Intrabone marrow transplantation of unwashed cord blood using reduced-intensity conditioning treatment: a phase I study

Differential CXCR4 expression on hematopoietic progenitor cells versus stem cells directs homing and engraftment

Gene therapy involves a substantial loss of hematopoietic stem and progenitor cells (HSPC) during processing and homing. Intra-BM (i.b.m.) transplantation can reduce homing losses, but prior studies have not yielded promising results. We studied the mechanisms involved in homing and engraftment of i.b.m. transplanted and i.v. transplanted genetically modified (GM) human HSPC. We found that i.b.m. HSPC transplantation improved engraftment of hematopoietic progenitor cells (HPC) but not of long-term repopulating hematopoietic stem cells (HSC). Mechanistically, HPC expressed higher functional levels of CXCR4 than HSC, conferring them a retention and homing advantage when transplanted i.b.m. Removing HPC and transplanting an HSC-enriched population i.b.m. significantly increased long-term engraftment over i.v. transplantation. Transient upregulation of CXCR4 on GM HSC-enriched cells, using a noncytotoxic portion of viral protein R (VPR) fused to CXCR4 delivered as a protein in lentiviral particles, resulted in higher homing and long-term engraftment of GM HSC transplanted either i.v. or i.b.m. compared with standard i.v. transplants. Overall, we show a mechanism for why i.b.m. transplants do not significantly improve long-term engraftment over i.v. transplants. I.b.m. transplantation becomes relevant when an HSC-enriched population is delivered. Alternatively, CXCR4 expression on HSC, when transiently increased using a protein delivery method, improves homing and engraftment specifically of GM HSC.

Engraftment Effects after Intra-Bone Marrow versus Intravenous Allogeneic Stem Cell Transplantation in a Reduced-Intensity Conditioning Dog Leukocyte Antigen-Identical Canine Model

Following conventional i.v. hematopoietic stem cell transplantation (IV-HSCT), most of the hematopoietic stem cells get trapped in peripheral organs and do not reach the bone marrow niche. A promising approach to overcome this cell loss during the homing process seems to be the infusion of hematopoietic stem cells directly into the bone marrow cavity (intra-bone marrow [IBM]-HSCT). This study aimed to investigate the engraftment efficiency of IBM-HSCT compared with IV-HSCT following reduced-intensity conditioning in a canine HSCT model. Furthermore, the impact of 2 different graft infusion rates during IBM-HSCT on the engraftment was evaluated. Dogs received 4.5 Gy total body irradiation for conditioning at day -1 and 15 mg/kg cyclosporin A twice daily at days -1 to +35 as immunosuppression. The IV-HSCT group (n = 7) received unmodified bone marrow. The IBM-HSCT cohorts received buffy coat-enriched bone marrow that was applied into the humerus and femur simultaneously with an infusion time of either 10 minutes (IBM10; n = 8) or 60 minutes (IBM60; n = 7). Statistical analyses were performed using the Kruskal-Wallis test followed by the Mann-Whitney U test with Bonferroni correction for multiple comparisons. Statistical significance was declared at Bonferroni-adjusted P < .017. All dogs initially engrafted. One dog of the IBM10 cohort died at day +15 from infection. All 21 evaluable dogs developed a durable mixed donor chimerism over the course of 112 days. Engraftment kinetics did not differ significantly across the 3 groups. Leukocyte and platelet nadirs, as well as the durations of leukopenia and thrombocytopenia, were comparable in the 3 groups. Signs of toxicity for ingestion, body temperature, activity, and defecation did not show statistically significant differences among the 3 groups; only weight loss was greater in the IBM60 group compared with the IV group. IBM-HSCT following reduced-intensity conditioning resulted in an engraftment efficiency and hematopoietic recovery comparable to that seen with conventional IV-HSCT. In addition, modification of the graft infusion rate had no impact on engraftment and hematopoietic recovery in the canine IBM-HSCT model.

