Functional and structural similarity of V gamma 9V delta 2 T cells in humans and Aotus monkeys, a primate infection model for Plasmodium falciparum malaria.

Gammadelta T cells are implicated to play crucial roles during early immune responses to pathogens. A subset of human gammadelta T cells carrying the Vgamma9Vdelta2 TCR recognize small, phosphorylated nonpeptidic Ags. However, the precise role of these cells and the ligands recognized in human immune responses against pathogens remains unclear because of the lack of suitable animal models. We have analyzed the reactivity of spleen cells of the New World monkey Aotus nancymaae against isopentenyl pyrophosphate (IPP), a phosphorylated microbial metabolite selectively activating Vgamma9Vdelta2 T cells. Spleen cells were stimulated by IPP and the expanding cell population expressed the Vgamma9 TCR. TRGV-J and TRDV-D-J rearrangements expressed by IPP-stimulated cells of Aotus were analyzed by RT-PCR and DNA sequencing. The TRGV-J and TRDV-D-J rearrangements expressed by IPP-stimulated Aotus and human gammadelta T cells were similar with respect to 1) TCR gene segment usage, 2) a high degree of germline sequence homology of the TCR gene segments used, and 3) the diversity of the CDR3 regions. Phylogenetic analysis of human, Pan troglodytes, and A. nancymaae TRGV gene segments showed that the interspecies differences are smaller than the intraspecies differences with TRGV9 gene segments located on a distinct clade of the phylogenetic tree. The structural and functional conservation of Vgamma9Vdelta2 T cells in A. nancymaae and humans implicates a functionally important and evolutionary conserved mechanism of recognition of phosphorylated microbial metabolites.

Sequence and diversity of T-cell receptor beta-chain V and J genes of the owl monkey Aotus nancymaae.

The New World primate Aotus nancymaae is susceptible to infection with the human malaria parasite Plasmodium falciparum and has therefore been recommended by the World Health Organization as a model for the evaluation of malaria vaccine candidates. Recently, we have shown that Aotus TCRVA genes and TCRJA segments exhibit a high degree of similarity to human counterparts. In the present report we used reverse transcription polymerase chain reaction to analyze the sequences of A. nancymaae TCR beta-chain gene rearrangements. Alignment with human sequences and phylogenetic comparison identified 18 distinct Aotus TCRBV genes homologous to the human TCRBV gene families 2, 4, 5, 6, 7, 9, 12, 15, 24, and 28. Multiple Aotus genes were found in the TCRBV4, 5, 6, and 7 families. Some of these TCRBV genes aligned best to the same human gene and thus do not seem to have separate human homologues. Amino acid sequences of the Aotus TCRBV genes were 77 to 90% identical to their closest human counterparts. Ten distinct Aotus TCRBJ segments homologous to the human segments J1-1, J1-2, J1-4, J1-5, J1-6, J2-1, J2-2, J2-3, J2-4, J2-5 were found. In some cases the amino acid sequences of Aotus and human TCRBJ segments were completely identical. A comparison of the proportion of synonymous and non-synonymous substitutions in Aotus vs human beta-chain-encoding genes revealed a dominance of synonymous substitutions in TCRBJ segments and of nonsynonymous substitutions in TCRBV segments. Dominance of nonsynonymous substitutions was more pronounced in TCRBV CDR1 and CDR2 regions than in the framework regions. No evidence for the emergence of new TCRBJ segments or TCRBV families was found. These results confirm that the TCR repertoire in primates is remarkably stable and support the concept of using Aotus monkeys as an infection model for the evaluation of future subunit vaccine candidates.