Cytomegalovirus-specific T cells are primed early after cord blood transplant but fail to control virus in vivo

Cytomegalovirus-specific neutralizing antibodies effectively prevent uncontrolled infection after allogeneic hematopoietic stem cell transplantation

Cytomegalovirus (CMV) infection remains one of the most frequent and life-threatening infectious complications after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Herein, we comprehensively compared the immune cells of patients with uncontrolled and controlled CMV infection post-allo-HSCT and found that B-cells were extraordinarily insufficient because of impaired B-cells reconstitution in the uncontrolled infection group. Furthermore, in the controlled infection group, reconstructed B-cells showed signatures of mature B-cells, high expression of CXCR4 and IFITM1, and enrichment of CMV-associated B-cell receptors, which were lacking in the uncontrolled infection group. Consistently, sera from the uncontrolled infection group failed to inhibit CMV infection via neutralizing virus in vitro because of its lower content of anti-CMV-specific immunoglobulin G (IgG) than the controlled infection group. Overall, these results highlighted the contribution of B cells and anti-CMV-specific neutralizing IgGs to the restraint of CMV infection post-allo-HSCT, suggesting their potential as a supplementary treatment to improve outcomes.

CMV infection combined with acute GVHD associated with poor CD8+ T-cell immune reconstitution and poor prognosis post-HLA-matched allo-HSCT

Cytomegalovirus (CMV) infection and acute graft-versus-host disease (aGVHD) are two major complications that contribute to a poor prognosis after hematopoietic stem cell transplantation (HSCT). Superior early immune reconstitution (IR) is associated with improved survival after HSCT. However, when all three factors, CMV infection, aGVHD, and IR, are concomitantly considered, the effects of the triple events on HSCT are still unknown and should be studied further. Thus we enrolled 185 patients who were diagnosed as hematological malignancies and treated with HLA-matched sibling transplantation (MST) between January 2010 and December 2014, of whom 83 were positive for CMV infection and 82 had aGVHD. Results showed that patients with both aGVHD and CMV infection had significantly higher non-relapse mortality (NRM), lower overall survival (OS), and delayed CD8+ T-cell IR. Multivariate analyses showed that both aGVHD combined with CMV infection and delayed CD8+ T-cell IR were independent risk factors for prognosis post-MST. Recurrent CMV infections are associated with poor CD8+ T-cell reconstitution. However, superior IR could protect against the negative effects of aGVHD and CMV infection on the transplant outcomes.

The generation and application of antigen-specific T cell therapies for cancer and viral-associated disease

Immunotherapy with antigen-specific T cells is a promising, targeted therapeutic option for patients with cancer as well as for immunocompromised patients with virus infections. In this review, we characterize and compare current manufacturing protocols for the generation of T cells specific to viral and non-viral tumor-associated antigens. Specifically, we discuss: (1) the different methodologies to expand virus-specific T cell and non-viral tumor-associated antigen-specific T cell products, (2) an overview of the immunological principles involved when developing such manufacturing protocols, and (3) proposed standardized methodologies for the generation of polyclonal, polyfunctional antigen-specific T cells irrespective of donor source. Ex vivo expanded cells have been safely administered to treat numerous patients with virus-associated malignancies, hematologic malignancies, and solid tumors. Hence, we have performed a comprehensive review of the clinical trial results evaluating the safety, feasibility, and efficacy of these products in the clinic. In summary, this review seeks to provide new insights regarding antigen-specific T cell technology to benefit a rapidly expanding T cell therapy field.

Risk factors and outcomes of cytomegalovirus infection in children post cord blood transplantation with focus on impact of graft-versus-host disease and immunosuppressants

Cytomegalovirus (CMV) infection remains an important cause of morbidity and mortality post cord blood transplantation (CBT). It has been suggested that the graft-versus-host disease (GVHD) and immunosuppressants have an impact on CMV infection. This study evaluated the incidence, outcomes, and risk factors of CMV infection, while focusing on GVHD and the use of immunosuppressants, in 103 children who had received CBT. Among the patients, 92.2% were positive for CMV serology, while CMV antigenemia was observed in 68.9% and CMV disease developed in 26.2%. CMV enterocolitis was the most common, followed by retinitis and pneumonia. Patients with positive CMV serology and grade II to IV GVHD were independently associated with CMV antigenemia. Recurrent CMV antigenemia was observed significantly more frequently in patients with extensive chronic GVHD. Patients with CMV disease showed significantly worse overall survival, relapse-free survival, and non-relapse mortality than those without CMV disease. In conclusion, CMV infection is common post-CBT in countries with a high rate of CMV seropositivity in the general population and is related to worse outcomes. GVHD severity is associated with the development and recurrence of CMV infection. Thus, efforts need to be made to prevent CMV infection in children post-CBT.

