosting, differ from those generated by infection or adenoviral (ChAdOx1-S and Gam-COVID-Vac) or inactivated viral (BBIBP-CorV) vaccines. We analyzed human lymph nodes after infection or mRNA vaccination for correlates of serological differences. Antibody breadth against viral variants is lower after infection compared with all vaccines evaluated but improves over several months. Viral variant infection elicits variant-specific antibodies, but prior mRNA vaccination imprints serological responses toward Wuhan-Hu-1 rather than variant antigens. In contrast to disrupted germinal centers (GCs) in lymph nodes during infection, mRNA vaccination stimulates robust GCs containing vaccine mRNA and spike antigen up to 8 weeks postvaccination in some cases. SARS-CoV-2 antibody specificity, breadth, and maturation are affected by imprinting from exposure history and distinct histological and antigenic contexts in infection compared with vaccination.

An adjuvant strategy enabled by modulation of the physical properties of microbial ligands expands antigen immunogenicity.

Activation of the innate immune system via pattern recognition receptors (PRRs) is key to generate lasting adaptive immunity. PRRs detect unique chemical patterns associated with invading microorganisms, but whether and how the physical properties of PRR ligands influence the development of the immune response remains unknown. Through the study of fungal mannans, we show that the physical form of PRR ligands dictates the immune response. Soluble mannans are immunosilent in the periphery but elicit a potent pro-inflammatory response in the draining lymph node (dLN). By modulating the physical form of mannans, we developed a formulation that targets both the periphery and the dLN. When combined with viral glycoprotein antigens, this mannan formulation broadens epitope recognition, elicits potent antigen-specific neutralizing antibodies, and confers protection against viral infections of the lung. Thus, the physical properties of microbial ligands determine the outcome of the immune response and can be harnessed for vaccine development.

Rational design of a 'two-in-one' immunogen DAM drives potent immune response against mpox virus.

The global outbreak of the mpox virus (MPXV) in 2022 highlights the urgent need for safer and more accessible new-generation vaccines. Here, we used a structure-guided multi-antigen fusion strategy to design a 'two-in-one' immunogen based on the single-chain dimeric MPXV extracellular enveloped virus antigen A35 bivalently fused with the intracellular mature virus antigen M1, called DAM. DAM preserved the natural epitope configuration of both components and showed stronger A35-specific and M1-specific antibody responses and in vivo protective efficacy against vaccinia virus (VACV) compared to co-immunization strategies. The MPXV-specific neutralizing antibodies elicited by DAM were 28 times higher than those induced by live VACV vaccine. Aluminum-adjuvanted DAM vaccines protected mice from a lethal VACV challenge with a safety profile, and pilot-scale production confirmed the high yield and purity of DAM. Thus, our study provides innovative insights and an immunogen candidate for the development of alternative vaccines against MPXV and other orthopoxviruses.

Protective neutralizing antibodies from human survivors of Crimean-Congo hemorrhagic fever.

Crimean-Congo hemorrhagic fever virus (CCHFV) is a World Health Organization priority pathogen. CCHFV infections cause a highly lethal hemorrhagic fever for which specific treatments and vaccines are urgently needed. Here, we characterize the human immune response to natural CCHFV infection to identify potent neutralizing monoclonal antibodies (nAbs) targeting the viral glycoprotein. Competition experiments showed that these nAbs bind six distinct antigenic sites in the Gc subunit. These sites were further delineated through mutagenesis and mapped onto a prefusion model of Gc. Pairwise screening identified combinations of non-competing nAbs that afford synergistic neutralization. Further enhancements in neutralization breadth and potency were attained by physically linking variable domains of synergistic nAb pairs through bispecific antibody (bsAb) engineering. Although multiple nAbs protected mice from lethal CCHFV challenge in pre- or post-exposure prophylactic settings, only a single bsAb, DVD-121-801, afforded therapeutic protection. DVD-121-801 is a promising candidate suitable for clinical development as a CCHFV therapeutic.

