Adenovirus-specific CD4+ T cell clones recognizing endogenous antigen inhibit viral replication in vitro through cognate interaction

Adenoviral fiber-knob based vaccination elicits efficient neutralizing antibodies and T cell responses against adenovirus infection

BACKGROUND

Human adenoviruses (HAdVs) frequently cause common respiratory or gastrointestinal infections among children, adults, individuals with immune deficiencies, and other vulnerable populations with varying degree of symptoms, ranging from mild to server, and in some cases, even fatalities. Despite the significant clinical impact of HAdVs, there is currently no approved vaccine available.

METHODS

This study explores the potential of the adenovirus type 5 fiber knob (Ad5-FK) to stimulate the production of Ad-specific neutralizing antibodies and T-cell responses in mice. Based on structure predictions, we first expressed Ad5-FK in E. coli and confirmed the assembly of FK into its trimeric form. After testing the binding capability of the trimeric FK to susceptible cells, the immunogenicity of the protein in combination with the c-di-AMP adjuvant was assessed in BALB/c mice.

RESULTS

The purified Ad5-FK exhibited self-trimerization and maintained correct conformation akin to the authentic FK structure. This facilitated effective binding to susceptible HEK293 cells. Notably, the protein demonstrated significant inhibition of HEK293 cells infection by rAd5-GFP. Immunization of BALB/c mice with Ad5-FK, or Ad5-FK mixed with c-di-AMP yielded FK-specific antibodies with potent neutralization capacity. Significantly, Ad5-FK was found to elicit a vigorous CD4+ T-cell response in the immunized mice.

CONCLUSION

Our findings underscore the efficacy of FK-based vaccine in eliciting anti-Ad humoral immune response and CD4 T-cell immune reactions essential for protection against viral infections.

Single-cell transcriptomics in bone marrow delineates CD56dimGranzymeK+ subset as intermediate stage in NK cell differentiation

Human natural killer (NK) cells in lymphoid tissues can be categorized into three subsets: CD56^brightCD16⁺, CD56^dimCD16⁺ and CD69⁺CXCR6⁺ lymphoid tissue-resident (lt)NK cells. How the three subsets are functionally and developmentally related is currently unknown. Therefore, we performed single-cell RNA sequencing combined with oligonucleotide-conjugated antibodies against CD56, CXCR6, CD117 and CD34 on fresh bone marrow NK cells. A minor CD56^dimGzmK⁺ subset was identified that shared features with CD56^bright and CD56^dimGzmK^- NK cells based on transcriptome, phenotype (NKG2A^highCD16^lowKLRG1^highTIGIT^high) and functional analysis in bone marrow and blood, supportive for an intermediate subset. Pseudotime analysis positioned CD56^bright, CD56^dimGzmK⁺ and CD56^dimGzmK^- cells in one differentiation trajectory, while ltNK cells were developmentally separated. Integrative analysis with bone marrow cells from the Human Cell Atlas did not demonstrate a developmental connection between CD34⁺ progenitor and NK cells, suggesting absence of early NK cell stages in bone marrow. In conclusion, single-cell transcriptomics provide new insights on development and differentiation of human NK cells.

T and NK Cells in IL2RG-Deficient Patient 50 Years After Hematopoietic Stem Cell Transplantation

The first successful European hematopoietic stem cell transplantation (HSCT) was performed in 1968 as treatment in a newborn with IL2RG deficiency using an HLA-identical sibling donor. Because of declining naive T and natural killer (NK) cells, and persistent human papilloma virus (HPV)-induced warts, the patient received a peripheral stem cell boost at the age of 37 years. NK and T cells were assessed before and up to 14 years after the boost by flow cytometry. The boost induced renewed reconstitution of functional NK cells that were 14 years later enriched for CD56dimCD27+ NK cells. T-cell phenotype and T-cell receptor (TCR) repertoire were simultaneously analyzed by including TCR Vβ antibodies in the cytometry panel. Naive T-cell numbers with a diverse TCR Vβ repertoire were increased by the boost. Before and after the boost, clonal expansions with a homogeneous TIGIT and PD-1 phenotype were identified in the CD27− and/or CD28− memory population in the patient, but not in the donor. TRB sequencing was applied on sorted T-cell subsets from blood and on T cells from skin biopsies. Abundant circulating CD8 memory clonotypes with a chronic virus-associated CD57+KLRG1+CX3CR1+ phenotype were also present in warts, but not in healthy skin of the patient, suggesting a link with HPV. In conclusion, we demonstrate in this IL2RG-deficient patient functional NK cells, a diverse and lasting naive T-cell compartment, supported by a stem cell boost, and an oligoclonal memory compartment half a century after HSCT.