CMV Infection in Hematopoietic Stem Cell Transplantation: Prevention and Treatment Strategies

Purpose of Review

Cytomegalovirus (CMV) remains a major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (Allo-HSCT). New strategies and methods for prevention and management of CMV infection are urgently needed. We aim to review the new developments in diagnostics, prevention, and management strategies of CMV infection in Allo-HSCT recipients.

Recent Findings

The approval of the novel anti-CMV drug letermovir in 2017 has led to an increase in the use of antiviral prophylaxis as a preferred approach for prevention in many centers. Real-world studies have shown efficacy similar to the clinical trial. CMV-specific T cell-mediated immunity assays identify patients with immune reconstitution and predict disease progression. Phase 2 trials of maribavir have shown its efficacy as preemptive therapy and treatment of resistant and refractory CMV infections. Adoptive T cell therapy is an emerging option for treatment of refractory and resistant CMV. Of the different CMV vaccine trials, PepVax has shown promising results in a phase 1 trial.

Summary

CMV cell-mediated immunity assays have potential to be used as an adjunctive test to develop individualized management plan by identifying the patients who develop immune reconstitution; however, further prospective interventional studies are needed. Maribavir and adoptive T cell therapy are promising new therapies for treatment of CMV infections. CMV vaccine trials for prevention are also under way.

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.

Impact of HLA class I allele-level mismatch on viral infection within 100 days after cord blood transplantation

Viral infection is more frequently reported in cord blood transplantation (CBT) than in transplantation of other stem cell sources, but its precise mechanism related to antiviral host defenses has not been elucidated yet. To evaluate the effect of human leukocyte antigen (HLA) class I allele-level incompatibility on viral infection in CBT, we conducted a single-center retrospective study. Total 94 patients were included, and viral infections were detected in 32 patients (34%) within 100 days after CBT. HLA-C mismatches in graft-versus-host direction showed a significantly higher incidence of viral infection (hazard ratio (HR), 3.67; p = 0.01), while mismatches in HLA-A, -B, or -DRB1 were not significant. Overall HLA class I mismatch was also a significant risk factor and the predictor of post-CBT viral infection (≥ 3 mismatches, HR 2.38, p = 0.02), probably due to the insufficient cytotoxic T cell recognition and dendritic cell priming. Patients with viral infection had significantly worse overall survival (52.7% vs. 72.1%; p = 0.02), and higher non-relapse mortality (29.3% vs. 9.8%; p = 0.01) at 5 years. Our findings suggest that appropriate graft selection as well as prophylaxis and early intervention for viral infection in such high-risk patients with ≥ 3 HLA class I allele-level mismatches, including HLA-C, may improve CBT outcomes.

Cytomegalovirus-Mediated T Cell Receptor Repertoire Perturbation Is Present in Early Life

