Optimization of Intrabone Delivery of Hematopoietic Progenitor Cells in a Swine Model Using Cell Radiolabeling with [89]zirconium

Abstract

y Both senior authors contributed equally to this manuscript as part of an NIH trans-Institute collaboration.Intrabone (IB) hematopoietic cell transplantation (HCT) of umbilical cord blood in humans remains experimental and the technique has not been optimized. It is unknown whether hematopoietic progenitor cells (HPCs) injected IB are initially retained in the marrow or rapidly enter into the venous circulation before homing to the marrow. To develop an IB-injection technique that maximizes HPC marrow-retention, we tracked radiolabeled human HPCs following IB-injection into swine. We developed a method to radionuclide-label HPCs using a long-lived positron emitter 89 Zr and protamine sulfate that resulted in cellularretention of low-dose radioactivity. This approach achieved radioactivity levels sufficient for detection by positron emission tomography with both high sensitivity and spatial resolution when fused with computed tomography. We found that conditions utilized in pilot IB-HCT clinical trials conducted by others led to both rapid drainage into the central venous circulation and cellular extravasation into surrounding muscle and soft tissues. By optimizing the needle design, using continuous real-time intramarrow pressure monitoring, and by reducing the infusion-volume and infusion-rate, we overcame this limitation and achieved high retention of HPCs in the marrow. This method of IB cellular delivery is readily applicable in the clinic and could be utilized in future investigational IB-HCT trials aimed at maximizing marrow retention of HPCs.

A prospective multicenter phase II study of intrabone marrow transplantation of unwashed cord blood using reduced‐intensity conditioning

“…How many CB cells should be confined to the BM at an early phase after IBMI remains to be determined. If more CB cells need to be confined to the BM, we may have to use a mechanical injection device to administer CB cells into the BM . Although IBM‐CBT studies, including ours, have just begun to yield successful outcomes, there are still many questions to be answered.…”

“…However, despite a small volume of CB (5‐6 mL) being injected into the BM, the majority of CB cells are considered to rapidly enter the systemic circulation. Although the detailed behavior of HSCs after IBMI remains unknown, Pantin et al recently reported the kinetics of HSCs injected into the BM at an early phase of transplantation in a swine model, using 89Zr‐Df‐labeled human peripheral blood stem cells (PBSCs). According to their study, when a slow “hand‐push,” as used by both Frassoni et al and ourselves, was performed during IBM injection, 44.7%‐88.2% (median, 59.5%) of HSCs were observed in the lung 1 hour after transplantation.…”

“…In trabecular bones such as the pelvis, an increase in the intramarrow pressure caused by IBMI easily causes the extravasation of HSCs into the bloodstream. According to a recent report by Pantin et al, as an increased intramarrow pressure during IBMI using the pelvis easily pushes out HSCs from the BM into the bloodstream, the volume of HSC suspension and speed of IBMI have to be strictly controlled to confine HSCs to the BM. In recent clinical studies that showed the usefulness of IBM‐CBT, the volume injected into one site of the pelvis was as small as 5‐6 mL .…”

Progress and obstacles towards generating hematopoietic stem cells from pluripotent stem cells

“…Optimally, technical manipulations and culture conditions for differentiating HSCs from PSCs will evolve that will maintain and/or enhance expression and function of molecules that mediate marrow homing. Alternatively, techniques to improve intra-marrow delivery of HSC may facilitate engraftment of PSC-derived HSC, without requiring systemic homing capabilities [71]. …”

Pre- and postmortem imaging of transplanted cells

“…19,20 The observation of stem cells labeled with radiotracers can not only provide researchers with information about the fate of these cells, but can also enable optimization of the delivery route and technique. 21 The increasing requirement for a detailed visualization of stem cells often leads to the development of multimodal approaches. Some newly introduced radioisotopes, such as 52 Mn, can also be visualized by both PET and magnetic resonance imaging (MRI) scanners.…”