Mohammed Rafii-El-Idrissi Benhnia

Selective CD4+ T Cell Help for Antibody Responses to a Large Viral Pathogen: Deterministic Linkage of Specificities

Antibody responses are critical components of protective immune responses to many pathogens, but parameters determining which proteins are targeted remain unclear. Vaccination with individual MHC-II-restricted vaccinia virus (VACV, smallpox vaccine) epitopes revealed that CD4(+) T cell help to B cells was surprisingly nontransferable to other virion protein specificities. Many VACV CD4(+) T cell responses identified in an unbiased screen targeted antibody virion protein targets, consistent with deterministic linkage between specificities. We tested the deterministic linkage model by efficiently predicting new vaccinia MHC II epitopes (830% improved efficiency). Finally, we showed CD4(+) T cell help was limiting for neutralizing antibody development and protective immunity in vivo. In contrast to the standard model, these data indicate individual proteins are the unit of B cell-T cell recognition for a large virus. Therefore, MHC restriction is a key selective event for the antiviral antibody response and is probably important for vaccine development to large pathogens.

Vaccinia Virus Extracellular Enveloped Virion Neutralization In Vitro and Protection In Vivo Depend on Complement

ABSTRACT Antibody neutralization is an important component of protective immunity against vaccinia virus (VACV). Two distinct virion forms, mature virion and enveloped virion (MV and EV, respectively), possess separate functions and nonoverlapping immunological properties. In this study we examined the mechanics of EV neutralization, focusing on EV protein B5 (also called B5R). We show that neutralization of EV is predominantly complement dependent. From a panel of high-affinity anti-B5 monoclonal antibodies (MAbs), the only potent neutralizer in vitro (90% at 535 ng/ml) was an immunoglobulin G2a (IgG2a), and neutralization was complement mediated. This MAb was the most protective in vivo against lethal intranasal VACV challenge. Further studies demonstrated that in vivo depletion of complement caused a >50% loss of anti-B5 IgG2a protection, directly establishing the importance of complement for protection against the EV form. However, the mechanism of protection is not sterilizing immunity via elimination of the inoculum as the viral inoculum consisted of a purified MV form. The prevention of illness in vivo indicated rapid control of infection. We further demonstrate that antibody-mediated killing of VACV-infected cells expressing surface B5 is a second protective mechanism provided by complement-fixing anti-B5 IgG. Cell killing was very efficient, and this effector function was highly isotype specific. These results indicate that anti-B5 antibody-directed cell lysis via complement is a powerful mechanism for clearance of infected cells, keeping poxvirus-infected cells from being invisible to humoral immune responses. These findings highlight the importance of multiple mechanisms of antibody-mediated protection against VACV and point to key immunobiological differences between MVs and EVs that impact the outcome of infection.

NKT cells prevent chronic joint inflammation after infection with Borrelia burgdorferi

Borrelia burgdorferi is the etiologic agent of Lyme disease, a multisystem inflammatory disorder that principally targets the skin, joints, heart, and nervous system. The role of T lymphocytes in the development of chronic inflammation resulting from B. burgdorferi infection has been controversial. We previously showed that natural killer T (NKT) cells with an invariant (i) TCR α chain (iNKT cells) recognize glycolipids from B. burgdorferi, but did not establish an in vivo role for iNKT cells in Lyme disease pathogenesis. Here, we evaluate the importance of iNKT cells for host defense against these pathogenic spirochetes by using Vα14i NKT cell-deficient (Jα18−/−) BALB/c mice. On tick inoculation with B. burgdorferi, Jα18−/− mice exhibited more severe and prolonged arthritis as well as a reduced ability to clear spirochetes from infected tissues. Vα14i NKT cell deficiency also resulted in increased production of antibodies directed against both B. burgdorferi protein antigens and borrelial diacylglycerols; the latter finding demonstrates that anti-glycolipid antibody production does not require cognate help from Vα14i NKT cells. Vα14i NKT cells in infected wild-type mice expressed surface activation markers and produced IFNγ in vivo after infection, suggesting a participatory role for this unique population in cellular immunity. Our data are consistent with the hypothesis that the antigen-specific activation of Vα14i NKT cells is important for the prevention of persistent joint inflammation and spirochete clearance, and they counter the long-standing notion that humoral rather than cellular immunity is sufficient to facilitate Lyme disease resolution.

