The Evolving Landscape of Stem Cell Therapies for Huntington's Disease.

Huntington's disease (HD) is a fatal, inherited neurodegenerative disorder marked by the progressive and selective loss of spiny projection neurons (SPNs), resulting in a characteristic triad of motor, cognitive, and psychiatric symptoms. Despite ongoing research, no disease-modifying treatments are available, and existing therapies are limited to symptomatic relief. Stem cell-based approaches represent a promising avenue to restore striatal circuitry by replacing lost neurons and/or delivering trophic support to preserve the remaining neural tissue.In this review, we present a critical analysis of past and current clinical trials exploring cell-based therapies for HD. Early studies using human fetal tissue were hindered by sample heterogeneity and inconsistent outcomes, ultimately limiting their clinical applicability. More recent trials have shifted focus toward mesenchymal stem cells (MSCs), which are valued for their neuroprotective secretome but are not suitable for neuronal replacement. To address these limitations, human pluripotent stem cells (hPSCs) have emerged as a renewable and scalable source for the development of advanced therapy medicinal products (ATMPs). In vitro differentiation protocols mimic key developmental signaling pathways to generate striatal-like neural progenitor cells (NPCs). We review the cellular composition of these hPSC-derived ATMPs and summarize findings from preclinical transplantation studies, including data on graft survival, neuronal maturation, synaptic integration, and functional recovery. In addition, we discuss other emerging strategies such as direct neuronal reprogramming. Finally, we examine the major challenges that remain-such as ensuring graft safety, consistency, and regulatory compliance-and highlight the importance of international collaboration to overcome these barriers and accelerate clinical translation.