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Distinguishing chronic lymphoproliferative disorders of NK cells (CLPD-NK) from reactive NK-cell expansion is challenging. We assessed the value of killer immunoglobulin-like receptor(KIR) phenotyping and targeted high-throughput sequencing in a cohort of 114 consecutive patients with NK cell proliferation, retrospectively assigned to a CLPD-NK group (n = 46) and a reactive NK group (n = 68). We then developed an NK-cell clonality score combining flow cytometry and molecular profiling with a positive predictive value of 93%. STAT3 and TET2 mutations were respectively identified in 27% and 34% of the patients with CLPD-NK, constituting a new diagnostic hallmark for this disease. TET2-mutated CLPD-NK preferentially exhibited a CD16low phenotype, more frequently displayed a lower platelet count, and was associated with other hematologic malignancies such as myelodysplasia. To explore the mutational clonal hierarchy of CLPD-NK, we performed whole-exome sequencing of sorted, myeloid, T, and NK cells and found that TET2 mutations were shared by myeloid and NK cells in 3 of 4 cases. Thus, we hypothesized that TET2 alterations occur in early hematopoietic progenitors which could explain a potential link between CLPD-NK and myeloid malignancies. Finally, we analyzed the transcriptome by RNA sequencing of 7 CLPD-NK and evidenced 2 groups of patients. The first group displayed STAT3 mutations or SOCS3 methylation and overexpressed STAT3 target genes. The second group, including 2 TET2-mutated cases, significantly underexpressed genes known to be downregulated in angioimmunoblastic T-cell lymphoma. Our results provide new insights into the pathogenesis of NK-cell proliferative disorders and, potentially, new therapeutic opportunities., (© 2021 by The American Society of Hematology.)

To determine if p53 abnormalities could be involved in the pathogenesis of T- or natural killer (NK)-cell lymphomas, we investigated 51 cases of these lymphomas for the expression of p53 and its relationship with p53 gene mutations, the expression of the p21 protein as well as the proliferative and apoptotic indices. Overexpression of p53 was found in 19 cases (37%), whereas mutations of the p53 gene were observed in only 5 of 28 tested cases. The analysis of immunohistochemical data showed some entity-related phenotypic profiles. Anaplastic large cell lymphomas showed a frequent overexpression of p53 (7/8 cases) and p21 (6/8 cases) proteins and rare p53 mutations (1/7 cases), suggesting accumulation of a functional wild type p53 protein able to induce p21 expression. Nodal peripheral T-cell lymphomas unspecified showed relatively frequent overexpression of p53 protein (5/7 cases), infrequent p21 expression (2/7 cases), and rare p53 gene mutations (1/6 cases). In angioimmunoblastic lymphomas, the common phenotype was p53-/p21- (15/17 cases), with only a few scattered p53-positive cells, which, on the basis of double staining results, were mostly Epstein-Barr virus-infected B cells. A p53 gene mutation was only found in 1 case (1/8 cases) of angioimmunoblastic lymphoma, which showed cytologic tumor progression. Mycosis fungoides showed p53 overexpression in 2 of 4 cases, including 1 case with p53 gene mutation and features of cytologic tumor progression. Nasal NK/T lymphomas showed p53 overexpression in 2 of 5 cases, 1 of which had a p53 gene mutation. Finally, all lymphoblastic T-cell lymphomas (5 cases) and gammadelta hepatosplenic T-cell lymphomas (3 cases) were negative for expression of p53 and p21 proteins. We conclude that p53 protein overexpression is a common finding in some entities of T- and T/NK-cell lymphomas, whereas a p53 gene mutation is a rare, sporadic, and rather late event associated with tumor progression in some instances. The p53/p21 expression pattern appears to be variable in T- and T/NK-cell lymphoma entities, reinforcing the concept of distinct, entity-related mechanisms of pathogenesis in these tumors.

