Novel clonality assays for T cell lymphoma in cats targeting the T cell receptor beta, T cell receptor delta, and T cell receptor gamma loci

Feline Hodgkin-like lymphoma: A morphological, immunohistochemical, and molecular study

Fourteen feline nodal lymphomas previously diagnosed as Hodgkin-like lymphoma (HLL) were studied through histologic, immunohistochemical, and molecular analyses to further characterize feline HLL. The cohort comprised 12 domestic shorthair and 2 Maine coon cats, with a male/female ratio of 1.3 and a median age of 9.5 years. Reed-Sternberg and Hodgkin cells were observed in 14/14 HLLs, while a minority of cells resembling lymphocyte-predominant cells were observed in 5/14 (36%) cases. Neoplastic cells were embedded in a mixed reactive background mainly composed of T and B lymphocytes and histiocytes. Necrosis was present in 9/14 (64%) cases. Various percentages of neoplastic cells were positive for CD30, PAX5, and MUM1 in 14/14 cases and for CD20 in 12/14 (86%) cases. Polymerase chain reaction (PCR) for antigen receptor rearrangements (PARR) by agarose gel electrophoresis identified clonal immunoglobulin heavy chain (IGH) in 9/14 (64%) cases, clonal T-cell receptor-gamma (TRG) rearrangements in 4/14 (29%) cases, and polyclonal IGH and TRG in 1 case. The predominance of Reed-Sternberg and Hodgkin cells and a CD30+/PAX5+/MUM1+ immunophenotype were consistent findings in this case series and align with the human classic form of Hodgkin lymphoma (HL). However, in contrast to the human tumor, most feline HLLs express CD20. Based on the human HL classification, feline HLLs were further categorized as lymphocyte-rich (6/14, 43%), mixed cellularity (4/14, 29%), nodular sclerosis (2/14, 14%), and lymphocyte-depleted (2/14, 14%). Feline HLL is a complex neoplasm that requires refinement of diagnostic criteria to improve classification and management.

First report of indolent cutaneous T-cell lymphoma in a fennec fox (Vulpes zerda)

A 10-year-old fennec fox (Vulpes zerda) was presented for multifocal regions of chronic alopecia and crusting. Cutaneous lymphocytosis was diagnosed through histopathological examination and immunohistochemical investigation. Clonal rearrangement of the T-cell receptor gamma locus supports that lymphocytosis in this case was an indolent lymphoma.

Concurrent mucosal and transmural feline intestinal T-cell lymphomas show differing T-cell clonality

The clonality of 14 feline intestinal small and large T-cell lymphomas were examined, which consisted of concurrent mucosal and transmural lymphomas, respectively. Histologically, the small cell lymphomas were localized to the mucosal region and were observed adjacent to large T-cell lymphoma lesions. The large T-cell lymphomas were spread throughout the submucosal region, forming transmural lesions. Both cell types were immunohistochemically stained using anti-cluster of differentiation 3 antibody. For clonality analysis, genomic DNA was extracted from formalin-fixed, paraffin-embedded sections of the mucosal and transmural lesions, separately. Clonality analysis was performed using primer sets targeting T cell receptor beta, T cell receptor delta, and T cell receptor gamma loci. In 12/14 cats, the results of the clonality analysis for T-cells differed between the mucosal and transmural lesions. Despite the fact that the cellular morphologies differed between lesion types, the T-cell clonality was consistent in 1/14 cats, suggesting a common clonal origin. In the remaining case, the clonal relationship between the 2 lesions could not be determined. These results indicate that concurrent lymphomas with small and large T-cells in their mucosal and transmural lesions, respectively, develop via separate pathogenic mechanisms.

Clinicopathologic features and clinical outcome in a cat with nodal T-zone lymphoma

Case summary

An 11-year-old male castrated domestic shorthair cat presented with increased respiratory effort, pleural effusion, lymphadenopathy, lethargy and decreased appetite with weight loss. A diagnosis of T-zone lymphoma was made from histopathology of an extirpated popliteal lymph node that had a marked paracortical expansion of small lymphocytes and prominent high endothelial venule proliferation. T-cell receptor gamma (TRG) molecular clonality PCR yielded a clonal rearrangement and immunohistochemistry demonstrated that the neoplastic lymphocytes expressed CD3 and did not express CD20. The cat was initially treated with two doses of intravenous vincristine and oral prednisolone followed by oral chlorambucil. The pleural effusion, lymphadenopathy, lymphocytosis, abdominal organomegaly and lethargy resolved, and the cat's appetite and body weight returned to normal. At the time of manuscript submission, the cat continued to do well, more than 24 months after presentation.

