Selective depletion of donor alloreactive T cells without loss of antiviral or antileukemic responses

Immunotherapy with CD25/CD71-allodepleted T cells to improve T-cell reconstitution after matched unrelated donor hematopoietic stem cell transplant: a randomized trial

BACKGROUND AIMS

Delayed immune reconstitution is a major challenge after matched unrelated donor (MUD) stem cell transplant (SCT). In this randomized phase 2 multi-center trial, Adoptive Immunotherapy with CD25/71 allodepleted donor T cells to improve immunity after unrelated donor stem cell transplant (NCT01827579), the authors tested whether allodepleted donor T cells (ADTs) can safely be used to improve immune reconstitution after alemtuzumab-based MUD SCT for hematological malignancies.

METHODS

Patients received standard of care or up to three escalating doses of ADTs generated through CD25+/CD71+ immunomagnetic depletion. The primary endpoint of the study was circulating CD3+ T-cell count at 4 months post-SCT. Twenty-one patients were treated, 13 in the ADT arm and eight in the control arm.

RESULTS

The authors observed a trend toward improved CD3+ T-cell count at 4 months in the ADT arm versus the control arm (230/µL versus 145/µL, P = 0.18), and three ADT patients achieved normal CD3+ T-cell count at 4 months (>700/µL). The rates of significant graft-versus-host disease (GVHD) were comparable in both cohorts, with grade ≥2 acute GVHD in seven of 13 and four of eight patients and chronic GVHD in three of 13 and three of eight patients in the ADT and control arms, respectively.

CONCLUSIONS

These data suggest that adoptive transfer of ADTs is safe, but that in the MUD setting the benefit in terms of T-cell reconstitution is limited. This approach may be of more use in the context of more rigorous T-cell depletion.

Infusion of Alloanergized Donor Lymphocytes after CD34-selected Haploidentical Myeloablative Hematopoietic Stem Cell Transplantation

Purpose: Allogeneic hematopoietic stem-cell transplantation (HSCT) is a curative treatment for many hematologic cancers. Use of haploidentical (mismatched) donors increases HSCT availability but is limited by severe graft-versus-host disease (GvHD) and delayed immune reconstitution. Alloanergization of donor T cells is a simple approach to rebuild immunity while limiting GvHD after haploidentical HSCT, but the optimal T-cell dose and impact on immune reconstitution remain unknown.Patients and Methods: We performed a multicenter phase I trial of alloanergized donor lymphocyte infusion (aDLI) after CD34-selected myeloablative haploidentical HSCT. The primary aim was feasibility and safety with secondary aims of assessing the less frequently addressed issue of impact on immune reconstitution.Results: Nineteen patients with high-risk acute leukemia or myelodysplasia were enrolled. Engraftment occurred in 18 of 19 patients (95%). Pre-aDLI, 12 patients (63%) had bacteremia, nine of 17 at-risk patients (53%) reactivated CMV, and one developed acute GvHD. Sixteen patients received aDLI at dose levels 1 (10³ T cells/kg, n = 4), 2 (10⁴, n = 8), and 3 (10⁵, n = 4). After aDLI, five patients developed clinically significant acute GvHD, and four of 14 at-risk patients (29%) reactivated CMV. T-cell recovery was significantly greater, and functional virus- and tumor-associated antigen-specific T cells were detectable earlier in patients receiving dose level 2 or 3 versus dose level 1/no aDLI. Alloanergization of donor cells expanded the CD4⁺ T-regulatory cell frequency within aDLI, which increased further in vivo without impeding expansion of virus- and tumor-associated antigen-specific T cells.Conclusions: These data demonstrate safety and a potential role for aDLI in contributing to immune reconstitution and expanding tolerogenic regulatory T cells in vivo after CD34-selected myeloablative haploidentical HSCT. Clin Cancer Res; 24(17); 4098-109. ©2018 AACR.

Management of adenovirus infection in patients after haematopoietic stem cell transplantation: State-of-the-art and real-life current approach: A position statement on behalf of the Infectious Diseases Working Party of the European Society of Blood and Marrow Transplantation

The important insights gained over the past years in diagnosis and treatment of invasive adenoviral infections provide new paradigms for the monitoring and clinical management of these life-threatening complications. A meeting was held to discuss and subsequently disseminate the current advances in our understanding of the aetiology/pathogenesis and future treatment options facilitating effective control or prevention of adenovirus-related diseases in the allogeneic haematopoietic stem cell transplant setting. Invited experts in the field discussed recent progress with leading members of the Infectious Diseases Working Party of the European Society of Blood and Marrow Transplantation at the "State-of-the-art" Meeting in Poznan, Poland, in October 2017. In this review article, the panel of experts presents a concise summary of the current evidence based on published data from the last 15 years and on recent achievements resulting from real-life practice. The present position statement reflects an expert opinion on current approaches to clinical management of adenovirus infections in patients undergoing allogeneic haematopoietic stem cell transplant and provides graded recommendations of the panel for diagnostic approaches and preemptive therapy reflecting the present state of knowledge.

Virus-Specific T Cells for the Immunocompromised Patient

While progress has been made in the treatment of both hematologic cancers and solid tumors, chemorefractory or relapsed disease often portends a dismal prognosis, and salvage chemotherapy or radiation expose patients to intolerable toxicities and may not be effective. Hematopoietic stem cell transplant offers the promise of cure for many patients, and while mismatched, unrelated or haploidentical donors are increasingly available, the recipients are at higher risk of severe immunosuppression and immune dysregulation due to graft versus host disease. Viral infections remain a primary cause of severe morbidity and mortality in this patient population. Again, many therapeutic options for viral disease are toxic, may be ineffective or generate resistance, or fail to convey long-term protection. Adoptive cell therapy with virus-specific T cells (VSTs) is a targeted therapy that is efficacious and has minimal toxicity in immunocompromised patients with CMV and EBV infections in particular. Products have since been generated specific for multiple viral antigens (multi-VST), which are not only effective but also confer protection in 70–90% of recipients when used as prophylaxis. Notably, these products can be generated from either virus-naive or virus-experienced autologous or allogeneic sources, including partially matched HLA-matched third-party donors. Obstacles to effective VST treatment are donor availability and product generation time. Banking of third-party VST is an attractive way to overcome these constraints and provide products on an as-needed basis. Other developments include epitope discovery to broaden the number of viral antigens targets in a single product, the optimization of VST generation from naive donor sources, and the modification of VSTs to enhance persistence and efficacy in vivo.

