Eras of designer Tregs: Harnessing synthetic biology for immune suppression

Chimeric antigen receptor T cell therapy for autoimmune disease

Infusion of T cells engineered to express chimeric antigen receptors (CARs) that target B cells has proven to be a successful treatment for B cell malignancies. This success inspired the development of CAR T cells to selectively deplete or modulate the aberrant immune responses that underlie autoimmune disease. Promising results are emerging from clinical trials of CAR T cells targeting the B cell protein CD19 in patients with B cell-driven autoimmune diseases. Further approaches are being designed to extend the application and improve safety of CAR T cell therapy in the setting of autoimmunity, including the use of chimeric autoantibody receptors to selectively deplete autoantigen-specific B cells and the use of regulatory T cells engineered to express antigen-specific CARs for targeted immune modulation. Here, we highlight important considerations, such as optimal target cell populations, CAR construct design, acceptable toxicities and potential for lasting immune reset, that will inform the eventual safe adoption of CAR T cell therapy for the treatment of autoimmune diseases.

Role of FoxP3+ Regulatory T Cells in Modulating Immune Responses to Adeno-Associated Virus Gene Therapy

Adeno-associated virus (AAV) gene therapy is making rapid strides owing to its wide range of therapeutic applications. However, development of serious immune responses to the capsid antigen or the therapeutic transgene product hinders its full clinical impact. Immune suppressive (IS) drug treatments have been used in various clinical trials to prevent the deleterious effects of cytotoxic T cells to the viral vector or transgene, although there is no consensus on the best treatment regimen, dosage, or schedule. Regulatory T cells (Tregs) are crucial for maintaining tolerance against self or nonself antigens. Of importance, Tregs also play an important role in dampening immune responses to AAV gene therapy, including tolerance induction to the transgene product. Approaches to harness the tolerogenic effect of Tregs include the use of selective IS drugs that expand existing Tregs, and skew activated conventional T cells into antigen-specific peripherally induced Tregs. In addition, Tregs can be expanded ex vivo and delivered as cellular therapy. Furthermore, receptor engineering can be used to increase the potency and specificity of Tregs allowing for suppression at lower doses and reducing the risk of disrupting protective immunity. Because immune-mediated toxicities to AAV vectors are a concern in the clinic, strategies that can enhance or preserve Treg function should be considered to improve both the safety and efficacy of AAV gene therapy.

Genetic engineering of regulatory T cells for treatment of autoimmune disorders including type 1 diabetes

Suppression of pathogenic immune responses is a major goal in the prevention and treatment of type 1 diabetes. Adoptive cell therapy using regulatory T cells (Tregs), a naturally suppressive immune subset that is often dysfunctional in type 1 diabetes, is a promising approach to achieving localised and specific immune suppression in the pancreas or site of islet transplant. However, clinical trials testing administration of polyclonal Tregs in recent-onset type 1 diabetes have observed limited efficacy despite an excellent safety profile. Several barriers to efficacy have been identified, including lack of antigen specificity, low cell persistence post-administration and difficulty in generating sufficient cell numbers. Fortunately, the emergence of advanced gene editing techniques has opened the door to new strategies to engineer Tregs with improved specificity and function. These strategies include the engineering of FOXP3 expression to produce a larger source of suppressive cells for infusion, expressing T cell receptors or chimeric antigen receptors to generate antigen-specific Tregs and improving Treg survival by targeting cytokine pathways. Although these approaches are being applied in a variety of autoimmune and transplant contexts, type 1 diabetes presents unique opportunities and challenges for the genetic engineering of Tregs for adoptive cell therapy. Here we discuss the role of Tregs in type 1 diabetes pathogenesis and the application of Treg engineering in the context of type 1 diabetes.

Engineering an Autonucleolytic Mammalian Suspension Host Cell Line to Reduce DNA Impurity Levels in Serum-Free Lentiviral Process Streams

We engineered HEK293T cells with a transgene encoding tetracycline-inducible expression of a Staphylococcus aureus nuclease incorporating a translocation signal. We adapted the unmodified and nuclease-engineered cell lines to grow in suspension in serum-free media, generating the HEK293TS and NuPro-2S cell lines, respectively. Transient transfection yielded 1.19 × 106 lentiviral transducing units per milliliter (TU/mL) from NuPro-2S cells and 1.45 × 106 TU/mL from HEK293TS cells. DNA ladder disappearance revealed medium-resident nuclease activity arising from NuPro-2S cells in a tetracycline-inducible manner. DNA impurity levels in lentiviral material arising from NuPro-2S and HEK293TS cells were undetectable by SYBR Safe agarose gel staining. Direct measurement by PicoGreen reagent revealed DNA to be present at 636 ng/mL in lentiviral material from HEK293TS cells, an impurity level reduced by 89% to 70 ng/mL in lentiviral material from NuPro-2S cells. This reduction was comparable to the 23 ng/mL achieved by treating HEK293TS-derived lentiviral material with 50 units/mL Benzonase.

Promises and Pitfalls of Next-Generation Treg Adoptive Immunotherapy

Regulatory T cells (Tregs) are fundamental to maintaining immune homeostasis by inhibiting immune responses to self-antigens and preventing the excessive activation of the immune system. Their functions extend beyond immune surveillance and subpopulations of tissue-resident Treg cells can also facilitate tissue repair and homeostasis. The unique ability to regulate aberrant immune responses has generated the concept of harnessing Tregs as a new cellular immunotherapy approach for reshaping undesired immune reactions in autoimmune diseases and allo-responses in transplantation to ultimately re-establish tolerance. However, a number of issues limit the broad clinical applicability of Treg adoptive immunotherapy, including the lack of antigen specificity, heterogeneity within the Treg population, poor persistence, functional Treg impairment in disease states, and in vivo plasticity that results in the loss of suppressive function. Although the early-phase clinical trials of Treg cell therapy have shown the feasibility and tolerability of the approach in several conditions, its efficacy has remained questionable. Leveraging the smart tools and platforms that have been successfully developed for primary T cell engineering in cancer, the field has now shifted towards "next-generation" adoptive Treg immunotherapy, where genetically modified Treg products with improved characteristics are being generated, as regards antigen specificity, function, persistence, and immunogenicity. Here, we review the state of the art on Treg adoptive immunotherapy and progress beyond it, while critically evaluating the hurdles and opportunities towards the materialization of Tregs as a living drug therapy for various inflammation states and the broad clinical translation of Treg therapeutics.