Reconstitution of adenovirus-specific cell-mediated immunity in pediatric patients after hematopoietic stem cell transplantation

Antiviral cellular therapy for enhancing T-cell reconstitution before or after hematopoietic stem cell transplantation (ACES): a two-arm, open label phase II interventional trial of pediatric patients with risk factor assessment

Viral infections remain a major risk in immunocompromised pediatric patients, and virus-specific T cell (VST) therapy has been successful for treatment of refractory viral infections in prior studies. We performed a phase II multicenter study (NCT03475212) for the treatment of pediatric patients with inborn errors of immunity and/or post allogeneic hematopoietic stem cell transplant with refractory viral infections using partially-HLA matched VSTs targeting cytomegalovirus, Epstein-Barr virus, or adenovirus. Primary endpoints were feasibility, safety, and clinical responses (>1 log reduction in viremia at 28 days). Secondary endpoints were reconstitution of antiviral immunity and persistence of the infused VSTs. Suitable VST products were identified for 75 of 77 clinical queries. Clinical responses were achieved in 29 of 47 (62%) of patients post-HSCT including 73% of patients evaluable at 1-month post-infusion, meeting the primary efficacy endpoint (>52%). Secondary graft rejection occurred in one child following VST infusion as described in a companion article. Corticosteroids, graft-versus-host disease, transplant-associated thrombotic microangiopathy, and eculizumab treatment correlated with poor response, while uptrending absolute lymphocyte and CD8 T cell counts correlated with good response. This study highlights key clinical factors that impact response to VSTs and demonstrates the feasibility and efficacy of this therapy in pediatric HSCT.

Adenoviral penton and hexon proteins are equivalent immunogenic targets of virus-specific T cells after HSCT in children

BACKGROUND

Human adenovirus (HAdV) infection is a serious complication that can lead to significant morbidity and mortality, especially in immunocompromised pediatric patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT). Control and elimination of HAdV requires the presence of the respective antiviral T cells, and adoptive transfer of virus-specific T cells has become an important new treatment option for patients refractory to antiviral treatment. Although the adenoviral capsid protein hexon was shown to be a major immunodominant T-cell target across HAdV species, up to 30% of HAdV-seropositive donors show no T-cell responses to the overlapping peptide pool spanning the entire protein.

OBJECTIVES AND STUDY DESIGN

Our group has recently verified the capsid protein penton as a second immunodominant target in HAdV infection. Here, we aimed to investigate the prevalence of both penton- and hexon-specific HAdV T cells and their impact in virus control after HSCT. Therefore, we analyzed the prevalence and characteristics of HAdV-specific T cells in 33 consecutive pediatric patients with HAdV reactivation following allogeneic HSCT and correlated them with viral load analysis.

RESULTS AND CONCLUSION

Our study demonstrates that penton is an important immunodominant target antigen of HAdV reactivation/infection after HSCT in most patients. We demonstrate that in the majority of patients, both penton- and hexon-specific T cells appear at similar time intervals after transplantation. Despite the prevalence for either hexon- or penton-specific T cells in individual patients, we were unable to attribute the pre-dominance to specific HLA types or HAdV serotypes. The occurrence of HAdV-specific T cells was closely linked to viral control arguing for immune monitoring strategies to tailor antiviral treatment and adoptive T cell therapy.

Reducing infectious complications after allogeneic stem cell transplant

INTRODUCTION

Infections remain a significant problem, in patients undergoing an allogeneic hematopoietic stem-cell transplant (HSCT) and efforts have been made over the years, to reduce the incidence, morbidity and mortality of infectious complications.

AREAS COVERED

This manuscript is focused on the epidemiology, risk factors and prevention of infections after allogeneic HSCT. A systematic literature review was performed using the PubMed database, between November 2019 and January 2020, with the following MeSH terms: stem-cell transplantation, infection, fungal, bacterial, viral, prophylaxis, vaccines, prevention. The authors reviewed all the publications, and following a common revision, a summary report was made and results were divided in three sections: bacterial, fungal and viral infections.

EXPERT OPINION

Different infections occur in the early, intermediate and late post-transplant period, due to distinct risk factors. Improved diagnostic techniques, pre-emtive therapy and better prophylaxis of immunologic complications, have reduced the morbidity and mortality of infections. The role of the gut microbiota is under careful scrutiny and may further help us to identify high-risk patients.

Adoptive cell therapies for posttransplant infections

PURPOSE OF REVIEW

Viral and fungal infections cause significant morbidity and mortality following hematopoietic stem-cell transplantation (HSCT), primarily due to the prolonged and complex immunodeficient state that results from conditioning chemo-radiotherapy and subsequent prophylaxis of graft vs. host disease. Although currently available antimicrobial pharmacotherapies have demonstrated short-term efficacy, their toxicities often preclude long-term use, and cessation if frequently associated with recurrent infection. Adoptive cell therapy (ACT) offers the potential to more rapidly reconstitute antimicrobial immune responses in the posttransplant setting.

