Infusion of suicide-gene-engineered donor lymphocytes after family haploidentical haemopoietic stem-cell transplantation for leukaemia (the TK007 trial): a non-randomised phase I-II study

Immune Effector Cell-associated Hemophagocytic Lymphohistiocytosis-like Syndrome (IEC-HS)

Immune effector cell-associated hemophagocytic lymphohistiocytosis-like syndrome (IEC-HS) is a complication of adoptive cell therapy. Presenting with clinical manifestations of hyperinflammation and surrogate indicators of hyperinflammation such as elevations in serum ferritin and hepatic transaminases, decreasing cell counts, and hypofibrinogenemia, IEC-HS resembles primary and other forms of secondary hemophagocytic lymphohistiocytosis. Nonetheless, this is an iatrogenic complication resulting from the induction of hyperinflammatory pathways during T-cell-mediated anticancer targeting. Distinct from cytokine release syndrome, IEC-associated neurotoxicity syndrome, and IEC-associated hematotoxicity, IEC-HS can be life-threatening. Identification of IEC-HS, optimization of treatment strategies, and use of supportive care are critical to improving outcomes.

Novel strategies to manage CAR-T cell toxicity

The immune-related adverse events associated with chimeric antigen receptor (CAR)-T cell therapy result in substantial morbidity as well as considerable cost to the health-care system, and can limit the use of these treatments. Current therapeutic strategies to manage immune-related adverse events include interleukin-6 receptor (IL-6R) blockade and corticosteroids. However, because these interventions do not always address the side effects, nor prevent progression to higher grades of adverse events, new approaches are needed. A deeper understanding of the cell types involved, and their associated signalling pathways, cellular metabolism and differentiation states, should provide the basis for alternative strategies. To preserve treatment efficacy, cytokine-mediated toxicity needs to be uncoupled from CAR-T cell function, expansion, long-term persistence and memory formation. This may be achieved by targeting CAR or independent cytokine signalling axes transiently, and through novel T cell engineering strategies, such as low-affinity CAR-T cells, reversible on-off switches and versatile adaptor systems. We summarize the current management of cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome, and review T cell- and myeloid cell-intrinsic druggable targets and cellular engineering strategies to develop safer CAR-T cells.

Engineering CD5-targeting CAR-NK cells from peripheral blood for the treatment of CD5-positive hematological malignancies

BACKGROUND

The therapeutic application of chimeric antigen receptor (CAR) T cells in T-cell malignancies faces substantial limitations owing to fratricide and potential T cell aplasia, primarily attributed to the shared expression of target antigens, such as CD5, between normal and malignant T cells. Although natural killer (NK) cell-based immunotherapy is a promising alternative approach, its efficacy in treating hematologic malignancies remains to be fully elucidated.

METHODS

CD5-targeted CAR-modified primary NK cells, T cells and NK92 cell lines were generated and comprehensively evaluated for their anti-tumor efficacy through in vitro cytotoxicity assays and xenograft mouse models. Furthermore, preliminary investigation of the herpes simplex virus-1 thymidine kinase (HSV-TK) suicide switch system in CAR-NK cells were conducted using ganciclovir (GCV) as the activating agent.

RESULTS

CAR-NK cells exhibited significantly increased cytotoxic activity against CD5-positive cell lines and primary tumor cells, compared to NK, CAR-NK92, and CAR-T cells. Moreover, CAR-NK cells effectively decreased the leukemic burden and extended survival in murine model. Additionally, an off-switch utilizing the HSV-TK switch system successfully eradicated CAR-NK cells for safety considerations.

CONCLUSIONS

This study developed a controllable CD5 CAR-NK cells that exhibit high efficacy against T-cell malignancies, although further validation is necessary to assess their clinical potential.

CAR T or NK cells targeting mismatched HLA-DR molecules in acute myeloid leukemia after allogeneic hematopoietic stem cell transplant

Acute myeloid leukemia (AML)-specific target antigens are difficult to identify. Here we demonstrate that HLA-DRB1 can serve as a leukemia-specific target of chimeric antigen receptor (CAR) T cells in patients with AML after allogeneic hematopoietic stem cell transplantation (allo-HCT). We identified KG2032 as a monoclonal antibody specifically bound to AML cells in about half of patients, but not to normal leukocytes other than B lymphocytes. KG2032 reacted with a subset of HLA-DRB1 molecules, specifically those in which the 86th amino acid was not aspartic acid. KG2032 reacted minimally with nonhematopoietic tissues. These results indicate that KG2032 reactivity is highly specific for AML cells in patients who carry KG2032-reactive HLA-DRB1 alleles and who received allo-HCT from a donor carrying KG2032-nonreactive HLA-DRB1 alleles. KG2032-derived CAR T or natural killer cells showed significant anti-leukemic activity in preclinical models in female mice, suggesting that they may cure patients with AML who are incurable with allo-HCT.

Allogeneic Hemopoietic Cell Transplantation as a Paradigm for Cellular Immunotherapy

BACKGROUND

Allogeneic hematopoietic cell transplantation (alloHCT) is an established curative treatment for hematological malignancies and other severe blood disorders. However, alloHCT is also known for its significant side effects.

SUMMARY

Here we review recent advances in targeted molecular therapy, immunotherapy, infectiology, and diagnostics that have enhanced the tolerability and efficacy of alloHCT, expanding its use to less fit and elderly patients. We analyze developments in conditioning regimens, donor selection, and the management of graft versus host disease (GVHD) and infections and discuss posttransplantation strategies to prevent relapse.

KEY MESSAGE

In a fresh perspective, alloHCT can serve as a platform to enhance the potential of emerging targeted and immune therapies.

CAR T Cell Nanosymbionts: Revealing the Boundless Potential of a New Dyad

Cancer treatment has traditionally focused on eliminating tumor cells but faces challenges such as resistance and toxicity. A promising direction involves targeting the tumor microenvironment using CAR T cell immunotherapy, which has shown potential for treating relapsed and refractory cancers but is limited by high costs, resistance, and toxicity, especially in solid tumors. The integration of nanotechnology into ICAM cell therapy, a concept we have named "CAR T nanosymbiosis", offers new opportunities to overcome these challenges. Nanomaterials can enhance CAR T cell delivery, manufacturing, activity modulation, and targeting of the tumor microenvironment, providing better control and precision. This approach aims to improve the efficacy of CAR T cells against solid tumors, reduce associated toxicities, and ultimately enhance patient outcomes. Several studies have shown promising results, and developing this therapy further is essential for increasing its accessibility and effectiveness. Our "addition by subtraction model" synthesizes these multifaceted elements into a unified strategy to advance cancer treatment paradigms.

Novel conditioning and prophylaxis regimens for relapse prevention

The last 20 years witnessed relevant clinical advancements in the field of hematopoietic cell transplantation (HCT) for leukemia patients. The introduction of novel conditioning regimens, a better prophylaxis and management of graft- versus-host disease, and an ameliorated posttransplant support system improved safety and, therefore, outcomes. On the other hand, leukemia relapse remains the major cause of allogeneic HCT failure. Efforts have been made to understand the mechanisms of leukemia relapse, and new insights that clarify how donor immunity exerts graft-versus- leukemia (GVL) activity are available. Such studies set the base to design novel transplant strategies that can improve disease control. In our review we begin by discussing the most relevant criteria to choose a donor that provides a strong GVL effect. We also report some of the novel conditioning regimens that aim to deliver and extend myeloablation in order to reduce the disease burden at time of graft infusion. Finally, we discuss how the graft can be manipulated to limit the use of immune suppression and ensure potent antileukemic activity.

