PD-L1 assessment in pediatric rhabdomyosarcoma: a pilot study

Abstract

BackgroundRhabdomyosarcomas (RMSs) are the most frequent soft tissue sarcoma in children and adolescents, defined by skeletal muscle differentiation and the status of FOXO1 fusions. In pediatric malignancies, in particular RMS, scant and controversial observations are reported about PD-L1 expression as a putative biomarker and few immune checkpoint clinical trials are conducted.MethodsPD-L1 assessment was evaluated by immunohistochemistry (IHC) utilizing two anti-PDL1 antibodies, in a pilot cohort of 25 RMS. Results were confirmed in primary and commercial RMS cell lines by cytofluorimetric analysis and IHC.ResultsPD-L1 expression was detectable, by both anti-PD-L1 antibodies, in the immune contexture of immune cells infiltrating and/or surrounding the tumor, in 15/25 (60%) RMS, while absent expression was observed in neoplastic cells. Flow cytometry analysis and PD-L1 IHC of commercial and primary RMS cell lines confirmed a very small percentage of PD-L1 positive-tumor cells, under the detection limits of conventional IHC. Interestingly, increased PD-L1 expression was observed in the immune contexture of 4 RMS cases post chemotherapy compared to their matched pre-treatment samples.ConclusionHere we identify a peculiar pattern of PD-L1 expression in our RMS series with scanty positive-tumor cells detected by flow cytometry, and recurrent expression in the immune cells surrounding or infiltrating the tumor burden.Electronic supplementary materialThe online version of this article (10.1186/s12885-018-4554-8) contains supplementary material, which is available to authorized users.

Tumor response and endogenous immune reactivity after administration of HER2 CAR T cells in a child with metastatic rhabdomyosarcoma

“…In sarcomas, despite pre-clinical studies suggesting a potential role for checkpoint inhibitor therapy, early clinical trials using pembrolizumab or nivolumab as single agents have shown very limited efficacy 44 , 45 . There are no reports of pediatric sarcoma with CR to anti-PD-1 therapy alone, and pre-clinical studies on expression of PD-L1 in pediatric RMS are limited 46 . In view of the upregulation of PD-1 on CD8+ CAR+ T cells following repeat infusions during CR1, we reasoned that incorporating pembrolizumab with CAR T cells could improve CAR T-cell function and lead to clinical benefit in our patient.…”

Age-Related Alterations in Immune Contexture Are Associated with Aggressiveness in Rhabdomyosarcoma

“…All antibodies were incubated with a commercially available detection kit (EnVision™ FLEX+, Dako, Denmark) in an automated Immunostainer (Dako Autostainer System—Link 48). The status of PD-L1 protein expression was also investigated utilizing clone anti PD-L1 22C3 (Dako, Glostrup, Denmark), as previously described [47].…”

Emerging trends in immunotherapy for pediatric sarcomas

“…In OS, PD-L1 expression correlates with immune cell infiltration, including NK cells, T cells, and dendritic cells, as well as significantly poorer 5-year event free survival [17]. Although PD-L1 blockade has shown effect in various cancers, Majzner et al recently characterized the frequency of PD-L1 expression in several sarcomas and reported only minimal expression on tumor cells of OS, EWS, and RMS samples [23, 24]. Despite these data, PD-L1 expression on tumor cells may not be necessary for immunotherapeutic effect from immune checkpoint blockade (ICB) [25]; moreover, the role of microRNA may be equally important [26].…”