Human cytomegalovirus (CMV) is a highly prevalent herpesvirus, particularly in sub-Saharan Africa, where it is endemic from infancy. The T cell response against CMV is important in keeping the virus in check, with CD8 T cells playing a major role in the control of CMV viraemia. Human leukocyte antigen (HLA) B*44:03-positive individuals raise a robust response against the NEGVKAAW (NW8) epitope, derived from the immediate-early-2 (IE-2) protein. We previously showed that the T cell receptor (TCR) repertoire raised against the NW8-HLA-B*44:03 complex was oligoclonal and characterised by superdominant clones, which were shared amongst unrelated individuals (i.e., "public"). Here, we address the question of how stable the CMV-specific TCR repertoire is over the course of infection, and whether substantial differences are evident in TCR repertoires in children, compared with adults. We present a longitudinal study of four HIV/CMV co-infected mother-child pairs, who in each case express HLA-B*44:03 and make responses to the NW8 epitope, and analyse their TCR repertoire over a period spanning more than 10 years. Using high-throughput sequencing, the paediatric CMV-specific repertoire was found to be highly diverse. In addition, paediatric repertoires were remarkably similar to adults, with public TCR responses being shared amongst children and adults alike. The CMV-specific repertoire in both adults and children displayed strong fluctuations in TCR clonality and repertoire architecture over time. Previously characterised superdominant clonotypes were readily identifiable in the children at high frequency, suggesting that the distortion of the CMV-specific repertoire is incurred as a direct result of CMV infection rather than a product of age-related "memory inflation." Early distortion of the TCR repertoire was particularly apparent in the case of the TCR-β chain, where oligoclonality was low in children and positively correlated with age, a feature we did not observe for TCR-α. This discrepancy between TCR-α and -β chain repertoire may reflect differential contribution to NW8 recognition. Altogether, the results of the present study provide insight into the formation of the TCR repertoire in early life and pave the way to better understanding of CD8 T cell responses to CMV at the molecular level.

Therapeutic advantages provided by banked virus-specific T-cells of defined HLA-restriction

We have developed banks of EBV and CMV-specific T-cell lines generated from healthy seropositive third party donors and characterized them as to their HLA type, virus specificity, lack of alloreactivity, and HLA restriction. We here summarize results of studies employing these immediately accessible, broadly-applicable third party virus-specific T-cells for adoptive therapy of EBV lymphomas and CMV infections in allo-HCT recipients. We describe the characteristics contributing to their safety. We also discuss several distinctive advantages of banked third party virus-specific T-cells selected on the basis of their HLA restriction, particularly in the treatment of Rituximab-non-responsive EBV⁺ lymphomas and drug refractory CMV infections complicating HLA non-identical transplants.

Cytomegalovirus replication is associated with enrichment of distinct γδ T cell subsets following lung transplantation: A novel therapeutic approach?

BACKGROUND

Anti-viral treatments to control cytomegalovirus (CMV) after lung transplantation (LTx) are associated with toxicity and anti-viral resistance. Cellular immunotherapy with virus-specific cytotoxic T cells has yielded promising results but requires donor/recipient matching. γδ T cells are involved in anti-viral immunity and can recognize antigens independently of major histocompatibility complex molecules and may not require the same level of matching. We assessed the phenotype of circulating γδ T cells after LTx to identify the candidate populations for CMV immunotherapy.

METHODS

Peripheral blood mononuclear cells were isolated from lung transplant recipients before transplantation and at routine bronchoscopies after LTx. Patients were stratified by risk of CMV disease into moderate risk (recipient CMV seropositive, n = 15) or high risk (HR) (recipient CMV seronegative/donor CMV seropositive, n = 10). CMV replication was classified as polymerase chain reaction positive (>150 copies/ml) in blood and/or bronchoalveolar lavage within the first 18 months. The phenotype of γδ T cells was assessed by multicolor flow cytometry, and T-cell receptor (TCR) sequences were determined by deep sequencing.

RESULTS

In HR lung transplant recipients with CMV replication, we observed striking phenotypic changes in γδ T cells, marked by an increase in the proportion of effector Vδ1+ γδ T cells expressing the activating natural killer cell receptor NKG2C. Moreover, we observed a remarkable increase in TCR diversity.

CONCLUSIONS

NKG2C+ Vδ1+ γδ T cells were associated with CMV replication and may indicate their potential to control infection. As such, we propose that they could be a potential target for cellular therapy against CMV.

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.

Mixed vs full donor engraftment early after hematopoietic cell transplant: Impact on incidence and control of cytomegalovirus infection