Relevance and novel information

T-zone lymphoma is a common indolent lymphoma in dogs, but it has only been histopathologically described in one cat before this report. This is the first report to describe the clinical presentation, clinicopathologic findings and outcome for a cat with T-zone lymphoma.

Single cell RNA-sequencing of feline peripheral immune cells with V(D)J repertoire and cross species analysis of T lymphocytes

Introduction

The domestic cat (Felis catus) is a valued companion animal and a model for virally induced cancers and immunodeficiencies. However, species-specific limitations such as a scarcity of immune cell markers constrain our ability to resolve immune cell subsets at sufficient detail. The goal of this study was to characterize circulating feline T cells and other leukocytes based on their transcriptomic landscape and T-cell receptor repertoire using single cell RNA-sequencing.

Methods

Peripheral blood from 4 healthy cats was enriched for T cells by flow cytometry cell sorting using a mouse anti-feline CD5 monoclonal antibody. Libraries for whole transcriptome, αβ T cell receptor transcripts and γδ T cell receptor transcripts were constructed using the 10x Genomics Chromium Next GEM Single Cell 5' reagent kit and the Chromium Single Cell V(D)J Enrichment Kit with custom reverse primers for the feline orthologs.

Results

Unsupervised clustering of whole transcriptome data revealed 7 major cell populations - T cells, neutrophils, monocytic cells, B cells, plasmacytoid dendritic cells, mast cells and platelets. Sub cluster analysis of T cells resolved naive (CD4+ and CD8+), CD4+ effector T cells, CD8+ cytotoxic T cells and γδ T cells. Cross species analysis revealed a high conservation of T cell subsets along an effector gradient with equitable representation of veterinary species (horse, dog, pig) and humans with the cat. Our V(D)J repertoire analysis identified a subset of CD8+ cytotoxic T cells with skewed TRA and TRB gene usage, conserved TRA and TRB junctional motifs, restricted TRA/TRB pairing and reduced diversity in TRG junctional length. We also identified a public γδ T cell subset with invariant TRD and TRG chains and a CD4+ TEM-like phenotype. Among monocytic cells, we resolved three clusters of classical monocytes with polarization into pro- and anti-inflammatory phenotypes in addition to a cluster of conventional dendritic cells. Lastly, our neutrophil sub clustering revealed a larger mature neutrophil cluster and a smaller exhausted/activated cluster.

Discussion

Our study is the first to characterize subsets of circulating T cells utilizing an integrative approach of single cell RNA-sequencing, V(D)J repertoire analysis and cross species analysis. In addition, we characterize the transcriptome of several myeloid cell subsets and demonstrate immune cell relatedness across different species.

Investigating comparative polymerase chain reaction for antigen receptor rearrangement analysis in different types of feline lymphoma samples

