Three-Family $SO(10)$ Grand Unification in String Theory
  The construction of a supersymmetric $SO(10)$ grand unification with 5 left-handed and 2 right-handed families in the four-dimensional heterotic string theory is presented. The model has one $SO(10)$ adjoint Higgs field. The $SO(10)$ current algebra is realized at level 3. 
Zurab Kakushadze and S.-H. Henry Tye