Targeted gene delivery systems for T-cell engineering

T lymphocytes are indispensable for the host systems of defense against pathogens, tumors, and environmental threats. The therapeutic potential of harnessing the cytotoxic properties of T lymphocytes for antigen-specific cell elimination is both evident and efficacious. Genetically engineered T-cells, such as those employed in CAR-T and TCR-T cell therapies, have demonstrated significant clinical benefits in treating cancer and autoimmune disorders. However, the current landscape of T-cell genetic engineering is dominated by strategies that necessitate in vitro T-cell isolation and modification, which introduce complexity and prolong the development timeline of T-cell based immunotherapies. This review explores the complexities of gene delivery systems designed for T cells, covering both viral and nonviral vectors. Viral vectors are known for their high transduction efficiency, yet they face significant limitations, such as potential immunogenicity and the complexities involved in large-scale production. Nonviral vectors, conversely, offer a safer profile and the potential for scalable manufacturing, yet they often struggle with lower transduction efficiency. The pursuit of gene delivery systems that can achieve targeted gene transfer to T cell without the need for isolation represents a significant advancement in the field. This review assesses the design principles and current research progress of such systems, highlighting the potential for in vivo gene modification therapies that could revolutionize T-cell based treatments. By providing a comprehensive analysis of these systems, we aim to contribute valuable insights into the future development of T-cell immunotherapy.

Synthetic biology approaches for enhancing safety and specificity of CAR-T cell therapies for solid cancers

CAR-T cell therapies have been successful in treating numerous hematologic malignancies as the T cell can be engineered to target a specific antigen associated with the disease. However, translating CAR-T cell therapies for solid cancers is proving more challenging due to the lack of truly tumor-associated antigens and the high risk of off-target toxicities. To combat this, numerous synthetic biology mechanisms are being incorporated to create safer and more specific CAR-T cells that can be spatiotemporally controlled with increased precision. Here, we seek to summarize and analyze the advancements for CAR-T cell therapies with respect to clinical implementation, from the perspective of synthetic biology and immunology. This review should serve as a resource for further investigation and growth within the field of personalized cellular therapies.

Advances in CAR-T-cell therapy in T-cell malignancies

Significant advances have been made in chimeric antigen receptor T (CAR-T)-cell therapy for the treatment of recurrent or refractory B-cell hematologic malignancies. However, CAR-T-cell therapy has not yet achieved comparable success in the management of aggressive T-cell malignancies. This article reviews the challenges of CAR-T-cell therapy in treating T-cell malignancies and summarizes the progress of preclinical and clinical studies in this area. We present an analysis of clinical trials of CAR-T-cell therapies for the treatment of T-cell malignancies grouped by target antigen classification. Moreover, this review focuses on the major challenges encountered by CAR-T-cell therapies, including the nonspecific killing due to T-cell target antigen sharing and contamination with cell products during preparation. This review discusses strategies to overcome these challenges, presenting novel therapeutic approaches that could enhance the efficacy and applicability of CAR-T-cell therapy in the treatment of T-cell malignancies. These ideas and strategies provide important information for future studies to promote the further development and application of CAR-T-cell therapy in this field.

Fate control engagement augments NK cell responses in LV/hu-IL-12 transduced sarcoma

INTRODUCTION

NK cells are an untapped resource for cancer therapy. Sarcomas transduced with lentiviruses to express human IL-12 are only cleared in mice bearing mature human NK cells. However, systemic inflammation limits IL-12 utilization. Fate control a.k.a. "suicide mechanisms" regulate unchecked systemic inflammation caused by cellular immunotherapies. Despite increasing utilization, there remains limited data on immune consequences or tumor-directed effects of fate control.

OBJECTIVES

We sought to engage the mutant thymidylate kinase (mTMPK) metabolic fate control system to regulate systemic inflammation and assess the impact on NK cell effector functions.

METHODS

Primary human sarcoma short-passage samples and cell lines were transduced with LV/hu-IL-12_mTMPK engineering expression of IL-12 and an AZT-associated fate control enzyme. We assessed transduced sarcoma responses to AZT engagement and subsequent modulation of NK cell functions as measured by inflammatory cytokine production and cytotoxicity.

RESULTS

AZT administration to transduced (LV/hu-IL-12_mTMPK) short-passage primary human sarcomas and human Ewing sarcoma, osteosarcoma, and rhabdomyosarcoma cell lines, abrogated the robust expression of human IL-12. Fate control activation elicited a specific dose-dependent cytotoxic effect measured by metabolic activity (WST-1) and cell death (Incucyte). NK effector functions of IFN-γ and cytotoxic granule release were significantly augmented despite IL-12 abrogation. This correlated with preferentially induced expression of NK cell activation ligands.

CONCLUSIONS

mTMPK fate control engagement terminates transduced sarcoma IL-12 production and triggers cell death, but also augments an NK cell-mediated response coinciding with metabolic stress activating surface ligand induction. Fate control engagement could offer a novel immune activation method for NK cell-mediated cancer clearance.

Design Principles of a Novel Construct for HBB Gene-Editing and Investigation of Its Gene-Targeting Efficiency in HEK293 Cells

Beta-thalassemia is one of the most common monogenic inherited disorders worldwide caused by different mutations in the hemoglobin subunit beta (HBB) gene. Genome-editing based on clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 system (CRISPR/Cas9) has raised the hope for life-long gene therapy of beta-thalassemia. In a proof-of-concept study, we describe the detailed design and assess the efficacy of a novel homology-directed repair (HDR)-based CRISPR construct for targeting the HBB locus. The selected sgRNAs were designed and cloned into an optimized CRISPR plasmid. The HDR donor templates containing a reporter and a selection marker flanked by the piggyBac Inverted Tandem Repeat (ITRs), the homology arms and the delta thymidine kinase (ΔTK) gene for negative selection were constructed. The efficiency of on-target mutagenesis by the eSpCas9/sgRNAs was assessed by mismatch assays. HDR-positive cells were isolated by treatment with G418 or selection based on truncated Neuron Growth Factor Receptor (tNGFR) expression using the Magnetic Activated Cell Sorting (MACS) method followed by ganciclovir (GCV) treatment to eliminate cells with random genomic integration of the HDR donor template. In-out PCR and sanger sequencing confirmed HDR in the isolated cells. Our data showed ~ 50% efficiency for co-transfection of CRISPR/donor template plasmids in HEK293 cells and following G418 treatment, the HDR efficiency was detected at ~ 37.5%. Moreover, using a clinically-relevant strategy, HDR events were validated after selection for tNGFR+ cells followed by negative selection for ΔTK by GCV treatment. Thus, our HDR-based gene-editing strategy could efficiently target the HBB locus and enrich for HDR-positive cells.

Stem Cell Therapy for Repair of the Injured Brain: Five Principles

Cell therapy holds great promise for regenerative treatment of disease. Despite recent breakthroughs in clinical research, applications of cell therapies to the injured brain have not yielded the desired results. We pinpoint current limitations and suggest five principles to advance stem cell therapies for brain regeneration. While we focus on cell therapy for stroke, all principles also apply for other brain diseases.

