Loss of CD45 cell surface expression in canine T-zone lymphoma results from reduced gene expression

Canine T zone lymphoma is a tumor of mature, previously activated αβ T cells

T cell lymphomas are a diverse group of tumors found in both dogs and humans, originating from various normal T cell types. Identifying the origin of neoplastic lymphocytes can offer valuable insights into the pathogenesis and clinical behavior of these tumors. T zone lymphoma (TZL) in dogs is characterized by the absence of CD45 expression, a strong breed predilection, and its association with adult-onset demodicosis-a condition believed to be linked to immunosuppression. In this study, our aim was to employ transcriptomic and functional data to determine the normal counterpart of TZL. Identifying the normal counterpart may help us understand both how these tumors arise and explain their clinical behavior. Gene expression profiling using NanoString and RNA seq was used to compare the transcriptome between neoplastic T zone cells, normal canine T cells and publicly available gene sets using Gene Set Enrichment Analysis. Mitogen, anti-CD3 stimulation and PMA/ionomycin stimulation were used to assess T cell proliferation in vitro, and intracellular cytokine production was measured by flow cytometry. Gene expression profiling revealed that TZL is most likely derived from an activated or memory alpha-beta T cell but the cells do not fall cleanly into an effector subtype. TZL cells express CD4-specific transcription factors GATA3 and THPOK, even though TZL cells more commonly express CD8, or neither CD4 nor CD8. TZL cells produce high levels of interferon gamma and tumor necrosis factor alpha when stimulated, further supporting the hypothesis that they are derived from an antigen experienced T cell. TZL cells do not proliferate when stimulated through the T cell receptor but will divide when the T cell receptor is bypassed with PMA and ionomycin. The observation that these cells are derived from a mature, previously activated T cell is the first step in understanding the genesis of this unique T cell tumor.

CD45 inhibition in myeloid leukaemia cells sensitizes cellular responsiveness to chemotherapy

Myeloid malignancies are a group of blood disorders characterized by the proliferation of one or more haematopoietic myeloid cell lineages, predominantly in the bone marrow, and are often caused by aberrant protein tyrosine kinase activity. The protein tyrosine phosphatase CD45 is a trans-membrane molecule expressed on all haemopoietic blood cells except that of platelets and red cells. CD45 regulates various cellular physiological processes including proliferation, apoptosis, and lymphocyte activation. However, its role in chemotherapy response is still unknown; therefore, the aim of this study was to investigate the role of CD45 in myeloid malignancies in terms of cellular growth, apoptosis, and response to chemotherapy. The expression of CD45 on myeloid leukaemia primary cells and cell lines was heterogeneous with HEL and OCI-AML3 cells showing the highest level. Inhibition of CD45 resulted in increased cellular sensitivity to cytarabine and ruxolitinib, the two main therapies for AML and MPN. Bioinformatics analysis identified genes whose expression was correlated with CD45 expression such as JAK2, ACTR2, THAP3 Serglycin, and PBX-1 genes, as well as licensed drugs (alendronate, allopurinol, and balsalazide), which could be repurposed as CD45 inhibitors which effectively increases sensitivity to cytarabine and ruxolitinib at low doses. Therefore, CD45 inhibition could be explored as a potential therapeutic partner for treatment of myeloid malignancies in combination with chemotherapy such as cytarabine especially for elderly patients and those showing chemotherapy resistance.

Comparative analysis of the aberrant immunophenotype and clinical characteristics in dogs with lymphoma: a study of 27 cases

Introduction

Aberrant lymphoma phenotypes are frequently found in dogs, but the clinical implications are sparse.

Methods

Twenty-seven dogs with aberrant lymphoma diagnosed using flow cytometry between 2017 and 2023 were analyzed. Major paraneoplastic syndromes, prognostic factors, and clinical features of lymphoma were compared to their immunophenotypes.

Results

Twenty-seven dogs had aberrant immunophenotypes, with MHCII- (48%) and CD3+/CD21+ (44%) being the most commonly identified aberrancies. In B-cell lymphoma, the most frequent aberrancies were MHC II- (53%), CD3+/CD21+ (41%), CD34+ (24%), and CD79a- (24%). Meanwhile, in T-cell lymphoma, CD3+/CD21+ (63%), CD4-/CD8-(50%), CD5- (50%), and CD45- (50%) were the most common. The platelet-neutrophil ratio was significantly higher in the CD3+/CD21+ group than in the other groups, where either one or both markers were not expressed (55.23 ± 39.64; 18.72 ± 14.95, respectively; p = 0.001). Serum albumin concentration was significantly lower in the MHCII-group (2.59 g/dL, 95% CI 2.31-2.87) than in the MHCII+ group (3.06 g/dL, 95% CI 2.88-3.23; p = 0.009). CD34 expression showed significant correlations with cranial mediastinal mass, WHO clinical substage, and fever (p = 0.028, p = 0.041, and p = 0.047, respectively). MHCII expression was correlated with adverse reactions to chemotherapy, cranial mediastinal masses, and fever (p = 0.009, p = 0.023, and p < 0.001, respectively). No statistically significant differences in the survival period were observed for any of the phenotypic aberrancies.

