Limited adaptability of virtual memory CD8 T cells to chronic viral infection

Antigen-inexperienced CD8 T cells include naïve and virtual memory (VM) subsets. VM CD8 T cells exhibit a memory-like phenotype despite lacking prior exposure to their specific antigen. While they can efficiently respond to and control acute infections where pathogens are cleared, their response during chronic infection remains poorly characterized. Using a chronic lymphocytic choriomeningitis virus infection model, we found that VM CD8 T cells exhibit a diminished response to persistent antigen stimulation compared to naïve CD8 T cells. Mechanistically, VM CD8 T cells show impaired engagement of the T cell exhaustion program due to lower TOX expression, resulting in a marked reduction of TCF1⁺ stem-like CD8 T cells which are critical for sustaining antigen-specific responses during chronic infection. Instead, VM CD8 T cells preferentially differentiate into KLRG1⁺PD-1^- cells, a population rarely observed in naïve-derived progeny. Moreover, VM-derived CD8 T cells exhibit limited expansion following PD-1 blockade, consistent with their reduced TCF1⁺ stem-like compartment. In summary, VM CD8 T cells fail to properly engage the exhaustion program during chronic viral infection, leading to a fundamental limitation in their adaptability to persistent antigen-stimulation.