Immunotherapy using TCR and especially CAR transgenic T cells is a rapidly advancing field with the potential to become standard of care for the treatment of multiple diseases. While all current FDA approved CAR T cell products are generated using lentiviral gene transfer, extensive work is put into CRISPR/Cas mediated gene delivery to develop the next generation of safer and more potent cell products. One limitation of all editing systems is the size restriction of the knock-in cargo. Targeted integration under control of an endogenous promotor and/or signaling cascades opens the possibility to reduce CAR gene size to absolute minimum. Here we demonstrate that a first-generation CAR payload can be reduced to its minimum component - the antigen-binding domain - by targeted integration under control of the CD3ε promoter generating a CAR-CD3ε fusion protein that exploits the endogenous TCR signaling cascade. Miniaturizing CAR payload in this way results in potent CAR activity while simultaneously retaining the primary antigen recognition function of the TCR. Introducing CAR-specificity using a CAR binder only while maintaining endogenous TCR function may be an appealing design for future autologous CAR T cell therapies.

Adoptive cellular therapies with T cells are increasingly used to treat a variety of conditions. For instance, in a recent phase 1/2 trial, we prophylactically administered multivirus-specific T-cell products to protect recipients of T-cell-depleted allogeneic stem cell grafts against viral reactivation. To establish treatment efficacy, it is important to determine the fate of the individual transferred T-cell populations. However, it is difficult to unequivocally distinguish progeny of the transferred T-cell products from recipient- or stem cell graft-derived T cells that survived T-cell depletion during conditioning or stem cell graft manipulation. Using messenger RNA sequencing of the T-cell receptor β-chains of the individual virus-specific T-cell populations within these T-cell products, we were able to track the multiple clonal virus-specific subpopulations in peripheral blood and distinguish recipient- and stem cell graft-derived virus-specific T cells from the progeny of the infused T-cell products. We observed in vivo expansion of virus-specific T cells that were exclusively derived from the T-cell products with similar kinetics as the expansion of virus-specific T cells that could also be detected before the T-cell product infusion. In addition, we demonstrated persistence of virus-specific T cells derived from the T-cell products in most patients who did not show viral reactivation. This study demonstrates that virus-specific T cells from prophylactically infused multiantigen-specific T-cell products can expand in response to antigen encounter in vivo and even persist in the absence of early viral reactivation.

CAR T cell therapy is a rapidly growing area of oncological treatments having a potential of becoming standard care for multiple indications. Coincidently, CRISPR/Cas gene-editing technology is entering next-generation CAR T cell product manufacturing with the promise of more precise and more controllable cell modification methodology. The intersection of these medical and molecular advancements creates an opportunity for completely new ways of designing engineered cells to help overcome current limitations of cell therapy. In this manuscript we present proof-of-concept data for an engineered feedback loop. We manufactured activation-inducible CAR T cells with the help of CRISPR-mediated targeted integration. This new type of engineered T cells expresses the CAR gene dependent on their activation status. This artifice opens new possibilities to regulate CAR T cell function both in vitro and in vivo. We believe that such a physiological control system can be a powerful addition to the currently available toolbox of next-generation CAR constructs.

