CHO cells were first developed by Dr. Theodore Puck in 1957 for research purposes (Puck, 1957, Puck et al., 1958), resulting in limited productivity and the need to improve their performance. Therefore, we established our original CHO host cells from Chinese hamster ovaries, CHO-MK cells, that are compatible with industrial purposes. Having been screened and selected for high growth and high productivity, CHO-MK cells were successfully developed and are capable of meeting industrial needs such as for large-scale biopharmaceutical manufacturing (Masuda et al., 2024). References Masuda K, Kubota M, Nakazawa Y, Iwama C, Watanabe K, Ishikawa N, Tanabe Y, Kono S, Tanemura H, Takahashi S, Makino T, Okumura T, Horiuchi T, Nonaka K, Murakami S, Kamihara M, Omasa T. Establishment of a novel cell line, CHO-MK, derived from Chinese hamster ovary tissues for biologics manufacturing. J. Biosci.Bioeng., 2024. https://doi.org/10.1016/j.jbiosc.2024.02.005 (https://doi.org/10.1016/j.jbiosc.2024.02.005) Puck TT, Cieciura SJ, Robinson A. Genetics of somatic mammalian cells. III. Long-term cultivation of euploid cells from human and animal subjects. J Exp Med 1958, 108:945–956. https://doi.org/10.1084/jem.108.6.945 (https://doi.org/10.1084/jem.108.6.945)(Open access). Puck TT. The genetics of somatic mammalian cells. Adv Biol Med Phys 1957, 5:75-101. https://doi.org/10.1016/b978-1-4832-3111-2.50006-7(https://doi.org/10.1016/b978-1-4832-3111-2.50006-7)

CHO-MK host cells have unique characteristics with an excellent growth rate, showing a short doubling time of less than 10 hours (Masuda et al., 2024). CHO-MK cells have a high metabolic rate and excellent viability, even at high culture densities. Consequently, CHO-MK cells can achieve high protein expression resulting in a high titer production of therapeutic proteins, which is unsurpassed by the conventional CHO cells. Reference Masuda K, Kubota M, Nakazawa Y, Iwama C, Watanabe K, Ishikawa N, Tanabe Y, Kono S, Tanemura H, Takahashi S, Makino T, Okumura T, Horiuchi T, Nonaka K, Murakami S, Kamihara M, Omasa T. Establishment of a novel cell line, CHO-MK, derived from Chinese hamster ovary tissues for biologics manufacturing. J. Biosci.Bioeng., 2024. https://doi.org/10.1016/j.jbiosc.2024.02.005(https://doi.org/10.1016/j.jbiosc.2024.02.005)

CHO-MK host cells were established in our facilities by our experienced and expert scientists. At the beginning, we initiated the primary culture from isolated Chinese hamster ovary tissues. The immortalized cells were generated by spontaneous immortalization through continuous passaging and observation of cell morphology. The immortalized cells were then adapted to serum-free suspension culture. Finally, the fastest growing cells with high productivity were selected at a certain population doubling level (PDL) and used to produce host cell banks (HCBs) (Masuda et al., 2024). Documentation regarding the origin of Chinese hamsters, the culture history, etc., is available for Common Technical Document (CTD) submission. Reference Masuda K, Kubota M, Nakazawa Y, Iwama C, Watanabe K, Ishikawa N, Tanabe Y, Kono S, Tanemura H, Takahashi S, Makino T, Okumura T, Horiuchi T, Nonaka K, Murakami S, Kamihara M, Omasa T. Establishment of a novel cell line, CHO-MK, derived from Chinese hamster ovary tissues for biologics manufacturing. J. Biosci.Bioeng., 2024. https://doi.org/10.1016/j.jbiosc.2024.02.005(https://doi.org/10.1016/j.jbiosc.2024.02.005)

Multicolor fluorescence in situ hybridization (mFISH) analysis suggests that the karyotype of CHO-MK cells is similar to that of the Chinese hamster (Masuda et al., 2024). Further, the Whole Genome Sequencing analysis (WGS) and sequencing of the expression cassette showed no genetic instabilities in CHO-MK cells (unpublished data). Reference Masuda K, Kubota M, Nakazawa Y, Iwama C, Watanabe K, Ishikawa N, Tanabe Y, Kono S, Tanemura H, Takahashi S, Makino T, Okumura T, Horiuchi T, Nonaka K, Murakami S, Kamihara M, Omasa T. Establishment of a novel cell line, CHO-MK, derived from Chinese hamster ovary tissues for biologics manufacturing. J. Biosci.Bioeng., 2024. https://doi.org/10.1016/j.jbiosc.2024.02.005(https://doi.org/10.1016/j.jbiosc.2024.02.005)

We have passed the safety tests for viral and other microorganism contamination and received the Certificate of Analysis (CoA) issued by BioReliance® which is recognized by the United States Food and Drug Administration (FDA). Notably, viruses, fungi, yeasts, bacteria, and mycoplasmas were not detected in CHO-MK host cells. The complete documentation can also be provided for Common Technical Document (CTD) submission.