CD8 ⁺ T cells and risk for bacterial pneumonia and all-cause mortality among HIV-infected women

Background: Bacterial pneumonia risk is disproportionately high among those infected with HIV. This risk is present across all CD4 ⁺ T-cell levels (TCLs), suggesting that additional factors govern susceptibility. This study examines CD8 ⁺ TCLs and risk for HIV-associated bacterial pneumonia and all-cause mortality. Methods: Demographic, clinical, and laboratory data were obtained for 885 HIV-infected women enrolled in the HIV Epidemiologic Research Study (HERS). Bacterial pneumonia cases were identified using clinical, microbiological, and radiographic criteria. CD8 ⁺ TCLs were assessed at 6-month intervals. Statistical methods included Cox proportional hazards regression modeling and covariateadjusted survival estimates. Results: Relative to a referent CD8 ⁺ TCL of 401-800 cells per cubic millimeter, risk for bacterial pneumonia was significantly higher when CD8 ⁺ TCLs were <400 (hazard ratio 1.65, P = 0.017, 95% confidence interval 1.10 to 2.49), after adjusting for age, CD4 ⁺ TCL, viral load, and antiretroviral use. There was also a significantly higher risk of death when CD8 ⁺ TCLs were ≤400 cells per cubic millimeter (hazard ratio 1.45, P = 0.04, 95% confidence interval 1.02 to 2.06). Covariate-adjusted survival estimates revealed shorter time to pneumonia and death in this CD8 ⁺ TCL category, and the overall associations of the categorized CD8 ⁺ TCL with bacterial pneumonia and all-cause mortality were each statistically significant (P = 0.017 and P < 0.0001, respectively). Conclusions: CD8 ⁺ TCL ≤400 cells per cubic millimeter was associated with increased risk for pneumonia and all-cause mortality in HIV-infected women in the HERS cohort, suggesting that CD8 ⁺ TCL could serve as an adjunctive biomarker of pneumonia risk and mortality in HIV-infected individuals.