HLA type-independent generation of antigen-specific T cells for adoptive immunotherapy

The Identity Card of T Cells-Clinical Utility of T-cell Receptor Repertoire Analysis in Transplantation

There is a clear medical need to change the current strategy of "one-size-fits-all" immunosuppression for controlling transplant rejection to precision medicine and targeted immune intervention. As T cells play a key role in both undesired graft rejection and protection, a better understanding of the fate and function of both alloreactive graft-deteriorating T cells and those protecting to infections is required. The T-cell receptor (TCR) is the individual identity card of each T cell clone and can help to follow single specificities. In this context, tracking of lymphocytes with certain specificity in blood and tissue in clinical follow up is of especial importance. After overcoming technical limitations of the past, novel molecular technologies opened new avenues of diagnostics. Using advantages of next generation sequencing, a method was established for T-cell tracing by detection of variable TCR region as identifiers of individual lymphocyte clones. The current review describes principles of laboratory and computational methods of TCR repertoire analysis, and gives an overview on applications for the basic understanding of transplant biology and immune monitoring. The review also delineates methodological pitfalls and challenges. With the outlook on prediction of antigens in immune-mediated processes including those of unknown causative pathogens, monitoring the fate and function of individual T cell clones, and the adoptive transfer of protective effector or regulatory T cells, this review highlights the current and future capability of TCR repertoire analysis.

Comprehensive Characterization of a Next-Generation Antiviral T-Cell Product and Feasibility for Application in Immunosuppressed Transplant Patients

Viral infections have a major impact on morbidity and mortality of immunosuppressed solid organ transplant (SOT) patients because of missing or failure of adequate pharmacologic antiviral treatment. Adoptive antiviral T-cell therapy (AVTT), regenerating disturbed endogenous T-cell immunity, emerged as an attractive alternative approach to combat severe viral complications in immunocompromised patients. AVTT is successful in patients after hematopoietic stem cell transplantation where T-cell products (TCPs) are manufactured from healthy donors. In contrast, in the SOT setting TCPs are derived from/applied back to immunosuppressed patients. We and others demonstrated feasibility of TCP generation from SOT patients and first clinical proof-of-concept trials revealing promising data. However, the initial efficacy is frequently lost long-term, because of limited survival of transferred short-lived T-cells indicating a need for next-generation TCPs. Our recent data suggest that Rapamycin treatment during TCP manufacture, conferring partial inhibition of mTOR, might improve its composition. The aim of this study was to confirm these promising observations in a setting closer to clinical challenges and to deeply characterize the next-generation TCPs. Using cytomegalovirus (CMV) as model, our next-generation Rapamycin-treated (Rapa-)TCP showed consistently increased proportions of CD4⁺ T-cells as well as CD4⁺ and CD8⁺ central-memory T-cells (T_CM). In addition, Rapamycin sustained T-cell function despite withdrawal of Rapamycin, showed superior T-cell viability and resistance to apoptosis, stable metabolism upon activation, preferential expansion of T_CM, partial conversion of other memory T-cell subsets to T_CM and increased clonal diversity. On transcriptome level, we observed a gene expression profile denoting long-lived early memory T-cells with potent effector functions. Furthermore, we successfully applied the novel protocol for the generation of Rapa-TCPs to 19/19 SOT patients in a comparative study, irrespective of their history of CMV reactivation. Moreover, comparison of paired TCPs generated before/after transplantation did not reveal inferiority of the latter despite exposition to maintenance immunosuppression post-SOT. Our data imply that the Rapa-TCPs, exhibiting longevity and sustained T-cell memory, are a reasonable treatment option for SOT patients. Based on our success to manufacture Rapa-TCPs from SOT patients under maintenance immunosuppression, now, we seek ultimate clinical proof of efficacy in a clinical study.

