https://cogforlife.org/guidance/
(additional links on original page)
Fetal cell line: AdVac® technology uses PER.C6® cell line (info here) originating from a healthy 18-week-old aborted child.
Did Johnson & Johnson use the PER.C6 fetal cell line in research and production? Yes, they did in the research and development of the vaccine, as explained in this scientific report from July 2020 in Nature journal and in this scientific report from September 2020 also in Nature journal. To propogate the virus in the PER.C6 cells means to grow it in them. They will need to do this in ongoing manufacturing.