Cross-reactions between the cytotoxic T-lymphocyte responses of human immunodeficiency virus-infected African and European patients

Abstract

The great variability of protein sequences from human immunodeficiency virus (HIV) type 1 (HIV-1) isolates represents a major obstacle to the development of an effective vaccine against this virus. The surface protein (Env), which is the predominant target of neutralizing antibodies, is particularly variable. Here we examine the impact of variability among different HIV-1 subtypes (clades) on cytotoxic T-lymphocyte (CTL) activities, the other major component of the antiviral immune response. CTLs are produced not only against Env but also against other structural proteins, as well as some regulatory proteins. The genetic subtypes of HIV-1 were determined for Env and Gag from several patients infected either in France or in Africa. The cross-reactivities of the CTLs were tested with target cells expressing selected proteins from HIV-1 isolates of clade A or B or from HIV type 2 isolates. All African patients were infected with viruses belonging to clade A for Env and for Gag, except for one patient who was infected with a clade A Env-clade G Gag recombinant virus. All patients infected in France were infected with clade B viruses. The CTL responses obtained from all the African and all the French individuals tested showed frequent cross-reactions with proteins of the heterologous clade. Epitopes conserved between the viruses of clades A and B appeared especially frequent in Gag p24, Gag p18, integrase, and the central region of Nef. Cross-reactivity also existed among Gag epitopes of clades A, B, and G, as shown by the results for the patient infected with the clade A Env-clade G Gag recombinant virus. These results show that CTLs raised against viral antigens from different clades are able to cross-react, emphasizing the possibility of obtaining cross-immunizations for this part of the immune response in vaccinated individuals.

FIG. 1

Phylogenetic analysis of gag nucleotide sequences. The phylogenetic tree was generated by the neighbor-joining method and drawn with Njplot. The numbers given at the branch points are the 50% threshold majority consensus values for 100 bootstrap replicates. The lengths of the horizontal branches are proportional to the relative evolutionary distances; vertical distances are for clarity only. The strains isolated from the African patients described in this study, as well as the strain used to produce the recombinant vaccinia viruses encoding the gag gene (92CAR3252), are shown in bold type.

FIG. 2

CTL activities in patients carrying viruses B18 (infected with clade A HIV-1) (A) and CO3M (infected with clade B HIV-1) (B). Effector cells were tested after in vitro restimulation with autologous blast cells. Target cells were infected with recombinant vaccinia viruses expressing the Env, Gag, Pol, or Nef protein of clade A and B isolates.

FIG. 3

Recognition of known epitopes by CTLs from African patients. CTLs were produced by in vitro stimulation with synthetic peptides. They were tested against target cells previously treated with the corresponding peptide or infected with recombinant vaccinia virus (Vac) (except for the B12 cell line, because effector cells were not available). The HLA typing was as follows: for B12, HLA-A3/32, B41/−, C3/6; for B22, HLA-A2/30, B27/44, C2/−; and for B18, HLA-A2/31, B13/55, C2/6. The target cells were heterologous EBV-LCL sharing HLA-A3 with B12 CTLs, HLA-B27 with B22 CTLs, or HLA-A2 with B18 CTLs.