mRNA- and Adenovirus-Based Vaccines against SARS-CoV-2 in HIV-Positive People

About two years have passed since the identification of SARS-CoV-2 in China. The rapid spread of this virus all over the world and its high transmissibility and pathogenicity in humans have resulted in a global pandemic. The negative impact of COVID-19 on health, society and the economy at the global level has pushed researchers and pharmaceutical companies to develop effective vaccines to fight SARS-CoV-2. Thanks to this collaborative effort, the first COVID-19 vaccine was developed in less than a year. Since then, several COVID-19 vaccines have been validated for use by the World Health Organization. Among these, mRNA- (BNT162b2 and mRNA1273) and adenovirus-based (ChAdOx1) vaccines were developed through the use of novel technologies. While all three of these vaccines have shown effectiveness against the COVID-19 disease and their immunogenicity was characterized in clinical trials in the general population, data on their efficacy and immunogenicity in people living with HIV (PLWH) are limited. In this review, we provide a description of the characteristics of mRNA- and adenovirus-based vaccines and of the immune response elicited in the general population by vaccination. Then we describe the use of these vaccines and their efficacy and immunogenicity in people living with HIV and we conclude with a discussion regarding some open questions concerning the use of mRNA- and adenovirus-based COVID-19 vaccines in PLWH.

Local therapy with an engineered oncolytic adenovirus enables antitumor response in non-injected melanoma tumors in mice treated with aPD-1

Intratumoral immunotherapies are entering clinical use but concerns remain regarding their effects on non-injected tumors. Here, we studied the impact of local treatment with an adenovirus coding for TNFa and IL-2 on systemic antitumor response in animals receiving aPD-1 (anti-programmed cell death protein 1) therapy. Using bilateral murine melanoma models, we tested systemic tumor response to combined therapy with anti-PD-1 and an adenovirus coding for TNFa and IL-2 ("virus"). Virus was given intratumorally (to one of the two tumors only) and aPD-1 monoclonal antibody systemically. We evaluated both tumors' response to treatment, overall survival, metastasis development, and immunological mechanisms involved with response. Consistent tumor control was observed in both injected and non-injected tumors, including complete response in all treated animals receiving aPD-1+ virus therapy. Mechanistically, virus injections enabled potent effector lymphocyte response locally, with systemic effects in non-injected tumors facilitated by aPD-1 treatment. Moreover, adenovirus therapy demonstrated immunological memory formation. Virus therapy was effective in preventing metastasis development. Local treatment with TNFa and IL-2 coding adenovirus enhanced systemic response to aPD-1 therapy, by re-shaping the microenvironment of both injected and non-injected tumors. Therefore, our pre-clinical data support the rationale for a trial utilizing a combination of aPD-1 plus virus for the treatment of human cancer.

Adenoviral vector-based platforms for developing effective vaccines to combat respiratory viral infections

Since the development of the first vaccine against smallpox over two centuries ago, vaccination strategies have been at the forefront of significantly impacting the incidences of infectious diseases globally. However, the increase in the human population, deforestation and climate change, and the rise in worldwide travel have favored the emergence of new viruses with the potential to cause pandemics. The ongoing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic is a cruel reminder of the impact of novel pathogens and the suboptimal capabilities of conventional vaccines. Therefore, there is an urgent need to develop new vaccine strategies that allow the production of billions of doses in a short duration and are broadly protective against emerging and re-emerging infectious diseases. Extensive knowledge of the molecular biology and immunology of adenoviruses (Ad) has favored Ad vectors as platforms for vaccine design. The Ad-based vaccine platform represents an attractive strategy as it induces robust humoral and cell-mediated immune responses and can meet the global demand in a pandemic situation. This review describes the status of Ad vector-based vaccines in preclinical and clinical studies for current and emerging respiratory viruses, particularly coronaviruses, influenza viruses and respiratory syncytial viruses.

