An immunophenotypic study of canine leukemias and preliminary assessment of clonality by polymerase chain reaction

Then is a relative lack of information in the veterinary literature regardi ng the immunophenotypes present in canine leukemias. Utilizing a panel of t hirty monoclonal antibodies, canine leukemias were assessed by flow cytomet ry alone or by flow cytometry in combination with immunocytochemical staini ng of smears. Canine chronic lymphocytic leukemia (CLL) occurred in older d ogs (mean age 9.75 years; range 1.5-15 years; n = 73 cases). Blood lymphocy te counts ranged from 15,000 to 1,600,000/mu l, Surprisingly, 73% of CLL ca ses involved proliferation of T lymphocytes (CD3+), and 54% of CLL cases ha d large granular lymphocyte (LGL) morphology. LGL CLL's were almost exclusi vely proliferation's of T cells that expressed CD8 and the leukointegrin al pha D beta 2 and more frequently expressed T cell receptor (TCR) alpha beta (69%) than TCR gamma delta (31%). The non-LGL T cell CLL cases (19% of CLL ) involved proliferation of TCR alpha beta T cells in which no consistent p attern of CD4 or CD8 expression was found. B cell CLL, based on expression of CD21 or CD79a, comprised 26% of canine CLL cases. These results are in m arked contrast to people where greater than 95% of CLL cases involve prolif eration of B lymphocytes. Thirty eight (38) acute leukemias were also immun ophenotyped. The majority (55%) of these leukemias had a phenotype most con sistent with a myeloid origin. Acute LGL leukemias were also observed (7/38 ), although less commonly than the CLL counterpart. CD34 expression was com mon in acute. non-LGL leukemias of dogs, both myeloid and lymphoid. In some circumstances, it can be difficult to differentiate a reactive (polyclonal ) lymphoid proliferation from a neoplastic (monoclonal) one, Therefore, as an adjunct to phenotypic studies, we have developed a polymerase chain reac tion (PCR) based test for assessment of clonality in T cell proliferations. The test amplifies the junction of the variable gamma (V gamma) and joinin g gamma (J gamma) gene segments region of the TCR gamma genes. Preliminary data indicates that our test is effective and is capable of differentiating a neoplastic from a reactive lymphoproliferative process. (C) 1999 Elsevie r Science B.V. All rights reserved.