T-cell receptor gene rearrangement in canine mycosis fungoides: further support for a canine model of cutaneous T-cell lymphoma.

Canine cutaneous T-cell lymphoma (CTCL) is a morphologic and immunophenotypic simulant of human mycosis fungoides (MF) characterized by an infiltrate of atypical, hyperconvoluted, epidermotropic T cells. To further support our hypothesis that canine MF is a useful model for the study of human CTCL, we have used Southern blotting to search for clonal T-cell proliferations in canine MF. Cellular DNA was extracted from normal dog buffy coat cells (n = 8), lesional canine MF skin (n = 8), canine MF buffy coat cells (n = 7), normal dog skin (n = 3), and normal human buffy coat cells (n = 5), digested with a panel of restriction enzymes and Southern blotted onto nylon membranes. All cases of canine MF were also immunophenotyped with anti-canine monoclonal antibodies to CD4, CD8, CD18, CD45RA, canine class II, T-cell activation antigens, and pan-B-cell antigens. Normal dogs gave reproducible digestion patterns in blood and skin, which differed from the human germline patterns when probed with a human T-cell receptor (TCR), beta chain constant region (C beta) cDNA. Common germline bands between the species included the 3.5-kb Eco RI, 3.4-kb Bam HI, 5.4-kb Sac I. These results confirmed that the TCR-beta gene is evolutionarily conserved between dog and man. Immunostaining revealed that 3/7 cases were CD4+ canine CTCL and 4/7 were CD8+ canine CTCL. Rearranged bands, deletion of germline bands, as well as minor alterations in electrophoretic mobility were observed in lesional DNA from seven of eight cases of canine MF, with at least two restriction digests in each case. Dog rearrangements were best detected with Bgl II, Eco RI, Eco RV, and Sac I, whereas deletions were detected with Bgl II, Sac I, Eco RV, and Bam HI. These studies demonstrate the presence of clonal TCR rearrangement in canine MF, further supporting the similarity of this tumor to human MF and its role as an animal model of CTCL.