Mouse marginal zone B cells harbor specificities similar to human broadly neutralizing HIV antibodies

Fingolimod-Conjugated Charge-Altering Releasable Transporters Efficiently and Specifically Deliver mRNA to Lymphocytes In Vivo and In Vitro

Charge-altering releasable transporters (CARTs) are a class of oligonucleotide delivery vehicles shown to be effective for delivery of messenger RNA (mRNA) both in vitro and in vivo. Here, we exploited the chemical versatility of the CART synthesis to generate CARTs containing the small-molecule drug fingolimod (FTY720) as a strategy to increase mRNA delivery and expression in lymphocytes through a specific ligand-receptor interaction. Fingolimod is an FDA-approved small-molecule drug that, upon in vivo phosphorylation, binds to the sphingosine-1-phosphate receptor 1 (S1P1), which is highly expressed on lymphocytes. Compared to its non-fingolimod-conjugated analogue, the fingolimod-conjugated CART achieved superior transfection of activated human and murine T and B lymphocytes in vitro. The higher transfection of the fingolimod-conjugated CARTs was lost when cells were exposed to a free fingolimod before transfection. In vivo, the fingolimod-conjugated CART showed increased mRNA delivery to marginal zone B cells and NK cells in the spleen, relative to CARTs lacking fingolimod. Moreover, fingolimod-CART-mediated mRNA delivery induces peripheral blood T-cell depletion similar to free fingolimod. Thus, we show that functionalization of CARTs with a pharmacologically validated small molecule can increase transfection of a cellular population of interest while conferring some of the targeting properties of the conjugated small molecule to the CARTs.

Therapeutic activity of an inhaled potent SARS-CoV-2 neutralizing human monoclonal antibody in hamsters

SARS-CoV-2 infection results in viral burden in the respiratory tract, enabling transmission and leading to substantial lung pathology. The 1212C2 fully human monoclonal antibody was derived from an IgM memory B cell of a COVID-19 patient, has high affinity for the Spike protein receptor binding domain, neutralizes SARS-CoV-2, and exhibits in vivo prophylactic and therapeutic activity in hamsters when delivered intraperitoneally, reducing upper and lower respiratory viral burden and lung pathology. Inhalation of nebulized 1212C2 at levels as low as 0.6 mg/kg, corresponding to 0.03 mg/kg lung-deposited dose, reduced the viral burden below the detection limit and mitigated lung pathology. The therapeutic efficacy of an exceedingly low dose of inhaled 1212C2 supports the rationale for local lung delivery for dose-sparing benefits, as compared to the conventional parenteral route of administration. These results suggest that the clinical development of 1212C2 formulated and delivered via inhalation for the treatment of SARS-CoV-2 infection should be considered.

The 1212C2 human monoclonal antibody potently neutralizes SARS-CoV-2

1212C2 mAb was isolated from an IgM memory B cell of a recovered COVID-19 patient

Inhaled 1212C2 mAb is rapidly distributed in the lungs

Inhaled 1212C2 mAb treatment reduces viral burden and lung pathology in hamsters

Histone H2A-Reactive B Cells Are Functionally Anergic in Healthy Mice With Potential to Provide Humoral Protection Against HIV-1

Peripheral tolerance is essential for silencing weakly autoreactive B cells that have escaped central tolerance, but it is unclear why these potentially pathogenic B cells are retained rather than being eliminated entirely. Release from peripheral tolerance restraint can occur under certain circumstances (i.e., strong TLR stimulus), that are present during infection. In this regard, we hypothesized that autoreactive B cells could function as a reserve population that can be activated to contribute to the humoral immune response, particularly with pathogens, such as HIV-1, that exploit immune tolerance to avoid host defense. In this study, we identify a population of autoreactive B cells with the potential to neutralize HIV-1 and experimentally release them from the functional restrictions of peripheral tolerance. We have previously identified murine monoclonal antibodies that displayed autoreactivity against histone H2A and neutralized HIV-1 in vitro. Here, we identify additional H2A-reactive IgM monoclonal antibodies and demonstrate that they are both autoreactive and polyreactive with self and foreign antigens and are able to neutralize multiple clades of tier 2 HIV-1. Flow cytometric analysis of H2A-reactive B cells in naïve wildtype mice revealed that these B cells are present in peripheral B cell populations and we further document that murine H2A-reactive B cells are restrained by peripheral tolerance mechanisms. Specifically, we show endogenous H2A-reactive B cells display increased expression of the inhibitory mediators CD5 and phosphatase and tensin homolog (PTEN) phosphatase and fail to mobilize calcium upon immunoreceptor stimulation; all characterized markers of anergy. Moreover, we show that toll-like receptor stimulation or provision of CD4 T cell help induces the in vitro production of H2A-reactive antibodies, breaking tolerance. Thus, we have identified a novel poly/autoreactive B cell population that has the potential to neutralize HIV-1 but is silenced by immune tolerance.

