Identification of a Subset of Peripheral T-Cell Lymphoma, Not Otherwise Specified, Characterized By FOXP3-Positive Regulatory T-Cell Phenotype, HTLV-1 Negativity and Poor Outcome

Background: T-cell malignancies originating from regulatory T (Treg) cells are almost exclusively confined to human T-cell leukemia virus 1 (HTLV-1) associated adult T-cell leukemia/lymphoma (ATLL), although sporadic cases of other peripheral T-cell lymphomas (PTCLs) with hypothesized Treg derivation have been reported.

Patients and methods: We investigated a series of 169 well characterized PTCLs for the expression of Treg-cell phenotypic markers FOXP3, CD25 and CD4 by immunohistochemistry (IHC) using tissue microarray on formalin-fixed paraffin embedded tissue. Clinico-pathological data for patients enrolled were retrieved from the Danish Lymphoma Registry and medical records. Treg tumors were further invetsigated by Affymetrix OncoScan analysis and Illumina Infinium HumanMethylation450 BeadChips.

Results: Variable amounts of FOXP3-positive Treg cells were often (99% of the cases) found as part of the non-neoplastic cellular infiltrate. However, in five cases (3%) classified as PTCL, not otherwise specified (PTCL-NOS) the vast majority of what morphologically appeared to be the neoplastic cell population displayed a strong positivity for FOXP3, CD4, CD25 and CD3 suggesting a probable Treg origin of these cells. Cases were HTLV-1 negative and showed monoclonal rearrangements of the T-cell receptor genes. All cases were male older than 60 years and showed an aggressive clinical course with overall survival less than two years, despite all patients had low IPI-risk profile at the time of diagnosis. The PTCL with Treg phenotype showed a complex pattern of chromosomal imbalances. Moreover, as compared to normal T-cell subsets their DNA methylation profiles were mostly related to that of normal Treg cells but significantly differed from that.

Conclusions: We suggest that FOXP3-positve PTCL, in the absence of HTLV-1 infection, constitute a distinct entity separated from PTCL-NOS, occurring predominantly in elderly male patients and characterized by a highly aggressive clinical behavior. Further genomic analyses are ongoing. The identification and characterization of these cases may be useful to guide upfront therapeutic strategies.