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

Immune reconstitution and cidofovir administration rescue human adenovirus hepatitis after allogeneic hematopoietic cell transplantation

Human adenovirus infection (HAdV) may be fatal in patients undergoing allogeneic hematopoietic cell transplantation (HCT). Cidofovir is effective in only a part of the post-HCT HAdV infection. Therefore, posttransplant immune reconstitution is important for HAdV clearance. We describe the detailed immune reconstitution and response of adenovirus-specific T cells in a patient with inborn errors of immunity who had disseminated HAdV infection with hepatitis post-HCT and was treated with cidofovir. Though the patient received cidofovir for only 19 days starting from Day 72 after HCT because of renal dysfunction, we observed T-cell reconstitution, a decrease in HAdV copy number, and amelioration of the symptoms of HAdV infection after Day 90. We initially observed expanded NK and CD8+CD45RO+ memory subsets and later gradual increase of naïve T cells eveloped after cessation of cidofovir treatment. An increase in adenovirus-specific IFN-γ secretion from 2 to 4 months after HCT was confirmed by ELISpot assay. The progression of immune reconstitution and cidofovir treatment are considered to have contributed to survival in this patient. Optimization of transplantation methods, prompt appropriate antiviral medication, and virus-specific T-cell therapy would be necessary as the better strategy for systemic HAdV infection.

Phenotypic and functional characterization of posoleucel, a multivirus-specific T cell therapy for the treatment and prevention of viral infections in immunocompromised patients

BACKGROUND

Deficits in T cell immunity translate into increased risk of severe viral infection in recipients of solid organ and hematopoietic cell transplants. Thus, therapeutic strategies that employ the adoptive transfer of virus-specific T cells are being clinically investigated to treat and prevent viral diseases in these highly immunocompromised patients. Posoleucel is an off-the-shelf multivirus-specific T cell investigational product for the treatment and prevention of infections due to adenovirus, BK virus, cytomegalovirus, Epstein-Barr virus, human herpesvirus 6 or JC virus.

METHODS

Herein we perform extensive characterization of the phenotype and functional profile of posoleucel to illustrate the cellular properties that may contribute to its in vivo activity.

RESULTS AND CONCLUSIONS

Our results demonstrate that posoleucel is enriched for central and effector memory CD4+ and CD8+ T cells with specificity for posoleucel target viruses and expressing a broad repertoire of T cell receptors. Antigen-driven upregulation of cell-surface molecules and production of cytokine and effector molecules indicative of proliferation, co-stimulation, and cytolytic potential demonstrate the specificity of posoleucel and its potential to mount a broad, polyfunctional, and effective Th1-polarized antiviral response upon viral exposure. We also show the low risk for off-target and nonspecific effects as evidenced by the enrichment of posoleucel in memory T cells, low frequency of naive T cells, and lack of demonstrated alloreactivity in vitro. The efficacy of posoleucel is being explored in four placebo-controlled clinical trials in transplant recipients to treat and prevent viral infections (NCT05179057, NCT05305040, NCT04390113, NCT04605484).

Clinical manifestations, prognostic factors, and outcomes of adenovirus pneumonia after allogeneic hematopoietic stem cell transplantation

BACKGROUND

Severe pneumonia is one of the most important causes of mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Adenovirus (ADV) is a significant cause of severe viral pneumonia after allo-HSCT, and we aimed to identify the clinical manifestations, prognostic factors, and outcomes of ADV pneumonia after allo-HSCT.

METHODS

Twenty-nine patients who underwent allo-HSCT at the Peking University Institute of Hematology and who experienced ADV pneumonia after allo-HSCT were enrolled in this study. The Kaplan-Meier method was used to estimate the probability of overall survival (OS). Potential prognostic factors for 100-day OS after ADV pneumonia were evaluated through univariate and multivariate Cox regression analyses.

RESULTS

The incidence rate of ADV pneumonia after allo-HSCT was approximately 0.71%. The median time from allo-HSCT to the occurrence of ADV pneumonia was 99 days (range 17-609 days). The most common clinical manifestations were fever (86.2%), cough (34.5%) and dyspnea (31.0%). The 100-day probabilities of ADV-related mortality and OS were 40.4% (95% CI 21.1%-59.7%) and 40.5% (95% CI 25.2%-64.9%), respectively. Patients with low-level ADV DNAemia had lower ADV-related mortality and better OS than did those with high-level (≥ 106 copies/ml in plasma) ADV DNAemia. According to the multivariate analysis, high-level ADV DNAemia was the only risk factor for intensive care unit admission, invasive mechanical ventilation, ADV-related mortality, and OS after ADV pneumonia.

CONCLUSIONS

We first reported the prognostic factors and confirmed the poor outcomes of patients with ADV pneumonia after allo-HSCT. Patients with high-level ADV DNAemia should receive immediate and intensive therapy.

Posoleucel in Kidney Transplant Recipients with BK Viremia: Multicenter, Randomized, Double-Blind, Placebo-Controlled Phase 2 Trial

Key Points

Posoleucel was generally safe, well tolerated, and associated with a greater reduction of BK viremia compared with placebo. BK viremia reduction occurred coincident with an increase in the circulating frequency of BK virus–specific T cells in posoleucel recipients. The presence and persistence of posoleucel was confirmed by T-cell receptor variable β sequencing.

Background

Kidney transplant recipients with BK virus infection are at risk of developing BK virus–associated nephropathy, allograft rejection, and subsequent graft loss. There are no approved treatments for BK virus infection. Posoleucel is an off-the-shelf, allogeneic, multivirus-specific T-cell investigational therapy targeting BK virus, as well as five other opportunistic viruses: adenovirus, cytomegalovirus, Epstein–Barr virus, human herpesvirus 6, and John Cunningham virus.

Methods

In this phase 2, double-blind study, kidney transplant recipients with BK viremia were randomized 1:1:1 to receive posoleucel weekly for 3 weeks and then every 14 days (bi-weekly dosing) or every 28 days (monthly dosing) or placebo for 12 weeks. Participants were followed for 12 weeks after completing treatment. The primary objective was safety; the secondary objective was plasma BK viral load reduction.

Results

Sixty-one participants were randomized and dosed. Baseline characteristics were similar across groups. No deaths, graft-versus-host disease, or cytokine release syndrome occurred. The proportion of patients who had adverse events (AEs) judged by the investigators to be treatment-related was slightly lower in recipients of posoleucel: 20% (4 of 20 patients) and 18% (4 of 22) in those infused on a bi-weekly and monthly schedule, respectively, and 26% (5 of 19) in placebo recipients. None of the grade 3–4 AEs or serious AEs in any group were deemed treatment-related. No deaths, graft-versus-host disease, or cytokine release syndrome occurred. Three participants had allograft rejection, but none were deemed treatment-related by investigators. In posoleucel recipients, BK viremia reduction was associated with an increase in the circulating frequency of BK virus–specific T cells, and the presence and persistence of posoleucel was confirmed by T-cell receptor sequencing.

Conclusions

Posoleucel was generally safe, well tolerated, and associated with a larger reduction of BK viremia compared with placebo. Limitations of this study include the relatively short duration of follow-up and lack of power to detect significant differences in clinical outcomes.

Clinical Trial registry name and registration number:

Study of Posoleucel (Formerly Known as ALVR105; Viralym-M) in Kidney Transplant Patients With BK Viremia, NCT04605484 .

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.

Virus-specific T-cells from third party or transplant donors for treatment of EBV lymphoproliferative diseases arising post hematopoietic cell or solid organ transplantation

EBV+ lymphomas constitute a significant cause of morbidity and mortality in recipients of allogeneic hematopoietic cell (HCT) and solid organ transplants (SOT). Phase I and II trials have shown that in HCT recipients, adoptive transfer of EBV-specific T-cells from the HCT donor can safely induce durable remissions of EBV+ lymphomas including 70->90% of patients who have failed to respond to treatment with Rituximab. More recently, EBV-specific T-cells generated from allogeneic 3rd party donors have also been shown to induce durable remission of EBV+ lymphomas in Rituximab refractory HCT and SOT recipients. In this review, we compare results of phase I and II trials of 3rd party and donor derived EBV-specific T-cells. We focus on the attributes and limitations of each product in terms of access, safety, responses achieved and durability. The limited data available regarding donor and host factors contributing to T cell persistence is also described. We examine factors contributing to treatment failures and approaches to prevent or salvage relapse. Lastly, we summarize strategies to further improve results for virus-specific immunotherapies for post-transplant EBV lymphomas.

