Anti-SARS-CoV-2 receptor-binding domain antibody evolution after mRNA vaccination.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection produces B cell responses that continue to evolve for at least a year. During that time, memory B cells express increasingly broad and potent antibodies that are resistant to mutations found in variants of concern1. As a result, vaccination of coronavirus disease 2019 (COVID-19) convalescent individuals with currently available mRNA vaccines produces high levels of plasma neutralizing activity against all variants tested1,2. Here we examine memory B cell evolution five months after vaccination with either Moderna (mRNA-1273) or Pfizer-BioNTech (BNT162b2) mRNA vaccine in a cohort of SARS-CoV-2-naive individuals. Between prime and boost, memory B cells produce antibodies that evolve increased neutralizing activity, but there is no further increase in potency or breadth thereafter. Instead, memory B cells that emerge five months after vaccination of naive individuals express antibodies that are similar to those that dominate the initial response. While individual memory antibodies selected over time by natural infection have greater potency and breadth than antibodies elicited by vaccination, the overall neutralizing potency of plasma is greater following vaccination. These results suggest that boosting vaccinated individuals with currently available mRNA vaccines will increase plasma neutralizing activity but may not produce antibodies with equivalent breadth to those obtained by vaccinating convalescent individuals.

Evolution of antibody immunity to SARS-CoV-2.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected 78 million individuals and is responsible for over 1.7 million deaths to date. Infection is associated with the development of variable levels of antibodies with neutralizing activity, which can protect against infection in animal models1,2. Antibody levels decrease with time, but, to our knowledge, the nature and quality of the memory B cells that would be required to produce antibodies upon reinfection has not been examined. Here we report on the humoral memory response in a cohort of 87 individuals assessed at 1.3 and 6.2 months after infection with SARS-CoV-2. We find that titres of IgM and IgG antibodies against the receptor-binding domain (RBD) of the spike protein of SARS-CoV-2 decrease significantly over this time period, with IgA being less affected. Concurrently, neutralizing activity in plasma decreases by fivefold in pseudotype virus assays. By contrast, the number of RBD-specific memory B cells remains unchanged at 6.2 months after infection. Memory B cells display clonal turnover after 6.2 months, and the antibodies that they express have greater somatic hypermutation, resistance to RBD mutations and increased potency, indicative of continued evolution of the humoral response. Immunofluorescence and PCR analyses of intestinal biopsies obtained from asymptomatic individuals at 4 months after the onset of coronavirus disease 2019 (COVID-19) revealed the persistence of SARS-CoV-2 nucleic acids and immunoreactivity in the small bowel of 7 out of 14 individuals. We conclude that the memory B cell response to SARS-CoV-2 evolves between 1.3 and 6.2 months after infection in a manner that is consistent with antigen persistence.

Convergent antibody responses to SARS-CoV-2 in convalescent individuals.

During the coronavirus disease-2019 (COVID-19) pandemic, severe acute respiratory syndrome-related coronavirus-2 (SARS-CoV-2) has led to the infection of millions of people and has claimed hundreds of thousands of lives. The entry of the virus into cells depends on the receptor-binding domain (RBD) of the spike (S) protein of SARS-CoV-2. Although there is currently no vaccine, it is likely that antibodies will be essential for protection. However, little is known about the human antibody response to SARS-CoV-21-5. Here we report on 149 COVID-19-convalescent individuals. Plasma samples collected an average of 39 days after the onset of symptoms had variable half-maximal pseudovirus neutralizing titres; titres were less than 50 in 33% of samples, below 1,000 in 79% of samples and only 1% of samples had titres above 5,000. Antibody sequencing revealed the expansion of clones of RBD-specific memory B cells that expressed closely related antibodies in different individuals. Despite low plasma titres, antibodies to three distinct epitopes on the RBD neutralized the virus with half-maximal inhibitory concentrations (IC50 values) as low as 2 ng ml-1. In conclusion, most convalescent plasma samples obtained from individuals who recover from COVID-19 do not contain high levels of neutralizing activity. Nevertheless, rare but recurring RBD-specific antibodies with potent antiviral activity were found in all individuals tested, suggesting that a vaccine designed to elicit such antibodies could be broadly effective.

