Adenoviral Infections after Transplantation of Positive Selected Stem Cells from Haploidentical Donors in Children: An Update

Case Series Using Salvage Haplo-Identical Stem Cells for Secondary Transplantation

In order to expand the donor pool and accessibility of the transplant procedure, it was necessary to introduce haplo-identical stem cell transplants in the Fundeni Clinical Institute from 2015. Even if the Romanian population is an ethnically compact white population, many of the patients referred for bone marrow transplant lack a suitable donor. Hematopoietic stem cell transplant from a haplo-identical donor is an alternative option for those patients without an HLA (Human Leucocyte Antigen)-matched donor (sibling or matched unrelated). This procedure was used also as a salvage option for those who experienced engraftment failure or the rejection of the first stem cell graft. In this case series, we present three such cases, with a haplo-transplant used as a salvage protocol (after an engraftment failure or rejection of the first transplanted cells). The patients we present were diagnosed with AML (acute myeloid leukemia) with MDS (myelodysplastic syndrome), MDS-RAEB 2 (myelodysplastic syndrome-refractory anemia with excess blasts 2), and SAA (severe aplastic anemia). In two of the three cases, the engraftment failure may have been due to the conditioning Fludarabine/Busulfan/Cyclophosphamide (Flu/Bu/CFA) used, combined with marrow grafts. In all three cases, the second transplant was of haplo-identical peripheral blood stem cells using Melphalan/Fludarabine (Mel/Flu) conditioning, the cells engrafted properly and the patients experienced complete chimerism, and two of them are alive with an excellent quality of life.

Key Aspects of the Immunobiology of Haploidentical Hematopoietic Cell Transplantation

Hematopoietic stem cell transplantation from a haploidentical donor is increasingly used and has become a standard donor option for patients lacking an appropriately matched sibling or unrelated donor. Historically, prohibitive immunological barriers resulting from the high degree of HLA-mismatch included graft-vs.-host disease (GVHD) and graft failure. These were overcome with increasingly sophisticated strategies to manipulate the sensitive balance between donor and recipient immune cells. Three different approaches are currently in clinical use: (a) ex vivo T-cell depletion resulting in grafts with defined immune cell content (b) extensive immunosuppression with a T-cell replete graft consisting of G-CSF primed bone marrow and PBSC (GIAC) (c) T-cell replete grafts with post-transplant cyclophosphamide (PTCy). Intriguing studies have recently elucidated the immunologic mechanisms by which PTCy prevents GVHD. Each approach uniquely affects post-transplant immune reconstitution which is critical for the control of post-transplant infections and relapse. NK-cells play a key role in haplo-HCT since they do not mediate GVHD but can successfully mediate a graft-vs.-leukemia effect. This effect is in part regulated by KIR receptors that inhibit NK cell cytotoxic function when binding to the appropriate HLA-class I ligands. In the context of an HLA-class I mismatch in haplo-HCT, lack of inhibition can contribute to NK-cell alloreactivity leading to enhanced anti-leukemic effect. Emerging work reveals immune evasion phenomena such as copy-neutral loss of heterozygosity of the incompatible HLA alleles as one of the major mechanisms of relapse. Relapse and infectious complications remain the leading causes impacting overall survival and are central to scientific advances seeking to improve haplo-HCT. Given that haploidentical donors can typically be readily approached to collect additional stem- or immune cells for the recipient, haplo-HCT represents a unique platform for cell- and immune-based therapies aimed at further reducing relapse and infections. The rapid advancements in our understanding of the immunobiology of haplo-HCT are therefore poised to lead to iterative innovations resulting in further improvement of outcomes with this compelling transplant modality.

Successful Treatment of Adenovirus Infection with Brincidofovir in an Immunocompromised Patient after Hematological Stem Cell Transplantation

Immunocompromised patients, including hematopoietic stem cell transplantation (HSCT), HIV, and malnourished patients, are at increased risk for viral infections with high incidences of morbidity and mortality. In HSCT patients, the infection risk is increased until immune reconstitution is re-established. Therapy with standard of care antiviral drugs, for example Cidofovir, is expensive, requires prolonged administration, and has unfavorable toxicity profiles. Our case describes the successful use of Brincidofovir (CMX001), a lipid-conjugate of the nucleotide analog Cidofovir, in a 9-year-old post-HSCT girl with disseminated adenovirus infection. The increased efficacy of Brincidofovir (BCV) against multiple viral infections, limited toxicity, and oral-administered schedule opens options in different resource settings.

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.

