T-Cell Receptor γ Chain Variable and Joining Region Genes of Subgroup 1 are Clonally Rearranged in Feline B- and T-Cell Lymphoma

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.

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.

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

BACKGROUND

T cell clonality assays in veterinary medicine currently target only the T cell receptor gamma (TRG) locus. Existing assays have suboptimal sensitivity because of insufficient primer coverage of all possible rearrangements.

OBJECTIVE

Develop higher sensitivity clonality assays targeting the TRG, delta (TRD), and beta (TRB) loci in cats.

ANIMALS

Cats with histopathologically confirmed lymphoma (n = 89), non-lymphoma (n = 35), and possible hepatic small cell lymphoma (n = 31).

METHODS

Molecular clonality assay development utilizing our recently reported topology and expressed repertoire data of the T cell receptor loci in cats. Determination of clonality status of lymphoma, non lymphoma, and possible hepatic small cell lymphoma samples, and calculation of assay sensitivity and specificity.

RESULTS

The new multiplex TRG assay yielded the highest sensitivity (95.5%). All assays yielded 100% specificity except for the new multiplex TRG assay (97.3%). The combination of the new TRG and TRB assays yielded sensitivity of 98.9% and specificity of 97.0%. The new TRG assay detected clonality in 17/31 possible small cell lymphoma livers, whereas an existing TRG assay detected clonality in 6/31 livers.

CONCLUSIONS AND CLINICAL IMPORTANCE

The assessment of multiple T cell loci compensates for the potential shortcomings of individual assays. Using a combination of molecular clonality assays will increase the overall sensitivity for the diagnosis of T-cell lymphoma in cats, especially intestinal, and hepatic small cell lymphoma. Hepatic small cell lymphomas detected by the new TRG assay utilized rarely expressed V and J genes not recognized by previous assays, likely indicating unique biology of hepatic small cell lymphoma in cats.

Revisiting lymphocyte clonality testing in feline B-cell lymphoma

Differentiation between resident mature lymphocyte populations and small-cell lymphoma cannot be made by cytological review alone and remains challenging in histopathological review. These cases warrant application of complementary tools like PCR-based immunoglobulin (IG) and T-cell receptor (TCR) clonality testing for confirmation. Although primer coverage of potential IG gene rearrangements in feline B-cell neoplasms constantly improves, the possibility of false negative and false positive test results still poses a problem. In this retrospective study, we assessed diagnostic sensitivity and specificity of a novel developed multiplex PCR assay for routine diagnosis of B-cell clonality. Therefore, 24 feline patients were subjected to comparative clonality testing by using different primer sets. Feline lymphoma cell lines and confirmed patient material served as positive control. Compared to previous studies, this novel developed multiplex PCR assay showed positive effects on diagnostic sensitivity, specificity, accuracy, and positive predictive value accompanied by a slight impairment of negative predictive value. Notably, none of the primer sets was superior; hence, we recommend the combined application of the herein tested primer sets in routine diagnostics. However, a more in-depth-evaluation of the dynamic of assay specific parameters in dependency on primer set usage requires prospective studies on larger cohorts of feline patients.

Molecular pathology in the cancer clinic - where are we now and where are we headed?

Molecular pathology is a developing sub-microscopic discipline of pathology that studies the effects of molecular variations and mutations on disease processes. The ultimate goal of molecular pathology in cancer is to predict risk, facilitate diagnosis and improve prognostication based on a complete understanding of the biological impact of specific molecular variations, mutations and dysregulations. This knowledge will provide the basis for customised cancer treatment, so-called precision medicine. Rapid developments in genomics have placed this field at the forefront of clinical molecular pathology and there are already a number of well-established genetic tests available for clinical use including PCR of antigen receptor rearrangement and KIT mutational analysis. Moving beyond tests assessing a single gene, there are significant research efforts utilising genomics to predict cancer risk, forecast aggressive behaviour and identify druggable mutations and therapeutic biomarkers. Researchers are also investigating the use of circulating cells and nucleic acid for clinically useful low morbidity genomic assessments. If we are to realise the full potential of molecular pathology and precision medicine there are a number of challenges to overcome. These include developing our understanding of the underlying biology (in particular intra-tumoural heterogeneity), methodological standardisation of assays, provision of adequate infrastructure and production of novel therapeutics backed by high-quality clinical data supporting the precision medicine approach. The era of molecular pathology holds the potential to revolutionise veterinary cancer care, but its impact on clinical practice will depend upon the extent to which the inherent challenges can be overcome.