Recovery of cytomegalovirus (CMV)-specific immunity after hematopoietic cell transplantation (HCT) is essential in controlling CMV infection. We hypothesize that mixed donor engraftment as measured by chimerism at day 30 in CMV D(+) HCTs and full chimerism in CMV D(-) HCTs will be predictive of CMV reactivation. Prospectively collected data for 407 CMV R+ HCT recipients transplanted from 2006 to 2014 at the University of Minnesota were retrospectively analyzed. Full and mixed donor engraftment were defined as ≥95% or <95% donor cells at day 30, respectively. Source of engraftment determination included preferentially peripheral blood CD3 fraction, then myeloid cell fraction (CD15+), then bone marrow. In 407 CMV R+ subjects, 77% (n = 313) were CMV D(-) cells from umbilical cord blood (n = 209), peripheral blood (n = 58) or marrow (n = 46). Fifty three per cent received reduced intensity conditioning (RIC). At day +30, full donor engraftment was seen in 82% of myeloablative and 55% of RIC transplants. The cumulative incidence of CMV infection 1-year after transplant was not different in patients with full (54%, n = 276) or mixed (53%, n = 131) donor engraftment. Control of CMV did not significantly differ among the two groups. In multiple regression analysis, there was no significant association between donor engraftment (mixed or full) and incidence or control of CMV.

Major TCR Repertoire Perturbation by Immunodominant HLA-B*44:03-Restricted CMV-Specific T Cells

Lack of disease during chronic human cytomegalovirus (CMV) infection depends on the maintenance of a high-frequency CMV-specific T cell response. The composition of the T cell receptor (TCR) repertoire underlying this response remains poorly characterised, especially within African populations in which CMV is endemic from infancy. Here we focus on the immunodominant CD8+ T cell response to the immediate-early 2 (IE-2)-derived epitope NEGVKAAW (NW8) restricted by HLA-B^*44:03, a highly prevalent response in African populations, which in some subjects represents >10% of the circulating CD8+ T cells. Using pMHC multimer staining and sorting of NW8-specific T cells, the TCR repertoire raised against NW8 was characterised here using high-throughput sequencing in 20 HLA-B^*44:03 subjects. We found that the CD8+ T cell repertoire raised in response to NW8 was highly skewed and featured preferential use of a restricted set of V and J gene segments. Furthermore, as often seen in immunity against ancient viruses like CMV and Epstein-Barr virus (EBV), the response was strongly dominated by identical TCR sequences shared by multiple individuals, or “public” TCRs. Finally, we describe a pair “superdominant” TCR clonotypes, which were germline or nearly germline-encoded and produced at remarkably high frequencies in certain individuals, with a single CMV-specific clonotype representing up to 17% of all CD8+ T cells. Given the magnitude of the NW8 response, we propose that this major skewing of CMV-specific immunity leads to massive perturbations in the overall TCR repertoire in HLA-B^*44:03 individuals.

Naïve T cells are activated by autologous HCMV-infected endothelial cells through NKG2D and can control HCMV transmission in vitro

Apart from classical antigen-presenting cells (APCs) like dendritic cells and macrophages, there are semiprofessional APCs such as endothelial cells (ECs) and Langerhans' cells. Human cytomegalovirus (HCMV) infects a wide range of cell types including the ECs which are involved in the trafficking and homing of T cells. By investigating the interaction of naïve T cells obtained from HCMV-seronegative umbilical cord blood with autologous HCMV-infected human umbilical vein ECs (HUVECs), we could show that the activation of naïve T cells occurred after 1 day of peripheral blood mononuclear cell (PBMC) exposure to HCMV-infected HUVECs. The percentage of activated T cells increased over time and the activation of naïve T cells was not induced by either autologous uninfected HUVECs or by autologous HCMV-infected fibroblasts. The activation of T cells occurred also when purified T cells were co-cultured with HCMV-infected HUVECs. In addition, in most of the donors only CD8⁺ T cells were activated, when the purified T cells were exposed to HCMV-infected HUVECs. The activation of naïve T cells was inhibited when the NKG2D receptor was blocked on the surface of T cells and among the different NKG2D ligands, we identified two ligands (ULBP4 and MICA) on HCMV-infected HUVECs which might be the interaction partners of the NKG2D receptor. Using a functional cell culture assay, we could show that these activated naïve T cells specifically inhibited HCMV transmission. Altogether, we identified a novel specific activation mechanism of naïve T cells from the umbilical cord by HCMV-infected autologous HUVECs through interaction with NKG2D.