Administration of Poly[di(sodium carboxylatoethylphenoxy)phosphazene] (PCEP) and Avian Beta Defensin as Adjuvants in Inactivated Inclusion Body Hepatitis Virus and its Hexon Protein-Based Experimental Vaccine Formulations in Chickens

Inclusion body hepatitis (IBH) is one of the major infectious diseases adversely affecting the poultry industry of the United States and Canada. Currently, no effective and safe vaccine is available for the control of IBH virus (IBHV) infection in chickens. However, based on the excellent safety and immunogenic profiles of experimental veterinary vaccines developed with the use of new generation adjuvants, we hypothesized that characterization of vaccine formulations containing inactivated IBHV or its capsid protein hexon as antigens, along with poly[di(sodium carboxylatoethylphenoxy)phosphazene] (PCEP) and avian beta defensin 2 (ABD2) as vaccine adjuvants, will be helpful in development of an effective and safe vaccine formulation for IBH. Our data demonstrated that experimental administration of vaccine formulations containing inactivated IBHV and a mixture of PCEP with or without ABD2 as an adjuvant induced significantly higher antibody responses compared with other vaccine formulations, while hexon protein-based vaccine formulations showed relatively lower levels of antibody responses. Thus, a vaccine formulation containing inactivated IBHV with PCEP or a mixture of PCEP and ABD2 (with a reduced dosage of PCEP) as an adjuvant may serve as a potential vaccine candidate. However, in order to overcome the risks associated with whole virus inactivated vaccines, characterization of additional viral capsid proteins, including fiber protein and penton of IBHV along with hexon protein in combination with more new generation adjuvants, will be helpful in further improvements of vaccines against IBHV infection.

Management of adenovirus in children after allogeneic hematopoietic stem cell transplantation

Adenovirus (ADV) can cause significant morbidity and mortality in children following haematopoietic stem cell transplantation (HSCT), with an incidence of up to 27% and notable associated morbidity and mortality. T-cell depleted grafts and severe lymphopenia are major risk factors for the development of adenovirus disease after HSCT. Current antiviral treatments are at best virostatic and may have significant side effects. Adoptive transfer of donor-derived virus-specific T cells has been shown to be an effective strategy for the prevention and treatment of ADV infection after HSCT. Here we review progress in the field and present a pathway for the management of adenovirus in the posttransplant setting.

Combination of Epstein-Barr virus nuclear antigen 1, 3 and lytic antigen BZLF1 peptide pools allows fast and efficient stimulation of Epstein-Barr virus-specific T cells for adoptive immunotherapy

BACKGROUND

Epstein-Barr virus (EBV) infection is a major cause of morbidity following hematopoietic stem cell transplantation. EBV-infected B cells may not respond to rituximab treatment and may lead to a life-threatening post-transplantation lymphoproliferative disorder. Adoptive cellular immunotherapy using EBV-lymphoblastoid cell lines (LCL) as stimulating antigen has proved effective in restoring specific immunity. However, EBV presents several immunodominant antigens, and developing a swift and effective clinical-grade immunotherapy relies on the definition of a Good Manufacturing Practices (GMP) universal stimulating antigen.

METHODS

Peripheral blood mononuclear cells (PBMCs) from six donors with a cellular immune response against EBV were immunoselected after stimulation with a new EBV antigen associated with an EBNA3 peptide pool.

RESULTS

After immunoselection, a mean of 0.53 ± 0.25 × 10⁶ cells was recovered consisting of a mean of 24.77 ± 18.01% CD4⁺-secreting interferon (IFN)-γ and 51.42 ± 26.92% CD8⁺-secreting IFN-γ. The T memory stem cell sub-population was identified. EBV-specific T cells were expanded in vitro, and their ability to secrete IFN-γ and to proliferate after re-stimulation with EBV antigen was confirmed. A specific lysis was observed against autologous target cells pulsed with EBV peptide pools (57.6 ± 11.5%) and against autologous EBV-LCL (18.3 ± 7.3%). A mean decrease of 94.7 ± 3.3% in alloreactivity against third-party donor mononuclear cells with EBV-specific T cells was observed compared with PBMCs before selection.

CONCLUSIONS

Our results show that a combination of peptide pools including EBNA3 is needed to generate EBV-specific T cells with good specific cytotoxicity and devoid of alloreactivity, but as yet GMP grade is not fully achieved.

