Hello @santina,

The BCG - Bacille Calmette-Guérin - vaccine has been administered for almost a century to prevent tuberculosis or TB. It has U.S. Food and Drug Administration approval.

The phase 1 study conducted by researchers at Massachusetts General Hospital (MGH) concluded that:
"Long-term follow-up of participants in clinical trials of a generic vaccine to reverse advanced type 1 diabetes finds significant clinical benefits, including restoration of near-normal blood sugar levels. Three years after receiving two administrations of the bacillus Calmette-Guérin (BCG) vaccine four weeks apart, all members of a group of adults with longstanding type 1 diabetes showed an improvement in HbA1c to near normal levels – improvement that persisted for the following five years."

This FAQ-page, related to BCG vaccine research, may help answer some of your questions:
https://www.massgeneral.org/News/assets/pdf/062118faustman_qa.pdf