Jeffrey Hillman from the University of Florida developed a genetically modified strain of Streptococcus mutans called BCS3-L1, that is incapable of producing lactic acid – the acid that dissolves tooth enamel – and aggressively replaces native flora. In laboratory tests, rats who were given BCS3-L1 were conferred with a lifetime of protection against S. mutans. BCS3-L1 colonizes the mouth and produces a small amount of a lantibiotic, called MU1140, which allows it to out-compete S. mutans. Hillman suggested that treatment with BCS3-L1 in humans could also provide a lifetime of protection, or, at worst, require occasional re-applications. He stated that the treatment would be available in dentists' offices and "will probably cost less than $100." The product was being developed by Oragenics, but was shelved in 2014, citing regulatory concerns and patent issues. In 2016, Oragenics received a 17-year patent for the product.
[0]: https://en.wikipedia.org/wiki/Caries_vaccine#Attempts_using_...
[1]: https://www.newscientist.com/article/dn1941-gm-bacteria-may-...