Canine CD4+ T‐cell lymphoma identified by flow cytometry exhibits a consistent histomorphology and gene expression profile

Abstract

T‐cell lymphomas (TCL) are a diverse group of neoplasms with variable diagnostic features, pathophysiologies, therapeutic responses and clinical outcomes. In dogs, TCL includes indolent and aggressive tumours such as T‐zone lymphoma (TZL) and peripheral T‐cell lymphoma (PTCL), respectively. Delineation of molecular subtypes and investigation into underlying pathophysiologies of aggressive TCLs remains inadequate. We investigate the correlations between flow cytometry and histopathology of 73 cases of nodal TCL. The majority of cases (82.2%) were characterized as CD4+ TCL by flow cytometry. Fewer cases were classified as CD8+ TCL (6.8%) or CD4−CD8− TCL (11.0%). All cases, regardless of immunophenotype, exhibited conserved histologic features consistent with the WHO classification of PTCL. Histologic subsets of PTCL corresponding to immunophenotypic features were not identified. Neoplastic cell size determined by flow cytometry correlated significantly with mitotic rate. RNA‐seq was performed on a subset of CD4+ PTCL cases (n = 6) and compared with sorted control CD4+ T‐cells. The gene expression pattern of CD4+ PTCL was similar between all cases regardless of breed. PTCL was enriched in pathways representing G‐coupled protein receptor signalling, extracellular matrix remodelling and vascular development, immune signalling and mitotic activity. Furthermore, global gene expression changes were consistent with downregulation of PTEN signalling and upregulation of the MTOR‐PI3K‐ATK axis. In this study, we evaluated the correlations between flow cytometry, histopathology and gene expression within a large cohort of nodal TCLs. We further demonstrate the ability of flow cytometry to identify a subtype of T‐cell lymphoma, CD4+ PTCL, with a uniform histomorphology and gene expression profile.

The Genetic and Molecular Basis for Canine Models of Human Leukemia and Lymphoma

“…A smaller number of cases express CD8, neither CD4 nor CD8, or both antigens. The cells do not express CD34, and gene expression profiling on a limited number of cases did not identify upregulated TdT expression compared to normal CD4 T cells (8). These findings support the classification of these tumors as mature T cell lymphomas, rather than precursor neoplasms despite the frequent mediastinal involvement.…”

“…This breed-specific predilection is striking and has been noted in numerous studies in both the U.S. and Europe (10,(72)(73)(74). cPTCL affects middle age dogs (median 7 years) and has a slight male predominance (8,72). Mediastinal involvement is seen in approximately half of cPTCL cases, and half of all cases are hypercalcemic (these features overlap but also exist independently).…”

“…Histology with immunohistochemistry (IHC) can provide a WHO subtype in most cases. Flow cytometry can be used to subclassify most forms of T cell lymphoma (7,8) but not different forms of B cell lymphoma. Clonality testing is also widely used for those cases where it is difficult to distinguish a reactive from a neoplastic process (9).…”

“…A study of 73 cases of nodal cPTCL with paired histology and immunophenotyping by flow cytometry demonstrated that cPTCL can be reliably diagnosed by flow cytometry alone (8). cPTCL most commonly expresses CD4, high levels of CD3, low levels of class II MHC and often exhibits loss of CD5 expression, similar to hPTCL.…”

“…Gene expression profiling by RNA seq (8), mutational analysis (44,80), and copy number variation (52,53) have been described in separate studies of canine T cell lymphoma. There is insufficient gene expression data currently available to determine the extent of heterogeneity of cPTCL, and if this disease can be subdivided into GATA3 and TBX21 associated tumors.…”