Adoptive Immune Effector Cell Therapies in Cancer and Solid Organ Transplantation: A Review

Cancer is one of the most devastating complications of kidney transplantation and constitutes one of the leading causes of morbidity and mortality among solid organ transplantation (SOT) recipients. Immunosuppression, although effective in preventing allograft rejection, inherently inhibits immune surveillance against oncogenic viral infections and malignancy. Adoptive cell therapy, particularly immune effector cell therapy, has long been a modality of interest in both cancer and transplantation, though has only recently stepped into the spotlight with the development of virus-specific T-cell therapy and chimeric antigen receptor T-cell therapy. Although these modalities are best described in hematopoietic cell transplantation and hematologic malignancies, their potential application in the SOT setting may hold tremendous promise for those with limited therapeutic options. In this review, we provide a brief overview of the development of adoptive cell therapies with a focus on virus-specific T-cell therapy and chimeric antigen receptor T-cell therapy. We also describe the current experience of these therapies in the SOT setting as well as the challenges in their application and future directions in their development.

Post-transplant malignancy: Focusing on virus-associated etiologies, pathogenesis, evidence-based management algorithms, present status of adoptive immunotherapy and future directions

Modern immunosuppression has led to a decrease in rejection rates and improved survival rates after solid organ transplantation. Increasing the potency of immunosuppression promotes post-transplant viral infections and associated cancers by impairing immune response against viruses and cancer immunoediting. This review reflects the magnitude, etiology and immunological characteristics of various virus-related post-transplant malignancies, emphasizing the need for future research. A multidisciplinary and strategic approach may serve best but overall literature evidence targeting it is sparse. However, the authors attempted to provide a more detailed update of the literature consensus for the prevention, diagnosis, management and surveillance of post-transplant viral infections and associated malignancies, with a focus on the current role of adoptive immunotherapy and the way forward. In order to achieve long-term patient and graft survival as well as superior post-transplant outcomes, collaborative research on holistic care of organ recipients is imperative.

EBV-induced T-cell responses in EBV-specific and nonspecific cancers

Epstein-Barr virus (EBV) is a ubiquitous human tumor virus associated with various malignancies, including B-lymphoma, NK and T-lymphoma, and epithelial carcinoma. It infects B lymphocytes and epithelial cells within the oropharynx and establishes persistent infection in memory B cells. With a balanced virus-host interaction, most individuals carry EBV asymptomatically because of the lifelong surveillance by T cell immunity against EBV. A stable anti-EBV T cell repertoire is maintained in memory at high frequency in the blood throughout persistent EBV infection. Patients with impaired T cell immunity are more likely to develop life-threatening lymphoproliferative disorders, highlighting the critical role of T cells in achieving the EBV-host balance. Recent studies reveal that the EBV protein, LMP1, triggers robust T-cell responses against multiple tumor-associated antigens (TAAs) in B cells. Additionally, EBV-specific T cells have been identified in EBV-unrelated cancers, raising questions about their role in antitumor immunity. Herein, we summarize T-cell responses in EBV-related cancers, considering latency patterns, host immune status, and factors like human leukocyte antigen (HLA) susceptibility, which may affect immune outcomes. We discuss EBV-induced TAA-specific T cell responses and explore the potential roles of EBV-specific T cell subsets in tumor microenvironments. We also describe T-cell immunotherapy strategies that harness EBV antigens, ranging from EBV-specific T cells to T cell receptor-engineered T cells. Lastly, we discuss the involvement of γδ T-cells in EBV infection and associated diseases, aiming to elucidate the comprehensive interplay between EBV and T-cell immunity.

Targeted cellular therapy for treatment of relapsed or refractory leukemia

While the mainstay of treatment for high-risk or relapsed, refractory leukemia has historically revolved around allogeneic hematopoietic stem cell transplant (allo-HSCT), targeted immunotherapies have emerged as a promising therapeutic option, especially given the poor prognosis of patients who relapse after allo-HSCT. Novel cellular immunotherapies that harness the cytotoxic abilities of the immune system in a targeted manner (often called "adoptive" cell therapy), have changed the way we treat r/r hematologic malignancies and continue to change the treatment landscape given the rapid evolution of these powerful, yet sophisticated precision therapies that often offer a less toxic alternative to conventional salvage therapies. Importantly, adoptive cell therapy can be allo-HSCT-enabling or a therapeutic option for patients in whom transplantation has failed or is contraindicated. A solid understanding of the core concepts of adoptive cell therapy is necessary for stem cell transplant physicians, nurses and ancillary staff given its proximity to the transplant field as well as its inherent complexities that require specific expertise in compliant manufacturing, clinical application, and risk mitigation. Here we will review use of targeted cellular therapy for the treatment of r/r leukemia, focusing on chimeric antigen receptor T-cells (CAR T-cells) given the remarkable sustained clinical responses leading to commercial approval for several hematologic indications including leukemia, with brief discussion of other promising investigational cellular immunotherapies and special considerations for sustainability and scalability.

Applications of Anti-Cytomegalovirus T Cells for Cancer (Immuno)Therapy

Infection with cytomegalovirus (CMV) is highly prevalent in the general population and largely controlled by CD8pos T cells. Intriguingly, anti-CMV T cells accumulate over time to extraordinarily high numbers, are frequently present as tumor-resident 'bystander' T cells, and remain functional in cancer patients. Consequently, various strategies for redirecting anti-CMV CD8pos T cells to eliminate cancer cells are currently being developed. Here, we provide an overview of these strategies including immunogenic CMV peptide-loading onto endogenous HLA complexes on cancer cells and the use of tumor-directed fusion proteins containing a preassembled CMV peptide/HLA-I complex. Additionally, we discuss conveying the advantageous characteristics of anti-CMV T cells in adoptive cell therapy. Utilization of anti-CMV CD8pos T cells to generate CAR T cells promotes their in vivo persistence and expansion due to appropriate co-stimulation through the endogenous (CMV-)TCR signaling complex. Designing TCR-engineered T cells is more challenging, as the artificial and endogenous TCR compete for expression. Moreover, the use of expanded/reactivated anti-CMV T cells to target CMV peptide-expressing glioblastomas is discussed. This review highlights the most important findings and compares the benefits, disadvantages, and challenges of each strategy. Finally, we discuss how anti-CMV T cell therapies can be further improved to enhance treatment efficacy.

Virus-Specific T-Cell Therapy for Viral Infections of the Central Nervous System: A Review

Opportunistic viral infections of the central nervous system represent a significant cause of morbidity and mortality among an increasing number of immunocompromised patients. Since antiviral treatments are usually poorly effective, the prognosis generally relies on the ability to achieve timely immune reconstitution. Hence, strategies aimed at reinvigorating antiviral immune activity have recently emerged. Among these, virus-specific T-cells are increasingly perceived as a principled and valuable tool to treat opportunistic viral infections. Here we briefly discuss how to develop and select virus-specific T-cells, then review their main indications in central nervous system infections, including progressive multifocal leukoencephalopathy, CMV infection, and adenovirus infection. We also discuss their potential interest in the treatment of progressive multiple sclerosis, or EBV-associated central nervous system inflammatory disease. We finish with the key future milestones of this promising treatment strategy.

