Clinical impact of NK-cell reconstitution after reduced intensity conditioned unrelated cord blood transplantation in patients with acute myeloid leukemia: analysis of a prospective phase II multicenter trial on behalf of the Société Française de Greffe de Moelle Osseuse et Thérapie Cellulaire and Eurocord

Immunology of cord blood T-cells favors augmented disease response during clinical pediatric stem cell transplantation for acute leukemia

Allogeneic hematopoietic stem cell transplantation (HSCT) has been an important and efficacious treatment for acute leukemia in children for over 60 years. It works primarily through the graft-vs.-leukemia (GVL) effect, in which donor T-cells and other immune cells act to eliminate residual leukemia. Cord blood is an alternative source of stem cells for transplantation, with distinct biological and immunological characteristics. Retrospective clinical studies report superior relapse rates with cord blood transplantation (CBT), when compared to other stem cell sources, particularly for patients with high-risk leukemia. Xenograft models also support the superiority of cord blood T-cells in eradicating malignancy, when compared to those derived from peripheral blood. Conversely, CBT has historically been associated with an increased risk of transplant-related mortality (TRM) and morbidity, particularly from infection. Here we discuss clinical aspects of CBT, the unique immunology of cord blood T-cells, their role in the GVL effect and future methods to maximize their utility in cellular therapies for leukemia, honing and harnessing their antitumor properties whilst managing the risks of TRM.

Role of NK cells in cord blood transplantation and their enhancement by the missing ligand effect of the killer-immunoglobulin like receptor

Natural killer (NK) cells are the first lymphocytes reconstituted after allogenic hematopoietic stem cell transplantation (HSCT). Especially, in cord blood transplantation (CBT), the increase in the number of NK cells is sustained for a long period. Although there are conflicting results, many studies show that early reconstitution of NK cells is associated with favorable CBT outcomes, suggesting that maximizing NK cell functions could improve the CBT outcome. Killer immunoglobulin-like receptors (KIRs) include inhibitory and stimulatory receptors, which can regulate NK-cell activity. Because some of the KIRs have HLA class I as their ligand, the KIR—ligand interaction on NK cells can be lost in some cases of CBT, which results in the activation of NK cells and alters HSCT outcome. Thus, effects of KIR–ligand mismatch under various conditions have been widely examined; however, the results have been controversial. Among such studies, those using the largest number of CBTs showed that HLA—C2 (KIR2DL1—ligand) mismatches have a favorable effect on the relapse rate and overall survival only when the CBT used methotrexate for graft-versus-host disease prophylaxis. Another study suggested that KIR—ligand mismatch is involved in reducing the relapse of acute myeloid leukemia, mediated by reactivation of cytomegalovirus. These results indicate that activation of NK cells by KIR—ligand mismatch may have favorable effects on CBT outcomes and could help enhance the NK-cell function.

CAR-NK Cells: A Chimeric Hope or a Promising Therapy?

Simple Summary

In recent years, innovative immunotherapy-based treatments have paved the way for a new approach to hematological malignancies. Instead of conventional chemotherapy, T cells have been genetically engineered to detect—and engage their cytotoxicity against—tumor cells, and their success story is astonishing. However, many setbacks—including insufficient efficacy, deficient autologous source, heavy side effects, and a hefty price—limit their use. A promising alternative could be chimeric antigen receptor NK cells, which possess interesting cytotoxicity and minimal graft-versus-host disease risk. In this article, we review the possible sources, the development techniques, the potential advantages, and the challenges faced in the field of chimeric antigen receptor NK cells.

Abstract

Immunotherapy with chimeric antigen receptor-engineered T cells (CAR-T) has revolutionized the treatment landscape of relapsed/refractory B-cell malignancies. Nonetheless, the use of autologous T cells has certain limitations, including the variable quality and quantity of collected effector T cells, extended time of cell processing, limited number of available CAR cells, toxicities, and a high cost. Thanks to their powerful cytotoxic capabilities, with proven antitumor effects in both haploidentical hematopoietic stem cell transplantation and adoptive cell therapy against solid tumors and hematological malignancies, Natural Killer cells could be a promising alternative. Different sources of NK cells can be used, including cellular lines, cord blood, peripheral blood, and induced pluripotent stem cells. Their biggest advantage is the possibility of using them in an allogeneic context without major toxic side effects. However, the majority of the reports on CAR-NK cells concern preclinical or early clinical trials. Indeed, NK cells might be more difficult to engineer, and the optimization and standardization of expansion and transfection protocols need to be defined. Furthermore, their short persistence after infusion is also a major setback. However, with recent advances in manufacturing engineered CAR-NK cells exploiting their cytolytic capacities, antibody-dependent cellular cytotoxicity (ADCC), and cytokine production, “off-the-shelf” allogeneic CAR-NK cells can provide a great potential in cancer treatments.