Abstract Background: Allogeneic haematopoietic stem cell transplantation (HCT) is a curative option for haematopoietic diseases. However, a major limitation to the success of HCT is graft-versus-host disease (GvHD). The use of T regulatory cells (Tregs) as prophylaxis or treatment for GvHD has now emerged with a number of active clinical trials. Whilst many studies use Tregs from the original HCT donor, the future of this cell therapy could be third-party Tregs. Cord Blood (CB), with its established banks, represents a potential source of third-party cells. However, isolating a high purity Treg cells from cryopreserved CB is difficult without employing flow sorting. Here we investigated the feasibility of using reversible streptamer technology-based selections to obtain clinical grade Tregs from cryopreserved CB units. Results: A streptamer-based Treg selection was developed with both single-step, CD25 only positive cell selection and two-step, CD4 then CD25 positive selection from cryopreserved CB units, to yield a method that can be readily adapted to full good manufacturing practice (GMP). The best purity was achieved with a two-step streptamer isolation method, giving median purities of 89% Tregs of total cells. This method took advantage of the reversible nature of the streptamer technology allowing for successive positive selections for CD4 + and then CD25 + cells from cryopreserved CB units in an enclosed bag system. Isolated Tregs subsequently demonstrated 300-fold culture expansion using anti-CD3/28 beads. The expanded cells contained high proportions of cells with a Treg phenotype (both by flow cytometry and epigenetics) and demonstrated suppressive function. Conclusions: Using streptamer selection, highly enriched Tregs could be isolated from cryopreserved CB. The method could be performed in an enclosed bag system utilizing readily available clinical processing materials. Moreover, Tregs selected in this manner could be expanded in culture to make a clinically relevant dose from a cryopreserved CB unit. Thus, streptamers represent a viable alternative to column based magnetic bead or fluorescent activated cell sorting (FACS)-based methods for selection of clinical grade Tregs from banked CB units.

Large-scale target cell isolation from patient blood preparations is one of the critical operations during drug product manufacturing for personalized cell therapy in immuno-oncology. Use of high-affinity murine antibody coated magnetic nanoparticles that remain on isolated cells is the current standard applied for this purpose. Here, we present the transformation of previously described technology — non-magnetic immunoaffinity column chromatography-based cell selection with reversible reagents into a new clinical-grade cell isolation platform called Automated Traceless Cell affinity chromatography (ATC). ATC is a fully closed and GMP-compliant cell selection and manufacturing system. Reversibility of reagents enables (sequential) positive cell selection, optionally in combination with depletion columns, enabling capture of highly specific cell subsets. Moreover, synergy with other Streptamer-based technologies allows novel uses beyond cell isolation including integrated and automated on-column target cell activation. In conclusion, ATC technology is an innovative as well as versatile platform to select, stimulate and modify cells for clinical manufacturing and downstream therapies.

T cell activation is a cornerstone in manufacturing of T cell-based therapies, and precise control over T cell activation is important in the development of the next generation T-cell based therapeutics. This need cannot be fulfilled by currently available methods for T cell stimulation, in particular not in a time dependent manner. Here, we describe a modular activation reagent called Expamers, which addresses these limitations. Expamers are versatile stimuli that are intended for research and clinical use. They are readily soluble and can be rapidly bound and removed from the cell surface, allowing nearly instantaneous initiation and termination of activation signal, respectively. Hence, Expamers enable precise regulation of T cell stimulation duration and provide promise of control over T cell profiles in future products. Expamers can be easily adopted to different T cell production formats and have the potential to increase efficacy of T cell immunotherapeutics.

Tumor-associated antigens (TAAs) are monomorphic self-antigens that are proposed as targets for immunotherapeutic approaches to treat malignancies. We investigated whether T cells with sufficient avidity to recognize naturally overexpressed self-antigens in the context of self-HLA can be found in the T-cell repertoire of healthy donors. Minor histocompatibility antigen (MiHA)-specific T cellswere used as a model, as the influence of thymic selection on the T-cell repertoire directed against MiHA can be studied in both self (MiHA(pos) donors) and non-self (MiHA(neg) donors) backgrounds. T-cell clones directed against the HLA*02:01-restricted MiHA HA-1H were isolated from HA-1H(neg)/HLA-A*02:01(pos) and HA1H(pos)/HLA-A*02:01(pos) donors. Of the 16 uniqueHA-1H-specificT-cell clones, five T-cell clones derived from HA-1H(neg)/HLA-A*02:01(pos) donors and one T-cell clone derived from an HA1H(pos)/HLA-A*02:01(pos) donor showed reactivity against HA-1H(pos) target cells. In addition, in total, 663 T-cell clones (containing at least 91 unique clones expressing different T-cell receptors) directed against HLA*02:01-restricted peptides of TAA WT1-RMF, RHAMM-ILS, proteinase-3-VLQ, PRAME-VLD, and NY-eso-1-SLL were isolated from HLA-A*02:01(pos) donors. Only 3 PRAME-VLD-specific and one NY-eso-1-SLL-specific T-cell clone provoked interferon-g production and/or cytolysis upon stimulation with HLA-A*02:01(pos) malignant cell lines (but not primary malignant samples) naturally overexpressing the TAA. These results show that self-HLA-restricted T cells specific for selfantigens such as MiHA in MiHA(pos) donors and TAAs are present in peripheral blood of healthy individuals. However, clinical efficacy would require highly effective in vivo priming by peptide vaccination in the presence of proper adjuvants or in vitro expansion of the low numbers of self-antigen-specific T cells of sufficient avidity to recognize endogenously processed antigen. (Blood. 2020;136(4):455-467)

