Hisashi Arase

Antigen-specific regulation of T cell response is crucial for limiting hyperimmune response. However, the molecular mechanisms governing specific immune regulation remain unclear. In this study, we discover that antibodies specific to the antigen peptide-MHC class II complex are produced during helper T cell responses to various antigens, including hen egg lysozyme and proteolipid protein peptide. These antibodies specifically inhibit T cell receptor (TCR) recognition of MHC class II molecules presenting specific antigen peptide. We term these antibodies ‘immune-induced TCR-like antibodies’ or iTabs. Immunization with peptides containing flanking residues induces iTabs whereas immunization with peptides lacking flanking residues does not. Furthermore, we show that immunization with iTab-inducible peptide or iTab treatment suppress autoimmune disease development in a mouse model of experimental autoimmune encephalomyelitis. Thus, our findings provide a strategy for suppressing antigen-specific helper T cell responses using specific peptides, potentially controlling autoimmune diseases.

Restoring effective antiviral immunity remains a major challenge in HIV infection. Among emerging immune checkpoint molecules, the inhibitory receptors LILRB1 and LILRB2 have been proposed as therapeutic targets, yet their in vivo function remains undefined due to the lack of cross-reactive blocking antibodies for relevant preclinical models. To address this, we developed a dual-specific blocking monoclonal antibody, mac20G10, targeting cynomolgus macaque LILRB1 and LILRB2 and assessed its immunomodulatory activity in an SIV model of infection. Pharmacodynamics analyses demonstrated that mac20G10 persisted in circulation and engaged target myeloid cells for up to 14 days without detectable adverse effects. A single administration prior to SIVmac251 infection enhanced early myeloid immune activation, characterized by increased frequencies of CD80 ⁺ pDC and CD80 ⁺ monocyte/macrophage subsets in blood and lymphoid tissues. These changes were accompanied by increased plasma levels of IFN-λ, IL8, and IL-1RA during acute infection. Although viral replication remained unchanged, mac20G10 treatment promoted the development of SIV-specific memory CD8⁺ T-cell responses. Together, these findings provide in vivo evidence that LILRB1 and LILRB2 function as myeloid immune checkpoints restraining antiviral priming, supporting this pathway as a rational target for combination immunotherapeutic strategies aimed at achieving durable HIV remission during analytic treatment interruption.

Anti-β2GPI/HLA-DR antibody, chronic endometritis (CE), and endometrial dysbiosis are likely to be associated with the etiologies of recurrent pregnancy loss (RPL). This prospective cohort study aimed to investigate these new risk factors together with conventional causes for RPL, and to evaluate pregnancy outcomes in women individually treated. A total of 87 women with RPL underwent conventional assessment together with anti-β2GPI/HLA-DR antibody measurements, CD138 immunohistochemistry for CE, and 16S rRNA sequence analysis for endometrial microbiome. Women with anti-β2GPI/HLA-DR antibody, CE, and endometrial dysbiosis received low-dose aspirin and heparin, antibiotics, and probiotics, respectively. Pregnancy outcomes of the participants were assessed. Anti-β2GPI/HLA-DR antibody, CE, non-Lactobacillus-dominant microbiome (NLDM)-1 (Lactobacillus + Bifidobacterium < 80%), and NLDM-2 (Lactobacillus without iners + Bifidobacterium < 80%) were detected in 16 (18.4%), 22 (25.3%), 27 (31.0%), and 46 (52.8%) women, respectively. Based on conventional assessment, 65.5% of women with RPL were classified as unexplained etiology; however, the percentage reduced to 16.1% when these new tests were assessed together. All 9 pregnancies with anti-β2GPI/HLA-DR antibody, 13 (92.9%) of 14 pregnancies with CE, and 24 (92.3%) of 26 pregnancies with NLDM-2 resulted in live birth. Assessment of these new tests may be clinically useful for reducing the proportion of unexplained RPL, and for providing high live birth rates if women receive relevant treatments.

Lipid nanoparticles (LNPs) are a powerful delivery platform for nucleic acid therapeutics such as mRNA vaccines and gene therapies. Central to their success are ionizable lipids, which facilitate the cellular uptake and endosomal escape of nucleic acids. However, achieving a high delivery efficiency often comes with the drawback of increased cytotoxicity. Here, we report a chemical, biological, and toxicological investigation into the three stereoisomers of ALC315, a mixture of which constitutes one of the most successful marketed ionizable lipids for LNPs. We demonstrate that the individual stereoisomers of ALC315 can be accessed by either the asymmetric chemical synthesis or chromatography of an intermediate. An LNP formulation based on a single stereoisomer of ALC315 enhances mRNA transfer efficiency while reducing the associated cytotoxicity in human cell lines. Our results underscore the potential of stereochemically pure ionizable lipids as key components in the development of next-generation nucleic acid therapies, offering an enhanced delivery performance and better safety profiles.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variants have acquired enhanced infectivity compared to earlier variants. To elucidate the underlying molecular mechanisms, we conducted CRISPR library screening to identify cell surface molecules that interact with the Omicron spike protein. Our findings revealed a significantly higher affinity between the Omicron spike and cell surface heparan sulfate compared to the wild-type spike. This increased binding affinity enables Omicron variants to infect cells expressing low levels of ACE2, which are minimally infected by the wild-type virus. Mutational analysis of heparan sulfate binding sites on the Omicron spike protein, coupled with electrostatic potential mapping, suggested that the accumulation of positively charged mutations has contributed to the enhanced heparan sulfate binding. Comparative analysis of heparan sulfate binding among Omicron subvariants—including BA.1, BA.2, BA.4, BA.5, XBB.1, and BA.2.86—revealed that most are likely to bind efficiently to heparan sulfate, but potential heparan sulfate binding sites of the spike protein have shifted from the early Omicron variants to more recent ones. Furthermore, we discovered that cell surface heparan sulfate proteoglycans are cleaved by TMPRSS2, a protease essential for wild-type SARS-CoV-2 infection. These findings suggest that SARS-CoV-2 is evolving to enhance its infectivity by optimizing its interaction with cell surface heparan sulfate. IMPORTANCE: The Omicron variant has evolved to become highly infectious by acquiring numerous mutations. Understanding the impact of these mutations can provide valuable insights into the drivers of viral evolution and aid in the development of improved viral surveillance and vaccines. Our study demonstrates that the Omicron variants contain mutations that enhance their ability to bind to heparan sulfate. Highly infectious human viruses often utilize heparan sulfate for infection, suggesting that heparan sulfate likely plays a crucial role in viral adaptation to human hosts. Furthermore, we found that cell surface heparan sulfate proteoglycans are sensitive to TMPRSS2, while most other cell surface proteins are resistant to TMPRSS2. Given that TMPRSS2 is known to enhance the infectivity of earlier severe acute respiratory syndrome coronavirus 2 variants but cleaves heparan sulfate proteoglycans, it is probable that the high heparan sulfate binding acquired by the Omicron variant contributes to its decreased infectivity against TMPRSS2-expressing cells compared to earlier variants.

