Sequence analysis of feline immunoglobulin mRNAs and the development of a felinized monoclonal antibody specific to feline panleukopenia virus

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.

A challenging case of lymphoproliferative disease in a cat

A 7-year-old male castrated Maine Coon cat presented with edema of the right hindlimb and a markedly enlarged right popliteal lymph node. A CBC showed a neutropenia of 1.5 × 10³ /μL. Radiographs and ultrasonographic examination were unremarkable. Cytology of the right popliteal lymph node revealed a mixed population of cells, consisting predominantly of medium to large plasmacytoid lymphocytes, low to moderate numbers of well-differentiated plasma cells and low numbers of small lymphocytes. Plasmacytoid lymphocytes had round nuclei with finely stippled chromatin and one prominent round nucleolus. Low numbers of binucleated cells and bizarre mitotic figures, and rare multinucleated cells were observed. Histopathologic examination of the lymph node showed effacement of the normal lymph node architecture by dense sheets of neoplastic cells. Round to polygonal tumor cells of intermediate size had a low to moderate amount of cytoplasm. Round to indented hyperchromatic nuclei were often eccentrically located and contained one distinct nucleolus. Anisocytosis and anisokaryosis were moderate and 21 mitoses/10 high power field (HPF) were present. Congo red staining was negative. High numbers of tumor cells were positive for lambda light chain immunoglobulin; moderate numbers stained positive for MUM-1. A clonal BCR gene rearrangement was detected with an immunoglobulin heavy chain target (IGH), immunoglobulin lambda light chain (IgL), and kappa deleting element (Kde). Differential diagnoses for the lymphoproliferative disease in this cat included lymphoplasmacytic lymphoma and myeloma-related disorder.