The phenotype of the Cryptococcus-specific CD4+ memory T-cell response is associated with disease severity and outcome in HIV-associated cryptococcal meningitis

Efficient phagocytosis and laccase activity affect the outcome of HIV-associated cryptococcosis

BACKGROUND

Cryptococcal meningitis (CM) is a leading cause of HIV-associated mortality globally. High fungal burden in cerebrospinal fluid (CSF) at diagnosis and poor fungal clearance during treatment are recognized adverse prognostic markers; however, the underlying pathogenic factors that drive these clinical manifestations are incompletely understood. We profiled a large set of clinical isolates for established cryptococcal virulence traits to evaluate the contribution of C. neoformans phenotypic diversity to clinical presentation and outcome in human cryptococcosis.

METHODS

Sixty-five C. neoformans isolates from clinical trial patients with matched clinical data were assayed in vitro to determine murine macrophage uptake, intracellular proliferation rate (IPR), capsule induction, and laccase activity. Analysis of the correlation between prognostic clinical and host immune parameters and fungal phenotypes was performed using Spearman's r, while the fungal-dependent impact on long-term survival was determined by Cox regression analysis.

RESULTS

High levels of fungal uptake by macrophages in vitro, but not the IPR, were associated with CSF fungal burden (r = 0.38, P = 0.002) and long-term patient survival (hazard ratio [HR] 2.6, 95% CI 1.2-5.5, P = 0.012). High-uptake strains were hypocapsular (r = -0.28, P = 0.05) and exhibited enhanced laccase activity (r = 0.36, P = 0.003). Fungal isolates with greater laccase activity exhibited heightened survival ex vivo in purified CSF (r = 0.49, P < 0.0001) and resistance to clearance following patient antifungal treatment (r = 0.39, P = 0.003).

CONCLUSION

These findings underscore the contribution of cryptococcal-phagocyte interactions and laccase-dependent melanin pathways to human clinical presentation and outcome. Furthermore, characterization of fungal-specific pathways that drive clinical manifestation provide potential targets for the development of therapeutics and the management of CM.

FUNDING

This work was made possible by funding from the Wellcome Trust (WT088148MF), the Medical Research Council (MR/J008176/1), the NIHR Surgical Reconstruction and Microbiology Research Centre and the Lister Institute for Preventive Medicine (to R.C. May), and a Wellcome Trust Intermediate fellowship (089966, to T. Bicanic). The C. neoformans isolates were collected within clinical trials funded by the British Infection Society (fellowship to T. Bicanic), the Wellcome Trust (research training fellowships WT069991, to A.E. Brouwer and WT081794, to J.N. Jarvis), and the Medical Research Council, United Kingdom (76201). The funding sources had no role in the design or conduct of this study, nor in preparation of the manuscript.

A neglected epidemic: fungal infections in HIV/AIDS

Invasive fungal infections (IFIs) are a major cause of HIV-related mortality globally. Despite widespread rollout of combined antiretroviral therapy, there are still up to 1 million deaths annually from IFIs, accounting for 50% of all AIDS-related death. A historic failure to focus efforts on the IFIs that kill so many HIV patients has led to fundamental flaws in the management of advanced HIV infection. This review, based on the EMBO AIDS-Related Mycoses Workshop in Cape Town in July 2013, summarizes the current state of the-art in AIDS-related mycoses, and the key action points required to improve outcomes from these devastating infections.

Macrophage Cryptococcus interactions: an update

Cryptococcus species are fungal pathogens that are a leading cause of mortality. Initial inoculation is through the pulmonary route and, if disseminated, results in severe invasive infection including meningoencephalitis. Macrophages are the dominant phagocytic cell that interacts with Cryptococcus. Emerging theories suggest that Cryptococcus microevolution in macrophages is linked to survival and virulence within the host. In addition, Cryptococcus elaborates virulence factors as well as usurps host machinery to establish macrophage activation states that are permissive to intracellular survival and replication. In this review, we provide an update of the recent findings pertaining to macrophage interaction with Cryptococcus and focus on new avenues for biomedical research.

Determinants of mortality in a combined cohort of 501 patients with HIV-associated Cryptococcal meningitis: implications for improving outcomes

Cerebrospinal fluid fungal burden, altered mental status, and rate of clearance of infection predict acute mortality in HIV-associated cryptococcal meningitis. The identification of factors associated with mortality informs strategies to improve outcomes.