Reconstitution of adaptive immunity after umbilical cord blood transplantation: impact on infectious complications

In comparison with allogeneic stem cell transplantation (alloHSCT) with other stem cell sources, umbilical cord blood transplantation (UCBT) was traditionally associated with increased risk of infections, particularly during the first 3 months after transplantation. Longitudinal studies of immune monitoring reported peculiar patterns of T- and B-cell recovery in the peripheral blood of UCB recipients during the first months post-transplantation. Overall, current data suggest delayed reconstitution of naive and memory CD4⁺ and CD8⁺ T-cell pools after UCBT. This is particularly true for adult recipients and for patients who received in vivo T-cell depleting approaches before the transplantation. Such delayed T-cell recovery may increase susceptibility of UCB recipients for developing opportunistic infections and viral reactivations. Regarding B-cell recovery, UCBT was associated with accelerated B-lymphopoiesis. Recent studies also reported evidence for faster functional memory B-cell recovery in UCB recipients. In this article, we briefly review T- and B-cell reconstitution after alloHSCT, with emphasis on peculiarities observed after UCBT. We further put these data in lines with risks of infections after UCBT.

The cumulative burden of double-stranded DNA virus detection after allogeneic HCT is associated with increased mortality

Strategies to prevent active infection with certain double-stranded DNA (dsDNA) viruses after allogeneic hematopoietic cell transplantation (HCT) are limited by incomplete understanding of their epidemiology and clinical impact. We retrospectively tested weekly plasma samples from allogeneic HCT recipients at our center from 2007 to 2014. We used quantitative PCR to test for cytomegalovirus, BK polyomavirus, human herpesvirus 6B, HHV-6A, adenovirus, and Epstein-Barr virus between days 0 and 100 post-HCT. We evaluated risk factors for detection of multiple viruses and association of viruses with mortality through day 365 post-HCT with Cox models. Among 404 allogeneic HCT recipients, including 125 cord blood, 125 HLA-mismatched, and 154 HLA-matched HCTs, detection of multiple viruses was common through day 100: 90% had ≥1, 62% had ≥2, 28% had ≥3, and 5% had 4 or 5 viruses. Risk factors for detection of multiple viruses included cord blood or HLA-mismatched HCT, myeloablative conditioning, and acute graft-versus-host disease (P values < .01). Absolute lymphocyte count of <200 cells/mm³ was associated with greater virus exposure on the basis of the maximum cumulative viral load area under the curve (AUC) (P = .054). The maximum cumulative viral load AUC was the best predictor of early (days 0-100) and late (days 101-365) overall mortality (adjusted hazard ratio [aHR] = 1.36, 95% confidence interval [CI] [1.25, 1.49], and aHR = 1.04, 95% CI [1.0, 1.08], respectively) after accounting for immune reconstitution and graft-versus-host disease. In conclusion, detection of multiple dsDNA viruses was frequent after allogeneic HCT and had a dose-dependent association with increased mortality. These data suggest opportunities to improve outcomes with better antiviral strategies.

Impact of early CMV reactivation in cord blood stem cell recipients in the current era

Several studies have reported an association between CMV reactivation and a decreased incidence of relapse for AML after adult donor allogeneic hematopoietic cell transplantation (HCT). Limited data, however, are available on the impact of CMV reactivation on relapse after cord blood (CB) stem cell transplantation. The unique combination of higher incidence of CMV reactivation in the seropositive recipient and lower incidence of graft versus host disease (GvHD) in CB HCT permits a valuable design to analyze the impact of CMV reactivation. Data from 1684 patients transplanted with CB between 2003 and 2010 for AML and ALL were analyzed. The median time to CMV reactivation was 34 days (range: 2-287). CMV reactivation and positive CMV serology were associated with increased non-relapse mortality (NRM) among both AML and ALL CB recipients (reactivation, AML: relative risk (RR) 1.41 (1.07-1.85); ALL: 1.60 (1.14-2.23); Serology, AML: RR 1.39 (1.05-1.85), ALL: RR 1.61 (1.18-2.19)). For patients with ALL, but not those with AML, this yielded inferior overall survival (P<0.005). Risk of relapse was not influenced by CMV reactivation or positive CMV serostatus for either disease.