Multifocal cutaneous non-epitheliotropic B-cell lymphoma in a cat

Case summary

Skin tumours are the second-most common form of feline cancer after haematopoietic neoplasms and are often malignant. Cutaneous lymphoma is uncommon in cats and can be classified as epitheliotropic (typically of T-cell origin) or non-epitheliotropic (either of T-cell or B-cell origin). The present study describes a case of multifocal cutaneous non-epitheliotropic B-cell lymphoma. The skin nodules were multiple and variable in size; showed rapid progression; were alopecic and erythematous in appearance and pruritic and ulcerated; and were mostly located on the trunk. Nodule biopsies revealed the presence of uniform medium-to-large round neoplastic cells that infiltrated the dermis and subcutis. The neoplasias were consistent with a round cell cutaneous tumour and did not show evidence of epitheliotropism. Furthermore, immunohistochemical assessments indicated an immunophenotype characterised by round cells with a strong membrane and cytoplasmic positivity for the CD20 antigen, consistent with a lymphocyte of B-cell origin.

Relevance and novel information

Cutaneous non-epitheliotropic B-cell lymphoma in cats is rare and was previously reported to appear as single dermal and subcutaneous masses that are variable in size and generally develop in the tarsal region. To our knowledge, this is the first report to describe multifocal cutaneous non-epitheliotropic B-cell lymphoma in a cat.

Assessment of immunoglobulin heavy chain, immunoglobulin light chain, and T-cell receptor clonality testing in the diagnosis of feline lymphoid neoplasia

BACKGROUND

Differentiation between neoplastic and reactive lymphocytic proliferations can be challenging in cats. PCR for antigen receptor rearrangements (PARR) testing is a useful diagnostic tool to assess clonality of a lymphoid population. Previous feline PARR studies evaluated clonality of complete immunoglobulin heavy chain V-D-J (IGH-VDJ) and T-cell receptor gamma (TRG) gene rearrangements.

OBJECTIVES

We aimed to evaluate the sensitivity and specificity of feline PARR primers targeting complete IGH-VDJ and TRG rearrangements, as well as incomplete IGH-DJ, kappa deleting element (Kde), and immunoglobulin lambda light chain (IGL) gene rearrangements in defined feline neoplasms and nonneoplastic controls.

METHODS

Fluorescently labeled PCR primers were designed to amplify complete IGH-VDJ, incomplete IGH-DJ, Kde, IGL, and TRG gene rearrangements in two multiplexed PCR reactions, and PCR products were analyzed by fragment analysis. Fresh tissue samples from 12 flow cytometrically confirmed B-cell lymphomas, 26 cytologically confirmed gastric and renal lymphomas of presumed B-cell origin, 30 flow cytometrically confirmed T-cell leukemias, and 11 negative control cats were tested.

RESULTS

Using four immunoglobulin primer sets (IGH-VDJ, IGH-DJ, Kde, and IGL), clonal immunoglobulin rearrangements were detected in 87% (33/38) of the presumed B-cell neoplasms. The IGH-VDJ reaction alone only detected clonality in 50% (19/38) of these cases. TRG rearrangements were clonal in 97% (29/30) of the T-cell leukemia cases. All negative control samples had polyclonal immunoglobulin and TRG rearrangements.

CONCLUSIONS

The PARR assay developed in this study is useful for assessing clonality in feline lymphoid neoplasms. Clonality assessment of incomplete IGH-DJ, Kde, and IGL rearrangements helped identify clonal B-cell neoplasms not detected with complete IGH-VDJ PARR alone.