Persistence of HIV-1 Env-Specific Plasmablast Lineages in Plasma Cells after Vaccination in Humans

Induction of persistent HIV-1 Envelope (Env) specific antibody (Ab) is a primary goal of HIV vaccine strategies; however, it is unclear whether HIV Env immunization in humans induces bone marrow plasma cells, the presumed source of long-lived systemic Ab. To define the features of Env-specific plasma cells after vaccination, samples were obtained from HVTN 105, a phase I trial testing the same gp120 protein immunogen, AIDSVAX B/E, used in RV144, along with a DNA immunogen in various prime and boost strategies. Boosting regimens that included AIDSVAX B/E induced robust peripheral blood plasmablast responses. The Env-specific immunoglobulin repertoire of the plasmablasts is dominated by VH1 gene usage and targeting of the V3 region. Numerous plasmablast-derived immunoglobulin lineages persisted in the bone marrow >8 months after immunization, including in the CD138+ long-lived plasma cell compartment. These findings identify a cellular linkage for the development of sustained Env-specific Abs following vaccination in humans.

IL-33 enhances the kinetics and quality of the antibody response to a DNA and protein-based HIV-1 Env vaccine

Induction of a sustained and broad antibody (Ab) response is a major goal in developing a protective HIV-1 vaccine. DNA priming alone shows reduced levels of immunogenicity; however, when combined with protein boosting is an attractive vaccination strategy for induction of humoral responses. Using the VC10014 DNA and protein-based vaccine consisting of HIV-1 envelope (Env) gp160 plasmids and trimeric gp140 proteins derived from an HIV-1 clade B infected subject who developed broadly neutralizing serum Abs, and which has been previously demonstrated to induce Tier 2 heterologous neutralizing Abs in rhesus macaques, we evaluated whether MPLA and IL-33 when administered during the DNA priming phase enhances the humoral response in mice. The addition of IL-33 during the gp160 DNA priming phase resulted in high titer gp120-specific plasma IgG after the first immunization. The IL-33 treated mice had higher plasma IgG Ab avidity, breadth, and durability after DNA and protein co-immunization with alum adjuvant as compared to MPLA and alum only treated mice. IL-33 was also associated with a significant IgM Env-specific response and expansion of peritoneal and splenic B-1b B cells. These results indicate that DNA priming in the presence of exogenous IL-33 qualitatively alters the HIV-1 Env-specific humoral response, improving the kinetics and breadth of potentially protective Ab.

Breaching peripheral tolerance promotes the production of HIV-1-neutralizing antibodies

Schroeder et al. demonstrate that when peripheral tolerance is relaxed, tier 2 HIV-1–neutralizing antibodies can be elicited and identify new autoreactive antibody specificities against histone H2A capable of neutralizing tier 2 HIV-1.

A subset of characterized HIV-1 broadly neutralizing antibodies (bnAbs) are polyreactive with additional specificities for self-antigens and it has been proposed immunological tolerance may present a barrier to their participation in protective humoral immunity. We address this hypothesis by immunizing autoimmune-prone mice with HIV-1 Envelope (Env) and characterizing the primary antibody response for HIV-1 neutralization. We find autoimmune mice generate neutralizing antibody responses to tier 2 HIV-1 strains with alum treatment alone in the absence of Env. Importantly, experimentally breaching immunological tolerance in wild-type mice also leads to the production of tier 2 HIV-1–neutralizing antibodies, which increase in breadth and potency following Env immunization. In both genetically prone and experimentally induced mouse models of autoimmunity, increased serum levels of IgM anti-histone H2A autoantibodies significantly correlated with tier 2 HIV-1 neutralization, and anti-H2A antibody clones were found to neutralize HIV-1. These data demonstrate that breaching peripheral tolerance permits a cross-reactive HIV-1 autoantibody response able to neutralize HIV-1.