Combination therapy with anti-HIV-1 antibodies maintains viral suppression.

Individuals infected with HIV-1 require lifelong antiretroviral therapy, because interruption of treatment leads to rapid rebound viraemia. Here we report on a phase 1b clinical trial in which a combination of 3BNC117 and 10-1074, two potent monoclonal anti-HIV-1 broadly neutralizing antibodies that target independent sites on the HIV-1 envelope spike, was administered during analytical treatment interruption. Participants received three infusions of 30 mg kg-1 of each antibody at 0, 3 and 6 weeks. Infusions of the two antibodies were generally well-tolerated. The nine enrolled individuals with antibody-sensitive latent viral reservoirs maintained suppression for between 15 and more than 30 weeks (median of 21 weeks), and none developed viruses that were resistant to both antibodies. We conclude that the combination of the anti-HIV-1 monoclonal antibodies 3BNC117 and 10-1074 can maintain long-term suppression in the absence of antiretroviral therapy in individuals with antibody-sensitive viral reservoirs.

Overexpression of wild type RRAS2, without oncogenic mutations, drives chronic lymphocytic leukemia.

BACKGROUND: Chronic lymphocytic leukemia (CLL) is the most frequent, and still incurable, form of leukemia in the Western World. It is widely accepted that cancer results from an evolutionary process shaped by the acquisition of driver mutations which confer selective growth advantage to cells that harbor them. Clear examples are missense mutations in classic RAS genes (KRAS, HRAS and NRAS) that underlie the development of approximately 13% of human cancers. Although autonomous B cell antigen receptor (BCR) signaling is involved and mutations in many tumor suppressor genes and oncogenes have been identified, an oncogenic driver gene has not still been identified for CLL. METHODS: Conditional knock-in mice were generated to overexpress wild type RRAS2 and prove its driver role. RT-qPCR analysis of a human CLL sample cohort was carried out to measure RRAS2 transcriptional expression. Sanger DNA sequencing was used to identify a SNP in the 3'UTR region of RRAS2 in human CLL samples. RNAseq of murine CLL was carried out to identify activated pathways, molecular mechanisms and to pinpoint somatic mutations accompanying RRAS2 overexpression. Flow cytometry was used for phenotypic characterization and shRNA techniques to knockdown RRAS2 expression in human CLL. RESULTS: RRAS2 mRNA is found overexpressed in its wild type form in 82% of the human CLL samples analyzed (n = 178, mean and median = 5-fold) as well as in the explored metadata. A single nucleotide polymorphism (rs8570) in the 3'UTR of the RRAS2 mRNA has been identified in CLL patients, linking higher expression of RRAS2 with more aggressive disease. Deliberate overexpression of wild type RRAS2 in mice, but not an oncogenic Q72L mutation in the coding sequence, provokes the development of CLL. Overexpression of wild type RRAS2 in mice is accompanied by a strong convergent selection of somatic mutations in genes that have been identified in human CLL. R-RAS2 protein is physically bound to the BCR and mediates BCR signals in CLL. CONCLUSIONS: The results indicate that overexpression of wild type RRAS2 is behind the development of CLL.

Neutralizing Activity of Broadly Neutralizing anti-HIV-1 Antibodies against Primary African Isolates.