Therapeutic alphavirus cross-reactive E1 human antibodies inhibit viral egress.

Alphaviruses cause severe arthritogenic or encephalitic disease. The E1 structural glycoprotein is highly conserved in these viruses and mediates viral fusion with host cells. However, the role of antibody responses to the E1 protein in immunity is poorly understood. We isolated E1-specific human monoclonal antibodies (mAbs) with diverse patterns of recognition for alphaviruses (ranging from Eastern equine encephalitis virus [EEEV]-specific to alphavirus cross-reactive) from survivors of natural EEEV infection. Antibody binding patterns and epitope mapping experiments identified differences in E1 reactivity based on exposure of epitopes on the glycoprotein through pH-dependent mechanisms or presentation on the cell surface prior to virus egress. Therapeutic efficacy in vivo of these mAbs corresponded with potency of virus egress inhibition in vitro and did not require Fc-mediated effector functions for treatment against subcutaneous EEEV challenge. These studies reveal the molecular basis for broad and protective antibody responses to alphavirus E1 proteins.

SARS-CoV-2 501Y.V2 variants lack higher infectivity but do have immune escape.

The 501Y.V2 variants of SARS-CoV-2 containing multiple mutations in spike are now dominant in South Africa and are rapidly spreading to other countries. Here, experiments with 18 pseudotyped viruses showed that the 501Y.V2 variants do not confer increased infectivity in multiple cell types except for murine ACE2-overexpressing cells, where a substantial increase in infectivity was observed. Notably, the susceptibility of the 501Y.V2 variants to 12 of 17 neutralizing monoclonal antibodies was substantially diminished, and the neutralization ability of the sera from convalescent patients and immunized mice was also reduced for these variants. The neutralization resistance was mainly caused by E484K and N501Y mutations in the receptor-binding domain of spike. The enhanced infectivity in murine ACE2-overexpressing cells suggests the possibility of spillover of the 501Y.V2 variants to mice. Moreover, the neutralization resistance we detected for the 501Y.V2 variants suggests the potential for compromised efficacy of monoclonal antibodies and vaccines.

N-terminal domain antigenic mapping reveals a site of vulnerability for SARS-CoV-2.

The SARS-CoV-2 spike (S) glycoprotein contains an immunodominant receptor-binding domain (RBD) targeted by most neutralizing antibodies (Abs) in COVID-19 patient plasma. Little is known about neutralizing Abs binding to epitopes outside the RBD and their contribution to protection. Here, we describe 41 human monoclonal Abs (mAbs) derived from memory B cells, which recognize the SARS-CoV-2 S N-terminal domain (NTD) and show that a subset of them neutralize SARS-CoV-2 ultrapotently. We define an antigenic map of the SARS-CoV-2 NTD and identify a supersite (designated site i) recognized by all known NTD-specific neutralizing mAbs. These mAbs inhibit cell-to-cell fusion, activate effector functions, and protect Syrian hamsters from SARS-CoV-2 challenge, albeit selecting escape mutants in some animals. Indeed, several SARS-CoV-2 variants, including the B.1.1.7, B.1.351, and P.1 lineages, harbor frequent mutations within the NTD supersite, suggesting ongoing selective pressure and the importance of NTD-specific neutralizing mAbs for protective immunity and vaccine design.

Novel approaches for vaccine development.

Vaccines are critical tools for maintaining global health. Traditional vaccine technologies have been used across a wide range of bacterial and viral pathogens, yet there are a number of examples where they have not been successful, such as for persistent infections, rapidly evolving pathogens with high sequence variability, complex viral antigens, and emerging pathogens. Novel technologies such as nucleic acid and viral vector vaccines offer the potential to revolutionize vaccine development as they are well-suited to address existing technology limitations. In this review, we discuss the current state of RNA vaccines, recombinant adenovirus vector-based vaccines, and advances from biomaterials and engineering that address these important public health challenges.

Structure, Function, and Antigenicity of the SARS-CoV-2 Spike Glycoprotein.