Redundancy and Plasticity of Neutralizing Antibody Responses Are Cornerstone Attributes of the Human Immune Response to the Smallpox Vaccine

ABSTRACT The smallpox vaccine is widely considered the gold standard for human vaccines, yet the key antibody targets in humans remain unclear. We endeavored to identify a stereotypic, dominant, mature virion (MV) neutralizing antibody target in humans which could be used as a diagnostic serological marker of protective humoral immunity induced by the smallpox vaccine (vaccinia virus [VACV]). We have instead found that diversity is a defining characteristic of the human antibody response to the smallpox vaccine. We show that H3 is the most immunodominant VACV neutralizing antibody target, as determined by correlation analysis of immunoglobulin G (IgG) specificities to MV neutralizing antibody titers. It was determined that purified human anti-H3 IgG is sufficient for neutralization of VACV; however, depletion or blockade of anti-H3 antibodies revealed no significant reduction in neutralization activity, showing anti-H3 IgG is not required in vaccinated humans (or mice) for neutralization of MV. Comparable results were obtained for human (and mouse) anti-L1 IgG and even for anti-H3 and anti-L1 IgG in combination. In addition to H3 and L1, human antibody responses to D8, A27, D13, and A14 exhibited statistically significant correlations with virus neutralization. Altogether, these data indicate the smallpox vaccine succeeds in generating strong neutralizing antibody responses not by eliciting a stereotypic response to a single key antigen but instead by driving development of neutralizing antibodies to multiple viral proteins, resulting in a “safety net” of highly redundant neutralizing antibody responses, the specificities of which can vary from individual to individual. We propose that this is a fundamental attribute of the smallpox vaccine.

B Cell-Specific Expression of B7-2 Is Required for Follicular Th Cell Function in Response to Vaccinia Virus

Follicular Th (TFH) cells are specialized in provision of help to B cells that is essential for promoting protective Ab responses. CD28/B7 (B7-1 and B7-2) interactions are required for germinal center (GC) formation, but it is not clear if they simply support activation of naive CD4 T cells during initiation of responses by dendritic cells or if they directly control TFH cells and/or directly influence follicular B cell differentiation. Using a model of vaccinia virus infection, we show that B7-2 but not B7-1 deficiency profoundly impaired TFH cell development but did not affect CD4 T cell priming and Th1 differentiation. Consistent with this, B7-2 but not B7-1 was required for acquisition of GC B cell phenotype, plasma cell generation, and virus-specific neutralizing Ab responses. Mixed adoptive transfer experiments indicated that bidirectional interactions between CD28 expressed on activated T cells and B7-2 expressed on follicular B cells were essential for maintenance of the TFH phenotype and GC B cell development. Our data provide new insight into the source and nature of molecules required for TFH cells to direct GC B cell responses.

Signaling through CD14 Attenuates the Inflammatory Response to Borrelia burgdorferi, the Agent of Lyme Disease

Lyme disease is a chronic inflammatory disorder caused by the spirochetal bacterium, Borrelia burgdorferi. In vitro evidence suggests that binding of spirochetal lipoproteins to CD14, a pattern recognition receptor expressed on monocytes/macrophages and polymorphonuclear cells, is a critical requirement for cellular activation and the subsequent release of proinflammatory cytokines that most likely contribute to symptomatology and clinical manifestations. To test the validity of this notion, we assessed the impact of CD14 deficiency on Lyme disease in C3H/HeN mice. Contrary to an anticipated diminution in pathology, CD14−/− mice exhibited more severe and persistent inflammation than did CD14+/+ mice. This disparity reflects altered gene regulation within immune cells that may engender the higher bacterial burden and serum cytokine levels observed in CD14−/− mice. Comparing their in vitro stimulatory activity, live spirochetes, but not lysed organisms, were a potent CD14-independent stimulus of cytokine production, triggering an exaggerated response by CD14−/− macrophages. Collectively, our in vivo and in vitro findings support the provocative notion that: 1) pattern recognition by CD14 is entirely dispensable for elaboration of an inflammatory response to B. burgdorferi, and 2) CD14-independent signaling pathways are inherently more destructive than CD14-dependent pathways. Continued study of CD14-independent signaling pathways may provide mechanistic insight into the inflammatory processes that underlie development of chronic inflammation.

Heavily Isotype-Dependent Protective Activities of Human Antibodies against Vaccinia Virus Extracellular Virion Antigen B5

ABSTRACT Antibodies against the extracellular virion (EV or EEV) form of vaccinia virus are an important component of protective immunity in animal models and likely contribute to the protection of immunized humans against poxviruses. Using fully human monoclonal antibodies (MAbs), we now have shown that the protective attributes of the human anti-B5 antibody response to the smallpox vaccine (vaccinia virus) are heavily dependent on effector functions. By switching Fc domains of a single MAb, we have definitively shown that neutralization in vitro—and protection in vivo in a mouse model—by the human anti-B5 immunoglobulin G MAbs is isotype dependent, thereby demonstrating that efficient protection by these antibodies is not simply dependent on binding an appropriate vaccinia virion antigen with high affinity but in fact requires antibody effector function. The complement components C3 and C1q, but not C5, were required for neutralization. We also have demonstrated that human MAbs against B5 can potently direct complement-dependent cytotoxicity of vaccinia virus-infected cells. Each of these results was then extended to the polyclonal human antibody response to the smallpox vaccine. A model is proposed to explain the mechanism of EV neutralization. Altogether these findings enhance our understanding of the central protective activities of smallpox vaccine-elicited antibodies in immunized humans.

