A novel transcriptional signature identifies T-cell infiltration in high-risk paediatric cancer.

BACKGROUND: Molecular profiling of the tumour immune microenvironment (TIME) has enabled the rational choice of immunotherapies in some adult cancers. In contrast, the TIME of paediatric cancers is relatively unexplored. We speculated that a more refined appreciation of the TIME in childhood cancers, rather than a reliance on commonly used biomarkers such as tumour mutation burden (TMB), neoantigen load and PD-L1 expression, is an essential prerequisite for improved immunotherapies in childhood solid cancers. METHODS: We combined immunohistochemistry (IHC) with RNA sequencing and whole-genome sequencing across a diverse spectrum of high-risk paediatric cancers to develop an alternative, expression-based signature associated with CD8+ T-cell infiltration of the TIME. Furthermore, we explored transcriptional features of immune archetypes and T-cell receptor sequencing diversity, assessed the relationship between CD8+ and CD4+ abundance by IHC and deconvolution predictions and assessed the common adult biomarkers such as neoantigen load and TMB. RESULTS: A novel 15-gene immune signature, Immune Paediatric Signature Score (IPASS), was identified. Using this signature, we estimate up to 31% of high-risk cancers harbour infiltrating T-cells. In addition, we showed that PD-L1 protein expression is poorly correlated with PD-L1 RNA expression and TMB and neoantigen load are not predictive of T-cell infiltration in paediatrics. Furthermore, deconvolution algorithms are only weakly correlated with IHC measurements of T-cells. CONCLUSIONS: Our data provides new insights into the variable immune-suppressive mechanisms dampening responses in paediatric solid cancers. Effective immune-based interventions in high-risk paediatric cancer will require individualised analysis of the TIME.Chelsea Mayoh, Andrew J. Gifford, Rachael Terry, Loretta M. S. Lau, Marie Wong, Padmashree Rao, Tyler Shai, Hee, Federica Saletta, Dong, Anh Khuong, Quang, Vicky Qin, Marion K. Mateos, Deborah Meyran, Katherine E. Miller, Aysen Yuksel, Emily V. A. Mould, Rachel Bowen, James, Dinisha Govender, Akanksha Senapati, Nataliya Zhukova, Natacha Omer, Hetal Dholaria, Frank Alvaro, Heather Tapp, Yonatan Diamond, Luciano Dalla Pozza, Andrew S. Moore, Wayne Nicholls, Nicholas G. Gottardo, Geoffrey McCowage, Jordan R. Hansford, Seong, Lin Khaw, Paul J. Wood, Daniel Catchpoole, Catherine E. Cottrell, Elaine R. Mardis, Glenn M. Marshall, Vanessa Tyrrell, Michelle Haber, David S. Ziegler, Orazio Vittorio, Joseph A. Trapani, Mark J. Cowley, Paul J. Neeson, and Paul G. Eker