Conclusion

Aberrant lymphomas are common in dogs. Some clinical prognostic factors that significantly correlate with aberrant immunophenotypes have been identified and can be applied clinically.

Nodal T-zone lymphoma and T-zone hyperplasia in dogs

T-zone lymphoma (TZL) is an indolent, nodal lymphoma that has been clinically characterized in detail in dogs, and T-zone hyperplasia (TZH) is a hyperplastic change in lymph nodes associated with antigen processing. In some cases, histopathological features of TZL and TZH are similar, and are difficult to differentiate by morphology alone. Since there have been few publications characterizing their immunohistochemical profiles, histological, immunohistochemical, and clonality examinations were performed using formalin-fixed paraffin-embedded samples of canine lymph nodes with TZL (14 cases) and canine lymph nodes with TZH associated with nonlymphocytic tumors (10 cases). Immunohistochemically, small- to medium-sized lymphocytes of TZL were immunopositive for CD3, CD5, and HLA-DR, and negative for CD45, FOXP3, and granzyme B (GRB) in all cases. Among these 14 cases, 11 were immunopositive for CD8 and 1 was CD20 positive. Paracortical lymphocytes in TZH were diffusely immunopositive for CD3, CD5, and CD45, with scattered immunopositivity for CD8, HLA-DR, FOXP3, and GRB, and negative for CD20 in all cases. A clonal TCR gene rearrangement was detected in 13/14 TZL and none of the TZH cases. The present study revealed that TZL is a clonal proliferation of monomorphic CD8+CD45-GRB- T cells, while TZH consists of an immunophenotypically heterogenous population of CD45+ T cells that are variably positive for CD8 and FOXP3. These results suggest that canine TZL is a clonal proliferation of naïve or premature cytotoxic T cells. Regarding TZH, variable immunopositivity for cytotoxic and regulatory T-cell antigens may reflect immune responses to a variety of regional neoplastic lesions.

Clinical and Clinical Pathological Presentation of 310 Dogs Affected by Lymphoma with Aberrant Antigen Expression Identified via Flow Cytometry

Phenotypic aberrancies have been reported occasionally in canine lymphomas. Here, we retrospectively collected 310 canine lymphomas with an aberrant phenotype detected via flow cytometry and describe their clinical and clinical pathological features at diagnosis. There were 152 T-cell lymphomas not otherwise specified (T-NOS), 101 T-zone lymphomas (TZL), 54 B-cell lymphomas, and 3 cases with two suspected concurrent neoplastic populations. The most represented aberrancies were: CD5-, CD4-CD8-, and CD3- in T-NOS lymphomas, CD21+, CD4-CD8-, and CD3- in TZLs, and CD34+, CD44-, and CD5+ in B-cell lymphomas. Among T-cell lymphomas, the aberrant expression of CD21 was significantly more frequent in TZL and the loss of CD5 and CD44 in T-NOS. More than 75% of dogs were purebred; males outnumbered females; the mean age at diagnosis was 8–10 years, depending on lymphoma subtype. A few dogs were symptomatic at the time of diagnosis, and 30% had peripheral blood abnormalities, in line with what is already reported for the general population of dogs with lymphoma. Further studies are needed to assess the pathogenetic mechanisms underlying each specific antigen aberrancy, as well as the diagnostic and prognostic role.

Immunophenotypic Characterization of Canine Nodal T-Zone Lymphoma

T-zone lymphoma (TZL) is an indolent nodal T-cell lymphoma most commonly observed in submandibular lymph nodes in dogs. The diagnosis is based on its distinct morphology and expression of CD3. TZL has been reported to have a low Ki67 index and to lack expression of CD45. The latter feature has been used to diagnose this type of lymphoma via fine needle aspirate and flow cytometry without confirmation of the characteristic tissue architecture. The goal of this study was to characterize the immunophenotype of canine nodal TZL in greater detail. Twenty-seven TZLs were selected based on their characteristic morphology. A tissue microarray was generated, and immunohistochemical expression of CD3, CD5, CD20, CD21, CD25, CD45, Bcl-6, and Ki67 was evaluated. Neoplastic T cells in all cases were positive for CD3, CD5, and CD25, and negative for CD20, CD21, and Bcl-6. Positive labelling for CD45 was detected in 2 of the 27 cases with the remaining 25 cases being negative. All cases had a low Ki67 index with an average index of 19.56%. For the CD45-positive TZLs, clonality of the T-cell antigen receptor gamma gene was confirmed in only one of these cases. The observed immunophenotype of canine TZL is similar to previous publications with the exception that 2 cases expressed CD45. Expression of CD45 in TZLs in this study emphasizes the importance of interpreting immunophenotypic findings in conjunction with histopathology to reach an accurate diagnosis and not to use lack of expression of a particular antigen as the sole diagnostic criterion.