Virus-specific T-cell banks for 'off the shelf' adoptive therapy of refractory infections

Adoptive immunotherapy with transplant donor-derived virus-specific T cells has emerged as a potentially curative approach for the treatment of drug-refractory EBV+lymphomas as well as CMV and adenovirus infections complicating allogeneic hematopoietic cell transplants. Adoptive transfer of HLA partially matched virus-specific T cells from healthy third party donors has also shown promise in the treatment of these conditions, with disease response rates of 50-76% and strikingly low incidences of toxicity or GVHD recorded in initial trials. In this review, we examine the reported experience with transplant donor and third party donor-derived virus-specific T cells, identifying characteristics of the viral pathogen, the T cells administered and the diseased host that contribute to treatment response or failure. We also describe the characteristics of virus-specific T-cell lines in our center's bank and the frequency with which in vitro culture promotes expansion of immunodominant T cells specific for epitopes that are presented by a limited array of prevalent HLA alleles, which facilitates their broad applicability for treatment.

Immune reconstitution after cord blood transplantation: peculiarities, clinical implications and management strategies

Umbilical cord blood (UCB) is now widely used as an alternative hematopoietic stem cell source for patients lacking closely matched related or unrelated adult donors. UCB transplantation has traditionally been associated with delayed engraftment, poor immune reconstitution and consequent increased risk of infection. More recent clinical studies, however, suggest that conditioning regimens and in particular the omission of in vivo T-cell depletion may play a crucial role in post-transplant T-cell expansion, facilitating a uniquely rapid immune recovery after UCB transplantation. The peculiar characteristics of UCB cells, the importance of thymic function and the role of conditioning regimens and graft-versus-host disease influencing immune reconstitution are described. The last part of the review reports available data on UCB, as well as third-party peripheral blood derived anti-viral cell therapy, which provides a novel approach to rescue UCB recipients with viral complications in the post-transplant period.

CMV reactivation drives posttransplant T-cell reconstitution and results in defects in the underlying TCRβ repertoire

Although cytomegalovirus (CMV) reactivation has long been implicated in posttransplant immune dysfunction, the molecular mechanisms that drive this phenomenon remain undetermined. To address this, we combined multiparameter flow cytometric analysis and T-cell subpopulation sorting with high-throughput sequencing of the T-cell repertoire, to produce a thorough evaluation of the impact of CMV reactivation on T-cell reconstitution after unrelated-donor hematopoietic stem cell transplant. We observed that CMV reactivation drove a >50-fold specific expansion of Granzyme B(high)/CD28(low)/CD57(high)/CD8(+) effector memory T cells (Tem) and resulted in a linked contraction of all naive T cells, including CD31(+)/CD4(+) putative thymic emigrants. T-cell receptor β (TCRβ) deep sequencing revealed a striking contraction of CD8(+) Tem diversity due to CMV-specific clonal expansions in reactivating patients. In addition to querying the topography of the expanding CMV-specific T-cell clones, deep sequencing allowed us, for the first time, to exhaustively evaluate the underlying TCR repertoire. Our results reveal new evidence for significant defects in the underlying CD8 Tem TCR repertoire in patients who reactivate CMV, providing the first molecular evidence that, in addition to driving expansion of virus-specific cells, CMV reactivation has a detrimental impact on the integrity and heterogeneity of the rest of the T-cell repertoire. This trial was registered at www.clinicaltrials.gov as #NCT01012492.

Engineered dendritic cells from cord blood and adult blood accelerate effector T cell immune reconstitution against HCMV

Human cytomegalovirus (HCMV) harmfully impacts survival after peripheral blood hematopoietic stem cell transplantation (PB-HSCT). Delayed immune reconstitution after cord blood (CB)-HSCT leads to even higher HCMV-related morbidity and mortality. Towards a feasible dendritic cell therapy to accelerate de novo immunity against HCMV, we validated a tricistronic integrase-defective lentiviral vector (coexpressing GM-CSF, IFN-α, and HCMV pp65 antigen) capable to directly induce self-differentiation of PB and CB monocytes into dendritic cells processing pp65 (“SmyleDCpp65”). In vitro, SmyleDCpp65 resisted HCMV infection, activated CD4⁺ and CD8⁺ T cells and expanded functional pp65-specific memory cytotoxic T lymphocytes (CTLs). CD34⁺ cells obtained from PB and CB were transplanted into irradiated NOD.Rag1^−/−.IL2γc^−/− mice. Donor-derived SmyleDCpp65 administration after PB-HSCT stimulated peripheral immune effects: lymph node remodeling, expansion of polyclonal effector memory CD8⁺ T cells in blood, spleen and bone marrow, and pp65-reactive CTL and IgG responses. SmyleDCpp65 administration after CB-HSCT significantly stimulated thymopoiesis. Expanded frequencies of CD4⁺/CD8⁺ T cell precursors containing increased levels of T-cell receptor excision circles in thymus correlated with peripheral expansion of effector memory CTL responses against pp65. The comparative in vivo modeling for PB and CB-HSCT provided dynamic and spatial information regarding human T and B cell reconstitution. In vivo potency supports future clinical development of SmyleDCpp65.