Virus-Specific T Cells: Promising Adoptive T Cell Therapy Against Infectious Diseases Following Hematopoietic Stem Cell Transplantation

Hematopoietic stem cell transplantation (HSCT) is a life-saving therapy for various hematologic disorders. Due to the bone marrow suppression and its long recovery period, secondary infections, like cytomegalovirus (CMV), Epstein-Bar virus (EBV), and adenovirus (AdV), are the leading causes of morbidity and mortality in HSCT cases. Drug resistance to the antiviral pharmacotherapies makes researchers develop adoptive T cell therapies like virus-specific T cell therapy. These studies have faced major challenges such as finding the most effective T cell expansion methods, isolating the expected subtype, defining the functionality of the end-cell population, product quality control, and clinical complications after the injection. This review discusses the viral infections after HSCT, T cells characteristics during chronic viral infection, application of virus-specific T cells (VSTs) for refractory infections, standard methods for producing VSTs and their limitation, clinical experiences on VSTs, focusing on outcomes and side effects that can be helpful in decision-making for patients and further researches.

Banking on virus-specific T cells to fulfill the need for off-the-shelf cell therapies

Adoptively transferred virus-specific T cells (VSTs) have shown remarkable safety and efficacy for the treatment of virus-associated diseases and malignancies in hematopoietic stem cell transplant (HSCT) recipients, for whom VSTs are derived from the HSCT donor. Autologous VSTs have also shown promise for the treatment of virus-driven malignancies outside the HSCT setting. In both cases, VSTs are manufactured as patient-specific products, and the time required for procurement, manufacture, and release testing precludes their use in acutely ill patients. Further, Good Manufacturing Practices-compliant products are expensive, and failures are common in virus-naive HSCT donors and patient-derived VSTs that are rendered anergic by immunosuppressive tumors. Hence, highly characterized, banked VSTs (B-VSTs) that can be used for multiple unrelated recipients are highly desirable. The major challenges facing B-VSTs result from the inevitable mismatches in the highly polymorphic and immunogenic human leukocyte antigens (HLA) that present internally processed antigens to the T-cell receptor, leading to the requirement for partial HLA matching between the B-VST and recipient. HLA mismatches lead to rapid rejection of allogeneic T-cell products and graft-versus-host disease induced by alloreactive T cells in the infusion product. Here, we summarize the clinical outcomes to date of trials of B-VSTs used for the treatment of viral infections and malignancies and their potential as a platform for chimeric antigen receptors targeting nonviral tumors. We will highlight the properties of VSTs that make them attractive off-the-shelf cell therapies, as well as the challenges that must be overcome before they can become mainstream.

Pathogen-specific T Cells: Targeting Old Enemies and New Invaders in Transplantation and Beyond

Adoptive immunotherapy with virus-specific cytotoxic T cells (VSTs) has evolved over the last three decades as a strategy to rapidly restore virus-specific immunity to prevent or treat viral diseases after solid organ or allogeneic hematopoietic cell-transplantation (allo-HCT). Since the early proof-of-principle studies demonstrating that seropositive donor-derived T cells, specific for the commonest pathogens post transplantation, namely cytomegalovirus or Epstein-Barr virus (EBV) and generated by time- and labor-intensive protocols, could effectively control viral infections, major breakthroughs have then streamlined the manufacturing process of pathogen-specific T cells (pSTs), broadened the breadth of target recognition to even include novel emerging pathogens and enabled off-the-shelf administration or pathogen-naive donor pST production. We herein review the journey of evolution of adoptive immunotherapy with nonengineered, natural pSTs against infections and virus-associated malignancies in the transplant setting and briefly touch upon recent achievements using pSTs outside this context.

Antigen-Specific T Cells and SARS-CoV-2 Infection: Current Approaches and Future Possibilities

COVID-19, a significant global health threat, appears to be an immune-related disease. Failure of effective immune responses in initial stages of infection may contribute to development of cytokine storm and systemic inflammation with organ damage, leading to poor clinical outcomes. Disease severity and the emergence of new SARS-CoV-2 variants highlight the need for new preventative and therapeutic strategies to protect the immunocompromised population. Available data indicate that these people may benefit from adoptive transfer of allogeneic SARS-CoV-2-specific T cells isolated from convalescent individuals. This review first provides an insight into the mechanism of cytokine storm development, as it is directly related to the exhaustion of T cell population, essential for viral clearance and long-term antiviral immunity. Next, we describe virus-specific T lymphocytes as a promising and efficient approach for the treatment and prevention of severe COVID-19. Furthermore, other potential cell-based therapies, including natural killer cells, regulatory T cells and mesenchymal stem cells are mentioned. Additionally, we discuss fast and effective ways of producing clinical-grade antigen-specific T cells which can be cryopreserved and serve as an effective "off-the-shelf" approach for rapid treatment of SARS-CoV-2 infection in case of sudden patient deterioration.

Applications of Virus specific T cell Therapies Post BMT

Hematopoietic stem cell transplantation (HSCT) has been used as a curative standard of care for moderate to severe primary immunodeficiency disorders as well as relapsed hematologic malignancies for over 50 years [1,2]. However, chronic and refractory viral infections remain a leading cause of morbidity and mortality in the immune deficient period following HSCT, where use of available antiviral pharmacotherapies is limited by toxicity and emerging resistance [3]. Adoptive immunotherapy using virus-specific T cells (VSTs) has been explored for over 2 decades [4,5] in patients post-HSCT and has been shown prior phase I-II studies to be safe and effective for treatment or preventions of viral infections including cytomegalovirus, Epstein-Barr virus, BK virus, and adenovirus with minimal toxicity and low risk of graft vs host disease [6-9]. This review summarizes methodologies to generate VSTs the clinical results utilizing VST therapeutics and the challenges and future directions for the field.

Adoptive T cell therapy cures mice from active hemophagocytic lymphohistiocytosis (HLH)

Primary hemophagocytic lymphohistiocytosis (HLH) is a hyperinflammatory syndrome caused by impaired lymphocyte cytotoxicity. First-line therapeutic regimens directed against activated immune cells or secreted cytokines show limited efficacy since they do not target the underlying immunological problem: defective lymphocyte cytotoxicity causing prolonged immune stimulation. A potential rescue strategy would be the adoptive transfer of ex vivo gene-corrected autologous T cells. However, transfusion of cytotoxicity-competent T cells under conditions of hyperinflammation may cause more harm than benefit. As a proof-of-concept for adoptive T cell therapy (ATCT) under hyperinflammatory conditions, we transferred syngeneic, cytotoxicity-competent T cells into mice with virally triggered active primary HLH. ATCT with functional syngeneic trigger-specific T cells cured Jinx mice from active HLH without life-threatening side effects and protected Perforin-deficient mice from lethal HLH progression by reconstituting cytotoxicity. Cured mice were protected long-term from HLH relapses. A threshold frequency of transferred T cells with functional differentiation was identified as a predictive biomarker for long-term survival. This study is the first proof-of-concept for ATCT in active HLH.

Immunocompromised host section: Adoptive T-cell therapy for dsDNA viruses in allogeneic hematopoietic cell transplant recipients

PURPOSE OF REVIEW

Double-stranded DNA (dsDNA) viruses remain important causes of morbidity and mortality after allogeneic hematopoietic cell transplantation (HCT). As treatment options are limited, adoptive therapy with virus-specific T cells (VST) is promising in restoring immunity and thereby preventing and treating virus infections. Here we review current evidence and recent advances in the field of VST for dsDNA viruses in allogeneic HCT recipients.

RECENT FINDINGS

Four different protocols for VST generation are currently used in clinical trials, and various products including multivirus-specific and off-the-shelf products are under investigation for prophylaxis, preemptive therapy or treatment. Data from nearly 1400 dsDNA-VST applications in allogeneic HCT patients have been published and demonstrated its safety. Although Epstein-Barr virus, cytomegalovirus, and adenovirus-specific T-cell therapy studies have predominated over the past 25 years, additional human herpes viruses were added to multivirus-specific T cells over the last decade and clinical evidence for polyomavirus-specific VST has just recently emerged. Response rates of around 70-80% have been reported, but cautious interpretation is warranted as data are predominantly from phase 1/2 studies and clinical efficacy needs to be confirmed in phase 3 studies.