Background. Cryptococcal meningitis (CM) is a leading cause of death in individuals infected with human immunodeficiency virus (HIV). Identifying factors associated with mortality informs strategies to improve outcomes.

Methods. Five hundred one patients with HIV-associated CM were followed prospectively for 10 weeks during trials in Thailand, Uganda, Malawi, and South Africa. South African patients (n = 266) were followed for 1 year. Similar inclusion/exclusion criteria were applied at all sites. Logistic regression identified baseline variables independently associated with mortality.

Results. Mortality was 17% at 2 weeks and 34% at 10 weeks. Altered mental status (odds ratio [OR], 3.1; 95% confidence interval [CI], 1.7–5.9), high cerebrospinal fluid (CSF) fungal burden (OR, 1.4 per log₁₀ colony-forming units/mL increase; 95% CI, 1.0–1.8), older age (>50 years; OR, 3.9; 95% CI, 1.4–11.1), high peripheral white blood cell count (>10 × 10⁹ cells/L; OR, 8.7; 95% CI, 2.5–30.2), fluconazole-based induction treatment, and slow clearance of CSF infection were independently associated with 2-week mortality. Low body weight, anemia (hemoglobin <7.5 g/dL), and low CSF opening pressure were independently associated with mortality at 10 weeks in addition to altered mental status, high fungal burden, high peripheral white cell count, and older age.

In those followed for 1 year, overall mortality was 41%. Immune reconstitution inflammatory syndrome occurred in 13% of patients and was associated with 2-week CSF fungal burden (P = .007), but not with time to initiation of antiretroviral therapy (ART).

Conclusions. CSF fungal burden, altered mental status, and rate of clearance of infection predict acute mortality in HIV-associated CM. The results suggest that earlier diagnosis, more rapidly fungicidal amphotericin-based regimens, and prompt immune reconstitution with ART are priorities for improving outcomes.

HIV and co-infections

Despite significant reductions in morbidity and mortality secondary to availability of effective combination anti-retroviral therapy (cART), human immunodeficiency virus (HIV) infection still accounts for 1.5 million deaths annually. The majority of deaths occur in sub-Saharan Africa where rates of opportunistic co-infections are disproportionately high. In this review, we discuss the immunopathogenesis of five common infections that cause significant morbidity in HIV-infected patients globally. These include co-infection with Mycobacterium tuberculosis, Cryptococcus neoformans, hepatitis B virus, hepatitis C virus, and Plasmodium falciparum. Specifically, we review the natural history of each co-infection in the setting of HIV, the specific immune defects induced by HIV, the effects of cART on the immune response to the co-infection, the pathogenesis of immune restoration disease (IRD) associated with each infection, and advances in the areas of prevention of each co-infection via vaccination. Finally, we discuss the opportunities and gaps in knowledge for future research.

Cryptococcosis-IRIS is associated with lower cryptococcus-specific IFN-γ responses before antiretroviral therapy but not higher T-cell responses during therapy

BACKGROUND

Cryptococcosis-associated immune reconstitution inflammatory syndrome (C-IRIS) may be driven by aberrant T-cell responses against cryptococci. We investigated this in human immunodeficiency virus (HIV)-infected patients with treated cryptococcal meningitis (CM) commencing combination antiretroviral therapy (cART).

METHODS

Mitogen- and cryptococcal mannoprotein (CMP)-activated (CD25+CD134+) CD4+ T cells and -induced production of interferon-gamma (IFN-γ), IL-10, and CXCL10 were assessed in whole blood cultures in a prospective study of 106 HIV-CM coinfected patients.

RESULTS

Patients with paradoxical C-IRIS (n = 27), compared with patients with no neurological deterioration (no ND; n = 63), had lower CMP-induced IFN-γ production in 24-hour cultures pre-cART and 4 weeks post-cART (P = .0437 and .0257, respectively) and lower CMP-activated CD4+ T-cell counts pre-cART (P = .0178). Patients surviving to 24 weeks had higher proportions of mitogen-activated CD4+ T cells and higher CMP-induced CXCL10 and IL-10 production in 24-hour cultures pre-cART than patients not surviving (P = .0053, .0436 and .0319, respectively). C-IRIS was not associated with higher CMP-specific T-cell responses before or during cART.

CONCLUSION

Greater preservation of T-cell function and higher CMP-induced IL-10 and CXCL10 production before cART are associated with improved survival while on cART. Lower CMP-induced IFN-γ production pre-cART, but not higher CMP-specific T-cell responses after cART, were risk factors for C-IRIS.