Combination therapy of vaccinia virus infection with human anti-H3 and anti-B5 monoclonal antibodies in a small animal model

BACKGROUND Treatment of rare severe side effects of vaccinia virus (VACV) immunization in humans is currently very challenging. VACV possesses two immunologically distinct virion forms in vivo - intracellular mature virion (MV, IMV) and extracellular virion (EV, EEV). METHODS Antibody-mediated therapeutic efficacy was determined against VACV infection in a small animal model of progressive vaccinia. The model consisted of severe combined immunodeficiency mice infected with VACV New York City Board of Health vaccine strain and treated with monoclonal antibodies (mAbs). RESULTS Here, we show that combination therapy with two fully human mAbs against an immunodominant MV antigen, H3 (H3L), and an EV antigen, B5 (B5R), provides significantly better protection against disease and death than either single human monoclonal or human vaccinia immune globulin, the currently licensed therapeutic for side effects of smallpox vaccination. CONCLUSIONS The preclinical studies validate that this combination of mAbs against H3 and B5 is a promising approach as a poxvirus infection treatment for use in humans.

Structural and Biochemical Characterization of the Vaccinia Virus Envelope Protein D8 and Its Recognition by the Antibody LA5.

ABSTRACT Smallpox vaccine is considered a gold standard of vaccines, as it is the only one that has led to the complete eradication of an infectious disease from the human population. B cell responses are critical for the protective immunity induced by the vaccine, yet their targeted epitopes recognized in humans remain poorly described. Here we describe the biochemical and structural characterization of one of the immunodominant vaccinia virus (VACV) antigens, D8, and its binding to the monoclonal antibody LA5, which is capable of neutralizing VACV in the presence of complement. The full-length D8 ectodomain was found to form a tetramer. We determined the crystal structure of the LA5 Fab-monomeric D8 complex at a resolution of 2.1 Å, as well as the unliganded structures of D8 and LA5-Fab at resolutions of 1.42 Å and 1.6 Å, respectively. D8 features a carbonic anhydrase (CAH) fold that has evolved to bind to the glycosaminoglycan (GAG) chondroitin sulfate (CS) on host cells. The central positively charged crevice of D8 was predicted to be the CS binding site by automated docking experiments. Furthermore, sequence alignment of various poxvirus D8 orthologs revealed that this crevice is structurally conserved. The D8 epitope is formed by 23 discontinuous residues that are spread across 80% of the D8 protein sequence. Interestingly, LA5 binds with a high-affinity lock-and-key mechanism above this crevice with an unusually large antibody-antigen interface, burying 2,434 Å2 of protein surface.

Monocyte Phenotype and Polyfunctionality Are Associated With Elevated Soluble Inflammatory Markers, Cytomegalovirus Infection, and Functional and Cognitive Decline in Elderly Adults

Monocytes are mediators of the inflammatory response and include three subsets: classical, intermediate, and nonclassical. Little is known about the phenotypical and functional age-related changes in monocytes and their association with soluble inflammatory biomarkers, cytomegalovirus infection, and functional and mental decline. We assayed the activation ex vivo and the responsiveness to TLR2 and TLR4 agonists in vitro in the three subsets and assessed the intracellular production of IL1-alpha (α), IL1-beta (β), IL-6, IL-8, TNF-α, and IL-10 of elderly adults (median 83 [67-90] years old;n= 20) compared with young controls (median 35 [27-40] years old;n= 20). Ex vivo, the elderly adults showed a higher percentage of classical monocytes that expressed intracellular IL1-α (p= .001), IL1-β (p= .001), IL-6 (p= .002), and IL-8 (p= .007). Similar results were obtained both for the intermediate and nonclassical subsets and in vitro. Polyfunctionality was higher in the elderly adults. The functionality ex vivo was strongly associated with soluble inflammatory markers. The activation phenotype was independently associated with the anti-cytomegalovirus IgG levels and with functional and cognitive decline. These data demonstrate that monocytes are key cell candidates for the source of the high soluble inflammatory levels. Our findings suggest that cytomegalovirus infection might be a driving force in the activation of monocytes and is associated with the functional and cognitive decline.