Mobilization of healthy donors with plerixafor affects the cellular composition of T-cell receptor (TCR)-αβ/CD19-depleted haploidentical stem cell grafts

Stem Cells Collection and Mobilization in Adult Autologous/Allogeneic Transplantation: Critical Points and Future Challenges

Achieving successful hematopoietic stem cell transplantation (HSCT) relies on two fundamental pillars: effective mobilization and efficient collection through apheresis to attain the optimal graft dose. These cornerstones pave the way for enhanced patient outcomes. The primary challenges encountered by the clinical unit and collection facility within a transplant program encompass augmenting mobilization efficiency to optimize the harvest of target cell populations, implementing robust monitoring and predictive strategies for mobilization, streamlining the apheresis procedure to minimize collection duration while ensuring adequate yield, prioritizing patient comfort by reducing the overall collection time, guaranteeing the quality and purity of stem cell products to optimize graft function and transplant success, and facilitating seamless coordination between diverse entities involved in the HSCT process. In this review, we aim to address key questions and provide insights into the critical aspects of mobilizing and collecting hematopoietic stem cells for transplantation purposes.

Mobilization-based engraftment of haematopoietic stem cells: a new perspective for chemotherapy-free gene therapy and transplantation

INTRODUCTION

In haematopoietic stem cell transplantation (HSCT), haematopoietic stem cells (HSCs) from a healthy donor replace the patient's ones. Ex vivo HSC gene therapy (HSC-GT) is a form of HSCT in which HSCs, usually from an autologous source, are genetically modified before infusion, to generate a progeny of gene-modified cells. In HSCT and HSC-GT, chemotherapy is administered before infusion to free space in the bone marrow (BM) niche, which is required for the engraftment of infused cells. Here, we review alternative chemotherapy-free approaches to niche voidance that could replace conventional regimens and alleviate the morbidity of the procedure.

SOURCES OF DATA

Literature was reviewed from PubMed-listed peer-reviewed articles. No new data are presented in this article.

AREAS OF AGREEMENT

Chemotherapy exerts short and long-term toxicity to haematopoietic and non-haematopoietic organs. Whenever chemotherapy is solely used to allow engraftment of donor HSCs, rather than eliminating malignant cells, as in the case of HSC-GT for inborn genetic diseases, non-genotoxic approaches sparing off-target tissues are highly desirable.

AREAS OF CONTROVERSY

In principle, HSCs can be temporarily moved from the BM niches using mobilizing drugs or selectively cleared with targeted antibodies or immunotoxins to make space for the infused cells. However, translation of these principles into clinically relevant settings is only at the beginning, and whether therapeutically meaningful levels of chimerism can be safely established with these approaches remains to be determined.

GROWING POINTS

In pre-clinical models, mobilization of HSCs from the niche can be tailored to accommodate the exchange and engraftment of infused cells. Infused cells can be further endowed with a transient engraftment advantage.

AREAS TIMELY FOR DEVELOPING RESEARCH

Inter-individual efficiency and kinetics of HSC mobilization need to be carefully assessed. Investigations in large animal models of emerging non-genotoxic approaches will further strengthen the rationale and encourage application to the treatment of selected diseases.

Addition of plerixafor in poorly mobilized allogeneic stem cell donors

Background

Peripheral blood stem cells (PBSCs) are the predominant graft source for adult allogeneic hematopoietic stem cell transplantation (HSCT). In poorly mobilized autologous donors, plerixafor improves collection outcomes. We examine plerixafor use in allogeneic donors who mobilize poorly with granulocyte colony‐stimulating factor (G‐CSF) in those who are healthy and those with pre‐existing medical conditions, and determine the optimal threshold to add plerixafor.

Study Design/Methods

We retrospectively examined all allogeneic PBSC collections from January 2013 to October 2020 at our center. Donors received G‐CSF 10 mcg/kg daily for 4 days before undergoing apheresis collection on day 5. Plerixafor was added based on poor CD34+ cell collection yield after the first or second collection day.

Results

Of the 1008 allogeneic donors, 41 (4.1%) received one dose of plerixafor in addition to G‐CSF due to poor collection yield. After starting plerixafor there was a 0.75‐ to 7.74‐fold (median 2.94) increase in CD34+ yield from the previous day. No donors with G‐CSF‐only mobilization who collected <2.0 × 10⁶ CD34+ cells/kg recipient weight on day one achieved the goal of ≥4.0 × 10⁶ CD34+ cells/kg recipient weight total over 2 days but 59.2% of donors who used rescue plerixafor did.