Improving the safety of T-Cell therapies using an inducible caspase-9 gene

Adoptive transfer of T cells can be an effective anticancer treatment. However, uncontrolled or unpredictable immediate or persistent toxic effects are a source of concern. The ability to conditionally eliminate aberrant cells in vivo is therefore becoming a critical step for the successful translation of this approach to the clinic. We review the evolution of safety systems, focusing on a suicide switch that can be expressed stably and efficiently in human T cells without impairing phenotype, function, or antigen specificity. This system is based on the fusion of human caspase-9 to a modified human FK-binding protein, allowing conditional dimerization in the presence of an otherwise bio-inert small molecule drug. When exposed to the synthetic dimerizing drug, the inducible caspase-9 becomes activated, resulting in the rapid apoptosis of cells expressing this construct. We have illustrated the clinical feasibility and efficacy of this approach after haploidentical hematopoietic stem cell transplant. Here we review the benefits and limitations of the approach.

Donor-Derived Regulatory T Cells Attenuate the Severity of Acute Graft-Versus-Host Disease after Cord Blood Transplantation

Allogeneic peripheral blood stem cell transplantation (allo-PBSCT) is a curative therapy for some types of hematological disorders. However, allo-PBSCT is commonly complicated with acute graft-versus-host disease (aGVHD), characterized by host tissues being attacked by the grafted donor lymphocytes due to disparities of human leukocyte antigen (HLA) between the donor and host. By contrast, cord blood transplantation (CBT) is typically associated with low-grade severity of aGVHD, but the underlying mechanisms remain unclear. Donor-derived CD4(+) alloreactive T cells (ATs) are of a specific lymphocyte subset, which can be activated by the recipient's HLA, and play a crucial role in the onset of aGVHD. In the present study, we aimed to explore the difference in the property of CD4(+) ATs between cord blood (CB) and adult peripheral blood (APB). We thus found that CB and APB CD4(+) ATs contained not only effector T cells (Teffs) that execute aGVHD, but also a distinct subset of FoxP3(+) regulatory T cells (Tregs) that may alleviate aGVHD. Importantly, CB CD4(+) ATs contained higher percentage of FoxP3(+) Tregs, compared to APB CD4(+) ATs (P < 0.001), while lower percentage of Teffs (Th1, Th2 and Th17 cells) was detected in CB CD4(+) ATs (P < 0.05, P < 0.001 and P < 0.05, respectively). Our findings suggest that FoxP3(+) Tregs in CB CD4(+) ATs may contribute to attenuating the severity of aGVHD observed after CBT.

Translational Implications for Off-the-shelf Immune Cells Expressing Chimeric Antigen Receptors

Chimeric antigen receptor (CAR) endows specificity to T-cells independent of human leukocyte antigen (HLA). This enables one immunoreceptor to directly target the same surface antigen on different subsets of tumor cells from multiple HLA-disparate recipients. Most approaches manufacture individualized CAR(+)T-cells from the recipient or HLA-compatible donor, which are revealing promising clinical results. This is the impetus to broaden the number of patients eligible to benefit from adoptive immunotherapy such as to infuse third-party donor derived CAR(+)T-cells. This will overcome issues associated with (i) time to manufacture T-cells, (ii) cost to generate one product for one patient, (iii) inability to generate a product from lymphopenic patients or patient's immune cells fail to complete the manufacturing process, and (iv) heterogeneity of T-cell products produced for or from individual recipients. Establishing a biobank of allogeneic genetically modified immune cells from healthy third-party donors, which are cryopreserved and validated in advance of administration, will facilitate the centralizing manufacturing and widespread distribution of CAR(+)T-cells to multiple points-of-care in a timely manner. To achieve this, it is necessary to engineer an effective strategy to avoid deleterious allogeneic immune responses leading to toxicity and rejection. We review the strategies to establish "off-the-shelf" donor-derived biobanks for human application of CAR(+)T-cells as a drug.

Expression of a dominant T-cell receptor can reduce toxicity and enhance tumor protection of allogeneic T-cell therapy

Due to the lack of specificity for tumor antigens, allogeneic T-cell therapy is associated with graft-versus-host disease. Enhancing the anti-tumor specificity while reducing the graft-versus-host disease risk of allogeneic T cells has remained a research focus. In this study, we demonstrate that the introduction of 'dominant' T-cell receptors into primary murine T cells can suppress the expression of endogenous T-cell receptors in a large proportion of the gene-modified T cells. Adoptive transfer of allogeneic T cells expressing a 'dominant' T-cell receptor significantly reduced the graft-versus-host toxicity in recipient mice. Using two bone marrow transplant models, enhanced anti-tumor activity was observed in the presence of reduced graft-versus-host disease. However, although transfer of T-cell receptor gene-modified allogeneic T cells resulted in the elimination of antigen-positive tumor cells and improved the survival of treated mice, it was associated with accumulation of T cells expressing endogenous T-cell receptors and the development of delayed graft-versus-host disease. The in-vivo deletion of the engineered T cells, mediated by endogenous mouse mammary tumor virus MTV8 and MTV9, abolished graft-versus-host disease while retaining significant anti-tumor activity of adoptively transferred T cells. Together, this study shows that the in-vitro selection of allogeneic T cells expressing high levels of a 'dominant' T-cell receptor can lower acute graft-versus-host disease and enhance anti-tumor activity of adoptive cell therapy, while the in-vivo outgrowth of T cells expressing endogenous T-cell receptors remains a risk factor for the delayed onset of graft-versus-host disease.

Specific removal of alloreactive T-cells to prevent GvHD in hemopoietic stem cell transplantation: rationale, strategies and perspectives

Hemopoietic stem cell transplantation (HSCT) is a standard procedure for treatment of malignant and non-malignant hematological diseases. HSCT donors include HLA-identical siblings, matched or mismatched unrelated donors and haploidentical related donors. Graft-versus-host disease (GvHD), mediated by donor alloreactive T-cells in the graft, can be triggered by minor histocompatibility antigens in HLA-identical pairs, by alleles at loci not considered for MUD-matching or by the mismatched haplotype in haplo-HSCT. Therefore, removal of donor T-cells, that contain the alloreactive precursors, is required, but T-cell depletion associates with opportunistic infections and with reduced graft-versus-leukemia effect. Selective T-cell depletion strategies have been introduced, like removal of αβ T-lymphocytes and of naive T-cells, two subsets including the alloreactive precursors, but the ultimate goal is specific removal of alloreactive T-cells. Here we review the different approaches to deplete alloreactive T-cells only and discuss pros and cons, specificity, efficiency and efficacy. Combinations of different methods and innovative approaches are also proposed for depleting specific alloreactive T-cells with high efficiency.

