Some people wonder whether the vaccines made using human embryo cells (chickenpox, rubella, hepatitis A, one version of shingles vaccine, and one version of the rabies vaccine) could cause harm if the DNA from the embryo cells “mixes” with the vaccine recipient’s DNA. This is not likely to happen:
- Stability of DNA - Because DNA is not stable when exposed to certain chemicals, much of it is destroyed in the process of making the vaccine. Therefore, the amount of human DNA in the final vaccine preparation is minimal (trillionths of a gram) and highly fragmented. Because the DNA is fragmented, it cannot possibly create a whole protein.
- Opportunity – DNA from the vaccine is not able to incorporate itself into cellular DNA. In fact, if this could be accomplished, gene therapy would be much easier than it has been.
Read more about the use of human embryo cells.
WHO requirements for the use of animal cells as in vitro substrates for the production of biologicals. Biologicals 1998;26:175-193.
Cell lines of human (e.g., WI-38, MRC-5) or monkey (FRhL-2) origin are non-tumorigenic and residual cellular DNA derived from these cells has not been, and is not, considered to pose any risk. Continuous cell line (CCL) substrates of human origin such as HeLa cells (derived from cervical cancer cells) or Namalva cells (derived from Burkett’s lymphoma) could have the potential to confer the capacity for unregulated cell growth or tumorigenic activity upon other cells. Risk assessment based on an animal oncogene model suggested that in vivo exposure to 1 ng (one-billionth of a gram) of cellular DNA —where 100 copies of an activated oncogene were present in the genome — could give rise to a transformational event 1 per 1 billion recipients. The risk associated with residual CCL DNA in a product is negligible when the amount of such DNA is 100 pg (a picogram is one-trillionth of a gram), which is the current maximal amount of CCL DNA allowed by the FDA.
Wierenga DE, Cogan J, Petricciani JC. Administration of tumor cell chromatin to immunosuppressed and non-immunosuppressed non-human primates. Biologicals 1995;23:221-224.
The authors addressed the issue of how risky DNA may be as a residual impurity by injecting both normal and immunosuppressed monkeys with 100 million genome equivalents of DNA from a human tumor cell line that is one million times the DNA (1 mg) allowed by WHO in a single dose of biological product (100 pg). DNA from a human tumor, saline, or cyclosporine doses were administered intravenously, intramuscularly, or intracerebrally on either a daily, weekly or one-time basis. Animals were observed for 8 years, none of which showed any evidence of tumor formation.
Lower J. Risk of tumor induction in vivo residual cellular DNA: quantitative considerations. J Med Virol 1990;31:50-53.
In 1987, the WHO Study Group compiled a list of experiments in which DNA of tumor viruses or DNA of the corresponding oncogenes were injected into suitable hosts to determine the amount required to induce tumors in half of the experimental animals. In this study, the author compared that information with the recommended residual cellular DNA limits (100 pg) in CCL biological products. The author determined that the number of oncogenes in 100 pg cellular DNA is less than one-billionth of the amount needed to induce tumors in experimental animals.
Yang H, Zhang L, Galinski M. A probabilistic model for risk assessment of residual host cell DNA in biological products. Vaccine 2010;28:3308-3311.
The authors assessed the oncogenic and infective potential of residual host cell DNA from a cell-based live, attenuated influenza vaccine that is manufactured in Madin Darby Canine Kidney (MDCK) cells. They determined that 230 billion doses of vaccine would need to be administered before an oncogene dosage equivalent would be reached, and 83 trillion doses would need to be administered to induce an infective event.
Temin HM. Overview of biological effects of addition of DNA molecules to cells. J Med Virol 1990;31:13-17.
A maximum cumulative probability of having a harmful effect is calculated to be less than 10-16 to 10-19 per DNA molecule from a cell without activated proto-oncogenes or active viral oncogenes.