Isolation and Characterization of a Fetal-Maternal Microchimeric Stem Cell Population in Maternal Hair Follicles Long after Parturition

Fetal-maternal microchimerism describes the acquisition of fetal stem cells (FSC) by the mother during pregnancy and their long-term persistence after parturition. FSC may engraft in a variety of maternal tissues especially if there is organ/tissue injury, but their role and mechanism of persistence still remains elusive. Clinical applications due to their pluripotency, immunomodulatory effects and accessibility make them good candidates for ex-vivo manipulation and autologous therapies. The hair follicles contain a distinctive niche for pluripotent stem cells (PSC). To date, there is no published evidence of fetal microchimerism in the hair follicle. In our study, follicular unit extraction (FUE) technique allowed easy stem cell cultures to be obtained while simple hair follicle removal by pull-out technique failed to generate stem cells in culture. We identified microchimeric fetal stem cells within the primitive population of maternal stem cells isolated from the hair follicles with typical mesenchymal phenotype, expression of PSC genes and differentiation potential towards osteocytes, adypocites and chondrocytes. This is the first study to isolate fetal microchimeric stem cells in adult human hair long after parturition. We presume a sanctuary partition mechanism with PSC of the mother deposited during early embryogenesis could explain their long-term persistence.

Tolerance in xenotransplantation

PURPOSE OF REVIEW

This review describes recent progress in tolerance-inducing strategies across xenogeneic immunological barriers as well as the potential benefit of a tolerance strategy for islets and kidney xenotransplantation.

RECENT FINDINGS

Using advanced gene editing technologies, xenotransplantation from multitransgenic alpha-1,3-galactosyltransferase knockout pigs has demonstrated marked prolongation of renal xenograft survival, ranging from days to greater than several months for life-supporting kidneys, and more than 2 years in a heterotopic nonlife-supporting cardiac xenograft model. Continuous administration of multiple immunosuppressive drugs has been required and attempts to taper immunosuppression have been unsuccessful. It appears likely that low levels of T cell dependent antibodies and activation of innate responses are responsible for xenograft loss. Mixed chimerism and thymic transplantation approaches have achieved xenogeneic tolerance in pig-to-mouse models and both have recently been extended to pig-to-baboon models. Encouraging results have been reported, including persistence of macrochimerism, prolonged pig skin graft survival, donor-specific unresponsiveness in vitro and detection of recent T cell emigrants in vivo.

SUMMARY

Although tolerance induction in vivo has not yet been achieved in pig-to-baboon models, recent results are encouraging that this goal will be attainable through genetic engineering of porcine donors.

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

Cord blood transplantation (CBT) is associated with delayed hematopoietic recovery and graft failure. To overcome these problems, we conducted a prospective, multicenter phase II study of intrabone marrow transplantation in which patients received reduced-intensity conditioning without anti-thymocyte globulin (ATG). The primary endpoint was the probability of full donor engraftment. Forty patients with hematologic malignancies were enrolled. Cord blood (CB) cells were injected without washing into 4 iliac bone sites (2 at each hemipelvis), at which approximately 6 mL of CB was administered at one site with local anesthesia. Full donor engraftment rate was 86.8%. The cumulative incidence of neutrophil and platelet engraftment was 86.4% and 85.5%, respectively. The median time to neutrophil (>0.5 × 10⁹ /L) and platelet (2.0 × 10⁹ /L) recovery was 17.5 and 44 days, respectively. The probability of severe acute graft-vs-host disease (GVHD) was 47.5%. The cumulative incidence of extensive chronic GVHD was 3.0%. The probability of relapse and non-relapse mortality was 30.4% and 28.0%, respectively. The survival rate at 3 years was 45.6%, although most patients were at an advanced stage. These results suggest that our intrabone marrow-CBT procedure without using ATG improves hematopoietic recovery and decreases the incidence of chronic GVHD, but does not decrease the incidence of acute GVHD.

