PD-L1 and CD8⁺PD1⁺ lymphocytes exist as targets in the pediatric tumor microenvironment for immunomodulatory therapy

Abstract

antibody; PD-1, programmed cell death 1; PD-L1, programmed cell death ligand 1; TIL, tumor-infiltrating lymphocyte.Recent monoclonal antibody trials targeting the PD1/PD-L1 immune-checkpoint pathway have shown remarkable success in treating adult malignancies, with PD-L1-expressing tumors showing the most objective response. However, little is known as to whether pediatric cancers have also adopted this immune evasion mechanism. We evaluated 115 pediatric tumors (taken at diagnosis) for PD-L1 expression and the presence of CD8 C tumor-infiltrating lymphocytes (TILs). Tumors with >5% PD-L1 membrane staining were scored positive. The presence of CD8 C TILs expressing PD-1 was assessed using dual-labeling immunohistochemistry. Data were evaluated against clinical demographics. The proportion of PD-L1 C tumors was 86% for alveolar rhabdomyosarcoma (12/14), 72% for high-risk neuroblastoma (31/ 43), 57% for Ewing's sarcoma (8/14), 50% for embryonal rhabdomyosarcoma (8/16) and 47% for osteosarcoma (7/15). Increased proportions of CD8 C TILs significantly correlated with PD-1 expression. When grouped by cancer type, those with the highest proportion of PD-L1 positivity showed poorest survival. PD-L1 C patients with a particularly high frequency of CD8 C TILs (but not those with low numbers CD8C TILs) had significantly better survival compared to PD-L1 negative patients. This study reveals the presence of an active PD-L1 pathway in a high proportion of pediatric cancers, as demonstrated by strong PD-L1 positivity and the presence of PD-1 expressing CD8 C TILs. In addition, patients with high proportions of CD8 C TILs showed better survival, suggesting that bolstering CD8 C T-cell responses through PD-1/PD-L1 blockade would be a viable treatment strategy, providing support for expediting these targeted immunotherapies in children. www.tandfonline.com e1029701-7 OncoImmunology Downloaded by [University of Manitoba Libraries] at 05

Targeting the PD-1 pathway in pediatric solid tumors and brain tumors

“…An early study did not identify PD-L1 expression in any of the 18 tested samples from neuroblastoma patients 40. In contrast, Chowdhury et al reported PD-L1 surface expression in 31 (72%) of 43 patient tumor samples,32 with lower survival in patients expressing PD-L1. Dondero et al confirmed that PD-1 expression is present in lymphocytes obtained from metastatic bone marrow samples, and that PD-L1 expression in tumor cells is inducible with interferon gamma 41.…”

“…In two of the larger studies to date of osteosarcoma, IHC analysis showed PD-L1 expression in 25%–47% of primary tumor samples, and tumors expressing PD-L1 were significantly more likely to have infiltrating immune cells, which often expressed PD-1 32,33. Importantly, PD-L1 expression correlated with worse event-free survival, and these findings are consistent with the concept that PD-L1 in tumor cells may interact with PD-1-expressing cells in the microenvironment to help evade immune rejection by the host.…”

“…One study demonstrated expression in 8 (57%) of 14 primary bone tumor samples,32 while 8 (38%) of 21 soft tissue primaries have reported PD-L1 expression in other studies 38,39. For rhabdomyosarcoma, the most common pediatric soft tissue sarcoma, data are limited but Chowdhury et al have reported expression in 13 (86%) of 15 alveolar rhabdomyosarcoma and 8 (50%) of 16 embryonal rhabdomyosarcoma patient samples 32. More robust analysis of the tumor microenvironment is not yet available, although infiltrating PD-1 CD8 lymphocytes are present in a subset of these tumors.…”

Checkpoint Proteins in Pediatric Brain and Extracranial Solid Tumors: Opportunities for Immunotherapy

“…Results have been variable likely due to a lack of standardized methods for scoring and reporting stains and because there are over a dozen PD-L1 antibodies that differ in their targeted epitope, isotype, source, and binding affinity (43). Despite these limitations, moderate to high PD-L1 expression was seen in pediatric sarcomas, whereas expression in Wilms tumor was low; however expression was more likely to occur in anaplastic Wilms and was associated with an increased risk of recurrence in favorable histology tumors (38, 39, 41, 42). Importantly, pediatric tumors with the highest proportion of PD-L1 positivity showed the poorest survival (38).…”

“…Studies in adult malignancies indicate that increased PD-L1 expression is associated with increased disease stage, presence of metastases, and refractory or relapsed disease (36, 37). Several studies have examined PD-L1 expression in pediatric solid tumors by immunohistochemistry (IHC) (Table 2) (38-42). Results have been variable likely due to a lack of standardized methods for scoring and reporting stains and because there are over a dozen PD-L1 antibodies that differ in their targeted epitope, isotype, source, and binding affinity (43).…”