Mesenchymal stromal cell therapy is associated with increased adenovirus-associated but not cytomegalovirus-associated mortality in children with severe acute graft-versus-host disease.

Beneficial effects of mesenchymal stromal cells (MSCs) in patients with severe steroid-refractory acute graft-versus-host disease (aGvHD) have been reported. However, controversy exists about the effect of MSCs on virus-specific T cells. We evaluated 56 patients with grade II-IV aGvHD who responded to steroids (n = 21) or were steroid refractory receiving either MSCs (n = 22) or other second-line therapy (n = 13). Although the overall incidence of cytomegalovirus (CMV), Epstein-Barr virus, and human adenovirus (HAdV) infections was not significantly increased, HAdV infection was associated with decreased survival in children treated with MSCs. Thus, we investigated in vitro the effects of MSCs on virus-specific T cells. Both CMV-specific and, to a lesser extent, HAdV-specific T-cell activation and proliferation were negatively affected by MSCs either after induction of a response in peripheral blood mononuclear cells (PBMCs) or after restimulation of virus-specific T-cell lines. In patient-derived PBMCs, CMV-specific proliferative responses were greatly decreased on first-line treatment of aGvHD with systemic steroids and slowly recovered after MSC administration and tapering of steroids. HAdV-specific T-cell proliferation could not be detected. In contrast, the proportion of CMV- and HAdV-specific effector T cells, measured as interferon-γ-secreting cells, remained stable or increased after treatment with MSCs. In conclusion, although in vitro experimental conditions indicated a negative impact of MSCs on CMV- and HAdV-specific T-cell responses, no solid evidence was obtained to support such an effect of MSCs on T-cell responses in vivo. Still, the susceptibility of steroid-refractory severe aGvHD patients to viral reactivation warrants critical viral monitoring during randomized controlled trials on second-line treatment including MSCs.

High titers of pre-existing adenovirus serotype-specific neutralizing antibodies in the host predict viral reactivation after allogeneic stem cell transplantation in children.

BACKGROUND: Human adenovirus (HAdV) infections are frequent in children after allogeneic stem cell transplantation (SCT) and may become fatal. Whether these infections occur through reactivation of endogenous virus or transmission via the graft remains a matter of debate. METHODS: In a cohort of 24 pediatric patients who received SCT, infections with 1 or more of 5 serotypes of HAdV (1, 2, 5, 6, and 31) were detected by culture. Neutralizing antibody (NAb) titers were measured in vitro by means of a virus neutralization assay. RESULTS: In 11 patients the infection was restricted to 1 site as demonstrated by culture only, and in 13 patients the HAdV infection was disseminated because plasma samples contained HAdV DNA. The 5 most commonly encountered HAdV serotypes caused 35 infectious episodes after SCT. Serum titers of NAb against these 5 serotypes of HAdV were measured before and after transplantation. High titers of NAb against a certain serotype in the recipient prior to SCT, reflecting previous infection, appeared to predispose for infection with the same serotype after SCT. In only 1 case of 41 independent samples of graft material, a very low level of HAdV DNA was detected. Antibody responses after SCT were detected in 21 of 35 infectious episodes. CONCLUSIONS: Together, these data suggest that adenoviral complications after SCT are caused by reactivation of endogenous persistent HAdV rather than by de novo infection from the donor or environment. This finding may offer a strategy of prophylactic treatment of high-risk patients before SCT to prevent infectious complications after allogeneic SCT.

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.

Co-ordinated isolation of CD8(+) and CD4(+) T cells recognizing a broad repertoire of cytomegalovirus pp65 and IE1 epitopes for highly specific adoptive immunotherapy.

BACKGROUND AIMS: Adoptive transfer of cytomegalovirus (CMV)-specific memory T cells can be used for treatment of CMV reactivation after allogeneic stem cell transplantation. As co-ordinated CD8(+) and CD4(+) T cells specific for a broad repertoire of CMV epitopes may be most effective for adoptive immunotherapy, the aim of this study was to isolate these cells from peripheral blood of CMV seropositive donors, irrespective of their HLA type. METHODS: Activation of CMV-specific CD8(+) and CD4(+) T cells was compared after stimulation of donor peripheral blood with minimal epitope peptides, pools of overlapping 15-mer peptides or full-length protein. Furthermore, the kinetics of interferon (IFN)-γ production after stimulation was analyzed to determine the optimal time-point for IFN-γ-based isolation of CMV-specific T cells. The specificity, phenotype and functionality of generated T-cell lines were analyzed. RESULTS: CMV protein-spanning 15-mer peptide pools induced simultaneous activation of both CD8(+) and CD4(+) CMV-specific T cells, while full-length CMV protein only efficiently activated CD4(+) CMV-specific T cells. Isolation of IFN-γ-secreting cells at the peak of the IFN-γ response after 4-h stimulation with CMV pp65 and IE1 peptide pools resulted in efficient enrichment of CMV-specific T cells. The T-cell lines contained high frequencies of CD8(+) and CD4(+) T cells recognizing multiple CMV pp65 and IE1 epitopes, and produced IFN-γ and tumor necrosis factor (TNF)-α upon specific restimulation. CONCLUSIONS: This study provides a feasible strategy for the rapid generation of clinical-grade CD8(+) and CD4(+) T-cell lines with high specificity for multiple CMV pp65 and IE1 epitopes, which may be used for effective adoptive immunotherapy.