Natural killer (NK) cells use inhibitory and activating immune receptors to differentiate between human cells and pathogens. Signalling by these receptors determines whether an NK cell becomes activated and destroys a target cell. In some cases, such as killer immunoglobulin-like receptors, immune receptors are found in pairs, with inhibitory and activating receptors containing nearly identical extracellular ligand-binding domains coupled to different intracellular signalling domains¹. Previous studies showed that repetitive interspersed family (RIFIN) proteins, displayed on the surfaces of Plasmodium falciparum-infected erythrocytes, can bind to inhibitory immune receptors and dampen NK cell activation^2,3, reducing parasite killing. However, no pathogen-derived ligand has been identified for any human activating receptor. Here we identified a clade of RIFINs that bind to inhibitory immune receptor KIR2DL1 more strongly than KIR2DL1 binds to the human ligand (MHC class I). This interaction mediates inhibitory signalling and suppresses the activation of KIR2DL1-expressing NK cells. We show that KIR2DL1-binding RIFINs are abundant in field-isolated strains from both Africa and Asia and reveal how the two RIFINs bind to KIR2DL1. The RIFIN binding surface of KIR2DL1 is conserved in the cognate activating immune receptor KIR2DS1. We find that KIR2DL1-binding RIFINs can also bind to KIR2DS1, resulting in the activation of KIR2DS1-expressing NK cells. This study demonstrates that activating killer immunoglobulin-like receptors can recruit NK cells to target a pathogen and reveals a potential role for activating immune receptors in controlling malaria infection.

Antigen-specific regulation of T cell response is crucial for limiting hyperimmune response. In this study, we discovered that antibodies specific to the antigen peptide-MHC class II complex are produced during helper T cell responses to various antigens. These antibodies specifically inhibited T cell receptor (TCR) recognition of MHC class II molecules presenting specific antigen peptide. We have termed these antibodies ‘immuneinduced TCR-like antibodies’ (iTabs). Immunization with peptides containing flanking residues induced iTabs, whereas immunization with peptides lacking flanking residues did not. Furthermore, immunization of iTab-inducible peptide as well as iTab treatment suppressed autoimmune disease development. Our findings provide a strategy for suppressing antigen-specific helper T cell responses using specific peptides, potentially controlling autoimmune diseases.

The tumor microenvironment (TME) contains a number of immune-suppressive cells such as T helper 1–polarized regulatory T cells (T _H 1-T _reg cells). However, little is known about the mechanism behind the abundant presence of T _H 1-T _reg cells in the TME. We demonstrate that selective depletion of arginase I (Arg1)–expressing tumor-associated macrophages (Arg1 ⁺ TAMs) inhibits tumor growth and concurrently reduces the ratio of T _H 1-T _reg cells in the TME. Arg1 ⁺ TAMs secrete the chemokine platelet factor 4 (PF4), which reinforces interferon-γ (IFN-γ)–induced T _reg cell polarization into T _H 1-T _reg cells in a manner dependent on CXCR3 and the IFN-γ receptor. Both genetic PF4 inactivation and PF4 neutralization hinder T _H 1-T _reg cell accumulation in the TME and reduce tumor growth. Collectively, our study highlights the importance of Arg1 ⁺ TAM–produced PF4 for high T _H 1-T _reg cell levels in the TME to suppress antitumor immunity.

Antibody dependent enhancement (ADE) is a serious concern in vaccine development. The canonical ADE pathways are dependent on the fragment crystallizable (Fc) region of the antibody. In SARS-CoV-2 several antibodies have been discovered that inflict ADE in vitro. These antibodies target the N-terminal domain (NTD) of the SARS-CoV-2 spike protein. We previously proposed that these NTD-targeting infection-enhancing antibodies (NIEAs) cross-link neighboring spike proteins via their NTDs, and that this results in a decoupling between the NTD and receptor binding domain (RBD), facilitating the “RBD down” to “up” transition. In this study we present a combination of molecular dynamics simulations and cryogenic electron microscopy data that, together, demonstrate that NIEAs are indeed able to cross-link neighboring SARS-CoV-2 spike proteins, and that this cross-linking results in a decoupling of the NTD and RBD domains. These findings provide support for an Fc region independent ADE pathway that is not only relevant for SARS-CoV-2 but also for other viruses of which the spike proteins undergo a conformational change upon host cell entry.