SUMMARY

Investigation on the 'ideal' composition of VST is ongoing. Several products recently entered phase 3 trials and may allow widespread clinical use in the near future.

Viral infection in hematopoietic stem cell transplantation: an International Society for Cell & Gene Therapy Stem Cell Engineering Committee review on the role of cellular therapy in prevention and treatment

Despite recent advances in the field of HSCT, viral infections remain a frequent causeof morbidity and mortality among HSCT recipients. Adoptive transfer of viral specific T cells has been successfully used both as prophylaxis and treatment of viral infections in immunocompromised HSCT recipients. Increasingly, precise risk stratification of HSCT recipients with infectious complications should incorporate not only pretransplant clinical criteria, but milestones of immune reconstitution as well. These factors can better identify those at highest risk of morbidity and mortality and identify a population of HSCT recipients in whom adoptive therapy with viral specific T cells should be considered for either prophylaxis or second line treatment early after inadequate response to first line antiviral therapy. Broadening these approaches to improve outcomes for transplant recipients in countries with limited resources is a major challenge. While the principles of risk stratification can be applied, early detection of viral reactivation as well as treatment is challenging in regions where commercial PCR assays and antiviral agents are not readily available.

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

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

Scheduled administration of virus-specific T cells for viral prophylaxis after pediatric allogeneic stem cell transplant

Infections with double-stranded DNA viruses are a significant cause of morbidity and mortality in pediatric patients following allogeneic hematopoietic stem cell transplantation (HSCT). Virus-specific T-cell therapies (VSTs) have been shown to be an effective treatment for infections with adenovirus, BK virus, cytomegalovirus (CMV), and Epstein-Barr virus (EBV). To date, prophylactic regimens to prevent or mitigate these infections using conventional antiviral medications provide suboptimal response rates. Here we report on a clinical trial (NCT03883906) performed to assess the feasibility of rapid manufacturing and early infusion of quadrivalent VSTs generated from stem cell donors ("donor-derived VSTs") into allogeneic HSCT recipients with minimal or absent viremia. Patients were eligible to receive scheduled VSTs as early as 21 days after stem cell infusion. Twenty-three patients received scheduled VSTs. Twenty of 23 patients had no viremia at the time of infusion, while 3 patients had very low-level BK viremia. Two developed clinically significant graft-versus-host disease (GVHD), although this incidence was not outside of expected incidence early after HSCT, and both were successfully treated with systemic corticosteroids (n = 2). Five patients were deemed treatment failures. Three developed subsequent significant viremia/viral disease (n = 3). Eighteen patients did not fail treatment, 7 of whom did not develop any viremia, while 11 developed low-level, self-limited viremia that resolved without further intervention. No infusion reactions occurred. In conclusion, scheduled VSTs appear to be safe and potentially effective at limiting serious complications from viral infections after allogeneic transplantation. A randomized study comparing this scheduled approach to the use of VSTs to treat active viremia is ongoing.

Rapid single-cell identification of Epstein-Barr virus-specific T-cell receptors for cellular therapy

BACKGROUND AND AIMS

Epstein-Barr virus (EBV) is associated with solid and hematopoietic malignancies. After allogeneic stem cell transplantation, EBV infection or reactivation represents a potentially life-threatening condition with no specific treatment available in clinical routine. In vitro expansion of naturally occurring EBV-specific T cells for adoptive transfer is time-consuming and influenced by the donor's T-cell receptor (TCR) repertoire and requires a specific memory compartment that is non-existent in seronegative individuals. The authors present highly efficient identification of EBV-specific TCRs that can be expressed on human T cells and recognize EBV-infected cells.

METHODS AND RESULTS

Mononuclear cells from six stem cell grafts were expanded in vitro with three HLA-B*35:01- or four HLA-A*02:01-presented peptides derived from six EBV proteins expressed during latent and lytic infection. Epitope-specific T cells expanded on average 42-fold and were single-cell-sorted and TCRαβ-sequenced. To confirm specificity, 11 HLA-B*35:01- and six HLA-A*02:01-restricted dominant TCRs were expressed on reporter cell lines, and 16 of 17 TCRs recognized their presumed target peptides. To confirm recognition of virus-infected cells and assess their value for adoptive therapy, three selected HLA-B*35:01- and four HLA-A*02:01-restricted TCRs were expressed on human peripheral blood lymphocytes. All TCR-transduced cells recognized EBV-infected lymphoblastoid cell lines.

CONCLUSIONS

The authors' approach provides sets of EBV epitope-specific TCRs in two different HLA contexts. Resulting cellular products do not require EBV-seropositive donors, can be adjusted to cell subsets of choice with exactly defined proportions of target-specific T cells, can be tracked in vivo and will help to overcome unmet clinical needs in the treatment and prophylaxis of EBV reactivation and associated malignancies.

Outcome of donor-derived TAA-T cell therapy in patients with high-risk or relapsed acute leukemia post allogeneic BMT

Patients with hematologic malignancies relapsing after allogeneic blood or marrow transplantation (BMT) have limited response to conventional salvage therapies, with an expected 1-year overall survival (OS) of <20%. We evaluated the safety and clinical outcomes following administration of a novel T-cell therapeutic targeting 3 tumor-associated antigens (TAA-T) in patients with acute leukemia who relapsed or were at high risk of relapse after allogeneic BMT. Lymphocytes obtained from the BMT donor were manufactured to target TAAs WT1, PRAME, and survivin, which are over-expressed and immunogenic in most hematologic malignancies. Patients received TAA-T infusions at doses of 0.5 to 4 × 107/m2. Twenty-three BMT recipients with relapsed/refractory (n = 11) and/or high-risk (n = 12) acute myeloid leukemia (n = 20) and acute lymphoblastic leukemia (n = 3) were infused posttransplant. No patient developed cytokine-release syndrome or neurotoxicity, and only 1 patient developed grade 3 graft-versus-host disease. Of the patients who relapsed post-BMT and received bridging therapy, the majority (n = 9/11) achieved complete hematologic remission before receiving TAA-T. Relapsed patients exhibited a 1-year OS of 36% and 1-year leukemia-free survival of 27.3% post-TAA-T. The poorest prognosis patients (relapsed <6 months after transplant) exhibited a 1-year OS of 42.8% postrelapse (n = 7). Median survival was not reached for high-risk patients who received preemptive TAA-T posttransplant (n = 12). Although as a phase 1 study, concomitant antileukemic therapy was allowed, TAA-T were safe and well tolerated, and sustained remissions in high-risk and relapsed patients were observed. Moreover, adoptively transferred TAA-T detected by T-cell receptor V-β sequencing persisted up to at least 1 year postinfusion. This trial was registered at clinicaltrials.gov as #NCT02203903.

An ISCT Stem Cell Engineering Committee Position Statement on Immune Reconstitution: the importance of predictable and modifiable milestones of immune reconstitution to transplant outcomes

Allogeneic stem cell transplantation is a potentially curative therapy for some malignant and non-malignant disease. There have been substantial advances since the approaches first introduced in the 1970s, and the development of approaches to transplant with HLA incompatible or alternative donors has improved access to transplant for those without a fully matched donor. However, success is still limited by morbidity and mortality from toxicity and imperfect disease control. Here we review our emerging understanding of how reconstitution of effective immunity after allogeneic transplant can protect from these events and improve outcomes. We provide perspective on milestones of immune reconstitution that are easily measured and modifiable.

