Background of anemia in myelodysplastic syndromes (MDS) with 5q deletion (del(5q)) is a haplo-insufficiency of the RPS14 gene. However, degree of anemia and quantity of erythropoiesis vary markedly between MDS patients with del(5q), even with a similar degree of RPS14 insufficiency, so that the question arises whether other influences may play a further relevant role in erythroid failure in this disease.
From 35 patients with low or intermediate-1 risk MDS with del(5q) who developed a transfusion-dependent anemia and were recruited and treated with lenalidomide (10 mg / d) within the MDS-003 study 38 +/− 33 months after diagnosis of MDS, bone marrow biopsies taken at 6 to 12-month time intervals after diagnosis of disease were evaluated for changes of erythropoiesis having occurred prior to lenalidomide therapy by morphometric, immunohistochemical, and molecular methods. A second group of patients with MDS treated with best supportive care (n = 307) served as a control. From each bone marrow biopsy, 20 000 nucleated cells were evaluated marking (1) nucleated erythroid cells (NEC) immunohistochemically using anti-HbA, glycophorin-C (GPC), CD71, and CD34 antibodies and (2) marrow macrophages by anti-CD68 antibody. By analogy to burst and colony forming units from in-vitro models, the numbers of erythroid precursor cells (EPC) were estimated by the numbers of erythroblastic islands (IslE) within marrow. Morphometrically assessed erythropoiesis was related to the mRNA expression of RPS14, SPARC, and TNF-alpha genes, nuclear p53 protein expression of NEC and their relevance for transfusion dependence and AML-free survival time of patients.
5q deletion predicted erythroid hypoplasia independently of the type of MDS, evidence of marrow fibrosis and AML transformation (P < 0.0005). During early-phase MDS with del(5q), anemia correlated with p53 overexpression of NEC and decreased numbers of HbA+ NEC (P < 0.00005). After the first year of disease, two alterations of erythropoiesis became more relevant which did not correlate to p53 overexpression of NEC: (1) a decline in the numbers of GPC+HbA- NEC indicating impaired differentiation of EPC to proerythroblasts which correlated with RPS14 insufficiency, and (2) a progressive decrease in the number of IslE indicating a block of differentiation at an earlier stage, the IslE forming EPC, which did not correlate to RPS14 gene expression, but to two other independent factors, a reduced SPARC and an increased TNF-alpha gene expression (P < 0.00005). The degree of TNF-alpha expression correlated to the number of a central component of the IslE, the (iron-presenting) macrophages, the potential source of TNF-alpha overexpression. Both alterations contributed significantly to erythroid hypoplasia and progressive transfusion dependence (P < 0.00005). Response to lenalidomide therapy continued for > 4 years (100% AML-free survival) when started during a phase with high numbers of p53 overexpressing NEC, but was short or poor with < 20 % AML-free survival when started during a phase when differentiation of erythropoiesis was impaired at a less mature stage (P = 0.0001). On the basis of these observations, a score predicting the efficacy of lenalidomide in individual patients could be constructed.
In MDS with del(5q), erythropoiesis significantly changes over time. In the early stage of disease, maturation defect of erythropoiesis mainly affects HbA+ NEC and correlates to p53 overexpression of NEC. In the course of disease, erythropoiesis becomes hypoplastic due to differentiation defects at the level of more immature erythroid (precursor) cells relating to a p53-independent mechanism of RPS14 insufficiency and altered SPARC as well as TNF-alpha gene expression. Efficacy of lenalidomide therapy is significantly impaired in the case of vanishing IslE, reduced SPARC and increased TNF-alpha gene expression.
Giagounidis:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees. Knight:Celgene Corp.: Employment.
Asterisk with author names denotes non-ASH members.