HIV-specific CD8⁺ T-cell immunity in humanized bone marrow-liver-thymus mice

Examining Chronic Inflammation, Immune Metabolism, and T Cell Dysfunction in HIV Infection

Chronic Human Immunodeficiency Virus (HIV) infection remains a significant challenge to global public health. Despite advances in antiretroviral therapy (ART), which has transformed HIV infection from a fatal disease into a manageable chronic condition, a definitive cure remains elusive. One of the key features of HIV infection is chronic immune activation and inflammation, which are strongly associated with, and predictive of, HIV disease progression, even in patients successfully treated with suppressive ART. Chronic inflammation is characterized by persistent inflammation, immune cell metabolic dysregulation, and cellular exhaustion and dysfunction. This review aims to summarize current knowledge of the interplay between chronic inflammation, immune metabolism, and T cell dysfunction in HIV infection, and also discusses the use of humanized mice models to study HIV immune pathogenesis and develop novel therapeutic strategies.

Spontaneous tumor regression mediated by human T cells in a humanized immune system mouse model

Immunodeficient mice reconstituted with a human immune system (HIS mice) give rise to human T cells, which make them an attractive system to study human immune responses to tumors. However, such HIS mice typically exhibit sub-optimal responses to immune challenges as well as fail to develop antigen-specific B or T cell memory. Here we report HIS mice mediate spontaneous regression of human B cell lymphoma Raji. Tumor regression was dependent on CD4+ and CD8+ T cell responses and resulted in T cell memory. The T cell memory elicited was mainly Raji-specific, however some level of cross-protection was also elicited to a related B cell lymphoma cell line Ramos. Single-cell RNAseq analysis indicated activation of CD8+ T cells in regressing Raji tumors as well as clonal expansion of specific T cell receptors (TCRs). Cloning of TCRs from Raji-infiltrating T cells into a Jurkat reporter cell line showed reactivity specific for Raji tumor cells. Overall, we report a platform for studying in vivo human T cell tumor immunity by highlighting spontaneous Raji tumor regression, clonal TCR expansion, and T cell memory in HIS mice.

Anatomical and physiological aspects of the HIV infection pathogenesis in animal models

Understanding the entire pathogenesis of HIV infection, from penetration at the gates of infection to the induction of severe immunodeficiency, is an essential tool for the development of new treatment methods. Less than 40 years of research into the mechanisms of HIV infection that lead to the development of acquired immunodeficiency syndrome have accumulated a huge amount of information, but HIV's own unique variability identifies new whitespaces. Despite the constant improvement of the protocols of antiretroviral therapy and the success of its use, it has not yet been possible to stop the spread of HIV infection. The development of new protocols and the testing of new groups of antiretroviral drugs is possible, first of all, due to the improvement of animal models of the HIV infection pathogenesis. Their relevance, undoubtedly increases, but still depends on specific research tasks, since none of the in vivo models can comprehensively simulate the mechanism of the infection pathology in humans which leads to multi-organ damage. The aim of the review was to provide up-to-date information on known animal models of HIV infection, focusing on the method of their infection and anatomical, physiological and pathological features.

Modulating HIV-1 envelope glycoprotein conformation to decrease the HIV-1 reservoir

Small CD4-mimetic compounds (CD4mc) sensitize HIV-1-infected cells to antibody-dependent cellular cytotoxicity (ADCC) by facilitating antibody recognition of epitopes that are otherwise occluded on the unliganded viral envelope (Env). Combining CD4mc with two families of CD4-induced (CD4i) antibodies, which are frequently found in plasma of HIV-1-infected individuals, stabilizes Env in a conformation that is vulnerable to ADCC. We employed new-generation SRG-15 humanized mice, supporting natural killer (NK) cell and Fc-effector functions to demonstrate that brief treatment with CD4mc and CD4i-Abs significantly decreases HIV-1 replication, the virus reservoir and viral rebound after ART interruption. These effects required Fc-effector functions and NK cells, highlighting the importance of ADCC. Viral rebound was also suppressed in HIV-1+-donor cell-derived humanized mice supplemented with autologous HIV-1+-donor-derived plasma and CD4mc. These results indicate that CD4mc could have therapeutic utility in infected individuals for decreasing the size of the HIV-1 reservoir and/or achieving a functional cure.