Phase II study of intrabone single unit cord blood transplantation for hematological malignancies

The outcomes of cord blood transplantation with non‐irradiated reduced‐intensity conditioning for hematological malignancies need to be improved because of graft failure and delayed engraftment. Intrabone infusion of cord blood cells has the potential to resolve the problems. In this phase II study, 21 adult patients with hematological malignancy received intrabone transplantation of serological HLA‐A, B, and DR ≥4/6 matched single cord blood with a median number of cryopreserved total nucleated cells of 2.7 × 10⁷/kg (range, 2.0–4.9 × 10⁷/kg) following non‐irradiated fludarabine‐based reduced‐intensity conditioning. Short‐term methotrexate and tacrolimus were given as graft‐versus‐host disease prophylaxis, and granulocyte colony‐stimulating factor was given after transplantation. No severe adverse events related to intrabone injection were observed. The cumulative incidences of neutrophils ≥0.5 × 10⁹/L, reticulocytes ≥1%, and platelets ≥20 × 10⁹/L recoveries were 76.2%, 71.4%, and 76.2%, respectively, with median time to recoveries of 17, 28, and 32 days after transplantation, respectively. The probability of survival with neutrophil engraftment on day 60 was 71.4%, and overall survival at 1 year after transplantation was 52.4%. The incidences of grade II–IV and III–IV acute graft‐versus‐host disease were 44% and 19%, respectively, with no cases of chronic graft‐versus‐host disease. The present study showed the safety of direct intrabone infusion of cord blood. Further analysis is required to confirm the efficacy of intrabone single cord blood transplantation with non‐irradiated reduced‐intensity conditioning for adult patients with hematological malignancy. This study was registered with UMIN‐CTR, number 000000865.

A phase I/II trial of intrabone marrow cord blood transplantation and comparison of the hematological recovery with the Japanese nationwide database

Intrabone marrow cord blood transplantation (IB-CBT) was proposed as a promising treatment modality to improve hematological recovery. However, clinical advantages of IB-CBT over conventional IV CBT have been unclear. We conducted a prospective single-center trial of IB-CBT to evaluate its safety and superiority in terms of hematological recovery. Fifteen adults with hematological malignancies were enrolled. A thawed and unwashed single cord blood unit was injected into the bilateral superior-posterior iliac crests under local anesthesia. Engraftments of neutrophils and platelets were achieved in 13 cases, with medians of 17 and 45 days, respectively. For the control, we extracted data from the Japanese nationwide database and compared the hematological recovery of contemporaneously transplanted 1135 CBT cases. Multivariate analysis revealed that IB-CBT enhanced platelet recovery (hazard ratio, 2.13; P=0.007), but neutrophil recovery did not differ significantly (hazard ratio, 1.70; P=0.19). Better donor chimerism was seen in the bone marrow of the ilium than of the sternum on day 14, suggesting that the local hematopoiesis at the injected site was established earlier than that at the remote bone marrow site. Collectively, IB-CBT was well tolerated and may enhance local engraftment, which promotes prompter platelet recovery than does IV-CBT.

Engraftment Efficiency after Intra-Bone Marrow versus Intravenous Transplantation of Bone Marrow Cells in a Canine Nonmyeloablative Dog Leukocyte Antigen-Identical Transplantation Model

An intra-bone marrow (IBM) hematopoietic stem cell transplantation (HSCT) is assumed to optimize the homing process and therefore to improve engraftment as well as hematopoietic recovery compared with conventional i.v. HSCT. This study investigated the feasibility and efficacy of IBM HSCT after nonmyeloablative conditioning in an allogeneic canine HSCT model. Two study cohorts received IBM HSCT of either density gradient (IBM-I, n = 7) or buffy coat (IBM-II, n = 6) enriched bone marrow cells. An historical i.v. HSCT cohort served as control. Before allogeneic HSCT experiments were performed, we investigated the feasibility of IBM HSCT by using technetium-99m marked autologous grafts. Scintigraphic analyses confirmed that most IBM-injected autologous cells remained at the injection sites, independent of the applied volume. In addition, cell migration to other bones occurred. The enrichment process led to different allogeneic graft volumes (IBM-I, 2 × 5 mL; IBM-II, 2 × 25 mL) and significantly lower counts of total nucleated cells in IBM-I grafts compared with IBM-II grafts (1.6 × 10⁸/kg versus 3.8 × 10⁸/kg). After allogeneic HSCT, dogs of the IBM-I group showed a delayed engraftment with lower levels of donor chimerism when compared with IBM-II or to i.v. HSCT. Dogs of the IBM-II group tended to reveal slightly faster early leukocyte engraftment kinetics than intravenously transplanted animals. However, thrombocytopenia was significantly prolonged in both IBM groups when compared with i.v. HSCT. In conclusion, IBM HSCT is feasible in a nonmyeloablative HSCT setting but failed to significantly improve engraftment kinetics and hematopoietic recovery in comparison with conventional i.v. HSCT.

