Dulbecco was recruited to the newly founded Salk Institute for Biological Studies in 1963, and Marguerite joined him as a research fellow in his group. They continued their work on tumor-causing viruses. However, their interests diverged, and in 1973, Marguerite was appointed as a research professor which was an independent position that allowed her to pursue her interest in origins of cancer. Her interests evolved to examining cellular immortalization in cancer cells, and the role of telomeres in this process. She published her last paper in 1998.