Study Evaluating Combination of Luspatercept in LR-MDS Without RS Having Failed or Being Ineligible to ESA

Part A of the trial=Dose-finding Study: Determination the optimal dose level in terms of both toxicity and efficacy for luspatercept + ESA

Part B : Determination of the superiority and efficacy of the association Luspatercept+ESA (erythroipoiesis Stimulating Agent) over luspatercept alone in patients with lower risk MDS who failed to achieve a response or who subsequently relapsed after ESA, wihtout disease progression