Association of age at antiretroviral therapy initiation with CD4 +  : CD8 + ratio recovery among virally suppressed people with HIV.

OBJECTIVE: To investigate the association of age at antiretroviral therapy (ART) initiation with CD4 +  : CD8 + T-cell ratio in virally suppressed people with HIV on long-term ART, and to characterize potential CD4 +  : CD8 + ratio recovery in this population by age. DESIGN: A longitudinal study of people attending an HIV clinic at the Royal Free Hospital NHS Trust, London, who initiated ART between 2001 and 2015, and achieved and maintained HIV-1 viral suppression (viral load <1,000 copies/ml). The association of age group at ART initiation with CD4 +  : CD8 + ratio at 5 and 10 years was assessed. METHODS: Multivariable linear regression was used to investigate the relationship between age at ART initiation and log CD4 +  : CD8 + ratio, adjusting for demographic factors (gender/HIV transmission route, ethnicity), baseline CD4 + count and calendar year. RESULTS: The sample included 1859 people aged 20-78 (75% men, 56% white ethnicity). Overall, median CD4 +  : CD8 + T-cell ratio increased from 0.24 at baseline to 0.77 at year 5 and 0.88 at year 10. Ratios increased among all age groups in unadjusted and adjusted models but increased less among older ages (baseline ages 60-69 and 70-79). Median ratios at year 5 were 0.85, 0.80, 0.72, 0.76, 0.6, and 0.44, respectively, among people aged 20-29, 30-39, 40-49, 50-59, 60-69 and 70-79 years at baseline. CONCLUSION: In a virally suppressed London population, age had a substantial impact on CD4 +  : CD8 + ratio recovery, especially for those starting ART after age 60 years. Results may indicate the level of CD4 +  : CD8 + ratio recovery possible in an HIV-positive, virally suppressed, aging population.

A phylogenetic approach to cultural evolution.

There has been a rapid increase in the use of phylogenetic methods to study the evolution of languages and culture. Languages fit a tree model of evolution well, at least in their basic vocabulary, challenging the view that blending, or admixture among neighbouring groups, was predominant in cultural history. Here, we argue that we can use language trees to test hypotheses about not only cultural history and diversification, but also bio-cultural adaptation. Phylogenetic comparative methods take account of the non-independence of cultures (Galton's problem), which can cause spurious statistical associations in comparative analyses. Advances in phylogenetic methods offer new possibilities for the analysis of cultural evolution, including estimating the rate of evolution and the direction of coevolutionary change of traits on the tree. They also enable phylogenetic uncertainty to be incorporated into the analyses, so that one does not have to treat phylogenetic trees as if they were known without error.