This is reminiscent of Coley's Toxins[1], an early experimental cancer treatment using Streptococcus pyogenes bacteria. Coley and other practitioners claimed some substantial success, but the mechanism of action was not understood, and the treatment varied so much that scientific verification was elusive.

(Note: I am affiliated with the linked website, but I didn't write the article in question)

[1] https://www.damninteresting.com/coleys-cancer-killing-concoc...