CMV promotes recipient T-cell immunity following reduced-intensity T-cell-depleted HSCT, significantly modulating chimerism status

Cytomegalovirus (CMV) remains a significant cause of morbidity after allogeneic hematopoietic stem cell transplantation (HSCT). Clinical risk varies according to a number of factors, including recipient/donor CMV serostatus. Current dogma suggests risk is greatest in seropositive recipient (R+)/seronegative donor (D-) transplants and is exacerbated by T-cell depletion. We hypothesized that in the setting of reduced-intensity T-cell-depleted conditioning, recipient-derived CMV-specific T cells escaping deletion may contribute significantly to CMV-specific immunity and might therefore also influence chimerism status. We evaluated 105 recipients of alemtuzumab-based reduced-intensity HSCT and collated details on CMV infection episodes and T-cell chimerism. We used CMV-specific HLA multimers to enumerate CMV-specific T-cell numbers and select cells to assess chimerism status in a subset of R+/D- and R+/seropositive donor patients. We show that in R+/D- patients, CMV-specific T cells are exclusively of recipient origin, can protect against recurrent CMV infections, and significantly influence the chimerism status toward recipients. The major findings were replicated in a separate validation cohort. T-cell depletion in the R+/D- setting may actually, therefore, foster more rapid reconstitution of protective antiviral immunity by reducing graft-vs-host directed alloreactivity and the associated elimination of the recipient T-cell compartment. Finally, conversion to donor chimerism after donor lymphocytes is associated with clinically occult transition to donor-derived immunity.

Incidence, nature and mortality of cytomegalovirus infection after double-unit cord blood transplant

Cord blood transplant (CBT) extends allograft access but is associated with a significant risk for cytomegalovirus (CMV) infection. We analyzed CMV infection in 157 CBT recipients transplanted for hematological malignancies. As compared with antigenemia testing, routine polymerase chain reaction (PCR) monitoring was associated with increased and earlier CMV infection detection (1-year incidence if seropositive 67% [median onset 41 days] vs. 100% at an earlier 33-day median [p < 0.001]) and decreased gastrointestinal disease. One-year CMV-related transplant-related mortality was 11% in CMV+ patients with 7/9 deaths associated with initial infection. Disease-free survival was lower in seropositive compared with seronegative patients (1-year: 55% vs. 73%, p = 0.02). However, in multivariate analysis adjusting for age, treatment failure risk in CMV+ patients was not significant (hazard ratio 1.52, p = 0.11). CMV infection is a major challenge in seropositive CBT recipients. While PCR surveillance permits early detection of viremia, new prophylaxis and therapeutic strategies are needed.

The role of the thymus in T-cell immune reconstitution after umbilical cord blood transplantation

Umbilical cord blood (UCB) is an alternative source of hematopoietic stem cells for patients without HLA-matched adult donors. UCB contains a low number of nucleated cells and mostly naive T cells, resulting in prolonged time to engraftment and lack of transferred T-cell memory. Although the first phase of T-cell reconstitution after UCB transplantation (UCBT) depends on peripheral expansion of transferred T cells, permanent T-cell reconstitution is mediated via a central mechanism, which depends on de novo production of naive T lymphocytes by the recipient's thymus from donor-derived lymphoid-myeloid progenitors (LMPs). Thymopoiesis can be assessed by quantification of recent thymic emigrants, T-cell receptor excision circle levels, and T-cell receptor repertoire diversity. These assays are valuable tools for monitoring posttransplantation thymic recovery, but more importantly they have shown the significant prognostic value of thymic reconstitution for clinical outcomes after UCBT, including opportunistic infections, disease relapse, and overall survival. Strategies to improve thymic entry and differentiation of LMPs and to accelerate recovery of the thymic stromal microenvironment may improve thymic lymphopoiesis. Here, we discuss the mechanisms and clinical implications of thymic recovery and new approaches to improve reconstitution of the T-cell repertoire after UCBT.

