Complicity without connection or communication

We use a novel laboratory experiment involving a die rolling task embedded within a coordination game to investigate whether complicity can emerge when decision-making is simultaneous, the potential accomplices are strangers and neither communication nor signaling is possible. Then, by comparing the behavior observed in this original game to that in a variant in which die-roll reporting players are paired with passive players instead of other die-roll reporters, while everything else is held constant, we isolate the effect of having a potential accomplice on the likelihood of an individual acting immorally. We find that complicity can emerge between strangers in the absence of opportunities to communicate or signal and that having a potential accomplice increases the likelihood of an individual acting immorally

Reactivation of virus-specific memory B cells

Humane Cytomegalovirus-Infektionen (hCMV) stellen ein erhebliches klinisches Problem für immunsupprimierte Personen wie z.B. Patienten nach Knochenmark- oder Stammzelltrans-plantation dar, da das Virus nach Primärinfektion lebenslang im Organismus verbleibt und jederzeit reaktiviert werden kann. Humorale Immunantworten sind entscheidend am kli-nischen Verlauf der hCMV-Infektion beteiligt, was u.a. in eigenen Arbeiten gezeigt werden konnte. Adoptiv transferierte CMV-spezifische Gedächtnis B Zellen (GBZ) schützen immun-supprimierte Mäuse, in Abwesenheit von T Zellen, vor letalen mCMV-Infektionen. Aufgrund dieser Erkenntnisse und dem Umstand, dass keine nebenwirkungsfreien, effektiven Behand-lungsmöglichkeiten existieren, könnte der adoptive Transfer von virus-spezifischen GBZ als neue Immuntherapie eingesetzt werden, um die humoralen Effektormechanismen mit antiviraler Aktivität in den Patienten zu verstärken. Allerdings sind die Prozesse der GBZ Reaktivierung derzeit noch nicht vollständig geklärt. Daher sollte in dieser Arbeit die hCMV-spezifische GBZ Antwort im Mausmodell qualitativ und quantitativ charakterisiert werden. In der vorliegenden Arbeit konnte ein experimentelles System etabliert werden, welches die Identifikation und Sortierung antigenspezifischer GBZ erlaubte. Mit Hilfe dieser Technik konnte gezeigt werden, dass adoptiver Transfer von weniger als 25 GBZ binnen vier Tagen nach erneutem Antigenkontakt zu signifikanten antigenspezifischen Serum-IgG-Titern in den Rezipiententieren führte. In vitro Analysen ergaben, dass GBZ nicht alleine durch die Gegenwart von Antigen zur Differenzierung in antikörperproduzierende Zellen stimuliert werden können, was auf die Notwendigkeit zusätzlicher Signale hindeutete. Analysen der GBZ Antworten in verschiedenen knock out Rezipienten, knochenmarkchimären Tieren oder nach in vivo Depletion spezifischer Zellpopulationen belegten, dass weder Makrophagen, CD11c-positive dendritische Zellen, follikulär dendritische Zellen noch Marginalzonen B Zellen essentiell an dem Prozess der GBZ Reaktivierung beteiligt sind. Des Weiteren konnte gezeigt werden, dass die Reaktivierung von GBZ nicht durch Fcγ-Rezeptoren vermittelt ist, jedoch entscheidend von der Struktur des Antigens abhängt. In vivo Zugänglichkeitsstudien legten den Schluss nahe, dass Gedächtnis B Zellen nicht präferentiell, wie bisher vermutet, in den Marginalzonen lokalisiert sind, da sie nicht verstärkt zugänglich für Antigene im Blutstrom sind und sich dadurch von Marginalzonen B Zellen unterscheiden. In weiteren Analysen konnte gezeigt werden, dass sich GBZ Antworten durch die Gegenwart von Interferon alpha verstärken lassen. Die Ergebnisse dieser Arbeit könnten z.B. in klinischen Studien dazu beitragen, das antivirale Potential von GBZ in Gegenwart bestimmter Immun-defizienzen zu nutzen oder zur Weiterentwicklung von Vakzinen dienen.Human cytomegalovirus (hCMV) is still a major infectious complication in immuno-suppressed individuals, such as transplant recipients due to the fact that after primary infection the virus remains lifelong in the host and can be reactivated from latency. Humoral immune responses are involved in the course of infection. Recently the murine model of CMV (mCMV) was used to investigate the potential of a cell-based strategy to support the humoral antiviral immune response. Adoptive transfer of mCMV-specific memory B cells (MBCs) provided long-term protection from the lethal course of infection in immunodeficient animals without the need of T cells. Because there are no effective and side-effect-free therapies in the treatment of CMV-infections available, adoptive transfer of virus-specific MBCs could be used as a novel immunotherapy to support the humoral effector-functions to combat infectious pathogens in severely immunodeficient patients. Because reactivation requirements for resting memory B cells are still incompletely understood, the hCMV-specific MBC response was qualitatively and quantitatively characterized. Within this work an experimental system was developed which enabled the identification and sorting of antigen-specific MBCs. By the use of this technique it could be shown that adoptive transfer of less than 25 MBCs leads to strong antigen-specific serum-IgG-titres in recipient mice within 4 days after antigenic recall. In vitro analysis showed that MBCs are not stimulated to differentiate into antibody producing cells by antigen alone, indicating the necessity of additional signals. Analysis of MBC responses in various knock out recipients, bone marrow chimeric mice or after in vivo ablation of specific cell populations revealed that neither macrophages, CD11c-positive dendritic cells, follicular dendritic cells nor marginal zone B cells are essentially involved in the process of MBC reactivation. Furthermore it became evident that reactivation of MBCs is not mediated by Fcγ-receptors but is crucial to the structure of the antigen. In vivo antibody labelling studies pointed to the fact that MBCs are not particularly enriched in the marginal zones of the spleen as supposed widely, because they did not show enhanced accessibility for blood-borne antigens which separates the latter from marginal zone B cells. Additionally a positive influence of interferon alpha was observed on the outcome of MBC responses. On the one hand the results obtained from this work could help immunosuppressed individuals to profit from the antiviral potential of MBC e.g. in clinical trials and on the other hand the provided data could be used in the development of more effective vaccines