Cats have the highest incidence of lymphoma among all animal species. Lymphoma accounts for 41% of all malignant tumors in cats and is responsible for 90% of hematopoietic tumors in felines. Biopsies are considered the gold standard for diagnosis. Polymerase chain reaction (PCR)-based clonality assessment of antigen receptor gene rearrangements can be a valuable complementary tool for identifying infiltrating B-and T-lymphocyte clones. Many studies have focused on intestinal cases but few have addressed mediastinal lymphoma. This study aims to: (1) investigate the clonality patterns of lymphoma samples from various anatomical sites, with a particular focus on mediastinal lymphoma, and (2) evaluate the sensitivity and specificity of the clonality analysis of pleural effusion samples in comparison with cytology, histology, immunohistochemistry, and immunocytochemistry for diagnosing mediastinal lymphoma. There were 82 cases, divided into 49 formalin-fixed and paraffin-embedded biopsy specimens (FFPE), 22 cell pellets, and 11 fresh tissue. This study examined the sensitivity and specificity of PCR for antigen receptor rearrangement (PARR) compared to immunohistochemistry (IHC) and immunocytochemistry. For T-cell receptor gamma chain genes, PARR demonstrated a sensitivity of 58.33% for both fresh tissue and FFPE samples, with a specificity of 100%. Cell pellet analysis exhibited a sensitivity of 64.71% and maintained 100% specificity. A combined analysis of fresh tissue and FFPE with cell pellets showed a sensitivity of 62.07%. For IGH, the sensitivity for fresh tissue and FFPE samples was 56.25%, while cell pellet analysis showed a sensitivity of 62.50%. When considering fresh tissue and FFPE samples, the sensitivity was 57.14%. In conclusion, molecular techniques have emerged as valuable tools for detecting lymphoma, especially in cases where traditional diagnostic methods yield inconclusive results, such as mediastinal lymphoma. While biopsy may not always be feasible, cytology and cell pellets obtained from pleural effusion offer alternative immunocytochemistry and molecular analysis samples, provided they are of sufficient quality and quantity. All sample types considered in this study were suitable for PARR to aid in cases with inconclusive results. Therefore, the sample selection should be tailored to the clinical situation.

Comparative analysis of primer sets for the assessment of clonality in feline lymphomas

Introduction

Lymphomas are among the most important and common malignant tumors in cats. Differentiating lymphomas from reactive lymphoid proliferations can be challenging, so additional tools such as clonality assessment by PCR are important in diagnosis finding. Several PCR assays have been developed to assess clonality in feline lymphomas. For T-cell lymphomas TRG (T-cell receptor gamma) genes are the preferred target whereas for B-cell lymphomas most primer sets target immunoglobulin heavy chain (IGH) genes. Here we compare commonly used diagnostic primer sets for the assessment of clonality in feline lymphomas under controlled conditions (i.e., identical sample set, PCR setup, amplicon detection system).

Methods

Formalin-fixed and paraffin-embedded samples from 31 feline T-cell lymphomas, 29 B-cell lymphomas, and 11 non-neoplastic controls were analyzed by PCR combined with capillary electrophoresis.

Results and discussion

We show that the combination of the primer sets published by Weiss et al. and Mochizuki et al. provided the best results for T-cell clonality, i.e., correctly assigns most populations as clonal or polyclonal. For B-cell clonality, the combination of the primer sets by Mochizuki et al. and Rout et al. gave the best results when omitting the Kde gene rearrangement due to its low specificity. This study rigorously evaluated various primer sets under uniform experimental conditions to improve accuracy of lymphoma diagnostic and provides a recommendation for achieving the highest diagnostic precision in lymphoma clonality analysis.

Jaundice caused by primary common bile duct lymphoma of a cat

A 10-year-old American Shorthair cat presented with anorexia and jaundice, and echogenic evaluation revealed diffuse thickening of the common bile duct (CBD) wall. An exploratory laparotomy was conducted, the lesion was evaluated as difficult to remove, and the cat was euthanized and autopsied. Histologically, round neoplastic cells proliferated in the mucosa of the CBD and infiltrated the hepatic lobe, pancreas, and duodenum. Immunohistochemistry revealed that the neoplastic cells were positive for cytoplasmic-CD3 and granzyme B, and TCR-gamma clonal rearrangement was detected. Based on these findings, the neoplasia was diagnosed as a primary CBD lymphoma originating from cytotoxic T or natural killer cells. To the best of our knowledge, this is the first reported case of feline primary CBD lymphoma. Although rare, lymphoma of the CBD should be considered in cats with jaundice and thickening of the CBD.

Clinical Use of Molecular Biomarkers in Canine and Feline Oncology: Current and Future

Molecular biomarkers are central to personalised medicine for human cancer patients. It is gaining traction as part of standard veterinary clinical practice for dogs and cats with cancer. Molecular biomarkers can be somatic or germline genomic alterations and can be ascertained from tissues or body fluids using various techniques. This review discusses how these genomic alterations can be determined and the findings used in clinical settings as diagnostic, prognostic, predictive, and screening biomarkers. We showcase the somatic and germline genomic alterations currently available to date for testing dogs and cats in a clinical setting, discussing their utility in each biomarker class. We also look at some emerging molecular biomarkers that are promising for clinical use. Finally, we discuss the hurdles that need to be overcome in going 'bench to bedside', i.e., the translation from discovery of genomic alterations to adoption by veterinary clinicians. As we understand more of the genomics underlying canine and feline tumours, molecular biomarkers will undoubtedly become a mainstay in delivering precision veterinary care to dogs and cats with cancer.