Multicenter flow cytometry proficiency testing of canine blood and lymph node samples

BACKGROUND

Flow cytometry (FC) is used increasingly in veterinary medicine for further characterization of hematolymphoid cells. Guidelines for optimizing assay performance and interpretation of results are limited, and concordance of results across laboratories is unknown.

OBJECTIVES

This study aimed to determine inter-investigator agreement on the interpretation of FC results from split samples analyzed in different laboratories using various protocols, cytometers, and software; and on the interpretation of archived FC standard (FCS) data files contributed by the different investigators.

METHODS

This was a multicenter observational cross-sectional study. Anticoagulated blood or lymph node aspirate samples from nine client-owned dogs were aliquoted and shipped to participating laboratories. Samples were analyzed with individual laboratory-developed protocols. In addition, FCS files from a set of separate samples from 11 client-owned dogs were analyzed by participating investigators. A person not associated with the study tabulated the results and interpretations. Agreement of interpretations was assessed with Fleiss' kappa statistic.

RESULTS

Prolonged transit times affected sample quality for some laboratories. Overall agreement among investigators regarding the FC sample interpretation was strong (κ = 0.86 ± 0.19, P < .001), and for specific categories, ranged from moderate to perfect. Agreement of the lymphoproliferation or other leukocyte sample category from the analysis of the FCS files was weak (κ = 0.58 ± 0.05, P < .001).

CONCLUSIONS

Lymphoproliferations were readily identified by FC, but identification of the categories of hematolymphoid neoplasia in fresh samples or archived files was variable. There is a need for a more standardized approach to maximize the enormous potential of FC in veterinary medicine.

A case of canine high-grade T-cell lymphoma immunophenotypically consistent with T-zone lymphoma

A 9-year-old spayed female Curly Coated Retriever was referred for evaluation of generalized peripheral lymphadenomegaly. The dog was clinically healthy on presentation with no anomalies detected on complete blood count, serum biochemistry, urinalysis, or three-view thoracic radiographs. Fine-needle aspiration (FNA) and cytology of the peripheral lymph nodes were consistent with lymphoma with an intermediate-sized lymphoid population. Flow cytometry of peripheral lymph nodes was consistent with a homogeneous population of CD4⁺ T cells that had lost expression of the pan-leukocyte antigen CD45. Variable expression of CD21, CD25, and class II major histocompatibility complex (MHC) were also noted. This was considered consistent with T-zone lymphoma (TZL), although the T cells were noted to be larger than usual based on flow cytometry. Due to the suspected indolent nature of this patient's disease and clinical progression, a careful monitoring approach was initially discussed with the owner. However, additional diagnostic testing was performed to confirm the diagnosis. Bone marrow cytology did not show any significant anomalies. The largest lymph node (left mandibular) was extirpated and submitted for histopathology. Based on the lymph node architecture, cellular features, and high mitotic activity, an unexpected diagnosis of peripheral T-cell lymphoma not otherwise specified (PTCL-NOS) was made. The dog was started on CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) chemotherapy. This case illustrates the limitations of using flow cytometry as the sole means of diagnosing TZL and highlights the importance of using complementary tests when subtyping canine lymphoma, which is significant when considering a patient's treatment plan and prognosis.

Increased frequency of CD45 negative T cells (T zone cells) in older Golden retriever dogs

T zone lymphoma (TZL) is characterized by the clonal expansion of T cells lacking expression of the pan-leukocyte antigen CD45 (TZ cells). A strong breed predisposition is observed in Golden retrievers. This study aimed to confirm aberrant CD45 mRNA expression and determine if Golden retrievers without clinical lymphoma have an increased frequency of circulating TZ cells. Gene expression analysis on confirmed TZL cases showed a significant decrease in CD45 expression compared to normal dogs. Peripheral blood samples from senior dogs, 242 Golden retrievers and 42 non-Golden retrievers, without evidence of lymphoproliferative disease were assessed for the presence of TZ cells by flow cytometry. Thirty-one percent of Golden retrievers had TZ cells compared to 14% of non-Golden retrievers. Thirty-four percent of Golden retrievers with TZ cells had a clonal T cell receptor gamma (TRG) gene rearrangement. Interestingly, 20% of Golden retrievers without TZ cells also had a clonal TRG rearrangement. Golden retrievers may have an increased risk of TZL due to an increased frequency of TZ cells.