Conclusion

Donors both healthy and those with pre‐existing disease responded well to plerixafor with minimal side effects. If the first‐day collection yield is less than ~63% of the collection goal, addition of plerixafor may be necessary to reach the collection goal and limit the number of collection days in allogeneic donors.

Efficacy and safety of a reduced dose of plerixafor in combination with granulocyte colony-stimulating factor in healthy haploidentical stem cell donors

BACKGROUND AND OBJECTIVES

Implementation of the technique of immunomagnetic selection requires the procurement of a large number of CD34+ cells from haploidentical donors within a single apheresis procedure. The release of stem cells with granulocyte colony-stimulating factor (G-CSF) alone is unsatisfactory in a number of donors, and plerixafor, a CXCR4 chemokine receptor antagonist, could be used as an additional mobilization agent. The aim of our study was to examine whether a lower dose of plerixafor (0.12 mg/kg) can provide sufficient increase in CD34+ cells in the peripheral blood of allogeneic healthy donors in comparison with a historical control group. In addition, we assessed the risk of inability to provide the recipient with a transplant containing the optimal dose of 8-10 × 10⁶ CD34+ cells/kg body weight of the recipient.

MATERIALS AND METHODS

In a prospective, single-arm study, we examined the results of 105 mobilizations in healthy adult haploidentical donors with G-CSF and plerixafor at a dose of 0.12 mg/kg. The historical control group consisted of 106 mobilizations with G-CSF and plerixafor at 0.24 mg/kg.

RESULTS

The median increase in the number of CD34+ cells from day 4 to day 5 of mobilization was 69 cells/μl (range, 28-240) versus 77 cells/μl (24-217) in the groups of 0.12 and 0.24 mg/kg of plerixafor, respectively (p-value 0.255). The apheresis products contained a median of 14.4 × 10⁶ /kg recipient body weight CD34+ cells versus 12.9 × 10⁶ /kg in the groups that received 0.12 and 0.24 mg/kg of plerixafor, respectively (p-value 0.118). The obtained differences were not significant, which means the application of a decreased dose of plerixafor did not affect the results of mobilization.

CONCLUSION

The obtained differences in collection were not significant, and thus the application of a decreased dose of plerixafor did not affect the results of mobilization.

HLA-haploidentical TCRαβ+/CD19+-depleted stem cell transplantation in children and young adults with Fanconi anemia

We report on the outcome of 24 patients with Fanconi anemia (FA) lacking an HLA matched related or unrelated donor, given an HLA-haploidentical T-cell receptor αβ (TCRαβ+) and CD19+ cell-depleted hematopoietic stem cell transplantation (HSCT) in the context of a prospective, single-center phase 2 trial. Sustained primary engraftment was achieved in 22 (91.6%) of 24 patients, with median time to neutrophil recovery of 12 days (range, 9-15 days) and platelet recovery of 10 days (range, 7-14 days). Cumulative incidences of grade 1 to 2 acute graft-versus-host disease (GVHD) and chronic GVHD were 17.4% (95% confidence interval [CI], 5.5%-35.5%) and 5.5% (95% CI, 0.8%-33.4%), respectively. The conditioning regimen, which included fludarabine, low-dose cyclophosphamide and, in most patients, single-dose irradiation was well tolerated; no fatal transplant-related toxicity was observed. With a median follow-up of 5.2 years (range, 0.3-8.7 years), the overall and event-free survival probabilities were 100% and 86.3% (95% CI, 62.8%-95.4%), respectively (2 graft failures and 1 case of poor graft function were considered as events). The 2 patients who experienced primary graft failure underwent a subsequent successful HSCT from the other parent. This is the first report of FA patients given TCRαβ+/CD19+-depleted haplo-HSCT in the context of a prospective trial, and the largest series of T-cell-depleted haplo-HSCT in FA reported to date. This trial was registered at www.clinicaltrials.gov as #NCT01810120.

Plerixafor added to G-CSF allows mobilization of a sufficient number of hematopoietic progenitors without impacting the efficacy of TCR-alpha/beta depletion in pediatric haploidentical and genoidentical donors failing to mobilize with G-CSF alone

BACKGROUND

Collection of a large number of early hematopoietic progenitors is essential for allogeneic apheresis products intended for TCR-alpha/beta depletion.

MATERIALS AND METHODS

We added plerixafor 0.24 mg/kg body weight (bw) on day 4 of high-dose filgrastim mobilization 10 hours prior to apheresis in 16 (30.5%) pediatric allogeneic donors who failed to recover a sufficient number of CD34+ cells.