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

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

Depletion of Alloreactive T-Cells by Anti-CD137-Saporin Immunotoxin

Depletion of alloreactive T-lymphocytes from allogeneic bone marrow tansplants may prevent graft-versus-host disease (GVHD) without impairing donor cell engraftment, immunity, and the graft-versus-leukemia (GVL) effect. Alloreactive T-cells may be identified by their expression, upon activation, of CD137, a costimulatory receptor and putative surrogate marker for antigen-specific effector T-cells. In this context, we tested the use of anti-CD137-saporin immunotoxin to selectively deplete mouse and human alloreactive T-cells. Anti-CD137 antibodies were internalized by cells within 4 h of binding to the cell surface CD137, and anti-CD137-saporin immunotoxin effectively killed polyclonally activated T-cells or antigen-stimulated T-cells. Transfer of donor T-cells after allodepletion with anti-CD137-saporin immunotoxin failed to induce any evident expression of GVHD; however, a significant GVL effect was observed. Targeting of CD137 with an immunotoxin was also effective in killing polyclonally activated or alloreactive human T-cells. Our results indicate that anti-CD137-saporin immunotoxin may be used to deplete alloreactive T-cells prior to bone marrow transplantation and thereby prevent GVHD and the relapse of leukemia.

Inducible caspase-9 suicide gene controls adverse effects from alloreplete T cells after haploidentical stem cell transplantation. Blood. 2015;125:4103-4113. [PMID: 25977584 DOI: 10.1182/blood-2015-02-628354]

To test the feasibility of a single T-cell manipulation to eliminate alloreactivity while sparing antiviral and antitumor T cells, we infused 12 haploidentical hematopoietic stem cell transplant patients with increasing numbers of alloreplete haploidentical T cells expressing the inducible caspase 9 suicide gene (iC9-T cells). We determined whether the iC9-T cells produced immune reconstitution and if any resultant graft-versus-host disease (GVHD) could be controlled by administration of a chemical inducer of dimerization (CID; AP1903/Rimiducid). All patients receiving >10(4) alloreplete iC9-T lymphocytes per kilogram achieved rapid reconstitution of immune responses toward 5 major pathogenic viruses and concomitant control of active infections. Four patients received a single AP1903 dose. CID infusion eliminated 85% to 95% of circulating CD3(+)CD19(+) T cells within 30 minutes, with no recurrence of GVHD within 90 days. In one patient, symptoms and signs of GVHD-associated cytokine release syndrome (CRS-hyperpyrexia, high levels of proinflammatory cytokines, and rash) resolved within 2 hours of AP1903 infusion. One patient with varicella zoster virus meningitis and acute GVHD had iC9-T cells present in the cerebrospinal fluid, which were reduced by >90% after CID. Notably, virus-specific T cells recovered even after AP1903 administration and continued to protect against infection. Hence, alloreplete iC9-T cells can reconstitute immunity posttransplant and administration of CID can eliminate them from both peripheral blood and the central nervous system (CNS), leading to rapid resolution of GVHD and CRS. The approach may therefore be useful for the rapid and effective treatment of toxicities associated with infusion of engineered T lymphocytes. This trial was registered at www.clinicaltrials.gov as #NCT01494103.

Seatbelts in CAR therapy: How Safe Are CARS?

T-cells genetically redirected with a chimeric antigen receptor (CAR) to recognize tumor antigens and kill tumor cells have been infused in several phase 1 clinical trials with success. Due to safety concerns related to on-target/off-tumor effects or cytokine release syndrome, however, strategies to prevent or abate serious adverse events are required. Pharmacologic therapies; suicide genes; or novel strategies to limit the cytotoxic effect only to malignant cells are under active investigations. In this review, we summarize results and toxicities of investigations employing CAR redirected T-cells, with a focus on published strategies to grant safety of this promising cellular application.

Antiviral T-cell therapy

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

iCaspase 9 Suicide Gene System

Although cellular therapies may be effective in cancer treatment, their potential for expansion, damage of normal organs, and malignant transformation is a source of concern. The ability to conditionally eliminate aberrant cells in vivo would ameliorate these concerns and broaden the application of cellular therapy. We devised an inducible T-cell safety switch that can be stably and efficiently expressed in human T cells without impairing phenotype, function, or antigen specificity. This system is based on the fusion of human caspase 9 to a modified human FK-binding protein, allowing conditional dimerization using a small-molecule drug. When exposed to a synthetic dimerizing drug, the inducible caspase 9 (iC9) becomes activated and leads to the rapid apoptosis of cells expressing this construct. We have demonstrated the clinical feasibility and efficacy of this approach after haploidentical hematopoietic stem cell transplant (haplo-HSCT). A single dose of a small-molecule drug (AP1903) eliminated more than 90 % of the modified T cells within 30 min after administration and symptoms resolved without recurrence. This system has the potential to broaden the clinical applications of cellular therapy.

Achievement of early complete donor chimerism in CD25+-activated leukocytes is a strong predictor of the development of graft-versus-host-disease after stem cell transplantation

Chimerism dynamics in bone marrow, peripheral blood (PB), and T lymphocytes (TL) has been associated with the development of various complications after allogeneic stem-cell transplantation (allo-SCT). In the present study, the usefulness of chimerism monitoring in CD25(+)-activated leukocytes (AL), together with that in bone marrow, PB, and TL, for the anticipation of complications after allo-SCT, has been analyzed in 68 patients. In AL, we observed a slower dynamics toward complete chimerism (CC) than in PB (p = 0.042), while no significant differences were found between TL and PB (p = 0.12). Complete chimerism achievement in AL at day +30 has shown to be an independent risk factor for the development of grade II-IV acute graft-versus-host disease (aGvHD; hazard ratio [95% confidence interval]: 11.9 [1.5-91.7]; p = 0.017). Moreover, among patients achieving CC in TL and AL at different time-points after SCT (n = 17/68), the incidence of grade II-IV aGvHD was significantly higher in patients who achieved CC earlier in AL (5/5) than in those who achieved CC earlier in TL (1/11; p = 0.001). Therefore, achievement of early complete donor chimerism in CD25(+) AL is a strong predictor for the development of aGvHD. Prospective analysis of chimerism in AL could improve the post-SCT management of immunosuppressive therapy in transplanted patients.