Cellular Strategies for Separating GvHD from GvL in Haploidentical Transplantation

GvHD still remains, despite the continuous improvement of transplantation platforms, a fearful complication of transplantation from allogeneic donors. Being able to separate GvHD from GvL represents the greatest challenge in the allogeneic transplant setting. This may be possible through continuous improvement of cell therapy techniques. In this review, current cell therapies are taken into consideration, which are based on the use of TCR alpha/beta depletion, CD45RA depletion, T regulatory cell enrichment, NK-cell-based immunotherapies, and suicide gene therapies in order to prevent GvHD and maximally amplify the GvL effect in the setting of haploidentical transplantation.

Innovative Genoceuticals in Human Gene Therapy Solutions: Challenges and Safe Clinical Trials of Orphan Gene Therapy Products

The success of gene therapy attempts is controversial and inconclusive. Currently, it is popular among the public, the scientific community, and manufacturers of Gene Therapy Medical Products. In the absence of any remedy or treatment options available for untreatable inborn metabolic orphan or genetic diseases, cancer, or brain diseases, gene therapy treatment by genoceuticals and T-cells for gene editing and recovery remains the preferred choice as the last hope. A new concept of "Genoceutical Gene Therapy" by using orphan 'nucleic acid-based therapy' aims to introduce scientific principles of treating acquired tissue damage and rare diseases. These Orphan Genoceuticals provide new scope for the 'genodrug' development and evaluation of genoceuticals and gene products for ideal 'gene therapy' use in humans with marketing authorization application (MAA). This perspective study focuses on the quality control, safety, and efficacy requirements of using 'nucleic acid-based and human cell-based new gene therapy' genoceutical products to set scientific advice on genoceutical-based 'orphan genodrug' design for clinical trials as per Western and European guidelines. The ethical Western FDA and European EMA guidelines suggest stringent legal and technical requirements on genoceutical medical products or orphan genodrug use for other countries to frame their own guidelines. The introduction section proposes lessknown 'orphan drug-like' properties of modified RNA/DNA, human cell origin gene therapy medical products, and their transgene products. The clinical trial section explores the genoceutical sources, FDA/EMA approvals for genoceutical efficacy criteria with challenges, and ethical guidelines relating to gene therapy of specific rare metabolic, cancer and neurological diseases. The safety evaluation of approved genoceuticals or orphan drugs is highlighted with basic principles and 'genovigilance' requirements (to observe any adverse effects, side effects, developed signs/symptoms) to establish their therapeutic use. Current European Union and Food and Drug Administration guidelines continuously administer fast-track regulatory legal framework from time to time, and they monitor the success of gene therapy medical product efficacy and safety. Moreover, new ethical guidelines on 'orphan drug-like genoceuticals' are updated for biodistribution of the vector, genokinetics studies of the transgene product, requirements for efficacy studies in industries for market authorization, and clinical safety endpoints with their specific concerns in clinical trials or public use.

Case report: Differential diagnosis of highly amplified anti-CD5 CAR T cells and relapsed lymphoma cells in a patient with refractory ALK positive anaplastic large cell lymphoma

BACKGROUND

Anaplastic Large Cell Lymphoma (ALCL) is one of the most common subtypes of T-cell lymphoma. Among these, refractory and relapsed (r/r) ALK positive ALCL lacks effective therapies. The chimeric antigen receptor-modified T (CAR-T) cell therapy holds great promise as a therapeutic strategy for this disease. However, it is not known yet whether anti-CD5 CAR-T cells are sufficient for the definitive treatment of relapsed ALK+ ALCL, nor the role of accurate laboratory-based diagnoses during CAR-T treatment.

CASE PRESENTATION

The adolescent patient received autologous T cells containing sequences encoding VH domains specific to CD5. Following the infusion, there was an increase in both the copy number and proportion of CAR-T cells in peripheral blood. IL-6 and ferritin levels in the patient exhibited significant fluctuations, with increases of 13 and 70 folds respectively, compared to baseline after the treatment. Additionally, adverse effects were observed, including grade 4 rash, grade 1 headache, nausea, and neck-pain. Surprisingly, a relapsed disease phenotype was identified based on the results of PET/CT and histopathological analysis of the inguinal lymph node biopsy. After conducting a thorough diagnostic assessment, which included flow cytometry, next-generation sequencing (NGS), examination of immune-related gene rearrangements, and analysis of the immune repertoire of T-cell receptors (TCR), we conclusively determined that the hyperplastic T cells identified in the lymph node were the result of an expansion of CAR-T cells. Ultimately, the patient has attained complete remission (CR) and has sustained a disease-free survival state for 815 days as of the cutoff date on August 30, 2023.

CONCLUSION

Taken together, the results demonstrate that anti-CD5 CAR-T cells can induce a clinical response in r/r ALK+ ALCL patient. Furthermore, this case underscores the importance of utilizing advanced technologies with high sensitivity and accuracy for biological detection in clinical laboratory diagnosis and prognosis in CAR-T cell treatment.

TRIAL REGISTRATION NUMBER

NCT04767308.

Advancing CART therapy for acute myeloid leukemia: recent breakthroughs and strategies for future development

Chimeric antigen receptor (CAR) T therapies are being developed for acute myeloid leukemia (AML) on the basis of the results obtained for other haematological malignancies and the need of new treatments for relapsed and refractory AML. The biggest challenge of CART therapy for AML is to identify a specific target antigen, since antigens expressed in AML cells are usually shared with healthy haematopoietic stem cells (HSC). The concomitant expression of the target antigen on both tumour and HSC may lead to on-target/off-tumour toxicity. In this review, we guide researchers to design, develop, and translate to the clinic CART therapies for the treatment of AML. Specifically, we describe what issues have to be considered to design these therapies; what in vitro and in vivo assays can be used to prove their efficacy and safety; and what expertise and facilities are needed to treat and manage patients at the hospital.

Dual-inhibitory domain iCARs improve the efficiency of the AND-NOT gate CAR T strategy

CAR (chimeric antigen receptor) T cell therapy has shown clinical success in treating hematological malignancies, but its treatment of solid tumors has been limited. One major challenge is on-target, off-tumor toxicity, where CAR T cells also damage normal tissues that express the targeted antigen. To reduce this detrimental side-effect, Boolean-logic gates like AND-NOT gates have utilized an inhibitory CAR (iCAR) to specifically curb CAR T cell activity at selected nonmalignant tissue sites. However, the strategy seems inefficient, requiring high levels of iCAR and its target antigen for inhibition. Using a TROP2-targeting iCAR with a single PD1 inhibitory domain to inhibit a CEACAM5-targeting CAR (CEACAR), we observed that the inefficiency was due to a kinetic delay in iCAR inhibition of cytotoxicity. To improve iCAR efficiency, we modified three features of the iCAR-the avidity, the affinity, and the intracellular signaling domains. Increasing the avidity but not the affinity of the iCAR led to significant reductions in the delay. iCARs containing twelve different inhibitory signaling domains were screened for improved inhibition, and three domains (BTLA, LAIR-1, and SIGLEC-9) each suppressed CAR T function but did not enhance inhibitory kinetics. When inhibitory domains of LAIR-1 or SIGLEC-9 were combined with PD-1 into a single dual-inhibitory domain iCAR (DiCARs) and tested with the CEACAR, inhibition efficiency improved as evidenced by a significant reduction in the inhibitory delay. These data indicate that a delicate balance between CAR and iCAR signaling strength and kinetics must be achieved to regulate AND-NOT gate CAR T cell selectivity.