Innate Immune Reconstitution in Humanized Bone Marrow-Liver-Thymus (HuBLT) Mice Governs Adaptive Cellular Immune Function and Responses to HIV-1 Infection

Humanized bone marrow-liver-thymus (HuBLT) mice are a revolutionary small-animal model that has facilitated the study of human immune function and human-restricted pathogens, including human immunodeficiency virus type 1 (HIV-1). These mice recapitulate many aspects of acute and chronic HIV-1 infection, but exhibit weak and variable T-cell responses when challenged with HIV-1, hindering our ability to confidently detect HIV-1-specific responses or vaccine effects. To identify the cause of this, we comprehensively analyzed T-cell development, diversity, and function in HuBLT mice. We found that virtually all HuBLT were well-reconstituted with T cells and had intact TCRβ sequence diversity, thymic development, and differentiation to memory and effector cells. However, there was poor CD4+ and CD8+ T-cell responsiveness to physiologic stimuli and decreased TH1 polarization that correlated with deficient reconstitution of innate immune cells, in particular monocytes. HIV-1 infection of HuBLT mice showed that mice with higher monocyte reconstitution exhibited greater CD8+ T cells responses and HIV-1 viral evolution within predicted HLA-restricted epitopes. Thus, T-cell responses to immune challenges are blunted in HuBLT mice due to a deficiency of innate immune cells, and future efforts to improve the model for HIV-1 immune response and vaccine studies need to be aimed at restoring innate immune reconstitution.

CD133 mRNA-Loaded Dendritic Cell Vaccination Abrogates Glioma Stem Cell Propagation in Humanized Glioblastoma Mouse Model

Cancer stem cells are initiating cells of cancer and propagate its growth through self-renewal and differentiation of its daughter cells. CD133 is a cell surface antigen that is present on glioma stem cells and has been used to prospectively isolate glioma stem cells. We hypothesized that a major histocompatibility complex (MHC)-independent and long-lasting immune response against CD133 could be generated by transfecting CD133 mRNA into dendritic cells and vaccinating animals with experimental gliomas. To test this hypothesis, we developed a novel humanized mouse model using CD34-positive hematopoietic stem cells. We confirmed the robust simultaneous activation of CD8- and CD4-positive T cells by dendritic cell vaccination with modified CD133 mRNA leading to a potent and long-lived immune response, with subsequent abrogation of CD133-positive glioma stem cell propagation and tumor growth. This study for the first time demonstrates in both a humanized mouse model and in a syngeneic mouse model of glioblastoma that targeting a glioma stem cell-associated antigen is an effective strategy to target and kill glioma stem cells. This novel and simple humanized mouse model for immunotherapy is a significant advance in our ability to test human-specific immunotherapies for glioblastoma.

HIV-1 and SIV Infection Are Associated with Early Loss of Lung Interstitial CD4+ T Cells and Dissemination of Pulmonary Tuberculosis

Lung interstitial CD4+ T cells are critical for protection against pulmonary infections, but the fate of this population during HIV-1 infection is not well described. We studied CD4+ T cells in the setting of HIV-1 infection in human lung tissue, humanized mice, and a Mycobacterium tuberculosis (Mtb)/simian immunodeficiency virus (SIV) nonhuman primate co-infection model. Infection with a CCR5-tropic strain of HIV-1 or SIV results in severe and rapid loss of lung interstitial CD4+ T cells but not blood or lung alveolar CD4+ T cells. This is accompanied by high HIV-1 production in these cells in vitro and in vivo. Importantly, during early SIV infection, loss of lung interstitial CD4+ T cells is associated with increased dissemination of pulmonary Mtb infection. We show that lung interstitial CD4+ T cells serve as an efficient target for HIV-1 and SIV infection that leads to their early depletion and an increased risk of disseminated tuberculosis.

Corleis et al. show that lung parenchymal CD4+ T cells are permissive to HIV-1-dependent cell death. CD4+ T cell loss is highly significant in the interstitium but not the alveolar space, and loss of interstitial CD4+ T cells is associated with extrapulmonary dissemination of M. tuberculosis.

Immunization of BLT Humanized Mice Redirects T Cell Responses to Gag and Reduces Acute HIV-1 Viremia