RECENT FINDINGS

Traditional approaches to manufacture of adoptive T-cell therapies are time consuming and limited to single pathogen specificity. Recent advances in the understanding of immunogenic epitopes, improved methods for pathogen-specific T-cell isolation and cultureware technologies is allowing for rapid generation of ACTs for clinical use.

SUMMARY

The current review summarizes the potential infectious targets and manufacturing methodologies for ACTs and contrasts their clinical efficacy and safety to currently available pharmacotherapies for patients recovering after HSCT.

Identification of the best-suited donor for generating virus-specific T cells

BACKGROUND AND OBJECTIVES

Administration of virus-specific T cells (VSTs) is a viable antiviral treatment strategy after allogeneic HSCT, even if conventional therapies fail. Third-party donors are often chosen for the generation of the VST product. The eligibility of the donor has to be tested in a rigorous donor screening procedure, since the isolation technology only targets pre-existing VSTs.

MATERIALS AND METHODS

In a period of 3 years, we performed 32 VST treatments for 28 patients. Targeting four different viruses, 284 healthy individuals underwent 417 donor screening procedures. VSTs were counted by flow cytometry detecting interferon-gamma (IFN-γ) producing T cells. Generation of the VSTs was performed from leukapheresis products in a fully automated and closed system using magnetic cell separation.

RESULTS

The mean circulating VST frequencies ranged from 0·006% to 0·328%. The average yield of viable VSTs in the product was 1·83·10₆ cells, while the average VST dose calculated for the patient's body weight was 4·63·10₄ /kg. The mean purity - percentage of VSTs within the T cells - of all T-cell products was 62·9%. Correlation was identified between the frequency of the VSTs in the peripheral blood of the donor and the VST numbers of the end product; the strongest correlation was seen for CMV.

CONCLUSION

This paper focuses on the T-cell donors, highlighting some key points on the donor selection process. Based on the findings in connection with the CMV therapies, peripheral VST seems to be the best predictor of the VST content of the final product administered to the patient.

Viral-specific T-cell response in hemorrhagic cystitis after haploidentical donor stem cell transplantation

Viral hemorrhagic cystitis (HC) after hematopoietic stem cell transplantation (HSCT) can be devastating. Standard treatment modalities have not been well established, but immune reconstitution may be necessary for sustained viral clearance. We studied five pediatric patients who developed viral HC after haplo-identical HSCT. All patients developed virus-specific CD4- and CD8-positive T cells, and the emergence of these viral-specific T cells was temporally associated with successful viral clearance.

Preventing stem cell transplantation-associated viral infections using T-cell therapy

Hematopoietic stem cell transplantation is the treatment of choice for many hematologic malignancies and genetic diseases. However, viral infections continue to account for substantial post-transplant morbidity and mortality. While antiviral drugs are available against some viruses, they are associated with significant side effects and are frequently ineffective. This review focuses on the immunotherapeutic strategies that have been used to prevent and treat infections over the past 20 years and outlines different refinements that have been introduced with the goal of moving this therapy beyond specialized academic centers.

Antiviral T-cell therapy

Serious viral infections are a common cause of morbidity and mortality after allogeneic stem cell transplantation. They occur in the majority of allograft recipients and are fatal in 17–20%. These severe infections may be prolonged or recurrent and add substantially to the cost, both human and financial, of the procedure. Many features of allogeneic stem cell transplantation contribute to this high rate of viral disease. The cytotoxic and immunosuppressive drugs administered pretransplant to eliminate the host hematopoietic/immune system and any associated malignancy, the delay in recapitulating immune ontogeny post‐transplant, the immunosuppressive drugs given to prevent graft versus host disease (GvHD), and the effects of GvHD itself, all serve to make stem cell transplant recipients vulnerable to disease from endogenous (latent) and exogenous (community) viruses, and to be incapable of controlling them as quickly and effectively as most normal individuals.

Adenovirus infections in immunocompetent and immunocompromised patients

Human adenoviruses (HAdVs) are an important cause of infections in both immunocompetent and immunocompromised individuals, and they continue to provide clinical challenges pertaining to diagnostics and treatment. The growing number of HAdV types identified by genomic analysis, as well as the improved understanding of the sites of viral persistence and reactivation, requires continuous adaptions of diagnostic approaches to facilitate timely detection and monitoring of HAdV infections. In view of the clinical relevance of life-threatening HAdV diseases in the immunocompromised setting, there is an urgent need for highly effective treatment modalities lacking major side effects. The present review summarizes the recent progress in the understanding and management of HAdV infections.