Adjuvant Therapy Using Mistletoe Containing Drugs Boosts the T-Cell-Mediated Killing of Glioma Cells and Prolongs the Survival of Glioma Bearing Mice

Viscum album L. extracts (VE) are applied as complementary cancer therapeutics for more than one century. Extracts contain several compounds like mistletoe lectins (ML) 1-3 and viscotoxins, but also several minor ingredients. Since ML-1 has been described as one of the main active components harboring antitumor activity, purified native or recombinant ML-1 has been also used in clinical trials in the last years. The present study examined and compared the immunoboosting effects of three ML-1 containing drugs (the extract ISCADOR Qu, the recombinant ML-1 Aviscumine, and purified native ML-1) in the context of the T-cell mediated killing of glioma cells. Additionally we examined the possible underlying T-cell stimulating mechanisms. Using cocultures of immune and glioma cells, a PCR-based microarray, quantitative RT-PCR, and an antibody-based array to measure cytokines in blood serum, immunosupporting effects were determined. A highly aggressive, orthotopic, immunocompetent syngeneic mouse glioma model was used to determine the survival of mice treated with ISCADOR Qu alone or in combination with tumor irradiation and temozolomide (TMZ). Treatment of glioblastoma (GBM) cells with ISCADOR Qu that contains a high ML concentration, but also viscotoxins and other compounds, as well as with Aviscumine or native ML-1, enhanced the expansion of cancer cell-specific T-cells as well as T-cell-mediated tumor cell lysis, but to a different degree. In GBM cells all three ML-1-containing preparations modulated the expression of immune response associated genes. In vivo, subcutaneous ISCADOR Qu injections at increasing concentration induced cytokine release in immunocompetent VM/Dk-mice. Finally, ISCADOR Qu, if applied in combination with tumor irradiation and TMZ, further prolonged the survival of glioma mice. Our findings indicate that ML-1 containing drugs enhance anti-GBM immune responses and work in synergy with radiochemotherapy. Therefore, adjuvant mistletoe therapy should be considered as an auspicious treatment option for glioma patients.

Robust Production of Cytomegalovirus pp65-Specific T Cells Using a Fully Automated IFN-γ Cytokine Capture System

BACKGROUND

Cytomegalovirus(CMV)-related diseases are a serious cause of morbidity and mortality following hematopoietic stem cell transplantation (HSCT). CMV-specific cytotoxic T lymphocytes (CMV-CTLs) have been reported as an alternative to antiviral drugs that provide long-term CMV-specific immunity without major side effects. However, their application has been limited by the prolonged manufacturing process required.

METHODS

In this study, we applied the IFN-γ cytokine capture system (CCS) using the fully automated CliniMACS Prodigy device for rapid production of CMV-CTLs, which may be applicable in clinically urgent CMV-related diseases. Five validation runs were performed using apheresis samples from randomly selected CMV-seropositive healthy blood donors. Successive processes, including antigen stimulation, anti-IFN-γ labeling, magnetic enrichment and elution, were then performed automatically using the CliniMACS Prodigy, which took approximately 13 h.

RESULTS

The original apheresis samples consisted mainly of CD45RA+ CD62L+ naïve T cells as well as 0.3% IFN-γ-secreting CD3+ T cells that showed a response to the CMV pp65 antigen (CD3+ IFN-γ+ cells). Following IFN-γ enrichment, the target fraction contained 51.3% CD3+ IFN-γ+ cells with a reduction in naïve T cells and selection of CD45RA- CD62L- and CD45RA+ CD62L- memory T cells. Furthermore, extended culture of these isolated cells revealed functional activity, including efficient proliferation, sustained antigen-specific IFN-γ secretion, and cytotoxicity against pp65-pulsed target cells.

CONCLUSION

The findings reported here suggest that the IFN-γ CCS by the CliniMACS Prodigy is a simple and robust approach to produce CMV-CTLs, which may be applicable for the treatment of clinically urgent CMV-related diseases.

Putting a price tag on novel autologous cellular therapies

Cell therapies, especially autologous therapies, pose significant challenges to researchers who wish to move from small, probably academic, methods of manufacture to full commercial scale. There is a dearth of reliable information about the costs of operation, and this makes it difficult to predict with confidence the investment needed to translate the innovations to the clinic, other than as small-scale, clinician-led prescriptions. Here, we provide an example of the results of a cost model that takes into account the fixed and variable costs of manufacture of one such therapy. We also highlight the different factors that influence the product final pricing strategy. Our findings illustrate the need for cooperative and collective action by the research community in pre-competitive research to generate the operational models that are much needed to increase confidence in process development for these advanced products.