The emergence of SARS-CoV-2 has resulted in >90,000 infections and >3,000 deaths. Coronavirus spike (S) glycoproteins promote entry into cells and are the main target of antibodies. We show that SARS-CoV-2 S uses ACE2 to enter cells and that the receptor-binding domains of SARS-CoV-2 S and SARS-CoV S bind with similar affinities to human ACE2, correlating with the efficient spread of SARS-CoV-2 among humans. We found that the SARS-CoV-2 S glycoprotein harbors a furin cleavage site at the boundary between the S1/S2 subunits, which is processed during biogenesis and sets this virus apart from SARS-CoV and SARS-related CoVs. We determined cryo-EM structures of the SARS-CoV-2 S ectodomain trimer, providing a blueprint for the design of vaccines and inhibitors of viral entry. Finally, we demonstrate that SARS-CoV S murine polyclonal antibodies potently inhibited SARS-CoV-2 S mediated entry into cells, indicating that cross-neutralizing antibodies targeting conserved S epitopes can be elicited upon vaccination.

The Impact of Mutations in SARS-CoV-2 Spike on Viral Infectivity and Antigenicity.

The spike protein of SARS-CoV-2 has been undergoing mutations and is highly glycosylated. It is critically important to investigate the biological significance of these mutations. Here, we investigated 80 variants and 26 glycosylation site modifications for the infectivity and reactivity to a panel of neutralizing antibodies and sera from convalescent patients. D614G, along with several variants containing both D614G and another amino acid change, were significantly more infectious. Most variants with amino acid change at receptor binding domain were less infectious, but variants including A475V, L452R, V483A, and F490L became resistant to some neutralizing antibodies. Moreover, the majority of glycosylation deletions were less infectious, whereas deletion of both N331 and N343 glycosylation drastically reduced infectivity, revealing the importance of glycosylation for viral infectivity. Interestingly, N234Q was markedly resistant to neutralizing antibodies, whereas N165Q became more sensitive. These findings could be of value in the development of vaccine and therapeutic antibodies.

Shared Immunogenic Poly-Epitope Frameshift Mutations in Microsatellite Unstable Tumors.

Microsatellite instability-high (MSI-H) tumors are characterized by high tumor mutation burden and responsiveness to checkpoint blockade. We identified tumor-specific frameshifts encoding multiple epitopes that originated from indel mutations shared among patients with MSI-H endometrial, colorectal, and stomach cancers. Epitopes derived from these shared frameshifts have high population occurrence rates, wide presence in many tumor subclones, and are predicted to bind to the most frequent MHC alleles in MSI-H patient cohorts. Neoantigens arising from these mutations are distinctly unlike self and viral antigens, signifying novel groups of potentially highly immunogenic tumor antigens. We further confirmed the immunogenicity of frameshift peptides in T cell stimulation experiments using blood mononuclear cells isolated from both healthy donors and MSI-H cancer patients. Our study uncovers the widespread occurrence and strong immunogenicity of tumor-specific antigens derived from shared frameshift mutations in MSI-H cancer and Lynch syndrome patients, suitable for the design of common "off-the-shelf" cancer vaccines.

Potent Henipavirus Neutralization by Antibodies Recognizing Diverse Sites on Hendra and Nipah Virus Receptor Binding Protein.

Hendra (HeV) and Nipah (NiV) viruses are emerging zoonotic pathogens in the Henipavirus genus causing outbreaks of disease with very high case fatality rates. Here, we report the first naturally occurring human monoclonal antibodies (mAbs) against HeV receptor binding protein (RBP). All isolated mAbs neutralized HeV, and some also neutralized NiV. Epitope binning experiments identified five major antigenic sites on HeV-RBP. Animal studies demonstrated that the most potent cross-reactive neutralizing mAbs, HENV-26 and HENV-32, protected ferrets in lethal models of infection with NiV Bangladesh 3 days after exposure. We solved the crystal structures of mAb HENV-26 in complex with both HeV-RBP and NiV-RBP and of mAb HENV-32 in complex with HeV-RBP. The studies reveal diverse sites of vulnerability on RBP recognized by potent human mAbs that inhibit virus by multiple mechanisms. These studies identify promising prophylactic antibodies and define protective epitopes that can be used in rational vaccine design.

