  Nonlinear topological photonics is an emerging field aiming at extending the
fascinating properties of topological states to the realm where interactions
between the system constituents cannot be neglected. Interactions can indeed
trigger topological phase transitions, induce symmetry protection and
robustness properties for the many-body system. Moreover when coupling to the
environment via drive and dissipation is also considered, novel collective
phenomena are expected to emerge. Here, we report the nonlinear response of a
polariton lattice implementing a non-Hermitian version of the
Su-Schrieffer-Heeger model. We trigger the formation of solitons in the
topological gap of the band structure, and show that these solitons demonstrate
robust nonlinear properties with respect to defects, because of the underlying
sub-lattice symmetry. Leveraging on the system non-Hermiticity, we engineer the
drive phase pattern and unveil bulk solitons that have no counterpart in
conservative systems. They are localized on a single sub-lattice with a spatial
profile alike a topological edge state. Our results demonstrate a tool to
stabilize the nonlinear response of driven dissipative topological systems,
which may constitute a powerful resource for nonlinear topological photonics.
