Shifting Dynamics of Intestinal Macrophages during Simian Immunodeficiency Virus Infection in Adult Rhesus Macaques

Dual role for microbial short-chain fatty acids in modifying SIV disease trajectory following anti-α4β7 antibody administration

BACKGROUND

Human Immunodeficiency Virus (HIV)/Simian Immunodeficiency Virus (SIV) infection is associated with significant gut damage, similar to that observed in patients with inflammatory bowel disease (IBD). This pathology includes loss of epithelial integrity, microbial translocation, dysbiosis, and resultant chronic immune activation. Additionally, the levels of all-trans-retinoic acid (atRA) are dramatically attenuated. Data on the therapeutic use of anti-α4β7 antibodies has shown promise in patients with ulcerative colitis and Crohn's disease. Recent evidence has suggested that the microbiome and short-chain fatty acid (SCFA) metabolites it generates may be critical for anti-α4β7 efficacy and maintaining intestinal homeostasis.

MATERIALS AND METHODS

To determine whether the microbiome contributes to gut homeostasis after anti-α4β7 antibody administered to SIV-infected rhesus macaques, faecal SCFA concentrations were determined, 16S rRNA sequencing was performed, plasma viral loads were determined, plasma retinoids were measured longitudinally, and gut retinoid synthesis/response gene expression was quantified.

RESULTS

Our results suggest that anti-α4β7 antibody facilitates the return of retinoid metabolism to baseline levels after SIV infection. Furthermore, faecal SCFAs were shown to be associated with retinoid synthesis gene expression and rebound viral loads after therapy interruption.

CONCLUSIONS

Taken together, these data demonstrate the therapeutic advantages of anti-α4β7 antibody administration during HIV/SIV infection and that the efficacy of anti-α4β7 antibody may depend on microbiome composition and SCFA generation.

Targeting HIV persistence in the tissue

PURPOSE OF REVIEW

The complex nature and distribution of the HIV reservoir in tissue of people with HIV remains one of the major obstacles to achieve the elimination of HIV persistence. Challenges include the tissue-specific states of latency and viral persistence, which translates into high levels of reservoir heterogeneity. Moreover, the best strategies to reach and eliminate these reservoirs may differ based on the intrinsic characteristics of the cellular and anatomical reservoir to reach.

RECENT FINDINGS

While major focus has been undertaken for lymphoid tissues and follicular T helper cells, evidence of viral persistence in HIV and non-HIV antigen-specific CD4 + T cells and macrophages resident in multiple tissues providing long-term protection presents new challenges in the quest for an HIV cure. Considering the microenvironments where these cellular reservoirs persist opens new venues for the delivery of drugs and immunotherapies to target these niches. New tools, such as single-cell RNA sequencing, CRISPR screenings, mRNA technology or tissue organoids are quickly developing and providing detailed information about the complex nature of the tissue reservoirs.

SUMMARY

Targeting persistence in tissue reservoirs represents a complex but essential step towards achieving HIV cure. Combinatorial strategies, particularly during the early phases of infection to impact initial reservoirs, capable of reaching and reactivating multiple long-lived reservoirs in the body may lead the path.

Early treatment with anti-α4β7 antibody facilitates increased gut macrophage maturity in SIV-infected rhesus macaques

Despite advances in combination antiretroviral therapy (cART), people living with HIV (PLWH) continue to experience gastrointestinal dysfunction. Infusions of anti-α4β7 monoclonal antibodies (mAbs) have been proposed to increase virologic control during simian immunodeficiency virus (SIV) infection in macaques with mixed results. Recent evidences suggested that therapeutic efficacy of vedolizumab (a humanized anti-α4β7 mAb), during inflammatory bowel diseases depends on microbiome composition, myeloid cell differentiation, and macrophage phenotype. We tested this hypothesis in SIV-infected, anti-α4β7 mAb-treated macaques and provide flow cytometric and microscopic evidence that anti-α4β7 administered to SIV-infected macaques increases the maturity of macrophage phenotypes typically lost in the small intestines during SIV disease progression. Further, this increase in mature macrophage phenotype was associated with tissue viral loads. These phenotypes were also associated with dysbiosis markers in the gut previously identified as predictors of HIV replication and immune activation in PLWH. These findings provide a novel model of anti-α4β7 efficacy offering new avenues for targeting pathogenic mucosal immune response during HIV/SIV infection.