Adoptive Cellular Therapy for Multiple Myeloma Using CAR- and TCR-Transgenic T Cells: Response and Resistance

Despite the substantial improvement of therapeutic approaches, multiple myeloma (MM) remains mostly incurable. However, immunotherapeutic and especially T cell-based approaches pioneered the therapeutic landscape for relapsed and refractory disease recently. Targeting B-cell maturation antigen (BCMA) on myeloma cells has been demonstrated to be highly effective not only by antibody-derived constructs but also by adoptive cellular therapies. Chimeric antigen receptor (CAR)-transgenic T cells lead to deep, albeit mostly not durable responses with manageable side-effects in intensively pretreated patients. The spectrum of adoptive T cell-transfer covers synthetic CARs with diverse specificities as well as currently less well-established T cell receptor (TCR)-based personalized strategies. In this review, we want to focus on treatment characteristics including efficacy and safety of CAR- and TCR-transgenic T cells in MM as well as the future potential these novel therapies may have. ACT with transgenic T cells has only entered clinical trials and various engineering strategies for optimization of T cell responses are necessary to overcome therapy resistance mechanisms. We want to outline the current success in engineering CAR- and TCR-T cells, but also discuss challenges including resistance mechanisms of MM for evading T cell therapy and point out possible novel strategies.

Large-scale manufacturing and characterization of CMV-CD19CAR T cells

BACKGROUND

Adoptive transfer of CD19-specific chimeric antigen receptor (CD19CAR) T cells can induce dramatic disease regression in patients with B cell malignancies. CD19CAR T cell therapy may be limited by insufficient engraftment and persistence, resulting in tumor relapse. We previously demonstrated a proof of principle that cytomegalovirus (CMV)-specific T cells can be isolated and enriched prior to CD19CAR transduction to produce CMV-CD19CAR T cells, and that these CMV-CD19CAR T cells can be expanded in vivo through CMV vaccination, resulting in better tumor control in a murine model. Here we developed a clinical platform for generating CMV-CD19CAR T cells.

METHODS

Peripheral blood mononuclear cells (PBMCs) collected from CMV-seropositive healthy donors were stimulated with a good manufacturing practices-grade PepTivator overlapping CMVpp65 peptide pool and enriched for CMV-responsive interferon γ (IFNγ)+T cells using IFNγ Catchmatrix, within the CliniMACS Prodigy Cytokine Capture System (Miltenyi Biotec). Resulting CMV-specific T cells were transduced with a lentiviral vector encoding a second generation CD19R:CD28:ζ/EGFRt CAR and expanded with interleukin 2 (IL-2) and IL-15 for 15 days before characterization.

RESULTS

CMV-specific T cells were enriched from 0.8%±0.5 of input PBMC to 76.3%±11.6 in nine full-scale qualification runs (absolute yield of 4.2±3.3×10⁶ IFNγ+T cells from an input of 1×10⁹ PBMCs). Average CD19CAR transduction efficiency of CMV-specific T cells was 27.0%±14.2 in the final products, which underwent rapid expansion, resulting in a total cell dose of 6.2±0.9 × 10⁶ CD19CAR-tranduced T cells with CMV specificity (ie, functionally bispecific). CMV-CD19CAR T cells were polyclonal, expressed memory markers but had low expression of exhaustion markers, responded to both CD19 and CMVpp65 stimulation with rapid proliferation and exhibited antigen-specific effector functions against both CD19-expressing tumors and CMVpp65 antigen. The final products passed release criteria for clinical use.

CONCLUSIONS

We demonstrated the feasibility of our large-scale platform for generating CMV-CD19CAR T cells for clinical application. We plan to initiate a clinical trial at City of Hope using CMV-CD19CAR T cells for patients with intermediate/high-grade B cell non-Hodgkin's lymphoma immediately after autologous hematopoietic cell transplantation followed by vaccination with a novel CMV vaccine based on Modified Vaccinia Ankara (Triplex) 28 days and 56 days post-T cell infusion.

Protective T cell receptor identification for orthotopic reprogramming of immunity in refractory virus infections

Viral infections cause life-threatening disease in immunocompromised patients and especially following transplantation. T cell receptor (TCR) engineering redirects specificity and can bring significant progress to emerging adoptive T cell transfer (ACT) approaches. T cell epitopes are well described, although knowledge is limited on which TCRs mediate protective immunity. In this study, refractory adenovirus (AdV) infection after hematopoietic stem cell transplantation (HSCT) was treated with ACT of highly purified Hexon5-specific T cells using peptide major histocompatibility complex (pMHC)-Streptamers against the immunodominant human leukocyte antigen (HLA)-A∗0101-restricted peptide LTDLGQNLLY. AdV was successfully controlled through this oligoclonal ACT. Novel protective TCRs were isolated ex vivo and preclinically engineered into the TCR locus of allogeneic third-party primary T cells by CRISPR-Cas9-mediated orthotopic TCR replacement. Both TCR knockout and targeted integration of the new TCR in one single engineering step led to physiological expression of the transgenic TCR. Reprogrammed TCR-edited T cells showed strong virus-specific functionality such as cytokine release, effector marker upregulation, and proliferation capacity, as well as cytotoxicity against LTDLGQNLLY-presenting and AdV-infected targets. In conclusion, ex vivo isolated TCRs with clinical proven protection through ACT could be redirected into T cells from naive third-party donors. This approach ensures that transgenic TCRs are protective with potential off-the-shelf use and widened applicability of ACT to various refractory emerging viral infections.

T-cell depleted haploidentical hematopoietic cell transplantation for pediatric malignancy

Access to allogenic hematopoietic cell transplantation (HCT), a potentially curative treatment for chemotherapy-resistant hematologic malignancies, can be limited if no human leukocyte antigen (HLA) identical related or unrelated donor is available. Alternative donors include Cord Blood as well as HLA-mismatched unrelated or related donors. If the goal is to minimize the number of HLA disparities, partially matched unrelated donors are more likely to share 8 or 9 of 10 HLA alleles with the recipient. However, over the last decade, there has been success with haploidentical HCT performed using the stem cells from HLA half-matched related donors. As the majority of patients have at least one eligible and motivated haploidentical donor, recruitment of haploidentical related donors is frequently more rapid than of unrelated donors. This advantage in the accessibility has historically been offset by the increased risks of graft rejection, graft-versus-host disease and delayed immune reconstitution. Various ex vivo T-cell depletion (TCD) methods have been investigated to overcome the immunological barrier and facilitate immune reconstitution after a haploidentical HCT. This review summarizes historical and contemporary clinical trials of haploidentical TCD-HCT, mainly in pediatric malignancy, and describes the evolution of these approaches with a focus on serial improvements in the kinetics of immune reconstitution. Methods of TCD discussed include in vivo as well as ex vivo positive and negative selection. In addition, haploidentical TCD as a platform for post-HCT cellular therapies is discussed. The present review highlights that, as a result of the remarkable progress over half a century, haploidentical TCD-HCT can now be considered as a preferred alternative donor option for children with hematological malignancy in need of allogeneic HCT.

Modified T cells as therapeutic agents

Immunotherapy is now a well-established modality in the treatment of cancer. Although several platforms to redirect the immune response exist, the use of genetically modified T cells has garnered particular attention in recent years. This is due, in large part, to their success in the treatment of B-cell malignancies. Adoptively transferred T cells have also demonstrated efficacy in the treatment of systemic viral infections that occur following hematopoietic cell transplantation prior to immune reconstitution. Here we discuss the techniques that enable redirection of T lymphocytes to treat cancer or infection and the current indications for these therapies.

Development of CMV-CD19 bi-specific CAR T cells with post-infusion in vivo boost using an anti-CMV vaccine

Adoptive transfer of in vitro expanded, chimeric antigen receptor (CAR)-redirected CD19-specific T cells can induce dramatic disease regression in patients with leukemia and lymphomas. However, the full potential of this emerging modality is hampered in some cancer settings by a significant rate of therapeutic failure arising from the attenuated engraftment and persistence of CAR-redirected T cells, and tumor relapse following adoptive transfer. Here, we discuss an advanced strategy that facilitates post-infusion in vivo boosting of CAR T cells via CMV vaccination, to mediate durable remission of B cell malignancies by engrafting a CAR molecule onto a CMV-specific T cell. We also discuss a feasible and unique platform for the generation of the CMV-CD19CAR T cells for clinical application. This new approach would overcome multiple challenges in current CAR T cell technology including: short T cell persistence, limited duration of response, and inability to re-stimulate T cells after relapse or persistent disease.

