Objectives: Cryptococcus neoformans is the most important fungal pathogen causing CNS-related mortality and morbidity world-wide. Although CM is generally viewed as a disease caused by weak immunity, evidence accumulates that exuberant host immune responses significantly contribute to the pathogenesis of CM. To this end, we developed a murine model of CM that reproduces major features of inflammatory CNS injury in CM patients and found that the exuberant CNS inflammation, driven by ultra Th1-polarized T cells and inflammatory monocytes, promotes severe immunopathology with neurological deterioration. Regulatory T cells (Tregs) are the crucial component of this immunoregulatory network, and their dysfunction is linked to inflammatory complications of CM in human patients. Our published and unpublished Preliminary Data now support that Treg play crucial roles in limiting the pathological inflammation within the Cryptococcus-infected CNS. Our preliminary data further show that Treg specifically express chemokine receptor CCR8 and that Treg-recruitment kinetics is paralleled by the upregulation of CCR8 ligand chemokine CCL1, supporting the importance of the CCL1/CCR8 axis in mediating CNS migration of Treg. We show that among all cellular populations within the CNS, Treg are the major, if not sole producer of the immune- regulatory cytokine IL-10 and Amphiregulin (Areg), factor known to promote wound healing and tissue repair. Hypothesis: Hypothesis that CCL1/CCR8-axis-recruited Treg protect against severe CNS damage and subsequent mortality in mice with CM via production of IL-10 and Areg and that Treg-based immunotherapies will reduce morbidity and mortality in mice with CM. To test distinct parts of this hypothesis we will: Aim 1. To demonstrate that CCR8-recruited Treg protect the brain from inflammatory pathology in CM 1.a. determine if Treg limit excessive CNS inflammation during CM, especially reducing pathological elements of the CNS host response 1.b. define whether and how Treg reduce neuropathological processes in the CM-afflicted brain 1.c. demonstrate the dependence of the CCR8 axis for CNS Treg accumulation and their function during CM. Aim 2: To define the therapeutic effects of Treg in CM 2.a. demonstrate that Treg enhancement by IL-2 immune complex therapy protects mice from fatal CM pathology 2.b. determine if CCR8+ versus CCR8- Treg adoptive transfer protects mice from fatal CM pathology Aim 3: To determine the mechanisms by which Treg limit CNS inflammation and promote neurological repair during CM 3.a. determine if Treg-derived IL-10 is required for limiting pathological CNS inflammation during CM 3.b. define whether Treg-derived Areg promotes neurological repair during CM. Research Plan and Methods: This proposal will use our established mouse model of CM, which accurately recapitulates severe paradoxical immune responses experienced by patients with C. neoformans CNS infection. We will manipulate Treg system (remove or expand T...