Humanized Immunoglobulin Mice: Models for HIV Vaccine Testing and Studying the Broadly Neutralizing Antibody Problem

A vaccine that can effectively prevent HIV-1 transmission remains paramount to ending the HIV pandemic, but to do so, will likely need to induce broadly neutralizing antibody (bnAb) responses. A major technical hurdle toward achieving this goal has been a shortage of animal models with the ability to systematically pinpoint roadblocks to bnAb induction and to rank vaccine strategies based on their ability to stimulate bnAb development. Over the past 6 years, immunoglobulin (Ig) knock-in (KI) technology has been leveraged to express bnAbs in mice, an approach that has enabled elucidation of various B-cell tolerance mechanisms limiting bnAb production and evaluation of strategies to circumvent such processes. From these studies, in conjunction with the wealth of information recently obtained regarding the evolutionary pathways and paratopes/epitopes of multiple bnAbs, it has become clear that the very features of bnAbs desired for their function will be problematic to elicit by traditional vaccine paradigms, necessitating more iterative testing of new vaccine concepts. To meet this need, novel bnAb KI models have now been engineered to express either inferred prerearranged V(D)J exons (or unrearranged germline V, D, or J segments that can be assembled into functional rearranged V(D)J exons) encoding predecessors of mature bnAbs. One encouraging approach that has materialized from studies using such newer models is sequential administration of immunogens designed to bind progressively more mature bnAb predecessors. In this review, insights into the regulation and induction of bnAbs based on the use of KI models will be discussed, as will new Ig KI approaches for higher-throughput production and/or altering expression of bnAbs in vivo, so as to further enable vaccine-guided bnAb induction studies.

Blood B Lymphocyte Stimulator (BLyS)/BAFF levels may reflect natural immunity to HIV in highly exposed uninfected Beninese Commercial Sex Workers

We have previously shown that excess B lymphocyte Stimulator (BLyS)/BAFF in plasma and on surface of blood dendritic cells (DC) of HIV-infected progressors coincides with B-cell dysregulations and increased frequencies of "precursor" innate marginal zone (MZ)-like B-cells. In contrast, both blood BLyS levels and frequencies of this population remained unaltered in HIV elite-controllers. Based on these observations, we hypothesized that control of BLyS and innate B-cell status could be associated with natural immunity against HIV infection. Therefore, we assessed blood BLyS levels and B-cell status in HIV highly-exposed commercial sex workers (CSWs) from Benin. We found blood BLyS levels of HIV-uninfected CSWs were lower than those observed in both HIV-infected CSW and HIV-uninfected non-CSW groups. Furthermore, levels of BLyS expression on blood T-cells and monocytes were lower in HIV-uninfected CSWs when compared to HIV-infected CSWs, but higher than those observed for HIV-uninfected non-CSWs. Concomitantly, HIV-infected CSWs presented a dysregulated blood B-cell compartment, characterized by increased total IgG1, increased frequencies of populations presenting immature and/or innate profiles and a higher ratio of IgG(+)/IgA(+) plasmablasts. In contrast, relatively low levels of BLyS in the blood of HIV-uninfected CSWs coincided with a rather preserved B-cell compartment.

DNA vaccine molecular adjuvants SP-D-BAFF and SP-D-APRIL enhance anti-gp120 immune response and increase HIV-1 neutralizing antibody titers

Broadly neutralizing antibodies (bNAbs) specific for conserved epitopes on the HIV-1 envelope (Env) are believed to be essential for protection against multiple HIV-1 clades. However, vaccines capable of stimulating the production of bNAbs remain a major challenge. Given that polyreactivity and autoreactivity are considered important characteristics of anti-HIV bNAbs, we designed an HIV vaccine incorporating the molecular adjuvants BAFF (B cell activating factor) and APRIL (a proliferation-inducing ligand) with the potential to facilitate the maturation of polyreactive and autoreactive B cells as well as to enhance the affinity and/or avidity of Env-specific antibodies. We designed recombinant DNA plasmids encoding soluble multitrimers of BAFF and APRIL using surfactant protein D as a scaffold, and we vaccinated mice with these molecular adjuvants using DNA and DNA-protein vaccination strategies. We found that immunization of mice with a DNA vaccine encoding BAFF or APRIL multitrimers, together with interleukin 12 (IL-12) and membrane-bound HIV-1 Env gp140, induced neutralizing antibodies against tier 1 and tier 2 (vaccine strain) viruses. The APRIL-containing vaccine was particularly effective at generating tier 2 neutralizing antibodies following a protein boost. These BAFF and APRIL effects coincided with an enhanced germinal center (GC) reaction, increased anti-gp120 antibody-secreting cells, and increased anti-gp120 functional avidity. Notably, BAFF and APRIL did not cause indiscriminate B cell expansion or an increase in total IgG. We propose that BAFF and APRIL multitrimers are promising molecular adjuvants for vaccines designed to induce bNAbs against HIV-1.