Potential Diagnostic and Prognostic Biomarkers for Adenovirus Respiratory Infection in Children and Young Adults

Human Adenoviruses (HAdV) are known to be potentially associated with strong inflammatory responses and morbidity in pediatric patients. Although most of the primary infections are self-limiting, the severity of clinical presentation, the elevation of the white blood cell count and inflammatory markers often mimic a bacterial infection and lead to an inappropriate use of antibiotics. In infections caused by HAdV, rapid antigen detection kits are advisable but not employed routinely; costs and feasibility of rapid syndromic molecular diagnosis may limit its use in the in-hospital setting; lymphocyte cultures and two-sampled serology are time consuming and impractical when considering the use of antibiotics. In this review, we aim to describe the principal diagnostic tools and the immune response in HAdV infections and evaluate whether markers based on the response of the host may help early recognition of HAdV and avoid inappropriate antimicrobial prescriptions in acute airway infections.

Virus-specific T cells for adenovirus infection after stem cell transplantation are highly effective and class II HLA restricted

Infection with adenoviruses is a common and significant complication in pediatric patients after allogeneic hematopoietic stem cell transplantation. Treatment options with traditional antivirals are limited by poor efficacy and significant toxicities. T-cell reconstitution is critical for the management of adenoviral infections, but it generally takes place months after transplantation. Ex vivo-generated virus-specific T cells (VSTs) are an alternative approach for viral control and can be rapidly generated from either a stem cell donor or a healthy third-party donor. In the context of a single-center phase 1/2 clinical trial, we treated 30 patients with a total of 43 infusions of VSTs for adenoviremia and/or adenoviral disease. Seven patients received donor-derived VSTs, 21 patients received third-party VSTs, and 2 received VSTs from both donor sources. Clinical responses were observed in 81% of patients, with a complete response in 58%. Epitope prediction and potential epitope identification for common HLA molecules helped elucidate HLA restriction in a subset of patients receiving third-party products. Intracellular interferon-γ expression in T cells in response to single peptides and response to cell lines stably transfected with a single HLA molecule demonstrated HLA-restricted CD4+ T-cell response, and these results correlated with clinical outcomes. Taken together, these data suggest that VSTs are a highly safe and effective therapy for the management of adenoviral infection in immunocompromised hosts. The trials were registered at www.clinicaltrials.gov as #NCT02048332 and #NCT02532452.

Immune Response against Adenovirus in Acute Upper Respiratory Tract Infections in Immunocompetent Children

During acute upper respiratory tract infections (AURTIs) caused by Adenoviruses, the mix of severe clinical presentation, together with elevation of white blood cells (WBCs) and C-reactive protein (CRP), often mimicking bacterial infection, leads to an inappropriate use of antibiotics. We studied 23 immunocompetent children admitted to our Pediatric Emergency Unit with signs of acute Adenoviral AURTIs, aiming at better clarifying the biological background sustaining this clinical presentation. Infection etiology was tested with nasopharyngeal swabs, serology, and DNA-PCR. During fever peaks and subsequent recovery, we assessed WBC count with differential, CRP, procalcitonin, serum concentration of six inflammatory cytokines, and lymphocyte subset populations. Results: IL-6 and IL-8 were found elevated in the acute phase, whereas a significant decrease during recovery was found for IL-6 and IL-10. We highlighted an increase of B lymphocytes in the acute phase; conversely, during recovery, an increase in T regulatory cells was noted. Monocytes and leukocytes were found markedly elevated during fever peaks compared to convalescence. All patients recovered uneventfully. The composition of lymphocyte population subsets and serum alterations are the main drivers of an overprescribed antibiotic. Examination of hospital admissions and performance is needed in further investigations to rule out bacterial infections or inflammatory syndromes.

