Background: Mycosis fungoides (MF) is a form of cutaneous T-cell lymphoma (CTCL) characterized by progression of clonal, epidermotropic T cells with the proliferative (Ki-67+) T-cell fraction primarily confined to the epidermis in early CTCL.
Objective: Our purpose was to determine whether the malignant clone (recognized by its clonal T-cell receptor [TCR] rearrangement) might also be localized to the epidermal compartment by differential Southern blot analysis.
Methods: A rapid heat-saline technique was used to separately isolate epidermal and dermal DNA from 11 patients with CTCL (1 with disease in the pre-MF stage, 4 with patch-stage MF, 3 with plaque-stage MF, 1 with tumor-stage MF, 1 with Sézary syndrome, and 1 with non-MF peripheral T-cell lymphoma). Whole and heat-saline separated 6 mm biopsy specimens (obtained from the same lesion) were analyzed by standard Southern blotting with 5 to 10 micrograms of DNA digested with BamHI, HindIII, or EcoRI in each case. Filters were probed with a 32P-labeled TCR-C beta complementary DNA. Skin compartment localization of TCR-C beta rearrangement was compared with results of diagnostic immunophenotyping and expression of proliferating cell nuclear antigen.
Results: DNA yields were as follows: from the whole specimens, 14.5 to 62.5 micrograms; from epidermal sheets, 2 to 42.5 micrograms; and from the dermis specimens, 2.5 to 25.5 micrograms. Whole and separated specimens from one patient with plaque-stage disease, three with patch-stage disease, and one patient with pre-MF disease revealed no rearrangement. Six patients had detectable gene rearrangements in the whole specimen by Southern blot; four of six had identical rearrangements in only the epidermal fragment (including the Sézary syndrome biopsy specimen) and not the dermis. The other two patients had only dermal TCR-C beta rearrangement. No relation was seen between immunophenotype or proliferating cell nuclear antigen expression and the localization of TCR-C beta rearrangements. However, the degree of epidermotropism significantly correlated with the presence of TCR-C beta rearrangements in the epidermal sheets.
Conclusion: This study demonstrates that the malignant clone in CTCL can be localized to the epidermal compartment in most cases in which a TCR rearrangement is detectable and that these clones are associated with epidermal proliferation of lymphocytes. This technique of differential epidermal versus dermal Southern analysis for TCR rearrangement may improve sensitivity by helping to distinguish reactive from malignant T-cell populations in future studies of the pathogenesis of CTCL.