BLT (bone marrow-liver-thymus) humanized mice, which reconstitute a functional human immune system, develop prototypic human virus-specific CD8⁺ T cell responses following infection with human immunodeficiency virus type 1 (HIV-1). We explored the utility of the BLT model for HIV-1 vaccine development by immunizing BLT mice against the conserved viral Gag protein, utilizing a rapid prime-boost protocol of poly(lactic-co-glycolic) acid microparticles and a replication-defective herpes simplex virus (HSV) recombinant vector. After HIV-1 challenge, the mice developed broad, proteome-wide gamma interferon-positive (IFN-γ⁺) T cell responses against HIV-1 that reached magnitudes equivalent to what is observed in HIV-1-infected individuals. The functionality of these responses was underscored by the consistent emergence of escape mutations in multiple CD8⁺ T cell epitopes during the course of infection. Although prechallenge vaccine-induced responses were largely undetectable, the Gag immunization increased both the magnitude and the kinetics of anamnestic Gag-specific T cell responses following HIV-1 infection, and the magnitude of these postchallenge Gag-specific responses was inversely correlated with acute HIV-1 viremia. Indeed, Gag immunization was associated with a modest but significant 0.5-log reduction in HIV-1 viral load when analyzed across four experimental groups of BLT mice. Notably, the HSV vector induced elevated plasma concentrations of polarizing cytokines and chemotactic factors, including interleukin-12p70 (IL-12p70) and MIP-1α, which were positively correlated with the magnitude of Gag-specific responses. Overall, these results support the ability of BLT mice to recapitulate human pathogen-specific T cell responses and to respond to immunization; however, additional improvements to the model are required to develop a robust system for testing HIV-1 vaccine efficacy.IMPORTANCE Advances in the development of humanized mice have raised the possibility of a small-animal model for preclinical testing of an HIV-1 vaccine. Here, we describe the capacity of BLT humanized mice to mount broadly directed HIV-1-specific human T cell responses that are functionally active, as indicated by the rapid emergence of viral escape mutations. Although immunization of BLT mice with the conserved viral Gag protein did not result in detectable prechallenge responses, it did increase the magnitude and kinetics of postchallenge Gag-specific T cell responses, which was associated with a modest but significant reduction in acute HIV-1 viremia. Additionally, the BLT model revealed immunization-associated increases in the plasma concentrations of immunomodulatory cytokines and chemokines that correlated with more robust T cell responses. These data support the potential utility of the BLT humanized mouse for HIV-1 vaccine development but suggest that additional improvements to the model are warranted.

Lentiviral Vector-Based Dendritic Cell Vaccine Suppresses HIV Replication in Humanized Mice

HIV-1-infected individuals are treated with lifelong antiretroviral drugs to control the infection. A means to strengthen the antiviral T cell response might allow them to control viral loads without antiretroviral drugs. We report the development of a lentiviral vector-based dendritic cell (DC) vaccine in which HIV-1 antigen is co-expressed with CD40 ligand (CD40L) and a soluble, high-affinity programmed cell death 1 (PD-1) dimer. CD40L activates the DCs, whereas PD-1 binds programmed death ligand 1 (PD-L1) to prevent checkpoint activation and strengthen the cytotoxic T lymphocyte (CTL) response. The injection of humanized mice with DCs transduced with vector expressing CD40L and the HIV-1 SL9 epitope induced antigen-specific T cell proliferation and memory differentiation. Upon HIV-1 challenge of vaccinated mice, viral load was suppressed by 2 logs for 6 weeks. Introduction of the soluble PD-1 dimer into a vector that expressed full-length HIV-1 proteins accelerated the antiviral response. The results support development of this approach as a therapeutic vaccine that might allow HIV-1-infected individuals to control virus replication without antiretroviral therapy.

HIV Impacts CD34+ Progenitors Involved in T-Cell Differentiation During Coculture With Mouse Stromal OP9-DL1 Cells

HIV-1 causes the loss of CD4⁺ T cells via depletion or impairment of their production. The latter involves infection of thymocytes, but the involvement of hematopoietic CD34⁺ cells remains unclear even though HIV-positive patients frequently manifest myelosuppression. In order to have a closer look at the impact of HIV-1 on T-lineage differentiation, this study utilized the OP9-DL1 coculture system, which supports in vitro T-lineage differentiation of human hematopoietic stem/progenitor cells. In the newly developed in vitro OP9-DL1/HIV-1 model, cord-derived CD34⁺ cells were infected with CXCR4-tropic HIV-1_NL4−3 and cocultured. The HIV-infected cocultures exhibited reduced CD4⁺ T-cell growth at weeks 3–5 post infection compared to autologous uninfected cocultures. Further assays and analyses revealed that CD34⁺CD7⁺CXCR4⁺ cells can be quickly depleted as early as 1 week after infection of the subset, and this was accompanied by the emergence of rare CD34⁺CD7⁺CD4⁺ cells. A subsequent theoretical model analysis suggested potential influence of HIV-1 on the differentiation rate or death rate of lymphoid progenitor cells. These results indicate that CXCR4-tropic HIV-1 strains may impact the dynamics of CD34⁺CD7⁺ lymphoid progenitor cell pools, presumably leading to impaired T-cell production potential.

