Introduction

The development and clinical application of expanded stem cells has been of huge interest in trauma and orthopaedics as a way to reverse bone and soft tissue injury with the delivery of these multipotent cells (1). Cartilage injury and subsequent osteoarthritis have significant social and economic implications for making them a research and treatment priority.

Content

There has been a number of clinical studies investigating the treatment of chondral lesions using mainly bone marrow, synovial and fat derived expanded stem cells(2,3). There has been only a few comparative studies of MSC’s verses autologous chondrocytes and these have failed to demonstrate a significant difference(4,5). In comparison to chondrocytes, MSC’s are a very heterogenous population and potentially there is need for greater characterisation in order to identify the optimum “curative cell”. Alternatively, the concept of MSC and chondrocyte co-culture may direct better repair through paracrine signalling.

As a consequence of greater processing, the manufacture costs will increase and so greater clinical efficacy will be required in order to justify the health economic benefit. Based on the comparative early clinical experience and results relative to ACI, we need to look at strategies to reduce the manufacture costs if MSC’s are to be a viable treatment option in clinical practice. Potential stratergies could include:

Using minimally manipulated cells through an optimised one stage procedure

-A single stage procedure with a minimally manipulated cell product removes the need for an initial cell biopsy. By avoiding the significant regulation around Advanced Therapeutic Medicinal Products, the cost of product can be significantly reduced. There are a number of commercially available kits currently available for harvesting and concentrating bone marrow and fat cells. The vast majority of the clinical results within the literature are case series using Bone Marrow Concentrate(6) with only one animal study comparing BMAC to MSC’s. The current clinical evidence suggests there is therapeutic benefit to a single stage procedure. Further research is required to optimise processing in order to maximise cell harvesting and potentially cell characterisation.

The use of Allogenic cells

– Allogenic cells would enable a single stage procedure removing the need for an initial tissue biopsy. There is also the potential to treat many patients from a single tissue sample further reducing treatment costs(7).

Injection versus implantation

An injectable treatment would avoid the need for an invasive surgery and its associated costs to implant the cell treatment. Further potential savings could be made by removing the need for a scaffold to insert into the defect. Concern exists regarding the potential high rate of cell death following injection and whether cells will incite host repair at the site of the chondral lesion.(8)

Streamlined regulatory environment for cartilage related ATMP’s

All ATMP’s are currently managed under the same guidance, one which is similar to that used in the pharmaceutical industry. Due to the nature of chondral lesions and the associated pathology that commonly occurs (which excludes the majority of patients from clinical trials), bringing a new treatment can be very expensive and protracted. Modification of the current regulation would benefit the area of cartilage repair and accelerate future development

References

1. Cucchiarini M, Orth P, Rey-Rico A, Venkatesan JK, Madry H. Current perspectives in stem cell research for knee cartilage repair. Stem Cells Cloning Adv Appl. 2014 Jan;1.

2. Kim YS, Choi YJ, Lee SW, Kwon OR, Suh DS, Heo DB, Koh YG. Assessment of clinical and MRI outcomes after mesenchymal stem cell implantation in patients with knee osteoarthritis: a prospective study. Osteoarthritis Cartilage. 2016 Feb;24(2):237-45. doi: 10.1016/j.joca.2015.08.009. Epub 2015 Aug 28.

3. Kim YS, Choi YJ, Koh YG. Mesenchymal stem cell implantation in knee osteoarthritis: an assessment of the factors influencing clinical outcomes. Am J Sports Med. 2015 Sep;43(9):2293-301. doi: 10.1177/0363546515588317. Epub 2015 Jun 25.

4. Nejadnik H, Hui JH, Feng Choong EP, Tai BC, Lee EH.Autologous bone marrow-derived mesenchymal stem cells versus autologous chondrocyte implantation: an observational cohort study. Am J Sports Med. 2010 Jun;38(6):1110-6. doi: 10.1177/0363546509359067. Epub 2010 Apr 14.

5. Akgun I, Unlu MC, Erdal OA, Ogut T, Erturk M, Ovali E, Kantarci F, Caliskan G, Akgun Y. Matrix-induced autologous mesenchymal stem cell implantation versus matrix-induced autologous chondrocyte implantation in the treatment of chondral defects of the knee: a 2-year randomized study. Arch Orthop Trauma Surg. 2015 Feb;135(2):251-263. doi: 10.1007/s00402-014-2136-z. Epub 2014 Dec 30.

