Rhesus macaque rectal and duodenal tissues exhibit B-cell sub-populations distinct from peripheral blood that continuously secrete antigen-specific IgA in short-term explant cultures

Isolating Rat Intestinal Explants for In Vitro Cultures

The small intestine is an important organ primarily involved in digestion of food and absorption of nutrients. In vitro intestinal models are being developed to study this organ in health and disease. Intestinal explants can be used in such investigations since they contain all the major intestinal cell types. A detailed procedure to isolate intestinal explants from the rat jejunum is described. A protocol for culturing them in vitro for up to 24 hr is also provided. © 2019 by John Wiley & Sons, Inc.

Mucosal vaccine efficacy against intrarectal SHIV is independent of anti-Env antibody response

It is widely believed that protection against acquisition of HIV or SIV infection requires anti-envelope (anti-Env) antibodies, and that cellular immunity may affect viral loads but not acquisition, except in special cases. Here we provide evidence to the contrary. Mucosal immunization may enhance HIV vaccine efficacy by eliciting protective responses at portals of exposure. Accordingly, we vaccinated macaques mucosally with HIV/SIV peptides, modified vaccinia Ankara-SIV (MVA-SIV), and HIV-gp120-CD4 fusion protein plus adjuvants, which consistently reduced infection risk against heterologous intrarectal SHIVSF162P4 challenge, both high dose and repeated low dose. Surprisingly, vaccinated animals exhibited no anti-gp120 humoral responses above background and Gag- and Env-specific T cells were induced but failed to correlate with viral acquisition. Instead, vaccine-induced gut microbiome alteration and myeloid cell accumulation in colorectal mucosa correlated with protection. Ex vivo stimulation of the myeloid cell-enriched population with SHIV led to enhanced production of trained immunity markers TNF-α and IL-6, as well as viral coreceptor agonist MIP1α, which correlated with reduced viral Gag expression and in vivo viral acquisition. Overall, our results suggest mechanisms involving trained innate mucosal immunity together with antigen-specific T cells, and also indicate that vaccines can have critical effects on the gut microbiome, which in turn can affect resistance to infection. Strategies to elicit similar responses may be considered for vaccine designs to achieve optimal protective efficacy.

Follicular helper T cell and memory B cell immunity in CHC patients

Chronic hepatitis C (CHC) is associated with biological activity of T follicular helper (Tfh) cells and memory B cells (MBCs). However, the nature of Tfh cell subsets that are responsible for MBCs in CHC patients has not been evaluated. This study aimed to investigate Tfh and MBC immunity before and after direct-acting antiviral (DAA) therapy in patients with CHC. A total of 31 CHC patients and 15 healthy controls (HCs) were recruited. Individual patients were treated with sofosbuvir/ribavirin (SOF/RBV) or in combination with pegylated interferon alpha-2a (PEG-IFN-α-2a) for 12 weeks. Immunofluorescence revealed the frequency of ICOS⁺CD4⁺CXCR5⁺ active Tfh cells in liver tissue of CHC patients was higher than that of healthy control. Tfh and B cell co-culture experiments showed that Tfh2 cells from CHC patients have potential ability to induce B cell differentiation and IgG production. Flow cytometry showed that the frequencies of CD21^-CD27⁺IgD^- activated MBCs, ICOS⁺CD4⁺CXCR5⁺ activated Tfh cells, Tfh1 (IFN-γ⁺CD4⁺CXCR5⁺) cells, and Tfh2 (IL-4⁺CD4⁺CXCR5⁺) cells, but not of Tfh17 (IL-17⁺CD4⁺CXCR5⁺) cells, increased in CHC patients before and after DAA therapy. Collectively, ICOS⁺ Tfh, Tfh1, Tfh2 cells, and MBCs participated in the antiviral treatment process of SOF/RBV with or without PEG-IFN-α-2a in CHC patients, and their activity was further enhanced during the treatment. KEY MESSAGES: This study aimed to investigate Tfh cells and MBC immunity in CHC patients. CD21^-CD27⁺IgD^- activated MBCs increased in CHC patients before and after treatment. Tfh1 and Tfh2 cells increased in CHC patients before and after antiviral treatment. Intrahepatic activated Tfh cells increased in CHC patients before treatment. Tfh2 cells from CHC patients have a stronger ability to induce B cell differentiation.