RESULTS

On day 4 of G-CSF, the median CD34+ cell count in peripheral blood was 6 per μL (range 4-9 per μL) in 6 poor mobilizers and 16 per μL (range 12-19 per μL) in insufficient mobilizers. In all donors, the threshold of 50 CD34+ cells/μL was achieved, and the median increase was 14.8-fold in poor mobilizers and 6.5-fold in insufficient mobilizers, whereas it was 3.45-fold increase in those mobilized with G-CSF alone.

DISCUSSION

In all donors, a predefined number of >10 × 10⁶ CD34+ cells/kg of recipient bw before depletion was reached in the apheresis product. The use of plerixafor did not affect the purity of further TCR-alpha/beta depletion. Side effects were mild to moderate and consisted of nausea and vomiting.

CONCLUSION

Thus, the safety and high efficacy of plerixafor was proven in healthy pediatric allogeneic hematopoietic cell donors.

Plerixafor-based mobilization in pediatric healthy donors with unfavorable donor/recipient body weight ratio resulted in a better CD34+ collection yield: A retrospective analysis

INTRODUCTION

In order to propose risk-adapted mobilization algorithms, several authors have tried to look for predictive factors of the CD34⁺ yield in healthy pediatric donors. Donor recipient body weight ratio (D/R ratio) was identified as one of the main variables related with the success to achieve the target cell dose for transplantation. According to this variable we modified the mobilization schedule.

MATERIAL AND METHODS

We report the results of 46 mobilizations and apheresis procedures performed in our center with unfavorable D/R ratio. Mobilization was attempted by the standard regime of G-CSF (10 mcg/kg/24 hours) in 28 cases (60.9%), with high dose G-CSF (10 mcg/kg/12 hours) in 9 cases (19.6%), and with plerixafor and G-CSF single dose regime in 9 cases (19.6%).

RESULTS

CD34⁺ cell quantification before apheresis is closely related to CD34⁺ yield, being the only factor related to collected CD34⁺ cells (beta .71; P < .0001). The mobilization efficiency was higher in plerixafor group compared to the other two schedules (P < .0001). By using plerixafor for mobilization, we achieved the target CD34⁺ cell dose of ≥2 × 10⁶ /kg per recipient body weight in all cases with unfavorable D/R ratio. It was observed that 17.4% of cases that not reached the established target cell dose were located in the standard or high-dose mobilization regimes. This difference is even greater for optimal collections (≥5 × 10⁶ /kg), since of the 54.3% cases that did not reach this goal none was mobilized by plerixafor.

CONCLUSION

Tailoring the mobilization regime we can reach the target cell dose, even in those cases with the worst D/R ratio.

Salvage treatment with plerixafor in poor mobilizing allogeneic stem cell donors: results of a prospective phase II-trial

We conducted a prospective clinical trial to investigate the safety and efficacy of plerixafor (P) in allogeneic peripheral blood stem cells (PBSC) donors with poor mobilization response to standard-dose granulocyte colony-stimulating factor (G-CSF), defined by <2 × 10⁶ CD34 + cells/kg recipient body-weight (CD34+/kg RBW) after 1st apheresis. A single dose of 240 µg/kg P was injected subcutaneously at 10 p.m. on the day of the 1st apheresis. Thirty-seven allogeneic PBSC donors underwent study treatment. The median CD34+ count in peripheral blood was 15/µl on Day 1 after G-CSF alone, versus 44/µl on Day 2 after G-CSF plus P (p < 0.001). The median yield of CD34+ cells was 1.1 × 10⁸ on Day 1 and 2.8 × 10⁸ on Day 2. In contrast to a median yield of only 1.31 × 10⁶ CD CD34+/kg RBW on Day 1, triggering study inclusion, a median of 3.74 × 10⁶ CD CD34+/kg RBW were collected with G-CSF plus P on Day 2. Of 37 donors, 21 reached the target cell count of >4.5 × 10⁶ CD34+/kg RBW (57%, 95%CI 40-73%). No donor experienced a severe adverse event requiring treatment. In conclusion, P might be considered on a case-by-case basis for healthy allogeneic donors with very poor stem cell mobilization success after G-CSF.

