Immune escape precedes breakthrough human immunodeficiency virus type 1 viremia and broadening of the cytotoxic T-lymphocyte response in an HLA-B27-positive long-term-nonprogressing child

Abstract

The emergence of cytotoxic T-lymphocyte (CTL) escape mutations in human immunodeficiency virus type 1 (HIV-1) proteins has been anecdotally associated with progression to AIDS, but it has been difficult to determine whether viral mutation is the cause or the result of increased viral replication. Here we describe a perinatally HIV-infected child who maintained a plasma viral load of <400 copies/ml for almost a decade until a nonbinding escape mutation emerged within the immunodominant CTL epitope. The child subsequently experienced a reemergence of HIV-1 viremia accompanied by a marked increase in the number of CTL epitopes targeted. This temporal pattern suggests that CD8 escape can play a causal role in the loss of immune control.

FIG. 1.

Longitudinal clinical, CTL, and viral sequence data for patient TCH-043. AZT, zidovudine; DDI, didanosine; SFC, spot-forming cells. (Top panel) Longitudinal changes in viral load and CD4 count from time of diagnosis to present. Where viral load measurements were beneath the limit of detection, the threshold value is shown. Viral sequencing was performed at the time points indicated (×), given in years of patient age. (Middle panel) Longitudinal changes in CTL recognition of three immunodominant epitopes were assessed by an IFN-γ ELISPOT assay. A26-EL9 was not tested when the patient was 7.2 years old, but a 17-mer containing this epitope (AFSPEVIPMFSALSEGA; indicated by an asterisk) was not recognized. The dotted vertical line indicates the earliest measurable return of viremia (640 copies/ml) at age 9.4 years. (Bottom panel) Fraction of autologous viral sequences containing the R132T mutation.

FIG. 2.

Broadening of CTL response precedes viral breakthrough. Recognition of overlapping 15-mer peptides spanning clade B HIV-1 Gag, Nef, RT, and gp41 was assessed by an IFN-γ ELISPOT assay when the patient was 7.4 years old (2 years before viral breakthrough) and 9.2 years old (2 months before viral breakthrough). In addition, 18-mer peptides spanning all other HIV-1 gene products (gp120, Rev, Tat, Vpr, Vpu, Vif, protease, and integrase) were tested when the patient was 9.2 years old but not at 7.4 years of age. Missing data are indicated by asterisks.

FIG. 3.

Longitudinal HIV-1 sequence changes in B27-KK10. (Top panel) Longitudinal changes within the Gag epitope B27-KK10 were determined by clonal sequencing of samples from patient TCH-043 and the subject's mother. The R132T mutation in B27-KK10 was present in a minority of clones when the patient was 7.8 years old but became the predominant species at the time of viral breakthrough at age 9.4 years. Minor variants are shown in gray. The number of clones with given mutations per total number of clones is given in the final column. (Bottom panel) Maximum likelihood phylogenetic tree showing the evolution of HIV in patient TCH-043 over time. Branch color corresponds to the time point at which each clone was isolated (given as age of patient TCH-043 in years). All viral clones within the shaded box possess the R132T mutation. All branch lengths are drawn to scale.