Mechanisms and strategies for safe chimeric antigen receptor T-cell activity control

The clinical application of chimeric antigen receptor (CAR) T-cell therapy has rapidly changed the treatment options for terminally ill patients with defined blood-borne cancer types. However, CAR T-cell therapy can lead to severe therapy-associated toxicities including CAR-related hematotoxicity, ON-target OFF-tumor toxicity, cytokine release syndrome (CRS) or immune effector cell-associated neurotoxicity syndrome (ICANS). Just as CAR T-cell therapy has evolved regarding receptor design, gene transfer systems and production protocols, the management of side effects has also improved. However, because of measures taken to abrogate adverse events, CAR T-cell viability and persistence might be impaired before complete remission can be achieved. This has fueled efforts for the development of extrinsic and intrinsic strategies for better control of CAR T-cell activity. These approaches can mediate a reversible resting state or irreversible T-cell elimination, depending on the route chosen. Control can be passive or active. By combination of CAR T-cells with T-cell inhibiting compounds, pharmacologic control, mostly independent of the CAR construct design used, can be achieved. Other strategies involve the genetic modification of T-cells or further development of the CAR construct by integration of molecular ON/OFF switches such as suicide genes. Alternatively, CAR T-cell activity can be regulated intracellularly through a self-regulation function or extracellularly through titration of a CAR adaptor or of a priming small molecule. In this work, we review the current strategies and mechanisms to control activity of CAR T-cells reversibly or irreversibly for preventing and for managing therapy-associated toxicities.

The graft-versus-leukemia effect of prophylactic donor lymphocyte infusions after allogeneic stem cell transplantation is equally effective in relapse prevention but safer compared to spontaneous graft-versus-host disease

Therapeutic donor lymphocyte infusions (tDLI) are used to reinforce the graft-versus-leukemia (GvL) effect in relapse after allogeneic stem cell transplantation (alloSCT). In contrast, the role of prophylactic DLI (proDLI) in preventing leukemia relapse has been less clearly established, although supported by retrospective, case-control, and registry analyses. We report a prospective, monocentric, ten year cohort of patients with high risk acute leukemias (AL) or myelodysplasia (MDS) in whom proDLI were applied beyond day +120 post alloSCT to compensate for lack of GvL.272 consecutive allotransplanted AL or MDS patients in complete remission and off immunosuppression at day +120 were stratified according to the prior appearance of relevant GvHD (acute GvHD °II-IV or extensive chronic GvHD) as a clinical indicator for GvL. Escalating doses of unmodified proDLI were applied to 72/272 patients without prior relevant GvHD. Conversely, 157/272 patients with prior spontaneous GvHD did not receive proDLI, nor did 43/272 patients with contraindications (uncontrolled infections, patient refusal, DLI unavailability).By day 160-landmark analysis (median day of first DLI application), proDLI recipients had significantly higher five-year overall (OS) and disease free survival (DFS) (77% and 67%) than patients with spontaneous GvHD (54% and 53%) or with contraindications (46% and 45%) (p=0.003). Relapse incidence for patients with proDLI (30%) or spontaneous GvHD (29%) was significantly lower than in patients with contraindications (39%; p=0.021). With similar GvHD incidence beyond day +160, non-relapse mortality (NRM) was less with proDLI (5%) than without proDLI (18%; p=0.036).In conclusion, proDLI may be able to compensate for lack of GvL in alloSCT recipients with high risk AL or MDS.

Enrichment strategies to enhance genome editing

Genome editing technologies hold great promise for numerous applications including the understanding of cellular and disease mechanisms and the development of gene and cellular therapies. Achieving high editing frequencies is critical to these research areas and to achieve the overall goal of being able to manipulate any target with any desired genetic outcome. However, gene editing technologies sometimes suffer from low editing efficiencies due to several challenges. This is often the case for emerging gene editing technologies, which require assistance for translation into broader applications. Enrichment strategies can support this goal by selecting gene edited cells from non-edited cells. In this review, we elucidate the different enrichment strategies, their many applications in non-clinical and clinical settings, and the remaining need for novel strategies to further improve genome research and gene and cellular therapy studies.

The future of CAR T-cell therapy for B-cell acute lymphoblastic leukemia in pediatrics and adolescents

INTRODUCTION

Antigen down-regulation and early chimeric antigen receptor (CAR) T cell loss have emerged as 2 major challenges threatening outcomes following CD19-specific CAR T cell therapy for children and young adults with B-cell acute lymphoblastic leukemia (B-ALL). In addressing the future of CAR T cell therapy for B-ALL, innovative strategies to avert antigen downregulation and enhance CAR persistence warrant prioritized focus.

AREAS COVERED

We describe promising engineering strategies to refine CAR constructs to reverse exhaustion, develop regulatable CARs, optimize manufacturing, enrich for immune memory and disrupt immune inhibition. We additionally focus on alternative targeting to CD19-monospecific targeting and contextualize possibilities for expanded CAR utilization.

EXPERT OPINION

We describe research advances as they are independently reported, however anticipate an integrative strategy incorporating complementary modifications will be required to effectively address CAR loss, overcome antigen downregulation and enhance reliability and durability of CAR T cell responses for B-ALL.

Tuning CARs: recent advances in modulating chimeric antigen receptor (CAR) T cell activity for improved safety, efficacy, and flexibility

Cancer immunotherapies utilizing genetically engineered T cells have emerged as powerful personalized therapeutic agents showing dramatic preclinical and clinical results, particularly in hematological malignancies. Ectopically expressed chimeric antigen receptors (CARs) reprogram immune cells to target and eliminate cancer. However, CAR T cell therapy's success depends on the balance between effective anti-tumor activity and minimizing harmful side effects. To improve CAR T cell therapy outcomes and mitigate associated toxicities, scientists from different fields are cooperating in developing next-generation products using the latest molecular cell biology and synthetic biology tools and technologies. The immunotherapy field is rapidly evolving, with new approaches and strategies being reported at a fast pace. This comprehensive literature review aims to provide an up-to-date overview of the latest developments in controlling CAR T cell activity for improved safety, efficacy, and flexibility.

How I treat high-risk acute myeloid leukemia using preemptive adoptive cellular immunotherapy

Allogeneic hematopoietic stem cell transplantation (alloHSCT) is a potentially curative treatment for patients with high-risk acute leukemias, but unfortunately disease recurrence remains the major cause of death in these patients. Infusion of donor lymphocytes (DLI) has the potential to restore graft-versus-leukemia immunologic surveillance; however, efficacy varies across different hematologic entities. Although relapsed chronic myeloid leukemia, transplanted in chronic phase, has proven remarkably susceptible to DLI, response rates are more modest for relapsed acute myeloid leukemia and acute lymphoblastic leukemia. To prevent impending relapse, a number of groups have explored administering DLI preemptively on detection of measurable residual disease (MRD) or mixed chimerism. Evidence for the effectiveness of this strategy, although encouraging, comes from only a few, mostly single-center retrospective, nonrandomized studies. This article seeks to (1) discuss the available evidence supporting this approach while highlighting some of the inherent challenges of MRD-triggered treatment decisions post-transplant, (2) portray other forms of postremission cellular therapies, including the role of next-generation target-specific immunotherapies, and (3) provide a practical framework to support clinicians in their decision-making process when considering preemptive cellular therapy for this difficult-to-treat patient population.