Helper Innate Lymphoid Cells in Allogenic Hematopoietic Stem Cell Transplantation and Graft Versus Host Disease

Helper Innate Lymphoid Cells (hILCs), including ILC1s, ILC2s, and ILC3s, are mainly localized at the mucosal barriers where they play an important role in tissue regeneration and homeostasis through the secretion of specific sets of cytokines. The recent identification of a circulating ILC precursor able to generate all ILC mature subsets in physiological conditions, suggests that “ILC-poiesis” may be important in the context of hematopoietic stem cell transplantation (HSCT). Indeed, in HSCT the conditioning regimen (chemotherapy and radiotherapy) and Graft vs Host Disease (GvHD) may cause severe damages to mucosal tissues. Therefore, it is conceivable that rapid reconstitution of the hILC compartment may be beneficial in HSCT, by promoting mucosal tissue repair/regeneration and providing protection from opportunistic infections. In this review, we will summarize the evidence for a role of hILCs in allogenic HSCT for the treatment of hematological malignancies in all its steps, from the preparative regimen to the immune reconstitution in the recipient. The protective properties of hILCs at the mucosal barrier interfaces make them an attractive target to exploit in future cellular therapies aimed at improving allogenic HSCT outcome.

Pre-transplant myeloid and immune suppression, upfront plerixafor mobilization and post-transplant cyclophosphamide: novel strategy for haploidentical transplant in sickle cell disease

Allogenic hematopoietic stem cell transplant is the only curative option for symptomatic sickle cell disease (SCD). HLA haploidentical related donor transplants are associated with high graft failure rates. We conceptualized a novel protocol (APOLLO protocol) using pre-transplant immune and myelosuppression (PTIS) using fludarabine, cyclophosphamide, and dexamethasone followed by augmented John Hopkins protocol by adding thiotepa to conditioning. Twenty-five consecutive patients suffering from symptomatic SCD were enrolled into the study. We added upfront plerixafor to granulocyte colony stimulating factor (GCSF) for mobilization of healthy donors. Graft versus host disease (GvHD) prophylaxis was done using post-transplant cyclophosphamide, sirolimus, and mycophenolate mofetil. Graft failure was not seen in any of our patients. Five patients developed acute grade II/IV GvHD (4 classical acute, 1 late onset), 3 had limited chronic GvHD. Out of 25 evaluable patients, 22 are alive and disease free, making an overall survival (OS) and disease-free survival (DFS) of 88% with a median follow up of 485 days (range 198-802). T-cell-replete haploidentical transplant with PTIS, augmented John Hopkins conditioning and plerixafor based mobilization is a safe and effective way of treating patients suffering from SCD with minimal or no risk of graft failure and acceptable GvHD rates.

Unrelated donor vs HLA-haploidentical α/β T-cell- and B-cell-depleted HSCT in children with acute leukemia

Traditionally, hematopoietic stem cell transplantation (HSCT) from both HLA-matched related and unrelated donors (UD) has been used for treating children with acute leukemia (AL) in need of an allograft. Recently, HLA-haploidentical HSCT after αβ T-cell/B-cell depletion (αβhaplo-HSCT) was shown to be effective in single-center studies. Here, we report the first multicenter retrospective analysis of 127 matched UD (MUD), 118 mismatched UD (MMUD), and 98 αβhaplo-HSCT recipients, transplanted between 2010 and 2015, in 13 Italian centers. All these AL children were transplanted in morphological remission after a myeloablative conditioning regimen. Graft failure occurred in 2% each of UD-HSCT and αβhaplo-HSCT groups. In MUD vs MMUD-HSCT recipients, the cumulative incidence of grade II to IV and grade III to IV acute graft-versus-host disease (GVHD) was 35% vs 44% and 6% vs 18%, respectively, compared with 16% and 0% in αβhaplo-HSCT recipients (P < .001). Children treated with αβhaplo-HSCT also had a significantly lower incidence of overall and extensive chronic GVHD (P < .01). Eight (6%) MUD, 32 (28%) MMUD, and 9 (9%) αβhaplo-HSCT patients died of transplant-related complications. With a median follow-up of 3.3 years, the 5-year probability of leukemia-free survival in the 3 groups was 67%, 55%, and 62%, respectively. In the 3 groups, chronic GVHD-free/relapse-free (GRFS) probability of survival was 61%, 34%, and 58%, respectively (P < .001). When compared with patients given MMUD-HSCT, αβhaplo-HSCT recipients had a lower cumulative incidence of nonrelapse mortality and a better GRFS (P < .001). These data indicate that αβhaplo-HSCT is a suitable therapeutic option for children with AL in need of transplantation, especially when an allele-matched UD is not available.

