Human diploid cell strains (HDCSs), possessing identical chromosome sets known to be free of all known adventitious agents, are of great use in developing human vaccines. However it is extremely difficult to obtain qualified HDCSs that can satisfy the requirements for the mass production of vaccines. We have developed a new HDCS, Walvax-2, which we derived from the lung tissue of a 3-month-old fetus. We established primary, master and working cell banks successfully from reconstituted frozen cells. Observations during the concurrent propagation of Walvax-2 and MRC-5 cells revealed differences in terms of growth rate, cell viability and viral sensitivities. Specifically, Walvax-2 cells replicated more rapidly than MRC-5 cells, with Walvax-2 cells attaining the same degree of confluence in 48 hours as was reached by MRC-5 cells in 72 hours. Moreover, Walvax-2 cells attained 58 passages of cell doublings whereas MRC-5 reached 48 passages during this period. We also assessed the susceptibility of these cells to rabies, hepatitis A, and Varicella viruses. Analysis of virus titers showed the Walvax-2 cells to be equal or superior to MRC-5 cells for cultivating these viruses. Furthermore, in order to characterize the Walvax-2 cell banks, a series of tests including cell identification, chromosomal characterization, tumorigenicity, as well as tests for the presence of microbial agents, exogenous viruses, and retroviruses, were conducted according to standard international protocols. In conclusion, results from this study show that Walvax-2 cell banks are a promising cell substrate and could potentially be used for the manufacturing of HDCVs.
Keywords: ATCC, American Type Culture Collection; CCID50, 50% cell culture infectious dose; CCTCC, China Center for Type Culture Collection; CPE, cytopathogenic effect; ELISA, enzyme-linked immuno sorbent Assay; FFU, fluorescent focus units; G6PD, glucose 6 phosphate dehydrogenase; GM, growth medium; HAV, hepatitis A virus; HDCSs, human diploid cell strains; HDCV, human diploid cell vaccine; LD, lactate dehydrogenase; MCB, master cell bank; MDCK, Madin–Darby canine kidney; MOI, multiplicity of infection; NIFDC, National Institute for Food and Drug Control; PAGE, polyacrylamide gelelectrophoresis; PCB, primary cell bank; PFU, plaque forming units; PPLO; STR, Short tandem repeats; VZV, varicella zoster virus; WCB, Working cell bank; biological characteristics; cell substrate; human diploid cell strain (HDCSs); human diploid cell vaccines (HDCVs); pleuropneumonia-Like organisms; viral sensitivities.