Human Cancer Biology Immune Suppression in Premalignant Respiratory Papillomas: Enriched Functional CD4þFoxp3þ Regulatory T Cells and PD-1/PD-L1/L2 Expression

Purpose: Respiratory papillomas, caused by human papillomaviruses types 6 and 11 (HPV6/11), are premalignant lesions with potential formalignant conversion. The cytokine and chemokinemicromilieu of papillomas is TH2-likewith amarked absence of IFN-g expression. To illuminatewhypatientswith recurrent respiratory papillomatosis (RRP) fail to effectively control their disease, we further investigated the suppressive cellular microenvironment in papillomas. Experimental Design: CD4þCD25þCD127low/ Foxp3þ regulatory T cells (Treg) and CD4þCD25 CD127 Foxp3 T cells within papillomas were characterized and isolated. Their suppressor function was measured by inhibition of peripheral blood mononuclear cell (PBMC) proliferation. Expression of PD-1, CD69, and Helios was identified on these T cells. PD-L1, PD-L2, CCL17, and CCL22 mRNA was also identified in papillomas by quantitative PCR. Results: Functional Tregs were markedly enriched in papillomas and strongly inhibited anti-CD3 and anti-CD28 antibody activated PBMC proliferation. The natural Treg marker Helios was reduced on Tregs from papillomas, indicating that the majority of Tregs in papillomas are adaptive. The majority of the papilloma-derived CD4þ T cells expressed the CD4þCD25 CD127 Foxp3 PD1þCD69þ phenotype and failed to suppress PBMCproliferation, suggesting that they are chronically activated and exhausted. The Treg-attracting chemokine CCL22was equally expressed by all laryngeal tissues examined.However, CCL17 was robustly expressed by papillomas compared with unaffected laryngeal tissues from RRP patients and individuals without RRP. PD-L1 was elevated in papillomas compared with control laryngeal tissues. Conclusions: Papilloma CD4þ T cells are enriched with functional Tregs, and the adaptive Helios Treg fractionwas increased within the TH2-like papillomamicromilieu. CD4 þCD25 CD127 Foxp3 T-cells failed to suppress PBMC proliferation and may be exhausted. The PD-1/PDL-1 pathway may represent an additional immunosuppressive mechanism that contributes to defective HPV6/11 clearance in RRP. Clin Cancer Res; 18(7); 1925–35. 2012 AACR.