Immune-Phenotyping and Transcriptomic Profiling of Peripheral Blood Mononuclear Cells From Patients With Breast Cancer: Identification of a 3 Gene Signature Which Predicts Relapse of Triple Negative Breast Cancer

Background: Interactions between the immune system and tumors are highly reciprocal in nature, leading to speculation that tumor recurrence or therapeutic resistance could be influenced or predicted by immune events that manifest locally, but can be detected systemically.

Methods: Multi-parameter flow cytometry was used to examine the percentage and phenotype of natural killer (NK) cells, myeloid-derived suppressor cells (MDSCs), monocyte subsets and regulatory T (Treg) cells in the peripheral blood of of 85 patients with breast cancer (50 of whom were assessed before and after one cycle of anthracycline-based chemotherapy), and 23 controls. Transcriptomic profiles of peripheral blood mononuclear cells (PBMCs) in 23 patients were generated using a NanoString gene profiling platform.

Results: An increased percentage of immunosuppressive cells such as granulocytic MDSCs, intermediate CD14⁺⁺CD16⁺ monocytes and CD127^negCD25^highFoxP3⁺ Treg cells was observed in patients with breast cancer, especially patients with stage 3 and 4 disease, regardless of ER status. Following neoadjuvant chemotherapy, B cell numbers decreased significantly, whereas monocyte numbers increased. Although chemotherapy had no effect on the percentage of Treg, MDSC and NK cells, the expression of inhibitory receptors CD85j, LIAR and NKG2A and activating receptors NKp30 and NKp44 on NK cells increased, concomitant with a decreased expression of NKp46 and DNAM-1 activating receptors. Transcriptomic profiling revealed a distinct group of 3 patients in the triple negative breast cancer (TNBC) cohort who expressed high levels of mRNA encoding genes predominantly involved in inflammation. The analysis of a large transcriptomic dataset derived from the tumors of patients with TNBC revealed that the expression of CD163, CXCR4, THBS1 predicted relapse-free survival.

Conclusions: The peripheral blood immunome of patients with breast cancer is influenced by the presence and stage of cancer, but not by molecular subtypes. Furthermore, immune profiling coupled with transcriptomic analyses of peripheral blood cells may identify patients with TNBC that are at risk of relapse after chemotherapy.

Differences in Cellular Composition of Peripheral Blood Stem Cell Grafts from Healthy Stem Cell Donors Mobilized with Either Granulocyte Colony-Stimulating Factor (G-CSF) Alone or G-CSF and Plerixafor

This study was conducted to characterize and compare peripheral blood stem cell grafts from healthy donors who underwent granulocyte colony-stimulating factor (G-CSF) mobilization and subsequently received 1 dose of plerixafor after insufficient stem cell yields were achieved at the first apheresis. Aliquots from 35 donors were collected from the first apheresis after mobilization with G-CSF alone and from the second apheresis after additional plerixafor administration. Samples were freshly analyzed for cellular subsets by 8-color flow cytometry. Leukapheresis samples mobilized with additional plerixafor showed a significant increase of total nucleated cells, including B cells, CD4⁺ and CD8⁺ T cells, and CD34⁺ hematopoietic stem and progenitor cells. Absolute numbers of plasmacytoid dendritic cells were also significantly increased, whereas no changes were detected for myeloid dendritic cells. Furthermore, absolute numbers of regulatory T cells increased, with naive CD45RA⁺ regulatory T cells showing the highest rise. Finally, strikingly higher numbers of myeloid-derived suppressor cells were detected in the plerixafor and G-CSF-mobilized graft. The mobilization of peripheral stem cells in healthy donors with G-CSF and plerixafor led to a significant difference in cellular graft composition compared with G-CSF alone. The clinical impact of the different cell composition for the graft recipient warrants further clinical investigation.

Higher CD45RA+ Regulatory T Cells in the Graft Improves Outcome in Younger Patients Undergoing T Cell-Replete Haploidentical Transplantation: Where Donor Age Matters

To understand the phenomenon of early alloreactivity (EA) in younger children undergoing post-transplantation cyclophosphamide (PTCy)-based haploidentical transplantation, we studied the graft composition and the immune reconstitution in 32 consecutive patients (aged 2 to 25 years) undergoing PTCy and T cell costimulation blockade based peripheral blood stem cell transplantation with emphasis on CD45RA⁺ subset of regulatory T cells (Tregs). All but 1 engrafted, and 14 patients experienced EA (acute graft-versus-host disease grades II to IV, n = 8; and post-transplantation hemophagocytic syndrome, n = 6) with a cumulative incidence of 43.7%; 42% developed mild chronic graft-versus-host disease. The overall survival was 70.2% with a nonrelapse mortality of 16.8% at a median of 19 months. Age < 10 years, donor age > 45 years, and poor recovery of Tregs correlated with EA. Not Tregs but higher CD45RA⁺ Tregs in the graft was associated with less EA (11.7% versus 32.5%, P = .0001). Higher donor age correlated with a lower CD45RA⁺ Tregs in the graft (P = .01). However, only higher CD45RA⁺ Treg percentage in the graft favorably impacted EA as well as nonrelapse mortality and overall survival. Our study demonstrates a critical role for CD45RA⁺ Tregs in determining EA and outcome after PTCy-based haploidentical peripheral blood stem cell transplantation, and the age-related physiologic decline in this population might be responsible for adverse impact of donor age.