Optimization of intrabone delivery of hematopoietic progenitor cells in a swine model using cell radiolabeling with [89]zirconium

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 cellular-retention 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 intra-marrow 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.

Expansion and homing of umbilical cord blood hematopoietic stem and progenitor cells for clinical transplantation

The successful expansion of hematopoietic stem and progenitor cells (HSPCs) from umbilical cord blood (UCB) for transplantation could revolutionize clinical practice by improving transplantation-related outcomes and making available UCB units that have suboptimal cell doses for transplantation. New cytokine combinations appear able to promote HSPC growth with minimal differentiation into mature precursors and new agents, such as insulin-like growth factor-binding protein 2, are being used in clinical trials. Molecules that simulate the HSPC niche, such as Notch ligand, have also shown promise. Further improvements have been made with the use of mesenchymal stromal cells, which have made possible UCB expansion without a potentially deleterious prior CD34/CD133 cell selection step. Chemical molecules, such as copper chelators, nicotinamide, and aryl hydrocarbon antagonists, have shown excellent outcomes in clinical studies. The use of bioreactors could further add to HSPC studies in future. Drugs that could improve HSPC homing also appear to have potential in improving engraftment times in UCB transplantation. Technologies to expand HSPC from UCB and to enhance the homing of these cells appear to have attained the goal of accelerating hematopoietic recovery. Further discoveries and clinical studies are likely to make the goal of true HSPC expansion a reality for many applications in future.

Prolonged Survival of a Refractory Acute Myeloid Leukemia Patient after a Third Hematopoietic Stem Cell Transplantation with Umbilical Cord Blood following a Second Relapse

Although hematopoietic stem cell transplantation (HSCT) has been considered to be the only way for potential cure of relapsed acute myeloid leukemia (AML), there has been no report on a third HSCT in patients with multiple relapsed AML. Here, we report a case of 53-year-old female who received a successful third allogeneic HSCT after relapse of AML following a second allogeneic HSCT. She was treated with a toxicity reduced conditioning regimen and received direct intrabone cord blood transplantation (CBT) using a single unit of 5/6 HLA-matched cord blood as a graft source. Graft-versus-host disease prophylaxis was performed with a single agent of tacrolimus to increase graft-versus-leukemia effect. She is in remission for 8 months since the direct intrabone CBT. This report highlights not only the importance of individually adjusted approach but also the need for further investigation on the role of HSCT as a treatment modality in patients with refractory or multiple relapsed AML.

Improving engraftment and immune reconstitution in umbilical cord blood transplantation

Umbilical cord blood (UCB) is an important source of hematopoietic stem cells (HSC) for allogeneic transplantation when HLA-matched sibling and unrelated donors (MUD) are unavailable. Although the overall survival results for UCB transplantation are comparable to the results with MUD, UCB transplants are associated with slow engraftment, delayed immune reconstitution, and increased opportunistic infections. While this may be a consequence of the lower cell dose in UCB grafts, it also reflects the relative immaturity of cord blood. Furthermore, limited cell numbers and the non-availability of donor lymphocyte infusions currently prevent the use of post-transplant cellular immunotherapy to boost donor-derived immunity to treat infections, mixed chimerism, and disease relapse. To further develop UCB transplantation, many strategies to enhance engraftment and immune reconstitution are currently under investigation. This review summarizes our current understanding of engraftment and immune recovery following UCB transplantation and why this differs from allogeneic transplants using other sources of HSC. It also provides a comprehensive overview of promising techniques being used to improve myeloid and lymphoid recovery, including expansion, homing, and delivery of UCB HSC; combined use of UCB with third-party donors; isolation and expansion of natural killer cells, pathogen-specific T cells, and regulatory T cells; methods to protect and/or improve thymopoiesis. As many of these strategies are now in clinical trials, it is anticipated that UCB transplantation will continue to advance, further expanding our understanding of UCB biology and HSC transplantation.