Individualization of Hematopoietic Stem Cell Transplantation Using Alpha/Beta T-Cell Depletion

Cellular Strategies for Separating GvHD from GvL in Haploidentical Transplantation

GvHD still remains, despite the continuous improvement of transplantation platforms, a fearful complication of transplantation from allogeneic donors. Being able to separate GvHD from GvL represents the greatest challenge in the allogeneic transplant setting. This may be possible through continuous improvement of cell therapy techniques. In this review, current cell therapies are taken into consideration, which are based on the use of TCR alpha/beta depletion, CD45RA depletion, T regulatory cell enrichment, NK-cell-based immunotherapies, and suicide gene therapies in order to prevent GvHD and maximally amplify the GvL effect in the setting of haploidentical transplantation.

Non-Conventional Allogeneic Anti-BCMA Chimeric Antigen Receptor-Based Immune Cell Therapies for Multiple Myeloma Treatment

MM, characterized by the progressive accumulation of clonal plasma cells in bone marrow, remains a severe medical problem globally. Currently, almost all MM patients who have received standard treatments will eventually relapse. Autologous anti-BCMA CAR-T cells are one of the FDA-approved immunotherapy cell-based products for treating adults with relapsed or refractory (r/r) multiple myeloma. However, this type of CAR-T cell product has several limitations, including high costs, long manufacturing times, and possible manufacturing failure, which significantly hinder its wider application for more patients. In this review, we summarized the current development stage of applying other types of immune cells to bring the anti-BCMA CAR-T therapy from autologous to allogeneic. In general, anti-BCMA CAR gene-edited αβ T cells and CAR-Natural Killer (NK) cells are at the forefront, with multiple clinical trials ongoing, while CAR-γδ T cells and CAR-invariant Natural Killer T (iNKT) cells are still in pre-clinical studies. Other immune cells such as macrophages, B cells, and dendritic cells have been mainly developed to target other antigens and have the potential to be used to target BCMA. Nevertheless, additional regulatory requirements might need to be taken into account in developing these non-conventional allogenic anti-BCMA CAR-based cell products.

Allogeneic stem cell transplantation in the treatment of acute myeloid leukemia: An overview of obstacles and opportunities

As an important treatment for acute myeloid leukemia, allogeneic hematopoietic stem cell transplantation (allo-HSCT) plays an important role in reducing relapse and improving long-term survival. With rapid advancements in basic research in molecular biology and immunology and with deepening understanding of the biological characteristics of hematopoietic stem cells, allo-HSCT has been widely applied in clinical practice. During allo-HSCT, preconditioning, the donor, and the source of stem cells can be tailored to the patient’s conditions, greatly broadening the indications for HSCT, with clear survival benefits. However, the risks associated with allo-HSCT remain high, i.e. hematopoietic reconstitution failure, delayed immune reconstitution, graft-versus-host disease, and post-transplant relapse, which are bottlenecks for further improvements in allo-HSCT efficacy and have become hot topics in the field of HSCT. Other bottlenecks recognized in the current treatment of individuals diagnosed with acute myeloid leukemia and subjected to allo-HSCT include the selection of the most appropriate conditioning regimen and post-transplantation management. In this paper, we reviewed the progress of relevant research regarding these aspects.

Gamma delta T-cell reconstitution after allogeneic HCT: A platform for cell therapy

Allogeneic Hematopoietic stem cell transplantation (allo-HCT) is a curative platform for several hematological diseases. Despite its therapeutic benefits, the profound immunodeficiency associated with the transplant procedure remains a major challenge that renders patients vulnerable to several complications. Today, It is well established that a rapid and efficient immune reconstitution, particularly of the T cell compartment is pivotal to both a short-term and a long-term favorable outcome. T cells expressing a TCR heterodimer comprised of gamma (γ) and delta (δ) chains have received particular attention in allo-HCT setting, as a large body of evidence has indicated that γδ T cells can exert favorable potent anti-tumor effects without inducing severe graft versus host disease (GVHD). However, despite their potential role in allo-HCT, studies investigating their detailed reconstitution in patients after allo-HCT are scarce. In this review we aim to shed lights on the current literature and understanding of γδ T cell reconstitution kinetics as well as the different transplant-related factors that may influence γδ reconstitution in allo-HCT. Furthermore, we will present data from available reports supporting a role of γδ cells and their subsets in patient outcome. Finally, we discuss the current and future strategies to develop γδ cell-based therapies to exploit the full immunotherapeutic potential of γδ cells in HCT setting.

