IDH mutation, glioma immunogenicity, and therapeutic challenge of primary mismatch repair deficient IDH‐mutant astrocytoma PMMRDIA: a systematic review

Abstract

In 2021, Suwala et al. described Primary Mismatch Repair Deficient IDH‐mutant Astrocytoma (PMMRDIA) as a distinct group of gliomas. In unsupervised clustering, PMMRDIA forms distinct cluster, separate from other IDH‐mutant gliomas, including IDH‐mutant gliomas with secondary mismatch repair (MMR) deficiency. In the published cohort, three patients received treatment with an immune checkpoint blocker (ICB), yet none exhibited a response, which aligns with existing knowledge about the decreased immunogenicity of IDH‐mutant gliomas in comparison to IDH‐wildtype. In the case of PMMRDIA, the inherent resistance to the standard‐of‐care temozolomide caused by MMR deficiency is an additional challenge. It is known that a gain‐of‐function mutation of IDH1/2 genes produces the oncometabolite R‐2‐hydroxyglutarate (R‐2‐HG), which increases DNA and histone methylation contributing to the characteristic glioma‐associated CpG island methylator phenotype (G‐CIMP). While other factors could be involved in remodeling the tumor microenvironment (TME) of IDH‐mutant gliomas, this systematic review emphasizes the role of R‐2‐HG and the subsequent G‐CIMP in immune suppression. This highlights a potential actionable pathway to enhance the response of ICB, which might be relevant for addressing the unmet therapeutic challenge of PMMRDIA.