The incidence of head and neck squamous cell carcinoma (HNSCC) is decreasing, while within this group the number of oropharyngeal SCC (OSCC) is rising, especially in young adults. The human papillomavirus type 16 (HPV16) is attributable for 45-90% of these OSCC, which interestingly results in a better response to therapy compared to HPV-negative OSCC. This improved clinical outcome is independent of nodal status, age, stage, tumor differentiation or gender. As previously HPV16-specific T-cell responses were measured in blood and tumor of HPV16+ OSCC, we hypothesized that these T-cells impact the tumor microenvironment and thereby support a better therapeutic efficacy.
Tumor sections of 87 OSCC patients were HPV typed by GP5+/6+ PCR and stained for p16 expression by immunohistochemistry. Freshly dispersed and cryopreserved tumor tissues were used for phenotypical analysis (CYTOF and flow cytometer) to determine the leukocyte infiltration composition. Moreover, the ex vivo HPV16-specific T-cell reactivity was determined in these samples.
In our cohort, 57% of OSCC patients were HPV16+ and these patients showed the best overall survival (p<0.0001, HR 6.9), as estimated by Kaplan-Meier curves and log-rank analysis. In 63% of these HPV16+ OSCC patients an intratumoral HPV16 E6/E7-specific T-cell reactivity was detected. Notably, no proliferative T-cell responses were observed in the HPV-negative OSCC patients. Within the HPV16+ OSCC patient group the presence of HPV16-specific immunity correlated with a better clinical outcome (p=0.0003, HR 23.9). Also grouping of these HPV16+ OSCC patients according to their p16 expression, showed that p16+ patients are doing better (p<0.0001, HR 11.8). As overexpression of p16 is directly associated with the expression of the viral oncoproteins E6 and E7, the association between p16 expression and intratumoral HPV16-specific T-cell reactivity (p<0.0001) is in line with this. In vitro mechanistic studies revealed that OSCC cell lines promoted monocyte to differentiate into tumor-promoting M2 macrophages, which can be prevented by cytokines secreted by HPV16-specific T cells. Importantly, the resident M2 macrophages could be redirected into better antigen-presenting cells in terms of phenotypically (induction of co-stimulatory molecules) and functionally (>IL-12 and <IL-10 production). Interestingly, the type 1 T-cell cytokines also interfered directly with proliferation and cell death of OSCC cells.
The intratumoral HPV16-specific T-cell responses, elicited by HPV16+ OSCC, is an important component for the clinical efficacy of standard therapy.
Funding: Dutch Cancer Society UL 2013-6146