Allogeneic Chimeric Antigen Receptor Therapy in Lymphoma

The therapeutic armamentarium has significantly expanded since the approval of various CD19-targeting chimeric antigen receptor T cell (CAR-T) therapies in non-Hodgkin lymphoma (NHL). These CAR-Ts are patient-specific and require a complex, resource, and time-consuming process. While this appears promising, autologous CAR-Ts are limited due to the lack of accessibility, manufacturing delays, and variable product quality. To overcome these, allogeneic (allo) CARs from healthy donors appear appealing. These can be immediately available as “off the shelf” ready-to-use products of standardized and superior quality exempt from the effects of an immunosuppressive tumor microenvironment and prior treatments, and potentially with lower healthcare utilization using industrialized scale production. Allogeneic CARs, however, are not devoid of complications and require genomic editing, especially with αβ T cells to avoid graft versus host disease (GvHD) and allo-rejection by the recipient’s immune system. Tools for genomic editing such as TALEN and CRISPR provide promise to develop truly “off the shelf” universal CARs and further advance the field of cellular immunotherapy. Several allogeneic CARs are currently in early phase clinical trials, and preliminary data is encouraging. Longer follow-up is required to truly assess the feasibility and safety of these techniques in the patients. This review focuses on the strategies for developing allogeneic CARs along with cell sources and clinical experience thus far in lymphoma.

Optimizing Blood Stem Cell Transplants Through Cellular Engineering

Haematopoietic stem cell transplants (HSCT) are used in the treatment of blood cancers, autoimmune diseases, and metabolic disorders. Over 1.5 million transplants have been performed around the world thus far. In an attempt to enhance the efficacy of the cells used for transplantation, efforts are underway to use cellular engineering to increase cell numbers through: (1) the expansion of hematopoietic stem and progenitor cells (HSPC); (2) cellular subset selection to remove cells that cause graft-versus-host disease (GvHD), while adding back cells, which can mediate anti-tumor and anti-viral immunity; (3) the use of immune regulatory cells, such as mesenchymal stromal cells (MSC) and regulatory T cells (Tregs) to control GvHD; (4) the use of immune effector cells to mount immunological control of tumor cells before, after, or independent of blood stem cell transplants.

The Roles of γδ T Cells in Hematopoietic Stem Cell Transplantation

The αβ T-cell-depleted hematopoietic stem cell transplantation (HSCT) leads to lower relapse and better outcome, and may correlate strongly with expansion of donor-derived γδ T cells. γδ T cells play an important role in immune reconstitution and can exert a graft-versus-leukemia effect after HSCT. This review showed the recent literature on immune functions of γδ T cells after HSCT. The discrepancies between studies of γδ T cells in graft-versus-host disease may cause by its heterogeneous and various distinct subsets. And reconstitution of γδ T cells may play a potential immunoregulatory role in the infections after HSCT.

Outcomes with CD34-Selected Stem Cell Boost for Poor Graft Function after Allogeneic Hematopoietic Stem Cell Transplantation: A Systematic Review and Meta-Analysis

Poor graft function (PGF) is a life-threatening complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT) characterized by multilineage cytopenia in the absence of mixed donor chimerism (<95% donor), relapse, or severe graft-versus-host disease (GVHD). We present a systemic review and meta-analysis aimed at assessing the outcomes with CD34-selected stem cell boost (SCB) for PGF in adult allo-HSCT recipients. We screened a total of 1753 records identified from 4 databases (PubMed, Embase, Cochrane, and ClinicalTrials.gov) following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines, using the search terms "hematological malignancies," "hematopoietic stem cell transplantation," "CD34 antigen(s)," "graft failure," and "poor graft function," from the date of inception to January 2021. After excluding review, duplicate, and nonrelevant articles, we included 7 studies reporting outcomes following administration of CD34-selected SCB for PGF after allo-HSCT, including hematologic complete response (CR) and overall response rate (ORR), GVHD, and overall survival (OS). Quality evaluation was done using the National Institutes of Health quality assessment tool. Pooled analysis was done using the R 'meta' package, and proportions with 95% confidence intervals (CIs) were computed. The inter-study variance was calculated using the Der Simonian-Laird estimator. We identified 209 patients who received CD34-selected SCB for PGF after allo-HSCT. The median age was 49 years (range, 18 to 69 years), and 61% were men. Primary graft sources included peripheral blood stem cells (72%) and bone marrow (28%). Donor types were matched sibling (37%), matched unrelated (36%), mismatched unrelated (22%), and haploidentical donors (5%). The median time from allo-HSCT to SCB was 138 days (range, 113 to 450 days). The median SCB dose was 3.45 × 10⁶ CD34 cells/kg (range, 3.1 to 4.9 × 10⁶ cells/kg). CR and ORR were 72% (95% CI, 63% to 79%; I² = 26%) and 80% (95% CI, 74% to 85%; I² = 0%), respectively. After a median follow-up of 42 months (range, 30 to 77 months), the actuarial survival rate was 54% (95% CI, 47% to 61%; I² = 0%). OS ranged from 80% at 1 year to 40% at 9 years. The incidences of acute and chronic GVHD after SCB were 17% (95% CI, 13% to 23%; I² = 0%) and 18% (95% CI, 8% to 34%; I² = 76%), respectively. Nonrelapse mortality was reported in 42 patients, with a pooled rate of 27% (95% CI, 17% to 40; I² = 59%), and death due to relapse was reported in 25 patients, with a pooled rate of 17% (95% CI, 11% to 23%; I² = 0%). Our data show that CD34-selected SCB improves outcomes after PGF post allo-HSCT with an acceptable toxicity profile. The literature lacks high-quality randomized evidence, and there remains an unmet need for prospective studies to address the optimal dosing and manipulation of SCB. © 2021 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

