Prognostic relevance of tumor-infiltrating lymphocytes and immune checkpoints in pediatric medulloblastoma

Abstract

Pediatric medulloblastomas are the most frequently diagnosed embryonal tumors of the central nervous system. Current therapies cause severe neurological and cognitive side effects including secondary malignancies. Cellular immunotherapy might be key to improve survival and to avoid morbidity. Efficient killing of tumor cells using immunotherapy requires to overcome cancer-associated strategies to evade cytotoxic immune responses. Here, we examined the immune response and immune evasion strategies in pediatric medulloblastomas. Cytotoxic T-cells, infiltrating medulloblastomas with variable activation status, showed no correlation with overall survival of the patients. We found limited numbers of PD1⁺ T-cells and complete absence of PD-L1 on medulloblastomas. Medulloblastomas downregulated immune recognition molecules MHC-I and CD1 d. Intriguingly, expression of granzyme inhibitors SERPINB1 and SERPINB4 was acquired in 23% and 50% of the tumors, respectively. Concluding, pediatric medulloblastomas exploit multiple immune evasion strategies to overcome immune surveillance. Absence of PD-L1 expression in medulloblastoma suggest limited or no added value for immunotherapy with PD1/PD-L1 blockers.

Keywords: PD-1; PD-L1; Serpin; brain cancer; immune evasion; medulloblastoma; pediatric; tumor-infiltrating lymphocytes.

Figure 1.

Distribution of tumor infiltrating lymphocytes in pediatric medulloblastoma. Distribution of CD3⁺ T-cells in pediatric medulloblastoma resembles two distinct patterns i.e. perivascular (left panel) and intratumoral (right panel) that often coincide. Scale bar equals 100 μm.

Figure 2.

Expression of immune checkpoints and evasion markers in pediatric medulloblastoma. A) Immunohistochemical staining of immune (evasion) markers HLA-A, HLA-B and CD1 d in one case of pediatric medulloblastoma demonstrating that expression of all these markers is absent compared to endothelium and TILs. B) Examples of SerpinB1, SerpinB4 expression in pediatric medulloblastoma. SerpinB9 expression was not detected in pediatric medulloblastoma. C) Expression PD-L1 was not detected in pediatric medulloblastoma by immunohistochemistry. PD-1 positive TILs (arrowheads) are predominantly present at the peripheral zone of the tumor. Positive controls: placenta (PD-L1) and tonsil (PD-1). Scale bar equals 100 μm.

Figure 3.

TILs and survival of pediatric medulloblastoma patients. Survival analysis of pediatric medulloblastoma patients stratified for amount of TILs. High and low number of TILs was determined by median split.