I finally got it:
=IF([Gate1 Rvw]="","",IF([BD Status]="Qualified Gate 1",[Gate1 Rvw],IF([Gate2 Rvw]="","",IF([BD Status]="Qualified Gate 2",[Gate2 Rvw],IF([Gate3 Rvw]="","",IF([BD Status]="Qualified Gate 3",[Gate3 Rvw],IF([Gate4 Rvw]="","",IF([BD Status]="Qualified Gate 4",[Gate4 Rvw],""))))))))