New diagnostic tests for Tuberculosis (TB) infection currently in the research and development pipeline are not a single, identified "new test" but rather a category of advancements based on specific scientific principles. These emerging tests aim to improve upon existing methods by focusing on how the body's immune system reacts to Mycobacterium tuberculosis, the bacterium that causes TB.
Core Principles of Emerging TB Tests
The fundamental concept behind these new tests revolves around eliciting an immune response to Mycobacterium tuberculosis-specific antigens [17]. This means they are designed to detect the body's specific immunological memory or ongoing reaction to the TB bacteria, distinguishing it from reactions to other environmental mycobacteria or BCG vaccination.
These innovative tests are being developed with strategies similar to established TB diagnostic methods, such as the Tuberculin Skin Test (TST) and Interferon-Gamma Release Assays (IGRAs). They leverage distinct ways to measure the immune system's engagement with TB-specific proteins.
How New Tests Function
The pipeline of new TB infection tests incorporates two primary approaches for measuring the immune response:
| Test Type | Measurement Approach | Key Characteristic/Readout | Similar to Existing Method |
|---|---|---|---|
| In Vivo | Eliciting an immune response directly within the body | Size of skin induration (swelling/redness) | TST |
| In Vitro | Eliciting an immune response from isolated immune cells in a laboratory | Magnitude of cytokine release (e.g., from a blood sample) | IGRA |
- In Vivo Approaches: Similar to the traditional TST, some new tests aim to stimulate a localized immune response directly within a living organism, typically by injecting specific antigens into the skin. The resulting reaction, such as the size of a skin induration, indicates prior exposure and sensitization to Mycobacterium tuberculosis [17].
- In Vitro Approaches: These tests involve collecting a sample (such as blood) from the individual and stimulating their immune cells with Mycobacterium tuberculosis-specific antigens in a controlled laboratory setting. The magnitude of cytokine release, which are signaling proteins produced by immune cells, then serves as a marker for TB infection [17]. This method parallels IGRAs, which measure interferon-gamma (a type of cytokine) production.
Importance of Specific Antigens
The use of Mycobacterium tuberculosis-specific antigens is crucial for enhancing the accuracy of these new tests. Unlike older tests that might react to antigens common across various mycobacteria or the BCG vaccine, these specific antigens help differentiate true TB infection from other exposures, potentially leading to fewer false positives and more precise diagnosis.
While specific names of these "new tests" are not yet widely available as they are "in the pipeline," their conceptual framework indicates a future for more refined and reliable TB diagnostics.
