Inducible indoleamine 2,3-dioxygenase 1 and programmed death ligand 1 expression as the potency marker for mesenchymal stromal cells.

AIM: Establishment of a potency assay in the manufacturing of clinical-grade mesenchymal stromal cells (MSCs) has been a challenge due to issues of relevance to function, timeline and variability of responder cells. In this study, we attempted to develop a potency assay for MSCs. METHODS: Clinical-grade bone marrow-derived MSCs were manufactured. The phenotype and immunosuppressive functions of the MSCs were evaluated based on the International Society for Cellular Therapy guidelines. Resting MSCs licensed by interferon (IFN)-γ exposure overnight were evaluated for changes in immune suppression and immune-relevant proteins. The relationship of immune-relevant protein expression with immunosuppression of MSCs was analyzed. RESULTS: MSC supressed third-party T-lymphocyte proliferation with high inter-donor and inter-test variability. The suppression of T-lymphocyte proliferation by IFN-γ-licensed MSCs correlated with that by resting MSCs. Many cellular proteins were up-regulated after IFN-γ exposure, including indoleamine 2,3-dioxygenase 1 (IDO-1), programmed death ligand 1 (PD-L1), vascular cell adhesion molecule 1 (VCAM-1), intercellular adhesion molecule 1 (ICAM-1) and bone marrow stromal antigen 2 (BST-2). The expression levels of IDO-1 and PD-L1 on licensed MSCs, not VCAM-1, ICAM-1 or BST-2 on licensed MSCs, correlated with MSC suppression of third-party T-cell proliferation. CONCLUSION: A flow cytometry-based assay of MSCs post-IFN-γ exposure measuring expression of intracellular protein IDO-1 and cell surface protein PD-L1 captures two mechanisms of suppression and offers the potential of a relevant, rapid assay for MSC-mediated immune suppression that would fit with the manufacturing process.

Routine filtration of hematopoietic stem cell products: the time has arrived.

BACKGROUND: Most blood products are infused at the time of transfusion through a standard blood filter, designed to capture macroaggregates and cellular debris that might be harmful to the patient if infused. Hematopoietic stem cell products are not universally filtered, likely due to concern about loss of viable stem cells in the filtration process. STUDY DESIGN AND METHODS: We conducted a two-phase study to better understand the safety of routine filtration. First, surplus cryopreserved stem cell products were thawed and filtered, with markers of viability and potency measured. Second, routine filtration was implemented as part of routine practice at our center, and date of neutrophil and platelet (PLT) recovery was compared to historical controls. RESULTS: In the first phase, there was no difference seen in any markers of viability or potency for products after routine filtration. Based on those results, routine filtration was implemented. There was no difference in neutrophil or PLT engraftment. Thus, in this study, routine filtration did not impact the number of viable stem cells and did not delay engraftment. CONCLUSION: Given the very real harm posed by infusion of macroaggregates and cellular debris, and no clear disadvantage to filtration, routine filtration of stem cell products should be considered the standard of care.

The effect of urea on aqueous hydrophobic contact-pair interactions.

Urea is perhaps the most common denaturant used for studying proteins. However the mechanism of denaturation is still not well understood. Recent theoretical work suggests that van der Waals interactions between urea and non-polar amino acid residues are a major contributor to the protein denaturation process. However, there are few experimental data measuring the effect of urea on hydrophobic interactions. In this work we have determined how the addition of urea to the aqueous solvent affects the contact-pair formed between alkyl and phenyl groups in model compounds: the data indicate that for solutes having a radius smaller than 2.87 Å cavity formation energetics dominate, therefore the addition of urea promotes the formation of hydrophobic contact pairs; while for larger solutes, van der Waals interactions have the largest magnitude, causing urea to disrupt the formation of contact pairs. The influence of urea on hydrophobic interactions is shown to be continuous in the 1-8 M concentration range and is well-correlated with the predictions of scaled particle theory. This demonstrates that the effect of urea on hydrophobic contact pairs can be explained by the changes observed in the solvent packing density, without having to invoke changes in the hydrogen bonding network of water.