Quantification of the HA-1 gene product at the RNA level; relevance for immunotherapy of hematological malignancies.

Minor histocompatibility antigens can induce cytotoxic T cells that play an important role in the graft-versus-leukemia and graft-versus-host-disease (GvHD) activity after stem cell transplantation. Minor histocompatibility antigens (mHags) with expression limited to the hematopoietic system may have a prominent role in the graft-versus-leukemia reaction. Earlier in vitro studies demonstrated that cytotoxic T cells specific for the minor histocompatibility antigen HA-1 only lysed cells of hematopoietic origin. Despite this limited expression, an HA-1 mismatch is associated with GvHD. Yet, the hematopoietic-restricted HA-1 membrane expression motivated us to develop an ex vivo HA-1-specific protocol for cellular immunotherapy of relapsed leukemia. To ensure the feasibility and safety of such cellular therapy, broad HA-1 RNA analysis is indispensable. Here we demonstrate the hematopoietic-restricted expression at the HA-1 gene transcriptional level with high RNA expression in normal and in malignant hematopoietic cells and background expression levels in nonhematopoietic cells. In tissues that showed low HA-1 RNA expression, hematopoietic cells were present as demonstrated by CD45 RNA expression analyzed in parallel. Thus, the mHag HA-1 can function as an excellent target antigen for immunotherapy of hematological malignancies with no or low risk of GvHD.