Bifunctional cancer cell-based vaccine concomitantly drives direct tumor killing and antitumor immunity

The administration of inactivated tumor cells is known to induce a potent antitumor immune response; however, the efficacy of such an approach is limited by its inability to kill tumor cells before inducing the immune responses. Unlike inactivated tumor cells, living tumor cells have the ability to track and target tumors. Here, we developed a bifunctional whole cancer cell-based therapeutic with direct tumor killing and immunostimulatory roles. We repurposed the tumor cells from interferon-β (IFN-β) sensitive to resistant using CRISPR-Cas9 by knocking out the IFN-β-specific receptor and subsequently engineered them to release immunomodulatory agents IFN-β and granulocyte-macrophage colony-stimulating factor. These engineered therapeutic tumor cells (ThTCs) eliminated established glioblastoma tumors in mice by inducing caspase-mediated cancer cell apoptosis, down-regulating cancer-associated fibroblast-expressed platelet-derived growth factor receptor β, and activating antitumor immune cell trafficking and antigen-specific T cell activation signaling. This mechanism-based efficacy of ThTCs translated into a survival benefit and long-term immunity in primary, recurrent, and metastatic cancer models in immunocompetent and humanized mice. The incorporation of a double kill-switch comprising herpes simplex virus-1 thymidine kinase and rapamycin-activated caspase 9 in ThTCs ensured the safety of our approach. Arming naturally neoantigen-rich tumor cells with bifunctional therapeutics represents a promising cell-based immunotherapy for solid tumors and establishes a road map toward clinical translation.

Safety switch optimization enhances antibody-mediated elimination of CAR T cells

Activation of a conditional safety switch has the potential to reverse serious toxicities arising from the administration of engineered cellular therapies, including chimeric antigen receptor (CAR) T cells. The functionally inert, non-immunogenic cell surface marker derived from human epidermal growth factor receptor (EGFRt) is a promising safety switch that has been used in multiple clinical constructs and can be targeted by cetuximab, a clinically available monoclonal antibody. However, this approach requires high and persistent cell surface expression of EGFRt to ensure that antibody-mediated depletion of engineered cells is rapid and complete. Here we show that incorporating a short juxtamembrane sequence into the EGFRt polypeptide enhances its expression on the surface of T cells and their susceptibility to antibody-dependent cellular cytotoxicity (ADCC). Incorporating this optimized variant (EGFRopt) into bicistronic and tricistronic CAR designs results in more rapid in vivo elimination of CAR T cells and robust termination of their effector activity compared to EGFRt. These studies establish EGFRopt as a superior safety switch for the development of next-generation cell-based therapeutics.

Emerging approaches for preventing cytokine release syndrome in CAR-T cell therapy

Chimeric antigen receptor (CAR) T cells have demonstrated remarkable anti-tumor efficacy against hematological malignancies, such as leukemia and lymphoma. However, patients treated with CAR-T cells frequently experience cytokine release syndrome (CRS), one of the most life-threatening adverse events of the therapy induced by systemic concentrations of pro-inflammatory cytokines throughout the body. Immunosuppressants such as tocilizumab are currently administered to treat the onset and progression of CRS symptoms. In order to reduce the risk of CRS, newly designed next-generation CAR-T treatments are being developed for both hematopoietic malignancies and solid tumors. In this review, we discuss six classes of interesting approaches that control cytokine production of CAR-T cell therapy: adaptor-based strategies, orthogonal cytokine-receptor pairs, regulation of macrophage cytokine activity, autonomous neutralization of key cytokines, kill switches and methods of reversible suppression of CARs. With these strategies, future CAR-T cell therapies will be designed to preemptively inhibit CRS, minimize the patients' suffering, and maximize the number of benefiting patients.

Optimized NGFR-derived hinges for rapid and efficient enrichment and detection of CAR T cells in vitro and in vivo

Chimeric antigen receptor (CAR) T cell therapy has demonstrated unprecedented success with high remission rates for heavily pretreated patients with hematological malignancies. The hinge connecting the extracellular antigen recognition unit to the transmembrane domain provides the length and flexibility of the CAR constructs and ensures that the CAR can reach the target antigen and mediate recognition and killing of target cells. The hinge can also include specific amino acid sequences to improve CAR expression, influence T cell proliferation, and facilitate CAR T cell detection, enrichment, and even elimination. Here, we report the generation of two novel hinge domains derived from the low-affinity p75 chain of the human nerve growth factor receptor (NGFR), termed N3 and N4, which, when incorporated into the CAR backbone, allow detection as well as high-grade enrichment of CAR T cells with GMP-compatible immunomagnetic reagents. After optimizing the MACS protocol for excellent CAR T cell purity and yield, we demonstrated that N3- and N4-hinged CAR T cells are as efficacious as their CD8-hinged counterparts in vitro against hematological blasts and also in vivo in the control of acute monocytic leukemia in an immunodeficient mouse xenograft model. Thus, both hinges could potentially be an integral part of future CAR designs and universally applicable in clinical applications.

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

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

Emerging Novel Combined CAR-T Cell Therapies

Simple Summary

As a result of FDA approval of CAR-T cell treatments in the last few years, this immunotherapy has provided further direction to precision medicine through its combination with other therapeutic approaches. In the past year, several review articles have been published focusing on advances in this fast-developing field, especially with respect to efforts to overcome hurdles associated with applying CAR-T cells in solid tumors. This review paper focuses on combining CAR-T cell therapy with small molecule drugs, up-to-date progress in CAR-T cell therapy research, and advances in combined CAR-T immunotherapy with other treatments targeting solid tumors.

Abstract

Chimeric antigen receptors (CAR) T cells are T cells engineered to express membrane receptors with high specificity to recognize specific target antigens presented by cancer cells and are co-stimulated with intracellular signals to increase the T cell response. CAR-T cell therapy is emerging as a novel therapeutic approach to improve T cell specificity that will lead to advances in precision medicine. CAR-T cells have had impressive outcomes in hematological malignancies. However, there continue to be significant limitations of these therapeutic responses in targeting solid malignancies such as heterogeneous antigens in solid tumors, tumor immunosuppressive microenvironment, risk of on-target/off-tumor, infiltrating CAR-T cells, immunosuppressive checkpoint molecules, and cytokines. This review paper summarizes recent approaches and innovations through combination therapies of CAR-T cells and other immunotherapy or small molecule drugs to counter the above disadvantages to potentiate the activity of CAR-T cells.

Chimeric antigen receptor T-cell therapy in acute myeloid leukemia

PURPOSE OF REVIEW

Treatment outcome of relapsed or refractory AML patients remains dismal and new treatment options are needed. Adoptive cell therapy using CAR-T cells is a potentially interesting approach in this.

RECENT FINDINGS

Several potentially interesting AML targets are being investigated with CAR-T therapy with over 60 clinical trials listed on clinicaltrials.gov. The first clinical data are only just emerging with mixed results, once more proving that further research is needed.

SUMMARY

Adoptive cell therapy using chimeric antigen receptor T cells is being investigated in AML through many clinical trials. So far, no AML-specific antigen has been identified, requiring additional strategies to mitigate on-target off-tumor toxicity and to increase efficacy. Focus point is to acquire control over the CAR T cells once administered. Strategies to do so include biodegradable CARs, inducible CARs, suicide-switch containing CARs and two-component modular CARs. Limited and mixed results are available, confirming the risk of lasting toxicity for nonswitchable CARs. Initial results of modular CARs suggest toxicity can be mitigated whilst maintaining CAR activity by the use of modular CAR concepts that allows for 'ON' and 'OFF' switching.

