Affiliation:
1. Department of Medicine, University of Massachusetts Chan Medical School, Worcester, Massachusetts, USA
2. Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA
Abstract
ABSTRACT
The global burden of infections due to the pathogenic fungus
Cryptococcus
is substantial in persons with low CD4
+
T-cell counts. Previously, we deleted three chitin deacetylase genes from
Cryptococcus neoformans
to create a chitosan-deficient, avirulent strain, designated as
cda1∆2∆3∆
, which, when used as a vaccine, protected mice from challenge with virulent
C. neoformans
strain KN99. Here, we explored the immunological basis for protection. Vaccine-mediated protection was maintained in mice lacking B cells or CD8
+
T cells. In contrast, protection was lost in mice lacking α/β T cells or CD4
+
T cells. Moreover, CD4
+
T cells from vaccinated mice conferred protection upon adoptive transfer to naive mice. Importantly, while monoclonal antibody-mediated depletion of CD4
+
T cells just prior to vaccination resulted in complete loss of protection, significant protection was retained in mice depleted of CD4
+
T cells after vaccination but prior to challenge. Vaccine-mediated protection was lost in mice genetically deficient in interferon-γ (IFNγ), tumor necrosis factor alpha (TNFα), or interleukin (IL)-23p19. A robust influx of leukocytes and IFNγ- and TNFα-expressing CD4
+
T cells was seen in the lungs of vaccinated and challenged mice. Finally, a higher level of IFNγ production by lung cells stimulated ex vivo correlated with lower fungal burden in the lungs. Thus, while B cells and CD8
+
T cells are dispensable, IFNγ and CD4
+
T cells have overlapping roles in generating protective immunity prior to
cda1∆2∆3∆
vaccination. However, once vaccinated, protection becomes less dependent on CD4
+
T cells, suggesting a strategy for vaccinating HIV
+
persons prior to loss of CD4
+
T cells.
IMPORTANCE
The fungus
Cryptococcus neoformans
is responsible for >100,000 deaths annually, mostly in persons with impaired CD4
+
T-cell function such as AIDS. There are no approved human vaccines. We previously created a genetically engineered avirulent strain of
C. neoformans
, designated as
cda1∆2∆3∆
. When used as a vaccine,
cda1∆2∆3∆
protects mice against a subsequent challenge with a virulent
C. neoformans
strain. Here, we defined components of the immune system responsible for vaccine-mediated protection. We found that while B cells and CD8
+
T cells were dispensible, protection was lost in mice genetically deficient in CD4
+
T cells and the cytokines IFNγ, TNFα, or IL-23. A robust influx of cytokine-producing CD4
+
T cells was seen in the lungs of vaccinated mice following infection. Importantly, protection was retained in mice depleted of CD4
+
T cells following vaccination, suggesting a strategy to protect persons who are at risk of future CD4
+
T-cell dysfunction.
Funder
HHS | NIH | National Institute of Allergy and Infectious Diseases
Publisher
American Society for Microbiology