Subcutaneous panniculitis-like T-cell lymphoma: Morphological, immunophenotypical and clonality assessment in six cats

BACKGROUND

Primary cutaneous lymphoma represents 0.2%-3% of all feline lymphomas, with nonepitheliotropic lymphomas being the most common. In humans and dogs, subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a primary nonepitheliotropic lymphoma with a T-cell phenotype developing in the subcutis and often mimicking inflammation.

OBJECTIVE

The aim of this report is to describe pathological, phenotypical and clonal features of SPTCL in cats.

ANIMALS

Six cats with SPTCL were included in this study.

MATERIALS AND METHODS

Skin biopsies were formalin-fixed, routinely processed and stained. Histological and immunohistochemical investigation for anti-CD18, CD204, CD79a, CD20, CD3, FeLVp27and FeLVgp70 and clonality assessment were performed.

RESULTS

Four male and two female domestic shorthair cats, mean age 11.2 years, developed SPTCL in the abdominal (three), inguinal (two) and thoracic (one) regions. Variably pleomorphic neoplastic lymphoid cells were present in the panniculus in percentages, expanding the septa (six of six) and extending into fat lobules in one of six cats. Tumours were associated with elevated numbers of neutrophils (five of six), lesser macrophages (six of six) and variable necrosis (six of six). Neoplastic cells expressed CD3+ (six of six), with clonal T-cell receptor rearrangement detected in five of six cats.

CONCLUSIONS AND CLINICAL RELEVANCE

This is the first description of SPTCL in cats. Lesions can be confused with panniculitis, leading to delay in diagnosis and therapy. Awareness of this neoplastic disease is relevant to avoid misdiagnoses and to gain greater knowledge about the disease in cats.

ACVIM consensus statement guidelines on diagnosing and distinguishing low-grade neoplastic from inflammatory lymphocytic chronic enteropathies in cats

BACKGROUND

Lymphoplasmacytic enteritis (LPE) and low-grade intestinal T cell lymphoma (LGITL) are common diseases in older cats, but their diagnosis and differentiation remain challenging.

OBJECTIVES

To summarize the current literature on etiopathogenesis and diagnosis of LPE and LGITL in cats and provide guidance on the differentiation between LPE and LGITL in cats. To provide statements established using evidence-based approaches or where such evidence is lacking, statements based on consensus of experts in the field.

ANIMALS

None.

METHODS

A panel of 6 experts in the field (2 internists, 1 radiologist, 1 anatomic pathologist, 1 clonality expert, 1 oncologist) with the support of a human medical immunologist, was formed to assess and summarize evidence in the peer-reviewed literature and complement it with consensus recommendations.

RESULTS

Despite increasing interest on the topic for clinicians and pathologists, few prospective studies were available, and interpretation of the pertinent literature often was challenging because of the heterogeneity of the cases. Most recommendations by the panel were supported by a moderate or low level of evidence. Several understudied areas were identified, including cellular markers using immunohistochemistry, genomics, and transcriptomic studies.

CONCLUSIONS AND CLINICAL IMPORTANCE

To date, no single diagnostic criterion or known biomarker reliably differentiates inflammatory lesions from neoplastic lymphoproliferations in the intestinal tract of cats and a diagnosis currently is established by integrating all available clinical and diagnostic data. Histopathology remains the mainstay to better differentiate LPE from LGITL in cats with chronic enteropathy.

