KIR3DL2 expression in patients with adult T-cell lymphoma/leukaemia

How molecular advances may improve the diagnosis and management of PTCL patients

Peripheral T-cell lymphomas (PTCL) comprised more than 30 rare heterogeneous entities, representing 10 to 15% of adult non-Hodgkin lymphomas. Although their diagnosis is still mainly based on clinical, pathological, and phenotypic features, molecular studies have allowed for a better understanding of the oncogenic mechanisms involved and the refinement of many PTCL entities in the recently updated classifications. The prognosis remains poor for most entities (5-year overall survival < 30%), with current conventional therapies based on anthracyclin-based polychemotherapy regimen, despite many years of clinical trials. The recent use of new targeted therapies appears to be promising for relapsed/refractory patients, such as demethylating agents in T-follicular helper (TFH) PTCL. However further studies are needed to evaluate the proper combination of these drugs in the setting of front-line therapy. In this review, we will summarize the oncogenic events for the main PTCL entities and report the molecular targets that have led to the development of new therapies. We will also discuss the development of innovative high throughput technologies that aid the routine workflow for the histopathological diagnosis and management of PTCL patients.

KIR3DL2 contributes to the typing of acute adult T-cell leukemia and is a potential therapeutic target

Adult T-cell leukemia (ATL) is a lymphoid neoplasm caused by human T-cell leukemia virus type 1 (HTLV-1), which encodes the transcriptional activator Tax, which participates in the immortalization of infected T cells. ATL is classified into 4 subtypes: smoldering, chronic, acute, and lymphoma. We determined whether natural killer receptors (NKRs) were expressed in ATL. NKR expression (KIR2DL1/2DS1, KIR2DL2/2DL3/2DS2, KIR3DL2, NKG2A, NKG2C, and NKp46) was assessed in a discovery cohort of 21 ATL, and KIR3DL2 was then assessed in 71 patients with ATL. KIR3DL2 was the only NKR among those studied frequently expressed by acute-type vs lymphoma- and chronic/smoldering-type ATL (36 of 40, 4 of 16, and 1 of 15, respectively; P = .001), although acute- and lymphoma-type ATL had similar mutation profiles by targeted exome sequencing. The correlation of KIR3DL2 expression with promoter demethylation was determined by microarray-based DNA methylation profiling. To explore the role of HTLV-1, KIR3DL2 and TAX messenger RNA (mRNA) expression levels were assessed by PrimeFlow RNA in primary ATL and in CD4+ T cells infected with HTLV-1 in vitro. TAX mRNA and KIR3DL2 protein expressions were correlated on ATL cells. HTLV-1 infection triggered KIR3DL2 by CD4+ cells but Tax alone did not induce KIR3DL2 expression. Ex vivo, autologous, antibody-dependent cell cytotoxicity using lacutamab, a first-in-class anti-KIR3DL2 humanized antibody, selectively killed KIR3DL2+ primary ATL cells ex vivo. To conclude, KIR3DL2 expression is associated with acute-type ATL. Transcription of KIR3DL2 may be triggered by HTLV-1 infection and correlates with hypomethylation of the promoter. The benefit of targeting KIR3DL2 with lacutamab is being further explored in a randomized phase 2 study in peripheral T-cell lymphoma, including ATL (registered on https://clinicaltrials.gov as #NCT04984837).

Improving the diversity of captured full-length isoforms using a normalized single-molecule RNA-sequencing method

Human genes form a large variety of isoforms after transcription, encoding distinct transcripts to exert different functions. Single-molecule RNA sequencing facilitates accurate identification of the isoforms by extending nucleotide read length significantly. However, the gene or isoform diversity is lowly represented by the mRNA molecules captured by single-molecule RNA sequencing. Here, we show that a cDNA normalization procedure before the library preparation for PacBio RS II sequencing captures 3.2–6.0 fold more full-length high-quality isoform species for different human samples, as compared to the non-normalized capture procedure. Many lowly expressed, functionally important isoforms can be detected. In addition, normalized PacBio RNA sequencing also resolves more allele-specific haplotype transcripts. Finally, we apply the cDNA normalization based long-read RNA sequencing method to profile the transcriptome of human gastric signet-ring cell carcinomas, identify new cancer-specific transcriptome signatures, and thus, bring out the utility of the improved protocols in gene expression studies.

Hu et al. combine cDNA normalization before library preparation with a software tool to increase the capture of RNA isoform species in single-molecule RNA sequencing. They demonstrate that this approach can detect previously unknown transcripts in gastric signet-ring cell carcinomas that are not present in non-malignant tissue.

Updates in lymph node and skin pathology of adult T-cell leukemia/lymphoma, biomarkers, and beyond

Adult T-cell leukemia/lymphoma (ATLL) is a mature T-cell lymphoproliferative disorder associated with the human T lymphotropic virus (HTLV-1) infection. ATLL predominantly affects individuals within HTLV-1 endemic areas such as Japan, areas of Africa, South America, and the Caribbean. HTLV-1 preferentially infects CD4+ T-cells, and several genetic hits must occur before ATLL develops. ATLL is classically divided into four clinical variants based on manifestations of disease: acute, chronic, lymphomatous, and smouldering. As of 2019, a new subtype has been described: lymphoma type of ATL, extranodal primary cutaneous. In this review, emphasis will be taken to describe the common clinicopathologic manifestations of the disease, advances in biomarker discovery, mutational landscape and targeted therapeutic approaches to treat this highly aggressive and frequently lethal type of T-cell lymphoma.