Adoptive immunotherapy with genetically modified lymphocytes in allogeneic stem cell transplantation

Hematopoietic stem cell transplantation from a healthy donor (allo-HSCT) represents the most potent form of cellular adoptive immunotherapy to treat malignancies. In allo-HSCT, donor T cells are double edge-swords: highly potent against residual tumor cells, but potentially highly toxic, and responsible for graft versus host disease (GVHD), a major clinical complication of transplantation. Gene transfer technologies coupled with current knowledge on cancer immunology have generated a wide range of approaches aimed at fostering the immunological response to cancer cells, while avoiding or controlling GVHD. In this review, we discuss cell and gene therapy approaches currently tested in preclinical models and in clinical trials.

Long-term outcome after haploidentical stem cell transplant and infusion of T cells expressing the inducible caspase 9 safety transgene. Blood. 2014;123:3895-3905. [PMID: 24753538 DOI: 10.1182/blood-2014-01-551671]

Adoptive transfer of donor-derived T lymphocytes expressing a safety switch may promote immune reconstitution in patients undergoing haploidentical hematopoietic stem cell transplant (haplo-HSCT) without the risk for uncontrolled graft versus host disease (GvHD). Thus, patients who develop GvHD after infusion of allodepleted donor-derived T cells expressing an inducible human caspase 9 (iC9) had their disease effectively controlled by a single administration of a small-molecule drug (AP1903) that dimerizes and activates the iC9 transgene. We now report the long-term follow-up of 10 patients infused with such safety switch-modified T cells. We find long-term persistence of iC9-modified (iC9-T) T cells in vivo in the absence of emerging oligoclonality and a robust immunologic benefit, mediated initially by the infused cells themselves and subsequently by an apparently accelerated reconstitution of endogenous naive T lymphocytes. As a consequence, these patients have immediate and sustained protection from major pathogens, including cytomegalovirus, adenovirus, BK virus, and Epstein-Barr virus in the absence of acute or chronic GvHD, supporting the beneficial effects of this approach to immune reconstitution after haplo-HSCT. This study was registered at www.clinicaltrials.gov as #NCT00710892.

The cyclin dependent kinase inhibitor (R)-roscovitine mediates selective suppression of alloreactive human T cells but preserves pathogen-specific and leukemia-specific effectors

Graft versus host disease (GvHD), mediated by donor T cells, remains the primary cause of non-relapse mortality after allogeneic hematopoietic stem cell transplantation and novel therapeutic approaches are required. Cdk2 is a critical node of signal integration and programming of T cell responses towards immunity versus anergy but is dispensable for hematopoiesis and thymocyte development. We examined the effects of pharmacologic Cdk2 inhibition on alloreactive human T cells. Inhibition of Cdk2 blocked expansion of alloreactive T cells upon culture with HLA-mismatched dendritic cells and prevented generation of IFN-γ-producing alloantigen-specific effectors. In contrast, Cdk2 inhibition preserved effectors specific for Wilms' tumor 1 (WT1) leukemia antigen and for CMV as determined by WT1-specific and CMV-specific pentamers. Cdk2 inhibition preserved Treg cells, which have the ability to prevent GvHD while maintaining GvL. Thus, Cdk inhibitors may improve allogeneic HSCT by reducing alloreactivity and GvHD without loss of pathogen-specific and leukemia-specific immunity.

Accelerating immune reconstitution after hematopoietic stem cell transplantation

Viral infections remain a significant cause of morbidity and mortality after hematopoietic stem cell transplantation. Pharmacologic agents are effective against some pathogens, but they are costly and can be associated with significant toxicities. Thus, many groups have investigated adoptive T-cell transfer as a means of hastening immune reconstitution and preventing and treating viral infections. This review discusses the immunotherapeutic strategies that have been explored.

Optimization of methodology for production of CD25/CD71 allodepleted donor T cells for clinical use

BACKGROUND AIMS

Immunotherapy with allodepleted donor T cells improves immunity after T cell-depleted hematopoietic stem cell transplantation. We developed a methodology for selective depletion of alloreactive T cells after activation with host antigen-presenting cells by targeting T cells up-regulating CD25 and CD71. Combined depletion of these cells yields a pool of allodepleted donor T cells with antiviral properties with minimal capacity to cause graft-versus-host disease.

METHODS

Mature dendritic cells were irradiated and used to stimulate donor peripheral blood mononuclear cells for 4 days. The co-culture was stained with anti-CD71-biotin followed by CliniMACS CD25 and Anti-Biotin Reagents (Miltenyi Biotec GmbH; Bergisch Gladbach, Germany) before depletion on the CliniMACS Plus (Miltenyi Biotec GmbH). Residual alloreactivity was tested by flow cytometry, a secondary mixed lymphocyte reaction and limiting dilution analysis, and specific anti-viral immunity with pentamer staining. The large-scale protocol was tested under current good manufacturing practice conditions in five donor-recipient pairs of human leukocyte antigen-matched volunteer donors.

RESULTS

We developed a closed-system methodology using cell differentiation bags for cell culture and the COBE2991 Cell Processor (CaridianBCT, Lakewood, CO, USA). We also validated an anti-CD71-biotin generated for ex vivo clinical use. In five large-scale runs, the depleted fraction demonstrated excellent viability (99.9%), minimal residual expression of CD3/CD25 and CD3/CD71 (<0.2%) and passed tests for Mycoplasma, endotoxin, bacterial and fungal sterility. In secondary mixed lymphocyte reaction assays, the median response to host after allodepletion was 0%, whereas responses to third-party peripheral blood mononuclear cells were preserved (median, 105%; range 37%-350%). Limiting dilution analysis assays also demonstrated a reduction in response to host (median, -1.11 log) with preservation of third-party responses, and testing with human leukocyte antigen-restricted pentamers showed that populations of Epstein-Barr virus-specific and cytomegalovirus-specific CD8(+) T cells were retained after depletion.

CONCLUSIONS

We optimized a protocol for the combined immunomagnetic depletion of alloreactive CD25/CD71 T cells under current good manufacturing practice conditions and tested the efficacy in five donor-recipient pairs.

Haploidentical stem cell transplantation

The feasibility of stem cell transplantation across the major histocompatibility barrier-as in haploidentical stem cell transplantation-has been proved for some time in several studies. The main limitations include a higher graft failure rate, delayed immune reconstitution after transplantation with high rates of life-threatening infections, a higher incidence of post-transplant lymphoproliferative disease, and severe acute and chronic graft-versus-host disease. In an attempt to reduce the transplant-related morbidity/mortality, several techniques had been evaluated involving conditioning regimen intensity, graft engineering, post-transplant cellular therapy and immunosuppression. This review will describe the current situation. It will also discuss initiatives and strategies to overcome the limitations associated with transplant across the MHC barrier.

