T-cell lymphomas are lymphomas that affect T cells. There are four major types, and they account for about one in ten cases of non-Hodgkin lymphoma. aggressive: Sézary disease T-cell lymphomas are lymphomas that affect T cells. There are four major types, and they account for about one in ten cases of non-Hodgkin lymphoma. They can be associated with Epstein Barr virus and Human T-cell leukemia virus-1.