Respiratory Viruses in Solid Organ Transplant Recipients

Solid organ transplantation is often lifesaving, but does carry an increased risk of infection. Respiratory viral infections are one of the most prevalent infections, and are a cause of significant morbidity and mortality, especially among lung transplant recipients. There is also data to suggest an association with acute rejection and chronic lung allograft dysfunction in lung transplant recipients. Respiratory viral infections can appear at any time post-transplant and are usually acquired in the community. All respiratory viral infections share similar clinical manifestations and are all currently diagnosed using nucleic acid testing. Influenza has good treatment options and prevention strategies, although these are hampered by resistance to neuraminidase inhibitors and lower vaccine immunogenicity in the transplant population. Other respiratory viruses, unfortunately, have limited treatments and preventive methods. This review summarizes the epidemiology, clinical manifestations, therapies and preventive measures for clinically significant RNA and DNA respiratory viruses, with the exception of SARS-CoV-2. This area is fast evolving and hopefully the coming decades will bring us new antivirals, immunologic treatments and vaccines.

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.

Third-Party BK Virus-Specific Cytotoxic T Lymphocyte Therapy for Hemorrhagic Cystitis Following Allotransplantation

PURPOSE

BK virus-associated hemorrhagic cystitis (BKV-HC) is a common complication of allogenic hematopoietic stem cell transplantation (AHSCT), particularly in recipients of alternative donor transplants, which are being performed in increasing numbers. BKV-HC typically results in painful hematuria, urinary obstruction, and renal dysfunction, without a definitive therapeutic option.

METHODS

We performed a clinical trial (ClinicalTrials.gov identifier: NCT02479698) to assess the feasibility, safety, and efficacy of administering most closely HLA-matched third-party BKV-specific cytotoxic T lymphocytes (CTLs), generated from 26 healthy donors and banked for off-the-shelf use. The cells were infused into 59 patients who developed BKV-HC following AHSCT. Comprehensive clinical assessments and correlative studies were performed.

RESULTS

Response to BKV-CTL infusion was rapid; the day 14 overall response rate was 67.7% (40 of 59 evaluable patients), which increased to 81.6% among evaluable patients at day 45 (40 of 49 evaluable patients). No patient lost a previously achieved response. There were no cases of de novo grade 3 or 4 graft-versus-host disease, graft failure, or infusion-related toxicities. BKV-CTLs were identified in patient blood samples up to 3 months postinfusion and their in vivo expansion predicted for clinical response. A matched-pair analysis revealed that, compared with standard of care, after accounting for prognostic covariate effects, treatment with BKV-CTLs resulted in higher probabilities of response at all follow-up timepoints as well as significantly lower transfusion requirement.

CONCLUSION

Off-the-shelf BKV-CTLs are a safe and effective therapy for the management of patients with BKV-HC after AHSCT.

Rapidly expanded partially HLA DRB1-matched fungus-specific T cells mediate in vitro and in vivo antifungal activity

Invasive fungal infections are a major cause of disease and death in immunocompromised hosts, including patients undergoing allogeneic hematopoietic stem cell transplant (HSCT). Recovery of adaptive immunity after HSCT correlates strongly with recovery from fungal infection. Using initial selection of lymphocytes expressing the activation marker CD137 after fungal stimulation, we rapidly expanded a population of mainly CD4+ T cells with potent antifungal characteristics, including production of tumor necrosis factor α, interferon γ, interleukin-17, and granulocyte-macrophage colony stimulating factor. Cells were manufactured using a fully good manufacturing practice-compliant process. In vitro, the T cells responded to fungal antigens presented on fully and partially HLA-DRB1 antigen-matched presenting cells, including when the single common DRB1 antigen was allelically mismatched. Administration of antifungal T cells lead to reduction in the severity of pulmonary and cerebral infection in an experimental mouse model of Aspergillus. These data support the establishment of a bank of cryopreserved fungus-specific T cells using normal donors with common HLA DRB1 molecules and testing of partially HLA-matched third-party donor fungus-specific T cells as a potential therapeutic in patients with invasive fungal infection after HSCT.

Virus-specific T-cell therapy to treat BK polyomavirus infection in bone marrow and solid organ transplant recipients

BK polyomavirus (BKPyV) infection is a major complication of hematopoietic stem cell transplant (HSCT) and solid organ transplant (SOT). Treatment options are limited, poorly effective, and have significant toxicities. Cellular therapy using T cells directed against BKPyV is an emerging therapy, and we report efficacy in controlling BKPyV-associated disease in highly immunocompromised patients. Virus-specific T cells (VSTs) against BKPyV were manufactured using either blood from the patient's stem cell donor (donor-derived VSTs) or from unrelated donors (third-party VSTs). VSTs were used to treat BKPyV in 38 HSCT recipients and 3 SOT recipients between June 2017 and December 2019. Overall response rate was 86% in patients treated for BK viremia, 100% in patients treated for hemorrhagic cystitis, and 87% in patients treated for both BK viremia and hemorrhagic cystitis. No infusional toxicity, de novo graft-versus-host disease, or rejection of the organ occurred attributable to the VST infusion. BKPyV-specific immune responses were demonstrated by interferon-γ production by peripheral blood mononuclear cells postinfusion in response to BKPyV antigens. VSTs are a safe and potentially effective strategy to treat BKPyV and associated symptoms in recipients of HSCT and SOT. Cellular therapy should be considered for all patients with BKPyV and underlying immune suppression at risk of complications. This trial was registered at www.clinicaltrials.gov as #NCT02532452.

Adoptive therapy with CMV-specific cytotoxic T lymphocytes depends on baseline CD4+ immunity to mediate durable responses

Adoptive cell therapy using cytomegalovirus (CMV)-specific cytotoxic T lymphocytes (CMV-CTLs) has demonstrated efficacy posttransplant. Despite the predicted limited engraftment of CMV-CTLs derived from third-party donors, partially matched third-party donor-derived CMV-CTLs have demonstrated similar response rates to those derived from primary hematopoietic cell transplantation donors. Little is known about the mechanisms through which adoptive cellular therapies mediate durable responses. We performed a retrospective analysis of patients receiving CMV-CTLs for treatment of CMV viremia and/or disease after allogeneic transplant between September of 2009 and January of 2018. We evaluated whether response to adoptively transferred CMV-CTLs correlated with immune reconstitution (IR), using validated CD4+ IR milestones of 50 × 106/L and 200 × 106/L. In this analysis, a cohort of 104 patients received CMV-CTLs derived from a primary transplant donor (n = 25), a third-party donor (n = 76), or both (n = 3). Response to therapy did not increase the likelihood of achieving CD4+ IR milestones at 1 (P = .53 and P > .99) or 2 months (P = .12 and P = .33). The origin of CMV-CTLs did not impact subsequent CD4+ IR. CMV-CTLs appeared to interact with host immunity in mediating responses. Recipients with a baseline CD4 >50 × 106/L had higher response to therapy (P = .02), improved overall survival (P < .001), and protection from CMV-related death (P = .002). Baseline endogenous immunity appears to improve CMV-related and overall survival in this cohort and can be an important marker at the initiation of therapy.

The role of EBV in haematolymphoid proliferations: emerging concepts relevant to diagnosis and treatment

Epstein-Barr virus (EBV) is a ubiquitous gammaherpesvirus with >90% of the adult population worldwide harbouring latent infection. A small subset of those infected develop EBV-associated neoplasms, including a range of lymphoproliferative disorders (LPD). The diagnostic distinction of these entities appears increasingly relevant as our understanding of EBV-host interactions and mechanisms of EBV-driven lymphomagenesis improves. EBV may lower the mutational threshold for malignant transformation, create potential vulnerabilities related to viral alteration of cell metabolism and allow for improved immune targeting. However, these tumours may escape immune surveillance by affecting their immune microenvironment, limiting viral gene expression or potential loss of the viral episome. Methods to manipulate the latency state of the virus to enhance immunogenicity are emerging as well as the potential to detect so-called 'hit and run' cases where EBV has been lost. Finally, measurement of EBV DNA remains an important biomarker for screening and monitoring of LPD. Methods to distinguish EBV DNA derived from virions during lytic activation from latent, methylated EBV DNA present in EBV-associated neoplasms may broaden the utility of this testing, particularly in patients with compromised immune function. We highlight some of these emerging areas relevant to the diagnosis and treatment of EBV-associated LPD with potential applicability to other EBV-associated neoplasms.