Novel therapeutic and preventive strategies are needed to contain the HIV-1 epidemic. Broadly neutralizing human antibodies (bNAbs) with exceptional activity against HIV-1 are currently being tested in HIV-1 prevention trials. The selection of anti-HIV-1 bNAbs for clinical development was primarily guided by their in vitro neutralizing activity against HIV-1 Env pseudotyped viruses. Here we report on the neutralizing activity of 9 anti-HIV-1 bNAbs now in clinical development against 126 Clade A, C, D PBMC-derived primary African isolates. The neutralizing potency and breadth of the bNAbs tested was significantly reduced compared to pseudotyped viruses panels. The difference in sensitivity between pseudotyped viruses and primary isolates varied from 3- to nearly 100-fold depending on the bNAb and the HIV-1 clade. Thus, the neutralizing activity of bNAbs against primary African isolates differs from their activity against pseudovirus panels. The data have significant implications for interpreting the results of ongoing HIV-1 prevention trials.IMPORTANCE HIV remains a major public health problem worldwide, and new therapies and preventive strategies are necessary for controlling the epidemic. Broadly neutralizing antibodies (bNAbs) have been developed in the past decade to fill this gap. The neutralizing activity of these antibodies against diverse HIV strains has mostly been measured using Env-pseudotyped viruses, which overestimate bNAb coverage and potency. In this study we measured the neutralizing activity of nine bNAbs against clade A, C, and D HIV isolates derived from cells of African patients living with HIV and produced in peripheral blood mononuclear cells. We found that the coverage and potency of bNAbs were often significantly lower than what was predicted by Env-psuedotyped viruses, and that this decrease was related to the bNAb biding site class. This data is important for the planning and analysis of clinical trials that seek to evaluate bNAbs for the treatment and prevention of HIV infection in Africa.

Relationship between intact HIV-1 proviruses in circulating CD4+ T cells and rebound viruses emerging during treatment interruption.

Combination antiretroviral therapy controls but does not cure HIV-1 infection because a small fraction of cells harbor latent viruses that can produce rebound viremia when therapy is interrupted. The circulating latent virus reservoir has been documented by a variety of methods, most prominently by viral outgrowth assays (VOAs) in which CD4+ T cells are activated to produce virus in vitro, or more recently by amplifying proviral near full-length (NFL) sequences from DNA. Analysis of samples obtained in clinical studies in which individuals underwent analytical treatment interruption (ATI), showed little if any overlap between circulating latent viruses obtained from outgrowth cultures and rebound viruses from plasma. To determine whether intact proviruses amplified from DNA are more closely related to rebound viruses than those obtained from VOAs, we assayed 12 individuals who underwent ATI after infusion of a combination of two monoclonal anti-HIV-1 antibodies. A total of 435 intact proviruses obtained by NFL sequencing were compared with 650 latent viruses from VOAs and 246 plasma rebound viruses. Although, intact NFL and outgrowth culture sequences showed similar levels of stability and diversity with 39% overlap, the size of the reservoir estimated from NFL sequencing was larger than and did not correlate with VOAs. Finally, intact proviruses documented by NFL sequencing showed no sequence overlap with rebound viruses; however, they appear to contribute to recombinant viruses found in plasma during rebound.

Antigen phagocytosis by B cells is required for a potent humoral response.

Successful vaccines rely on activating a functional humoral response that results from promoting a proper germinal center (GC) reaction. Key in this process is the activation of follicular B cells that need to acquire antigens and to present them to cognate CD4 T cells. Here, we report that follicular B cells can phagocytose large antigen-coated particles, a process thought to be exclusive of specialized antigen-presenting cells such as macrophages and dendritic cells. We show that antigen phagocytosis by B cells is BCR-driven and mechanistically dependent on the GTPase RhoG. Using Rhog-/- mice, we show that phagocytosis of antigen by B cells is important for the development of a strong GC response and the generation of high-affinity class-switched antibodies. Importantly, we show that the potentiation effect of alum, a common vaccine adjuvant, requires direct phagocytosis of alum-antigen complexes by B cells. These data suggest a new avenue for vaccination approaches by aiming to deliver 1-3 µm size antigen particles to follicular B cells.

Mice Overexpressing Wild-Type RRAS2 Are a Novel Model for Preclinical Testing of Anti-Chronic Lymphocytic Leukemia Therapies.