Feline low-grade alimentary lymphoma: an emerging entity and a potential animal model for human disease

BACKGROUND

Low-grade alimentary lymphoma (LGAL) is characterised by the infiltration of neoplastic T-lymphocytes, typically in the small intestine. The incidence of LGAL has increased over the last ten years and it is now the most frequent digestive neoplasia in cats and comprises 60 to 75% of gastrointestinal lymphoma cases. Given that LGAL shares common clinical, paraclinical and ultrasonographic features with inflammatory bowel diseases, establishing a diagnosis is challenging. A review was designed to summarise current knowledge of the pathogenesis, diagnosis, prognosis and treatment of feline LGAL. Electronic searches of PubMed and Science Direct were carried out without date or language restrictions.

RESULTS

A total of 176 peer-reviewed documents were identified and most of which were published in the last twenty years. 130 studies were found from the veterinary literature and 46 from the human medicine literature. Heterogeneity of study designs and outcome measures made meta-analysis inappropriate. The pathophysiology of feline LGAL still needs to be elucidated, not least the putative roles of infectious agents, environmental factors as well as genetic events. The most common therapeutic strategy is combination treatment with prednisolone and chlorambucil, and prolonged remission can often be achieved. Developments in immunohistochemical analysis and clonality testing have improved the confidence of clinicians in obtaining a correct diagnosis between LGAL and IBD. The condition shares similarities with some diseases in humans, especially human indolent T-cell lymphoproliferative disorder of the gastrointestinal tract.

CONCLUSIONS

The pathophysiology of feline LGAL still needs to be elucidated and prospective studies as well as standardisation of therapeutic strategies are needed. A combination of conventional histopathology and immunohistochemistry remains the current gold-standard test, but clinicians should be cautious about reclassifying cats previously diagnosed with IBD to lymphoma on the basis of clonality testing. Importantly, feline LGAL could be considered to be a potential animal model for indolent digestive T-cell lymphoproliferative disorder, a rare condition in human medicine.

Microsatellites within the feline androgen receptor are suitable for X chromosome-linked clonality testing in archival material

Objectives A hallmark of neoplasms is their origin from a single cell; that is, clonality. Many techniques have been developed in human medicine to utilise this feature of tumours for diagnostic purposes. One approach is X chromosome-linked clonality testing using polymorphisms of genes encoded by genes on the X chromosome. The aim of this study was to determine if the feline androgen receptor gene was suitable for X chromosome-linked clonality testing. Methods The feline androgen receptor gene was characterised and used to test clonality of feline lymphomas by PCR and polyacrylamide gel electrophoresis, using archival formalin-fixed, paraffin-embedded material. Results Clonality of the feline lymphomas under study was confirmed and the gene locus was shown to represent a suitable target in clonality testing. Conclusions and relevance Because there are some pitfalls of using X chromosome-linked clonality testing, further studies are necessary to establish this technique in the cat.

Clonality Testing in Veterinary Medicine

The accurate distinction of reactive and neoplastic lymphoid proliferations can present challenges. Given the different prognoses and treatment strategies, a correct diagnosis is crucial. Molecular clonality assays assess rearranged lymphocyte antigen receptor gene diversity and can help differentiate reactive from neoplastic lymphoid proliferations. Molecular clonality assays are commonly used to assess atypical, mixed, or mature lymphoid proliferations; small tissue fragments that lack architecture; and fluid samples. In addition, clonality testing can be utilized to track neoplastic clones over time or across anatomic sites. Molecular clonality assays are not stand-alone tests but useful adjuncts that follow clinical, morphologic, and immunophenotypic assessment. Even though clonality testing provides valuable information in a variety of situations, the complexities and pitfalls of this method, as well as its dependency on the experience of the interpreter, are often understated. In addition, a lack of standardized terminology, laboratory practices, and interpretational guidelines hinders the reproducibility of clonality testing across laboratories in veterinary medicine. The objectives of this review are twofold. First, the review is intended to familiarize the diagnostic pathologist or interested clinician with the concepts, potential pitfalls, and limitations of clonality testing. Second, the review strives to provide a basis for future harmonization of clonality testing in veterinary medicine by providing diagnostic guidelines.

