Mouse anti-Human PIGH monoclonal antibody, clone 3G9

More than 10 genes are involved in the biosynthesis of glycosylphosphatidylinositol (GPI), which anchors many mammalian cell surface proteins to the membrane. Paroxysmal nocturnal hemoglobinuria (PNH) is caused by a somatic mutation in a GPI biosynthesis gene within the hematopoietic stem cell. The X-linked gene PIGA has been found to be mutated in all patients with PNH. This is probably because all other GPI synthesis genes are autosomal; hence two somatic mutations must occur to cause PNH, whereas one somatic mutation is sufficient to inactivate PIGA. Consistent with this notion, three other genes, PIGB, PIGF, and PIGH, are autosomal. Here we isolated a genomic clone of another GPI-synthesis gene, PIGC, and mapped it to chromosome 1q23-q25, further supporting this notion. PIGC is an intronless gene. We found an intronless pseudogene of PIGC, PIGCP1, and mapped it to chromosome 11p12-p13. The presence of a processed pseudogene is a common feature of PIGA, PIGF, and PIGC. (C) 1997 Academic Press.

Adult B-lymphoblastic leukemia (B-ALL) is a hematological malignancy characterized by genetic heterogeneity. Despite successful remission induction with classical chemotherapeutics and novel targeted agents, enduring remission is often hampered by disease relapse due to outgrowth of a pre-existing subclone resistant against the treatment. In this study, we show that small glycophosphatidylinositol (GPI)-anchor deficient CD52-negative B-cell populations are frequently present already at diagnosis in B-ALL patients, but not in patients suffering from other B-cell malignancies. We demonstrate that the GPI-anchor negative phenotype results from loss of mRNA expression of the PIGH gene, which is involved in the first step of GPI-anchor synthesis. Loss of PIGH mRNA expression within these B-ALL cells follows epigenetic silencing rather than gene mutation or deletion. The coinciding loss of CD52 membrane expression may contribute to the development of resistance to alemtuzumab (ALM) treatment in B-ALL patients resulting in the outgrowth of CD52-negative escape variants. Additional treatment with 5-aza-2 '-deoxycytidine may restore expression of CD52 and revert ALM resistance.