ICOS and Bcl6-dependent pathways maintain a CD4 T cell population with memory-like properties during tuberculosis.

Area of Science:

• Immunology
• T cell biology
• Infectious disease

Background:

• Effective control of Mycobacterium tuberculosis (Mtb) infection relies on robust CD4 T cell responses.
• The molecular mechanisms sustaining protective CD4 T cells during chronic Mtb infection remain unclear.

Purpose of the Study:

• To elucidate the molecular pathways governing the maintenance of Mtb-specific CD4 T cells during persistent infection.
• To compare the protective capacity of distinct CD4 T cell subsets during tuberculosis (TB).

Main Methods:

• Utilized MHCII tetramer technology to track Mtb-specific CD4 T cells.
• Analyzed the expression of PD-1, Bcl6, and ICOS in CD4 T cells from TB-infected lungs.
• Assessed the persistence, recall response, and protective immunity of transferred CD4 T cells in vivo.

Main Results:

• A subset of Mtb-specific CD4 T cells expressing PD-1 is maintained in the lung parenchyma during chronic TB.
• These PD-1(+) CD4 T cells provide superior protection against Mtb rechallenge compared to terminally differentiated Th1 cells.
• Generation and maintenance of these protective PD-1(+) cells depend on intrinsic Bcl6 and ICOS expression.

Conclusions:

• The molecular pathways sustaining CD4 T cells during chronic Mtb infection resemble those maintaining memory CD4 T cells in antigen-deprived environments.
• Targeting ICOS and Bcl6 pathways in CD4 T cells presents a potential strategy for developing novel TB vaccines.