6. Gobbi A, Whyte GP. Long-term Clinical Outcomes of One-Stage Cartilage Repair in the Knee With Hyaluronic Acid-Based Scaffold Embedded With Mesenchymal Stem Cells Sourced From Bone Marrow Aspirate Concentrate. Am J Sports Med. 2019 May 16:363546519845362. doi: 10.1177/0363546519845362.

7. de Windt TS, Vonk LA, Slaper-Cortenbach ICM, Nizak R, van Rijen MHP, Saris DBF. Allogeneic MSCs and Recycled Autologous Chondrons Mixed in a One-Stage Cartilage Cell Transplantion: A First-in-Man Trial in 35 Patients. Stem Cells. 2017 Aug;35(8):1984-1993. doi: 10.1002/stem.2657. Epub 2017 Jun 23.

8. Vega A, Martín-Ferrero MA, Del Canto F, Alberca M, García V, Munar A, Orozco L, Soler R, Fuertes JJ, Huguet M, Sánchez A, García-Sancho J.Treatment of Knee Osteoarthritis With Allogeneic Bone Marrow Mesenchymal Stem Cells: A Randomized Controlled Trial. Transplantation. 2015 Aug;99(8):1681-90. doi: 10.1097/TP.0000000000000678.

Introduction

Microfracture is one of the most common techniques used to treat cartilage lesions, however significant failure rates have been reported long term. Microfracture results in inferior fibrocartilage repair but also causes secondary changes to the mechanical properties of the subchondral bone. An increase in stiffness combined with intra-lesional osteophyte leads to increased stress on the fibrocartilage regenerate. BSt-Cargel(Smith & Nephew, Andover, MA)is a chitosan hydrogel/scaffold which following the addition of peripheral blood is intended to stabilize the blood clot in a cartilage lesion following MF. In a 80 patient RCTit resulted in histologically superior repair compared to microfracture alone with reduced bone changes suggesting a positive biological effect of the scaffold.

Content

BSt-Cargel can be applied both via an open or arthroscopic approach. Technical pearls to help with the procedure include:

1. Initially an open/mini-open approach is advised before moving on to an arthroscopic approach.

2. The lesion needs to be meticulously prepared, with vertical edges and it should be contained.

3. The BSt-Cargel can be mixed early and left on the side in order to reduce the setting time.

4. A water bath set at 37deg can be used to warm the chitosan prior to mixing with blood in order to further reduce the setting time

5. It is important not to over-fill the lesion.

Arthroscopic technique can be improved by, leaving the accessory tap open in order to allow air into the knee, ensuring the lesion can be visualised when the lesion is flat (and the knee is flexed), using suction on a needle in order to maintain a dry environment and using switching sticks to improve visualisation.

With the aim of providing a cartilage treatment that provides a source of mononucleated cells avoiding the need for subchondral perforations we investigated the combination of Bone Marrow Concentrate (BMAC) and BSt-Cargel to create a cell seeded implant with comparative properties to standard BSt-Cargel mixed with blood.

Design. Whole blood and bone marrow were harvested from 12 patients who underwent cartilage repair surgery using BMaC after informed consent. a validated in vitro testing model was used to assess the following 6 conditions: (1) BSt-Cargel mixed with whole blood (Cg-WB), (2) BSt-Cargel mixed with bone marrow (Cg-BM), (3) BSt-Cargel mixed with bone marrow concentrate (Cg-BMaC), (4) whole blood (WB), (5) bone marrow (BM), and (6) bone marrow concentrate and batroxobin (BMaC-BtX). Cell retention and viability within the BSt-Cargel/ BMaC clots were investigated using confocal microscopy.

Results. in our study, BM and BMaC (processed using the Harvest, SmartPrep2 system combined with heparin and reactivated with batroxibin) when combined with BSt-Cargel produced a product that had similar clot contraction, macroscopic properties, and histological appearance to standard BStCargel mixed with blood. Mononucleated cells from the BMaC were retained within the scaffold and remained viable until clot dissolution in vitro.

By combining BSt-Cargel with BMaC in the manner described, bone marrow–derived mononucleated cells can be retained within the chondral defect potentially negating the need for microfracture. Subsequently we have undertaken the procedure in the clinical setting and the early results of a subsequent clinical series will be presented.