B-cell chronic lymphocytic leukemia (B-CLL) is the most common type of leukemia in the Western world. Mutation in different genes, such as TP53 and ATM, and deletions at specific chromosomic regions, among which are 11q or 17p, have been described to be associated to worse disease prognosis. Recent research from our group has demonstrated that, contrary to what is the usual cancer development process through missense mutations, B-CLL is driven by the overexpression of the small GTPase RRAS2 in its wild-type form without activating mutations. Some mouse models of this disease have been developed to date and are commonly used in B-CLL research, but they present different disadvantages such as the long waiting period until the leukemia fully develops, the need to do cell engraftment or, in some cases, the fact that the model does not recapitulate the alterations found in human patients. We have recently described Rosa26-RRAS2fl/flxmb1-Cre as a new mouse model of B-CLL with a full penetrance of the disease. In this work, we have validated this mouse model as a novel tool for the development of new therapies for B-CLL, by testing two of the most broadly applied targeted agents: ibrutinib and venetoclax. This also opens the door to new targeted agents against R-RAS2 itself, an approach not yet explored in the clinic.

Recreation of an antigen-driven germinal center in vitro by providing B cells with phagocytic antigen.

Successful vaccines rely on activating a functional humoral immune response through the generation of class-switched high affinity immunoglobulins (Igs). The germinal center (GC) reaction is crucial for this process, in which B cells are selected in their search for antigen and T cell help. A major hurdle to understand the mechanisms of B cell:T cell cooperation has been the lack of an antigen-specific in vitro GC system. Here we report the generation of antigen-specific, high-affinity, class-switched Igs in simple 2-cell type cultures of naive B and T cells. B cell antigen uptake by phagocytosis is key to generate these Igs. We have used the method to interrogate if T cells confer directional help to cognate B cells that present antigen and to bystander B cells. We find that bystander B cells do not generate class-switched antibodies due to a defective formation of T-B conjugates and an early conversion into memory B cells.

COVID-19 antibody development fueled by HIV-1 broadly neutralizing antibody research.

PURPOSE OF REVIEW: The coronavirus disease 2019 (COVID-19) pandemic has caught the world unprepared, with no prevention or treatment strategies in place. In addition to the efforts to develop an effective vaccine, alternative approaches are essential to control this pandemic, which will most likely require multiple readily available solutions. Among them, monoclonal anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies have been isolated by multiple laboratories in record time facilitated by techniques that were first pioneered for HIV-1 antibody discovery. Here, we summarize how lessons learned from anti-HIV-1 antibody discovery have provided fundamental knowledge for the rapid development of anti-SARS-CoV-2 antibodies. RECENT FINDINGS: Research laboratories that successfully identified potent broadly neutralizing antibodies against HIV-1 have harnessed their antibody discovery techniques to isolate novel potent anti-SARS-CoV-2 antibodies, which have efficacy in animal models. These antibodies represent promising clinical candidates for treatment or prevention of COVID-19. SUMMARY: Passive transfer of antibodies is a promising approach when the elicitation of protective immune responses is difficult, as in the case of HIV-1 infection. Antibodies can also play a significant role in post-exposure prophylaxis, in high-risk populations that may not mount robust immune responses after vaccination, and in therapy. We provide a review of the recent approaches used for anti-SARS-CoV-2 antibody discovery and upcoming challenges in the field.

Persistent cellular immunity to SARS-CoV-2 infection.

SARS-CoV-2 is responsible for an ongoing pandemic that has affected millions of individuals around the globe. To gain further understanding of the immune response in recovered individuals, we measured T cell responses in paired samples obtained an average of 1.3 and 6.1 mo after infection from 41 individuals. The data indicate that recovered individuals show persistent polyfunctional SARS-CoV-2 antigen-specific memory that could contribute to rapid recall responses. Recovered individuals also show enduring alterations in relative overall numbers of CD4+ and CD8+ memory T cells, including expression of activation/exhaustion markers, and cell division.

Evolution of Antibody Immunity to SARS-CoV-2.

