Generation of mesenchymal stem cells as a medicinal product in organ transplantation.

PURPOSE OF REVIEW: Mesenchymal stem cells (MSCs) are emerging as an alternative treatment in solid-organ transplantation. The use of MSCs as a therapeutic product requires the translation of basic research protocols into a production process under good manufacturing practice (GMP) to obtain a safe product of high quality. This requires a different mindset from the academic setting of changing protocols into a well defined, controlled and documented process. This review describes some of the challenges faced by culturing MSCs as a medicinal product. RECENT FINDINGS: Clinical-grade MSCs are used in the clinical trials and proved to be safe as a medicinal product. Because of the differences in the type of MSCs and in the production process, clinical outcome is not always comparable. New standardized methods in the culture condition such as the use of alternatives for fetal bovine serum (FBS), standardized plating densities or the use of bioreactors may further standardize the production process. SUMMARY: To generate MSCs as a medicinal product in organ transplantation, regulation requires that MSCs have to be generated under GMP. During the whole production process, all critical steps should be known and described. Further steps should be taken to optimize and standardize the production process.

The immunomodulatory properties of mesenchymal stem cells and their use for immunotherapy.

There is growing interest in the use of mesenchymal stem cells (MSC) for immune therapy. Clinical trials that use MSC for treatment of therapy resistant graft versus host disease, Crohn's disease and organ transplantation have initiated. Nevertheless, the immunomodulatory effects of MSC are only partly understood. Clinical trials that are supported by basic research will lead to better understanding of the potential of MSC for immunomodulatory applications and to optimization of such therapies. In this manuscript we review some recent literature on the mechanisms of immunomodulation by MSC in vitro and animal models, present new data on the secretion of pro-inflammatory and anti-inflammatory cytokines, chemokines and prostaglandins by MSC under resting and inflammatory conditions and discuss the hopes and expectations of MSC-based immune therapy.

The microtubule regulator stathmin is an endogenous protein agonist for TLR3.

TLR3 recognizes dsRNAs and is considered of key importance to antiviral host-defense responses. TLR3 also triggers neuroprotective responses in astrocytes and controls the growth of axons and neuronal progenitor cells, suggesting additional roles for TLR3-mediated signaling in the CNS. This prompted us to search for alternative, CNS-borne protein agonists for TLR3. A genome-scale functional screening of a transcript library from brain tumors revealed that the microtubule regulator stathmin is an activator of TLR3-dependent signaling in astrocytes, inducing the same set of neuroprotective factors as the known TLR3 agonist polyinosinic:polycytidylic acid. This activity of stathmin crucially depends on a long, negatively charged alpha helix in the protein. Colocalization of stathmin with TLR3 on astrocytes, microglia, and neurons in multiple sclerosis-affected human brain indicates that as an endogenous TLR3 agonist, stathmin may fulfill previously unsuspected regulatory roles during inflammation and repair in the adult CNS.

A novel rationale for inhibition of gelatinase B in multiple sclerosis: MMP-9 destroys alpha B-crystallin and generates a promiscuous T cell epitope.

The small heat shock protein alphaB-crystallin is considered as a candidate autoantigen in multiple sclerosis (MS) lesions. Gelatinase B or matrix metalloproteinase (MMP)-9 is a proteinase establishing various disease-promoting feedback loops in autoimmune diseases. Human alphaB-crystallin was digested with natural gelatinase B and all cleavage sites were identified by a combined approach of mass spectrometry and peptide sequencing analysis. Previously identified immunodominant and cryptic epitopes of alphaB-crystallin in mice and rats were generated and largely left intact by MMP-9 processing. The alphaB-crystallin peptide 1-16, generated as a remnant epitope, provoked a significant T cell response in alphaB-crystallin knockout mice. None of the remnant peptides was encephalitogenic when injected intracerebrally into mice or induced MMP-9 in vitro. Gelatinase B is thus able to release T cell epitopes from intact alphaB-crystallin, but their pathogenic role remains unclear.