Cytology of endoscopically obtained biopsies for the diagnosis of chronic intestinal diseases in cats

OBJECTIVE

To evaluate the diagnostic value of cytology of endoscopically obtained biopsies in cats presented for chronic gastrointestinal complaints with emphasis on the diagnosis of low-grade alimentary lymphoma (LGAL).

MATERIALS AND METHODS

Data of endoscopically obtained duodenal biopsies from 137 cats were evaluated retrospectively. Cytology was performed using the squash smear technique with subsequent Diff Quick® staining. Pathological findings were categorized according to type and grade of the inflammatory infiltrate. Moreover, reports were reviewed with regard to diagnosis of LGAL. Histopathology reports were analysed correspondingly and compared to cytology results. Histopathological samples were further evaluated by immunohistochemistry (IHC) if a diagnosis of LGAL had been expressed.

RESULTS

Squash smear preparation of intestinal biopsies was adequate for cytological examination in >97% of cases. Using histopathology as gold standard, with cytology, a sensitivity and specificity for detection of a pathologic process in feline intestinal biopsies of 68.1% and 70.6% were calculated, respectively. Regarding the detection of lymphoplasmacytic (LPE) and eosinophilic enteritis a statistically significant correlation with histopathology (p<0.05) was observed. With regard to grade of the inflammatory infiltrate, a weak correlation was calculated (r=0.482). Of 21 cats diagnosed or suspected with LGAL by cytology, IHC confirmed nine cases whereas 11 cases were reclassified as LPE. None of the confirmed LGAL had been missed with histopathology. A sensitivity of 60.0% and specificity of 90.6% for cytological detection of feline LGAL was obtained.

CONCLUSION AND CLINICAL RELEVANCE

The sensitivity of cytology to diagnose LGAL is low and it has no additional significance to histological biopsies.

Molecular characterization of the feline T-cell receptor γ alternate reading frame protein (TARP) ortholog

T-cell receptor γ alternate reading frame protein (TARP) is expressed by human prostate epithelial, prostate cancer, and mammary cancer cells, but is not found in normal mammary tissue. To date, this protein has only been described in humans. Additionally, no animal model has been established to investigate the potential merits of TARP as tumor marker or a target for adoptive tumor immunotherapy. In this study conducted to characterize feline T-cell receptor γ sequences, constructs very similar to human TARP transcripts were obtained by RACE from the spleen and prostate gland of cats. Transcription of TARP in normal, hyperplastic, and neoplastic feline mammary tissues was evaluated by conventional RT-PCR. In felines similarly to the situation reported in humans, a C-region encoding two open reading frames is spliced to a J-region gene. In contrast to humans, the feline J-region gene was found to be a pseudogene containing a deletion within its recombination signal sequence. Our findings demonstrated that the feline TARP ortholog is transcribed in the prostate gland and mammary tumors but not normal mammary tissues as is the case with human TARP.

Weigners fixative-an alternative to formalin fixation for histology with improved preservation of nucleic acids

Formalin fixation and paraffin embedding (FFPE) is the standard method for tissue storage in histopathology. However, FFPE has disadvantages in terms of user health, environment, and nucleic acid integrity. Weigners fixative has been suggested as an alternative for embalming cadavers in human and veterinary anatomy. The present study tested the applicability of Weigners for histology and immunohistochemistry and the preservation of nucleic acids. To this end, a set of organs was fixed for 2 days and up to 6 months in Weigners (WFPE) or formalin. WFPE tissues from the skin, brain, lymphatic tissues, liver, and muscle had good morphologic preservation, comparable to formalin fixation. The quality of kidney and lung samples was inferior to FFPE material due to less accentuated nuclear staining and retention of proteinaceous interstitial fluids. Azan, Turnbull blue, toluidin, and immunohistochemical stainings for CD79a, cytokeratin, vimentin, and von Willebrand factor led to comparable results with both fixates. Of note, immunohistochemical detection of CD3 was possible after 6 months in WFPE but not in FFPE tissues. mRNA, miRNA, and DNA from WFPE tissues had superior quality and allowed for amplification of miRNA, 400-bp-long mRNA, and 1000-bp-long DNA fragments after 6 months of fixation in WFPE. In summary, Weigners fixative is a nonhazardous alternative to formalin, which provides a good morphologic preservation of most organs, a similar sensitivity for protein detection, and a superior preservation of nucleic acids. Weigners may therefore be a promising alternative to cryopreservation and may be embraced by people affected by formalin allergies.