KIR in Allogeneic Hematopoietic Stem Cell Transplantation: Need for a Unified Paradigm for Donor Selection

Allogeneic hematopoietic stem cell transplantation (aHSCT) is a lifesaving therapy for hematological malignancies. For years, a fully matched HLA donor was a requisite for the procedure. However, new immunosuppressive strategies have enabled the recruitment of viable alternative donors, particularly haploidentical donors. Over 95% of patients have at least two potential haploidentical donors available to them. To identify the best haploidentical donor, the assessment of new immunogenetic criteria could help. To this end, the clinical benefit of KIR genotyping in aHSCT has been widely studied but remains contentious. This review aims to evaluate the importance of KIR-driven NK cell alloreactivity in the context of aHSCT and explain potential reasons for the discrepancies in the literature. Here, through a non-systematic review, we highlight how the studies in this field and their respective predictive models or scoring strategies could be conceptually opposed, explaining why the role of NK cells remains unclear in aHCST outcomes. We evaluate the limitations of each published prediction model and describe how every scoring strategy to date only partly delivers the requirements for optimally effective NK cells in aHSCT. Finally, we propose approaches toward finding the optimal use of KIR genotyping in aHSCT for a unified criterion for donor selection.

Optimizing allogeneic grafts in hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is widely used in the treatment of hematological diseases. It is well known that allogeneic grafts play a key role in predicting transplantation prognosis. Hematopoietic stem cells (HSCs) are a functional part of grafts and are capable of reconstructing hematopoiesis and immunity, but purified HSCs have not been identified or isolated to date. In clinical practice, allogeneic grafts have been optimized to improve transplantation outcomes. The optimized grafts are considered to engraft successfully, reconstruct immunity rapidly, and exert a graft-vs-leukemia (GVL) effect without causing severe graft-vs-host disease (GvHD). In the last several decades, considerable efforts have been made in searching for optimized grafts based on different graft manipulation approaches and different graft sources. Currently, there is no uniform standard for optimized grafts in allogeneic transplantation. In the future, sorting out the cellular elements responsible for the effects of allo-HSCT might be a research direction for further optimization of grafts. In this review, we propose the concept of optimized grafts and summarize the recent advances made in the process of optimizing grafts.

Depletion of T cells via Inducible Caspase 9 Increases Safety of Adoptive T-Cell Therapy Against Chronic Hepatitis B

T-cell therapy with T cells that are re-directed to hepatitis B virus (HBV)-infected cells by virus-specific receptors is a promising therapeutic approach for treatment of chronic hepatitis B and HBV-associated cancer. Due to the high number of target cells, however, side effects such as cytokine release syndrome or hepatotoxicity may limit safety. A safeguard mechanism, which allows depletion of transferred T cells on demand, would thus be an interesting means to increase confidence in this approach. In this study, T cells were generated by retroviral transduction to express either an HBV-specific chimeric antigen receptor (S-CAR) or T-cell receptor (TCR), and in addition either inducible caspase 9 (iC9) or herpes simplex virus thymidine kinase (HSV-TK) as a safety switch. Real-time cytotoxicity assays using HBV-replicating hepatoma cells as targets revealed that activation of both safety switches stopped cytotoxicity of S-CAR- or TCR-transduced T cells within less than one hour. In vivo, induction of iC9 led to a strong and rapid reduction of transferred S-CAR T cells adoptively transferred into AAV-HBV-infected immune incompetent mice. One to six hours after injection of the iC9 dimerizer, over 90% reduction of S-CAR T cells in the blood and the spleen and of over 99% in the liver was observed, thereby limiting hepatotoxicity and stopping cytokine secretion. Simultaneously, however, the antiviral effect of S-CAR T cells was diminished because remaining S-CAR T cells were mostly non-functional and could not be restimulated with HBsAg. A second induction of iC9 was only able to deplete T cells in the liver. In conclusion, T cells co-expressing iC9 and HBV-specific receptors efficiently recognize and kill HBV-replicating cells. Induction of T-cell death via iC9 proved to be an efficient means to deplete transferred T cells in vitro and in vivo containing unwanted hepatotoxicity.

Conditional control of chimeric antigen receptor T-cell activity through a destabilizing domain switch and its chemical ligand

BACKGROUND AIMS

Despite the impressive efficacy of chimeric antigen receptor (CAR) T-cell therapy, adverse effects, including cytokine release syndrome and neurotoxicity, impede its therapeutic application, thus making the modulation of CAR T-cell activity a priority. The destabilizing domain mutated from Escherichia coli dihydrofolate reductase (DHFR) is inherently unstable and degraded by proteasomes unless it is stabilized by its chemical ligand trimethoprim (TMP), a Food and Drug Administration-approved drug. Here the authors reveal a strategy to modulate CAR T-cell activity at the protein level by employing DHFR and TMP as a chemical switch system.

METHODS

First, the system was demonstrated to work in human primary T cells. To introduce the system to CAR T cells, DHFR was genetically fused to the carboxyl terminal of a third-generation CAR molecule targeting CD19 (CD19-CAR), constructing the CD19-CAR-DHFR fusion.

RESULTS

The CD19-CAR-DHFR molecule level was shown to be modulated by TMP. Importantly, the incorporation of DHFR had no impact on the recognition specificity and normal function of the CAR molecule. Little adverse effect on cell proliferation and apoptosis was detected. It was proved that TMP could regulate cytokine secretion and the in vitro cytotoxicity of CD19-CAR-DHFR T cells. Furthermore, the in vivo anti-tumor efficacy was demonstrated to be controllable through the manipulation of TMP administration. The approach to control CD19-CAR also succeeded in 19-BBZ(71), another CD19-targeting CAR with a different structure.

CONCLUSIONS

The proposed approach based on DHFR and TMP provides a facile strategy to bring CAR T-cell therapy under conditional user control, and the strategy may have the potential to be transplantable.

Peripheral blood stem and progenitor cell collection in pediatric candidates for ex vivo gene therapy: a 10-year series

Hematopoietic stem and progenitor cell (HSPC)-based gene therapy (GT) requires the collection of a large number of cells. While bone marrow (BM) is the most common source of HSPCs in pediatric donors, the collection of autologous peripheral blood stem cells (PBSCs) is an attractive alternative for GT. We present safety and efficacy data of a 10-year cohort of 45 pediatric patients who underwent PBSC collection for backup and/or purification of CD34⁺ cells for ex vivo gene transfer. Median age was 3.7 years and median weight 15.8 kg. After mobilization with lenograstim/plerixafor (n = 41) or lenograstim alone (n = 4) and 1−3 cycles of leukapheresis, median collection was 37 × 10⁶ CD34⁺ cells/kg. The procedures were well tolerated. Patients who collected ≥7 and ≥13 × 10⁶ CD34⁺ cells/kg in the first cycle had pre-apheresis circulating counts of at ≥42 and ≥86 CD34⁺ cells/μL, respectively. Weight-adjusted CD34⁺ cell yield was positively correlated with peripheral CD34⁺ cell counts and influenced by female gender, disease, and drug dosage. All patients received a GT product above the minimum target, ranging from 4 to 30.9 × 10⁶ CD34⁺ cells/kg. Pediatric PBSC collection compares well to BM harvest in terms of CD34⁺ cell yields for the purpose of GT, with a favorable safety profile.