Laminin Isoforms in Human Dental Pulp: Lymphatic Vessels Express Laminin-332, and Schwann Cell-Associated Laminin-211 Modulates CD163 Expression of M2-like Macrophages

Laminin, a basement membrane heterotrimeric glycoprotein composed of α/β/γ subunits, has important tissue-specific functions in the control of cellular behavior. Our recent study showed the colocalization of CD163+ M2-like macrophages with Schwann cells in human dental pulp, leading us to hypothesize that the laminin isoform of Schwann cells is associated with CD163 expression. The present study investigated the distribution of laminin isoforms in human dental pulp and the underlying mechanisms that affect macrophage phenotypes. Immunofluorescence analysis indicated that blood vessels were exclusively positive for laminin α4 and α5, whereas laminin α2 was associated with Schwann cells. Unexpectedly, laminin α3/laminin-332 (α3β3γ2) was detected on lymphatic vessels. In intact and carious teeth, CD163+ cells were associated with laminin α2, whereas CD206 single-positive cells were present inside, outside, and along blood vessels. In vitro incubation of THP-1 macrophages in plates coated with laminin-211/511 or its functionally analogous E8 fragments of α-chain (E8-α) indicated that cell shapes differed between macrophages grown on laminin-211/E8-α2 and macrophages grown on laminin-511/E8-α5. Laminin-211/E8-α2-coated plates upregulated CD163 expression, compared with laminin-511/E8-α5-coated plates. Integrin α3- and integrin α6-neutralizing Abs altered the shape of THP-1 macrophages and upregulated mRNA levels of CD206 and CD163 in macrophages grown on laminin-511; the neutralizing Abs did not affect macrophages grown on laminin-211. These findings suggest that laminin isoforms differentially regulate macrophage behavior via distinct integrin-laminin affinities. Of note, laminin-332 is expressed by pulpal lymphatic vessels, the existence of which has been debated; laminin-211 might have a role in maintaining CD163 expression on macrophages.

The Role of Intestinal Macrophages in Gastrointestinal Homeostasis: Heterogeneity and Implications in Disease

Intestinal macrophages play a key role in the gut immune system and the regulation of gastrointestinal physiology, including gut motility and secretion. Their ability to keep the gut from chronic inflammation despite constantly facing foreign antigens has been an important focus in gastrointestinal research. However, the heterogeneity of intestinal macrophages has impeded our understanding of their specific roles. It is now becoming clear that subsets of intestinal macrophages play diverse roles in various gastrointestinal diseases. This occurs through a complex interplay between cytokine production and enteric nervous system activation that differs for each pathologic condition. Key diseases and disorders in which intestinal macrophages play a role include postoperative ileus, inflammatory bowel disease, necrotizing enterocolitis, as well as gastrointestinal disorders associated with human immunodeficiency virus and Parkinson's disease. Here, we review the identification of intestinal macrophage subsets based on their origins and functions, how specific subsets regulate gut physiology, and the potential for these heterogeneous subpopulations to contribute to disease states. Furthermore, we outline the potential for these subpopulations to provide unique targets for the development of novel therapies for these disorders.

Immune Profile of the Normal Maternal-Fetal Interface in Rhesus Macaques and Its Alteration Following Zika Virus Infection