Augmentation of anti-tumor immunity by adoptive T-cell transfer after allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HCT) is currently the standard of care for most patients with high-risk acute leukemias and some other hematologic malignancies. Although HCT can be curative, many patients who undergo allogeneic HCT will later relapse. There is, therefore, a critical need for the development of novel post-HCT therapies for patients who are at high risk for disease recurrence following HCT. One potentially efficacious approach is adoptive T-cell immunotherapy, which is currently undergoing a renaissance that has been inspired by scientific insight into the key issues that impeded its previous clinical application. Translation of the next generation of adoptive T-cell therapies to the allogeneic HCT setting, using donor T cells of defined specificity and function, presents a unique set of challenges and opportunities. The challenges, progress and future of adoptive T-cell therapy following allogeneic HCT are discussed in this review.

Emerging concepts in haematopoietic cell transplantation

Haematopoietic cell transplantation (HCT) is the most widely used form of cellular therapy. It is the only known cure for some haematological malignancies and has recently been used in additional clinical settings, such as allograft tolerance induction and treatment of autoimmune diseases. Recent advances have enabled HCT in a wider range of patients with improved outcomes. This Review summarizes the latest developments in this therapy, focusing on issues that will affect future advancement.

A foundation for universal T-cell based immunotherapy: T cells engineered to express a CD19-specific chimeric-antigen-receptor and eliminate expression of endogenous TCR

Clinical-grade T cells are genetically modified ex vivo to express a chimeric antigen receptor (CAR) to redirect specificity to a tumor associated antigen (TAA) thereby conferring antitumor activity in vivo. T cells expressing a CD19-specific CAR recognize B-cell malignancies in multiple recipients independent of major histocompatibility complex (MHC) because the specificity domains are cloned from the variable chains of a CD19 monoclonal antibody. We now report a major step toward eliminating the need to generate patient-specific T cells by generating universal allogeneic TAA-specific T cells from one donor that might be administered to multiple recipients. This was achieved by genetically editing CD19-specific CAR(+) T cells to eliminate expression of the endogenous αβ T-cell receptor (TCR) to prevent a graft-versus-host response without compromising CAR-dependent effector functions. Genetically modified T cells were generated using the Sleeping Beauty system to stably introduce the CD19-specific CAR with subsequent permanent deletion of α or β TCR chains with designer zinc finger nucleases. We show that these engineered T cells display the expected property of having redirected specificity for CD19 without responding to TCR stimulation. CAR(+)TCR(neg) T cells of this type may potentially have efficacy as an off-the-shelf therapy for investigational treatment of B-lineage malignancies.

Cytomegalovirus-specific regulatory and effector T cells share TCR clonality--possible relation to repetitive CMV infections

Cytomegalovirus (CMV) infections have a major impact on morbidity and mortality of transplant patients. Among the complex antiviral T-cell response, CMV-IE-1 antigen-specific CD8+ cells are crucial for preventing CMV disease but do not protect from recurring/lasting CMV reactivation. Recently, we confirmed that adoptive transfer of autologous IE-1/pp65-specific T-cell lines was able to combat severe CMV disease; however, the control of CMV infection was only temporary. We hypothesized that CMV-induced regulatory T cells (iTreg) might be related to recurring/lasting CMV infection. In fact, kidney transplant patients with recurring CMV infections expressed enhanced suppression on CMV response. Analysis of in vitro expanded CD4+ epitope-specific cells revealed that CMV-specific CD4+CD25(high) Treg cells functionally suppress CD25(low) effector T cells (Teff) upon epitope-specific reactivation. Their phenotype is similar to iTreg - CD39(high) /Helios-/IL-2(low) /IFNγ(high) /IL-10±/TGFß-LAP±/FOXP3+ and methylated foxp3 locus. Remarkably, in vitro expanded CD4+CD25(high) iTreg share the same dominant TCR-Vβ-CDR3 clones with functionally distinct CD4+CD25(low) Teff. Moreover, the same clones were present in freshly isolated CD4+CD25(high) and CD4+CD25(low) T cells suggesting their in vivo generation. These findings directly demonstrate that Teff and iTreg can differentiate from one "mother" clone with specificity to the same viral epitope and indicate that peripheral iTreg generation is related to frequent antigen appearance.

Inducible apoptosis as a safety switch for adoptive cell therapy

BACKGROUND

Cellular therapies could play a role in cancer treatment and regenerative medicine if it were possible to quickly eliminate the infused cells in case of adverse events. We devised an inducible T-cell safety switch that is based on the fusion of human caspase 9 to a modified human FK-binding protein, allowing conditional dimerization. When exposed to a synthetic dimerizing drug, the inducible caspase 9 (iCasp9) becomes activated and leads to the rapid death of cells expressing this construct.

METHODS

We tested the activity of our safety switch by introducing the gene into donor T cells given to enhance immune reconstitution in recipients of haploidentical stem-cell transplants. Patients received AP1903, an otherwise bioinert small-molecule dimerizing drug, if graft-versus-host disease (GVHD) developed. We measured the effects of AP1903 on GVHD and on the function and persistence of the cells containing the iCasp9 safety switch.

RESULTS

Five patients between the ages of 3 and 17 years who had undergone stem-cell transplantation for relapsed acute leukemia were treated with the genetically modified T cells. The cells were detected in peripheral blood from all five patients and increased in number over time, despite their constitutive transgene expression. A single dose of dimerizing drug, given to four patients in whom GVHD developed, eliminated more than 90% of the modified T cells within 30 minutes after administration and ended the GVHD without recurrence.

CONCLUSIONS

The iCasp9 cell-suicide system may increase the safety of cellular therapies and expand their clinical applications. (Funded by the National Heart, Lung, and Blood Institute and the National Cancer Institute; ClinicalTrials.gov number, NCT00710892.).