Retroviral gene therapy in Germany with a view on previous experience and future perspectives

Gene therapy can be used to restore cell function in monogenic disorders or to endow cells with new capabilities, such as improved killing of cancer cells, expression of suicide genes for controlled elimination of cell populations, or protection against chemotherapy or viral infection. While gene therapies were originally most often used to treat monogenic diseases and to improve hematopoietic stem cell transplantation outcome, the advent of genetically modified immune cell therapies, such as chimeric antigen receptor modified T cells, has contributed to the increased numbers of patients treated with gene and cell therapies. The advancement of gene therapy with integrating retroviral vectors continues to depend upon world-wide efforts. As the topic of this special issue is "Spotlight on Germany," the goal of this review is to provide an overview of contributions to this field made by German clinical and research institutions. Research groups in Germany made, and continue to make, important contributions to the development of gene therapy, including design of vectors and transduction protocols for improved cell modification, methods to assess gene therapy vector efficacy and safety (e.g., clonal imbalance, insertion sites), as well as in the design and conduction of clinical gene therapy trials.

The Role of Allogeneic Hematopoietic Stem Cell Transplantation in Pediatric Leukemia

Allogeneic hematopoietic stem cell transplantation (HSCT) offers potentially curative treatment for many children with high-risk or relapsed acute leukemia (AL), thanks to the combination of intense preparative radio/chemotherapy and the graft-versus-leukemia (GvL) effect. Over the years, progress in high-resolution donor typing, choice of conditioning regimen, graft-versus-host disease (GvHD) prophylaxis and supportive care measures have continuously improved overall transplant outcome, and recent successes using alternative donors have extended the potential application of allotransplantation to most patients. In addition, the importance of minimal residual disease (MRD) before and after transplantation is being increasingly clarified and MRD-directed interventions may be employed to further ameliorate leukemia-free survival after allogeneic HSCT. These advances have occurred in parallel with continuous refinements in chemotherapy protocols and the development of targeted therapies, which may redefine the indications for HSCT in the coming years. This review discusses the role of HSCT in childhood AL by analysing transplant indications in both acute lymphoblastic and acute myeloid leukemia, together with current and most promising strategies to further improve transplant outcome, including optimization of conditioning regimen and MRD-directed interventions.

Novel CAR T therapy is a ray of hope in the treatment of seriously ill AML patients

Acute myeloid leukemia (AML) is a serious, life-threatening, and hardly curable hematological malignancy that affects the myeloid cell progenies and challenges patients of all ages but mostly occurs in adults. Although several therapies are available including chemotherapy, allogeneic hematopoietic stem cell transplantation (alloHSCT), and receptor-antagonist drugs, the 5-year survival of patients is quietly disappointing, less than 30%. alloHSCT is the major curative approach for AML with promising results but the treatment has severe adverse effects such as graft-versus-host disease (GVHD). Therefore, as an alternative, more efficient and less harmful immunotherapy-based approaches such as the adoptive transferring T cell therapy are in development for the treatment of AML. As such, chimeric antigen receptor (CAR) T cells are engineered T cells which have been developed in recent years as a breakthrough in cancer therapy. Interestingly, CAR T cells are effective against both solid tumors and hematological cancers such as AML. Gradually, CAR T cell therapy found its way into cancer therapy and was widely used for the treatment of hematologic malignancies with successful results particularly with somewhat better results in hematological cancer in comparison to solid tumors. The AML is generally fatal, therapy-resistant, and sometimes refractory disease with a disappointing low survival rate and weak prognosis. The 5-year survival rate for AML is only about 30%. However, the survival rate seems to be age-dependent. Novel CAR T cell therapy is a light at the end of the tunnel. The CD19 is an important target antigen in AML and lymphoma and the CAR T cells are engineered to target the CD19. In addition, a lot of research goes on the discovery of novel target antigens with therapeutic efficacy and utilizable for generating CAR T cells against various types of cancers. In recent years, many pieces of research on screening and identification of novel AML antigen targets with the goal of generation of effective anti-cancer CAR T cells have led to new therapies with strong cytotoxicity against cancerous cells and impressive clinical outcomes. Also, more recently, an improved version of CAR T cells which were called modified or smartly reprogrammed CAR T cells has been designed with less unwelcome effects, less toxicity against normal cells, more safety, more specificity, longer persistence, and proliferation capability. The purpose of this review is to discuss and explain the most recent advances in CAR T cell-based therapies targeting AML antigens and review the results of preclinical and clinical trials. Moreover, we will criticize the clinical challenges, side effects, and the different strategies for CAR T cell therapy.

Navigating CAR-T cells through the solid-tumour microenvironment

The adoptive transfer of T cells that are engineered to express chimeric antigen receptors (CARs) has shown remarkable success in treating B cell malignancies but only limited efficacy against other cancer types, especially solid tumours. Compared with haematological diseases, solid tumours present a unique set of challenges, including a lack of robustly expressed, tumour-exclusive antigen targets as well as highly immunosuppressive and metabolically challenging tumour microenvironments that limit treatment safety and efficacy. Here, we review protein- and cell-engineering strategies that seek to overcome these obstacles and produce next-generation T cells with enhanced tumour specificity and sustained effector function for the treatment of solid malignancies.

Bringing Advanced Therapies for Parkinson's Disease to the Clinic: The Scientist's Perspective

After many years of preclinical development, cell and gene therapies have advanced from research tools in the lab to clinical-grade products for patients, and today they constitute more than a quarter of all new Phase I clinical trials for Parkinson’s disease. Whereas efficacy has been convincingly proven for many of these products in preclinical models, the field is now entering a new phase where the functionality and safety of these products will need to stand the test in clinical trials. If successful, these new products can have the potential to provide patients with a one-time administered treatment which may alleviate them from daily symptomatic dopaminergic medication.

Optogenetic Control of Non-Apoptotic Cell Death

Herein, a set of optogenetic tools (designated LiPOP) that enable photoswitchable necroptosis and pyroptosis in live cells with varying kinetics, is introduced. The LiPOP tools allow reconstruction of the key molecular steps involved in these two non-apoptotic cell death pathways by harnessing the power of light. Further, the use of LiPOPs coupled with upconversion nanoparticles or bioluminescence is demonstrated to achieve wireless optogenetic or chemo-optogenetic killing of cancer cells in multiple mouse tumor models. LiPOPs can trigger necroptotic and pyroptotic cell death in cultured prokaryotic or eukaryotic cells and in living animals, and set the stage for studying the role of non-apoptotic cell death pathways during microbial infection and anti-tumor immunity.

Optimization of CAR-T Cell-Based Therapies Using Small-Molecule-Based Safety Switches

Chimeric antigen receptor T cell therapy has demonstrated antileukemia efficacy. However, this therapeutic approach is hampered by severe cytokine release syndrome, which is a major impediment to its widespread application in the clinic. The safety of this approach can be improved by engineering a rapid and reversible "off" or "on" safety switch for CAR-T cells. Cutting-edge investigations combining the advantages of genetic engineering and chemical technology have led to the invention of small-molecule-based safety switches for CAR-T cells. Small molecules such as FITC, folate, rimiducid, rapamycin, proteolysis-targeting chimera (PROTAC) compounds, and dasatinib are being investigated to design such safety switches. Optimized CAR-T cells may have enhanced therapeutic efficiency with fewer adverse effects. Herein we summarize and classify current novel small-molecule-based safety switches for CAR-T cells that aim to provide pharmacological control over the activities and toxicities associated with CAR-T cell-based cancer immunotherapies.

