Biomarker analysis in polycythemia vera under interferon-alpha treatment: clonality, EEC, PRV-1, and JAK2 V617F.

Three consecutive polycythemia vera (PV) patients were analyzed before and during pegylated-interferon (rIFNalpha) treatment for the following markers: (1) granulocyte and CD34(+) cell clonality, (2) Jak2V617F expression, (3) PRV-1 mRNA overexpression, and (4) Epo-independent colony (EEC) growth. Before rIFNalpha therapy, all patients displayed clonal hematopoiesis, 100% Jak2V617F expression as well as PRV-1 overexpression, and EEC growth. After rIFNalpha treatment, all three patients demonstrated polyclonal hematopoiesis. Nonetheless, Jak2V617F expression, PRV-1 overexpression, and EEC-growth remained detectable, albeit at lower levels. We conclude that reemergence of polyclonal hematopoiesis after rIFNalpha treatment may be achieved in a substantial proportion of patients. However, this does not constitute elimination of the PV clone. These data demonstrate the usefulness of novel markers in monitoring minimal residual disease and caution against discontinuation of rIFNalpha treatment after hematologic remission. Long-term follow-up of large patient cohorts is required to determine whether rIFNalpha treatment can cause complete molecular remissions in PV.

PRV-1 mRNA expression discriminates two types of essential thrombocythemia.

Essential thrombocythemia (ET) is a heterogeneous disorder. For example, the growth of erythropoietin-independent erythroid colonies, termed "endogenous erythroid colonies (EECs)", has previously been observed in only 50% of ET patients. We have recently described the overexpression of a hematopoietic receptor, PRV-1 (polycythemia rubra vera-1), in patients with polycythemia vera (PV). Here, we compare PRV-1 expression and EEC formation in a cohort of 30 patients with ET; 50% of the ET patients in our cohort displayed EEC growth. Likewise, 50% of the ET patients overexpressed PRV-1. Remarkably, only the 15 ET patients displaying EEC growth showed elevated PRV-1 expression, while the 15 EEC-negative ET patients expressed normal PRV-1 levels. It has previously been reported that EEC-positive ET patients develop PV during long-term follow-up. Here, we show that 40% of the PRV-1-positive patients develop symptoms of PV during the course of their disease. In contrast, none of the 15 PRV-1-negative patients displayed such symptoms (p=0.017). Moreover, PRV-1-positive patients had a significantly higher number of thromboembolic or microcirculatory events (p=0.003). We propose that PRV-1-positive ET comprise a pathophysiologically distinct subgroup of patients, one that is at risk for the development of complications and for the emergence of PV.

Cloning of PRV-1, a novel member of the uPAR receptor superfamily, which is overexpressed in polycythemia rubra vera.

Polycythemia vera (PV) is a clonal stem cell disorder characterized by hyperproliferation of the erythroid, myeloid, and megakaryocytic lineages. Although it has been shown that progenitor cells of patients with PV are hypersensitive to several growth factors, the molecular pathogenesis of this disease remains unknown. To investigate the molecular defects underlying PV, we used subtractive hybridization to isolate complementary DNAs (cDNAs) differentially expressed in patients with PV versus normal controls. We isolated a novel gene, subsequently named PRV-1, which is highly expressed in granulocytes from patients with PV (n = 19), but not detectable in normal control granulocytes (n = 21). Moreover, PRV-1 is not expressed in mononuclear cells from patients with chronic myelogenous leukemia (n = 4) or acute myelogenous leukemia (n = 5) or in granulocytes from patients with essential thrombocythemia (n = 4) or secondary erythrocytosis (n = 4). Northern blot analysis showed that PRV-1 is highly expressed in normal human bone marrow and to a much lesser degree in fetal liver. It is not expressed in a variety of other tissues tested. Although PRV-1 is not expressed in resting granulocytes from normal controls, stimulation of these cells with granulocyte colony-stimulating factor induces PRV-1 expression. The PRV-1 cDNA encodes an open reading frame of 437 amino acids, which contains a signal peptide at the N-terminus and a hydrophobic segment at the C-terminus. In addition, PRV-1 contains 2 cysteine-rich domains homologous to those found in the uPAR/Ly6/CD59/snake toxin-receptor superfamily. We therefore propose that PRV-1 represents a novel hematopoietic receptor. (Blood. 2000;95:2569-2576)

[Blood of patients with acute leukemia increases the leukocyte count in the peripheral blood of mice]. / Serum bolesnika obolelih od akutne leukemije povecava broj leukocita u perifernoj krvi miseva.

Serum of 23 patients suffering from acute myeloid leukemia were given to groups of six mice (s.c. 0.6 ml); 3 and 5 days later the total number of leucocytes, granulocytes and lymphocytes was determined in the peripheral blood of mice. Serums of all patients caused significant increase of leucocytes in mice 3 and/or 5 days after the serum's application. In most cases the increase was caused by increased number of granulocytes and lymphocytes, and in 6 cases only by increase of granulocytes or only lymphocytes. This increase can also be thought of as a stimulation of leukocytopoiesis by increased concentration of hematopoetic growth factors in blood of those suffering from acute leukemia.