Germinal center selection and the development of memory B and plasma cells: Germinal center differentiation and selection

Summary:  A hallmark of adaptive immune responses is the generation of long-lived protection after primary exposure to a pathogen. In humoral responses, this protection stems from a combination of sustained antibody titers and long-lived memory B cells (MBCs), with the former deriving from long-lived plasma cells (PCs). Both types of cell are thought to primarily derive from the germinal center (GC), a unique structure that forms during the immune response to many types of antigenic stimuli. GCs are seeded by antigen-specific B and T cells that were previously activated in the early stages of the response. The GC does not directly or immediately generate effector function; rather, it is a site of intense B-cell proliferation and cell death. GC B cells undergo both somatic hypermutation and isotype switch, and a Darwinian process very efficiently selects B cells with higher fitness for survival and expansion. GC B cells adopt a unique activation and transcriptional state, and the cells become poised to differentiate to either MBCs or PCs. Despite this general understanding of the events in the GC, the mechanisms that control both affinity selection as well as differentiation have not been well worked out. In this review, we address what is known about what determines whether GC B cells become MBCs or PCs. This is discussed in the broader context of the origins of both cell types, whether from the GC or potentially other sources. We present a model encompassing recent data from several laboratories including our own that suggests that the GC undergoes a temporal switch that alters the nature of its output from MBCs to PCs as the response progresses. We will discuss B-cell receptor signaling in the GC as it relates to potential mechanisms for affinity-based selection during the reaction