X-Chromosome Inactivation Pattern Analysis for the Assessment of Cell Clonality in Cats

X-chromosome inactivation pattern (XCIP) analysis has been widely used to assess cell clonality in various types of neoplasms in humans. In the present study, a polymerase chain reaction–based feline XCIP analysis using the feline androgen receptor gene was developed. To construct the system of the analysis, polymorphism in CAG tandem repeats within the feline androgen receptor gene was explored using somatic DNAs from 50 male and 103 female cats. CAG tandem repeats in exon 1 of the feline androgen receptor gene were found to be polymorphic, containing 15 to 22 CAG repeats. Of the 103 female cats, 70 (68%) were heterozygous for the number of CAG repeats, indicating the possible usefulness of XCIP analysis in cats. Application of the feline XCIP analysis to 3 feline mammary gland adenocarcinoma cell lines revealed distinctly skewed XCIPs in these cell lines, indicating their clonal origins. Twelve (80%) of the 15 primary tissue/cell samples obtained from cats with various neoplastic diseases showed skewed XCIPs. Moreover, bone marrow samples from 3 cats with myelodysplastic syndrome were also found to have skewed XCIPs. The polymerase chain reaction–based XCIP analysis developed in this study can provide information on cell clonality in female cats, potentially facilitating the differential diagnosis of various disorders in cats.

Feline alimentary lymphoma: 1. Classification, risk factors, clinical signs and non-invasive diagnostics

PRACTICAL RELEVANCE

Alimentary lymphoma (AL) occurs commonly in cats and exists as distinct subtypes that differ in their clinical course, response to treatment and prognosis. Accurate diagnosis is important to guide appropriate treatment.

CLINICAL CHALLENGES

Differentiation of low-grade alimentary lymphoma from lymphoplasmacytic enteritis can be challenging, especially where endoscopic intestinal biopsies, which sample only the mucosa and submucosa, are used. The major differentials for intermediate- and high-grade alimentary lymphoma are other neoplastic and non-neoplastic intestinal mass lesions. The diagnosis of large granular lymphocyte lymphoma requires vigilance as it may be missed with routine diagnostics.

PATIENT GROUP

AL affects predominantly middle- to old-aged domestic crossbred cats (median age 10-13 years).

EVIDENCE BASE

The evidence supporting this review is grade II, III and IV, derived from prospective studies, retrospective case series, reviews, extrapolation from other species, pathophysiological justification and the combined clinical experience of those working in the field.

Feline alimentary lymphoma: 2. Further diagnostics, therapy and prognosis

PRACTICAL RELEVANCE

Accurate diagnosis of the distinct subtypes of alimentary lymphoma (AL) that occur in cats is important as there are major differences between them in clinical presentation, treatment and prognosis. Unlike intermediate- and high-grade alimentary lymphoma (I/HGAL) and large granular lymphocyte lymphoma (LGLL), which can often be diagnosed by aspiration cytology, full-thickness intestinal biopsies are usually required for the diagnosis of low-grade alimentary lymphoma (LGAL).

CLINICAL CHALLENGES

LGAL is an increasingly recognised clinical problem and it can be challenging to differentiate from inflammatory disease. Where there is ambiguity on histology, further diagnostics (immunophenotyping and clonality analysis) may be required. The diagnosis of LGLL requires an index of suspicion as it may be missed with routine diagnostics. While cats with LGAL typically achieve durable remissions with oral prednisolone and chlorambucil, I/HGAL runs a more aggressive clinical course and requires multi-agent chemotherapeutic protocols. Information on the treatment of LGLL is limited and this form of AL has the poorest prognosis. Preliminary studies suggest that abdominal irradiation may potentially be of benefit in cats with AL and further investigations are warranted.

EVIDENCE BASE

The evidence supporting this review is derived from grade II, III and IV prospective studies, retrospective case series, reviews, extrapolation from other species, pathophysiological justification and the combined clinical experience of those working in the field.