IMPORTANCE

Recent identification of antibodies that neutralize most HIV-1 strains has revived hopes and efforts to create novel vaccines that can effectively stimulate HIV-1 neutralizing antibodies. However, the multiple immune evasion properties of HIV have hampered these efforts. These include the instability of the gp120 trimer, the inaccessibility of the conserved sequences, highly variable protein sequences, and the loss of HIV-1-specific antibody-producing cells during development. We have shown previously that tumor necrosis factor (TNF) superfamily ligands, including BAFF and APRIL, can be multitrimerized using the lung protein SP-D (surfactant protein D), enhancing immune responses. Here we show that DNA or DNA-protein vaccines encoding BAFF or APRIL multitrimers, IL-12p70, and membrane-bound HIV-1 Env gp140 induced tier 1 and tier 2 neutralizing antibodies in a mouse model. BAFF and APRIL enhanced the immune reaction, improved antibody binding, and increased the numbers of anti-HIV-1 antibody-secreting cells. Adaptation of this vaccine design may prove useful in designing preventive HIV-1 vaccines for humans.

Autoreactivity in HIV-1 broadly neutralizing antibodies: implications for their function and induction by vaccination

PURPOSE OF REVIEW

This review discusses progress in understanding the impact of immune tolerance on inducing broadly neutralizing antibodies (bnAbs), and how such knowledge can be incorporated into novel immunization approaches.

RECENT FINDINGS

Over 120 bnAbs have now been isolated, all of which bear unusual features associated with host tolerance controls, but paradoxically may also be required for their function. Evidence that poly/autoreactivity of membrane proximal external region bnAbs can invoke such controls has been demonstrated by knock-in technology, highlighting its potential for studying the impact of tolerance in the generation of bnAb lineages to distinct HIV-1 envelope targets. The requirement for extensive affinity maturation in developing neutralization breadth/potency during infection is being examined, and similar studies in the setting of immunization will be aided by testing novel vaccine approaches in knock-in models that either selectively express reverted V(D)J rearrangements, or unrearranged germline segments, from which bnAb lineages originate.

SUMMARY

It is increasingly apparent that immune tolerance, sometimes invoked by self-reactivity that overlaps with bnAb epitope specificity, adds to a formidable set of roadblocks impeding bnAb induction. The path to an effective HIV-1 vaccine may thus benefit from a deeper understanding of host controls, including categorizing those that are unique or common at distinct bnAb targets, and ranking those most feasible to overcome by immunization. Ultimately, such emerging information will be critical to incorporate into new vaccine approaches that can be tested in human trials.

IL-10 and lymphotoxin-α expression profiles within marginal zone-like B-cell populations are associated with control of HIV-1 disease progression

Understanding how the immune system facilitates or controls HIV-1 disease progression has important implications for the design of effective interventions. We report that although B-cell dysregulations associated with HIV-1 disease progression are accompanied by an overall decrease in the percentage of total blood B-cells, we observe an increase in relative frequencies of cells presenting characteristics of both transitional immature and first-line marginal zone (MZ) B-cell populations, we designated as precursor MZ-like B-cells. B-cells with similar attributes have been associated with IL-10 expression and "regulatory" potential. As such, the relative frequencies of precursor MZ-like B-cells expressing IL-10 are increased in the blood of viremic HIV-1-infected individuals when compared to HIV-negative subjects. Importantly, in aviremic HIV-1 Elite-Controllers (EC), we found unaltered relative percentages of precursor MZ-like B-cells which presented normal IL-10 expression patterns. Furthermore, EC had increased relative frequencies of blood MZ-like B-cells expressing LT-α. Thus in contrast to viremic HIV-1-infected individuals, EC present MZ-like B-cell populations which IL-10 and LT-α expression profiles may favour homeostasis of immune responses and lymphoid microenvironments.