The CD8 coreceptor plays a critical role in the recognition of foreign
antigens by mature T cells and in the development of class I-restrict
ed T cells. CD8 can be expressed on the surface of T cells as either a
heterodimer composed of an alpha and beta chain, or as a homodimer co
mposed of two alpha chains. In this report, we show that a CD8 beta tr
ansgene that lacks a cytoplasmic domain can suppress expression of wil
d-type endogenous CD8 beta and act as a dominant negative mutation. We
show that this dominant negative CD8 beta transgene interferes with t
he development of mature CD8 T cells to different extents depending on
the individual class I-restricted TCR. These data suggest CD8 beta pl
ays a role in thymic development, and that different class I-restricte
d TCRs differ in their dependence on the cytoplasmic tail of CD8 beta.