Several cytokines have been implicated in the pathogenesis of human lymphomas. Among them, interleukin-10 (IL-10) is a pleiotropic cytokine with various biological effects on B and T lymphocytes. Its expression has been essentially studied in B-cell lymphomas, where it appears to act as an autocrine growth factor. BCRF1 (also called viral IL-10), an open reading frame of Epstein-Barr virus, exhibits extensive sequence and functional homologies with human IL-10. Some entities belonging to T- or natural killer (NK)-cell lymphomas are characterized by a frequent association with Epstein-Barr virus. We analyzed 39 cases of peripheral T-cell lymphoma, as well as 7 cases of nasal NK-cell lymphoma, for the presence of IL-10 transcripts by in situ hybridization, to see whether this cytokine was expressed in these tumors and whether its expression could be related to their histological subtype and to the presence of Epstein-Barr virus. Because the riboprobe used for in situ hybridization recognizes both human and viral IL-10, 12 cases were also analyzed by reverse transcription-polymerase chain reaction to verify the human or viral origin of IL-10. It was found that 8 of 11 (73%) anaplastic large cell lymphomas (ALCLs), 2 of 11 (18%) pleomorphic T-cell lymphomas, and 3 of 7 (43%) nasal NK-cell lymphomas exhibited a large number of IL-10-expressing cells, whereas only rare scattered cells were detected in angioimmunoblastic (11 of 11) and in gammadelta T-cell lymphomas (6 of 6). In ALCLs, the pattern of IL-10 mRNA-expressing cells showed an overlapping with the CD30 staining and preferential localization in sinusal and perifollicular areas, thereby suggesting that IL-10-expressing cells were tumor cells. Furthermore, IL-10 transcripts were detected in the SU-DHL-1 anaplastic lymphoma cell line. No correlation with Epstein-Barr virus profile was found, because all cases of ALCL were negative for EBER 1 and 2 genes by in situ hybridization. We confirmed the presence of human IL-10 mRNA by reverse transcription-polymerase chain reaction in ALCLs as well as in NK-cell lymphomas, whereas viral IL-10 was not detected. Thus, human and not viral IL-10 is frequently expressed by tumor cells in ALCLs and nasal NK-cell lymphomas. In view of its function in the proliferation and the differentiation of cytotoxic T and NK cells, and its immunosuppressive properties, IL-10 may have a role in the pathogenesis of these lymphomas.

Non-Hodgkin's lymphomas are divided into B- and T-cell neoplasms. The existence and the clinical relevance of lymphomas derived from the third lymphocyte lineage, ie, natural killer (NK) cells are still controversial. NK cells are lymphocytes that mediate cytotoxicity without prior sensitization. NK cells also have phenotypic and genotypic characteristics: they express the NK-related antigen CD56, T-cell markers such as CD2 and CD7, but do not express CD5 and T-cell receptor (TCR) proteins, and their TCR locus is not rearranged. Therefore, if NK cell lymphomas exist, they should express some T-cell markers, but not alpha beta or gamma delta TCR proteins. Such lymphomas are actually called TCR silent peripheral T cell lymphomas (PTCL). To detect and characterize NK cell lymphomas, we investigated the immunophenotype and immunogenotype of 35 patients with TCR silent PTCL. The first group included 16 patients with a lymphoma of CD5-CD56+ phenotype, which is identical to normal NK cells. These patients had either a nasal/nasopharyngeal lymphoma (11 cases) or a lymphoma with predominant non-nasal/non-nodal initial involvement (five cases). Eight of the nine cases for which immunogenotypic data were available lacked clonal rearrangement of the TCR gamma genes. Thus, these tumors are likely to be NK cell lymphomas. The second group of 15 cases had a CD5+ phenotype (14 were CD56-, and 1 was CD56+) and clonal rearrangement of TCR gamma genes, indicating that they were true PTCL with unproductive TCR rearrangement. The four remaining cases were CD5- CD56- lymphomas and disclosed either a clonal (two cases) or no clonal (two cases) rearrangements of the TCR gamma genes. Altogether these findings show that CD5-CD56+ so-called "TCR silent PTCL" bear the immunophenotype and immunogenotype of normal NK cells and display peculiar clinical features distinct from true PTCL.