Trump’s Covid Treatments Were Tested in Cells Derived From Fetal Tissue The “cell lines” used to develop monoclonal antibodies, as well as remdesivir and vaccines, began with fetal tissue decades ago. A microscopic view of 293T cells derived from embryonic kidneys, which several companies are using to develop Covid-19 therapies.Credit...Juan Mabromata/Agence France-Presse — Getty Images When the T