Human Bone Marrow-Resident Natural Killer Cells Have a Unique Transcriptional Profile and Resemble Resident Memory CD8+ T Cells

Human lymphoid tissues harbor, in addition to CD56^bright and CD56^dim natural killer (NK) cells, a third NK cell population: CD69⁺CXCR6⁺ lymphoid tissue (lt)NK cells. The function and development of ltNK cells remain poorly understood. In this study, we performed RNA sequencing on the three NK cell populations derived from bone marrow (BM) and blood. In ltNK cells, 1,353 genes were differentially expressed compared to circulating NK cells. Several molecules involved in migration were downregulated in ltNK cells: S1PR1, SELPLG and CD62L. By flow cytometry we confirmed that the expression profile of adhesion molecules (CD49e⁻, CD29^low, CD81^high, CD62L⁻, CD11c⁻) and transcription factors (Eomes^high, Tbet^low) of ltNK cells differed from their circulating counterparts. LtNK cells were characterized by enhanced expression of inhibitory receptors TIGIT and CD96 and low expression of DNAM1 and cytolytic molecules (GZMB, GZMH, GNLY). Their proliferative capacity was reduced compared to the circulating NK cells. By performing gene set enrichment analysis, we identified DUSP6 and EGR2 as potential regulators of the ltNK cell transcriptome. Remarkably, comparison of the ltNK cell transcriptome to the published human spleen-resident memory CD8⁺ T (Trm) cell transcriptome revealed an overlapping gene signature. Moreover, the phenotypic profile of ltNK cells resembled that of CD8⁺ Trm cells in BM. Together, we provide transcriptional and phenotypic data that clearly distinguish ltNK cells from both the CD56^bright and CD56^dim NK cells and substantiate the view that ltNK cells are tissue-resident cells, which are functionally restrained in killing and have low proliferative activity.

Cellular Immunotherapy for Hematologic Malignancies: Beyond Bone Marrow Transplantation

Immunotherapy has changed treatment practices for many hematologic malignancies. Even in the current era of targeted therapy, chemotherapy remains the backbone of treatment for many hematologic malignancies, especially in acute leukemias, where relapse remains the major cause of mortality. Application of novel immunotherapies in hematology attempts to harness the killing power of the immune system against leukemia and lymphoma. Cellular immunotherapy is evolving rapidly for high-risk hematologic disorders. Recent advances include chimeric antigen-receptor T cells, mesenchymal stromal/stem cells, dendritic cell tumor vaccines, cytokine-induced killer cells, and virus-specific T cells. The advantages of nontransplantation cellular immunotherapy include suitability for patients for whom transplantation has failed or is contraindicated, and a potentially less-toxic treatment alternative to transplantation for relapsed/refractory patients. This review examines those emerging cellular immunotherapies that are changing treatment paradigms for patients with hematologic malignancies.

Human Lymphoid Tissues Harbor a Distinct CD69+CXCR6+ NK Cell Population

Knowledge of human NK cells is based primarily on conventional CD56(bright) and CD56(dim) NK cells from blood. However, most cellular immune interactions occur in lymphoid organs. Based on the coexpression of CD69 and CXCR6, we identified a third major NK cell subset in lymphoid tissues. This population represents 30-60% of NK cells in marrow, spleen, and lymph node but is absent from blood. CD69(+)CXCR6(+) lymphoid tissue NK cells have an intermediate expression of CD56 and high expression of NKp46 and ICAM-1. In contrast to circulating NK cells, they have a bimodal expression of the activating receptor DNAX accessory molecule 1. CD69(+)CXCR6(+) NK cells do not express the early markers c-kit and IL-7Rα, nor killer cell Ig-like receptors or other late-differentiation markers. After cytokine stimulation, CD69(+)CXCR6(+) NK cells produce IFN-γ at levels comparable to CD56(dim) NK cells. They constitutively express perforin but require preactivation to express granzyme B and exert cytotoxicity. After hematopoietic stem cell transplantation, CD69(+)CXCR6(+) lymphoid tissue NK cells do not exhibit the hyperexpansion observed for both conventional NK cell populations. CD69(+)CXCR6(+) NK cells constitute a separate NK cell population with a distinct phenotype and function. The identification of this NK cell population in lymphoid tissues provides tools to further evaluate the cellular interactions and role of NK cells in human immunity.

Virus-specific T-cell therapy in solid organ transplantation

This article reviews the current state of T-cell therapy as therapeutic option for virus-associated diseases against the background of the most common viral complications and their standard treatment regimens after SOT. The available data of clinical T-cell trials in SOT are summarized. References to the hematopoietic stem cell transplantation are made if applicable data in SOT are not available and their content was considered likewise valid for cell therapy in SOT. Moreover, aspects of different manufacturing approaches including beneficial product characteristics and the importance of GMP compliance are addressed.