The maternal decidua is an immunologically complex environment that balances maintenance of immune tolerance to fetal paternal antigens with protection of the fetus against vertical transmission of maternal pathogens. To better understand host immune determinants of congenital infection at the maternal-fetal tissue interface, we performed a comparative analysis of innate and adaptive immune cell subsets in the peripheral blood and decidua of healthy rhesus macaque pregnancies across all trimesters of gestation and determined changes after Zika virus (ZIKV) infection. Using one 28-color and one 18-color polychromatic flow cytometry panel we simultaneously analyzed the frequency, phenotype, activation status and trafficking properties of αβ T, γδ T, iNKT, regulatory T (Treg), NK cells, B lymphocytes, monocytes, macrophages, and dendritic cells (DC). Decidual leukocytes showed a striking enrichment of activated effector memory and tissue-resident memory CD4+ and CD8+ T lymphocytes, CD4+ Tregs, CD56+ NK cells, CD14+CD16+ monocytes, CD206+ tissue-resident macrophages, and a paucity of B lymphocytes when compared to peripheral blood. t-distributed stochastic neighbor embedding (tSNE) revealed unique populations of decidual NK, T, DC and monocyte/macrophage subsets. Principal component analysis showed distinct spatial localization of decidual and circulating leukocytes contributed by NK and CD8+ T lymphocytes, and separation of decidua based on gestational age contributed by memory CD4+ and CD8+ T lymphocytes. Decidua from 10 ZIKV-infected dams obtained 16-56 days post infection at third (n=9) or second (n=1) trimester showed a significant reduction in frequency of activated, CXCR3+, and/or Granzyme B+ memory CD4+ and CD8+ T lymphocytes and γδ T compared to normal decidua. These data suggest that ZIKV induces local immunosuppression with reduced immune recruitment and impaired cytotoxicity. Our study adds to the immune characterization of the maternal-fetal interface in a translational nonhuman primate model of congenital infection and provides novel insight in to putative mechanisms of vertical transmission.

Comparison of predictors for terminal disease progression in simian immunodeficiency virus/simian-HIV-infected rhesus macaques

OBJECTIVES

CD4+ T-cell decline and increasing virus levels are considered hallmarks of HIV/AIDS pathogenesis but we previously demonstrated in rhesus macaques that tissue macrophage destruction by simian immunodeficiency virus (SIV) infection associated with increased monocyte turnover also appear to impact pathogenesis. It remains unclear, however, which factors best predict onset of terminal disease progression and survival time. The objective of this study, therefore, was to directly compare these co-variates of infection for predicting survival times in retrospective studies of SIV/simian-HIV (SHIV)-infected adult rhesus macaques.

METHODS

Rhesus macaques were infected with various strains of SIV/SHIV and evaluated longitudinally for monocyte turnover, CD4+ T-cell loss, plasma viral load, and SIV/SHIV strain. Correlation analyses and machine learning algorithm modeling were applied to compare relative contributions of each of the co-variates to survival time.

RESULTS

All animals with AIDS-related clinical signs requiring euthanasia exhibited increased monocyte turnover regardless of CD4+ T-cell level, viral strain, or plasma viral load. Regression analyses and machine learning algorithms indicated a stronger correlation and contribution between increased monocyte turnover and reduced survival time than between CD4+ T-cell decline, plasma viral load, or virus strain and reduced survival time. Decision tree modeling categorized monocyte turnover of 13.2% as the initial significant threshold that best predicted decreased survival time.

CONCLUSION

These results demonstrate that monocytes/macrophages significantly affect HIV/SIV pathogenesis outcomes. Monocyte turnover analyses are not currently feasible in humans, so there is a need to identify surrogate biomarkers reflecting tissue macrophage damage that predict HIV infection disease progression.

Development of a Geropathology Grading Platform for nonhuman primates

A geropathology grading platform (GGP) for assessing age-related lesions has been established and validated for in inbred strain of mice. Because nonhuman primates (NHPs) share significant similarities in aging and spontaneous chronic diseases with humans, they provide excellent translational value for correlating histopathology with biological and pathological events associated with increasing age. Descriptive age-associated pathology has been described for rhesus macaques and marmosets, but a grading platform similar to the mouse GGP does not exist. The value of these NHP models is enhanced by considerable historical data from clinical, bio-behavioral, and social domains that align with health span in these animals. Successful adaptation of the mouse GGP for NHPs will include 1) expanding the range of organs examined; 2) standardizing necropsy collection, tissue trimming, and descriptive lesion terminology; 3) expanding beyond rhesus macaques and marmosets to include other commonly used NHPs in research; and 4) creating a national resource for age-related pathology to complement the extensive in-life datasets. Adaptation of the GGP to include translational models other than mice will be crucial to advance geropathology designed to enhance aging research.