Regulators of CD8+ T-cell mediated vaccine immunity against pulmonary fungal infections

Mudalagiriyappa, Srinivasu

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https://hdl.handle.net/2142/116077 Copy

Description

Title

Regulators of CD8+ T-cell mediated vaccine immunity against pulmonary fungal infections

Author(s)

Mudalagiriyappa, Srinivasu

Issue Date

2022-07-14

Director of Research (if dissertation) or Advisor (if thesis)

Nanjappa, Som G

Doctoral Committee Chair(s)

Nanjappa, Som G

Committee Member(s)

• Zuckermann, Federico A
• Lau, Gee W
• Gaskins, H. Rex
• Steelman, Andrew J

Department of Study

Pathobiology

Discipline

VMS - Pathobiology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Vaccine-immunity
• CD8+ T cells
• Pulmonary fungal infections
• Opportunistic fungal infections
• CD43
• Sialophorin

Abstract

Invasive fungal infections cause severe morbidity and mortality in immunocompromised patients posing a significant burden on medical health. Therapeutic options are few and futile due to poor early diagnosis and emerging drug resistance. Therefore, the development of safe and effective vaccine candidates for at-risk populations is of paramount importance, given that there are no licensed fungal vaccines to date. Accumulating evidence suggests that CD4+ T cells control fungal infections by secreting proinflammatory cytokines to bolster the functions of innate immune cells, including macrophages, neutrophils, monocytes, dendritic cells, and epithelial cells (Hernández-Santos & Gaffen, 2012; LeibundGut-Landmann et al., 2012; Wüthrich et al., 2012). However, most of the immune-compromised population is due to a deficiency of CD4+ T cells. We asked if residual immunity can be exploited for fungal vaccine immunity. Previously, our group has shown that in the absence of CD4+ T cells, IL-17A produced by vaccine-induced CD8+ T cells (Tc17) mediate sterilizing immunity against pulmonary fungal pathogens. Vaccine-induced CD8+ T cells persisted as memory cells without plasticity, portrayed stem cell-like attributes, and were capable of producing multiple cytokines including GM-CSF, IFN, TNF, and IL-17A (Nanjappa et al., 2012a; Nanjappa., 2017). Multifunctional CD8+ T cells are reported in many infections or after vaccinations which correlated with better immunity (Darrah et al., 2007). Previously we reported the formation of polycytokine producing antifungal CD8+ T cells following fungal vaccination. Notably, vaccine-induced memory Tc17 cells predominantly expressed GM-CSF, a cytokine shown to regulate immunity and pathology. However, GM-CSF expression by Th17 cells was necessary for instigating autoimmunity in experimental autoimmune encephalomyelitis (EAE) models, and GM-CSF deficient mice were resistant to EAE (Duncker et al., 2018; McQualter et al., 2001). In COVID-19 patients, the virus-specific GM-CSF expressing Th17 cells were correlated with the disease severity. Thus, the conundrum of GM-CSF+ T17 for fungal immunity or overt pathology. In Chapter II, we sought to understand the role of GM-CSF+ Tc17 cells for vaccine immunity using pulmonary Blastomyces infection. Using a mouse model of vaccination and lethal pulmonary challenge in a mixed bone marrow chimera mice experiment, we found that GM-CSF+ Tc17 cells are necessary for vaccine-immunity without precipitating unwarranted immunopathology. Induction of GM-CSF+ Tc17 cells to a fungal vaccine required IL-1 and IL-23 signaling but not GM-CSF. Despite the studies suggesting a potential role of IL-23 for memory homeostasis of Tc17 cells, our study suggested its dispensability in the maintenance of memory Tc17 and GM-CSF+ Tc17 cells. Nevertheless, full maturation of GM-CSF+ Tc17 effector cells following vaccination required IL-23. The effective T cell recall response is necessary to mount sterilizing immunity against the infections, and several proinflammatory cytokines are involved in this process. Next, we asked if IL-23 is required for recall responses of GM-CSF+ Tc17 cells, including redifferentiation that is reminiscent of vaccine responses. We found that IL-23 was involved in recall responses by recruiting Tc17 cell subsets into the lungs, but not for the re-differentiation of GM-CSF+ Tc17 cells for vaccine immunity and mitigating the immunopathology of the lungs. Collectively, GM-CSF+ Tc17 cells bolster the vaccine-immunity against lethal fungal pneumonia. Vaccine potency and efficacy depend on the elements of innate immunity potentiating the adaptive immunity, and vaccine efficacy is evaluated using markers of adaptive immune responses. In Chapter III, to identify a marker of fungal vaccine efficacy, we explored the phenotypic memory markers that are characteristic of CD8+ T cell attributes. Despite some nuances with many attributes of T cells, we found phenotypic marker sialophorin (CD43) that was preferentially associated with antifungal memory cytokine producing CD8+ T cells. CD43 is a co-stimulatory molecule on T cells that can modulate immune responses. More specifically, CD43 was negatively associated with memory development by inflating the apoptosis of antigen-specific effector CD8+ T cells following viral infection (Onami et al., 2002). Additionally, CD43 was shown to negatively affect T cell activation due to its bulky structure and negative charges. This dogma differed from our observations that the glycosylated CD43 was preferentially retained on the fungal-specific cytokine-producing memory CD8+ T cells. A study showed that CD43 expression on CD8+ T cells positively regulated the clonal burst size and tissue trafficking of effector cells during the early phase of immune responses (Clark & Baum, 2012; Gringhuis et al., 2009). Thus, we explored the functional role of the CD43 expression on CD8+ T cells for fungal vaccine immunity. In Chapter III, we used both in vitro and in vivo mouse model systems to decipher the functional role of CD43 for antifungal immunity by CD8+ T cells. We found that CD43 deficiency severely impaired CD8+ T cell responses of both type 1 and type 3 responses to the experimental fungal vaccine. The defect was associated with poor lineage-specific differentiation and proliferation of effector CD8+ T cells. Using the adoptive transfer experiments, we found that cell-intrinsic expression of CD43 by CD8+ T cells was necessary for the effector responses. Further, in a gain-of-function study, supplementation of CD43 agonist mAb augmented the CD8+ T cell cytokine responses to fungal antigen in vitro. Pulmonary challenge infection of vaccinated mice showed that CD43 was required for vaccine immunity recapitulating the weaker vaccine responses. However, the recall responses of effector CD8+ T cells in the lung were independent of CD43 mediated recruitment, suggesting the predominant role of CD43 in the induction of robust vaccine responses. Finally, we explored if CD43 could be used as a marker for vaccine potency. Using a model of fungal antigens vaccination with adjuvants, we found a strong correlation of CD43 expressing effector CD8+ T cells in the lung with the vaccine immunity. Further, CD43+ CD8+ T cells correlated with activation of neutrophils that are shown to be important for important for killing the yeast. Thus, our study revealed that CD43 is an essential host-target element to bolster vaccine responses and as a potential biomarker of fungal immunity.

Graduation Semester

2022-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Srinivasu Mudalagiriyappa

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