  Modeling lepton-nucleus scattering with the accuracy required to extract
neutrino-oscillation parameters from long- and short-baseline experiments
necessitates retaining most quantum-mechanical effects. One such effect is the
interference between one- and two-body current operators in the transition
currents, which has been known to enhance the cross-sections, especially in
transverse kinematics. In this work, we incorporate such interference in the
spectral function formalism, which combines relativistic currents and
kinematics with an accurate description of the initial target state. Our
analysis of lepton-scattering off $^{12}$C demonstrates that interference
effects appreciably enhance the transverse electromagnetic response functions
and the flux-folded neutrino-nucleus cross section, in both cases, improving
the agreement with experimental data. We discuss the impact on the
neutrino-oscillation program and the determination of nucleon axial form
factors.
