To determine whether the protective effect of RA/TPA-mediated differentiation is derived from cell autonomous or non-cell autonomous factors, we performed dose-response survival assays on naïve neuroblastoma cells in culture for 24 hours with different concentrations of 6-OHDA diluted in fresh media or six-day conditioned media from cells treated with Neurobasal-A media (NBA) containing FBS, RA or RA/TPA (Fig. 2C–D, inset table, E). The gene discussed is PLAT; the disease is neuroblastoma.