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.

Characterization of urinary CD4⁺ and CD8⁺ T cells in kidney transplantation patients with polyomavirus BK infection and allograft rejection

BACKGROUND AND OBJECTIVES

The objective of this study was to characterize CD4(+) and CD8(+) T-cell populations in blood and urine of renal transplant patients with BK virus (BKV) infection or allograft rejection.

MATERIALS AND METHODS

Percentages and absolute numbers of CD4(+) and CD8(+) effector memory T-cell subtype (TEM ) and terminal differentiated T cells (TTD ) in renal transplant patients with BKV infection (n = 14), with an episode of allograft rejection (n = 9), and in uncomplicated renal transplant patients with a stable kidney function (n = 12) were measured and compared using 4-color fluorescence-activated cell sorting. Results were correlated with the number of CD4(+) and CD8(+) T cells in renal biopsies.

RESULTS

In patients with allograft rejection, the number of urinary CD4(+) TEM and CD8(+) TEM cells was significantly increased compared to patients with BKV infection or patients without complications. Positive correlation was found between the number of CD4(+) and CD8(+) cells in the renal biopsies and the number of CD4(+) and CD8(+) cells in urine. In patients with rejection, after 2 months of immunosuppressive therapy, a reduction in urinary CD8(+) TEM cells was found.

CONCLUSIONS

CD4(+) TEM and CD8(+) TEM cells in urine could be a marker to distinguish allograft rejection from BKV-associated nephropathy and to monitor therapy effectiveness in renal transplant patients with allograft rejection.

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.

22q11.2 deletion syndrome with life-threatening adenovirus infection

Adenovirus causes significant morbidity and mortality in immunocompromised children. We report how an infusion of HLA-matched sibling donor T lymphocytes rapidly eradicated life-threatening, high-level adenoviremia in a child with complete DiGeorge syndrome (22q11.2 deletion) who went on to reconstitute a diverse, donor-derived, postthymic T-cell repertoire.

Communication between human mast cells and CD4(+) T cells through antigen-dependent interactions

Mast cells (MCs) are immune cells residing in tissues where pathogens are first encountered. It has been indicated that MCs might also be involved in setting the outcome of T-cell responses. However, little is known about the capacity of human MCs to express MHC class II and/or to capture and present antigens to CD4(+) T cells. To study the T-cell stimulatory potential of human MCs, CD34(+) stem cell derived MCs were generated. These cells expressed HLA-DR when stimulated with IFN-γ, and, importantly, presented peptide and protein for activation of antigen-specific CD4(+) T cells. The interplay between MC and T cell led to increased HLA-DR expression on MCs. MCs were present in close proximity to T cells in tonsil and expressed HLA-DR and CD80, indicating their ability to present antigens to CD4(+) T cells in T-cell areas of human LNs. Our data show that MCs can present native antigens to human CD4(+) T cells and that HLA-DR expressing MCs are present in tonsil tissue, indicating that human MCs can directly activate T cells and provide a rationale to study the potential of MCs to prime and/or skew human T-cell responses.

Selection of perforin expressing CD4+ adenovirus-specific T-cells with artificial antigen presenting cells

Adenoviruses (HAdV) can cause life threatening infections, especially in paediatric patients after allogeneic stem cell transplantation (SCT). Yet, no effective antiviral medication is available. One treatment option is adoptive transfer of HAdV-specific T-cells from the graft donor into the patient. Especially CD4+ T-cells are critical to control HAdV infection. To allow for applicability of CD4+ T-cells in adoptive therapy, sufficient numbers of HAdV-specific T-cells with low levels of residual alloreactive T-cells are required. In this study, we explored the possibility to selectively expand and isolate functional HAdV-specific T-cells from PBMCs in response to 15-mer peptides using artificial antigen-presenting cells (aAPCs), composed of liposomes harbouring HAdV-peptide/HLA-Class-II complexes. HAdV-specific T-cells generated using this method produce mainly pro-inflammatory cytokines, express perforin and granzyme B, kill HAdV-infected cells effectively and are not alloreactive. Thus, the generation and isolation of HAdV-specific CD4+ T-cells seem a critical step towards specific adoptive therapy for HAdV infections after allogeneic SCT.