Virus-specific T-cell therapy in solid organ transplantation

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

A revised strategy for monitoring BKV-specific cellular immunity in kidney transplant patients

Reactivation of Polyomavirus BKV is a severe complication in kidney transplant patients. Current treatment requires close monitoring, and modification of immunosuppressive drugs. As an important additional tool, the monitoring of BKV immunity has been based on detection of cytokine-secreting T cells upon BKV-antigen challenge. However, low frequent BKV-specific T cells are often barely detectable and their roles in BKV clearance remain unclear. Here, we analyzed the effects of immunosuppressive agents on BKV-specific T cells in vitro. Significant reductions in expression of several markers, and reduced killing functions upon treatment with calcineurin but not mTOR inhibitors were detected. However, effects of these drugs on expression of surface markers and GranzymeB were substantially less striking than effects on cytokine expression. Consequently, we applied a novel detection strategy for BKV-specific T cells in immunosuppressed kidney transplant patients using these more robust markers, and showed significantly improved sensitivity compared with the conventional IFNγ-based method. Using this strategy and 17-color flow cytometry, we found BKV-specific helper and cytolytic CD4+ T-cell subsets that differed in their memory phenotype, which corresponded with BKV clearance in kidney transplant patients. Thus, our results offer an improved detection strategy for BKV-specific T cells in kidney transplant patients, and shed light on the contributions of these cells to BKV clearance.

Peripheral blood-derived virus-specific memory stem T cells mature to functional effector memory subsets with self-renewal potency

Memory T cells expressing stem cell-like properties have been described recently. The capacity of self-renewal and differentiation into various memory/effector subsets make them attractive for adoptive T cell therapy to combat severe virus infections and tumors. The very few reports on human memory stem T cells (T(SCM)) are restricted to analyses on polyclonal T cells, but extensive data on Ag-specific T(SCM )are missing. This might be due to their very low frequency limiting their enrichment and characterization. In this article, we provide functional and phenotypic data on human viral-specific T(SCM), defined as CD8(+)CD45RA(+)CCR7(+)CD127(+)CD95(+). Whereas <1% of total T cells express the T(SCM) phenotype, human CMV-specific T(SCM) can be detected at frequencies similar to those seen in other subsets, resulting in ∼ 1 /10,000 human CMV-specific T(SCM). A new virus-specific expansion protocol of sort-purified T(SCM) reveals both upregulation of various T cell subset markers and preservation of their stem cell phenotype in a significant proportion, indicating both self-renewal and differentiation potency of virus-specific T cells sharing their TCR repertoire. Furthermore, we describe a simplified culture protocol that allows fast expansion of virus-specific T(SCM) starting from a mixed naive T/T(SCM) pool of PBLs. Due to the clinical-grade compatibility, this might be the basis for novel cell therapeutic options in life-threatening courses of viral and tumor disease.

The role of CD4(+) T cells in BKV-specific T cell immunity

Reactivation of polyomavirus BK (BKV) infection represents a severe complication in kidney transplant (KTX) patients. We previously reported an association between a declining BK viral load and the reconstitution of CD4(+) T cell BKV-specific immunity in patients following kidney transplantation. However, the specific contribution of CD4(+) T cells in the regulation of BKV-replication is unknown. Nevertheless, in vitro enrichment of BKV-specific T cells and subsequent adoptive T cell transfer may improve the restoration of immune competence in KTX patients with BKV infection. To date, strategies to capture human BKV-specific T cells with the ensuing expansion to clinically useful numbers are lacking. Here, we demonstrated a comprehensive flow cytometric analysis of the BKV-specific T cell response that permits access to the majority of T cells specific for immunodominant BKV antigens. A full-spectrum evaluation of the BKV-specific T cell response was performed by stimulating peripheral blood mononuclear cells (PBMC) with a mixture of BKV immunodominant peptide pools at varying concentrations and measuring activation marker expression and cytokine secretion. We also examined the effects of co-stimulation and PBMC resting time prior to activation. We defined the narrow range of stimulation conditions that permit the capture and expansion of functional BKV-specific T cell lines. The generated BKV-specific T cell lines showed the highest specificity and functionality when the T cells were captured according to IFNγ-secretion. This study highlights the multifunctional and cytolytic BKV-specific CD4(+) T cells as a dominant population within the generated T cell product. This method offers a novel approach for the generation of BKV-specific T cell lines for adoptive immunotherapy and underscores the critical role of CD4(+) T cells in the clearance of BKV.