Adoptive cell therapy for solid tumors: Chimeric antigen receptor T cells and beyond

Adoptive cell therapy with chimeric antigen receptor T cells has caused a significant revolution in the treatment of hematological malignancies. Unfortunately, for solid tumors, this treatment modality has been proven insufficient to achieve significant antitumor activity. The use of modified T cell receptors towards tumor-associated antigens (NY-ESO, MAGE-A4) has recently shown antitumor activity in synovial sarcoma. Also, treatment with tumor-infiltrating lymphocytes shows clinical activity in metastatic cervical cancer and melanoma resistant to checkpoint inhibitors. Strategies to improve results and broaden the applicability of therapeutic lymphocytes for solid tumors include local delivery, fourth generation chimeric antigen receptor T cells, off-the-shelf T lymphocytes and private neoantigen-directed cells, among others. In this review, we summarize the status of adoptive cell therapy using T cells for solid tumors and the investigational strategies being tested in this field.

Efficient Genetic Safety Switches for Future Application of iPSC-Derived Cell Transplants

Induced pluripotent stem cell (iPSC)-derived cell products hold great promise as a potential cell source in personalized medicine. As concerns about the potential risk of graft-related severe adverse events, such as tumor formation from residual pluripotent cells, currently restrict their applicability, we established an optimized tool for therapeutic intervention that allows drug-controlled, specific and selective ablation of either iPSCs or the whole graft through genetic safety switches. To identify the best working system, different tools for genetic iPSC modification, promoters to express safety switches and different safety switches were combined. Suicide effects were slightly stronger when the suicide gene was delivered through lentiviral (LV) vectors compared to integration into the AAVS1 locus through TALEN technology. An optimized HSV-thymidine kinase and the inducible Caspase 9 both mediated drug-induced, efficient in vitro elimination of transgene-positive iPSCs. Choice of promoter allowed selective elimination of distinct populations within the graft: the hOct4 short response element restricted transgene expression to iPSCs, while the CAGs promoter ubiquitously drove expression in iPSCs and their progeny. Remarkably, both safety switches were able to prevent in vivo teratoma development and even effectively eliminated established teratomas formed by LV CAGs-transgenic iPSCs. These optimized tools to increase safety provide an important step towards clinical application of iPSC-derived transplants.

Improved safety of induced pluripotent stem cell-derived antigen-presenting cell-based cancer immunotherapy

The tumorigenicity and toxicity of induced pluripotent stem cells (iPSCs) and their derivatives are major safety concerns in their clinical application. Recently, we developed granulocyte-macrophage colony-stimulating factor (GM-CSF)-producing proliferating myeloid cells (GM-pMCs) from mouse iPSCs as a source of unlimited antigen-presenting cells for use in cancer immunotherapy. As GM-pMCs are generated by introducing c-Myc and Csf2 into iPSC-derived MCs and are dependent on self-produced GM-CSF for proliferation, methods to control their proliferation after administration should be introduced to improve safety. In this study, we compared the efficacy of two promising suicide gene systems, herpes simplex virus-thymidine kinase (HSV-TK)/ganciclovir (GCV) and inducible caspase-9 (iCasp9)/AP1903, for safeguarding GM-pMCs in cancer immunotherapy. The expression of HSV-TK or iCasp9 did not impair the fundamental properties of GM-pMCs. Both of these suicide gene-expressing cells selectively underwent apoptosis after treatment with the corresponding apoptosis-inducing drug, and they were promptly eliminated in vivo. iCasp9/AP1903 induced apoptosis more efficiently than HSV-TK/GCV. Furthermore, high concentrations of GCV were toxic to cells not expressing HSV-TK, whereas AP1903 was bioinert. These results suggest that iCasp9/AP1903 is superior to HSV-TK/GCV in terms of both safety and efficacy when controlling the fate of GM-pMCs after priming antitumor immunity.

Characterization and Functional Analysis of CD44v6.CAR T Cells Endowed with a New Low-Affinity Nerve Growth Factor Receptor-Based Spacer

Effectiveness of adoptively transferred chimeric antigen receptor (CAR) T cells strongly depends on the quality of CAR-mediated interaction of the effector cells with the target antigen on tumor cells. A major role in this interaction is played by the affinity of the single-chain variable fragment (scFv) for the antigen, and by the CAR design. In particular, the spacer domain may impact on the CAR T cell function by affecting the length and flexibility of the resulting CAR. This study addresses the need to improve the manufacturing process and the antitumor activity of CD44v6-specific CAR T cells by defining the optimal structure of a spacer region derived from the extracellular domain of the human low-affinity nerve growth factor receptor (LNGFR). We tailored the LNGFR spacer to modulate CAR length to efficiently recognize distal or proximal epitopes and to allow selection of transduced CAR T cells by the use of clinical-grade validated manufacturing systems. The different LNGFR spacers investigated in this study are responsible for the generation of CAR T cells with a different memory phenotype, which is mainly related to the level of CAR expression and the extent of the associated tonic signaling. In particular, the CD44v6-NWN2.CAR T cells are enriched in central memory cells and show improved in vitro functions in terms of killing capability, and in vivo antitumor activity against hematological and solid tumors. Clinical Trial Registration numbers: clinicaltrial.gov NCT04097301; ClinicalTrials.gov, NCT00423124.

CAR-T cell persistence in the treatment of leukemia and lymphoma

Chimeric antigen receptor (CAR) T cells have emerged as a powerful therapeutic modality for cancer. Following encouraging clinical results, autologous anti-CD19 CAR-T cells first secured regulatory approval from the U.S. Food and Drug Administration in 2017 for the treatment of pediatric B cell acute lymphoblastic leukemia and for diffuse large B cell lymphoma (DLBCL), followed recently by mantle cell lymphoma. While long-term immunosurveillance is among the most important requirements for durable remissions in leukemia and a major potential benefit of immunotherapy, the exact determinants of CAR-T cell persistence remain elusive. Furthermore, it is less clear that long-term persistence is required for durable remission in lymphoma. In this review, we aim to describe the factors governing CAR-T cell persistence as well as unique approaches to exert control over engineered lymphocyte populations post-infusion. Additionally, we explore potential risks and associated clinical considerations arising from prolonged surveillance by highly reactive cytotoxic T lymphocytes.

Prodrugs and prodrug-activated systems in gene therapy

The inclusion of genes that control cell fate (so-called suicide, or kill-switch, genes) into gene therapy vectors is based on a compelling rationale for the safe and selective elimination of aberrant transfected cells. Prodrug-activated systems were developed in the 1980s and 1990s and rely on the enzymatic conversion of non-active prodrugs to active metabolites that lead to cell death. Although considerable effort and ingenuity has gone into vector design for gene therapy, less attention has been directed at the efficacy or associated adverse effects of the prodrug systems employed. In this review, we discuss prodrug systems employed in clinical trials and consider their role in the field of gene therapy. We highlight potential drawbacks associated with the use of specific prodrugs, such as systemic toxicity of the activated compound, the paucity of data on biodistribution of prodrugs, bystander effects, and destruction of genetically modified cells, and how these can inform future advances in cell therapies.