Safety and efficacy of CMX001 as salvage therapy for severe adenovirus infections in immunocompromised patients

No therapeutic agent has yet been established as the definitive therapy for adenovirus infections. We describe the clinical experience of 13 immunocompromised patients who received CMX001 (hexadecyloxypropyl cidofovir), an orally bioavailable lipid conjugate of cidofovir, for adenovirus disease. We retrospectively analyzed 13 patients with adenovirus disease and viremia treated with CMX001; data were available for ≥ 4 weeks after initiation of CMX001 therapy. Virologic response (VR) was defined as a 99% drop from baseline or undetectable adenovirus DNA in serum. The median age of the group was 6 years (range, 0.92-66 years). One patient had severe combined immunodeficiency, 1 patient was a small bowel transplant recipient, and 11 were allogeneic stem cell transplant recipients. Adenovirus disease was diagnosed at a median of 75 days (range, 15-720 days) after transplantation. All patients received i.v. cidofovir for a median of 21 days (range, 5-90 days) before CMX001 therapy. The median absolute lymphocyte count at CMX001 initiation was 300 cells/μL (range, 7-1500 cells/μL). Eight patients (61.5%) had a ≥ 1 log10 drop in viral load after the first week of therapy. By week 8, 9 patients (69.2%) demonstrated a VR, with a median time to achieve VR of 7 days (range, 3-35 days). The change in absolute lymphocyte count was inversely correlated with the change in log10 viral load only at week 6 (r = -0.74; P = .03). Patients with VR had longer survival than those without VR (median 196 days versus 54.5 days; P = .04). No serious adverse events were attributed to CMX001 during therapy. CMX001 may be a promising therapeutic option for the treatment of severe adenovirus disease in immunocompromised patients.

Transplant outcomes in acute leukemia. II

Currently, it is possible to find a hematopoietic stem cell (HSC) donor for virtually all patients with acute leukemia who have an indication to receive an allogeneic hematopoietic stem cell transplant (HSCT) and lack a human leukocyte antigen (HLA)-identical sibling or a well-matched HLA unrelated donor (URD). According to the ethnicity of the patients and the donor registry, approximately 25% to 60% of patients will not find an 8/8 HLA-matched unrelated donor. Other alternative donors, such as HLA-mismatched related donor or unrelated donor umbilical cord blood (UCB), have emerged to solve the lack of a sibling or well-matched URD. In the haploidentical HSCT setting, new techniques of T-cell depletion, new approaches using combinations of immunosuppressive drugs or different conditioning regimens, and developments on immunotherapy have focused attention on this option. Therefore, any physician has to carefully evaluate, for each patient in need of an allograft, all of the possible alternatives in order to choose the best HSC donor, taking into account type of disease to be transplanted, urgency of transplantation, donor characteristics, and center experience. This review evaluates the current status of haploidentical HSCT in acute leukemia, its advantages and remaining limitations compared to other stem cell sources, and how these data may be used in the development of donor selection algorithms.

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.

Stem cell source and outcome after hematopoietic stem cell transplantation (HSCT) in children and adolescents with acute leukemia

Allogeneic hematopoietic stem cell transplantation from siblings, unrelated donors or HLA mismatched family members has become an important procedure to offer a chance of cure to children and adolescents with acute leukemia at high risk of relapse and those with certain genetic diseases. Bone marrow (BM) was the only stem cell source for many years. During the past 15 years, peripheral blood stem cells from granulocyte colony-stimulating factor (G-CSF) mobilized healthy donors, or umbilical cord blood from related or unrelated donors, have become available. Each stem cell source has different risks/benefits for patients and donors, the choice depending not only on availability, but also on HLA compatibility and urgency of the HSCT. This review will analyze the advantages and limitations of each of these options, and the main criteria which can be applied when choosing the appropriate stem cell source for pediatric transplant recipients with acute leukemia.

Functional characterization of alloreactive T cells identifies CD25 and CD71 as optimal targets for a clinically applicable allodepletion strategy

