PD-1 Expression Is Markedly Upregulated on Intratumoral CD4⁺ and CD8⁺ T Cells in Follicular Lymphoma and Is Associated with T-Cell Exhaustion.

Follicular lymphoma is one of the most immune-responsive of all human malignancies. However, immunoregulatory mechanisms in the tumor microenvironment may impair the efficacy of immunotherapies such as vaccines and adoptive T-cell therapy. The inhibitory receptor programmed death 1 (PD1), a negative regulator of activated T cells was recently shown to be upregulated on the surface of HIV-specific CD4⁺ and CD8⁺ T cells in humans and was associated with impaired T-cell function. Blockade of the immunoregulatory PD-1/PD-ligand 1 (PD-L1) pathway with antibodies against the PD-L1 augmented the function of HIV-specific CD4⁺ and CD8⁺ T cells (Day CL et al, Nature, 2006). To investigate the role of PD-1 in lymphoma, we examined PD-1 expression on peripheral blood mononuclear cells (PBMC) and intratumoral T cells in patients with follicular lymphoma prior to therapy. We observed that PD-1 expression is significantly upregulated on peripheral blood and intratumoral CD4⁺ and CD8⁺ T cells in patients with follicular lymphoma as compared with normal donor PBMC. Furthermore, PD-1 expression was significantly higher on intratumoral (mean 61%, range 34% to 86%) compared with peripheral blood CD4⁺ T cells (mean 25%, range 9 to 40%). Likewise, PD-1 expression was significantly higher on intratumoral (mean 44%, range 31% to 69%) compared with peripheral blood CD8⁺ T cells (mean 16%, range 9 to 31%). PD-1 expression on CD4⁺ and CD8⁺ T cells was associated with impaired type 1 cytokine production (IL-2, TNFa, and IFNg) and blockade of the PD-1/PD-ligand pathway with antibodies against PD-1 significantly enhanced T-cell function. These data indicate that the immunoregulatory PD-1/PD-ligand pathway is operative in patients with follicular lymphoma. Moreover, this pathway of reversible T-cell impairment provides a potential target for enhancing the function of exhausted T-cells in follicular lymphoma in combination with other immunomodulatory strategies such as vaccines and adoptive T-cell therapy.