High tunnel magnetoresistance (TMR) in perpendicular magnetic tunnel junctions (p-MTJs) with tetragonal Mn-based electrodes is expected to play a key role in the realization of practical high-density magnetic memories, advanced THz devices, and magnetic sensors. In this study, we demonstrated the use of bcc-Co-based alloys, such as bcc-Co and bcc-CoMn binary alloys, as antiferromagnetically coupled interlayers for MnGa-based p-MTJs. The interlayer of bcc-Co enhanced the TMR ratio of MnGa-based MTJs by 70% at 300 K and 145% at 10 K. Furthermore, the TMR ratio of the MTJ with the bcc-CoMn interlayer was enhanced up to 85 (209)% at 300 (10) K at a thickness of 0.8 nm. The enhancement in the TMRs can be attributed to the electronic band with the Δ1 symmetry of the bcc-Co-based alloy. In addition, the Co-based interlayer supported the growth of a high-quality MgO barrier sufficient for sustaining the coherency of the tunnel electrons from the Bloch state in the ferromagnetic electrode. These results suggest that bcc-Co-based interlayers are promising interlayer materials for MnGa-based p-MTJs.