[Allogeneic CAR-NK cells: A promising alternative to autologous CAR-T cells - State of the art, sources of NK cells, limits and perspectives]

Immunotherapy with chimeric antigen receptor engineered-T cells (CAR-T) has revolutionized the landscape of treatment of relapsed or refractory B-cell. However, the use of autologous T cells has limitations: variable quality of collected effector T cells, duration of the process sometimes incompatible with uncontrolled hemopathy, limited number of available CAR cells, sometimes fatal toxicities, extremely high cost. Natural Killer (NK) cells are an interesting alternative to T cells. NK cells are very powerful cytotoxic effectors that have demonstrated an anti-tumor effect after haploidentical hematopoietic stem cells transplantation or in adoptive cell therapy against a number of solid or hematological tumors. Mainly, they can be used in allogeneic situations without causing major toxic side effects. The sources of NK cells are multiple: cell line, cord blood, peripheral blood, induced pluripotent stem cells. Recent advances in manufacturing engineered CAR-NK cells make it possible to promote antibody-dependent cell-mediated cytotoxicity (ADCC), as well as the activation and persistence of these cells, notably via the cytokine Il-15. The majority of the reports on CAR-NK cells concern pre-clinical or early clinical trials. However, the many advantages of "off-the-shelf" allogeneic CAR-NK cells provide great potential in cancer treatments.

Altered effect of killer immunoglobulin-like receptor-ligand mismatch by graft versus host disease prophylaxis in cord blood transplantation

The role of killer immunoglobulin-like receptor-ligand mismatch (KIR-ligand mismatch) between donors and recipients undergoing cord blood transplantation (CBT) is controversial. If each immunosuppressant differently affects natural killer (NK) cell function, the effect of KIR-ligand mismatch may be altered depending on the type of graft versus host disease (GVHD) prophylaxis. To verify this hypothesis, the difference in the effect of KIR-ligand mismatch was retrospectively assessed between patients who received CBT for acute leukemia, myelodysplastic syndrome, or chronic myeloid leukemia, as well as GVHD prophylaxis comprising tacrolimus plus methotrexate (MTX) or mycophenolate mofetil (MMF). In the MMF group (n = 1363), KIR-ligand mismatch augmented the incidence of non-relapse mortality (NRM; hazard ratio [HR], 1.40; P = 0.008), which worsened overall survival (OS; HR, 1.30, P = 0.0077). In the analysis of each KIR-ligand mismatch type, HLA-C2 mismatch had a favorable effect on relapse incidence (HR, 0.56; P = 0.0043) and OS (HR, 0.72; P = 0.037) only in the MTX group. In the MMF group, HLA-A3/A11 mismatch worsened NRM (HR, 1.93; P < 0.001) and OS (HR, 1.48; P = 0.014). These results imply that the effects of KIR-ligand mismatch differ with the type of GVHD prophylaxis and that assessing the KIR-ligand mismatch status is important for CBT.

Reduced leukemia relapse through cytomegalovirus reactivation in killer cell immunoglobulin-like receptor-ligand-mismatched cord blood transplantation

Cytomegalovirus (CMV) reactivation in cord blood transplantation (CBT) may result in the proliferation and maturation of natural killer (NK) cells. Similarly, a mismatch of the killer cell immunoglobulin-like receptor (KIR)-ligand induces NK cell activation. Therefore, if CMV reactivation occurs in the presence of KIR-ligand mismatch, it might improve CBT outcomes. We assessed the difference in the effect of CMV reactivation in the presence of KIR-ligand mismatch on disease relapse in the graft-versus-host direction. A total of 2840 patients with acute myeloid leukemia, acute lymphoblastic leukemia, myelodysplastic syndrome, and chronic myeloid leukemia were analyzed. Among those with a HLA-Bw4/A3/A11 (KIR3DL-ligand) mismatch, CMV reactivation up to 100 days following CBT had a favorable impact on relapse (18.9% vs. 32.9%, P = 0.0149). However, this effect was not observed in cases without the KIR3DL-ligand mismatch or in those with or without a HLA-C1/C2 (KIR2DL-ligand) mismatch. The multivariate analysis suggested that CMV reactivation had a favorable effect on relapse only in cases with a KIR3DL-ligand mismatch (hazard ratio 0.54, P = 0.032). Moreover, the interaction effect between CMV reactivation and KIR3DL-ligand mismatch on relapse was significant (P = 0.039). Thus, our study reveals the association between KIR-ligand mismatches and CMV reactivation, which will enhance CBT outcomes.

