Allogenic Bone Marrow Mesenchymal Stem Cells Infusion in Patients With Steroid-refractory GVHD- A Phase I/II Clinical Trial

Allogeneic haematopoietic stem cell transplant has become first choice of treatment for many malignant and non malignant haematological disorders. Although great progress has been made to prevent and minimize transplant-associated complications, yet graft versus host disease (GVHD) remains a significant complication affecting these the outcome in these patients. It is a severe inflammatory condition that arises when recipient tissues are attacked by immune mediated donor T cells during transplantation. Acute GVHD predominately affects the skin, upper and lower GI tract, liver and occasionally the eye and oral mucosa, whereas chronic GVHD resembles more with autoimmune disorders in its clinical symptoms. These symptoms can be organ-specific or generalized throughout body.

The pathophysiology of GVHD shows that it has different phases. In first phase i.e., afferent phase, damage to host tissue occurs. In second phase i.e., Induction and expansion phase, donor T cells are triggered and activated by recipient and donor APC as well as the inflammatory cytokines. Activated T cells produce IL-2 and IFN-γ (or Th1 response). Allogeneic immune response is amplified by IL-2, which activates more T cells and natural killer cell responses, triggering macrophages to release TNF-α and further inflammation damages skin and gut. The third phase i.e., effector phase, is characterized by cytotoxic damage against host cells by activated donor T-cell-mediated through Fas-Fas ligand interaction, perforin-granzyme and TNF-α. The latter has a central role in the pathophysiology, stimulating cytokine production (IL-1, IL-6, IL-10, IL-12 and TNF-α). This dysregulation leads to the clinical manifestations of acute GVHD.

The cells involved in GVHD pathophysiology include CD4+ T cells; for maintaining the expansion of CD8+ T cells that mediate GVHD, APCs; these have role in the initiation phase of acute GVHD as described in murine models and Natural killer (NK) cells; contribute to tissue damage in the effector phase by releasing inflammatory cytokines and nitric oxide. However, natural killer cells mediate cell death by two important pathways: Fas-Fas-ligand-mediated apoptosis and perforin-granzyme-B-mediated cytolysis.

HLA differences between donor and recipient are the major predictor of GVHD. Other affecting factors include age, gender mismatch between donor and recipient, minor histocomapatability antigen expression difference(mHA) in otherwise identical HSCT, donor age, source and dose of stem cells (PBSCT greater risk than BM), intensity of conditioning and GVHD prophylaxis.

Steroids are the first line therapy for acute GVHD patients and are standard treatment for grade II-IV acute GVHD. Adverse effects of glucocorticoids include hypertension hyperglycemia and psychosis, immunosuppression, infections, myopathy, osteoporosis and avascular necrosis of bone, cataracts and fat re-distribution etc. If acute GVHD is not improved after 5-7 days treatment with steroids then it is considered as steroid-refractory. Various agents that are being investigated from last two decades as second line therapy include low-dose MTX, MMF, extracorporeal photopheresis, IL-2R targeting, antibody therapy against CD3, CD7, CD25, CD52, CD147, IL-2R, IL-1, and TNF-α (i.e., basiliximab, daclizumab, denileukin, diftitox and alemtuzumab), horse ATG, etanercept, infliximab, and sirolimus and recently infusions of mesenchymal stem cells.