Radially branched deployment for more efficient cell transplantation at the scale of the human brain

Abstract

Background: In preclinical studies, cell transplantation into the brain has shown great promise for the treatment of a wide range of neurological diseases. However, the use of a straight cannula and syringe for cell delivery to the human brain does not approximate cell distribution achieved in animal studies. This technical deficiency may limit the successful clinical translation of cell transplantation.

Objective: To develop a stereotactic device that effectively distributes viable cells to the human brain. Our primary aims were to (1) minimize the number of transcortical penetrations required for transplantation, (2) reduce variability in cell dosing and (3) increase cell survival.

Methods: We developed a modular cannula system capable of radially branched deployment (RBD) of a cell delivery catheter at variable angles from the longitudinal device axis. We also developed an integrated catheter-plunger system, eliminating the need for a separate syringe delivery mechanism. The RBD prototype was evaluated in vitro and in vivo with subcortical injections into the swine brain. Performance was compared to a 20G straight cannula with dual side ports, a device used in current clinical trials.

Results: RBD enabled therapeutic delivery in a precise 'tree-like' pattern branched from a single initial trajectory, thereby facilitating delivery to a volumetrically large target region. RBD could transplant materials in a radial pattern up to 2.0 cm from the initial penetration tract. The novel integrated catheter-plunger system facilitated manual delivery of small and precise volumes of injection (1.36 ± 0.13 µl per cm of plunger travel). Both dilute and highly concentrated neural precursor cell populations tolerated transit through the device with high viability and unaffected developmental potential. While reflux of infusate along the penetration tract was problematic with the use of the 20G cannula, RBD was resistant to this source of cell dose variability in agarose. RBD enabled radial injections to the swine brain when used with a modern clinical stereotactic system.

Conclusions: By increasing the total delivery volume through a single transcortical penetration in agarose models, RBD strategy may provide a new approach for cell transplantation to the human brain. Incorporation of RBD or selected aspects of its design into future clinical trials may increase the likelihood of successful translation of cell-based therapy to the human patient.

Figure 1. Components of the radially branched deployment (RBD) prototype

(A) outer guide tube, (B) inner guide tube, (C) cell delivery catheter, (D) plunger wire. These separated RBD components assemble in a nested manner.

Figure 2. Open and closed configurations of the outer guide tube side port

The side port can be opened (D) or closed (B) by the user through rotation (c, curved arrow) and linear translation (b or d, straight arrows) of the inner guide tube via manipulation of the proximal inner guide tube controls (A).

Figure 3. Control and safety elements of the RBD prototype

The RBD prototype is shown here integrated with the Clearpoint SMARTframe. (A) Plunger lock. This torquer at the catheter proximal end controls movement of the plunger wire. (B) Catheter lock. This Touhy borst adaptor provides a gas tight seal at the most proximal end and must be opened to allow linear translation of the catheter within the inner guide tube. (C) Side port lock. With this Touhy bost adaptor, the RBD prototype can be locked in either the open or closed configurations. (D). Depth stop. This stop collar, affixed to the SMARTframe, controls the depth and rotation of RBD outer guide tube.

Figure 4. Radial catheter deployment

(A–B) As the user advances the catheter through the catheter lock at the proximal end, the catheter emerges from the side port along a radially-oriented path. (C–G) Sequential images taken of catheter deployment overlaid upon an image of the actual final deployed position. The tip of the catheter is dyed blue, to allow easier visualization. (H) Four examples of the variable distances and catheter paths that can be attained with RBD. The same RBD guide tube assembly was used to deploy four different catheters, each with a unique radius of curvature. The final position of each catheter was photographed and merged into a single image. (I) Example of multiple catheter deployments branched from a single cannula trajectory. The final position of six catheter deployments, each performed at a different rotational angle and depth, was photographed and merged, demonstrating the resulting “tree-like” pattern of deployment.

Figure 5. The integrated catheter-plunger system

Advancing the plunger wire within the bore of the catheter delivers precise volumes of cells through the distal ports.

Figure 6. NPC differentiation after transit through the RBD cell delivery catheter

(A,C,E) Differentiation of NPCs that did not transit the device (control). (B,D,F) Differentiation of NPCs that were dispensed through the RBD catheter-plunger system. (A,B) GFAP (red), astrocyte marker. (C,D) Tuj1 (green), neuronal marker. (E,F) O4 (green) oligodendrocyte marker.

Figure 7. Evaluation of infusion reflux

Distribution of Allura Red AC dye in agarose gel after delivery through the RBD prototype (A–C) or the 20G cannula-syringe system (D–F).

Figure 8. Use of the RBD prototype with the Clearpoint SMARTframe for delivery to the swine brain

(A–D) Distribution of fluorescent beads after delivery with the RBD prototype. Arrows in (A) and (C) indicate the locations of radial delivery paths, and (B) and (D) show corresponding higher power fluorescent images of the deposited beads (green).

Figure 9. Schematic illustrating the use of RBD to deliver cells to a larger human brain target

By deploying the catheter at multiple rotational angles and depths, transplantation to larger target regions, such as the putamen (pink), can be achieved with a single transcortical brain penetration.