Polyomavirus-associated nephropathy

Polyomaviruses BK and JC are ubiquitous viruses with high seroprevalence rates in general population. Following primary infection, polyomaviruses BK and JC persist latently in different sites, particularly in the reno-urinary tract. Reactivation from latency may occur in normal subjects with asymptomatic viruria, while it can be associated to nephropathy (PVAN) in kidney transplantat recipients. PVAN may occur in 1%-10% of renal transplant patients with loss of the transplanted organ in 30% up to 80% of the cases. Etiology of PVAN is mainly attributable to BK virus, although approximately 5% of the cases may be due to JC. Pathogenesis of PVAN is still unknown, although viral replication and the lack of immune control play a major role. Immunosuppression represents the condicio sine qua non for the development of PVAN and the modulation of anti-rejection treatment represents the first line of intervention, given the lack of specific antiviral agents. At moment, an appropriate immunemodulation can only be accomplished by early identification of viral reactivacation by evaluation of polyomavirus load on serum and/or urine specimens, particularly in the first year post-trasplantation. Viro-immunological monitoring of specific cellular immune response could be useful to identify patients unable to recover cellular immunity posttransplantation, that are at higher risk of viral reactivation with development of PVAN. Herein, the main features of polyomaviruses BK and JC, biological properties, clinical characteristics, etiopathogenesis, monitoring and diagnosing of PVAN will be described and discussed, with an extended citation of related relevant literature data.

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.

Conference Scene: Autoimmunity and transplantation: basic science and clinic translation meet in Geneva. 9th International Conference on New Trends in Immunosuppression and Immunotherapy 4-6 February 2010, Geneva, Switzerland

Scientists interested in the field of immunomodulation meet every 2 years to discuss new regulatory mechanisms and targets of intervention for the treatment of autoimmunity and transplant rejection. This article highlights the 9th International Conference on New Trends in Immunosuppression and Immunotherapy, which was held in February 2010 in Geneva, Switzerland.

Effective and long-term control of EBV PTLD after transfer of peptide-selected T cells

Posttransplantation lymphoproliferative disease (PTLD) associated with Epstein-Barr virus (EBV) is a life-threatening complication after allogeneic hematopoietic stem cell transplantation. PTLD is efficiently prevented by adoptive transfer of EBV-specific T cells from the donor. To make EBV-specific T cells available in urgent clinical situations, we developed a rapid protocol for their isolation by overnight stimulation of donor blood cells with peptides derived from 11 EBV antigens, interferon-gamma surface capture, and immunomagnetic separation. Six patients with PTLD received 1 transfusion of EBV-specific T cells. No response was seen in 3 patients who had late-stage disease with multiorgan dysfunction at the time of T-cell transfer. In 3 patients who received T cells at an earlier stage of disease, we observed complete and stable remission of PTLD. Two patients have remained free from EBV-associated disease for more than 2 years. CD8(+) T cells specific for EBV early antigens rapidly expanded after T-cell transfer, temporarily constituted greater than 20% of all peripheral blood lymphocytes, and were maintained throughout the observation period. Thus, a rapid and sustained reconstitution of a protective EBV-specific T-cell memory occurred after the infusion of small numbers of directly isolated EBV-specific T cells.

Adenovirus infections in solid organ transplant recipients

PURPOSE OF REVIEW

Adenoviruses are emerging as important viral pathogens in solid organ transplant recipients, impacting morbidity, graft survival and even mortality. This review will discuss the current understanding of the epidemiology, diagnosis and therapy of adenovirus infection in transplant recipients.

RECENT FINDINGS

Advances in the field include the use of polymerase chain reaction in the diagnosis of adenoviral infection, a better understanding of the epidemiology, immune response and potential new therapies, including preemptive and adoptive immunotherapy strategies. Adenoviral infections appear to be common, especially in pediatric solid organ transplant. Generally well tolerated, some high-risk patients may develop disseminated disease causing graft failure, which may lead to retransplant and/or death. Antiviral therapy and immunotherapy may play a role in these patients, although prospective controlled data are not available at this time.

SUMMARY

Although new tools and a better understanding of the epidemiology, risk factors and therapies for adenovirus are beginning to materialize, prospective, controlled trials, using careful definitions, and standardized methodologies need to be performed to more fully clarify these issues in solid organ transplant recipients.

