**Core Concept**
Bacillus Calmette-Guérin (BCG) vaccine is a live attenuated vaccine derived from Mycobacterium bovis, used primarily for immunization against tuberculosis. It works by stimulating the immune system to produce a cellular response against the M. tuberculosis bacterium.

**Why the Correct Answer is Right**
BCG vaccine acts as an immuno-stimulant by inducing a cell-mediated immune response, which involves the activation of macrophages and the production of cytokines. This response helps to control the growth of M. tuberculosis bacteria and provides long-term immunity against the disease. The BCG vaccine is administered intradermally, where it is phagocytosed by dendritic cells and presented to T-cells, leading to the activation of a specific immune response.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while it may be a vaccine, it is not an immuno-stimulant. Vaccines can be either live attenuated or inactivated, and some may not stimulate an immune response at all (e.g., toxoids).
**Option B:** This option is incorrect because it is not a vaccine.
**Option C:** This option is incorrect because it is a medication used to treat conditions like tuberculosis, but it is not an immuno-stimulant.

**Clinical Pearl / High-Yield Fact**
BCG vaccine is the only vaccine that has been shown to have a protective effect against severe forms of tuberculosis, such as miliary tuberculosis and tuberculous meningitis. It is also used as a diagnostic tool to assess the immune response of individuals who have been exposed to M. tuberculosis.

**Correct Answer: C. BCG vaccine is an immuno-stimulant that induces a cell-mediated immune response against M. tuberculosis.**