Recombinant Albumin: A multitalented player on the cell therapy media stage

Introduction

The treatment or prevention of a disease through the administration of cells that have been selected, manipulated, or altered outside of the body, is defined as cell therapy¹. In practicum, cell-based therapeutic products have been used for almost 90 years in the form of blood transfusions²; and, for more than 50 years through bone marrow transplants^1,3. This technological development period has led to massive improvements in terms of tools and instruments designated for cell characterization, isolation, and in vitro manipulation. Due to these developments, cellular therapies now include elaborate products such as cell-infused support matrices to regenerate damaged or injured tissues, cell-based therapeutic vaccines for cancer, and cell-based therapeutic drugs for treatment of cardiovascular, inflammatory, autoimmune, neurodegenerative diseases, and cancer¹. In the last couple of years, an increasing number of novel cell-based products have advanced through clinical trials and obtained regulatory approval^4,5, expanding these therapies to a higher level, making them one of the most contemporary and up-to-date treatments in the clinic.

Updated regulatory demands for cell therapies and additives

For a stable final cell product to be delivered to the patient, it is essential to ensure product efficacy and safety. As such, updated regulations have been put in place emphasizing the need for extensive validation procedures for regulatory approval. The rules governing advanced medicinal products now demand that the production of cell-based therapies and its excipients to be made in Good Manufacturing Practice facilities (GMP) and to be fully certified⁶. As such, the selection of which additives to use to make cell therapies more efficient and safer, or to achieve a longer shelf-life for example, is now at the forefront of the cell therapy manufacturing strategy. On one side, an additive can maintain the critical quality attributes (CQA) of the final product⁷; and, on the other, can also lead to obtaining regulatory approval more easily.

Human albumin at the service of cell therapies

Albumin is one of the most popular additives used. Due to its omnipresence in our bodies; and its dual functionality as a buffer and storage-tank for various metals, hormones, and fatty acids needed for different cellular mechanisms at different time-points⁸, this molecule’s versatility makes it a common choice in therapeutic R&D. It can be used in many different situations: from tackling challenges in manufacturing, to formulation-based troubles, or to improve storage/handling conveniences. As such, albumin can be used in different medicine development stages and to smooth industrial production procedures.

Albumin, a cell culture media defensive shield

Albumin has been a cornerstone in cell-culture media to promote cell growth⁹ and cell viability¹⁰. The biochemical properties of albumin are responsible for several important interactions with substances present in the cell culture medium, that have a direct or indirect impact on the cell¹¹. A key interaction of albumin with cultured cells involves its antioxidant properties, which are quite relevant for both the extracellular and intracellular environment. For example, in cell culture, oxidative stress is created by Reactive Oxygen Species (ROS) generated by the interaction of a high oxygen tension, the various medium components and the general cellular metabolism¹². As such, cells in culture are at an increased risk of damage due to the generated ROS; and, furthermore, they also have a reduced capacity of antioxidant mechanisms in the intracellular compartment, due to the ex-vivo culture¹³. The free reduced thiol (Cys-34) of albumin is a major contributor to plasma’s overall anti-oxidative capacity; but albumin can also bind metal ions and scavenge free radicals as a substitute substrate for other moieties¹⁴, making albumin a prime scavenger for cell culture ROS. Not only that, but this protein can also bind to the external surface of the cell membrane, through non-specific adsorption, and provide cell protection preventing physical damage of the cells caused by the hydrodynamic stress generated in culture¹¹. Furthermore, albumin in cell culture media has also been shown to improve cell graft transplantation by reducing apoptosis in expanded culture cells, evaluated as a reduced caspase-3 activity in different cell types^15-17. As such, albumin offers numerous possibilities as a defensive shield in cell culture media.

Albumin, a protective transport hub

Albumin has also been used in cell therapies as a stabilizer. For example, for the maintenance of endothelial and smooth muscle cells for heart tissue grafts, researchers have investigated different concentrations of albumin, in comparison to normal saline, to store refrigerated cells for different periods of time¹⁸. The authors concluded that 2.5% was an optimum concentration of albumin in the cell-storage media, due to their increased viability and post-storage adherence, which are essential characteristics for a successful cell treatment.

Albumin was also studied as a formulation buffer to foster high cell viability upon transportation between cell therapy sites. In a recent study to treat severe burn and chronic wound patients with autologous sprayed keratinocytes, different carrier solutions for transporting these cells were studied¹⁹. The carrier solution needed to provide a vehicle that could maintain the cell phenotype, function and viability over the transportation time from the manufacturing to the administration sites; with the possibility that sometimes they would have to be stored overnight, when the treatment was not immediately possible. The results showed that cells stored in saline plus 2.5% albumin had higher viability after 1, 3 and 24h¹⁹. As such, the researchers from this study concluded the suitability of Saline+2.5% Albumin as a cell transportation solution for clinical use; and the carrier choice for the innovative cell therapy clinical trial that is now following.

Albumin, a supporter of cryopreservation and off-the-shelf cell therapy products

Not only a protective medium for transportation, albumin also offers a safe solution to optimize cell performance when cryopreservation is needed, for example in the context of stem cell therapies. Extended shelf life of cellular-based therapies is highly advantageous and cryopreservation is a crucial step for commercial stem cell therapies, allowing off-the-shelf products and usage-upon-need. Researchers have shown that cryopreservation of pluripotent mesenchymal cells in DMSO supplemented with albumin led to prolonged cell stability and diminished apoptosis upon thawing, retaining cell multipotentiality; and, as such, the ability to differentiate into different cellular lineages⁷. Also, in the context of hematopoietic stem cells, scientists have shown improved cell recovery and viability, with faster engraftment of thawed products when using a premixed storage solution of albumin²⁰. More recently, researchers have incorporated albumin into an optimized chemically defined cryopreservation media to enhance the stability of previously expanded T Lymphocytes²¹. Their results show that cells cryopreserved in the albumin based-media, maintained better cell viability and identity over time.

Recombinant human albumin: a new level of control

Albumin has been commonly isolated by fractionating human plasma (plasma-derived albumin, pdAlbumin); but, unfortunately, this entails possible contamination by viruses or prions²². In contrast, recombinant human albumin (rAlb) has been successfully produced with a high level of purity using different types of production systems, such as yeasts^23,24. The production of rAlb overcame the availability and potential infectivity problems that can be associated with this important protein. rAlb produced by means of streamlined technologies are structurally identical to pdAlbumin, with safe and minimal levels of detectable manufacture-derived components; and, without undefined-variable contaminants, as seen with pdAlbumin sources^7,20,25. As such rAlb, as an animal and human component-free product, provides a stronger therapeutic control, with batch-to-batch consistency, which means additional regulatory benefits in a cell therapy context.

Conclusions

There’s no doubt that the role of albumin in cell culture is gaining ground and establishing itself. Its relevance and benefits in cell therapy applications include the creation of a transportation environment that sustains cell viability, a source of nutrients that promote cell proliferation and preserve cells by scavenging toxins/ROS; and, an insulation from chemical and shear stresses present in cell culture. But, a point to remember is that even though structurally similar, not all albumins are equal. Albumedix, with over 30 years of experience in developing rAlb products (e.g., Recombumin), understands albumin intricate biology and how to best harness its vast potential in the medical field. By providing a consistent, safe and optimized albumin source, Albumedix aims to enhance its functional properties and create confidence in novel cell therapies.

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