One of Dr. Yueh-hsiu Chien's main research focuses is to define γδ T cell function so that we can better understand host immune defense. γδ T cells, together with B cells and αβ T cells, are the only cells that use somatic V, D, J gene rearrangement to generate diverse antigen receptors. All three types of cells are present together in all but the most primitive vertebrates, suggesting that each population contributes to host immune competence uniquely and that all three are necessary for maintaining immune competence.