Diagnosis and treatment of adenovirus infection in immunocompromised patients

In immunocompromised patients, human adenovirus (HAdV) infections can cause life-threatening multiorgan disease. This review summarizes the incidence and risk factors of invasive human adenovirus infections in immunocompromised patients as well as the recently developed standards for diagnostic methods and strategies according to the predominant risk factors in adults and children. Recommendations for preemptive and therapeutic treatment strategies and the outcome in different risk groups are presented. Novel therapeutic approaches including CMX001, a new orally bioavailable lipid conjugate of cidofovir and the transfer of adenovirus-specific donor T cells in the context of allogeneic stem cell transplantation are discussed.

Infusion of donor-derived CD19-redirected virus-specific T cells for B-cell malignancies relapsed after allogeneic stem cell transplant: a phase 1 study

Autologous T cells expressing a CD19-specific chimeric antigen receptor (CD19.CAR) are active against B-cell malignancies, but it is unknown whether allogeneic CD19.CAR T cells are safe or effective. After allogeneic hematopoietic stem cell transplantation (HSCT), infused donor-derived virus-specific T cells (VSTs) expand in vivo, persist long term, and display antiviral activity without inducing graft-vs-host disease; therefore, we determined whether donor VSTs, engineered to express CD19.CAR, retained the characteristics of nonmanipulated allogeneic VSTs while gaining antitumor activity. We treated 8 patients with allogeneic (donor-derived) CD19.CAR-VSTs 3 months to 13 years after HSCT. There were no infusion-related toxicities. VSTs persisted for a median of 8 weeks in blood and up to 9 weeks at disease sites. Objective antitumor activity was evident in 2 of 6 patients with relapsed disease during the period of CD19.CAR-VST persistence, whereas 2 patients who received cells while in remission remain disease free. In 2 of 3 patients with viral reactivation, donor CD19.CAR-VSTs expanded concomitantly with VSTs. Hence CD19.CAR-VSTs display antitumor activity and, because their number may be increased in the presence of viral stimuli, earlier treatment post-HSCT (when lymphodepletion is greater and the incidence of viral infection is higher) or planned vaccination with viral antigens may enhance disease control.

Identification of a novel HLA-A*24:02-restricted adenovirus serotype 11-specific CD8+ T-cell epitope for adoptive immunotherapy

Subgroup B adenovirus serotype 11 (Ad11) occasionally causes fatal infections in immunocompromised patients. The present study describes a novel Ad11 epitope presented by HLA-A*24:02 that could be used for adoptive immunotherapy. Ten synthetic Ad11 hexon protein-derived nonamer peptides that bound to HLA-A*24:02 were selected by a computer algorithm and MHC stabilization assay. Stimulation of peripheral blood mononuclear cells from HLA-A*24:02+ donors with each of these synthetic peptides induced peptide-specific CD8(+) T-cells for three peptides. Testing the reactivity of these peptide-specific CD8(+) T-cells against various target cells confirmed that peptide TYFNLGNKF is naturally processed in Ad11-infected cells and is presented by HLA-A*24:02. Emergence of TYFNLGNKF-specific CD8(+) T-cells coincided with the clearance of adenoviruses in a patient with Ad11 disease. Importantly, TYFNLGNKF-specific CD8(+) T-cells were suggested to be not serotype cross-reactive. The novel HLA-A*24:02-restricted Ad11 epitope could be used for anti-Ad11 adoptive immunotherapy and to monitor immunity to Ad11 using MHC tetramers.

Molecular diagnosis and management of viral infections in hematopoietic stem cell transplant recipients

Viral infections after allogeneic hematopoietic stem cell transplantation (HSCT) are important complications associated with high morbidity and mortality. In this setting, reactivations of persisting latent viral pathogens from donor and/or recipient cells play a central role whereas the sterile environment of transplant units renders new infections less likely. The viruses currently regarded as most relevant in the HSCT setting include particularly the herpes virus family--specifically cytomegalovirus (CMV), Epstein-Barr virus (EBV), and human herpesvirus 6 (HHV-6)--as well as human adenoviruses (AdVs) and the polyoma virus BK (BKV). Timely detection and monitoring of virus copy numbers are prerequisites for successful preemptive treatment approaches. Pre- and post-transplant surveillance by sensitive and quantitative molecular methods has therefore become an essential part of the diagnostic routine. In this review, we discuss diagnostic aspects and the clinical management of the most important viral infections in HSCT recipients, with a focus on pediatric patients.

