Since BTLA expression is upregulated on CD4 + and CD8 + T lymphocytes from patients with CLL, whereas no changes on surface HVEM were detected on this immune subset, we hypothesize that BTLA may inhibit T cell-mediated responses through cis complexes as well as by trans interaction with HVEM on leukemic cells. This evidence concerns the gene BTLA and B-cell chronic lymphocytic leukemia.