Research Program Focus

Understanding the basic mechanisms of immunity to viral infections.

Research Program Statement

The Lund lab works to elucidate mechanisms of mucosal immune protection and mucosal immunoregulation, particularly in the context of virus infection. We focus on furthering our understanding of basic mechanisms of anti-viral and mucosal immunity using both mouse models as well as human tissues. Current projects include defining the role of tissue-resident memory T cells and regulatory T cells during mucosal virus infection, identifying novel mucosal immune correlates of protection from HIV-1 infection, investigating immune responses and immunoregulatory mechanisms in individuals naturally infected with SARS-CoV, and discovering new genes involved in immune responses to flavivirus infection, including both Zika and West Nile viruses, using the Collaborative Cross. The goal of these studies is to improve clinical interventions for virus infections of public health importance.

FUNDED PROJECTS IN THE LAB

Regulatory T-cell modulation of immunity to mucosal viral infections

Regulatory T cells are well known for their role in dampening the immune responses to self-antigens and thereby helping to prevent autoimmune disease. Additionally, recent work has highlighted the importance of regulatory T cells in immunity to infectious disease. Thus, the question arises as to how regulatory T cells can participate in both of these goals that are so important to human survival – preventing damaging immune responses to self while simultaneously permitting immune responses to be generated to fight foreign infectious agents. Previous studies have pointed to a role for regulatory T cells in limiting late immune responses to various infectious agents, thereby minimizing immune response-induced tissue damage while preventing or diminishing pathogen clearance. However, we recently demonstrated a novel and unexpected role for regulatory T cells in facilitating early immune responses to genital herpes simplex-2 (HSV-2) infection in orchestrating the timely trafficking of immune effector cells to the site of infection where they can fight infection. Therefore, this unexpected finding of an immune response-promoting function of regulatory T cells has subsequently led to several new lines of work that will be addressed in the lab.

Specifically, we will first address the role of regulatory T cells during the immune response to primary and secondary challenge with genital HSV-2 infection. This has important implications for vaccine design for sexually transmitted viruses, since how the population of regulatory T cells could change and perhaps impact the “memory” immune response that is generated subsequent to a primary antigenic challenge such as a vaccine is currently unknown. Secondly, we will extend our studies of the role of regulatory T cells during a second common mucosal infection that is considered to be a major public health threat- influenza virus infection. Thirdly, following up on work from our previous studies, we will characterize the mechanisms by which regulatory T cells modulate dendritic cell function during mucosal viral infections. Finally, we will determine if regulatory T cells must be antigen-specific in order to respond to genital HSV-2 infection. Results from these studies will help to reveal the roles of regulatory T cells during various types of mucosal viral infections at different mucosal surfaces of the body, as well as the different roles that regulatory T cells could play at various phases of the immune response to viruses. We expect that knowledge gained from this research program will assist in the generation of improved clinical interventions for mucosal viral infections, including vaccines. Our previously published work as well as recently generated and unpublished data in the lab suggests that regulatory T cells play several important roles in the immune response to viruses; thus, gaining an understanding of exactly what these cells do as well as where and when in the course of both a primary and secondary immune response is vital for designing future vaccines that will allow regulatory T cells to effectively assist in generating and maintaining protective immune responses.

Identification of Novel Mucosal Immune Mechanisms involved in Protection from HIV-1

More than 30 years into the global HIV-1 epidemic, novel HIV-1 prevention strategies are still being sought. A challenge to the design of an effective HIV-1 vaccine is the lack of known natural correlates of protection from infection. A relevant model to identify such correlates is offered by individuals who remain seronegative despite repeated HIV-1 exposures (HIV-1-exposed seronegatives, HESN). Studies of HESN have uncovered evidence of potential immune correlates of protection from HIV-1 infection in the form of HIV-specific immune responses and reduced immune activation, or immune quiescence. However, the vast majority of these studies were focused on immunity within the peripheral blood rather than mucosal sites of initial virus entry and replication. Thus, we plan to use mucosal sampling of a novel cohort including male and female HESN from HIV-serodiscordant couples and HIV-unexposed (HUSN) men and women, combined with state-of-the-art immunological techniques, to identify novel mucosal immune mechanisms of protection from HIV-1.