Prophylactic infusion of selected donor T cells can be an effective method to restore specific immunity after T-cell-depleted allogeneic stem cell transplantation (TCD-alloSCT). In this phase I/II study, we aimed to reduce the risk of viral complications and disease relapses by administrating donor-derived CD8 pos T cells directed against cytomegalovirus (CMV), Epstein-Barr virus (EBV) and adenovirus antigens, tumor-associated antigens (TAA) and minor histocompatibility antigens (MiHA). Twenty-seven of thirty-six screened HLA-A*02:01 pos patients and their CMV pos and/or EBV pos donors were included. Using MHC-I- Strep tamers, 27 T-cell products were generated containing a median of 5.2 × 10 6 cells. Twenty-four products were administered without infusion-related complications at a median of 58 days post alloSCT. No patients developed graft-versus-host disease during follow-up. Five patients showed disease progression without coinciding expansion of TAA/MiHA-specific T cells. Eight patients experienced CMV- and/or EBV-reactivations. Four of these reactivations were clinically relevant requiring antiviral treatment, of which two progressed to viral disease. All resolved ultimately. In 2/4 patients with EBV-reactivations and 6/8 patients with CMV-reactivations, viral loads were followed by the expansion of donor-derived virus target-antigen-specific T cells. In conclusion, generation of multi-antigen-specific T-cell products was feasible, infusions were well tolerated and expansion of target-antigen-specific T cells coinciding viral reactivations was illustrated in the majority of patients.

BACKGROUND:Adoptive transfer of donor-derived T cells can be applied to improve immune reconstitution in immune-compromised patients after allogeneic stem cell transplantation. The separation of beneficial T cells from potentially harmful T cells can be achieved by using the major histocompatibility complex (MHC) I-Streptamer isolation technology, which has proven its feasibility for the fast and pure isolation of T-cell populations with a single specificity. We have analyzed the feasibility of the simultaneous isolation of multiple antigen-specific T-cell populations in one procedure by combining different MHC I-Streptamers.METHODS:First, the effect of combining different amounts of MHC I-Streptamers used in the isolation procedure on the isolation efficacy of target antigen-specific T cells and on the number of off-target co-isolated contaminating cells was assessed. The feasibility of this approach was demonstrated in large-scale validation procedures targeting both high and low frequent T-cell populations using the Good Manufacturing Practice (GMP)-compliant CliniMACS Plus device.RESULTS:T-cell products targeting up to 24 different T-cell populations could be isolated in one, simultaneous MHC I-Streptamer procedure, by adjusting the amount of MHC I- Streptamers per target antigen-specific T-cell population. Concurrently, the co-isolation of potentially harmful contaminating T cells remained below our safety limit. This technology allows the reproducible isolation of high and low frequent T-cell populations. However, the expected therapeutic relevance of direct clinical application without in vitro expansion of these low frequent T-cell populations is questionable.DISCUSSION:This study provides a feasible, fast and safe method for the generation of highly personalized MHC I-Streptamer isolated T-cell products for adoptive immunotherapy.

