**Phase I Study on Placental Expanded Mesenchymal-Like Cells (PLX-R18) as a Treatment for Poor Graft Function Following Hematopoietic Cell Transplantation**
Hematopoietic cell transplantation (HCT) is a life-saving procedure used to treat a variety of hematologic malignancies, bone marrow failure syndromes, and other severe blood disorders. However, one of the most challenging complications following HCT is poor graft function (PGF), a condition characterized by insufficient recovery of blood cell counts despite successful engraftment of donor cells. PGF can lead to life-threatening complications such as severe infections, bleeding, and anemia, and current treatment options are limited. In recent years, placental expanded mesenchymal-like cells (PLX-R18) have emerged as a promising therapeutic candidate for addressing this unmet medical need. A Phase I clinical study has been conducted to evaluate the safety and efficacy of PLX-R18 in patients with PGF, offering new hope for improving outcomes in this vulnerable patient population.
### Understanding Poor Graft Function (PGF)
PGF is a rare but serious complication of HCT, occurring in approximately 5-27% of patients depending on the type of transplant and conditioning regimen used. It is defined by persistent cytopenias (low levels of white blood cells, red blood cells, and platelets) despite full donor chimerism, meaning that the donor cells have successfully engrafted but are not functioning adequately. PGF can result from a variety of factors, including damage to the bone marrow microenvironment, immune-mediated suppression of hematopoiesis, or insufficient support for stem cell proliferation and differentiation.
Current treatment strategies for PGF include supportive care (e.g., transfusions and growth factor administration), second transplants, or donor-derived stem cell boosts. However, these approaches are often associated with significant risks, including graft-versus-host disease (GVHD), infections, and treatment-related mortality. This underscores the urgent need for novel therapies that can safely and effectively restore hematopoiesis in patients with PGF.
### What Are PLX-R18 Cells?
PLX-R18 cells are a type of mesenchymal-like stromal cell derived from the human placenta. These cells are expanded ex vivo using proprietary technology developed by Pluristem Therapeutics, enabling the production of large quantities of highly potent cells. PLX-R18 cells are not stem cells themselves but are known to secrete a wide range of bioactive molecules, including cytokines, chemokines, and growth factors, that can modulate the immune system, promote tissue repair, and support hematopoiesis.
Preclinical studies have demonstrated that PLX-R18 cells can enhance the recovery of blood cell counts in animal models of bone marrow failure and radiation-induced damage. These effects are thought to be mediated through the cells’ ability to create a supportive microenvironment for hematopoietic stem and progenitor cells, reduce inflammation, and stimulate the