  Recent investigations seem to favor a cosmological dynamics according to
which the accelerated expansion of the Universe may have already peaked and is
now slowing down again \cite{sastaro}. As a consequence, the cosmic
acceleration may be a transient phenomenon. We investigate a toy model that
reproduces such a background behavior as the result of a time-dependent
coupling in the dark sector which implies a cancelation of the "bare"
cosmological constant. With the help of a statistical analysis of Supernova
Type Ia (SNIa) data we demonstrate that for a certain parameter combination a
transient accelerating phase emerges as a pure interaction effect.