Immunotherapy of human papilloma virus induced disease

Immunotherapy is the generic name for treatment modalities aiming to reinforce the immune system against diseases in which the immune system plays a role. The design of an optimal immunotherapeutic treatment against chronic viruses and associated diseases requires a detailed understanding of the interactions between the target virus and its host, in order to define the specific strategies that may have the best chance to deliver success at each stage of disease. Recently, a first series of successes was reported for the immunotherapy of Human Papilloma Virus (HPV)-induced premalignant diseases but there is definitely room for improvement. Here I discuss a number of topics that in my opinion require more study as the answers to these questions allows us to better understand the underlying mechanisms of disease and as such to tailor treatment.

Polyomavirus JC-targeted T-cell therapy for progressive multiple leukoencephalopathy in a hematopoietic cell transplantation recipient

Progressive multifocal leukoencephalopathy (PML) associated with polyomavirus JC (JCV) infection has been reported to be usually fatal in allogeneic hematopoietic SCT (HSCT) recipients. We present the case of a 19-year-old HSCT patient diagnosed with JCV-associated PML after prolonged immunosuppression for severe GVHD. No short-term neurological improvement was observed after antiviral treatment and discontinuation of immunosuppressive therapy. Donor-derived JCV Ag-specific CTLs were generated in vitro after stimulation with 15-mer peptides derived from VP1 and large T viral proteins. After adoptive CTL infusion, virus-specific cytotoxic cells were shown in the peripheral blood, JCV-DNA was cleared in the cerebrospinal fluid and the patient showed remarkable improvement. Adoptive T-lymphocyte therapy with JCV-specific CTLs was feasible and had no side effects. This case suggests that adoptive transfer of JCV-targeted CTLs may contribute to restore JCV-specific immune competence and control PML in transplanted patients.

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.

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.

Ex vivo detection of adenovirus specific CD4+ T-cell responses to HLA-DR-epitopes of the Hexon protein show a contracted specificity of T(HELPER) cells following stem cell transplantation

Human adenovirus (HAdV) is a cause of significant morbidity and mortality in immunocompromised patients, especially after stem cell transplantation (SCT). Viral clearance has been attributed to CD4(+) T-cell responses against the Hexon-protein, but the frequency of specific T(HELPER) cells is extremely low or not detectable ex vivo and preference for different CD4(+) T-cell epitopes is variable among individuals. We therefore analyzed 44 healthy donors and 6 SCT-recipients for Hexon-specific CD4(+)-responses ex vivo, to identify epitopes which would be broadly applicable. We selected 19 candidate epitopes with predicted restriction to HLA-DR1/DR3/DR4/DR7; 16 were located within the highly conserved regions, indicating cross-reactivity of T cells among HAdV-subspecies. Ten epitopes induced CD4(+)-proliferation in >50% of individuals, confirmed by intracellular IFN-gamma detection. Three SCT recipients who recovered from an infection with HAdV displayed reactivity towards only a single hexon epitope, whereas healthy individuals were responsive to two to eight epitopes (median 3). The ex vivo detection of Hexon-specific CD4(+) T-cells, without any long-term culture in vitro, enables the detection and generation of HAdV-specific CD4(+) T cells for adoptive T-cell transfer against HAdV-infection post SCT.

Race between retroviral spread and CD4+ T-cell response determines the outcome of acute Friend virus infection

Retroviruses can establish persistent infection despite induction of a multipartite antiviral immune response. Whether collective failure of all parts of the immune response or selective deficiency in one crucial part underlies the inability of the host to clear retroviral infections is currently uncertain. We examine here the contribution of virus-specific CD4(+) T cells in resistance against Friend virus (FV) infection in the murine host. We show that the magnitude and duration of the FV-specific CD4(+) T-cell response is directly proportional to resistance against acute FV infection and subsequent disease. Notably, significant protection against FV-induced disease is afforded by FV-specific CD4(+) T cells in the absence of a virus-specific CD8(+) T-cell or B-cell response. Enhanced spread of FV infection in hosts with increased genetic susceptibility or coinfection with Lactate dehydrogenase-elevating virus (LDV) causes a proportional increase in the number of FV-specific CD4(+) T cells required to control FV-induced disease. Furthermore, ultimate failure of FV/LDV coinfected hosts to control FV-induced disease is accompanied by accelerated contraction of the FV-specific CD4(+) T-cell response. Conversely, an increased frequency or continuous supply of FV-specific CD4(+) T cells is both necessary and sufficient to effectively contain acute infection and prevent disease, even in the presence of coinfection. Thus, these results suggest that FV-specific CD4(+) T cells provide significant direct protection against acute FV infection, the extent of which critically depends on the ratio of FV-infected cells to FV-specific CD4(+) T cells.