A Hitchhiker's guide to humanized mice: new pathways to studying viral infections

Humanized mice are increasingly appreciated as an incredibly powerful platform for infectious disease research. The often very narrow species tropism of many viral infections, coupled with the sometimes misleading results from preclinical studies in animal models further emphasize the need for more predictive model systems based on human cells rather than surrogates. Humanized mice represent such a model and have been greatly enhanced with regards to their immune system reconstitution as well as immune functionality in the past years, resulting in their recommendation as a preclinical model by the US Food and Drug Administration. This review aims to give a detailed summary of the generation of human peripheral blood lymphocyte-, CD34⁺ haematopoietic stem cell- and bone marrow/liver/thymus-reconstituted mice and available improved models (e.g. myeloid- or T-cell-only mice, MISTRG, NSG-SGM3). Additionally, we summarize human-tropic viral infections, for which humanized mice offer a novel approach for the study of disease pathogenesis as well as future perspectives for their use in biomedical, drug and vaccine research.

Human Cytomegalovirus Induces Cellular and Humoral Virus-specific Immune Responses in Humanized BLT Mice

The strict species specificity of Human Cytomegalovirus (HCMV) has impeded our understanding of antiviral adaptive immune responses in the context of a human immune system. We have previously shown that HCMV infection of human hematopoietic progenitor cells engrafted in immune deficient mice (huNSG) results in viral latency that can be reactivated following G-CSF treatment. In this study, we characterized the functional human adaptive immune responses in HCMV latently-infected huBLT (humanized Bone marrow-Liver-Thymus) mice. Following infection, huBLT mice generate human effector and central memory CD4+ and CD8+ T-cell responses reactive to peptides corresponding to both IE and pp65 proteins. Additionally, both HCMV specific IgM and IgG B-cell responses with the ability to neutralize virus were detected. These results indicate that the HCMV huBLT mouse model may provide a valuable tool to study viral latency and reactivation as well as evaluate HCMV vaccines and immune responses in the context of a functional human immune system.

Humanized chimeric mouse models of hepatitis B virus infection

Hepatitis B virus (HBV) infection is associated with an increased risk of hepatic cirrhosis, hepatocellular carcinoma, fulminant hepatitis and end-stage hepatic failure. Despite the availability of anti-HBV therapies, HBV infection remains a major global public health problem. Developing an ideal animal model of HBV infection to clarify the details of the HBV replication process, the viral life cycle, the resulting immunoresponse and the precise pathogenesis of HBV is difficult because HBV has an extremely narrow host range and almost exclusively infects humans. In this review, we summarize and evaluate animal models available for studying HBV infection, especially focusing on humanized chimeric mouse models, and we discuss future development trends regarding immunocompetent humanized mouse models that can delineate the natural history and immunopathophysiology of HBV infection.

HTLV-1 Infection and Neuropathogenesis in the Context of Rag1-/-γc-/- (RAG1-Hu) and BLT Mice

To date, the lack of a suitable small animal model has hindered our understanding of Human T-cell lymphotropic virus (HTLV)-1 chronic infection and associated neuropathogenesis defined as HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The host immune response plays a critical role in the outcome of HTLV-1 infection, which could be better tested in the context of humanized (hu) mice. Thus, we employ here the Balb/c-Rag1^-/-γc^-/- or Rag1 as well as Bone marrow-Liver-Thymic (BLT) mouse models for engraftment of human CD34⁺ hematopoietic stem cells. Flow cytometry and histological analyses confirmed reconstitution of Rag1 and BLT mice with human immune cells. Following HTLV-1 infection, proviral load (PVL) was detected in the blood of Rag-1 and BLT hu-mice as early as 2 weeks post-infection (wpi) with sustained elevation in the subsequent weeks followed by Tax expression. Additionally, infection was compared between adult and neonatal Rag1 mice with both PVL and Tax expression considerably higher in the adult Rag1 mice as compared to the neonates. Establishment of peripheral infection led to lymphocytic infiltration with concomitant Tax expression and resulting myelin disruption within the central nervous system of infected mice. In addition, up-regulation in the expression of several immune checkpoint mediators such as programmed cell death-1 (PD-1), T-cell Ig and ITIM domain (TIGIT), and T cell Ig and mucin domain-3 protein (Tim-3) were observed on CD8⁺ T cells in various organs including the CNS of infected hu-mice. Collectively, these studies represent the first attempt to establish HTLV-1 neuropathogenesis in the context of Rag-1 and BLT hu-mice as potential novel tools for understanding HTLV-1 neuropathogenesis and testing of novel therapies such as immune checkpoint blockade in the amelioration of chronic HTLV-1 infection.