Adoptive T-cell therapy of a lung transplanted patient with severe CMV disease and resistance to antiviral therapy

Infections with cytomegalovirus (CMV) can induce severe complications after transplantation, particularly in patients resistant to virostatic therapy. Adoptive transfer of CMV-specific T-cell lines has demonstrated promising results in patients after hematopoietic stem cell transplantation. However, the generation of specific T-cell lines ex vivo and their function in vivo is complicated in solid organ transplant (SOT) recipients. Here, we present the successful adoptive transfer of autologous CMV-specific T cells to a lung transplant recipient with ganciclovir-resistant CMV-pneumonia requiring mechanical ventilation. Infused T cells rapidly expanded in vivo and efficiently inhibited viral replication as confirmed by extensive longitudinal immunological monitoring. After full recovery, the patient was released from the clinic. After 4 weeks, the infection reappeared and persisted at a low level even after a second T-cell infusion. Our experimental data indicate that this could be the consequence of the late differentiated phenotype of the infused T cells and therefore their insufficient longevity in vivo. In summary, our report signifies the high therapeutic potential of adoptive immunotherapy in the treatment of SOT recipients when all other measures show no effect. Further studies have to elucidate the most potent strategies to generate antigen-specific T cells with high functional capacity and robust long-term persistence.

Cellular immune responses to BK virus

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Clonotype analysis of cytomegalovirus-specific cytotoxic T lymphocytes

Cytotoxic T lymphocytes (CTL) control the replication of human cytomegalovirus (CMV). Previous studies assessed the clonotypic composition of CTL specific for individual immunodominant peptides within a certain HLA context. Such an approach has inherent limitations and may not assess the true clonal CTL response in vivo. Here, the clonotypic composition of CMV-specific CTL was determined in HLA-A2, CMV-seropositive kidney transplant recipients and healthy blood donors after stimulation of peripheral blood mononuclear cells with either a pp65 whole-peptide pool or a single immunodominant peptide. Even after stimulation with the whole peptide pool, CMV-specific CTL remained monoclonal or oligoclonal. Regarding intraindividual variation, the CDR3 motifs of the dominant clones were identical to those observed in CTL generated by the single immunodominant peptide. Sequencing of the CDR3 regions demonstrated significant interindividual variation; however, structural homology was observed for immunodominant clonotypes in three individuals. In conclusion, the highly focused T cell receptor repertoire found after stimulation with either a single immunodominant peptide or a peptide pool demonstrates a pivotal role for immunodominant epitopes in the generation of a clonal repertoire. These results provide new insights into the regulation of CMV clonal dominance and may contribute to the design and monitoring of adoptive immunotherapy.

PD-1 expression and IL-2 loss of cytomegalovirus- specific T cells correlates with viremia and reversible functional anergy

Cytomegalovirus (CMV) represents a major cause of infectious complications after transplantation. Recently, chronic infections with lymphocyte choriomeningitis virus (LCMV), HIV or HCV were shown to be associated with functionally exhausted T cells characterized by high expression of the programmed death (PD)-1 molecule and altered cytokine expression patterns. We therefore hypothesized that functional exhaustion of CMV-specific CD4 T cells may determine impaired CMV control in patients after renal transplantation. In viremic transplant recipients, a significantly higher proportion of CMV-specific CD4 T cells was PD-1 positive (median 40.9%, 17.0-88.7%) as compared to nonviremic transplant patients (8.8%, 0.8-80.5%), dialysis patients (8.8%, 0-36.7%) or controls (3.2%, 0.3-15.4%, p < 0.0001). In line with functional impairment, PD-1-positive T cells produced significantly less IFNgamma as compared to PD-1-negative T cells (p < 0.0001). Moreover, unlike controls or nonviremic patients, CMV-specific T cells from viremic patients showed a significant loss of IL-2 production (p < 0.0001). Interestingly, functional anergy of CMV-specific CD4 T cells was reversible in that antibody-mediated blockade of PD-1 signaling with its ligands PD-L1/-L2 led to an up to 10-fold increase in CMV-specific proliferation. In conclusion, expression of PD-1 defines a reversible defect of CMV-specific CD4 T cells that is associated with viremia, and blocking PD-1 signaling may provide a potential target for enhancing the function of exhausted T cells in chronic CMV infection.