Cytomegalovirus (CMV) infection is a common, potentially life-threatening complication following allogeneic hematopoietic stem cell transplantation (allo-HSCT). We assessed prospectively the safety and efficacy of stem cell-donor- or third-party-donor-derived CMV-specific T cells for the treatment of persistent CMV infections after allo-HSCT in a phase I/IIa trial. Allo-HSCT patients with drug-refractory CMV infection and lacking virus-specific T cells were treated with a single dose of ex vivo major histocompatibility complex-Streptamer-isolated CMV epitope-specific donor T cells. Forty-four allo-HSCT patients receiving a T-cell-replete (D + repl; n =28) or T-cell-depleted (D + depl; n =16) graft from a CMV-seropositive donor were screened for CMV-specific T-cell immunity. Eight D + depl recipients received adoptive T-cell therapy from their stem cell donor. CMV epitope-specific T cells were well supported and became detectable in all treated patients. Complete and partial virological response rates were 62.5% and 25%, respectively. Owing to longsome third-party donor (TPD) identification, only 8 of the 57 CMV patients transplanted from CMV-seronegative donors (D − ) received antigen-specific T cells from partially human leukocyte antigen (HLA)-matched TPDs. In all but one, TPD-derived CMV-specific T cells remained undetectable. In summary, adoptive transfer correlated with functional virus-specific T-cell reconstitution in D + depl patients. Suboptimal HLA match may counteract expansion of TPD-derived virus-specific T cells in D − patients.

Antje Tunger, Rebekka Wehner, Malte von Bonin, Denise K€ uhn, Falk Heidenreich, Sarah Matko, Magdalena Nauerth, Elke R€ ucker-Braun, Sevina Dietz, Cornelia S. Link, Anne Eugster, Marcus Odendahl, Dirk H. Busch, Torsten Tonn, Ezio Bonifacio, Lothar Germeroth, Johannes Schetelig, Michael P. Bachmann, Martin Bornh€auser and Marc Schmitz Institute of Immunology, Medical Faculty, TU Dresden, Dresden, Germany; National Center for Tumor Diseases, University Hospital Carl Gustav Carus, TU Dresden, Germany; Department of Medicine I, University Hospital of Dresden, Dresden, Germany; German Cancer Consortium (DKTK), Dresden, Germany; German Cancer Research Center (DKFZ), Heidelberg, Germany; Center for Regenerative Therapies Dresden (CRTD), Medical Faculty, TU Dresden, Dresden, Germany; Institute of Transfusion Medicine, German Red Cross Blood Donation Service North-East, Dresden, Germany; Institute for Medical Microbiology, Immunology and Hygiene, TU Munich, Munich, Germany; Juno Therapeutics GmbH, G€ottingen, Germany; Department of Radioimmunology, Institute of Radiopharmaceutical Cancer Research, Helmholtz Center Dresden-Rossendorf, Dresden, Germany

Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative treatment approach for patients with acute myeloid leukemia (AML) and chronic lymphocytic leukemia (CLL). Graft versus leukemia (GVL) effects, which are exerted by donor T cells directed against leukemic-associated antigens (LAAs), are considered to play a crucial role in disease eradication. Although the expansion of cytotoxic T lymphocytes (CTLs) specific for cytomegalovirus (CMV) in response to an infection has been shown in multiple studies, data on CTLs mediating GVL effects are limited. To evaluate a potential increase or decrease of T lymphocytes specific for LAAs in the setting of allogeneic HSCT, we monitored leukemia-specific CD8+ T cells throughout the first year after HSCT in 18 patients using streptamer technology. A broad panel of promising LAAs was selected: Wilms tumor protein, proteinase 3, receptor for hyaluronan acid-mediated motility, apoptosis regulator Bcl-2, survivin, nucleophosmin, and fibromodulin. T cells specifically directed against AML- or CLL-associated antigens were found at very low frequencies in peripheral blood. Substantial frequencies of LAA-specific T cells could not be measured at any time point by flow cytometry. In contrast, abundant CMV-pp65-specific T cells were detected in CMV-seropositive patient-recipient pairs and an increase prompted by CMV infection could be demonstrated. In conclusion, T lymphocytes with specificities for the aforementioned LAAs can only be detected in minimal quantities in the early phase after allogeneic HSCT.

