Disclosed herein, the parental antibodies from the hybridomas YTS 169.4.2.1 (YTS169) and 2.43 were engineered into minibody and diabody fragments. Both the YTS and 2.43 antibodies bind mCD8+. However, they differ in that the YTS 169 antibodies bind both Lyt2.1 and Lyt2.2 while the 2.43 antibodies bind an epitope that is Lyt2.2 specific. These novel minibodies and diabodies retained their antigen specificity as shown by flow cytometry and ImmunoPET imaging. Most importantly, both the 2.43 and YTS169 minibodies and diabodies produced high contrast ImmunoPET images of CD8+ lymphoid organs at only four hours post-injection.