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has infected 78 million individuals and is responsible for over 1.7 million deaths to date. Infection is associated with development of variable levels of antibodies with neutralizing activity that can protect against infection in animal models. Antibody levels decrease with time, but the nature and quality of the memory B cells that would be called upon to produce antibodies upon re-infection has not been examined. Here we report on the humoral memory response in a cohort of 87 individuals assessed at 1.3 and 6.2 months after infection. We find that IgM, and IgG anti-SARS-CoV-2 spike protein receptor binding domain (RBD) antibody titers decrease significantly with IgA being less affected. Concurrently, neutralizing activity in plasma decreases by five-fold in pseudotype virus assays. In contrast, the number of RBD-specific memory B cells is unchanged. Memory B cells display clonal turnover after 6.2 months, and the antibodies they express have greater somatic hypermutation, increased potency and resistance to RBD mutations, indicative of continued evolution of the humoral response. Analysis of intestinal biopsies obtained from asymptomatic individuals 4 months after coronavirus disease-2019 (COVID-19) onset, using immunofluorescence, or polymerase chain reaction, revealed persistence of SARS-CoV-2 nucleic acids and immunoreactivity in the small bowel of 7 out of 14 volunteers. We conclude that the memory B cell response to SARS-CoV-2 evolves between 1.3 and 6.2 months after infection in a manner that is consistent with antigen persistence.

Persistent Cellular Immunity to SARS-CoV-2 Infection.

SARS-CoV-2 is responsible for an ongoing pandemic that affected millions of individuals around the globe. To gain further understanding of the immune response in recovered individuals we measured T cell responses in paired samples obtained an average of 1.3 and 6.1 months after infection from 41 individuals. The data indicate that recovered individuals show persistent polyfunctional SARS-CoV-2 antigen specific memory that could contribute to rapid recall responses. In addition, recovered individuals show enduring immune alterations in relative numbers of CD4 + and CD8 + T cells, expression of activation/exhaustion markers, and cell division. SUMMARY: We show that SARS-CoV-2 infection elicits broadly reactive and highly functional memory T cell responses that persist 6 months after infection. In addition, recovered individuals show enduring immune alterations in CD4 + and CD8 + T cells compartments.

Antigen-responsive CD4+ T cell clones contribute to the HIV-1 latent reservoir.

Antiretroviral therapy suppresses but does not cure HIV-1 infection due to the existence of a long-lived reservoir of latently infected cells. The reservoir has an estimated half-life of 44 mo and is largely composed of clones of infected CD4+ T cells. The long half-life appears to result in part from expansion and contraction of infected CD4+ T cell clones. However, the mechanisms that govern this process are poorly understood. To determine whether the clones might result from and be maintained by exposure to antigen, we measured responses of reservoir cells to a small subset of antigens from viruses that produce chronic or recurrent infections. Despite the limited panel of test antigens, clones of antigen-responsive CD4+ T cells containing defective or intact latent proviruses were found in seven of eight individuals studied. Thus, chronic or repeated exposure to antigen may contribute to the longevity of the HIV-1 reservoir by stimulating the clonal expansion of latently infected CD4+ T cells.

Combination anti-HIV-1 antibody therapy is associated with increased virus-specific T cell immunity.

Combination antiretroviral therapy (ART) is highly effective in controlling human immunodeficiency virus (HIV)-1 but requires lifelong medication due to the existence of a latent viral reservoir1,2. Potent broadly neutralizing antibodies (bNAbs) represent a potential alternative or adjuvant to ART. In addition to suppressing viremia, bNAbs may have T cell immunomodulatory effects as seen for other forms of immunotherapy3. However, this has not been established in individuals who are infected with HIV-1. Here, we document increased HIV-1 Gag-specific CD8+ T cell responses in the peripheral blood of all nine study participants who were infected with HIV-1 with suppressed blood viremia, while receiving bNAb therapy during ART interruption4. Increased CD4+ T cell responses were detected in eight individuals. The increased T cell responses were due both to newly detectable reactivity to HIV-1 Gag epitopes and the expansion of pre-existing measurable responses. These data demonstrate that bNAb therapy during ART interruption is associated with enhanced HIV-1-specific T cell responses. Whether these augmented T cell responses can contribute to bNAb-mediated viral control remains to be determined.

Measuring SARS-CoV-2 neutralizing antibody activity using pseudotyped and chimeric viruses.