Tumor-infiltrating CD8(+) T lymphocytes associated with clinical outcome in anal squamous cell carcinoma

BACKGROUND

The prognostic significance of tumor-infiltrating CD8(+) T lymphocytes in anal squamous cell carcinoma (SCC) remains unclear. We designed the study to investigate the association between CD8(+) T cells and clinical prognosis among anal SCC patients.

METHODS

The density of CD8(+) T cells was assessed by immunohistochemistry. The numbers of CD8(+) T cells were counted and their relationship with clinicopathological factors and survival was explored.

RESULTS

A strong positive correlation was noted between intratumoral and peritumoral CD8(+) T cells (r = 0.77, P < 0.001). High intratumoral and peritumoral CD8(+) T cells was associated with well tumor differentiation, early-stage diagnosis, and better prognosis (P < 0.05). Better disease-free survival rates were demonstrated in patients with high CD8(+) T cell density in intratumoral nest (P = 0.01); peritumoral stroma (P = 0.004); and both in combination (P = 0.01). High peritumoral CD8(+) T cell was associated with overall survival (P = 0.025). In HIV-infected patients, high CD8(+) T cell density also had association with disease-free survival (P < 0.05).

CONCLUSIONS

High tumor-infiltrating CD8(+) T cell density showed the potential to indicate a favorable effect on prognosis and survival for anal SCC patients.

Application of Humanized Mice in Immunological Research

During the past decade, the development of humanized mouse models and their general applications in biomedical research greatly accelerated the translation of outcomes obtained from basic research into potential diagnostic and therapeutic strategies in clinic. In this chapter, we firstly present an overview on the history and current progress of diverse humanized mouse models and then focus on those equipped with reconstituted human immune system. The update advancement in the establishment of humanized immune system mice and their applications in the studies of the development of human immune system and the pathogenesis of multiple human immune-related diseases are intensively reviewed here, while the shortcoming and perspective of these potent tools are discussed as well. As a valuable bridge across the gap between bench work and clinical trial, progressive humanized mouse models will undoubtedly continue to play an indispensable role in the wide area of biomedical research.

HIV-1 Nef: a master manipulator of the membrane trafficking machinery mediating immune evasion

BACKGROUND

Many viral genomes encode a limited number of proteins, illustrating their innate efficiency in bypassing host immune surveillance. This concept of genomic efficiency is exemplified by the 9 kb RNA genome of human immunodeficiency virus 1 (HIV-1), encoding 15 proteins sub-divided according to function. The enzymatic group includes proteins such as the drug targets reverse transcriptase and protease. In contrast, the accessory proteins lack any known enzymatic or structural function, yet are essential for viral fitness and HIV-1 pathogenesis. Of these, the HIV-1 accessory protein Nef is a master manipulator of host cellular processes, ensuring efficient counterattack against the host immune response, as well as long-term evasion of immune surveillance. In particular, the ability of Nef to downmodulate major histocompatibility complex class I (MHC-I) is a key cellular event that enables HIV-1 to bypass the host's defenses by evading the adaptive immune response.

SCOPE OF REVIEW

In this article, we briefly review how various pathogenic viruses control cell-surface MHC-I, and then focus on the mechanisms and implications of HIV-1 Nef-mediated MHC-I downregulation via modulation of the host membrane trafficking machinery.

CONCLUSION

The extensive interaction network formed between Nef and numerous membrane trafficking regulators suggests that Nef's role in evading the immune surveillance system intersects multiple host membrane trafficking pathways.

SIGNIFICANCE

Nef's ability to evade the immune surveillance system is linked to AIDS pathogenesis. Thus, a complete understanding of the molecular pathways that are subverted by Nef in order to downregulate MHC-I will enhance our understanding of HIV-1's progression to AIDS.

Recent advances in humanized mice: accelerating the development of an HIV vaccine

Recent advances in the development of humanized mice hold great promise to advance our understanding of protective immunity to human immunodeficiency virus (HIV) infection and to aid in the design of an effective HIV vaccine. This supplement of the Journal of Infectious Diseases summarizes work in the humanized mouse model presented at an HIV Humanized Mouse workshop in Boston, Massachusetts, in November 2012, including recent advances in the development of humanized mice, the trafficking of human immune cells following mucosal HIV transmission, the role of immune activation and Toll-like receptor agonists in the control of HIV, the induction and efficacy of HIV-specific cellular and humoral immune responses, and the preclinical modeling of novel anti-HIV therapeutics. Many gaps remain in our understanding of how to design an effective HIV vaccine and novel therapeutics to eliminate the viral reservoir. Promising early results from studies in humanized mice suggest great potential and enthusiasm for this model to accelerate these critical areas of HIV research.