''... (T)o contain unknown lunar organisms that might endanger life on earth."

The Lunar Receiving Laboratory (LRL) became operational in 1969, its objective was to lower the risk of ''back contamination'' by astronauts and material brought from the Moon.  NASA had not planned for that eventuality when the Apollo program was implemented, so the LRL was designed and built (in less than three years) only after public concerns about the risk of alien pathogens. 
Today it is believed that if such contamination had been present the LRL would had been unable to contain it, mainly due to the procedures used to transport and handle its subjects and specimens. Oh well.

Lunar Receiving Laboratory Project History (2004)

https://archive.org/details/nasa_techdoc_20040200959