Canarypox vaccines induce antigen-specific human γδ T cells capable of interferon-γ production

Induction of human gamma delta T cells was investigated in subjects who were vaccinated with live recombinant canarypox virus expressing human immunodeficiency virus (HIV) proteins or soluble MN rgp120. Both canarypox and rgp120 induced antigen-specific lymphoproliferative and interferon (IFN)-gamma responses. However, only canarypox vaccination induced increased gamma delta T cell responses detectable after secondary in vitro expansion (P < .02). These enhanced <gamma>delta T cell responses were specific for canarypox but not HIV antigens. Canarypox-specific gamma delta T cells were predominantly V gamma9(+) and produced intracellular and secreted IFN-gamma. gamma delta T cell lines generated from canarypox vaccinees responded to canarypox antigens but not to mycobacterial antigens shown previously to induce bacille Calmette-Guerin-specific gamma delta T cells. Furthermore, canarypox vaccinations were associated with significantly higher NK cell expansions (P = .02). Increased IFN-gamma production by gamma delta T and NK cells could enhance the induction of protective type 1 memory immunity. Thus, stimulation of gamma delta T cells might be an important feature of live vaccines.