Characterization of a newly discovered T-cell receptor beta-chain heterodimer expressed on a CD8+ bone marrow subpopulation that promotes allogeneic stem cell engraftment.

The facilitating cell is a rare CD8+ bone marrow subpopulation that can enhance allogeneic hematopoietic stem cell engraftment across complete major histocompatibility complex barriers without inducing acute graft-versus-host disease. Here we describe a CD3epsilon-associated complex on the facilitating cell surface that consists of the T-cell receptor beta-chain disulfide-linked to a previously unknown 33-kilodalton glycoprotein. Provisionally called FCp33, this glycoprotein does not represent any of the known protein chains or surrogates associated with CD3-T-cell receptor beta. Expression of this CD3-T-cell receptor beta-FCp33 complex directly correlates with the facilitating cell's functional ability to enhance allogeneic stem cell engraftment in vivo.