Adenovirus-vectored SARS-CoV-2 vaccine expressing S1-N fusion protein

: Additional COVID-19 vaccines that are safe and immunogenic are needed for global vaccine equity. Here, we developed a recombinant type 5 adenovirus vector encoding for the SARS-CoV-2 S1 subunit antigen and nucleocapsid as a fusion protein (Ad5.SARS-CoV-2-S1N). A single subcutaneous immunization with Ad5.SARS-CoV-2-S1N induced a similar humoral response, along with a significantly higher S1-specific cellular response, as a recombinant type 5 adenovirus vector encoding for S1 alone (Ad5.SARS-CoV-2-S1). Immunogenicity was improved by homologous prime-boost vaccination, and further improved through intramuscular heterologous prime-boost vaccination using subunit recombinant S1 protein. Priming with low dose (1 × 1010 v.p.) of Ad5.SARS-CoV-2-S1N and boosting with either wild-type recombinant rS1 or B.1.351 recombinant rS1 induced a robust neutralizing response, which was sustained against Beta and Gamma SARS-CoV-2 variants. This novel Ad5-vectored SARS-CoV-2 vaccine candidate showed promising immunogenicity in mice and supports the further development of COVID-19-based vaccines incorporating the nucleoprotein as a target antigen

B cell repertoire analysis identifies new antigenic domains on glycoprotein B of human cytomegalovirus which are target of neutralizing antibodies.

Human cytomegalovirus (HCMV), a herpesvirus, is a ubiquitously distributed pathogen that causes severe disease in immunosuppressed patients and infected newborns. Efforts are underway to prepare effective subunit vaccines and therapies including antiviral antibodies. However, current vaccine efforts are hampered by the lack of information on protective immune responses against HCMV. Characterizing the B-cell response in healthy infected individuals could aid in the design of optimal vaccines and therapeutic antibodies. To address this problem, we determined, for the first time, the B-cell repertoire against glycoprotein B (gB) of HCMV in different healthy HCMV seropositive individuals in an unbiased fashion. HCMV gB represents a dominant viral antigenic determinant for induction of neutralizing antibodies during infection and is also a component in several experimental HCMV vaccines currently being tested in humans. Our findings have revealed that the vast majority (>90%) of gB-specific antibodies secreted from B-cell clones do not have virus neutralizing activity. Most neutralizing antibodies were found to bind to epitopes not located within the previously characterized antigenic domains (AD) of gB. To map the target structures of these neutralizing antibodies, we generated a 3D model of HCMV gB and used it to identify surface exposed protein domains. Two protein domains were found to be targeted by the majority of neutralizing antibodies. Domain I, located between amino acids (aa) 133-343 of gB and domain II, a discontinuous domain, built from residues 121-132 and 344-438. Analysis of a larger panel of human sera from HCMV seropositive individuals revealed positivity rates of >50% against domain I and >90% against domain II, respectively. In accordance with previous nomenclature the domains were designated AD-4 (Dom II) and AD-5 (Dom I), respectively. Collectively, these data will contribute to optimal vaccine design and development of antibodies effective in passive immunization

A single subcutaneous or intranasal immunization with adenovirus‐based SARS‐CoV‐2 vaccine induces robust humoral and cellular immune responses in mice

Optimal vaccines are needed for sustained suppression of SARS-CoV-2 and other novel coronaviruses. Here, we developed a recombinant type 5 adenovirus vector encoding the gene for the SARS-CoV-2 S1 subunit antigen (Ad5.SARS-CoV-2-S1) for COVID-19 immunization and evaluated its immunogenicity in mice. A single immunization with Ad5.SARS-CoV-2-S1 via S.C. injection or I.N delivery induced robust antibody and cellular immune responses. Vaccination elicited significant S1-specific IgG, IgG1, and IgG2a endpoint titers as early as 2 weeks, and the induced antibodies were long lasting. I.N. and S.C. administration of Ad5.SARS-CoV-2-S1 produced S1-specific GC B cells in cervical and axillary LNs, respectively. Moreover, I.N. and S.C. immunization evoked significantly greater antigen-specific T-cell responses compared to unimmunized control groups with indications that S.C. injection was more effective than I.N. delivery in eliciting cellular immune responses. Mice vaccinated by either route demonstrated significantly increased virus-specific neutralization antibodies on weeks 8 and 12 compared to control groups, as well as BM antibody forming cells (AFC), indicative of long-term immunity. Thus, this Ad5-vectored SARS-CoV-2 vaccine candidate showed promising immunogenicity following delivery to mice by S.C. and I.N. routes of administration, supporting the further development of Ad-based vaccines against COVID-19 and other infectious diseases for sustainable global immunization programs