Human Antibodies Protect against Aerosolized Eastern Equine Encephalitis Virus Infection.

Eastern equine encephalitis virus (EEEV) is one of the most virulent viruses endemic to North America. No licensed vaccines or antiviral therapeutics are available to combat this infection, which has recently shown an increase in human cases. Here, we characterize human monoclonal antibodies (mAbs) isolated from a survivor of natural EEEV infection with potent (<20 pM) inhibitory activity of EEEV. Cryo-electron microscopy reconstructions of two highly neutralizing mAbs, EEEV-33 and EEEV-143, were solved in complex with chimeric Sindbis/EEEV virions to 7.2 Å and 8.3 Å, respectively. The mAbs recognize two distinct antigenic sites that are critical for inhibiting viral entry into cells. EEEV-33 and EEEV-143 protect against disease following stringent lethal aerosol challenge of mice with highly pathogenic EEEV. These studies provide insight into the molecular basis for the neutralizing human antibody response against EEEV and can facilitate development of vaccines and candidate antibody therapeutics.

Antigen-Specific Adaptive Immunity to SARS-CoV-2 in Acute COVID-19 and Associations with Age and Disease Severity.

Limited knowledge is available on the relationship between antigen-specific immune responses and COVID-19 disease severity. We completed a combined examination of all three branches of adaptive immunity at the level of SARS-CoV-2-specific CD4+ and CD8+ T cell and neutralizing antibody responses in acute and convalescent subjects. SARS-CoV-2-specific CD4+ and CD8+ T cells were each associated with milder disease. Coordinated SARS-CoV-2-specific adaptive immune responses were associated with milder disease, suggesting roles for both CD4+ and CD8+ T cells in protective immunity in COVID-19. Notably, coordination of SARS-CoV-2 antigen-specific responses was disrupted in individuals ≥ 65 years old. Scarcity of naive T cells was also associated with aging and poor disease outcomes. A parsimonious explanation is that coordinated CD4+ T cell, CD8+ T cell, and antibody responses are protective, but uncoordinated responses frequently fail to control disease, with a connection between aging and impaired adaptive immune responses to SARS-CoV-2.

The T cell immune response against SARS-CoV-2.

The adaptive immune response is a major determinant of the clinical outcome after SARS-CoV-2 infection and underpins vaccine efficacy. T cell responses develop early and correlate with protection but are relatively impaired in severe disease and are associated with intense activation and lymphopenia. A subset of T cells primed against seasonal coronaviruses cross reacts with SARS-CoV-2 and may contribute to clinical protection, particularly in early life. T cell memory encompasses broad recognition of viral proteins, estimated at around 30 epitopes within each individual, and seems to be well sustained so far. This breadth of recognition can limit the impact of individual viral mutations and is likely to underpin protection against severe disease from viral variants, including Omicron. Current COVID-19 vaccines elicit robust T cell responses that likely contribute to remarkable protection against hospitalization or death, and novel or heterologous regimens offer the potential to further enhance cellular responses. T cell immunity plays a central role in the control of SARS-CoV-2 and its importance may have been relatively underestimated thus far.

Convergent Structures Illuminate Features for Germline Antibody Binding and Pan-Lassa Virus Neutralization.

