Molecular basis of reduced or absent expression of decay-accelerating factor in Cromer blood group phenotypes

The human erythrocyte blood group system Cromer consists of high- incidence and low-incidence antigens that reside on decay-accelerating factor (DAF; CD55), a glycosyl-phosphatidylinositol-anchored membrane protein that regulates complement activation on cell surfaces. In the Cromer phenotypes Dr(a-) and Inab there is reduced or absent expression of DAF, respectively. This study investigated the molecular basis of the reduced DAF expression by polymerase chain reaction amplification of genomic DNA and RNA/cDNA obtained from Epstein-Barr virus- transformed lymphoblastoid cell lines. Sequence analysis of the Inab propositus showed a single nucleotide substitution in exon 2 of the DAF gene and at the corresponding position in the cDNA, G314-->A resulting in Trp53-->Stop. This truncation near the amino terminus explains the complete absence of surface DAF in the Inab phenotype. A similar analysis was performed for two Dr(a-) individuals, including KZ, who was previously reported to be Inab phenotype but is now shown by immunochemical and serologic methods to be Dr(a-) phenotype. A single nucleotide change was found in exon 5 of the DAF gene, C649-->T resulting in Ser165-->Leu, which we had previously shown to lead to loss of the Dra epitope. However, two species of cDNA were found, one encoding full-length DAF with the single amino acid change and the more abundant species having a 44-nucleotide deletion. The 44 nucleotide deletion includes the single polymorphic site, which creates a cryptic branch point in the Dr(a-) allele that leads to use of a downstream cryptic acceptor splice site. This shifts the reading frame and leads to a premature stop codon that precludes membrane anchoring. Thus, the single point mutation in the Dr(a-) phenotype results in a novel use of alternative splicing and provides a molecular explanation for both the antigenicity and the reduced DAF expression seen in this phenotype.     

Treatment of acute nonlymphocytic leukemia: use of anthracycline- cytosine arabinoside induction therapy and comparison of two maintenance regimens

Patients with acute nonlymphocytic leukemia were given remission induction therapy consisting of cytosine arabinoside and an anthracycline. Those patients who experienced complete remission received two courses of consolidation therapy and were randomized to receive maintenance therapy consisting of either daily chemotherapy with reinforcements every 3 mo or reinforcement therapy only every 6 wk. The overall complete remission rate was 66%, with 80% complete remission for previously untreated patients less than 60 yr of age who did not have a prior history of malignancy. Remission durations were the same for patients treated with both maintenance regimens. The major determinant for successful remission induction therapy was patient age, with older patients frequently succumbing to intercurrent infection. Documented leukemic cell resistance to the therapy employed was only rarely encountered. Once remission was achieved, age was no longer a determinant of patient survival, since duration of remission was independent of age. Remission durations were directly related to leukemic cell retention of cytosine arabinoside triphosphate. Hence therapy for acute nonlymphocytic leukemia can be divided into two separate areas: remission induction and remission maintenance.