Abstract 2624: An FKBP5-based immunophenotype for assessment of the immunosuppression status and possible prediction of immunotherapy response in melanoma patients
Authors: Romano Simona , Simeone Ester , D'Angelillo Anna , D'Arrigo Paolo , Capasso Mario , Lasorsa Vito Alessandro , Tufano Martina , Rea Anna , Russo Michele , Zambrano Nicola , Ascierto Paolo Antonio , Romano Maria Fiammetta 
Published: July 2017

Abstract
Background and aim: FKBP51 is an immunophilin encoded by FKBP5 gene on chromosome 6. It is a protein resident in lymphocytes and involved in immune response. Recently, our group demonstrated that the inhibitory checkpoint PD-L1/PD1 promoted the alternative splicing of FKBP5 gene, resulting in increased expression of its variant 4, in PBMC of melanoma patients. The aim of this study was to address whether such a molecular signature could help in identifying an immune profile associated with increased probability of immunotherapy response.
Experimental Design: The splicing FKBP51 isoform or FKBP51s was measured in peripheral blood T lymphocytes subsets (CD3/CD4, CD3/CD8, CD25 and PD-L1) and CD14 monocytes from a cohort of 118 patients and 77 age- and sex-matched healthy controls, by flow cytometry. Blood samples were collected before patients underwent ipilimumab treatment. Furthermore, in 64 out of 118 patients, expression of FKBP51s was also assessed in regulatory T cells.
Results: Physiologically, each PBMC subset analyzed contained a fraction of an FKBP51spos component, which resulted expanded in melanoma patients. We also measured an increase in CD3/CD8 and PD-L1 lymphocytes in patients. CD4 T lymphocytes showed the FKBP51sneg fraction significantly impaired, which might reflect the condition of impaired T cell help. Treg count was increased, in accordance with previous studies. The count of FKBP51sposTregs defined a subgroup of nonresponder patients to ipilimumab, by 92.6%. A 2D hierarchical partitioning of data from FKBP51s-immunophenotype (heatmap) revealed 3 main clusters: C1 (33 pts, 51,5%), C2 (14 pts, 22%) and C3 (17 pts, 26,5%). FKBP51spos Treg subset appeared globally increased in all clusters. In C1, values of effector T cells and monocytes were not different from normal donors. C2 showed a significant increase of FKBP51spos PD-L1 monocytes and a significant probability of not responding (Chi-square=5.46; p=0.019). This finding is consistent with the hypothesis that response to ipilimumab is prevented by accessory cells exerting a negative immune regulatory control. C3 showed a significant increase of FKBP51s in overall lymphocyte subsets analyzed. Patients in this cluster showed reduced overall survival. This finding suggests that a prevalence of activation (CD25) and co-inhibitory (PD-L1) markers together with the expansion of FKBP51spos effector T cells might reflect a condition of chronic lymphocyte stimulation in some advanced melanoma patients, contributing to T cell-exhaustion.
Conclusions: FKBP51s-based immunophenotype of melanoma patients revealed several profiles virtually related to a negative immune regulatory control and highlights an impairment of a Treg subset endowed with increased suppressive potential. Such FKBP51sTreg subset is likely to be associated with immunotherapy response (Chi-square=9.916, p=0.002) .
Citation Format: Simona Romano, Ester Simeone, Anna D'Angelillo, Paolo D'Arrigo, Mario Capasso, Vito Alessandro Lasorsa, Martina Tufano, Anna Rea, Michele Russo, Nicola Zambrano, Paolo Antonio Ascierto, Maria Fiammetta Romano. An FKBP5-based immunophenotype for assessment of the immunosuppression status and possible prediction of immunotherapy response in melanoma patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2624. doi:10.1158/1538-7445.AM2017-2624