     Given our recent findings of an association of increased cervicovaginal HIV-neutralizing IgA and higher HIV-1 exposure, we hypothesize that immune responses within the genital mucosa will be altered in HESN compared to HUSN. Thus, in Aim 1 we will examine local T cell responses in the genital mucosa of HESN compared to HUSN, and we expect to observe increased responses and retention of these immune cells in individuals with higher HIV-1 exposure. As we and others have shown that immune quiescence appears to offer protection from HIV-1 infection, we propose to examine both HIV-specific immunity as well as immune activation in HESN and HUSN longitudinally. In parallel, we will examine the stability of these local T cell responses in the genital tract upon PrEP initiation by HESN men and women, as we have evidence of higher magnitude mucosal immune responses in PrEP users. Finally, using previously archived samples from the nested Partners PrEP case-control study, we will in test whether the novel changes in immune signatures we identify are correlated with protection from HIV-1 infection. In Aim 2, following up on our finding of differential cervicovaginal HIV-neutralizing IgA in women with higher HIV-1 exposure and with PrEP use, we will examine mechanisms of local antibody-secreting cells within the genital tract of men and women following HIV-1 exposure and PrEP initiation. In sum, upon completion of our proposed studies, we will have a complete characterization of adaptive immune responses and activation in the male and female genital tracts and blood in HESN upon HIV-1 exposure, with measures of the changes that occur longitudinally upon PrEP treatment. These studies will potentially inform vaccine and other HIV prevention strategies though identification of immune correlates of protection, and will also address a critical need to better understand mechanisms of the human mucosal immune responses, as such work will enhance our knowledge of the immunopathology of and immune-mediated protection to a range of chronic and infectious diseases.

The Regulatory Role of Natural Progesterone in Barrier Immunity 

The existence of biological sex-based differences in disease outcomes is well-established, but the underlying mechanisms are still poorly understood. Determining how the female sex hormone progesterone modulates immune responses and immune-associated pathologies has been particularly challenging. Progesterone is typically associated with restraining immune responses and reducing inflammation, with the expectation that this helps to induce immune tolerance for reproductive purposes. However, these previous findings could be at least in part due to the ability of certain forms of synthetic progesterone (including medroxyprogesterone acetate, which is sold under the name Depo Provera) to bind to the glucocorticoid receptor (GR). In contrast, the natural form of progesterone (pregn-4-ene-3,20-dione, or P4), which does not engage the GR, has been much less used in biological studies compared to synthetic progesterones. Here we propose to determine how P4 affects immunity in barrier tissues in steady-state conditions as well as during resolution of inflammation. We specifically focus on the effect of P4 on T cells with regulatory and inflammatory functions in the female reproductive tract using both primary human tissues and an animal model system. Importantly, our approach allows us to dissect direct and indirect effects of P4 on different components of the immune system, which is critical to understanding its mechanisms of action. Determining the effects of P4 is of urgent and utmost clinical relevance given the increasing clinical use of P4 across a wide range of diseases such as preventing the carcinogenic effects of post-menopausal estrogen replacement therapy, treating secondary amenorrhea, and preventing pre-term birth in high-risk pregnancies. Furthermore, our findings could help to provide a mechanistic framework for observed sex-based differences in autoimmunity and infectious disease outcomes.