Pathogenic Correlates of Simian Immunodeficiency Virus-Associated B Cell Dysfunction

We compared and contrasted pathogenic (in pig-tailed macaques [PTMs]) and nonpathogenic (in African green monkeys [AGMs]) SIVsab infections to assess the significance of the B cell dysfunction observed in simian (SIV) and human immunodeficiency virus (HIV) infections. We report that the loss of B cells is specifically associated with the pathogenic SIV infection, while in the natural hosts, in which SIV is nonpathogenic, B cells rapidly increase in both lymph nodes (LNs) and intestine. SIV-associated B cell dysfunction associated with the pathogenic SIV infection is characterized by loss of naive B cells, loss of resting memory B cells due to their redistribution to the gut, increases of the activated B cells and circulating tissue-like memory B cells, and expansion of the B regulatory cells (Bregs). While circulating B cells are virtually restored to preinfection levels during the chronic pathogenic SIV infection, restoration is mainly due to an expansion of the "exhausted," virus-specific B cells, i.e., activated memory cells and tissue-like memory B cells. Despite of the B cell dysfunction, SIV-specific antibody (Ab) production was higher in the PTMs than in AGMs, with the caveat that rapid disease progression in PTMs was strongly associated with lack of anti-SIV Ab. Neutralization titers and the avidity and maturation of immune responses did not differ between pathogenic and nonpathogenic infections, with the exception of the conformational epitope recognition, which evolved from low to high conformations in the natural host. The patterns of humoral immune responses in the natural host are therefore more similar to those observed in HIV-infected subjects, suggesting that natural hosts may be more appropriate for modeling the immunization strategies aimed at preventing HIV disease progression. The numerous differences between the pathogenic and nonpathogenic infections with regard to dynamics of the memory B cell subsets point to their role in the pathogenesis of HIV/SIV infections and suggest that monitoring B cells may be a reliable approach for assessing disease progression.IMPORTANCE We report here that the HIV/SIV-associated B cell dysfunction (defined by loss of total and memory B cells, increased B regulatory cell [Breg] counts, and B cell activation and apoptosis) is specifically associated with pathogenic SIV infection and absent during the course of nonpathogenic SIV infection in natural nonhuman primate hosts. Alterations of the B cell population are not correlated with production of neutralizing antibodies, the levels of which are similar in the two species. Rapid progressive infections are associated with a severe impairment in SIV-specific antibody production. While we did not find major differences in avidity and maturation between the pathogenic and nonpathogenic SIV infections, we identified a major difference in conformational epitope recognition, with the nonpathogenic infection being characterized by an evolution from low to high conformations. B cell dysfunction should be considered in designing immunization strategies aimed at preventing HIV disease progression.

Influence of Plasma Cell Niche Factors on the Recruitment and Maintenance of IRF4hi Plasma Cells and Plasmablasts in Vaccinated, Simian Immunodeficiency Virus-Infected Rhesus Macaques with Low and High Viremia