Production of good manufacturing practice-grade cytotoxic T lymphocytes specific for Epstein-Barr virus, cytomegalovirus and adenovirus to prevent or treat viral infections post-allogeneic hematopoietic stem cell transplant

Infections with a range of common community viruses remain a major cause of mortality and morbidity after allogeneic hematopoietic stem cell transplantation. T cells specific for cytomegalovirus (CMV), Epstein-Barr virus (EBV) and adenoviruses can safely prevent and infections with these three most common culprits, but the manufacture of individual T cell lines for each virus would be prohibitive in terms of time and cost. We have demonstrated that T cells specific for all three viruses can be manufactured in a single culture using monocytes and EBV-transformed B lymphoblastoid cell lines (LCLs), both transduced with an adenovirus vector expressing pp65 of CMV, as antigen-presenting cells. Trivirus-specific T cell lines produced from healthy stem cell donors could prevent and treat infections with all three viruses, not only in the designated recipient, but in unrelated, partially-HLA-matched third party recipients. We now provide the details and logistics of T cell manufacture.

Risk factors for molecular detection of adenovirus in pediatric hematopoietic stem cell transplantation recipients

Adenovirus (AdV) infections are a major cause of morbidity and mortality in patients undergoing hematopoietic stem cell transplantation (HSCT). To evaluate the use of molecular AdV testing in HSCT at our institution and identify risk factors for AdV viremia and disease, we performed a retrospective cohort study of all HSCT recipients who had undergone AdV polymerase chain reaction testing over a 2-year period. Two cohorts were identified: cohort 1, comprising patients testing positive for AdV (n = 7) and cohort 2, comprising patients testing negative (n = 36). Overall patient characteristics were not statistically significantly different between the 2 cohorts. A comparison of cohort 1 and cohort 2 identified the following medication exposures as risk factors influencing AdV status: preparatory regimens using fludarabine (relative risk [RR], 8.73; 95% confidence interval [CI], 1.18-64.27; P = .006), melphalan (RR, 3.47; 95% CI, 0.76-15.94: P = .08), and/or cyclophosphamide (RR, 0.18; 95% CI, 0.02-1.4; P = .05), and GVHD prophylaxis with methylprednisone (RR, 3.73; 95% CI, 1.01-13.9; P = .04). AdV-positive patients had higher grades of GVHD and higher rates of GVHD of the gastrointestinal tract (RR, 4; 95% CI, 1.18-13.5; P = .03) compared with AdV-negative patients. Four of the 7 AdV-positive patients had concomitant clinical manifestations of disease, including pneumonia, diarrhea, and/or disseminated disease. Clinical outcomes in symptomatic patients included resolution of disease in 2 patients and death in 2 patients. All 7 AdV-positive patients received antiviral therapy, including 1 patient with severe disseminated disease that resolved after administration of liposomal cidofovir. Our study at a large pediatric HSCT center provides important preliminary data for the development of a prospective trial destined to identify specific HCST patient subpopulations that might benefit most from molecular screening and early preemptive therapy.

Diagnostic value of quantitative PCR for adenovirus detection in stool samples as compared with antigen detection and cell culture in haematopoietic stem cell transplant recipients

Adenovirus (AdV) infections constitute a significant cause of morbidity and mortality during haematopoietic stem cell transplantation. Recent guidelines recommend repeated screening for AdV in whole blood (WB), with quantitative PCR (qPCR) as the reference standard. Despite pre-emptive antiviral treatment based on qPCR in WB, the mortality rate after disseminated AdV infection remains very high. The aim of our study was to advance early screening for AdV, using a standardized method, so as to enable the earlier initiation of antiviral treatment or adoptive immunotherapy. The diagnostic value of AdV DNA quantification in stool samples was investigated retrospectively and compared with antigen detection and cell culture in 21 patients with AdV infection, from 182 patients followed in the Transplant Unit of Nancy University Hospital Centre, including 18 patients with systemic infection. In 16/18 patients with positive AdV viraemia, AdV DNA was present in stool samples earlier than in WB (median, 42 days; range, 3-199 days), whereas both antigen detection and cell culture were still negative for 11/18 patients with systemic AdV infection. The course of AdV viral loads in stool samples was predictive of adenoviraemia (sensitivity, 89%). Very late and lethal AdV infections were observed in cord blood transplant recipients, and would have been detected much earlier with the use of qPCR on stool samples. This study confirmed that quantification of AdV in stool samples by qPCR is beneficial for the management of transplant recipients, with or without antigen detection.

