T69D/N pol mutation, human immunodeficiency virus type 1 RNA levels, and syncytium-inducing phenotype are associated with CD4 cell depletion during didanosine therapy.

The contribution of virologic and host factors to CD4 cell depletion associated with human immunodeficiency virus (HIV) type 1 was evaluated in children drawn from a larger efficacy trial of 2 doses of didanosine (ddI) monotherapy (Pediatric AIDS Clinical Trials Group 144). Thirty children, half with stable CD4 cell counts (non-progressors) and half with a marked decline in CD4 cells (progressors), were studied during 60-72 weeks of ddI therapy. The children were matched for age and CD4 cell counts at study entry. Three viral parameters, syncytium-inducing phenotype, higher virus load, and mutation in HIV-1 pol encoding the T69D/N mutation, were associated with disease progression. Disease progression was not associated with mutations in the reverse-transcriptase gene previously associated with resistance to ddI (L74V, K65R, or M184V). The selection of the T69D/N mutation in children with HIV-1 disease progression during ddI therapy suggests that this mutation confers a fitness advantage to the virus that may include resistance to ddI.