Effect of CD8⁺ cell content on umbilical cord blood transplantation in adults with hematological malignancies

Total nucleated (TNCs) and CD34(+) cells are considered major determinants of outcome after umbilical cord blood (UCB) transplantation but the effect of other cell subtypes present in the graft is unknown. This single-center cohort study included patients with hematological malignancies who received UCB transplantation after a myeloablative conditioning regimen. UCB units were primarily selected according to cell content, both TNCs and CD34(+) cells, and also according to the degree of HLA matching. Counts of several cell subtypes of the infused UCB unit, together with HLA disparities and other patient- and transplantation-related characteristics, were analyzed by multivariable methodology for their association with myeloid and platelet engraftment, graft-versus-host disease, nonrelapse mortality (NRM), disease-free survival (DFS), and overall survival (OS). Two hundred patients (median age, 32 years) were included in the study. In multivariable analyses, a greater number of CD8(+) cells was significantly associated with better results for myeloid (P = .001) and platelet (P = .008) engraftment, NRM (P = .02), DFS (P = .007), and OS (P = .01). CD34(+) cell content was predictive of myeloid engraftment (P < .001). This study suggests that the outcome after UCB transplantation in adults with hematological malignancies could be better when UCB grafts had a greater CD8(+) cell content.

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.

Risk factors of CMV infection in patients after umbilical cord blood transplantation: a multicenter study in China

OBJECTIVE

This retrospective study examined risk factors for cytomegalovirus (CMV) infection after umbilical cord blood transplantation (UCBT) and the impact of CMV infection on patient survival.

METHODS

In all 176 patients, plasma CMV DNA was negative prior to the transplantation, and examined twice a week for 100 d, and then once weekly for additional 300 d. Preemptive antiviral therapy (ganciclovir or foscarnet) was started in patients with >1,000/mL copies of CMV DNA but no full-blown CMV disease, and was discontinued upon two consecutive negative reports of blood CMV DNA test. The survival and risk factors for CMV infection or disease were examined using logistic regression.

RESULTS

CMV infection developed in 71% (125/176) of the patients, with a median onset of 32 d. Four patients (2.3%) developed CMV disease. Neither the 5-year overall survival (OS) nor event-free survival (EFS) differed significantly in infected patients vs. those with no infection (59.4% vs. 64.8%, P=0.194; 53.4% vs. 59.1%, P=0.226). A stepwise multivariate analysis indicated an association of CMV infection with age, high-dose glucocorticoids, the number of transplanted CD34(+) cells, and the number of platelet transfusion, but not with gender, the conditioning regimen, and the day of neutrophil recovery and chronic graft-versus-host disease (cGVHD).

CONCLUSIONS

CMV infection is very common after UCBT, but does not seem to affect long-term survival with preemptive antiviral treatment.

Diagnosis and treatment of viral diseases in recipients of allogeneic hematopoietic stem cell transplantation

Viral infections are important causes of morbidity and mortality after allogeneic stem cell hematopoietic transplantation (allo-HSCT). Although most viral infections present with asymptomatic or subclinical manifestations, viruses may result in fatal complications in severe immunocompromised recipients. Reactivation of latent viruses, such as herpesviruses, is frequent during the immunosuppression that occurs with allo-HSCT. Viruses acquired from community, such as the respiratory and gastrointestinal viruses, are also important pathogens of post-transplant viral diseases. Currently, molecular diagnostic methods have replaced or supplemented traditional methods, such as viral culture and antigen detection, in diagnosis of viral infections. The utilization of polymerase chain reaction facilitates the early diagnosis. In view of lacking efficacious agents for treatment of viral diseases, prevention of viral infections is extremely valuable. Application of prophylactic strategies including preemptive therapy reduces viral infections and diseases. Adoptive cellular therapy for restoring virus-specific immunity is a promising method in the treatment of viral diseases.