Quantitative and qualitative CD4 T cell immune responses related to adenovirus DNAemia in hematopoietic stem cell transplantation

The nature of adenovirus (AdV)-specific T cells that could best predict the capacity of immunocompromised host to fight AdV is unclear. To this aim, 47 pediatric patients were enrolled for at least 3 months either at allogeneic bone marrow transplantation (BMT) (23 genoidentical, 18 unrelated of which 9 were 10/10 and 9 were 9/10 HLA-matched) or at unrelated cord blood transplantation (n = 6). Enumeration of AdV-specific CD4 T cells secreting cytokines (flow cytometry) and proliferative responses to AdV ((3)HT-incorporation) were compared to AdV-DNAemia. A total of 44/47 patients did not evidence AdV-DNAemia. Thirty-two of 44 (73%) developed CD4-mediated interferon-gamma (IFN-γ) responses to AdV (median 0.36 CD4/μL of blood) since the first month post-HSCT (n = 11: 8 genoidentical and 3 unrelated) or the third month (n = 21 additional patients). At 3 months, both incidence and level intensities of AdV-specific CD4 appeared similar in genoidentical and unrelated BMT (70% and 80%; 0.36 and 0.21 CD4/μL, respectively) and not statistically different from age-matched controls (76%; 1.35 CD4/μL), whereas cord blood transplanted patients exhibited similar incidence but higher level intensities (67%; 1.49 CD4/μL). Polyfunctional (IL2 + IFN-γ) and proliferative responses appeared later, after the third month. Three of 4 9/10 HLA-matched unrelated HSCT that did not develop immunity to AdV presented chemotherapy-resistant AdV-DNAemia at 3 to 5 months post-hematopoietic stem cell transplantation (HSCT). Two were successfully treated with AdV-specific CTL infusion. Monitoring, since month 1 post-HSCT, of IFN-γ-secreting AdV-specific CD4 appears suitable for early detection of at-risk patients especially in 9/10 HLA-matched unrelated HSCT and preferable to monitoring of more delayed IL2- and proliferative responses.

Rapid generation of full clinical-grade human antiadenovirus cytotoxic T cells for adoptive immunotherapy

Adenovirus (ADV) infections are one of the major causes of morbidity and mortality after hematopoietic stem cell transplantation, despite new antiviral treatment strategies. We describe here a complete clinical-grade generation of human anti-ADV cytotoxic T cells to propose an adoptive immunotherapy. Peripheral blood mononuclear cells (PBMC) from 7 healthy donors, known for their good cellular immunity against ADV, were stimulated for 6 hours with a synthetic peptide pool covering the ADV5 Hexon protein interferon-gamma (IFN-gamma) secreting cells were isolated on a clinical device. After immunoselection, a mean number of 1.01 +/- 0.84 x 10(6) total nucleated cells was obtained. The isolated ADV-specific T cells were mainly CD4+ (mean=56% +/- 20.8%, yield=51% +/- 32.4%) but also CD8+ (mean=42% +/- 27%, yield = 56% +/- 39.3%). Isolated T lymphocytes (CTL) were expanded to carry out functional tests. Ability of the expanded CTL to secrete IFN-gamma and to proliferate after restimulation with the ADV peptide pool was confirmed. A high cytotoxicity against autologous target cells loaded with ADV antigens was observed but not against nonloaded target cells. We observed a decrease of 1.27 log of the allogeneic reaction against non HLA identical healthy donor PBMC with CTL compared with the PBMC before selection. Clinical-grade generation of ADV-specific T cells was achieved with a synthetic antigen. This technology has the advantage of being fast, and is sufficiently reactive to be proposed for immunotherapy if antiviral treatment fails.

How I treat adenovirus in hematopoietic stem cell transplant recipients

Adenovirus (AdV) infections are very common in the general pediatric population. The delayed clearance in young persons imposes a threat to immunocompromised patients after hematopoietic stem cell transplantation (HSCT), who can reactivate the virus, resulting in life-threatening disseminated disease. Although a definitive cure requires adequate immune reconstitution, 2 approaches appear to be feasible and effective to improve the outcomes of AdV infections. Strict monitoring with AdV quantitative polymerase chain reaction followed by preemptive treatment with low-dose (1 mg/kg) cidofovir 3 times a week, is effective in most cases to bridge the severely immunocompromised period shortly after HSCT, with acceptable toxicity rates. For centers who have the access, AdV-specific cytotoxic T cells can be the other important cornerstone of anti-AdV therapy with promising results so far. Methods to positively influence the reconstitution of the immune system after HSCT and optimizing new and currently available cellular immunotherapies will make HSCT safer against the threat of AdV infection/reactivation and associated disease.

