FRANKFURT—Bayer on Monday struck a partnership deal with Mammoth Biosciences to develop therapeutic tools based on CRISPR/CAS9 gene editing as the German drug maker seeks to widen its cell and gene therapy development efforts. Unlisted U.S. biotech firm Mammoth will initially receive $40 million from Bayer plus potential milestone payments of more than $1 billion contingent on scientific and commercial achievements. The initial focus of the collaboration will be liver-based diseases, the companies said in a joint statement on Monday. Mammoth, headquartered in the San Francisco Bay area, was co-founded by Nobel laureate Jennifer Doudna. She shared the 2020 Nobel Prize in Chemistry with Emmanuelle Charpentier for developing the CRISPR/CAS9 gene editing tool. Among previous steps to build a cell and gene therapy business, Bayer acquired BlueRock Therapeutics and Asklepios Biopharmaceutical in 2019 and 2020, respectively. In late 2020, it agreed on an alliance on anti-tumour immune cell therapies with …