Lassa virus (LASV) causes hemorrhagic fever and is endemic in West Africa. Protective antibody responses primarily target the LASV surface glycoprotein (GPC), and GPC-B competition group antibodies often show potent neutralizing activity in humans. However, which features confer potent and broadly neutralizing antibody responses is unclear. Here, we compared three crystal structures of LASV GPC complexed with GPC-B antibodies of varying neutralization potency. Each GPC-B antibody recognized an overlapping epitope involved in binding of two adjacent GPC monomers and preserved the prefusion trimeric conformation. Differences among GPC-antibody interactions highlighted specific residues that enhance neutralization. Using structure-guided amino acid substitutions, we increased the neutralization potency and breadth of these antibodies to include all major LASV lineages. The ability to define antibody residues that allow potent and broad neutralizing activity, together with findings from analyses of inferred germline precursors, is critical to develop potent therapeutics and for vaccine design and assessment.

Epigenetic scarring of exhausted T cells hinders memory differentiation upon eliminating chronic antigenic stimulation.

Exhausted CD8 T cells (TEX) are a distinct state of T cell differentiation associated with failure to clear chronic viruses and cancer. Immunotherapies such as PD-1 blockade can reinvigorate TEX cells, but reinvigoration is not durable. A major unanswered question is whether TEX cells differentiate into functional durable memory T cells (TMEM) upon antigen clearance. Here, using a mouse model, we found that upon eliminating chronic antigenic stimulation, TEX cells partially (re)acquire phenotypic and transcriptional features of TMEM cells. These 'recovering' TEX cells originated from the T cell factor (TCF-1+) TEX progenitor subset. Nevertheless, the recall capacity of these recovering TEX cells remained compromised as compared to TMEM cells. Chromatin-accessibility profiling revealed a failure to recover core memory epigenetic circuits and maintenance of a largely exhausted open chromatin landscape. Thus, despite some phenotypic and transcriptional recovery upon antigen clearance, exhaustion leaves durable epigenetic scars constraining future immune responses. These results support epigenetic remodeling interventions for TEX cell-targeted immunotherapies.

High-throughput and high-dimensional single-cell analysis of antigen-specific CD8+ T cells.

Although critical to T cell function, antigen specificity is often omitted in high-throughput multiomics-based T cell profiling due to technical challenges. We describe a high-dimensional, tetramer-associated T cell antigen receptor (TCR) sequencing (TetTCR-SeqHD) method to simultaneously profile cognate antigen specificities, TCR sequences, targeted gene expression and surface-protein expression from tens of thousands of single cells. Using human polyclonal CD8+ T cells with known antigen specificity and TCR sequences, we demonstrate over 98% precision for detecting the correct antigen specificity. We also evaluate gene expression and phenotypic differences among antigen-specific CD8+ T cells and characterize phenotype signatures of influenza- and Epstein-Barr virus-specific CD8+ T cells that are unique to their pathogen targets. Moreover, with the high-throughput capacity of profiling hundreds of antigens simultaneously, we apply TetTCR-SeqHD to identify antigens that preferentially enrich cognate CD8+ T cells in patients with type 1 diabetes compared to healthy controls and discover a TCR that cross-reacts with diabetes-related and microbiome antigens. TetTCR-SeqHD is a powerful approach for profiling T cell responses in humans and mice.

Memory-like HCV-specific CD8+ T cells retain a molecular scar after cure of chronic HCV infection.

In chronic hepatitis C virus (HCV) infection, exhausted HCV-specific CD8+ T cells comprise memory-like and terminally exhausted subsets. However, little is known about the molecular profile and fate of these two subsets after the elimination of chronic antigen stimulation by direct-acting antiviral (DAA) therapy. Here, we report a progenitor-progeny relationship between memory-like and terminally exhausted HCV-specific CD8+ T cells via an intermediate subset. Single-cell transcriptomics implicated that memory-like cells are maintained and terminally exhausted cells are lost after DAA-mediated cure, resulting in a memory polarization of the overall HCV-specific CD8+ T cell response. However, an exhausted core signature of memory-like CD8+ T cells was still detectable, including, to a smaller extent, in HCV-specific CD8+ T cells targeting variant epitopes. These results identify a molecular signature of T cell exhaustion that is maintained as a chronic scar in HCV-specific CD8+ T cells even after the cessation of chronic antigen stimulation.