Pathology in Practice.

In collaboration with the American College of Veterinary Pathologists.

Exploring the association of intratumoral immune cell infiltrates with histopathologic grade in canine mast cell tumors.

Cutaneous canine mast cell tumors (ccMCTs) vary in their biological behavior, treatment, and prognosis, based on their grade. Immune cell infiltration has been associated with prognosis and response to treatments in some human cancers, and immune-targeting therapeutics are increasingly being explored in veterinary oncology. However, currently little is known about the tumor microenvironment (TME) in ccMCTs. Therefore, the objective of this study was to determine the prevalence of T lymphocytes, T regulatory lymphocytes, PD-1+ cells and macrophages in low- and high-grade ccMCTs. Thirty low-grade and 20 high-grade formalin-fixed paraffin-embedded ccMCT samples were included. Immunohistochemistry (IHC) was performed to detect CD3, FOXP3, Iba1, and PD-1 on sequential sections. Three 400x fields with the highest numbers of CD3+ cells were identified for each tumor. The percentage of CD3+, FOXP3+, and Iba1+ cells, and the number of PD-1+ cells, was quantified in each of these three "hot-spot" fields using ImageJ software. Iba1 expression was significantly greater in high-grade compared to low-grade ccMCTs (mean = 12.5% vs. 9.6%, p = 0.043). PD-1 expression was low overall, but a significantly higher number of PD-1-expressing cells was observed in high-grade ccMCTs (median 1 vs. 0, p = 0.001). No significant difference was noted in CD3 and FOXP3 expression between ccMCT grades. Macrophages and PD-1+ cells were more frequent in high-grade, compared to low-grade ccMCTs. Further studies are needed to define the role of macrophages and rare PD-1+ cells in high-grade ccMCTs.

Canine memory T-cell subsets in health and disease.

A more complete understanding of canine T-lymphocyte immunity is necessary for improving diagnostic and therapeutic approaches to canine diseases, developing cell-based canine immunotherapeutics, and evaluating dogs as large mammal models for comparative immunology research. The aim of this study was to utilize CD45RA (indicating antigen inexperience) and CD62L (indicating lymph node homing capability), to quantify canine memory T-cell subsets in healthy dogs and dogs with various diseases. Peripheral blood mononuclear cells (PBMCs) were prospectively collected from dogs belonging to one of four groups:dermatologic inflammation (n = 9), solid tumors (n = 9), lymphoma (n = 9), and age-/weight-matched healthy control dogs (n = 15). Dogs receiving prednisone or any other immunomodulating medication within two weeks were excluded. Flow cytometry was performed and T-cell subsets were defined as CD4+ or CD8+, and naïve (TN), central memory (CM), effector memory (EM), or terminal effector memory re-expressing CD45RA (TEMRA). T-cell subset proportions were compared between each disease group and their healthy age-/weight-matched controls using a Mann-Whitney test. Significantly increased %CD8+ TN (P = 0.036) and decreased %CD8+ TEMRA (P = 0.045) were detected in dogs with dermatologic inflammation compared to healthy controls. Furthermore, %CD4+ TN positively correlated with Canine Atopic Dermatitis Extent and Severity Index (CADESI) score within the inflammation group (ρ = 0.817, P = 0.011). No significant differences between either cancer group and their healthy controls were detected. Taken together, these data indicate that dermatologic inflammation can alter proportions of peripheral blood T-cell subsets, possibly due to the migration of antigen-specific T-cells into tissues. Furthermore, these findings support the utility of CD45RA and CD62L in characterizing clinical canine immune responses.