In a recent study, we found that protection following simian immunodeficiency virus (SIV) exposure correlated with rectal plasma cell frequency in vaccinated female rhesus macaques. We sought to determine if the same macaques maintained high mucosal plasma cell frequencies postinfection and if this translated to reduced viremia. Although delayed SIV acquisition did not predict subsequent viral control, alterations existed in the distribution of plasma cells and plasmablasts between macaques that exhibited high or low viremia. Flow cytometric analysis of cells from rectal biopsy specimens, bone marrow, and mesenteric lymph nodes of vaccinated infected, unvaccinated infected, and uninfected macaques identified two main IRF4^hi subsets of interest: CD138⁺ plasma cells, and CD138^- plasmablasts. In rectal tissue, plasma cell frequency positively correlated with plasma viremia and unvaccinated macaques had increased plasma cells and plasmablasts compared to vaccinated animals. Likewise, plasmablast frequency in the mesenteric lymph node correlated with viremia. However, in bone marrow, plasmablast frequency negatively correlated with viremia. Accordingly, low-viremic macaques had a higher frequency of both bone marrow IRF4^hi subsets than did animals with high viremia. Significant reciprocal relationships between rectal and bone marrow plasmablasts suggested that efficient trafficking to the bone marrow as opposed to the rectal mucosa was linked to viral control. mRNA expression analysis of proteins involved in establishment of plasma cell niches in sorted bone marrow and rectal cell populations further supported this model and revealed differential mRNA expression patterns in these tissues.

IMPORTANCE

As key antibody producers, plasma cells and plasmablasts are critical components of vaccine-induced immunity to human immunodeficiency virus type 1 (HIV-1) in humans and SIV in the macaque model; however, few have attempted to examine the role of these cells in viral suppression postinfection. Our results suggest that plasmablast trafficking to and retention in the bone marrow play a previously unappreciated role in viral control and contrast the potential contribution of mucosal plasma cells to mediate protection at sites of infection with that of bone marrow plasmablasts and plasma cells to control viremia during chronic infection. Manipulation of niche factors influencing the distribution and maintenance of these critical antibody-secreting cells may serve as potential therapeutic targets to enhance antiviral responses postvaccination and postinfection.

In Vitro Intestinal and Liver Models for Toxicity Testing

The human body is exposed to hundreds of chemicals every day. Many of these toxicants have unknown effects on the body that can be deleterious. Furthermore, chemicals can have a synergistic effect, resulting in toxic responses of cocktails at relatively low individual exposure levels. The gastrointestinal (GI) tract and the liver are the first organs to be exposed to ingested pharmaceuticals and environmental chemicals. As a result, these organs often experience extensive damage from xenobiotics and their metabolites. In vitro models offer a promising method for testing toxic effects. Many advanced in vitro models have been developed for GI and liver toxicity. These models strive to recapitulate the in vivo organ architecture to more accurately model chemical toxicity. In this review, we discuss many of these advances, in addition to recent efforts to integrate the GI and the liver in vitro for a more holistic toxicity model.

Animal models in HIV-1 protection and therapy

PURPOSE OF REVIEW

The purpose of this review is to highlight major advances in the development and use of animal models for HIV-1 research during the last year.

RECENT FINDINGS

Animal model research during the last year has focused on the development and refinement of models; use of these models to explore key questions about HIV entry, immune control, and persistence; and key discoveries with these models testing therapeutic and vaccine concepts. Some of the greatest breakthroughs have been in understanding early events surrounding transmission, the effectiveness of broadly neutralizing human monoclonal antibodies as passive prophylaxis, and some new ideas in the area of eliminating the viral reservoir in established infection.

SUMMARY

Despite the lack of a flawless HIV-1 infection and pathogenesis model, the field utilizes several models that have already made important contributions to our understanding of early events, immune control, and the potential for novel therapies.

Reduced expression of CD27 by collagenase treatment: implications for interpreting b cell data in tissues

Surface markers have been used to identify distinct cell subpopulations and to delineate various stages of maturation or activation of lymphocytes. In particular CD27 is used for delineation of naïve and memory B cell populations, and is readily detected by flow cytometry. We here used flow cytometry to examine the expression of CD27 on lymphocytes isolated from various tissues of rhesus macaques, and found its expression was consistently low to absent on intestinal cell suspensions. However, immunohistochemistry revealed abundant CD27+ cells in intestinal tissue sections. Further investigation showed the marked loss of CD27 expression on processed intestinal cells was due to collagenase digestion of intestinal tissues, yet CD27 expression was recoverable within hours of cell isolation. By combining confocal microscopy, we confirmed that only a fraction of B cells express CD27, in contrast to expression on all T cells from tissues examined including the gut. Taken together, our results suggest that CD27 may be a memory marker for B cells, but not for T cells, since essentially all CD3 T cells expressed CD27. In summary, it is important to consider the influence of isolation procedures on cell surface expression of phenotypic markers, especially when examining tissue-resident lymphocytes by flow cytometry.