The humanized anti-HLA-DR moAb, IMMU-114, depletes APCs and reduces alloreactive T cells: implications for preventing GVHD

In contrast to the conventional immunosuppressive agents and nonselective T-cell-depleting antibodies, selective depletion of donor alloreactive T cells and/or host APCs, particularly DCs, represents a novel approach that can effectively control GVHD with less or no impairment of T-cell-mediated antiviral and GVL immunity. Here we report that IMMU-114, a humanized anti-human leukocyte antigen-DR (HLA-DR) moAb, efficiently depleted human PBMCs of all APCs, including B cells, monocytes, myeloid DC type-1 (mDC1), mDC2 and plasmacytoid DCs (pDCs). Early and late apoptosis of mDC1, mDC2 and pDCs, and late apoptosis of all APC subsets, were increased by IMMU-114 treatment. Although IMMU-114 had little, if any, effect on the survival and apoptosis of non-B lymphocytes (>80% of which are T cells and ∼1-2% of T cells express HLA-DR), it selectively inhibited the proliferation of purified HLA-DR(+) T cells rather than HLA-DR(-) T cells. As a consequence, IMMU-114 treatment resulted in suppressed T-cell proliferation and reduced CD25(+) alloreactive T cells in allogeneic MLRs. Given the critical roles of APCs and alloreactive T cells in the pathogenesis of GVHD, these results suggest that IMMU-114 may have therapeutic potential against GVHD.

Differential action of 3-hydroxyanthranilic acid on viability and activation of stimulated lymphocytes

Lymphocytes proliferation after antigen-driven activation leads to an increase in cell count, which could last some week, until apoptosis mechanisms allow the homeostatic control of the system. During the first days of this stimulation, activated lymphocytes display high resistance to apoptosis and to most immunosuppressive drugs. According to the literature, few compounds have been described to kill recently activated cells, by inhibiting metabolic processes fundamental to proliferation. The aim of our work was to evaluate comparatively these different compounds, in order to identify the best strategy to kill cells that have undergone proliferation, while sparing the repertoire of resting cells. After preliminary experiments, 3-HAA and bortezomib were selected as the most suitable compounds for our purposes. The possible synergic effect of 3-HAA with bortezomib or with manganese ions was also assessed. 3-HAA was confirmed to be the most reliable pharmacologic approach to inhibit proliferation with acceptable toxicity on resting cells. While in the case of PHA stimulation 3-HAA led to death of most lymphocytes, only a minor percentage of cells were killed after allo-stimulation, suggesting that the effect is proportional to the percentage of stimulated lymphocytes. Manganese ions further enhanced this effect, while results with bortezomib seemed to be less consistent. These results deserve further investigations to develop new procedures for targeting activated cells with pharmacological approaches.

Janus kinase-2 inhibition induces durable tolerance to alloantigen by human dendritic cell-stimulated T cells yet preserves immunity to recall antigen

Janus kinase-2 (JAK2) conveys receptor-binding signals by several inflammatory cytokines, including IL-6, via phosphorylation of signal transducer and activator of transcription 3 (STAT3). We demonstrate that selective JAK2 inhibition by TG101348 during initial encounters between human T cells and allogeneic monocyte-derived dendritic cells induces durable, profound, and specific T-cell tolerance upon reexposure to the same alloantigens. Subsequent responses by nonalloreactive T cells to stimulation de novo by a pathogenic nominal antigen remain intact. TG101348 also suppresses primed T-cell responses when present only during alloantigen restimulation. TG101348 ablates IL-6/JAK2-mediated phosphorylation of STAT3, but has no off-target effects on IL-2 or IL-15/JAK3/pSTAT5-dependent signaling, which sustain the responses of regulatory T cells (Tregs) and other effector T cells. JAK2 inhibition preserves Treg numbers and thereby enhances the ratio of CD4(+) Tregs to CD8(+)CD25(+) effector T cells in favor of Tregs. JAK2 inhibition also reduces the production of IL-6 and TNF-α in allogeneic MLRs, impairing the activation of central and effector memory T cells as well as the expansion of responder Th1 and Th17 cells. While we have reported the limitations of isolated IL-6R-α inhibition on dendritic cell-stimulated alloreactivity, we demonstrate here that JAK2 represents a relevant biologic target for controlling GVHD or allograft rejection without broader immune impairment.

Immunophenotyping at the time of diagnosis distinguishes two groups of nasopharyngeal carcinoma patients: implications for adoptive immunotherapy

Background: Adoptive immunotherapy with EBV-specific CTLs (EBV-CTL) has been used to treat EBV-associated nasopharyngeal carcinoma (NPC) but only a fraction of the patients shows noticeable clinical response.

Patients and Methods: Sixty-seven newly diagnosed NPC patients from 2005 to 2007 and 21 healthy donors were collected. Immunological parameters and immune function of PBMCs and EBV-CTL were analyzed by flow cytometer analysis (FACS) and ⁵¹Cr releasing experiment; Molecular characteristics on NPC tumor cells were investigated by immunochemical staining and statistic analysis.

Results: NPC patients can be classified into two groups based on the percentage of CD3⁺ T cells in peripheral blood before accepted any treatment, (>52.6%, mean-2SE from healthy controls, NPC Group 1; <52.6%, NPC Group 2). The patients in Group 2 showed a significant decrease of CD3⁺CD8⁺ T-cells, CD3⁺CD4⁺ T-cells and CD3⁺CD45RO⁺ memory T cells, and increase of CD3^-CD16⁺ NK cells compared to Group 1 patients and healthy controls (P<0.001). EBV-specific T cell responses, were weaker in this group of patients and their tumor cells expressed lower levels of the EBV encoded latent membrane protein (LMP)-1 and HLA class II protein compared with the patients of NPC Group 1 (P<0.05) .

Conclusion: These findings demonstrate that NPC patients could be distinguished on the basis of their immune status which will affect the efficacy of EBV-CTL immunotherapy.

The clinical value of concomitant Epstein Barr virus (EBV)-DNA load and specific immune reconstitution monitoring after allogeneic hematopoietic stem cell transplantation

BACKGROUND

Monitoring of EBV DNAemia after allogeneic hematopoietic stem cell transplantation (HSCT) is necessary, but not sufficient, to identify patients at risk of EBV-induced post-transplantation lymphoproliferative disorders (PTLD). Combining this with quantifying EBV-specific cellular immunity was shown to be helpful. In this study, we evaluated the value of IFNγ-Elispot assay in monitoring EBV DNAemia after HSCT.

METHODS

EBV-DNA load in whole blood was monitored at least weekly using real-time PCR in 40 recipients of HSCT. Quantitative and qualitative T-cell recoveries, including EBV-specific T-cell quantification by Elispot assay, were studied 60, 100, 180 and 360 days after HSCT.

