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Immunol Lett. 2009 Dec 2;127(1):60-7. doi: 10.1016/j.imlet.2009.09.002. Epub 2009 Sep 12.

TLR-9 signaling and TCR stimulation co-regulate CD8(+) T cell-associated PD-1 expression.

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  • 1MannKind Corporation, 28903 Avenue Paine, Valencia, CA, USA.


Elevated Programmed Death-1 (PD-1) expression can inhibit T cell activity and is a potential barrier to achieving persisting and optimal immunity via therapeutic vaccination. Using a direct lymph node-targeted vaccination procedure that enabled uncoupling of synthetic peptide (signal 1, TCR-mediated) and adjuvant (signal 2, non-TCR-mediated), we evaluated the impact of varied doses of Toll-like receptor (TLR)-9 ligand CpG oligodeoxynucleotide (ODN) adjuvant on epitope-specific CD8(+) T cell-associated PD-1 expression. Peptide vaccination without adjuvant yielded CD8(+) T cells with significantly elevated PD-1 expression. This conferred impaired function ex vivo, but was reversible by antibody-mediated PD-1 blockade. By comparison, peptide vaccination with escalating doses of CpG ODN adjuvant yielded higher magnitudes of CD8(+) T cells with progressively lower PD-1 expression and greater ex vivo function. CpG ODN adjuvant in context of titrated peptide doses for vaccination yielded the lowest overall PD-1 expression levels, demonstrating that fine-tuning both TCR-independent (adjuvant dose) and -dependent (antigen dose) stimuli can synergize to co-regulate PD-1 expression on epitope-specific CD8(+) T cells. These data hint at strategies to elicit PD-1(low) CD8(+) T cells using TLR-9 ligand adjuvants, and also shed light on the PD-1-regulated homeostasis of CD8(+) T cells.

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