Challenges in mucosal HIV vaccine development: lessons from non-human primate models

An efficacious HIV vaccine is urgently needed to curb the AIDS pandemic. The modest protection elicited in the phase III clinical vaccine trial in Thailand provided hope that this goal might be achieved. However, new approaches are necessary for further advances. As HIV is transmitted primarily across mucosal surfaces, development of immunity at these sites is critical, but few clinical vaccine trials have targeted these sites or assessed vaccine-elicited mucosal immune responses. Pre-clinical studies in non-human primate models have facilitated progress in mucosal vaccine development by evaluating candidate vaccine approaches, developing methodologies for collecting and assessing mucosal samples, and providing clues to immune correlates of protective immunity for further investigation. In this review we have focused on non-human primate studies which have provided important information for future design of vaccine strategies, targeting of mucosal inductive sites, and assessment of mucosal immunity. Knowledge gained in these studies will inform mucosal vaccine design and evaluation in human clinical trials.

Improved flow-based method for HIV/SIV envelope-specific memory B-cell evaluation in rhesus macaques

The ability to elicit potent and long-lasting broadly neutralizing HIV envelope (Env)-specific antibodies has become a key goal for HIV vaccine development. Consequently, the ability to rapidly and efficiently monitor development of memory B cells in pre-clinical and clinical vaccine trails is critical for continued progress in vaccine design. We have developed an improved flow cytometry-based method for the rapid and efficient identification of gp120-specific memory B cells in peripheral blood, bone marrow, and mucosal tissues which allows their direct staining without the need for prior cell sorting or enrichment. We demonstrate staining of both HIV and SIV Env-specific memory B cells in PBMC, bone marrow, and rectal tissue of vaccinated and infected rhesus macaques. Validation of the method is illustrated by statistically significant correlations with memory B cell levels quantified by ELISPOT assay and with serum binding antibody titers determined by ELISA. In addition to quantification, this method will bring the power of flow cytometry to the study of homing and trafficking of Env-specific memory B cells.

Phenotypes and distribution of mucosal memory B-cell populations in the SIV/SHIV rhesus macaque model

As vaccine-elicited antibodies have now been associated with HIV protective efficacy, a thorough understanding of mucosal and systemic B-cell development and maturation is needed. We phenotyped mucosal memory B-cells, investigated isotype expression and homing patterns, and defined plasmablasts and plasma cells at three mucosal sites (duodenum, jejunum and rectum) in rhesus macaques, the commonly used animal model for pre-clinical vaccine studies. Unlike humans, macaque mucosal memory B-cells lacked CD27 expression; only two sub-populations were present: naïve (CD21(+)CD27(-)) and tissue-like (CD21(-)CD27(-)) memory. Similar to humans, IgA was the dominant isotype expressed. The homing markers CXCR4, CCR6, CCR9 and α4β7 were differentially expressed between naïve and tissue-like memory B-cells. Mucosal plasmablasts were identified as CD19(+)CD20(+/-)HLA-DR(+)Ki-67(+)IRF4(+)CD138(+/-) and mucosal plasma cells as CD19(+)CD20(-)HLA-DR(-)Ki-67(-)IRF4(+)CD138(+). Both populations were CD39(+/-)CD27(-). Plasma cell phenotype was confirmed by spontaneous IgA secretion by ELISpot of positively-selected cells and J-chain expression by real-time PCR. Duodenal, jejunal and rectal samples were similar in B-cell memory phenotype, isotype expression, homing receptors and plasmablast/plasma cell distribution among the three tissues. Thus rectal biopsies adequately monitor B-cell dynamics in the gut mucosa, and provide a critical view of mucosal B-cell events associated with development of vaccine-elicited protective immune responses and SIV/SHIV pathogenesis and disease control.