RESULTS

Among the 35 evaluable patients, 14 (35%) presented EBV DNAemia, only 2/14 (14%) needing pre-emptive treatment with rituximab. The greatest risk factor for EBV DNAemia was the presence of anti-thymocyte globulin (ATG) (p=0.005). EBV-specific cellular immune recovery was monitored by IFNγ-Elispot assay. Using multivariate analysis, four factors were found to significantly influence IFNγ-Elispot results at defined times post-HSCT: EBV DNAemia, young age, global T-cell recovery and severe acute GVHD. In those cases where EBV DNAemia occurred and cleared spontaneously, Elispot results gave more than 1000 spot-forming cells (SFC)/10(6)PBMC.

CONCLUSION

Elispot assay may be usefully combined with EBV-DNA load monitoring to determine when a patient should receive pre-emptive treatment, or when the clinician should avoid Rituximab use which severely immunocompromises patients.

Induction of alloantigen-specific anergy in human peripheral blood mononuclear cells by alloantigen stimulation with co-stimulatory signal blockade

Allogeneic hematopoietic stem cell transplantation (AHSCT) offers the best chance of cure for many patients with congenital and acquired hematologic diseases. Unfortunately, transplantation of alloreactive donor T cells which recognize and damage healthy patient tissues can result in Graft-versus-Host Disease (GvHD)¹. One challenge to successful AHSCT is the prevention of GvHD without associated impairment of the beneficial effects of donor T cells, particularly immune reconstitution and prevention of relapse. GvHD can be prevented by non-specific depletion of donor T cells from stem cell grafts or by administration of pharmacological immunosuppression. Unfortunately these approaches increase infection and disease relapse^2-4. An alternative strategy is to selectively deplete alloreactive donor T cells after allostimulation by recipient antigen presenting cells (APC) before transplant. Early clinical trials of these allodepletion strategies improved immune reconstitution after HLA-mismatched HSCT without excess GvHD^{5, 6}. However, some allodepletion techniques require specialized recipient APC production^{6, 7}and some approaches may have off-target effects including depletion of donor pathogen-specific T cells⁸and CD4 T regulatory cells⁹.One alternative approach is the inactivation of alloreactive donor T cells via induction of alloantigen-specific hyporesponsiveness. This is achieved by stimulating donor cells with recipient APC while providing blockade of CD28-mediated co-stimulation signals¹⁰.This "alloanergization" approach reduces alloreactivity by 1-2 logs while preserving pathogen- and tumor-associated antigen T cell responses in vitro¹¹. The strategy has been successfully employed in 2 completed and 1 ongoing clinical pilot studies in which alloanergized donor T cells were infused during or after HLA-mismatched HSCT resulting in rapid immune reconstitution, few infections and less severe acute and chronic GvHD than historical control recipients of unmanipulated HLA-mismatched transplantation¹². Here we describe our current protocol for the generation of peripheral blood mononuclear cells (PBMC) which have been alloanergized to HLA-mismatched unrelated stimulator PBMC. Alloanergization is achieved by allostimulation in the presence of monoclonal antibodies to the ligands B7.1 and B7.1 to block CD28-mediated costimulation. This technique does not require the production of specialized stimulator APC and is simple to perform, requiring only a single and relatively brief ex vivo incubation step. As such, the approach can be easily standardized for clinical use to generate donor T cells with reduced alloreactivity but retaining pathogen-specific immunity for adoptive transfer in the setting of AHSCT to improve immune reconstitution without excessive GvHD.

Advances in adoptive immunotherapy to accelerate T-cellular immune reconstitution after HLA-incompatible hematopoietic stem cell transplantation

Although partially HLA-mismatched hematopoietic stem cell transplantation (HSCT) has become an important therapeutic option for children with primary immunodeficiencies, delayed reconstitution of the T-cell compartment remains a major clinical concern. Adoptive immunotherapies to provide recipients with a protective and diverse T-cell repertoire in the months following HSCT are warranted. In order to improve T-cell reconstitution after T-cell-depleted HSCT, different strategies are currently being studied. Some are based on administration of modified mature T cells (e.g., allodepleted T cells or pathogen-specific T cells). Others aim at accelerating de novo thymopoiesis from donor-derived hematopoietic stem cells in vivo via the administration of thymopoietic agents or the transfer of large numbers of T-cell precursors generated ex vivo. The present article will provide a brief summary of recent advances in the field of allodepletion and adoptive transfer of pathogen-specific T cells and a detailed discussion of strategies for enhancing thymopoiesis in vivo.

How I treat adenovirus in hematopoietic stem cell transplant recipients

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

Expansion of allospecific regulatory T cells after anergized, mismatched bone marrow transplantation

Transplantation of hematopoietic stem cells from healthy donors can cure patients with many diseases. Donor T cells can protect against recurrence of infection and disease, but some of these (alloreactive) T cells recognize patient tissues as foreign, causing graft-versus-host disease. Removing T cells from donor grafts before transplantation reduces graft-versus-host disease but increases infection and disease recurrence. Inactivation of alloreactive T cells by inducing tolerance to patient cells (anergization) before transplantation preserves beneficial donor T cell effects while reducing graft-versus-host disease. We show that this approach also results in expansion of regulatory T cells that specifically suppress alloreactive donor T cell responses in the recipient. In addition to reducing graft-versus-host disease, antigen-specific regulatory T cells generated with this strategy could suppress unwanted T cell responses that cause rejection of solid organ transplants and tissue damage in autoimmune disorders.

Challenges of T cell therapies for virus-associated diseases after hematopoietic stem cell transplantation

IMPORTANCE OF THE FIELD

Hematopoietic stem cell transplantation (HSCT) is the treatment of choice for many hematological malignancies and genetic disorders. The majority of patients do not have a human leukocyte antigen (HLA) identical sibling donor, and alternative stem cell sources include HLA-matched or mismatched unrelated donors and haploidentical related donors. However, alternative donor HSCT are associated with three major complications i) graft rejection; ii) graft-versus-host disease (GvHD); and iii) delayed immune reconstitution leading to viral infections and relapse.

AREAS COVERED IN THIS REVIEW

Graft rejection and the risk of GvHD can be significantly reduced by using intensive conditioning regimens, including in vivo T cell depletion as well as ex vivo T cell depletion of the graft. However, the benefits of removing alloreactive T cells from the graft are offset by the concomitant removal of T cells with anti-viral or anti-tumor activity as well as the profound delay in endogenous T cell recovery post-transplant. Thus, opportunistic infections, many of which are not amenable to conventional small-molecule therapeutics, are frequent in these patients and are associated with significant morbidity and high mortality rates. This review discusses current cell therapies to prevent or treat viral infections/reactivations post-transplant.

