Recognition of leukemic blasts by HLA-DPB1-specific cytotoxic T cell clones: a perspective for adjuvant immunotherapy post-bone marrow transplantation.

There is increasing evidence that the immune response plays a role in the prevention of leukemic relapses after allogeneic bone marrow transplantation (BMT). Producing this effect (referred to as the graft-versus-leukemia reaction or GVL) is a current goal of clinical transplantation. At present, all protocols rely on the injection of donor T cells with unknown specificities. In keeping with this approach, we recently proposed the use of a single allogeneic T cell clone transfected with the HSv-tk gene to target an HLA-DPB1 mismatch in the GVH direction. For this strategy to be successful, HLA-DP antigens must be expressed on leukemic cells, which should be recognised by the HLA-DP-specific T cell clone and subsequently destroyed. In the present study, differential expression of HLA-DR, -DQ and -DP was tested by fluorescence using monoclonal antibodies on a panel of 46 acute myeloid leukemias (AML), 28 acute lymphoblastic leukemias (ALL) and 31 chronic lymphocytic leukemias of B cell origin (B-CLL). The vast majority of leukemic cells expressed HLA-DP antigens although with considerable variability. HLA-DPB1 genotyped leukemic cells were used as target cells for an HLA-DPB1*0401-specific T cell clone. Specific recognition of leukemic blasts was demonstrated for 11 out of 11 B-CLL, 11 out of 19 AML and nine out of 16 ALL. These data show that most leukemic blasts are accessible to direct lysis by allogeneic HLA-DP-specific T cells.