December 12, 2014

Priming of hMSCs to Improve Potency

By Iain Farrance, Priya Baraniak, and Jon Rowley. RoosterBio.

In this blog, we will present internal data and information on priming RoosterBio’s bone marrow derived human MSCs (hMSC) with pro-inflammatory molecules and the impact of these priming protocols on hMSC immunomodulatory function and angiogenic cytokine secretion.

Human Mesenchymal Stem/Stromal Cells, or hMSCs, are key components of future therapeutics, engineered tissues, and medical devices. There are currently over 400 clinical trials investigating hMSCs as therapies (1). The trials have produced some promising results, with hMSCs generally deemed safe, and in some cases effective (2). It is believed that these versatile cells achieve their biologic and therapeutic effects by secreting a plethora of biomolecules (referred to as the MSC secretome) that moderate a variety of processes including angiogenesis, immunosuppression, and overall “tissue repair” (3-6). As the secretome is one of the likely Mechanisms of Actions (MOA) of hMSC therapies, there is a significant amount of recent work on engineering hMSC preparations to enhance secreted factors by genetic modification, by culture strategies, or by engineering the hMSC microenvironment (5, 7-11). In addition, a recent ISCT paper (12) advances the concept of “priming” hMSCs by exposing the cells to pro-inflammatory cytokines prior to implantation.

Thus, priming of hMSCs can have two primary purposes:

  1. To assess human MSC preparations in vitro as recommended by the ISCT and the FDA (12, 13), and
  2. To enhance hMSC potency (survival, immunosuppression, homing) prior to implantation (8, 9, 14).

As part of our standard quality control (QC) testing, RoosterBio analyzes the immunosuppressive capability of our cell lots through priming with IFN-γ. The hMSC response (i.e. immunomodulatory potential) is reported as a measure of indoleamine 2,3-dioxygenase (IDO) activity, determined by measuring the amino acid kynurenine in the culture supernatant.  The IDO enzyme converts L-tryptophan to N-formylkynurenine (or kynurenine), an immunosuppressive molecule that acts as an inhibitor of immune cell proliferation - including T cells (12, 15, 16).  Testing every hMSC lot for inducible IDO activity provides a quality assurance that the cells we release have some level of functional potency as it relates to immunomodulation– which we consider a key quality attribute of hMSCs.

While researchers are beginning to implement testing of hMSC preparations for inducible IDO activity prior to implantation, few are looking at the impact of priming on other hMSC functions.  Here, we present information on priming of RoosterBio’s hMSCs with IFN-γ ± TNF-α across multiple lots and donors and the impact of such treatment on hMSC IDO activity and angiogenic cytokine secretion.  The goal of this blog post is to demonstrate that priming has impacts on several functional properties of hMSCs, and that researchers should consider priming regimens to (a) understand the potency of their specific cell products, especially in inflammatory environments, and (b) to potentially increase potency of these cell products upon therapeutic administration.


Materials & Reagents
Cell culture reagents were purchased from Life Technologies, chemicals and reagents for kynurenine measurement were from Sigma, and cultureware was from Corning.  Other products are: Bone Marrow-derived human MSCs (BM-hMSC, part # MSC-001, RoosterBio) and RoosterBio High Performance Media kit (part # KT-001).

Table 1: Experimental design.

hMSC Priming