**3. Challenges and future direction**

**Disease Therapeutic Product(s) Cell Type Encapsulation**

β-Glucuronidase Mouse 2A-50

Glucagon-like peptide-1 Human mesenchymal

ovary cells

fibroblasts

stem cells

Human amniotic epithelial cells

Chinese hamster ovary cells

Human umbilical cord mesenchymal stromal cells

Human umbilical cord mesenchymal stem cells

myoblasts

ovary cells

Mouse C2C12 myoblasts

myoblasts mouse C2C12 myoblasts

Pig Sertoli cells Alginate

Atrial natriuretic peptideChinese hamster

Adipose stem cells AP-PLL-brPEG

NIH3T3 cells Alginate-barium

Fabry disease α-Galactosidase A Chinese hamster

Vascular endothelial growth factor

Polycythemic diseases Erythropoietin Mouse C2C12

factor (FGF-2)

Hemophilia B Factor IX Mouse C2C12

Acute skin flap ischemia Basic fibroblast growth

Laron syndrome Recombinant human

IGF-1

**Table 1.** Recent gene therapy studies by using encapsulated transgenic cells

Mucopolysaccharidosis

198 Gene Therapy - Principles and Challenges

Myocardial infarction

Hypertension and/or congestive heart failure

and wound

VII

**System**

Semipermeable Polymer Fiber

Alginate-poly-l-lysine [50]

CellBeadsTM [51]

Polymer (polysulfon) Hollow fibers

Alginate-Poly-l-Lysine-Alginate Microcapsules

microcapsules

microcapsules

Alginate-barium microcapsules

Alginate-barium microcapsules

Semipermeable polyethersulf hollow

Polycaprolactone

Microporous polyethersulfone hollow fibers

Alginate-poly-llysine-alginate microcapsules

Alginate-poly-llysine-alginate and alginate-poly-larginine-alginate microcapsules

microcapsules

fibers

tubes

**Ref.**

[49]

[23]

[27]

[52]

[21]

[53]

[54]

[55]

[56]

[57]

[58]

[59]

[60]

Recent clinical trials regarding gene therapy by using encapsulated transgenic cells are summarized in Table 2. For eventual clinical applications of encapsulated transgenic cells for gene therapy, however, there are still some issues that need to be addressed.[62,63]

#### **1. Protrusion of encapsulated cells**

Cell growth leads to protrusion of cells over time, which may cause the failure of immunoi‐ solation following *in vivo* transplantation. Bhujbal *et al*. reported a novel multilayer immunoi‐ solating encapsulation system aiming to prevent cell protrusion without compromising cell survival (Figure 8).[64]

#### **2. Scaling-up cell microencapsulation**

Cell encapsulation processes are usually performed at the lab scale. For successful clinical applications, massive production of encapsulated cells following good manufacturing practices (GMP) standardized procedures [65] for transplantation is critical. Different designs have been reported for scaling-up cell encapsulation. One design based on a 3D microfluidic approach, which contains a 3D air supply and multinozzle outlet, has been reported recently.[17]

#### **3. Monitor and control the encapsulated transgenic cells**

Once the therapy has reached its goal or when undesirable deleterious effects occur, nonin‐ vasive monitoring and deactivation/elimination of the encapsulated cells are critical for clinical practice.[63] Recently, Shen *et al.* [66] reported the encapsulation of recombinant cells by using a magnetized ferrofluid alginate for *in vivo* monitoring by magnetic resonance imaging (MRI). Moreover, magnetic field-controlled gene expression in encapsulated cells, coencapsulated with magnetic nanoparticles, has been reported. The cells were modified to produce thera‐ peutic products under the control of a heat-inducible promoter. Heat induction could be achieved by elevating the temperatures of the capsules through coencapsulated magnetic nanoparticles subjected to a magnetic field (Figure 9).[67] Catena *et al.* reported an interesting and smart system which shows potential for monitoring encapsulated cells and selectively eliminating them at a specific moment by using the SFGNESTGL triple reporter system.[68]



**Table 2.** Clinical trials of gene therapy involving encapsulated transgenic cells [61]

201

**Project Therapeutic Product(s) Target Disease(s) Phase Status**

Malignant glioma of

hemorrhage (ICH)

Early stage retinitis pigmentosa or Usher syndrome (type 2 or 3)

Macular telangiectasia

Anti-VEGF therapy Macular degeneration I and II Not yet recruiting

Nerve growth factor (NGF) Alzheimer's disease I Unknown

Solid tumour cancer I Recruiting

type 2

Eye disease achromatopsia

brain

Macular degeneration II Completed

I Completed

I and II Terminated

I and II Active

II Recruiting

II Recruiting

Ciliary neurotrophic factor

Insulin-like growth factor

Ciliary neurotrophic factor

Ciliary neurotrophic factor

Recombinant human ciliary neurotrophic factor

Irradiated autologous tumour cells

**Table 2.** Clinical trials of gene therapy involving encapsulated transgenic cells [61]

Glucagon-like peptide-1 Intracerebral

(CNTF)

receptor-1

(CNTF)

(CNTF)

participants with early stage retinitis pigmentosa

Degeneration

hemorrhage

achromatopsia

solid tumours

disease patients

A Study of an Encapsulated Cell Technology (ECT) Implant for Patients With Atrophic Macular

200 Gene Therapy - Principles and Challenges

Pilot immunotherapy trial for recurrent malignant gliomas

CNTF implants for CNGB3

Retinal imaging of subjects implanted with ciliary neurotrophic factor (CNTF) releasing encapsulated cell implant for early-stage retinitis pigmentosa

A phase 2 multicenter randomized clinical trial of CNTF FOR MacTel

MVX-ONCO-1 in patients with

encapsulated cell technology (ECT) for the treatment of recurrent choroidal neovascularization (CNV) secondary to age-related macular degeneration (AMD)

Encapsulated cell biodelivery of nerve growth factor to Alzheimer´s

Study of the intravitreal implantation of NT-503-3

GLP-1 CellBeads® for the treatment of stroke patients with spaceoccupying intracerebral

**Figure 8.** Cell growth within common APA capsules and multilayer capsules. Live cells were stained green while dead cells were stained red.[51]

**Figure 9.** Schematic representation of the magnetic field-controlled gene expression in encapsulated cells.[67]
