  We report lasing of moir\'e trapped interlayer excitons (IXs) by integrating
a pristine hBN-encapsulated MoSe$_2$/WSe$_2$ heterobilayer into a high-$Q$
($>10^4$) nanophotonic cavity. We control the cavity-IX detuning using a
magnetic field and measure their dipolar coupling strength to be $78 \pm 4\
\mathrm{\mu eV}$, fully consistent with the 82 $\mathrm{\mu eV}$ predicted by
theory. The emission from the cavity mode shows clear threshold-like behavior
as the transition is tuned into resonance with the cavity. We observe a
superlinear power dependence accompanied by a narrowing of the linewidth as the
distinct features of lasing. The onset and prominence of these threshold-like
behaviors are pronounced at resonance while weak off-resonance. Our results
show that a lasing transition can be induced in interacting moir\'e IXs with
macroscopic coherence extending over the length scale of the cavity mode. Such
systems raise interesting perspectives for low-power switching and synaptic
nanophotonic devices using two-dimensional materials.
