V617F JAK2 mutation is a reliable molecular marker of polycythemia vera (PV), potentially useful to monitor the effect of treatments in this disease. In a phase 2 study of pegylated (peg) IFN-␣-2a in PV, we performed prospective sequential quantitative evaluation of the percentage of mutated JAK2 allele (%V617F) by realtime polymerase chain reaction (PCR). The %V617F decreased in 24 (89%) of 27 treated patients, from a mean of 49% to a mean of 27% (mean decrease of 44%; P < .001), and no evidence for a plateau was observed. In one patient, mutant JAK2 was no longer detectable after 12 months. In 3 patients homozygous for the mutation, reappearance of 50% of wildtype allele was observed during treatment. The results seem to confirm the hypothesis that IFN-␣ preferentially targets the malignant clone in PV and show that %V617F assessment using a quantitative method may provide the first tool to monitor minimal residual disease in PV. This trial was registered at www. clinicaltrials.gov as #NCT00241241. (Blood.

These data support the hypothesis of the potential for a myogenic differentiation of bone marrow cells following engraftment in a nonischemic model of global cardiomyopathy. Bone marrow-derived cells amenable to cardiac differentiation are present in total unpurified bone marrow but not in the sca-1(pos) hematopoietic progenitor cell population. However, the very small number of transdifferentiated cells raises concerns over their functional efficacy.

Acute promyelocytic leukemia (APL) blasts possess a unique sensitivity to the differentiating effects of all-trans retinoic acid (ATRA). Multicenter trials confirm that the combination of differentiation and cytotoxic therapy prolongs survival in APL patients. However relapses still occur, and exquisite adaptation of therapy to prognostic factors is essential to aim at a possible cure of the disease. A heterogeneity was previously reported in the differentiation rate of patients' APL blasts, and it was postulated that this may reflect the in vivo heterogeneous outcome. In this study, it is demonstrated that patients of the APL93 trial whose leukemic cells achieved optimal differentiation with ATRA in vitro at diagnosis had a significantly improved event-free survival (P ‫؍‬ .01) and lower relapse rate (P ‫؍‬ .04). This analysis highlights the importance of the differentiation step in APL therapy and justifies ongoing studies aimed at identifying novel RA-differentiation enhancers. (Blood. 2001;98:2862-2864)