Generation of EBV-specific T cells for adoptive immunotherapy: a novel protocol using formalin-fixed stimulator cells to increase biosafety

Adoptive immunotherapy with in vitro generated Epstein-Barr virus (EBV)-specific T cells is a safe and effective treatment in patients with EBV-related complications after transplantation. More frequent use of EBV-specific T cells is held back by their cost and time-intensive generation under good manufacturing practice (GMP) conditions. Currently, EBV-specific T cells are produced by repetitive stimulation of peripheral blood mononuclear cells with EBV-infected lymphoblastoid cell lines (LCLs), a protocol that requires several open GMP-handling steps. The aim of the present study was to improve T-cell generation under GMP conditions. We introduce a novel generation protocol that replaces repetitive with short-term LCL stimulation of PMBCs. Vital and formalin-fixed LCLs were used to further increase biosafety. Stimulated T cells were selected by the clinically approved cytokine secretion assay followed by nonspecific expansion. Sufficient numbers of EBV-specific T-cell lines were generated with all protocols. Specific recognition and killing of EBV-infected targets was found and was independent of the generation protocol applied. The novel protocol based on formalin-fixed cells, selection, and expansion reduced open GMP-handling steps and increased biosafety. Furthermore, fixation will allow the use of transgenic LCLs (eg, with cytomegalovirus or tumor antigens) and thereby facilitate the generation of antigen-specific T cells directed against pathogens other than EBV.

Conditional immortalization of human B cells by CD40 ligation

It is generally assumed that human differentiated cells have a limited life-span and proliferation capacity in vivo, and that genetic modifications are a prerequisite for their immortalization in vitro. Here we readdress this issue, studying the long-term proliferation potential of human B cells. It was shown earlier that human B cells from peripheral blood of healthy donors can be efficiently induced to proliferate for up to ten weeks in vitro by stimulating their receptor CD40 in the presence of interleukin-4. When we applied the same stimuli under conditions of modified cell number and culture size, we were surprised to find that our treatment induced B cells to proliferate throughout an observation period of presently up to 1650 days, representing more than 370 population doublings, which suggested that these B cells were immortalized in vitro. Long-term CD40-stimulated B cell cultures could be established from most healthy adult human donors. These B cells had a constant phenotype, were free from Epstein-Barr virus, and remained dependent on CD40 ligation. They had constitutive telomerase activity and stabilized telomere length. Moreover, they were susceptible to activation by Toll-like receptor 9 ligands, and could be used to expand antigen-specific cytotoxic T cells in vitro. Our results indicate that human somatic cells can evade senescence and be conditionally immortalized by external stimulation only, without a requirement for genetic manipulation or oncoviral infection. Conditionally immortalized human B cells are a new tool for immunotherapy and studies of B cell oncogenesis, activation, and function.

4-1BB is superior to CD28 costimulation for generating CD8+ cytotoxic lymphocytes for adoptive immunotherapy

Artificial APCs (aAPCs) genetically modified to express selective costimulatory molecules provide a reproducible, cost-effective, and convenient method for polyclonal and Ag-specific expansion of human T cells for adoptive immunotherapy. Among the variety of aAPCs that have been studied, acellular beads expressing anti-CD3/anti-CD28 efficiently expand CD4+ cells, but not CD8+ T cells. Cell-based aAPCs can effectively expand cytolytic CD8+ cells, but optimal costimulatory signals have not been defined. 4-1BB, a costimulatory molecule expressed by a minority of resting CD8+ T cells, is transiently up-regulated by all CD8+ T cells following activation. We compared expansion of human cytolytic CD8+ T cells using cell-based aAPCs providing costimulation via 4-1BB vs CD28. Whereas anti-CD3/anti-CD28 aAPCs mostly expand naive cells, anti-CD3/4-1BBL aAPCs preferentially expand memory cells, resulting in superior enrichment of Ag-reactive T cells which recognize previously primed Ags and efficient expansion of electronically sorted CD8+ populations reactive toward viral or self-Ags. Using HLA-A2-Fc fusion proteins linked to 4-1BBL aAPCs, 3-log expansion of Ag-specific CD8+ CTL was induced over 14 days, whereas similar Ag-specific CD8+ T cell expansion did not occur using HLA-A2-Fc/anti-CD28 aAPCs. Furthermore, when compared with cytolytic T cells expanded using CD28 costimulation, CTL expanded using 4-1BB costimulation mediate enhanced cytolytic capacity due, in part, to NKG2D up-regulation. These results demonstrate that 4-1BB costimulation is essential for expanding memory CD8+ T cells ex vivo and is superior to CD28 costimulation for generating Ag-specific products for adoptive cell therapy.