Genetic and stochastic influences on the interaction of human immunodeficiency virus type 1 and cytotoxic T lymphocytes in identical twins

Abstract

Human immunodeficiency virus type 1 (HIV-1) evolves in vivo under selective pressure from CD8+ T-lymphocyte (CTL) responses, which are in turn determined by host and viral genetic factors, such as restricting major histocompatibility complex molecules and the available viral epitope sequences. However, CTL are derived stochastically through the random gene rearrangements to produce T-cell receptors (TCR), and the relative impact of genetic versus stochastic processes on CTL targeting of HIV and immune-driven viral evolution is unclear. Here we evaluate identical twins infected with HIV-1 as neonates from a common blood transfusion, with subsequently similar environmental exposures, thereby allowing controlled comparisons of CTL targeting and viral evolution. Seventeen years after infection, their CTL targeting of HIV-1 was remarkably similar. In contrast, their overall TCR profiles were highly dissimilar, and a dominant epitope was recognized by distinctly different TCR in each twin. Furthermore, their viral epitopes had diverged, and there was ongoing viral phylogenetic divergence between the twins between 12 and 17 years after infection. These results indicate that while CTL targeting is predominately genetically determined, stochastic influences render the interaction of HIV-1 and host immunity, and therefore viral escape and CTL efficacy, unpredictable.

FIG. 1.

Clinical course and treatment of identical twins infected with HIV-1 via neonatal blood transfusion. Peripheral blood CD4⁺ T-lymphocyte counts (closed symbols) and plasma HIV-1 RNA levels (open symbols) are plotted for both twins (circles, twin 1-05; triangles, twin 1-06). The antiretroviral drug treatment history is indicated. ZDV, zidovudine; ddc, dideoxycytidine; ddI, didanosine; NVP, nevirapine; 3TC, lamivudine; NLV, nelfinavir; EFV, efavirenz; D4T, stavudine; SQV, saquinavir; LPV/r, lopinavir-ritonavir.

FIG. 2.

HIV-1-specific CTL targeting of the twins. (a) The schematic indicates CTL targeting in the twins in 12/00 and 6/01. Upper and lower arrows indicate locations of recognized peptides for twins 1-05 and 1-06, respectively. (b) The screening clade B consensus peptides eliciting these responses by ELISpot are shown. The HIV-1 sequences in the twins (consensus of sequences obtained from PBMC) from 12/00 corresponding to recognized peptides or overlapping regions of consecutive peptides (containing the recognized epitope) are indicated. A dash indicates an amino acid identical to the clade B consensus sequence; x indicates lack of consensus among sequences.

FIG. 3.

T-cell receptor V_β spectratype analysis of CD8⁺ T lymphocytes. TCR V_β distributions were assessed and compared. (a) Spectratyping was performed using CD8⁺ T lymphocytes from both twins from 12/00. Representative profiles are shown for four V_β families. Of the numerous expanded peaks deviating from Gaussian distribution, a few were common to both twins (e.g., V_β13.2), but most were discordant (e.g., V_β11, V_β15, and V_β22). (b) Spectratyping was performed on CD8⁺ lymphocytes from the twins in 12/00 and 6/01. Spearman correlation coefficients of expanded peaks in intra- and intertwin comparisons are given. Identical analyses of eight unrelated HIV-1-seropositive control subjects (28 interindividual comparisons) revealed a mean correlation coefficient of 0.28 ± 0.19 (data not shown).

FIG. 4.

Peptide-specific T-cell receptor V_β spectratype analysis. PBMC from 9/01 were cultured in the presence or absence of the Pol peptide HKAIGTVLVGPTPVN (Pol 125-139; protease 69-83), which was the dominantly recognized peptide for both twins (accounting for approximately 50% of the detected HIV-1-specific CTL [data not shown]). Spectratyping then was performed on the CD8⁺ cells from each twin. Histograms from four representative V_β families are shown; peptide-stimulated expansions are shaded (peaks whose ratio versus the median of all peaks in the family increased by at least 2 and rose at least twofold after stimulation). The accompanying table indicates the specific peaks within each of the 24 V_β families that were expanded in response to peptide stimulation. N.D. indicates that data were not available.

FIG. 5.

Phylogenetic analysis of HIV-1 pol, env, and nef sequences. Phylogenetic relationships between pol (A), env (B), and nef (C) sequences from 1995 and 2000 are shown. Open and closed circles represent twin 1-05 sequences from 1995 and 2000, respectively; open and closed triangles represent twin 1-06 sequences from 1995 and 2000, respectively. HXB2, RF, and JR-CSF sequences were used as outgroups for the phylogenetic tree.