Cryptococcus neoformans and the closely related C. gattii are major causes of life-threatening opportunistic infection in persons with AIDS. For example, it has been estimated that in Sub-Saharan Africa, ~600,000 people die annually from cryptococcosis and many survivors are left permanently impaired. People are exposed to the fungus following inhalation into the lungs; in those with normal immune systems, the infection is resolved or contained. However, in patients with defects in cell-mediated immunity, particularly AIDS, C. neoformans has a propensity to grow and disseminate, particularly to the central nervous system where it causes a fatal meningoencephalitis. Even with antifungal therapy, mortality hovers around 30%. Although an effective preventative vaccine given to at risk populations would have a major salutary impact on global public health, there are no candidate vaccines in clinical development. Efforts have mostly focused on subunit vaccines and protective antibodies, approaches that even if successful likely would be too costly to use in resource-poor settings. We have created a candidate low-cost vaccine consisting of a highly attenuated triple deletion C. neoformans strain that lacks cell wall chitosan. Remarkably, mice receiving a single pulmonary inoculation with this chitosan-deficient strain are protected against a robust challenge with a highly virulent strain of wild type C. neoformans. Importantly, the vaccine strain is rapidly cleared from the lungs of severely immunocompromised mice and retains its capacity to protect even when heat-killed. In this R01 application, we seek to further characterize the chitosan-deficient strain as a potential vaccine candidate, to explore the mechanisms of protection, and to determine if the protection will be expressed in preclinical animal models that mimic the development of late stage AIDS. There are three specific aims.
In Aim 1, we will further characterize the vaccination protocol, determine the protective characteristics of the attenuated strain, develop a vaccine with broader protection, as well as examine the safety and durability of the vaccine.
In Aim 2, we will explore the mechanisms of protection in immunocompetent mice. We will determine the contributions of the innate, cellular and humoral immune defenses.
In Aim 3, we will examine the protection in mice with CD4+ T cell deficiencies to determine if the vaccination could be effective in patients that acquire AIDS. We will model when the vaccine should be administered and determine if the mechanisms of protection differ between immunocompetent and immunodeficient mice. We anticipate that by the end of the funding period, we will have completed the characterization in mice of a novel vaccine candidate to protect against cryptococcosis. If these studies are successful, as our preliminary data suggest they will be, the next steps will be further preclinical safety and efficay studies in other animal models and then commercialization to test in humans.
Fungal infections have become more prevalent in recent years due to the increase in the immunocompromised patient populations with AIDS, and those undergoing organ transplants and chemotherapies. Cryptococcus neoformans is a pathogenic fungus which kills over 600,000 people per year, mostly in underdeveloped countries. Current therapies are inadequate because they are not effective enough or have significant toxicity. In this application, we explore vaccination with a highly attenuated mutant strain of Cryptococcus that is protective against a subsequent challenge with a virulent, wild-type strain and determine the mechanism of protection. This attenuated strain could be the basis for a vaccine against C. neoformans that would be particularly useful in patients with HIV that are at risk for acquiring a Cryptococcus infection.
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|Upadhya, Rajendra; Lam, Woei C; Maybruck, Brian T et al. (2017) A fluorogenic C. neoformans reporter strain with a robust expression of m-cherry expressed from a safe haven site in the genome. Fungal Genet Biol 108:13-25|
|Upadhya, Rajendra; Lam, Woei C; Maybruck, Brian et al. (2016) Induction of Protective Immunity to Cryptococcal Infection in Mice by a Heat-Killed, Chitosan-Deficient Strain of Cryptococcus neoformans. MBio 7:|