Impact of Single-Dose Plerixafor as an Adjunct to Granulocyte Colony-Stimulating Factor-Based Peripheral Blood Stem Cell Mobilization on the Graft Composition and Outcome for T Cell-Replete Haploidentical Peripheral Blood Stem Cell Transplantation with Post-Transplantation Cyclophosphamide: A Comparative Study

We conducted a prospective study on T and natural killer (NK) cell subset composition of graft and transplant outcomes in T cell-replete haploidentical transplantation with a single dose of subcutaneous plerixafor (Px) added to granulocyte colony-stimulating factor (G-CSF)-based mobilization in allogeneic donors to collect 10 × 10⁶/kg CD34⁺ hematopoietic stem cells (HSCs) at single apheresis. Twnety-six donors received G-CSF + Px and 25 G-CSF alone for mobilization. Despite significantly lower peripheral blood (PB) CD34⁺ HSCs on day 4 in the G-CSF + Px group (33 [range, 6-47] cells/µL versus 81 [range, 50-168] cells/µL in the G-CSF group; P = .0001), PB CD34⁺ HSC count (median 136 versus 139 cells/µL) on day 5 as well as that in the graft (2.7 versus 2.3 × 10⁶/mL, P = .1) were comparable between the 2 groups. The total nucleated cell count was higher (3.4 versus 3.1 × 10⁸/mL, P = .05), but CD4⁺ T cells (2.3 versus 2.7 × 10⁷/mL, P = .09) were lower in the G-CSF group with mobilization of regulatory T cells being similar. NK cells were skewed toward the CD56⁺/16^- subset in both groups, varying significantly from the steady-state NK subset ratio in PB. The time to engraftment, incidences of acute and chronic graft-versus-host disease, nonrelapse mortality, and overall survival were also similar. Addition of single-dose Px to G-CSF mobilization improves CD34 recovery and does not significantly alter the T and NK cell composition of the graft, including regulatory T cells, with no adverse impact on transplant outcomes.

Outcome of children with acute leukemia given HLA-haploidentical HSCT after αβ T-cell and B-cell depletion

Children with AL given haplo-HSCT after αβ T- and B-cell depletion are exposed to a low risk of acute and chronic GVHD and NRM. The leukemia-free, GVHD-free survival of patients given this type of allograft is comparable to that of HLA-matched donor HSCT recipients.

T-Cell Manipulation Strategies to Prevent Graft-Versus-Host Disease in Haploidentical Stem Cell Transplantation

Allogeneic haematopoietic stem cell transplantation (HSCT) from an human leukocyte antigen (HLA)-identical donor can be curative for eligible patients with non-malignant and malignant haematological disorders. HSCT from alternative donor sources, such as HLA-mismatched haploidentical donors, is increasingly considered as a viable therapeutic option for patients lacking HLA-matched donors. Initial attempts at haploidentical HSCT were associated with vigorous bidirectional alloreactivity, leading to unacceptably high rates of graft rejection and graft-versus-host disease (GVHD). More recently, new approaches for mitigating harmful T-cell alloreactivity that mediates GVHD, while preserving the function of tumour-reactive natural killer (NK) cells and γδ T cells, have led to markedly improved clinical outcomes, and are successfully being implemented in the clinic. This article will provide an update on in vitro strategies and in vivo approaches aimed at preventing GVHD by selectively manipulating key components of the adaptive immune response, such as T-cell receptor (TCR)-αβ T cells and CD45RA-expressing naive T cells.