Comparison of in-house real-time quantitative PCR to the Adenovirus R-Gene kit for determination of adenovirus load in clinical samples

In the context of hematopoietic stem cell transplantation, adenovirus infections are associated with relevant mortality and morbidity. Detection of adenovirus DNA by quantitative PCR is the "gold standard" for these patients. A total of 150 samples, namely, 78 whole-blood, 22 cerebrospinal fluid, 24 digestive biopsy, and 26 stool samples, from 29 patients, including 24 hematopoietic stem cell transplant recipients, were tested for the detection of adenovirus using an in-house real-time quantitative PCR assay (A. Heim, C. Ebnet, G. Harste, and P. Pring-Akerblom, J. Med. Virol. 70:228-239, 2003) and the commercially available Adenovirus R-Gene kit. Adenovirus DNA was automatically isolated from whole-blood samples (Magna Pure LC system; Roche) or was manually extracted from other specimens (QIAamp; Qiagen) using the appropriate kit. The intra- and interassay reproducibilities and sensitivities were evaluated with cell culture supernatant dilutions. Of the 150 samples tested, 86 were found to be positive and 55 were found to be negative using both techniques. Nine (6%) discordant results were obtained. In most cases, discrepant results concerned samples with low viral loads. Quantitative results for all concordant positive samples were analyzed using the Spearman correlation test. A good correlation between the results of the in-house assay and those of the kit assay was obtained (r = 0.95; P < 0.001). Regarding the threshold cycle value for internal control spiked samples, none of the 150 samples tested contained a PCR inhibitor. In conclusion, a relevant correlation of results between the in-house assay and the kit assay, as well as the high-quality reproducibility and sensitivity of the kit assay, warranted its use for follow-up of hematopoietic stem cell transplantation recipients.

Absence of systemic immune response to adenovectors after intraocular administration to children with retinoblastoma

The ocular environment has been shown to induce tolerance to locally administered antigens. We therefore investigated whether there was a systemic immune response against adenoviral vectors injected into the vitreous of retinoblastoma patients enrolled in a phase 1 clinical trial of adenoviral-mediated thymidine kinase gene transfer. Sections of enucleated eyes were immunostained with antibodies against inflammatory cells. A trend toward increasing numbers of plasma cells, T cells, macrophages, and antigen-presenting cells was observed in the injected subjects' eyes, but systemically, there was no significant increase in the number of adenovirus-specific cytotoxic T lymphocytes (CTLs) or in adenovirus neutralizing antibodies. Therefore, in contrast to studies showing significant immunogenicity of Ad-RSVtk following injection into extraocular tumors, injection into the eye produces only a mild local inflammatory response without evidence of systemic cellular or humoral immune responses to adenovirus.

Combined CD8+ and CD4+ adenovirus hexon-specific T cells associated with viral clearance after stem cell transplantation as treatment for adenovirus infection

BACKGROUND

Human adenovirus can cause morbidity and mortality in immunocompromised patients after allogeneic stem cell transplantation. Reconstitution of adenovirus-specific CD4(+) T cells has been reported to be associated with sustained protection from adenovirus disease, but epitope specificity of these responses has not been characterized. Since mainly CD4(+) T cells and no CD8(+) T cells specific for adenovirus have been detected after allogeneic stem cell transplantation, the relative contribution of adenovirus-specific CD4(+) and CD8(+) T cells in protection from adenovirus disease remains to be elucidated.

DESIGN AND METHODS

The presence of human adenovirus hexon-specific T cells was investigated in peripheral blood of pediatric and adult allogeneic stem cell transplant recipients, who showed spontaneous resolution of disseminated adenovirus infection. Subsequently, a clinical grade method was developed for rapid generation of adenovirus-specific T-cell lines for adoptive immunotherapy.

RESULTS

Clearance of human adenovirus viremia coincided with emergence of a coordinated CD8(+) and CD4(+) T-cell response against adenovirus hexon epitopes in patients after allogeneic stem cell transplantation. Activation of adenovirus hexon-specific CD8(+) and CD4(+) T cells with a hexon protein-spanning peptide pool followed by interferon-γ-based isolation allowed rapid expansion of highly specific T-cell lines from healthy adults, including donors with very low frequencies of adenovirus hexon-specific T cells. Adenovirus-specific T-cell lines recognized multiple MHC class I and II restricted epitopes, including known and novel epitopes, and efficiently lysed human adenovirus-infected target cells.

CONCLUSIONS

This study provides a rationale and strategy for the adoptive transfer of donor-derived human adenovirus hexon-specific CD8(+) and CD4(+) T cells for the treatment of disseminated adenovirus infection after allogeneic stem cell transplantation.

