Trial Information

A Pilot Study to Demonstrate Safety and Feasibility of Cranial Reconstruction Using Mesenchymal Stromal Cells and Resorbable Biomaterials

Background: Cranial bone defects are often left following brain surgery, usually to allow
swelling of the brain to recover before subsequently re-implanting a protective covering of
the brain at a later time (cranioplasty). These procedures are performed anywhere over the
cranial vault, either unilaterally or bilaterally. The original piece of bone (autologous
bone plate = bone flap) is placed in a sterile container and stored in a refrigerator at
temperature of -40oC.

Weeks or months later, when the brain is relaxed, the scalp well healed and the patient's
medical condition permits, the individual is taken back to the operating room and the bone
is reimplanted (A procedure known as an autologous cranioplasty). The aim of the procedure
is to restore cosmesis and protection to the underlying brain and it can sometimes also
improve neurological symptoms by unknown mechanisms. Unfortunately these aims are not
always achieved and whilst technically straightforward the procedure is known to be
associated with a number of complications. Two of the most significant of these are
infection (such that the bone flap needs to be removed and replaced) and resorption (such
that the protective function is compromised). Overall 10% of autologous bone patients become
infected, 10% require replacement due to resorption and 12% become significantly resorbed,
then in 32% of case the autologous bone has failed.

In each case of cranioplasty failure the patient requires readmission, a second operation to
remove the bone flap, prolonged antibiotic therapy (in the case of infection), and then a
new custom-made plate and readmission for a third surgical procedure.

In most cases synthetic materials such as polymethylmethacrylate and titanium mesh are used
for reconstruction. Commonly reconstruction is carried out by the surgeon using such
materials to sculpt the cranioplasty. More recently, hydro formed titanium plates have been
used. This entails a process of CT scanning the defect, virtual reconstruction, 3D printing
of moulds, pressing the plate and hand finishing. Whilst highly successful in treating more
than 150 patients, the titanium cranioplasty remains in the patient for life and, as a
non-biological material, presents as a preferential site for infection (approximately 5% of
cases). In addition, medical CT images for assessment and treatment of neurological
conditions are compromised for life due to metal artefacts arising from the plates.
Furthermore, interference with metal scanning equipment commonly used for security purposes
also remains a life time issue. The patients with an infected titanium cranioplasty require
a fourth admission to remove the metal or polymer plate, extended antibiotic treatment and
then a fifth surgical procedure to reinsert a new cranioplasty.

Mesenchymal stromal cells (MSC): MSC are multipotent adult cells capable of differentiating
down multiple mesenchymal lineages. They are adherent fibroblastoid-like cells with an
extensive capacity for expansion. They reside within the connective tissue of most organs
and have been isolated from bone marrow, placenta, adipose tissue, umbilical cord, amniotic
fluid, circulating blood, various foetal tissues, skeletal muscle synovia, dental pulp,
liver, spleen, lung and dermis. Most work has focussed on MSC derived from bone marrow,
however, there are also some clinical reports using adipose tissue and placental derived
MSC. MSC from different sources may not be functionally equivalent or exhibit the same
differentiation potential. The main functions for bone marrow derived MSC with regards to
the present study is the ability to differentiate down the osteogenic lineage. It is this
ability to differentiate that has seen them applied to bony non-union and the treatment of
critical size bone skeletal deficits, and in particular the reconstruction of cranial voids.
In the current proposal Cell and Tissue Therapies W.A. at Royal Perth Hospital have
extensive experience and have applied for an TGA (Therapeutics Goods Administration, the
Australian Government regulatory authority) licence to manufacture and provide MSC for
patient treatment.

MSC are not immunogenic and escape recognition by alloreactive T cells and NK cells. They
have low level expression of HLA class I and no expression of HLA class II. They do not
express co-stimulatory molecules and are unable to induce T cell mediated immune response,
and therefore can be used as universal donor cells. Allogeneic cells have been widely used
in clinical trials in both immune modulation and tissue repair. The advantage of using
allogeneic cells is that donor age can be controlled. The literature indicates that MSC
harvested from donors older than 40 years are inferior. Since many of the patients being
treated with a cranioplasty are greater than 40 years of age, the use of allogeneic cells in
this study is preferable. Clinical human trials and animal studies support the use of
allogeneic cells.

Cranioplasty: The Department of Medical Engineering and Physics at Royal Perth Hospital is a
world leader in providing custom made implants and has been supplying custom made titanium
cranioplasties for fifteen years. The basic methodology which has been used to treat over
150 patients includes the reconstruction of the void using advanced software based on the
patients CT scan. Once the void has been reconstructed a female mould is created to press
the titanium plate. The plate is then hand finished and checked for fitment on a premade
defect model.

Bioceramic: Resorbable bioceramics such as hydroxyapatite and beta tri-calcium phosphate
have been used in the treatment of bony deficit for many years. For example, ChronOS
(Synthes GmbH, Oberdorf) bone graft substitute is a fully synthetic and resorbable bone
graft substitute consisting of beta-tricalcium phosphate with a compressive strength similar
to that of cancellous bone. The interconnected porosity acts as an osteconductive matrix for
the ingrowth of bone cells and blood vessels. Such materials are used for filling of bone
defects after trauma, reconstruction or correction in non-load bearing indications and
commonly these materials prescribe a method of perfusion of the granules in the operating
room with the patient's own bone marrow. Resorption of the bioceramics has been shown to
occur over a period of 6-18 months (Buser 1998).

Polymer Scaffold: There are a myriad of polymer materials used for surgery including in the
area of cranio-maxillofacial surgery. The most common polymer is poly(lactic acid). PLA
such as 70:30 poly(L-lactide-co-D,L-lactide) are made from a amorphous biodegradable
copolymer which will ultimately resorb in vivo. The bioceramics and polymer materials are
approved by the TGA for this indication.