The emergence of SARS-CoV-2 and the ensuing explosive epidemic of COVID-19 disease has generated a need for assays to rapidly and conveniently measure the antiviral activity of SARS-CoV-2-specific antibodies. Here, we describe a collection of approaches based on SARS-CoV-2 spike-pseudotyped, single-cycle, replication-defective human immunodeficiency virus type-1 (HIV-1), and vesicular stomatitis virus (VSV), as well as a replication-competent VSV/SARS-CoV-2 chimeric virus. While each surrogate virus exhibited subtle differences in the sensitivity with which neutralizing activity was detected, the neutralizing activity of both convalescent plasma and human monoclonal antibodies measured using each virus correlated quantitatively with neutralizing activity measured using an authentic SARS-CoV-2 neutralization assay. The assays described herein are adaptable to high throughput and are useful tools in the evaluation of serologic immunity conferred by vaccination or prior SARS-CoV-2 infection, as well as the potency of convalescent plasma or human monoclonal antibodies.

Measuring SARS-CoV-2 neutralizing antibody activity using pseudotyped and chimeric viruses.

The emergence of SARS-CoV-2 and the ensuing explosive epidemic of COVID19 disease has generated a need for assays to rapidly and conveniently measure the antiviral activity of SARSCoV-2-specific antibodies. Here, we describe a collection of approaches based on SARS-CoV-2 spike-pseudotyped, single-cycle, replication-defective human immunodeficiency virus type-1 (HIV-1) and vesicular stomatitis virus (VSV), as well as a replication-competent VSV/SARS-CoV-2 chimeric virus. While each surrogate virus exhibited subtle differences in the sensitivity with which neutralizing activity was detected, the neutralizing activity of both convalescent plasma and human monoclonal antibodies measured using each virus correlated quantitatively with neutralizing activity measured using an authentic SARS-CoV-2 neutralization assay. The assays described herein are adaptable to high throughput and are useful tools in the evaluation of serologic immunity conferred by vaccination or prior SARS-CoV-2 infection, as well as the potency of convalescent plasma or human monoclonal antibodies.

Convergent Antibody Responses to SARS-CoV-2 Infection in Convalescent Individuals.

During the COVID-19 pandemic, SARS-CoV-2 infected millions of people and claimed hundreds of thousands of lives. Virus entry into cells depends on the receptor binding domain (RBD) of the SARS-CoV-2 spike protein (S). Although there is no vaccine, it is likely that antibodies will be essential for protection. However, little is known about the human antibody response to SARS-CoV-21-5. Here we report on 149 COVID-19 convalescent individuals. Plasmas collected an average of 39 days after the onset of symptoms had variable half-maximal neutralizing titers ranging from undetectable in 33% to below 1:1000 in 79%, while only 1% showed titers >1:5000. Antibody cloning revealed expanded clones of RBD-specific memory B cells expressing closely related antibodies in different individuals. Despite low plasma titers, antibodies to three distinct epitopes on RBD neutralized at half-maximal inhibitory concentrations (IC50s) as low as single digit ng/mL. Thus, most convalescent plasmas obtained from individuals who recover from COVID-19 do not contain high levels of neutralizing activity. Nevertheless, rare but recurring RBD-specific antibodies with potent antiviral activity were found in all individuals tested, suggesting that a vaccine designed to elicit such antibodies could be broadly effective.

Combination of quadruplex qPCR and next-generation sequencing for qualitative and quantitative analysis of the HIV-1 latent reservoir.

HIV-1 infection requires lifelong therapy with antiretroviral drugs due to the existence of a latent reservoir of transcriptionally inactive integrated proviruses. The goal of HIV-1 cure research is to eliminate or functionally silence this reservoir. To this end, there are numerous ongoing studies to evaluate immunological approaches, including monoclonal antibody therapies. Evaluating the results of these studies requires sensitive and specific measures of the reservoir. Here, we describe a relatively high-throughput combined quantitative PCR (qPCR) and next-generation sequencing method. Four different qPCR probes covering the packaging signal (PS), group-specific antigen (gag), polymerase (pol), and envelope (env) are combined in a single multiplex reaction to detect the HIV-1 genome in limiting dilution samples followed by sequence verification of individual reactions that are positive for combinations of any two of the four probes (Q4PCR). This sensitive and specific approach allows for an unbiased characterization of the HIV-1 latent reservoir.