Effect of alemtuzumab-based T-cell depletion on graft compositional change in vitro and immune reconstitution early after allogeneic stem cell transplantation

BACKGROUND AIMS

To reduce the risk of graft-versus-host disease (GVHD) after allogeneic stem cell transplantation (alloSCT), T-cell depletion (TCD) of grafts can be performed by the addition of alemtuzumab (ALT) "to the bag" (in vitro) before transplantation. In this prospective study, the authors analyzed the effect of in vitro incubation with 20 mg ALT on the composition of grafts prior to graft infusion. Furthermore, the authors assessed whether graft composition at the moment of infusion was predictive for T-cell reconstitution and development of GVHD early after TCD alloSCT.

METHODS

Sixty granulocyte colony-stimulating factor-mobilized stem cell grafts were obtained from ≥9/10 HLA-matched related and unrelated donors. The composition of the grafts was analyzed by flow cytometry before and after in vitro incubation with ALT. T-cell reconstitution and incidence of severe GVHD were monitored until 12 weeks after transplantation.

RESULTS

In vitro incubation of grafts with 20 mg ALT resulted in an initial median depletion efficiency of T-cell receptor (TCR) α/β T cells of 96.7% (range, 63.5-99.8%), followed by subsequent depletion in vivo. Graft volumes and absolute leukocyte counts of grafts before the addition of ALT were not predictive for the efficiency of TCR α/β T-cell depletion. CD4^pos T cells were depleted more efficiently than CD8^pos T cells, and naive and regulatory T cells were depleted more efficiently than memory and effector T cells. This differential depletion of T-cell subsets was in line with their reported differential CD52 expression. In vitro depletion efficiencies and absolute numbers of (naive) TCR α/β T cells in the grafts after ALT incubation were not predictive for T-cell reconstitution or development of GVHD post- alloSCT.

CONCLUSIONS

The addition of ALT to the bag is an easy, fast and generally applicable strategy to prevent GVHD in patients receiving alloSCT after myeloablative or non-myeloablative conditioning because of the efficient differential depletion of donor-derived lymphocytes and T cells.

Impact of γδ T cells on clinical outcome of hematopoietic stem cell transplantation: systematic review and meta-analysis

Allogeneic hematopoietic stem cell transplantation (HSCT) using αβ T-/B-cell-depleted grafts recently emerged as a transplant strategy and highlighted the potential role of γδ T cells on HSCT outcomes. Our aim was to scrutinize available evidence of γδ T-cell impact on relapse, infections, survival, and acute graft-versus-host disease (aGVHD). We performed a systematic review and meta-analysis of studies assessing γδ T cells in HSCT. We searched PubMed, Web of Science, Scopus, and conference abstracts from inception to March 2019 for relevant studies. We included all studies that assessed γδ T cells associated with HSCT. Data were extracted independently by 2 investigators based on strict selection criteria. A random-effects model was used to pool outcomes across studies. Primary outcome was disease relapse. We also assessed infections, survival, and aGVHD incidence. The review was registered with PROSPERO (CRD42019133344). Our search returned 2412 studies, of which 11 (919 patients) were eligible for meta-analysis. Median follow-up was 30 months (interquartile range, 22-32). High γδ T-cell values after HSCT were associated with less disease relapse (risk ratio [RR], 0.58; 95% confidence interval [95% CI], 0.40-0.84; P = .004; I2 = 0%), fewer viral infections (RR, 0.59; 95% CI, 0.43-0.82; P = .002; I2 = 0%) and higher overall (HR, 0.28; 95% CI, 0.18-0.44; P < .00001; I2 = 0%) and disease-free survivals (HR 0.29; 95% CI, 0.18-0.48; P < .00001; I2 = 0%). We found no association between high γδ T-cell values and aGVHD incidence (RR, 0.72; 95% CI, 0.41-1.27; P = .26; I2 = 0%). In conclusion, high γδ T cells after HSCT is associated with a favorable clinical outcome but not with aGVHD development, suggesting that γδ T cells have a significant effect on the success of HSCT. This study was registered with PROSPERO as #CRD42019133344.