Heterologous vaccination against human tuberculosis modulates antigen-specific CD4+ T-cell function

Area of Science:

• Immunology
• Vaccinology
• Tuberculosis Research

Background:

• Heterologous prime-boost vaccination strategies are promising for tuberculosis (TB) prevention.
• Understanding the specific T-cell characteristics required for protective immunity after vaccination is critical.
• Bacille Calmette Guerin (BCG) and natural mycobacterial exposure prime T cells, but boost-induced changes need characterization.

Purpose of the Study:

• To characterize functional and phenotypic changes in specific CD4(+) T cells following MVA85A vaccination in diverse age groups (adults, adolescents, children).
• To investigate if MVA85A vaccination induces long-lived functional and phenotypic alterations in T cells primed by prior exposure.

Main Methods:

• Flow cytometry was used to analyze CD4(+) T cells identified by Ag85A peptide-bearing HLA class II tetramers.
• Proliferative potential and cytokine expression (IFN-γ, IL-2) of Ag85A-specific CD4(+) T cells were measured.
• Surface phenotypes (CD45RA, CCR7, CD27, CD38) and T-cell homing markers were assessed post-vaccination.

Main Results:

• MVA85A-induced CD4(+) T cells initially coexpressed IFN-γ, IL-2, skin homing integrins, and CD38.
• Following a contraction phase, T cells transitioned to a phenotype resembling pre-vaccination cells, predominantly expressing IL-2.
• Crucially, Ag85A-specific T-cell proliferative capacity was significantly higher 6-12 months post-vaccination compared to pre-vaccination levels.
• Surface phenotypes commonly associated with memory T cells did not correlate with observed functional enhancements.

Conclusions:

• MVA85A vaccination can modulate Ag85A-specific CD4(+) T-cell function, enhancing their recall potential.
• The study highlights that functional T-cell capacity, rather than surface phenotype alone, is a key indicator of vaccine-induced immune memory.
• These findings are important for designing effective TB vaccine strategies that induce durable protective immunity.