Observational prospective study of viral infections in children undergoing allogeneic hematopoietic cell transplantation: a 3-year GETMON experience

We studied surveillance, incidence and outcome of viral infections in children undergoing allogeneic hematopoietic cell transplantation (HCT) in the main pediatric transplant units in Spain. We prospectively collected data from first year post-HCT in every consecutive allogeneic HCT performed during 3 years (N = 215): first HCT = 188 and second HCT = 27; median age = 6.6 years (0.1-20.7). Most patients had acute leukemia (N = 137) and 135 recipients (63%) were CMV seropositive. A total of 46 patients underwent cord blood transplant, 133 patients underwent HCT from alternative donors (62%) and 101 patients received anti-thymocyte globulin. Observational time was completed in 137 patients, whereas the remaining 78 died after a median survival time of 99 days (3-352). CMV was monitored in all patients; adenovirus (ADV) and human herpesvirus 6 (HHV-6) were monitored in 101 and 33 patients, respectively. We found 145 viral infections in 103 patients: CMV (n = 42), ADV (n = 32), HHV-6 (n = 7), polyomavirus (n = 20), EBV (n = 6), VZV (n=17) and others (n = 8). CMV infection was significantly higher in seropositive patients (25 vs 7%) (P = 0.02). Extensive chronic GVHD (cGVHD) was significantly associated with an increased rate of viral infections (12 of 16 patients with cGVHD had infections vs 91 of 199 without GVHD) (P = 0.035). In total, 10 patients (4.6%) died of viral infections (CMV = 5, ADV = 3, respiratory = 2). We found a high incidence of viral infection, but mortality was low.

Adenovirus infections in solid organ transplant recipients

PURPOSE OF REVIEW

Adenoviruses are emerging as important viral pathogens in solid organ transplant recipients, impacting morbidity, graft survival and even mortality. This review will discuss the current understanding of the epidemiology, diagnosis and therapy of adenovirus infection in transplant recipients.

RECENT FINDINGS

Advances in the field include the use of polymerase chain reaction in the diagnosis of adenoviral infection, a better understanding of the epidemiology, immune response and potential new therapies, including preemptive and adoptive immunotherapy strategies. Adenoviral infections appear to be common, especially in pediatric solid organ transplant. Generally well tolerated, some high-risk patients may develop disseminated disease causing graft failure, which may lead to retransplant and/or death. Antiviral therapy and immunotherapy may play a role in these patients, although prospective controlled data are not available at this time.

SUMMARY

Although new tools and a better understanding of the epidemiology, risk factors and therapies for adenovirus are beginning to materialize, prospective, controlled trials, using careful definitions, and standardized methodologies need to be performed to more fully clarify these issues in solid organ transplant recipients.

Cytotoxic T lymphocyte therapy with donor T cells prevents and treats adenovirus and Epstein-Barr virus infections after haploidentical and matched unrelated stem cell transplantation

Viral infection or reactivation remains a major cause of morbidity and mortality after allogeneic stem cell transplantation. We now show that infusions of single cytotoxic T lymphocyte (CTL) lines (5 x 10(6)-1.35 x 10(8) cells/m(2)) with specificity for 2 commonly detected viruses, Epstein-Barr virus (EBV) and adenovirus, can be safely administered to pediatric transplantation recipients receiving partially human leukocyte antigen-matched and haploidentical stem cell grafts (n = 13), without inducing graft-versus-host disease. The EBV-specific component of the CTLs expanded in vivo and persisted for more than 12 weeks, but the adenovirus-specific component only expanded in vivo in the presence of concomitant adenoviral infection. Nevertheless, adenovirus-specific T cells could be detected for at least 8 weeks in peripheral blood, even in CTL recipients without viral infection, provided the adenovirus-specific component of their circulating lymphocytes was first expanded by exposure to adenoviral antigens ex vivo. After infusion, none of these 13 high-risk recipients developed EBV-associated lymphoproliferative disease, while 2 of the subjects had resolution of their adenoviral disease. Hence, bispecific CTLs containing both EBV- and adenovirus-specific T cells can safely reconstitute an antigen responsive "memory" population of CTLs after human leukocyte antigen-mismatched stem cell transplantation and may provide antiviral activity. This trial was registered at www.clinicaltrials.gov as #NCT00590083.

Nucleofection of DCs to generate Multivirus-specific T cells for prevention or treatment of viral infections in the immunocompromised host

Viral infections cause morbidity and mortality in allogeneic hematopoietic stem cell transplant (HSCT) recipients. To prevent and treat these, we have produced and infused cytotoxic T lymphocytes (CTLs) with specificity for Epstein-Barr virus (EBV), cytomegalovirus (CMV), and adenovirus (Adv), and shown that small numbers of infused cells proliferate in vivo and protect against all three viruses. Despite these encouraging results, broader implementation of this approach is limited by the need for infectious virus material (EBV), expensive production of clinical grade adenoviral vectors, and a prolonged (8-12 weeks) period of manufacture. There is also competition between virus-derived antigens within antigen-presenting cells (APCs), limiting extension to additional agents. We now describe an approach that uses DNA nucleofection of dendritic cells (DCs) with DNA plasmids that encode a range of immunodominant and subdominant viral antigens from CMV, EBV, BK, and Adv. Within 10 days, this methodology provides multivirus-reactive CTLs that lack alloreactivity. We further demonstrate that nucleofected DC stimulation can be combined with interferon-gamma (IFN-gamma) capture technology to produce even more rapid multivirus-CTL products for treatment of acute infection. These CTL generation procedures should increase the feasibility and applicability of T-cell therapy.