Strategies to overcome host immunity to adenovirus vectors in vaccine development

The first clinical evaluations of adenovirus (Ad)-based vectors for gene therapy were initiated in the mid-1990s and led to great anticipation for future utility. However, excitement surrounding gene therapy, particularly Ad-based therapy, was diminished upon the death of Jesse Gelsinger, and recent discouraging results from the HIV vaccine STEP trial have brought efficacy and safety issues to the forefront again. Even so, Ad vectors are still considered among the safest and most effective vaccine vectors. Innate and pre-existing immunity to Ad mediate much of the acute toxicities and reduced therapeutic efficacies observed following vaccination with this vector. Thus, innovative strategies must continue to be developed to reduce Ad-specific antigenicity and immune recognition. This review provides an overview and critique of the most promising strategies, including results from preclinical trials in mice and nonhuman primates, which aim to revive the future of Ad-based vaccines.

In situ adenovirus vaccination engages T effector cells against cancer

The efficacy of cancer immunotherapy is limited because of central and peripheral immune tolerance towards tumor-antigens. We propose a novel approach based on the fact that the immune system has not evolved tolerance towards adenoviruses (Ads) and that Ads have not evolved efficient mechanisms for immune-escape. The host-response to intratumoral Ad-vector injection in mice that were immunologically tolerant to neu-positive syngeneic mammary-cancer (MMC) was investigated. Intratumoral injection with replication-deficient, transgene-devoid Ad induced immune responses at two different anatomical sites: the tumor-draining lymph nodes and the tumor microenvironment. The lymph nodes supported the generation of both neu- and Ad-specific T effector cells, while inside the tumor microenvironment only Ad-specific T cells expanded. Importantly, Ad-specific T cells were anti-tumor-reactive despite the presence of active regulatory T cell-mediated immune tolerance inside MMC tumors and anti-tumor efficacy of Ad was increased by pre-immunization against Ad despite the production of Ad-neutralizing antibodies.

Cellular immune responses to BK virus

PURPOSE OF REVIEW

Defects in cellular immunity to persistent viral infections are associated with an increased frequency and severity of viral diseases after transplantation. Polyomavirus BK (BKV) infection has emerged as an important cause of virus-related nephropathy after kidney allograft. Cell-mediated immunity seems to have a central role in preserving BKV latency. However, characterization of BKV-specific immunity has only recently begun.

RECENT FINDINGS

Immune responses to BKV are not fully understood, but pioneer work points to cell-mediated immunity as a critical factor for the control of viral replication and recovery from BKV disease.

SUMMARY

Advances in immunological techniques will provide further insight into the specificity and patterns of cellular response to BKV, which should assist translation into improved patient management and development of immunotherapeutic approaches.

Adenovirus DNA polymerase is recognized by human CD8+ T cells

Donor lymphocytes have potential as a treatment for adenovirus (Ad) disease in haematopoietic stem cell transplant (SCT) recipients, but better understanding of Ad-specific T-cell responses is required. Most healthy adults exhibit memory T-cell responses to hexon, a capsid protein synthesized late after infection. However, since the Ad E3-19k downregulates major histocompatibility complex (MHC) class I molecules, cytotoxic T cells (CTLs) targeted to early viral proteins may be more effective in eliminating Ad-infected cells in vivo. Here we show that Ad-specific CTLs recognize the early region 2 proteins DNA polymerase (Pol) and DNA-binding protein (DBP). Firstly, memory Ad-specific CD8(+) T cells were amplified from healthy donors by in vitro stimulation with Ad-infected dendritic cells and found to exhibit MHC-restricted cytotoxicity to targets expressing Pol and DBP. Secondly, gamma interferon responses to HLA A2-binding motif peptides from Pol and DBP were directly detected in peripheral blood mononuclear cells (PBMCs) from a recently infected normal donor. Peptide-specific CTLs generated to Pol and DBP epitopes were confirmed to exhibit HLA A2-restricted killing of targets expressing Pol or DBP. Lastly, Pol-epitope-specific T cells were detected at similar or higher frequencies than hexon and DBP in three of three SCT recipients recovering from invasive Ad disease. Pol epitopes were well conserved among different Ad serotypes. Therefore, Pol is a promising target for immunotherapy of Ad disease.

