Characterization of MHC Class I and β-2-Microglobulin Expression in Pediatric Solid Malignancies to Guide Selection of Immune-Based Therapeutic Trials.

Over 10,000 US children are diagnosed with cancer yearly. Though outcomes have improved by optimizing conventional therapies, recent immunotherapeutic successes in adult cancers are emerging. Cytotoxic T lymphocytes (CTLs) are the primary executioners of adaptive antitumor immunity and require antigenic presentation in the context of major histocompatibility complex (MHC) class I and the associated β-2-microglobulin (B2M). Loss of MHC I expression is a common immune escape mechanism in adult malignancies, but pediatric cancers have not been thoroughly characterized. The essential nature of MHC I expression in CTL-mediated cell death may dictate the success of immunotherapies, which rely on eliciting an adaptive response. We queried pediatric tumor microarray databases for MHC I and B2M gene expression. We detected MHC I in pediatric tumor cell lines by flow cytometry and characterized MHC I and B2M expression in patient samples by immunohistochemistry. To determine whether therapeutic approaches might enhance MHC I expression in selected models in vitro, we tested effects of exposure to IFN-γ and histone deacetylase inhibitors. Pediatric tumors overall, as well as samples within select individual tumor subtypes, exhibit wide ranges of MHC I and B2M gene and protein expression. For most cell lines tested, MHC I was inducible in vitro. MHC I and B2M expression vary among pediatric tumor types and should be evaluated as potential biomarkers, which might identify patients most likely to benefit from MHC I dependent immunotherapies. Modulation of MHC I expression may be a promising mechanism for enhancing MHC I dependent immunotherapeutic efficacy.