Robust CD4+ T-cell recovery in adults transplanted with cord blood and no antithymocyte globulin

Quality of immune reconstitution after cord blood transplantation (CBT) without antithymocyte globulin (ATG) in adults is not established. We analyzed immune recovery in 106 engrafted adult CBT recipients (median age 50 years [range 22-70]) transplanted for hematologic malignancies with cyclosporine/mycophenolate mofetil immunoprophylaxis and no ATG. Patients were treated predominantly for acute leukemia (66%), and almost all (96%) underwent myeloablation. Recovery of CD4+ T cells was faster than CD8+ T cells with median CD4+ T-cell counts exceeding 200/mm3 at 4 months. Early post-CBT, effector memory (EM), and central memory cells were the most common CD4+ subsets, whereas effector and EM were the most common CD8+ T-cell subsets. Naive T-cell subsets increased gradually after 6 to 9 months post-CBT. A higher engrafting CB unit infused viable CD3+ cell dose was associated with improved CD4+ and CD4+CD45RA+ T-cell recovery. Cytomegalovirus reactivation by day 60 was associated with an expansion of total, EM, and effector CD8+ T cells, but lower CD4+ T-cell counts. Acute graft-versus-host disease (aGVHD) did not significantly compromise T-cell reconstitution. In serial landmark analyses, higher CD4+ T-cell counts and phytohemagglutinin responses were associated with reduced overall mortality. In contrast, CD8+ T-cell counts were not significant. Recovery of natural killer and B cells was prompt, reaching medians of 252/mm3 and 150/mm3 by 4 months, respectively, although B-cell recovery was delayed by aGVHD. Neither subset was significantly associated with mortality. ATG-free adult CBT is associated with robust thymus-independent CD4+ T-cell recovery, and CD4+ recovery reduced mortality risk.

Dynamic Changes of Inhibitory Killer-Immunoglobulin-Like Receptors on NK Cells after Allogeneic Hematopoietic Stem Cell Transplantation: An Initial Study

Killer-immunoglobulin-like receptors (KIRs) are critical natural killer (NK) cell regulators. The expression of KIRs is a dynamic process influenced by many factors. Their ligands-HLA(Human Leukocyte Antigen) class I molecules-are expressed on all nucleated cells that keep NK cells under control. In hematopoietic stem cell transplantation (HSCT), NK cells play an essential role in relapse protection. In the presented pilot study, we characterized the dynamic expression of inhibitory KIRS (iKIRs), which protect cells against untoward lysis, in donors and patients during the first three months after HSCT using flow cytometry. The expression of all iKIRs was highly variable and sometimes correlated with patients' clinical presentation and therapy regiment. Cyclophosphamide (Cy) in the graft-versus-host disease (GvHD) prevention protocol downregulated KIR2DL1 to just 25% of the original donor value, and the FEAM (Fludarabine + Etoposid + Ara-C + Melphalan) conditioning protocol reduced KIR2DL3. In lymphoid neoplasms, there was a slightly increased KIR2DL3 expression compared to myeloid malignancies. Additionally, we showed that the ex vivo activation of NK cells did not alter the level of iKIRs. Our study shows the influence of pre- and post-transplantation protocols on iKIR expression on the surface of NK cells and the importance of monitoring their cell surface.

High incidence but low mortality of EBV-reactivation and PTLD after alloHCT using ATG and PTCy for GVHD prophylaxis

We explore risk factors and impacts of post-transplant EBV-Reactivation (EBV-R) and PTLD in 270 patients that underwent RIC alloHCT using ATG-PTCy and cyclosporine for GVHD prophylaxis. Twenty-five (12%) patients had probable (n = 7) or proven (n = 18) PTLD. Patients were managed with reduction of immunosuppression and 22 with weekly rituximab (375 mg/m² IV). ORR was 84%; 8 (32%) recipients died, and one-year OS and NRM of patients with PTLD was 59.7% and 37%, respectively. One hundred seventy-two (63.7%) recipients had EBV-R. One-year OS and RFS of patients with EBV-R were 68.2% and 60.6%, and of EBV-Negative patients were 62.1% and 50.1%, respectively. High incidence but low mortality of EBV-R and PTLD was documented. EBV-R induced a protective effect on RFS in multivariable analysis (HR 0.91, p = .011). Therefore, EBV-R may have a protective effect on RFS in this setting. Further research is necessary to evaluate the interplay of EBV-R, immune reconstitution, and post-transplant outcomes.

