Two B cell epitopes of HIV-1 Tat protein have limited antigenic polymorphism in geographically diverse HIV-1 strains.

HIV-1 Tat, a secreted virally encoded toxin, enhances chronic viral replication and induces immune suppression, activities blocked in vitro and in vivo by anti-Tat antibodies. We mapped HIV-1 Tat B cell epitopes, determined sequence variation within them in 350 Tat sequences in GenBank, and determined antigenic cross-reactions between significant amino acid polymorphs. Two of the four B cell epitope sequences identified had limited or no antigenic polymorphism within geographically diverse strains. For epitope 1 in primates, (V,I)4DP(R,K,S,N)7L(E,D)9PW(N,K)12, the most frequent antigenic polymorphs were VDPRLEPWK in B clades (75%) and VDPNLEPWN in non-B clades (64%), with five additional sequences occurring at lower incidence. Epitope 2 in primates, K41(G,A)42LGISYGRK50, had no antigenic polymorphism. These two epitopes have potential utility for the generation of universal vaccine immunogens and therapeutic antibodies.