Role of HLA in hematopoietic SCT

HLA disparity between hematopoietic stem cell (HSC) donor and recipient triggers T-cell and NK-cell allorecognition, and induces the GVHD, GVL effect and/or may cause an engraftment failure. This review will cover the scope of human genomic variation, the methods of HLA typing and interpretation of high-resolution HLA results. We describe the main subsets of related and unrelated HSC donors and outline the main aspects of HLA disparity and their effect on the outcome of the patients after allogeneic HSC transplantation (HSCT). The HLA match between HSCT donor and recipient is crucial, but for many patients a perfectly matched donor is not available. The HSCT from the alternative mismatched donor with one allele/antigen mismatch (9/10) can be as beneficial as a HSCT from a fully matched donor, especially in younger patients. For the remaining patients, the donors with permissive mismatches may be the option. The permissiveness depends not only on the potential adverse effect of the HLA mismatches, but also on the urgency of the transplantation, the desirable GVL effect and the potential efficacy of the alternative therapy available for the patient.

Quantitative temporal and spatial distribution of adenovirus type 2 correlates with disease manifestations and organ failure during disseminated infection

Disseminated adenovirus (HAdV) infections are serious complications in allogenic stem cell transplant (SCT) recipients. Quantitative HAdV DNA detection in blood samples demonstrated the association of high virus loads with disease and improved early diagnosis. However, the pathogenesis of disseminated HAdV disease, for example sources of HAdV DNA shedding in the blood stream and association of HAdV replication sites with disease manifestations, remained obscure. In this report, 24 bioptic and autoptic organ and tissue samples of an adult SCT recipient suffering from disseminated infection were quantitatively analyzed for HAdV DNA. Results indicate subsequent virus replication in the colon, bone marrow and liver as origin of HAdV DNAemia, which increased from 1.4 x 10(4) copies/ml to a peak of 2 x 10(9) copies/ml over a period of 84 days in spite of antiviral therapy. Symptoms as diarrhoea, bone marrow failure and hepatic failure were clearly linked to high HAdV DNA concentrations in affected organs. For example, the HAdV DNA level was 2.2 x 10(3) copies/cell in a colon biopsy when the patient suffered from diarrhoea whereas only 1.1 x 10(1) copies/cell were detected when symptoms had improved. Focal HAdV infection of the liver as demonstrated by laser microdissection was followed by fulminant virus replication with 1.3 x 10(5) copies of HAdV DNA/cell causing terminal hepatic failure. In conclusion, pathogenesis of disseminated HAdV disease was associated with virus replication in affected organs and not immune mediated as suggested recently by a fatal case of gene therapy with a non-replication competent HAdV-C5 vector.

Adoptive cellular immunotherapy for viral diseases

Viral infections remain a major cause of morbidity and mortality after pediatric hematopoietic stem cell transplantation. Adoptive transfer of donor-derived virus-specific T cells can reconstitute antiviral immunity in recipients and be effective both in preventing and treating cytomegalovirus, Epstein-Barr virus and adenovirus infection. Current efforts are focused on providing protection toward a broader range of viruses safely, rapidly and effectively.

Identification of hexon-specific CD4 and CD8 T-cell epitopes for vaccine and immunotherapy

Adenoviral infections in the immunocompromised host are associated with significant morbidity and mortality. Although the adoptive transfer of adenovirus-specific T cells may prevent and treat such infections, the T-cell immune response to the multiplicity of adenovirus serotypes and subspecies that infect humans has not been well characterized, impeding the development of such approaches. We have, therefore, analyzed the specificities of T-cell responses to the viral capsid hexon antigen, since this structure is highly conserved in human pathogens. We screened 25 human cytotoxic T-cell lines with adenovirus specificity to extensively characterize their responses to adenoviral hexon and to identify a panel of novel CD4(+) and CD8(+) T-cell epitopes. Using a peptide library spanning the entire sequence of the hexon protein, we confirmed the responsiveness of these cytotoxic T-cell lines to seven peptides described previously and also identified 33 new CD4- or CD8-restricted hexon epitopes. Importantly, the majority of these epitopes were shared among different adenovirus subspecies, suggesting that T cells with such specificities could recognize and be protective against multiple serotypes, simplifying the task of effective adoptive transfer or vaccine-based immunotherapy for treating infection by this virus.