Impact of graft sources on immune reconstitution and survival outcomes following allogeneic stem cell transplantation

We evaluated the kinetics of immune reconstitution (IR) after allogeneic hematopoietic cell transplantation (HSCT) and analyzed the clinical effect of IR on posttransplant outcomes. Absolute lymphocyte and its subset counts were measured using flow cytometry on days 28, 100, 180, 365, and 730 after transplantation in 358 adult patients who underwent HSCT between 2009 and 2017. On day 100 after HSCT, 310 surviving patients were analyzed. Bone marrow transplantation (BMT), peripheral blood stem cell transplantation (PBSCT), and cord blood transplantation (CBT) were performed in 119, 55, and 136 patients, respectively. Mature B-cell and differentiated natural killer (NK) cell subset counts significantly increased after CBT. The 2-year overall survival (OS), nonrelapse mortality (NRM), cumulative incidence of relapse, and chronic GVHD in BMT, PBSCT, and CBT were 62%, 67%, and 76% (P = .021); 17%, 17%, and 13% (P = .82); 33%, 40%, and 27% (P = .063); and 43%, 45%, and 28% (P = .025), respectively. Multivariate analysis showed that higher CD16+CD57- NK cell counts correlated with lower disease relapse, whereas higher CD20+ B-cell counts correlated with lower NRM. OS-favoring factors were higher CD16+CD57- NK cell count (hazard ratio, 0.36; 95% confidence interval, 0.22-0.60; P < .001) and CD20+ B-cell count (hazard ratio, 0.53; 95% confidence interval, 0.30-0.93; P < .001) and lower Disease Risk/HCT-Specific Comorbidity index score. Collective contribution of graft source-specific and event-related immune reconstitution might yield better posttransplant outcomes in CBT.

Immune reconstitution following umbilical cord blood transplantation: IRES, a study of UK paediatric patients

To obtain a qualitative as well as quantitative view immune reconstitution following umbilical cord blood (UCB) transplantation of paediatric patients, we utilised a broad panel of flow cytometry markers to monitor the phenotypes of lymphoid and myeloid cells at 1-12 months post-transplant. Samples were received from 46 patients with a median age of 3.3 years and survival was 76% at 1 year. Monocytes were at similar or higher median levels than in adult controls at all times tested, with a high CD16+ proportion in the first 3 months. NK cells were also within adult ranges, with a CD56++ high proportion in the first 6 months. B cell recovery was seen from 2 months in most patients and T cells from 3 months, both were delayed with anti-thymocyte globulin (ATG) treatment. CD4:CD8 ratios were high in the first 6 months, and the proportion of T cells with recent thymic emigrant and naïve phenotypes rose from 3 months. NK and plasmacytoid dendritic cell numbers remained at reduced levels in patients not surviving to 1 year. Our results can serve as a useful reference for detailed monitoring of immune reconstitution in paediatric recipients of UCB.

Favorable Effect of Cytomegalovirus Reactivation on Outcomes in Cord Blood Transplant and Its Differences Among Disease Risk or Type

The effects of cytomegalovirus (CMV) reactivation on cord blood transplant (CBT) are unclear. We assessed the effect of CMV reactivation in adult single-unit CBT without in vivo T cell depletion. Of 3147 eligible cases, 2052 were acute myeloid leukemia (AML), 643 acute lymphoblastic leukemia (ALL), and 452 myelodysplastic syndrome (MDS). CMV reactivation up to 100 days after CBT was associated with better overall survival (OS) compared with no reactivation cases (57.3% versus 52.6% at 3 years after CBT), whereas nonrelapse mortality (NRM) was increased in ALL (16.2% versus 8.9%) and standard disease risk (17.1% versus 10.6%, P = .014) by CMV reactivation. On multivariate analysis, CMV reactivation had favorable effects on relapse in MDS (hazard ratio [HR], .55; P = .044) and high disease risk (HR, .77; P = .047). In NRM, only standard-risk cases showed adverse effects of CMV reactivation (HR, 1.56; P = .026). OS was significantly improved with CMV reactivation in a subgroup of patients with AML (HR, .84; P = .044), MDS (HR, .68; P = .048), and high disease risk (HR, .81; P = .013). This favorable effect of CMV reactivation on OS in AML and high disease risk cases was maintained even after considering the effect of grades II to IV acute graft-versus-host disease. Thus, CMV reactivation might have beneficial or adverse effects on relapse, NRM, and OS, depending on the disease type or disease risk.