Patterns of Lymphocytic Infiltrates Can Differentiate Feline Hepatic Lymphoma from Lymphocytic Portal Hepatitis

Hepatic lymphoma is poorly characterized in cats and differentiating between inflammation and lymphomas is often difficult. The diagnosis of hepatic lymphoma in humans relies on recognition of specific patterns of lymphocytic infiltrates and clonality testing of antigen receptors. Herein, we defined similar patterns of lymphocytic infiltrates in hepatic biopsies of cats and correlated them with clonality to determine which patterns are predictive of lymphoma. A retrospective study was performed on surgical biopsies from 44 cats. The immunophenotype was characterized using CD3 and CD20 on all 44 samples. All 44 samples were tested using PCR for T-cell receptor gamma-gene rearrangements. PCR for immunoglobulin heavy chain gene rearrangements was performed on 24 of these cats. Four patterns of lymphocytic infiltrates were characterized: (1) tightly periportal, (2) periportal and centrilobular, (3) nodular, and (4) periportal with sinusoidal extension. Other histomorphologic features (fibrosis, biliary hyperplasia, bile ductopenia, bile duct targeting, hepatic hematopoiesis, lipogranulomas, lymphonodular aggregates, other inflammatory cells) were also evaluated. The sensitivity and specificity of the lymphocytic patterns to diagnose lymphomas were determined using Bayesian Hui-Walter analysis (BLCM) against clonality results. Lymphocytic patterns 2, 3, and 4 accurately diagnosed hepatic lymphomas with a sensitivity and specificity of 82% (CI 95%: 0.65, 0.96) and 77% (CI 95%: 0.54, 1.00), respectively. None of the other microscopic features evaluated were predictive of a lymphoma or inflammation. Our study identified specific patterns of lymphocytic infiltration that differentiate feline hepatic lymphoma from inflammation while other histologic features were not associated with an accurate diagnosis.

Diagnostic utility of LDH measurement for determining the etiology of modified transudate pleural effusion in cats

Fluid analysis is an initial approach for determining the underlying causes of body cavity effusions. Modified transudate is commonly diagnosed in pleural effusion in cats, however, it provides limited diagnostic information. Aims of this study were to investigate common etiologies causing different pleural fluid types and to evaluate the usefulness of lactate dehydrogenase (LDH) for differentiating the etiology in modified transudates in cats. Pleural effusion samples from 122 cats were analyzed and classified into three types: transudate, modified transudate, and exudate. Causes of pleural effusion were classified into four conditions: cardiac disease, neoplasia, feline infectious peritonitis (FIP), and pyothorax. The relationship of underlying etiology and fluid types was described. The LDH levels in pleural fluid and plasma were compared between the causes in the samples classified as modified transudate. The fluid analysis of pleural effusion showed that modified transudate was the most common fluid type (44.2%). Neoplasia was predominantly diagnosed (38.5%) as the etiology of pleural effusion. There was no significant correlation between pleural fluid and plasma LDH level in any type of pleural fluid, suggesting that pleural fluid LDH does not appear to be affected by plasma LDH. The occurrence of modified transudate was not associated to its etiologies, however, the LDH level in modified transudates showed significant differences between etiologic groups. The LDH level in modified transudate was excellent in separating cardiac from non-cardiac diseases with a cut-off value of <535 U/L and separating FIP from non-FIP diseases with a cut-off value of >641 U/L. Based on the current findings, pleural fluid LDH can be a useful adjunctive marker for differentiating some causes of modified transudate pleural effusion and should be added in the routine diagnostic work-up of feline patients with pleural effusions.

A clonality analysis based on T-cell receptor beta and delta loci for high-grade gastrointestinal lymphoma in dogs

Clonality assays based on antigen receptors are used as adjunct examinations in the diagnosis of lymphoproliferative diseases. We investigated the usefulness of the T-cell receptor beta (TRB) and T-cell receptor delta (TRD) loci in clonality assays for high-grade gastrointestinal (GI) lymphoma in dogs. For TRB, we used primers reported previously; for TRD, we designed primers for each of the V and J genes based on genomic sequences. Genomic DNA was extracted from 39 formalin-fixed, paraffin-embedded sections of high-grade GI lymphoma diagnosed histologically. The sensitivity of TRB and TRD primers for GI lymphoma was 41.0% and 38.5%, respectively, which was lower than the 82.1% sensitivity of T-cell receptor gamma (TRG) primers However, some cases that could not be detected using TRG primers had clonality with either TRB or TRD primers. We found the TRG locus to be more suitable as a first choice for the assay of canine lymphoma clonality than the TRB and TRD loci. However, the detection rate of T-cell clonality may be enhanced using TRB and TRD primers for lymphoma cases not detected using TRG primers.