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.

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

Human adenovirus (HAdV) infection is a frequent and potentially severe complication following allogeneic stem cell transplantation in children. Because treatment with antiviral drugs is often ineffective, adoptive transfer of donor-derived HAdV-specific T cells able to control viral replication of HAdV of multiple serotypes may be an option for therapy. In healthy donors, predominantly HAdV-specific T cells expressing CD4 are detected. In this study, a preclinical in vitro model was used to measure the antiviral effect of HAdV-specific CD4+ T cells. CD4+ HAdV-specific T cell clones restricted by HLA class II molecules were generated and most of these clones recognized conserved peptides derived from the hexon protein. These cross-reactive T cell clones were able to control viral replication of multiple serotypes of HAdV in EBV-transformed B cells (B-LCL), melanoma cells (MJS) and primary bronchial epithelial cells through cognate interaction. The HAdV-specific CD4+ T cell clones were able to specifically lyse infected target cells using a perforin-dependent mechanism. Antigenic peptides were also presented to the CD4+ T cell clones when derived from endogenously produced hexon protein. Together, these results show that cross-reactive HAdV-specific CD4+ T cells can control replication of HAdV in vitro and provide a rationale for the use of HAdV-specific T cells in adoptive immunotherapy protocols for control of life-threatening HAdV-infections in immunocompromised patients.

Human CD4+ T cells stimulated by conserved adenovirus 5 hexon peptides recognize cells infected with different species of human adenovirus.

The immune response against human adenovirus (HAdV) has gained interest because of the application of HAdV-based vectors in gene therapy and the high incidence of infections in pediatric recipients of allogeneic stem cell grafts. Because antiviral medication is frequently ineffective, the option of adoptive transfer of HAdV-specific donor-derived T cells in these immunocompromised patients is investigated. To generate good manufacturing practice-compatible reagents, a panel of 63 long, overlapping, peptides of the hexon protein was screened for recognition by T cells. Five conserved peptides of 30 amino acids were identified that were recognized by the majority of adult donors. CD4+ T cells from long-term cultures of PBMC, stimulated with this set of five peptides, recognized cells infected with HAdV serotypes belonging to different species. These data demonstrate that adult human T cells preferentially recognize conserved sequences of amino acid residues from a structural protein of HAdV. In the context of gene therapy, this observation may limit the beneficial effect of switching to HAdV-based vectors derived from less common serotypes of HAdV in an attempt to circumvent pre-existing immunity. However, this cross-reactivity benefits the application of HAdV-specific T cells for adoptive immunotherapy in immunocompromised transplant recipients.

Immune reconstitution and clearance of human adenovirus viremia in pediatric stem-cell recipients.

BACKGROUND: Human adenovirus (HAdV) infections are increasingly frequent complications of allogeneic stem-cell transplantation (SCT), especially in children. Only a few data on the correlation between immune recovery and the course of HAdV infection are available, and data on HAdV-specific responses are lacking. METHODS: In a prospective study, we determined the correlation between the HAdV DNA load in plasma and lymphocyte reconstitution in 48 children after allogeneic SCT. Additionally, HAdV-specific humoral and cellular immune responses were investigated. RESULTS: HAdV infection occurred in 21 patients (44%), and, in 6 of these patients, the infection progressed to viremia, as demonstrated by the presence of HAdV DNA in plasma. Low lymphocyte counts at the onset of infection were predictive of HAdV viremia. Survival of patients with HAdV viremia was associated with an increase in lymphocyte counts during the first weeks after infection. In these patients, HAdV-specific CD4+ T cell responses, as well as increases in titers of neutralizing antibody, were detected after clearance of HAdV DNA from plasma. CONCLUSIONS: Lymphocyte reconstitution appears to play a crucial role in clearance of HAdV viremia and survival of the host, warranting further development of therapeutic interventions aimed at improving immune recovery.

Extensive cross-reactivity of CD4+ adenovirus-specific T cells: implications for immunotherapy and gene therapy.

Adenovirus (Ad)-specific T-cell responses in healthy adult donors were investigated. Ad5, inactivated by methylene blue plus visible light, induced proliferation and gamma interferon (IFN-gamma) production in peripheral blood mononuclear cells of the majority of donors. Responding T cells were CD4(+) and produced IFN-gamma upon restimulation with infectious Ad5 and Ads of different subgroups. T-cell clones showed distinct cross-reactivity patterns recognizing Ad serotypes from either one subgroup (C), two subgroups (B and C), or three subgroups (A, B, and C). This cross-reactivity of Ad-specific T cells has relevance both for Ad-based gene therapy protocols, as well as for the feasibility of T-cell-mediated adoptive immunotherapy in recipients of an allogeneic stem cell transplantation.