The cells were maintained at 37 °C and we characterized the evolution of the DNA assembly as a function of time using agarose gel electrophoresis (Figs. ). For both 2D-triangle and 3D-toroid programs, a band significantly shifted from that of the scaffold alone, which we attribute to the formation of self-assembled structures, was observed after 15 min of incubation and without much further evolution over time. For the 3D-toroids, this band was extracted for TEM observations, which confirmed the presence of toroidal shapes (Fig. ). The origamis appeared with a rough surface attributed to the non-specific adsorption of proteins present in the medium, and dimensions (77 ± 6 nm, n = 14) in agreement with the bare design (Fig. ). To our knowledge, this constitutes the first evidence that a molecular program of hundreds of synthetic DNA strands can faithfully self-assemble in the presence of live cells to produce user-defined DNA origamis. As observed in the absence of cells, the selfassembly process remained remarkably fast as it was completed in minutes timescale. We next investigated the stability of in situ self-assembled origamis over prolonged incubation with cells at 37 °C (Fig. ). Using agarose gel electrophoresis (Fig. ), we established the fraction of intact DNA origamis over time and found that the self-assembled DNA origamis remained stable for the first 6 hours without detectable degradation (Fig. ). Beyond this time, the fraction of intact origamis progressively decreased, eventually disappearing after 1 to 2 days (Fig. ). With a formation completed in a few minutes, in situ self-assembled origamis thus remained structurally well-formed for several hours in the presence of cells. Moreover, during the 2-day incubation with the molecular program, the HEK cells proliferated (Fig. ) and showed similar viability as in the absence of DNA (Fig. ), demonstrating that neither the presence of cocktail of hundreds of staples (400 nM), nor in situ self-assembly into origamis interfered with normal cell activity.