Clinical Relevance of Immunobiology in Umbilical Cord Blood Transplantation

Umbilical cord blood transplantation (UCBT) has been an important donor source for allogeneic hematopoietic stem cell transplantation, especially for patients who lack suitable matched donors. UCBT provides unique practical advantages, such as lower risks of graft-versus-host-disease (GVHD), permissive HLA mismatch, and ease of procurement. However, there are clinical challenges in UCBT, including high infection rates and treatment-related mortality in selected patient groups. These clinical advantages and challenges are tightly linked with cell-type specific immune reconstitution (IR). Here, we will review IR, focusing on T and NK cells, and the impact of IR on clinical outcomes. Better understanding of the immune biology in UCBT will allow us to further advance this field with improved clinical practice.

Natural Killer Cells as Allogeneic Effectors in Adoptive Cancer Immunotherapy

Natural killer (NK) cells are attractive within adoptive transfer settings in cancer immunotherapy due to their potential for allogeneic use; their alloreactivity is enhanced under conditions of killer immunoglobulin-like receptor (KIR) mismatch with human leukocyte antigen (HLA) ligands on cancer cells. In addition to this, NK cells are platforms for genetic modification, and proliferate in vivo for a shorter time relative to T cells, limiting off-target activation. Current clinical studies have demonstrated the safety and efficacy of allogeneic NK cell adoptive transfer therapies as a means for treatment of hematologic malignancies and, to a lesser extent, solid tumors. However, challenges associated with sourcing allogeneic NK cells have given rise to controversy over the contribution of NK cells to graft-versus-host disease (GvHD). Specifically, blood-derived NK cell infusions contain contaminating T cells, whose activation with NK-stimulating cytokines has been known to lead to heightened release of proinflammatory cytokines and trigger the onset of GvHD in vivo. NK cells sourced from cell lines and stem cells lack contaminating T cells, but can also lack many phenotypic characteristics of mature NK cells. Here, we discuss the available published evidence for the varying roles of NK cells in GvHD and, more broadly, their use in allogeneic adoptive transfer settings to treat various cancers.

HLA-C-restricted viral epitopes are associated with an escape mechanism from KIR2DL2+ NK cells in Lassa virus infection

Background

Lassa virus (LASV) is the etiologic agent of an acute hemorrhagic fever endemic in West Africa. Natural killer (NK) cells control viral infections in part through the interaction between killer cell immunoglobulin-like receptors (KIRs) and their ligands. LASV infection is associated with defective immune responses, including inhibition of NK cell activity in the presence of MHC-class 1⁺-infected target cells.

Methods

We compared individual KIR and HLA-class 1 genotypes of 68 healthy volunteers to 51 patients infected with LASV in Sierra Leone, including 37 survivors and 14 fatalities. Next, potential HLA-C1, HLA-C2, and HLA-Bw4 binding epitopes were in silico screened among LASV nucleoprotein (NP) and envelope glycoprotein (GP). Selected 10-mer peptides were then tested in peptide-HLA stabilization, KIR binding and polyfunction assays.

Findings

LASV-infected patients were similar to healthy controls, except for the inhibitory KIR2DL2 gene. We found a specific increase in the HLA-C1:KIR2DL2 interaction in fatalities (10/11) as compared to survivors (12/19) and controls (19/29). We also identified that strong of NP and GP viral epitopes was only observed with HLA-C molecules, and associated with strong inhibition of degranulation in the presence of KIR2DL⁺ NK cells. This inhibitory effect significantly increased in the presence of the vGP₄₂₀ variant, detected in 28.1% of LASV sequences.

Interpretation

Our finding suggests that presentation of specific LASV epitopes by HLA-C alleles to the inhibitory KIR2DL2 receptor on NK cells could potentially prevent the killing of infected cells and provides insights into the mechanisms by which LASV can escape NK-cell-mediated immune pressure.