Opportunistic viral infections and relapse are major complications in patients after T cell depleted allogeneic stem cell transplantation (TCD alloSCT). Since the application of unmodified donor lymphocyte infusion (DLI) early after alloSCT results in a high risk of graft versus host disease (GVHD), infusion of selected populations of virus-specific donor T cells can be an effective approach to safely restore anti-viral immunity early after alloSCT. As part of the EU FP7 consortium T Control, in this phase I/II study the feasibility and safety of the generation and administration of selected populations of donor-derived T cells targeting multiple antigens (Ag) is assessed. The multi Ag-specific T cell products contained T cells targeting cytomegalovirus (CMV), Epstein Bar virus (EBV) and adenovirus (AdV) as well as T cells targeting tumor associated Ag (TAA) and minor histocompatibility Ag (MiHA) to boost the graft versus leukemia (GVL) reactivity. To assess efficacy, in-vivo appearance or expansion of Ag-specific T cells, and the effect on viral reactivations and/or disease relapse was evaluated for 20 weeks after infusion until regular DLI was applied.

High epitope‐specific sensitivity of CD8+ T cells is required for optimal immune protection against intracellular pathogens as well as certain malignancies. The quality of antigen recognition of CD8+ T cells is usually described as “avidity” to its cognate peptide MHCI complex. T cell avidity is mainly dependent on the structural qualities of the T cell receptor (TCR), as convincingly demonstrated by recombinant TCR re‐expression experiments. Based on reversible MHCI multimer staining and koff‐rate measurements of monomeric peptide MHCI complexes, we recently established a microscopic assay for determining the structural avidity of individual CD8+ T cells. Here we demonstrate that this assay can be adapted for rapid flow‐cytometric avidity screening of epitope‐specific T cell populations. Furthermore, we show that—in combination with conventional nonreversible MHCI multimer staining—even very small epitope‐specific CD8+ T cell populations can be analyzed directly ex vivo without the need for previous TCR cloning or T cell sorting. This simplified approach provides highly accurate mean TCR‐ligand koff‐rate values for poly‐ or oligoclonal T cell populations and is ideally suited for high‐throughput applications in basic research as well as clinical settings. © 2016 International Society for Advancement of Cytometry

Tumor infiltrating lymphocyte (TIL) therapy has shown objective clinical response rates of 50% in stage IV melanoma patients in a number of clinical trials. Nevertheless, the majority of patients progress either directly upon therapy or after an initial period of tumor control. Recent data have shown that most TIL products that are used for therapy contain only low frequencies of T cells reactive against known melanoma‐associated epitopes. Because of this, the development of a technology to create T‐cell products that are enriched for reactivity against defined melanoma‐associated antigens would seem valuable, both to evaluate the tumoricidal potential of T cells directed against different antigen classes and to potentially increase response rates. Here, we developed and validated a conditional MHC streptamer‐based platform for the creation of TIL products with defined antigen reactivities. We have used this platform to successfully enrich both high‐frequency (≥1%) and low‐frequency (<1%) tumor‐specific CD8+ T‐cell populations, and thereby created T‐cell products with enhanced tumor recognition potential. Collectively, these data demonstrate that selection of antigen‐specific T‐cell populations can be used to create defined T‐cell products for clinical use. This strategy thus forms a highly flexible platform for the development of antigen‐specific cell products for personalized cancer immunotherapy.

Adoptive cell therapy using gene-modified T cells has demonstrated promising clinical outcomes in hematologic malignancies. Production of gene-modified T cells involves the selection of patient T cells, activation via stimulation through the endogenous T cell receptor (TCR) complex and a costimulatory domain, followed by introduction of a tumor antigen-specific TCR or chimeric antigen receptor (CAR) through gene modification. Here we characterize a soluble T cell stimulation reagent, known as an ExpamerTM reagent, in the production of therapeutic CAR T cells.