T-Cell Activation and Exhaustion in the HIV-Positive Female Genital Tract

HIV infection is a chronic viral infection that if untreated leads to progressive loss of the CD4 T cell compartment and eventually AIDS. In addition to loss of HIV-susceptible CD4 T cells, chronic HIV infection is characterized by robust systemic immune activation including B and T cell activation and proliferation and elevated levels of pro-inflammatory molecules. Indeed, the level of immune activation is strongly associated with HIV disease progression. Even upon antiretroviral therapy (ART) initiation and viral suppression, chronic HIV infection is associated with dysfunctional circulating immunity rather than a return to immune quiescence. Further, immune activation in mucosal compartments such as the gut can persist in chronically infected individuals, even with long-term ART. This chronic immune activation during HIV infection was first identified largely through study of men with HIV, though more recent studies have suggested that HIV-associated immune activation may manifest differently in women. Given that women are increasingly affected by HIV, with UNAIDS reporting that 53% of people living with HIV are women and girls as of 2020, it’s evident that there is a gap in our understanding of immune activation and dysfunction in women, particularly within the female genital tract (FGT) mucosa. A few initial studies have suggested that immune activation is elevated in the FGT of women with HIV, and that ART does not restore FGT immune status to homeostatic levels within the initial month of treatment. Thus, we propose to comprehensively evaluate immune activation and dysfunction in the FGT in settings of HIV infection with or without viral suppression for up to 24 months. In a well-characterized cohort of women with and without HIV infection in Mombasa, Kenya, we will test two primary hypotheses: 1) We hypothesize that HIV infection leads to increased immune activation in the FGT that persists after ART initiation and viral suppression, and 2) We hypothesize that that chronic and persistent HIV infection leads to exhaustion of mucosal tissue T cells within the FGT.  We will advance the prior research by including a more thorough investigation of immune activation including a focus on regulatory T cell (Treg)-mediated immunoregulatory mechanisms, and T cell exhaustion through use of high-throughput single-cell analysis, and we will examine the effects of longer-term viral suppression on immune activation and dysfunction in both the circulation and FGT. This will allow us to better understand how HIV infection may lead to negative FGT health outcomes.

Immunogenetic Determinants of HSV-2 Infection and Disease

Infection with genital Herpes Simplex virus-2 (HSV-2) is life-long, and there is currently no cure or preventative vaccine despite substantial efforts. Furthermore, current anti-viral drugs such as acyclovir do not fully eliminate viral shedding or symptomatic genital ulcers for all patients, underscoring the need for new prevention and therapeutic strategies. There is considerable variation in rates of symptomatic and asymptomatic shedding as well as symptomatic disease between HSV-infected individuals, yet little understanding of the reasons underlying this variability. It is hypothesized that environmental and life-style factors such as stress, as well as genetic factors could play roles. Thus, we propose to use the Collaborative Cross in conjunction with a mouse model of vaginal HSV-2 infection to uncover novel genetic regions associated with HSV-2 shedding and disease, as well as with tissue-specific immune responses to infection. By defining host genetic regions that regulate these infection and disease-related phenotypes, we hope to pave the way for the identification and subsequent development of novel host-targeted and/or immune-based HSV therapies and prevention strategies that could lessen the burden of this global infectious disease as well as other infections transmitted via a mucosal surface.

The Collaborative Cross (CC) is a population of recombinant inbred mouse strains with high levels of standing genetic variation, and was designed to allow for studies of the association between allelic variation in one or more genes and a phenotype of interest. We have successfully used the CC to screen for genetic loci involved in West Nile virus infection susceptibility and disease as well as immune phenotypes. We now propose to leverage our expertise with the CC as well as with the mouse model of HSV-2 to perform a screen of CC mouse strains for HSV-2 shedding, disease, and tissue inflammation phenotypes. Further, we will assess post-infection immune response phenotypes within both lymphoid tissues and tissue sites that are viral targets of disease, such as the genital tract and the central nervous system (CNS). We will use this data to perform quantitative trait loci (QTL) mapping to identify chromosomal regions associated with vaginal viral shedding rates and levels, virus-associated disease such as the formation of genital lesions and mortality, and immune cell responses at different times and in different tissues post-infection. Through this proposed work, we expect to identify novel HSV susceptibility alleles that could inform the rational design of host-targeted HSV treatments and prevention strategies. Additionally, it is increasingly recognized that immune cell phenotype and function can vary widely based on tissue location. This study will identify genetic regions associated with immune responses to infection in distinct tissue locations, including both lymphoid and mucosal tissues, to thus increase knowledge of the host genetic regulation of tissue-specific immune cell function following infection.