  We analyze a $XXZ$ spin-1/2 chain which is driven dissipatively at its
boundaries. The dissipative driving is modelled by Lindblad jump operators
which only act on both boundary spins. In the limit of large dissipation, we
find that the boundary spins are pinned to a certain value and at special
values of the interaction anisotropy, the steady states are formed by a rank-2
mixture of helical states with opposite winding numbers. Contrarily to previous
stabilization of topological states, these helical states are not protected by
a gap in the spectrum of the Lindbladian. By changing the anisotropy, the
transition between these steady states takes place via mixed states of higher
rank. In particular, crossing the value of zero anisotropy a totally mixed
state is found as the steady state. The transition between the different
winding numbers via mixed states can be seen in the light of the transitions
between different topological states in dissipatively driven systems. The
results are obtained developing a perturbation theory in the inverse
dissipative coupling strength and using the numerical exact diagonalization and
matrix product state methods.