Magnitude of Off-Target Allo-HLA Reactivity by Third-Party Donor-Derived Virus-Specific T Cells Is Dictated by HLA-Restriction

T-cell products derived from third-party donors are clinically applied, but harbor the risk of off-target toxicity via induction of allo-HLA cross-reactivity directed against mismatched alleles. We used third-party donor-derived virus-specific T cells as model to investigate whether virus-specificity, HLA restriction and/or HLA background can predict the risk of allo-HLA cross-reactivity. Virus-specific CD8^pos T cells were isolated from HLA-A^*01:01/B^*08:01 or HLA-A^*02:01/B^*07:02 positive donors. Allo-HLA cross-reactivity was tested using an EBV-LCL panel covering 116 allogeneic HLA molecules and confirmed using K562 cells retrovirally transduced with single HLA-class-I alleles of interest. HLA-B^*08:01-restricted T cells showed the highest frequency and diversity of allo-HLA cross-reactivity, regardless of virus-specificity, which was skewed toward multiple recurrent allogeneic HLA-B molecules. Thymic selection for other HLA-B alleles significantly influenced the level of allo-HLA cross-reactivity mediated by HLA-B^*08:01-restricted T cells. These results suggest that the degree and specificity of allo-HLA cross-reactivity by T cells follow rules. The risk of off-target toxicity after infusion of incompletely matched third-party donor-derived virus-specific T cells may be reduced by selection of T cells with a specific HLA restriction and background.

"Cerberus" T Cells: A Glucocorticoid-Resistant, Multi-Pathogen Specific T Cell Product to Fight Infections in Severely Immunocompromised Patients

Adoptive immunotherapy (AI) with pathogen-specific T cells is a promising alternative to pharmacotherapy for the treatment of opportunistic infections after allogeneic hematopoietic cell transplantation or solid organ transplantation. However, clinical implementation of AI is limited to patients not receiving high-dose steroids, a prerequisite for optimal T-cell function, practically excluding the most susceptible to infections patients from the benefits of AI. To address this issue, we here rapidly generated, clinical doses of a steroid-resistant T-cell product, simultaneously targeting four viruses (adenovirus, cytomegalovirus, Epstein Barr virus, and BK virus) and the fungus Aspergillus fumigatus, by genetic disruption of the glucocorticoid receptor (GR) gene using CRISPR/CAS9 ribonucleoprotein delivery. The product, “Cerberus” T cells (Cb-STs), was called after the monstrous three-headed dog of Greek mythology, due to its triple potential; specificity against viruses, specificity against fungi and resistance to glucocorticoids. Following efficient on-target GR disruption and minimal off-target editing, the generated Cb-STs maintained the characteristics of pentavalent-STs, their unedited counterparts, including polyclonality, memory immunophenotype, specificity, and cytotoxicity while they presented functional resistance to dexamethasone. Cb-STs may become a powerful, one-time treatment for severely immunosuppressed patients under glucocorticoids who suffer from multiple, life-threatening infections post-transplant, and for whom therapeutic choices are limited.

Infectious Complications in Paediatric Haematopoetic Cell Transplantation for Acute Lymphoblastic Leukemia: Current Status

Haematopoietic stem cell transplantation (HSCT) in paediatric patients with acute lymphoblastic leukaemia (ALL) is associated with a variety of infectious complications which result in significant morbidity and mortality. These patients are profoundly immunocompromised, and immune reconstitution after HSCT generally occurs in astrictly defined order. During the early phase after HSCT until engraftment, patients are at risk of infections due to presence of neutropenia and mucosal damage, with Gramme-positive and Gramme-negative bacteria and fungi being the predominant pathogens. After neutrophil recovery, the profound impairment of cell-mediated immunity and use of glucocorticosteroids for control of graft-vs.-host disease (GvHD) increases the risk of invasive mould infection and infection or reactivation of various viruses, such as cytomegalovirus, varicella zoster virus, Epstein-Barr virus and human adenovirus. In the late phase, characterised by impaired cellular and humoral immunity, particularly in conjunction with chronic GvHD, invasive infections with encapsulated bacterial infections are observed in addition to fungal and viral infections. HSCT also causes a loss of pretransplant naturally acquired and vaccine-acquired immunity; therefore, complete reimmunization is necessary to maintain long-term health in these patients. During the last two decades, major advances have been made in our understanding of and in the control of infectious complications associated with HSCT. In this article, we review current recommendations for the diagnosis, prophylaxis and treatment of infectious complications following HSCT for ALL in childhood.

SARS-CoV-2-specific T cells are rapidly expanded for therapeutic use and target conserved regions of the membrane protein

T-cell responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been described in recovered patients, and may be important for immunity following infection and vaccination as well as for the development of an adoptive immunotherapy for the treatment of immunocompromised individuals. In this report, we demonstrate that SARS-CoV-2-specific T cells can be expanded from convalescent donors and recognize immunodominant viral epitopes in conserved regions of membrane, spike, and nucleocapsid. Following in vitro expansion using a good manufacturing practice-compliant methodology (designed to allow the rapid translation of this novel SARS-CoV-2 T-cell therapy to the clinic), membrane, spike, and nucleocapsid peptides elicited interferon-γ production, in 27 (59%), 12 (26%), and 10 (22%) convalescent donors (respectively), as well as in 2 of 15 unexposed controls. We identified multiple polyfunctional CD4-restricted T-cell epitopes within a highly conserved region of membrane protein, which induced polyfunctional T-cell responses, which may be critical for the development of effective vaccine and T-cell therapies. Hence, our study shows that SARS-CoV-2 directed T-cell immunotherapy targeting structural proteins, most importantly membrane protein, should be feasible for the prevention or early treatment of SARS-CoV-2 infection in immunocompromised patients with blood disorders or after bone marrow transplantation to achieve antiviral control while mitigating uncontrolled inflammation.

T-Cell Therapeutics Targeting Human Parainfluenza Virus 3 Are Broadly Epitope Specific and Are Cross Reactive With Human Parainfluenza Virus 1

Human Parainfluenza Virus-3 (HPIV3) causes severe respiratory illness in immunocompromised patients and lacks approved anti-viral therapies. A phase I study of adoptively transferred virus-specific T-cells (VSTs) targeting HPIV3 following bone marrow transplantation is underway (NCT03180216). We sought to identify immunodominant epitopes within HPIV3 Matrix protein and their cross-reactivity against related viral proteins. VSTs were generated from peripheral blood of healthy donors by ex-vivo expansion after stimulation with a 15-mer peptide library encompassing HPIV3 matrix protein. Epitope mapping was performed using IFN-γ ELIspot with combinatorial peptide pools. Flow cytometry was used to characterize products with intracellular cytokine staining. In 10 VST products tested, we discovered 12 novel immunodominant epitopes. All products recognized an epitope at the C-terminus. On IFN-γ ELISpot, individual peptides eliciting activity demonstrated mean IFN-γ spot forming units per well (SFU)/1x10⁵ cells of 115.5 (range 24.5-247.5). VST products were polyfunctional, releasing IFN-γ and TNF-α in response to identified epitopes, which were primarily HLA Class II restricted. Peptides from Human Parainfluenza Virus-1 corresponding to the HPIV3 epitopes showed cross-reactivity for HPIV1 in 11 of 12 tested epitopes (mean cross reactivity index: 1.19). Characterization of HPIV3 epitopes may enable development of third-party VSTs to treat immune suppressed patients with HPIV infection.