Clinical features and treatment of adenovirus infections

Adenoviruses (Ads) are common opportunistic pathogens that are rarely associated with severe clinical symptoms in healthy individuals. In contrast, in patients with compromised immunity, Ad infections often result in disseminated and potentially life-threatening disease. Among these are AIDS patients, individuals with hereditary immunodeficiencies and recipients of solid organ or haematopoietic stem cell transplants (HSCT) who receive immunosuppressive therapy. The latter account for the largest number of severe Ad infections. There is currently no formally approved antiviral therapy for the treatment of severe Ad keratoconjunctivitis and life-threatening Ad infections in immunocompromised patients. Here we update current knowledge on Ad biology, the clinical features observed in different patient groups and specific immune responses towards Ad infections. In addition, we review current and future treatment options, including: (i) the antiviral drugs cidofovir, ribavirin and new investigational compounds, as evaluated in the clinic or in relevant animal models, as well as (ii) novel immunotherapeutic strategies.

T-cell lines specific for peptides of adenovirus hexon protein and devoid of alloreactivity against recipient cells can be obtained from HLA-haploidentical donors

Human adenovirus (HAdV) infection may cause life-threatening complications in recipients of hematopoietic stem cell transplantation (HSCT), the highest risk being observed in children given T-cell depleted haploidentical allografts. The effectiveness of pharmacologic therapy for HAdV infection is suboptimal. Recently, cell therapy was demonstrated to offer a unique opportunity to restore antiviral immune surveillance, leading to clearance of infection and prevention/treatment of disease. However, infusion of insufficiently selected HAdV-specific T cells in haplo-HSCT may increase the risk of graft-versus-host disease. We conducted scale-up experiments to validate a method of in vitro culture to expand T cells specific for HAdV from donor peripheral blood mononuclear cells (PBMC), based on stimulation with a pool of five 30-mer peptides derived from HAdV5 hexon protein, for use in recipients of haplo-HSCT. A total of 21 T-cell lines that included a majority of CD4 T lymphocytes, were generated. Nineteen of the 21 T-cell lines proliferated specifically against HAdV. The 2 nonspecific, and 3 T-cell lines with lower specific activity, included a median of 48% CD8 T cells. The 19 HAdV-specific T-cell lines showed a median 357-fold decrease in alloreactivity, compared with proliferation of noncultured donor PBMC in response to recipient PBMC, only 4/19 T-cell lines showing residual alloreactivity. Our data indicate that HAdV-specific CD4 T-cell lines with efficient in vitro antiviral response and low/undetectable alloreactivity against recipient targets may be expanded from PBMC of most human leukocyte antigen-haploidentical HSCT donors after stimulation with HAdV hexon protein-derived peptides. These T cells may be safely employed for adoptive treatment of HAdV complications.

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.

The CD4+ T-cell response to adenovirus is focused against conserved residues within the hexon protein

Adenovirus is a significant pathogen in immunocompromised patients and is widely utilized as a gene delivery vector, so a detailed understanding of the human immune response to adenovirus infection is critical. This study characterized the adenovirus-specific CD4+ T-cell response of healthy donors by incubation with whole virus or with individual hexon and fiber proteins. Adenovirus-specific CD4+ T cells averaged 0.26 % of the CD4+ T-cell pool and were detectable in all donors. T cells recognizing the highly conserved hexon protein accounted for 0.09 %, whereas no response was observed against the fiber protein. A panel of hexon-specific CD4+ T-cell clones was generated and shown to lyse targets infected with adenovirus from different serotypes and species. Three CD4 T-cell epitopes are described, which map to highly conserved regions of the hexon protein.