Phenotyping of canine lymphoma with monoclonal antibodies directed at cell surface antigens: classification, morphology, clinical presentation and response to chemotherapy.

Forty cases of naturally occurring canine lymphoma were studied using a panel of murine monoclonal antibodies which identify defined subsets of normal canine lymphocytes. The distribution of phenotypes was similar to that which is seen in man in that the majority (78 per cent) of canine lymphomas were of B-cell origin but a definite minority were phenotypically of T-cell (10 per cent) or non-B, non-T-cell (12 per cent) origin. The expression of Ia-like antigens was restricted to B-cell neoplasms. Within each histologic subgroup of canine lymphomas there was considerable heterogeneity of cell surface marker expression. Immunophenotype appeared to correlate with clinical presentation. Finally, the reactivity of lymphoma cells with murine monoclonal antibody DLy-6, an antibody which appears to react with a differentiation antigen on canine B and T cells, strongly predicted the outcome of initial induction chemotherapy in that all ten evaluable dogs with DLy-6-tumors achieved complete responses to initial chemotherapy while only four of 11 dogs with DLy-6+ tumors responded completely.