Amador, Catalina

Abstract Peripheral T-cell lymphomas (PTCLs) are heterogenous T-cell neoplasms often associated with epigenetic dysregulation. We investigated de novo DNA methyltransferase 3A (DNMT3A) mutations in common PTCL entities, including angioimmunoblastic T-cell lymphoma and novel molecular subtypes identified within PTCL–not otherwise specified (PTCL-NOS) designated as PTCL-GATA3 and PTCL-TBX21. DNMT3A-mutated PTCL-TBX21 cases showed inferior overall survival (OS), with DNMT3A-mutated residues skewed toward the methyltransferase domain and dimerization motif (S881–R887). Transcriptional profiling demonstrated significant enrichment of activated CD8+ T-cell cytotoxic gene signatures in the DNMT3A-mutant PTCL-TBX21 cases, which was further validated using immunohistochemistry. Genomewide methylation analysis of DNMT3A-mutant vs wild-type (WT) PTCL-TBX21 cases demonstrated hypomethylation in target genes regulating interferon-γ (IFN-γ), T-cell receptor signaling, and EOMES (eomesodermin), a master transcriptional regulator of cytotoxic effector cells. Similar findings were observed in a murine model of PTCL with Dnmt3a loss (in vivo) and further validated in vitro by ectopic expression of DNMT3A mutants (DNMT3A-R882, -Q886, and -V716, vs WT) in CD8+ T-cell line, resulting in T-cell activation and EOMES upregulation. Furthermore, stable, ectopic expression of the DNMT3A mutants in primary CD3+ T-cell cultures resulted in the preferential outgrowth of CD8+ T cells with DNMT3AR882H mutation. Single-cell RNA sequencing(RNA-seq) analysis of CD3+ T cells revealed differential CD8+ T-cell subset polarization, mirroring findings in DNMT3A-mutated PTCL-TBX21 and validating the cytotoxic and T-cell memory transcriptional programs associated with the DNMT3AR882H mutation. Our findings indicate that DNMT3A mutations define a cytotoxic subset in PTCL-TBX21 with prognostic significance and thus may further refine pathological heterogeneity in PTCL-NOS and suggest alternative treatment strategies for this subset.

Objective: To determine if subcortical, brainstem and cerebellar lesion pattern characteristics of the different types of tau‐negative frontotemporal lobar degeneration (FTLD) would be similar to neocortical and hippocampal patterns [Type 1 has neuronal cytoplasmic inclusions (NCI) and dystrophic neurites (DN), type 2 mainly DN, and type 3 mainly NCI (Mackenzie et al., 2006)]. Design/Methods: We analyzed 40 cases of tau‐negative FTLD from Mayo Clinic, Florida. For each case, 12 standardized sections covering 16 different brain regions or nuclei were sampled including neocortex, hippocampus, subcortical grey, brainstem and cerebellum. TDP‐43 immunohistochemistry was performed and abnormal immunoreactivity semiquantitated. Results: Thirty‐six cases were classified into one of the three types. For subcortical grey and brainstem regions, we did not see predominance of DN in type 2, and the density of NCI and DN were similar in type 3. Type 2 cases had significantly more NCI in basal ganglia compared to the other types (p<0.05). We found a trend that fine DN in hippocampal CA1 region was more frequent in type 1 compared to type 2 and 3 (p=0.07). A novel finding was that NCI were Pick body‐like in type 2 but granular‐like in type 3. Conclusion: This study extends the patterns of pathology previously described in the three variants of tau‐negative FTLD and shows how subcortical areas are affected by TDP‐43.

One-third of peripheral T-cell lymphomas are “not otherwise specified” (PTCL-NOS), but they have been subdivided into 2 subgroups based on gene expression profiling. Amador and colleagues generated an immunohistochemical algorithm that parallels the molecular separation of PTCL-NOS and provides useful prognostic information.