WHAT THE READER WILL GAIN

The reader will gain an understanding of the current state of cell therapy to prevent and treat viral infections post-HSCT, and will be introduced to preclinical studies designed to develop and validate new manufacturing procedures intended to improve therapeutic efficacy and reduce associated toxicities.

TAKE HOME MESSAGE

Reconstitution of HSCT recipients with antigen-specific T cells, produced either by allodepletion or in vitro reactivation, can offer an effective strategy to provide both immediate and long-term protection without harmful alloreactivity.

Combining CD19 redirection and alloanergization to generate tumor-specific human T cells for allogeneic cell therapy of B-cell malignancies

Allogeneic hematopoietic stem-cell transplantation can cure some patients with high-risk B-cell malignancies, but disease relapse following transplantation remains a significant problem. One approach that could be used to augment the donor T-cell-mediated antitumor effect is the infusion of allogeneic donor-derived T cells expressing a chimeric antibody receptor (CAR) specific to the B-cell antigen CD19. However, the use of such cells might result in toxicity in the form of graft-versus-host disease mediated by CD19-specific (CD19-CAR) T cells possessing alloreactive endogenous T-cell receptors. We therefore investigated whether nonalloreactive tumor-specific human T cells could be generated from peripheral blood mononuclear cells of healthy donors by the combination of CD19 redirection via CAR expression and subsequent alloanergization by allostimulation and concomitant blockade of CD28-mediated costimulation. Alloanergization of CD19-CAR T cells resulted in efficient and selective reduction of alloresponses in both CD4(+) and CD8(+) T cells, including allospecific proliferation and cytokine secretion. Importantly, T-cell effector functions including CAR-dependent proliferation and specific target cytolysis and cytokine production were retained after alloanergization. Our data support the application of CD19 redirection and subsequent alloanergization to generate allogeneic donor T cells for clinical use possessing increased antitumor activity but limited capacity to mediate graft-versus-host disease. Immunotherapy with such cells could potentially reduce disease relapse after allogeneic transplantation without increasing toxicity, thereby improving the outcome of patients undergoing allogeneic transplantation for high-risk B-cell malignancies.

Clinical expansion of cord blood-derived T cells for use as donor lymphocyte infusion after cord blood transplantation

Allogeneic stem cell transplantation (SCT) from cord blood (CB) as a stem cell source is a promising alternative when no human leukocyte antigen-matched donor is found. Donor lymphocyte infusion (DLI) is a possible treatment modality for threatening graft failure or relapse of an underlying malignancy after transplantation. Ethical and logistical reasons limit the possibility of DLI in the setting of CB SCT. To remedy this restriction, we performed expansion of donor T cells in vitro from CB grafts in a clinical setting for use as future DLI and characterized the expanded cells in comparison to T cells from CB acquired ex vivo and adult peripheral blood. T cells were expanded from grafts used for transplantation, upon CD3/CD28 crosslinking and culture in interleukin-2. Phenotype and function of T cells were assessed by flow cytometry and mixed lymphocyte culture assays. T-cell receptor repertoire distribution was evaluated with polymerase chain reaction-based spectratyping. We were able to amplify T cells to sufficient amounts for DLI in 13 out of 13 initiated expansions. Expanded T cells presented with an activated phenotype and could be induced to produce cytokines by a nonspecific stimulus. When exposed to allogeneic targets, expanded CB T cells proliferated at comparable levels to their ex vivo and adult blood counterparts. In summary, clinical expansion of CB T cells for DLI is feasible and may be a future modality for treatment of graft failure or relapse after SCT.

Cancer immunotherapy: will expanding knowledge lead to success in pediatric oncology?

The past 25 years have seen an increase in our understanding of immunology and further expansion in the clinical use of immunotherapeutic modalities. How immunotherapy will be integrated with chemotherapy, radiation, and surgery remains to be established. Although there have been successes in the field of immunotherapy, they have been inconsistent, and it is hoped that increased understanding of the basic principles of immunology will improve the consistency of beneficial effects. In this article, we briefly provide a general overview of our current understanding of the immune system, with a focus on concepts in tumor immunology, followed by a discussion of how these concepts are being used in the clinic.

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.

Cellular immunotherapy of cancer

Standard therapies for many common cancers remain toxic and are often ineffective. Cellular immunotherapy has the potential to be a highly targeted alternative, with low toxicity to normal tissues but a high capacity to eradicate tumor. In this chapter we describe approaches that generate cellular therapies using active immunization with cells, proteins, peptides, or nucleic acids, as well as efforts that use adoptive transfer of effector cells that directly target antigens on malignant cells. Many of these approaches are proving successful in hematologic malignancy and in melanoma. In this chapter we discuss the advantages and limitations of each and how over the next decade investigators will attempt to broaden their reach, increase their efficacy, and simplify their application.

Improved survival and preserved antiviral responses after combination therapy with daclizumab and infliximab in steroid-refractory graft-versus-host disease

Patients with steroid-refractory acute graft-versus-host disease (aGVHD) have a high mortality due to infections and progressive aGVHD. We investigated the combined use of 2 monoclonal antibodies (Mabs), daclizumab and infliximab in steroid-refractory aGVHD to selectively control the proliferation of alloreactive T cells and to target 2 different points in the cytokine cascade responsible for this complication. Twenty-two consecutive children who developed 25 episodes of steroid-refractory aGVHD after hematopoietic stem cell transplantation at our institution between September 2002 and July 2007 were treated with combination Mab therapy. Nineteen out of 22 patients responded, with a median response time of 15 days from the start of Mab therapy. Seven patients developed recurrent GVHD, 3 of whom received a second course of Mabs. Seven out of 22 patients developed chronic GVHD. There were 13 episodes of viral reactivations, 4 patients developed probable fungal infections. Impressively, however, there were only 2 infection-related deaths. Interferon-gamma enzyme-linked immunospot assays on selected patients showed preservation of responses to cytomegalovirus and Epstein-Barr virus and the ability to mount de novo responses to these pathogens after Mab therapy. At a median follow-up of 31 months, 15 of the 22 (68%) children are alive. The causes of death were progressive GVHD (3), obliterative bronchiolitis (2), and sepsis (2). These data suggest that combination treatment with daclizumab and infliximab is an effective therapeutic option for patients with steroid-refractory GVHD and seems to be associated with a low infection-related mortality compared with previous therapies.