Harnessing T Cells to Control Infections After Allogeneic Hematopoietic Stem Cell Transplantation

Dramatic progress in the outcome of allogeneic hematopoietic stem cell transplantation (allo-HSCT) from alternative sources in pediatric patients has been registered over the past decade, providing a chance to cure children and adolescents in need of a transplant. Despite these advances, transplant-related mortality due to infectious complications remains a major problem, principally reflecting the inability of the depressed host immune system to limit infection replication and dissemination. In addition, development of multiple infections, a common occurrence after high-risk allo-HSCT, has important implications for overall survival. Prophylactic and preemptive pharmacotherapy is limited by toxicity and, to some extent, by lack of efficacy in breakthrough infections. T-cell reconstitution is a key requirement for effective infection control after HSCT. Consequently, T-cell immunotherapeutic strategies to boost pathogen-specific immunity may complement or represent an alternative to drug treatments. Pioneering proof of principle studies demonstrated that the administration of donor-derived T cells directed to human herpesviruses, on the basis of viral DNA monitoring, could effectively restore specific immunity and confer protection against viral infections. Since then, the field has evolved with implementation of techniques able to hasten production, allow for selection of specific cell subsets, and target multiple pathogens. This review provides a brief overview of current cellular therapeutic strategies to prevent or treat pathogen-related complications after HSCT, research carried out to increase efficacy and safety, including T-cell production for treatment of infections in patients with virus-naïve donors, results from clinical trials, and future developments to widen adoptive T-cell therapy access in the HSCT setting.

Antigenic competition in the generation of multi-virus-specific cell lines for immunotherapy of human cytomegalovirus, polyomavirus BK, Epstein-Barr virus and adenovirus infection in haematopoietic stem cell transplant recipients

Adoptive transfer of multivirus-specific T cell lines (MVST) is an advanced tool for immunotherapy of virus infections after hematopoietic stem cell transplantation (HSCT). Their preparation includes activation of donor virus-specific T cells by the mixture of oligopeptides derived from immunodominant antigens of several most harmful viruses, i.e. human cytomegalovirus (HCMV), polyomavirus BK (BKV), Epstein-Barr virus (EBV) and adenovirus (ADV). The aim of our study was to find out whether antigenic competition may have an impact on the expansion of virus-specific T cells. MVST from several heathy blood donors were generated using a pulse of overlapping oligopeptides (PepMixes™, derived from the IE1 and pp65 CMV antigens, VP1 and LTAG BKV antigens, BZLF1 and EBNA1 proteins of EBV and hexon protein from ADV) and short time culture in the presence of IL-7 and IL-4. The amount of virus-specific T cells in MVST was measured by ELISPOT and flow cytometry after re-stimulation with individual antigens. To evaluate antigenic competition, MVST were expanded either with a complete set of antigens or with the mixture lacking some of them. MVST expanded with the antigen mixture including CMV antigens contained a lower proportion of the T cells of other antigen specificities. A similar inhibitory effect was not apparent for EBV-derived peptides. The competitive effect of CMV antigens was most pronounced in MVST from CMV-seropositive donors and was mediated by both IE1 and pp65-derived peptides. Antigenic competition did not influence the phenotype of either CMV- or BKV-specific T cells. Both T cell populations had an effector memory phenotype (CD45RO+, CD27-, CCR7-). However, CMV-specific T cells preferentially consist of CD8+ while in BKV-specific T cells, the CD4+ phenotype predominated. Modification of the MVST manufacture protocol to prevent antigenic competition may increase the efficacy of MVST in therapy of BKV infections in HSCT recipients.

Management of PTLD After Hematopoietic Stem Cell Transplantation: Immunological Perspectives

Post-transplant lymphoproliferative disorders (PTLDs) are life-threatening complications of iatrogenic immune impairment after allogeneic hematopoietic stem cell transplantation (HSCT). In the pediatric setting, the majority of PTLDs are related to the Epstein-Barr virus (EBV) infection, and present as B-cell lymphoproliferations. Although considered rare events, PTLDs have been increasingly observed with the widening application of HSCT from alternative sources, including cord blood and HLA-haploidentical stem cell grafts, and the use of novel agents for the prevention and treatment of rejection and graft-vs.-host disease. The higher frequency initially paralleled a poor outcome, due to limited therapeutic options, and scarcity of controlled trials in a rare disease context. In the last 2 decades, insight into the relationship between EBV and the immune system, and advances in early diagnosis, monitoring and treatment have changed the approach to the management of PTLDs after HSCT, and significantly ameliorated the prognosis. In this review, we summarize literature on the impact of combined viro-immunologic assessment on PTLD management, describe the various strategies for PTLD prevention and preemptive/curative treatment, and discuss the potential of novel immune-based therapies in the containment of this malignant complication.

Safety and feasibility of virus-specific T cells derived from umbilical cord blood in cord blood transplant recipients

Adoptive transfer of virus-specific T cells (VSTs) has been shown to be safe and effective in stem cell transplant recipients. However, the lack of virus-experienced T cells in donor cord blood (CB) has prevented the development of ex vivo expanded donor-derived VSTs for recipients of this stem cell source. Here we evaluated the feasibility and safety of ex vivo expansion of CB T cells from the 20% fraction of the CB unit in pediatric patients receiving a single CB transplant (CBT). In 2 clinical trials conducted at 2 separate sites, we manufactured CB-derived multivirus-specific T cells (CB-VSTs) targeting Epstein-Barr virus (EBV), adenovirus, and cytomegalovirus (CMV) for 18 (86%) of 21 patients demonstrating feasibility. Manufacturing for 2 CB-VSTs failed to meet lot release because of insufficient cell recovery, and there was 1 sterility breach during separation of the frozen 20% fraction. Delayed engraftment was not observed in patients who received the remaining 80% fraction for the primary CBT. There was no grade 3 to 4 acute graft-versus-host disease (GVHD) associated with the infusion of CB-VSTs. None of the 7 patients who received CB-VSTs as prophylaxis developed end-organ disease from CMV, EBV, or adenovirus. In 7 patients receiving CB-VSTs for viral reactivation or infection, only 1 patient developed end-organ viral disease, which was in an immune privileged site (CMV retinitis) and occurred after steroid therapy for GVHD. Finally, we demonstrated the long-term persistence of adoptively transferred CB-VSTs using T-cell receptor-Vβ clonotype tracking, suggesting that CB-VSTs are a feasible addition to antiviral pharmacotherapy.

Preclinical Development and Clinical-Scale Manufacturing of HIV Gag-Specific, LentivirusModified CD4 T Cells for HIV Functional Cure

Activation, infection, and eventual depletion of human immunodeficiency virus (HIV)-specific cluster of differentiation 4 (CD4) T cells are the crucial pathogenetic events in acquired immunodeficiency syndrome (AIDS). We developed a cell and gene therapy to reconstitute HIV-specific CD4 T cells and prevent their destruction by HIV. Antigen-specific CD4 T cells will provide helper functions to support antiviral cytotoxic T lymphocyte (CTL) function and the production of virus-specific antibodies. However, ex vivo expansion of HIV-specific CD4 T cells is poor and previous gene therapies focused on bulk CD4 T cells without enriching for an antigen-specific subset. We developed a method for manufacturing autologous CD4⁺ T cell products highly enriched with Gag-specific T cells. Rare Gag-specific CD4 T cells in peripheral blood mononuclear cells (PBMCs) were increased nearly 1,000-fold by stimulating PBMC with Gag peptides, followed by depleting nontarget cells and transducing with lentivirus vector AGT103 to protect against HIV-mediated depletion and inhibit HIV release from latently infected cells. The average percentage of HIV-specific CD4 cells in the final products was 15.13%, and the average yield was 7 × 10⁸ cells. The protocol for clinical-scale manufacturing of HIV-specific and HIV-resistant CD4 T cells is an important step toward effective immunotherapy for HIV disease.

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.