The clonality of tumor-infiltrating lymphocytes in African Kaposi's sarcoma

African Kaposi's sarcoma (KS) lesions contain human herpesvirus-8 (HHV-8) and Epstein-Barr virus (EBV), both of which are associated with various types of non-Hodgkin's lymphomas and are known to produce several factors suspected of lymphomagenic potential. The aim of this study was to evaluate tumor-infiltrating lymphocytes for the evidence of clonal expansion in African KS.

We used polymerase chain reaction (PCR)-based assays to determine the clonality of tumor-infiltrating lymphocytes in African KS lesions and compared the results to similar studies of patient-matched uninvolved skin and peripheral blood.

T cells were polyclonal in all samples tested. Peripheral blood B cells were also polyclonal; however, a minority of lesional and uninvolved skin samples exhibited evidence of restricted B-cell clonality. Correlation with immunohistological analysis revealed that this clonal B-cell restriction was secondary to the sparse nature of lesional B cells rather than their clonal overgrowth.

We conclude that, despite the putative lymphomagenic potential of HHV-8 and EBV and their co-existence in African KS lesions, tumor-infiltrating lymphocytes in these cases do not show evidence of clonal expansion that might be an early manifestation of lymphoma. Nevertheless, these studies are a case in point that sparse lymphoid subpopulations in lesional and uninvolved extranodal tissues can give rise to restricted clonal patterns that must be interpreted carefully to avoid the misdiagnosis of occult lymphoma.