Preservation of Antigen-Specific Functions of αβ T Cells and B Cells Removed from Hematopoietic Stem Cell Transplants Suggests Their Use As an Alternative Cell Source for Advanced Manipulation and Adoptive Immunotherapy

Hematopoietic stem cell transplantation is standard therapy for numerous hematological diseases. The use of haploidentical donors, sharing half of the HLA alleles with the recipient, has facilitated the use of this procedure as patients can rely on availability of a haploidentical donor within their family. Since HLA disparity increases the risk of graft-versus-host disease, T-cell depletion has been used to remove alloreactive lymphocytes from the graft. Selective removal of αβ T cells, which encompass the alloreactive repertoire, combined with removal of B cells to prevent EBV-related lymphoproliferative disease, proved safe and effective in clinical studies. Depleted αβ T cells and B cells are generally discarded as by-products. Considering the possible use of donor T cells for donor lymphocyte infusions or for generation of pathogen-specific T cells as mediators of graft-versus-infection effect, we tested whether cells in the discarded fractions were functionally intact. Response to alloantigens and to viral antigens comparable to that of unmanipulated cells indicated a functional integrity of αβ T cells, in spite of the manipulation used for their depletion. Furthermore, B cells proved to be efficient antigen-presenting cells, indicating that antigen uptake, processing, and presentation were fully preserved. Therefore, we propose that separated αβ T lymphocytes could be employed for obtaining pathogen-specific T cells, applying available methods for positive selection, which eventually leads to indirect allodepletion. In addition, these functional T cells could undergo additional manipulation, such as direct allodepletion or genetic modification.

Acute exercise mobilizes hematopoietic stem and progenitor cells and alters the mesenchymal stromal cell secretome

Transplantation of hematopoietic stem and progenitor cells (HSPC), collected from peripheral blood, is the primary treatment for many hematological malignancies; however, variable collection efficacy with current protocols merits further examination into factors responsible for HSPC mobilization. HSPCs primarily reside within the bone marrow and are regulated by mesenchymal stromal cells (MSC). Exercise potently and transiently mobilizes HSPCs from the bone marrow into peripheral circulation. Thus the purpose of the present study was to evaluate potential factors in the bone marrow responsible for HSPC mobilization, investigate potential sites of HSPC homing, and assess changes in bone marrow cell populations following exercise. An acute exercise bout increased circulating HSPCs at 15 min (88%, P < 0.001) that returned to baseline at 60 min. Gene expression for HSPC homing factors (CXCL12, vascular endothelial growth factor-a, and angiopoietin-1) were increased at 15 min in skeletal muscle and HSPC content was increased in the spleen 48 h postexercise (45%, P < 0.01). Acute exercise did not alter HSPCs or MSCs quantity in the bone marrow; however, proliferation of HSPCs (40%, P < 0.001), multipotent progenitors (40%, P < 0.001), short-term hematopoietic stem cells (61%, P < 0.001), long-term hematopoietic stem cells (55%, P = 0.002), and MSCs (20%, P = 0.01) increased postexercise. Acute exercise increased the content of the mobilization agent granulocyte-colony stimulating factor, as well as stem cell factor, interleukin-3, and thrombopoeitin in conditioned media collected from bone marrow stromal cells 15 min postexercise. These findings suggest that the MSC secretome is responsible for HSPC mobilization and proliferation; concurrently, HSPCs are homing to extramedullary sites following exercise.

Mechanisms for T cell tolerance induced with granulocyte colony-stimulating factor

Granulocyte colony-stimulating factor (G-CSF) has been widely accepted as a mediator of T cell tolerance. The immune modulatory effect of G-CSF on T cells is believed to be mediated exclusively through other effector cells, such as monocytes, tolerogenic dendritic cells (DC), and myeloid-derived suppressor cells. Recent advances confirmed the direct effects of G-CSF in inducing immune tolerance of T cells through the G-CSF-G-CSF receptor pathway and related molecular mechanisms. This review aims to summarize the findings associated with the direct and indirect mechanisms for T cell tolerance induced with G-CSF. The role of G-CSF in preventing graft-versus-host disease (GVHD) and in treating autoimmune diseases (ADs) is also discussed. It is conceivable that G-CSF and immune cell compositions, such as tolerogenic DC and CD4(+)CD25(+)Foxp3(+) T cells, modulated by G-CSF could become an integral part of the immunomodulatory therapies against GVHD and ADs in the future.

Plasmacytoid dendritic cells in allogeneic hematopoietic cell transplantation: benefit or burden?

Plasmacytoid dendritic cells (pDCs) bridge innate and adaptive immune responses and have important roles in hematopoietic engraftment, GvHD and graft-versus-leukemia responses following allogeneic hematopoietic cell transplantation (HCT). In addition, pDCs mediate antiviral immunity, particularly as they are the body's primary cellular source of type I interferon. Given their pleiotropic roles, pDCs have emerged as cells that critically impact transplant outcomes, including overall survival. In this article, we will review the pre-clinical and clinical literature, supporting the crucial roles that pDCs assume as key immune effector cells during HCT.

