A B S T R A C T PurposeMyelodysplastic syndromes (MDS) are characterized by ineffective hematopoiesis and progression to leukemia. Clinical and experimental evidence suggests an immune-mediated pathophysiology in some patients, in whom immunosuppressive therapy (IST) with horse antithymocyte globulin (h-ATG) and cyclosporine (CsA) can be effective. Because of the toxicities associated with h-ATG/CsA, we investigated an alternative regimen with alemtuzumab in MDS. Patients and MethodsWe conducted a nonrandomized, off-label, pilot, phase I/II study of alemtuzumab monotherapy in patients with MDS who were judged likely to respond to IST based on the following criteria: HLA-DR15-negative patients whose age plus the number of months of RBC transfusion dependence (RCTD) was less than 58; and HLA-DR15-positive patients whose age plus RCTD was less than 72. In total, 121 patients with MDS were screened, of whom 32 met eligibility criteria to receive alemtuzumab 10 mg/d intravenously for 10 days. Primary end points were hematologic responses at 3, 6, and 12 months after alemtuzumab. ResultsSeventeen (77%) of 22 evaluable intermediate-1 patients and four (57%) of seven evaluable intermediate-2 patients responded to treatment with a median time to response of 3 months. Four of seven evaluable responders with cytogenetic abnormalities before treatment had normal cytogenetics by 1 year after treatment. Five (56%) of nine responding patients evaluable at 12 months had normal blood counts, and seven (78%) of nine patients were transfusion independent. ConclusionAlemtuzumab is safe and active in MDS and may be an attractive alternative to ATG in selected patients likely to respond to IST.

The 5′-untranslated regions (5′-UTRs) of all gammaretroviruses contain a conserved “double hairpin motif” (ΨCD) that is required for genome packaging. Both hairpins (SL-C and SL-D) contain GACG tetraloops that, in isolated RNAs, are capable of forming “kissing” interactions stabilized by two intermolecular G-C base pairs. We have determined the three-dimensional structure of the double hairpin from the Moloney Murine Leukemia Virus (MoMuLV) ([ΨCD]2, 132-nucleotides, 42.8 kDaltons) using a 2H-edited NMR spectroscopy-based approach. This approach enabled the detection of 1H-1H dipolar interactions that were not observed in previous studies of isolated SL-C and SL-D hairpin RNAs using traditional 1H-1H correlated and 1H-13C-edited NMR methods. The hairpins participate in intermolecular cross-kissing interactions (SL-C to SL-D’ and SLC’ to SL-D), and stack in an end-to-end manner (SL-C to SL-D and SL-C’ to SL-D’) that gives rise to an elongated overall shape (ca. 95 Å by 45 Å by 25 Å). The global structure was confirmed by cryo-electron tomography (cryo-ET), making [ΨCD]2 simultaneously the smallest RNA to be structurally characterized to date by cryo-ET and among the largest to be determined by NMR. Our findings suggest that, in addition to promoting dimerization, [ΨCD]2 functions as a scaffold that helps initiate virus assembly by exposing a cluster of conserved UCUG elements for binding to the cognate nucleocapsid domains of assembling viral Gag proteins.

US National Institutes of Health.