Immunotherapy with allodepleted donor T cells (ADTs) improves immunity after T cell–depleted stem cell transplantation, but infection/relapse remain problematic. To refine this approach, we characterized the expression of surface markers/cytokines on proliferating alloreactive T cells (ATs). CD25 was expressed on 83% of carboxyfluorescein diacetate succinimidyl esterdim ATs, confirming this as an excellent target for allodepletion. Seventy percent of CD25− ATs expressed CD71 (transferrin receptor), identifying this as a novel marker to target ATs persisting after CD25 depletion. Comparison of residual alloreactivity after combined CD25/71 versus CD25 immunomagnetic depletion showed enhanced depletion of alloreactivity to host with CD25/71 depletion in both secondary (2°) mixed lymphocyte reactions (P < .01) and interferon-γ enzyme-linked immunospot assays (P < .05) with no effect on third-party responses. In pentamer/interferon-γ enzyme-linked immunospot assays, antiviral responses to cytomegalovirus, Epstein-Barr virus, and adenovirus were preserved after CD25/71 allodepletion. CD25/71 ADTs can be redirected to recognize leukemic targets through lentiviral transfer of a chimeric anti-CD19ζ T-cell receptor. Finally, we have established conditions for clinically applicable CD25/71 allodepletion under European Union Good Manufacturing Practice conditions, resulting in highly effective, reproducible, and selective depletion of ATs (median residual alloreactivity to host in 2° mixed lymphocyte reaction of 0.39% vs third-party response of 62%, n = 5). This strategy enables further clinical studies of adoptive immunotherapy with larger doses of ADTs to enhance immune reconstitution after T cell-depleted stem cell transplantation.

Haploidentical SCT in children: an update and future perspectives

Transplantation of haploidentical stem cells has become a well-established approach, which makes a potential donor available for almost all patients. This review focuses on current results and new strategies, especially in pediatric patients with malignant diseases. CD34(+) positive selection was the most common procedure for graft manipulation in the past years, whereas T and B cell depletion is a promising new method. GVHD could herewith be effectively reduced and primary engraftment was reported in 83-100% of patients after transplantation of high stem cell doses. For patients with ALL in remission, disease-free survival at 3 years ranged between 22 and 48%. TRM, mainly because of viral infections, was improved by the use of reduced-intensity conditioning (which helped to speed up T cell recovery) and by close monitoring of viral loads and prophylactic/preemptive therapy. The role of donor-derived Ag-specific T cells against viral and fungal antigens is currently under investigation. Patients with active disease at the time of transplantation had a poor outcome and several attempts to improve these results are currently evaluated, such as co-infusion of natural killer cells, co-transplantation of MSC, use of new antileukemic drugs and post-transplant immunotherapy.

Immune deficits in allogeneic hematopoietic stem cell transplant (HSCT) recipients

Immune deficits account for the high frequency of life threatening bacterial, viral, and fungal opportunistic infections seen in allogeneic HSCT recipients. Despite advances in infectious disease management, the integrity of host defenses remains the mainstay of defense. The intensity of the preparative regimen, degree of HLA matching, source of stem cells (marrow, blood, or cord), extent of T-cell depletion, and immunosuppressive therapy are some of the factors that impact the kinetics, characteristics, and quality of immune reconstitution. Graft-versus-host disease and its prophylaxis or treatment produce a host environment that is particularly vulnerable to infections. Mucosal disruption and prolonged severe neutropenia usually confine their impact to the early course of transplant. After initial engraftment, HSCT recipients remain at great risk for opportunistic infections and this is related to prolonged and severe T-lymphocyte dysfunction of a complex multifactorial nature. B cell dysfunction is less problematic clinically, but includes deficiencies of immunoglobulin subclasses and impaired ability to mount a vaccine response. Advances in understanding of these immune deficits have resulted in successful strategies including revaccination, growth factors, thymic protection, and adoptive cellular therapy with antigen-specific cells.

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.

Haploidentical stem cell transplantation for children with acute leukaemia

Some children with relapsed or high-risk acute leukaemia have an improved outcome if they have an allogeneic stem cell transplant, preferably from a sibling or well-matched unrelated donor. However, some children do not have these options or there is an urgent need to proceed to transplant because of disease status. We have investigated the role of haploidentical family members as donors in 34 patients with acute leukaemia (median age 11 years, range 1-16 years). Patients were conditioned with cyclophosphamide and total body irradiation (14.4 Gy in eight fractions) and received T-cell depleted peripheral blood stem cell grafts with a median CD34 cell dose of 13.8 x 10(6)/kg (range 4.2-35.1) and 0.7 x 10(4) CD3-positive cells/kg. The actuarial survival at 2 years was 26% (13-41%, 95% CI). Eight patients have survived disease-free with a median follow up of 62 months. They have good performance status and a median lymphocyte count of 1.8 x 10(9)/l. Relapse (14 patients) and adenoviral (six patients) or fungal infections (four patients) were the major causes of death. Haploidentical stem cell transplantation can produce medium term disease-free survival in a proportion of children with high-risk or relapsed acute leukaemia. None of the nine patients with acute myeloid leukaemia not in remission have survived.