Revving up Natural Killer Cells and Cytokine-Induced Killer Cells Against Hematological Malignancies

Natural killer (NK) cells belong to innate immunity and exhibit cytolytic activity against infectious pathogens and tumor cells. NK-cell function is finely tuned by receptors that transduce inhibitory or activating signals, such as killer immunoglobulin-like receptors, NK Group 2 member D (NKG2D), NKG2A/CD94, NKp46, and others, and recognize both foreign and self-antigens expressed by NK-susceptible targets. Recent insights into NK-cell developmental intermediates have translated into a more accurate definition of culture conditions for the in vitro generation and propagation of human NK cells. In this respect, interleukin (IL)-15 and IL-21 are instrumental in driving NK-cell differentiation and maturation, and hold great promise for the design of optimal NK-cell culture protocols. Cytokine-induced killer (CIK) cells possess phenotypic and functional hallmarks of both T cells and NK cells. Similar to T cells, they express CD3 and are expandable in culture, while not requiring functional priming for in vivo activity, like NK cells. CIK cells may offer some advantages over other cell therapy products, including ease of in vitro propagation and no need for exogenous administration of IL-2 for in vivo priming. NK cells and CIK cells can be expanded using a variety of clinical-grade approaches, before their infusion into patients with cancer. Herein, we discuss GMP-compliant strategies to isolate and expand human NK and CIK cells for immunotherapy purposes, focusing on clinical trials of adoptive transfer to patients with hematological malignancies.

Plerixafor on demand in ten healthy family donors as a rescue strategy to achieve an adequate graft for stem cell transplantation

BACKGROUND

In allogeneic hematopoietic stem cell (HSC) transplantation, the collection of an appropriate number of HSCs while maintaining a high level of safety for healthy donors is fundamental. Inadequate HSC mobilization can be seen with the standard use of granulocyte-colony-stimulating (G-CSF). Plerixafor (PL) is a chemokine receptor CXC Type 4-stromal-derived factor 1 inhibitor; its HSC-mobilizing properties are synergistic with G-CSF in poor mobilizing patients. The use of PL as adjuvant or alternative to G-CSF in healthy donors has shown a good safety profile but is so far off-label.

STUDY DESIGN AND METHODS

We report 10 healthy HSC donors treated with PL because of insufficient response to G-CSF alone or contraindication to G-CSF. Eight donors did not mobilize enough CD34+ cells with G-CSF alone because poor mobilizers or because insufficient HSCs were harvested according to the clinical need of the patient; in two cases G-CSF administration and marrow harvest were unfeasible or contraindicated in the donor.

RESULTS

The use of PL for mobilization increased the number of circulating CD34+ cells by 2.8-fold and the CD34+/kg collection by 3.0-fold. Only mild adverse events were reported (bone pain or discomfort) and not univocally attributable to PL. Rate of engraftment and graft-versus-host disease were similar to those seen in recipients of grafts from G-CSF only-mobilized donors.

CONCLUSION

We exposed 10 allogeneic donors to mobilization with PL. PL was well tolerated in all cases and ensured procurement of an adequate graft for transplantation resulting in a normal hematopoietic engraftment.

Mobilized peripheral blood grafts include more than hematopoietic stem cells: the immunological perspective

Although stem cell mobilization has been performed for more than 20 years, little is known about the effects of mobilizing agents on apheresis composition and the impact of graft cell subsets on patients' outcome. With the increasing use of plerixafor and the inclusion of poor mobilizers in autologous transplant procedures, new parameters other than CD34(+) stem cell dose are emerging; plerixafor seems to mobilize more primitive CD34(+)/CD38(-) stem cells compared with G-CSF, but their correlation with stable hematopoietic engraftment is still obscure. Immune recovery is as crucial as hematopoietic reconstitution, and higher T and natural killer cells infused within the graft have been correlated with better outcome in autologous transplant; recent studies showed increased mobilization of immune effectors with plerixafor compared with G-CSF, but further data are needed to clarify the clinical impact of these findings. In the allogeneic setting, much evidence suggests that mobilized T-cell alloreactivity is tempered by G-CSF, probably with the mediation of dendritic cells, even though no clear correlation with GVL and GVHD has been found. Plerixafor is not approved in healthy donors yet; early data suggest it might mobilize a GVHD protective balance of immune effectors, but further studies are needed to define its role in allogeneic transplant.