Increased expression of CD70 in relapsed acute myeloid leukemia after hypomethylating agents.

Acute myeloid leukemia (AML) is the most common acute leukemia in adults. While induction chemotherapy leads to remission in most patients, a significant number will experience relapse. Therefore, there is a need for novel therapies that can improve remission rates in patients with relapsed and refractory AML. CD70 is the natural ligand for CD27 (a member of the TNF superfamily) and appears to be a promising therapeutic target. Consequently, there is considerable interest in developing chimeric antigen receptor (CAR) T-cell therapy products that can specifically target CD70 in various neoplasms, including AML. In this study, we employed routine diagnostic techniques, such as immunohistochemistry and flow cytometry, to investigate the expression of CD70 in bone marrow samples from treatment-naïve and relapsed AML patients after hypomethylating agents (HMA). Also, we evaluated the impact of HMA on CD70 expression and examined CD70 expression in various leukemic cell subsets and normal hematopoietic progenitors.

Constitutive Turbodomains enhance expansion and antitumor activity of allogeneic BCMA CAR T cells in preclinical models.

The magnitude of CAR T cell expansion has been associated with clinical efficacy. Although cytokines can augment CAR T cell proliferation, systemically administered cytokines can result in toxicities. To gain the benefits of cytokine signaling while mitigating toxicities, we designed constitutively active synthetic cytokine receptor chimeras (constitutive Turbodomains) that signal in a CAR T cell-specific manner. The modular design of Turbodomains enables diverse cytokine signaling outputs from a single homodimeric receptor chimera and allows multiplexing of different cytokine signals. Turbodomains containing an IL-2/15Rß-derived signaling domain closely mimicked IL-15 signaling and enhanced CAR T cell potency. Allogeneic TurboCAR T cells targeting BCMA showed no evidence of aberrant proliferation yet displayed enhanced expansion and antitumor activity, prolonging survival and preventing extramedullary relapses in mouse models. These results illustrate the potential of constitutive Turbodomains to achieve selective potentiation of CAR T cells and demonstrate the safety and efficacy of allogeneic BCMA TurboCAR T cells, supporting clinical evaluation in multiple myeloma.

Allogeneic CAR T Cells Targeting DLL3 Are Efficacious and Safe in Preclinical Models of Small Cell Lung Cancer.

PURPOSE: Small cell lung cancer (SCLC) is an aggressive disease with limited treatment options. Delta-like ligand 3 (DLL3) is highly expressed on SCLC and several other types of neuroendocrine cancers, with limited normal tissue RNA expression in brain, pituitary, and testis, making it a promising CAR T-cell target for SCLC and other solid tumor indications. EXPERIMENTAL DESIGN: A large panel of anti-DLL3 scFv-based CARs were characterized for both in vitro and in vivo activity. To understand the potential for pituitary and brain toxicity, subcutaneous or intracranial tumors expressing DLL3 were implanted in mice and treated with mouse cross-reactive DLL3 CAR T cells. RESULTS: A subset of CARs demonstrated high sensitivity for targets with low DLL3 density and long-term killing potential in vitro. Infusion of DLL3 CAR T cells led to robust antitumor efficacy, including complete responses, in subcutaneous and systemic SCLC in vivo models. CAR T-cell infiltration into intermediate and posterior pituitary was detected, but no tissue damage in brain or pituitary was observed, and the hormone-secretion function of the pituitary was not ablated. CONCLUSIONS: In summary, the preclinical efficacy and safety data presented here support further evaluation of DLL3 CAR T cells as potential clinical candidates for the treatment of SCLC.

Design and Validation of Inducible TurboCARs with Tunable Induction and Combinatorial Cytokine Signaling.

Although cytokine support can enhance CAR T-cell function, coadministering cytokines or engineering CAR T cells to secrete cytokines can result in toxicities. To mitigate these safety risks, we engineered iTurboCAR T cells that coexpress a novel inducible Turbo (iTurbo) cytokine signaling domain. iTurbo domains consist of modular components that are customizable to a variety of activating inputs, as well as cytokine signaling outputs multiplexable for combinatorial signaling outcomes. Unlike most canonical cytokine receptors that are heterodimeric, iTurbo domains leverage a compact, homodimeric design that minimizes viral vector cargo. Using an iTurbo domain activated by the clinically validated dimerizer, AP1903, homodimeric iTurbo domains instigated signaling that mimicked the endogenous heterodimeric cytokine receptor. Different iTurbo domains programmed iTurboCAR T cells toward divergent phenotypes and resulted in improved antitumor efficacy. iTurbo domains, therefore, offer the flexibility for user-programmable signaling outputs, permitting control over cellular phenotype and function while minimizing viral cargo footprint.

Preclinical Development and Evaluation of Allogeneic CAR T Cells Targeting CD70 for the Treatment of Renal Cell Carcinoma.

CD70 is highly expressed in renal cell carcinoma (RCC), with limited expression in normal tissue, making it an attractive CAR T target for an immunogenic solid tumor indication. Here we generated and characterized a panel of anti-CD70 single-chain fragment variable (scFv)-based CAR T cells. Despite the expression of CD70 on T cells, production of CAR T cells from a subset of scFvs with potent in vitro activity was achieved. Expression of CD70 CARs masked CD70 detection in cis and provided protection from CD70 CAR T cell-mediated fratricide. Two distinct classes of CAR T cells were identified with differing memory phenotype, activation status, and cytotoxic activity. Epitope mapping revealed that the two classes of CARs bind unique regions of CD70. CD70 CAR T cells displayed robust antitumor activity against RCC cell lines and patient-derived xenograft mouse models. Tissue cross-reactivity studies identified membrane staining in lymphocytes, thus matching the known expression pattern of CD70. In a cynomolgus monkey CD3-CD70 bispecific toxicity study, expected findings related to T-cell activation and elimination of CD70-expressing cells were observed, including cytokine release and loss of cellularity in lymphoid tissues. Finally, highly functional CD70 allogeneic CAR T cells were produced at large scale through elimination of the T-cell receptor by TALEN-based gene editing. Taken together, these efficacy and safety data support the evaluation of CD70 CAR T cells for the treatment of RCC and has led to the advancement of an allogeneic CD70 CAR T-cell candidate into phase I clinical trials. SIGNIFICANCE: These findings demonstrate the efficacy and safety of fratricide-resistant, allogeneic anti-CD70 CAR T cells targeting renal cell carcinoma and the impact of CAR epitope on functional activity. See related commentary by Adotévi and Galaine, p. 2517.

Preclinical Efficacy and Safety Comparison of CD3 Bispecific and ADC Modalities Targeting BCMA for the Treatment of Multiple Myeloma.

The restricted expression pattern of B-cell maturation antigen (BCMA) makes it an ideal tumor-associated antigen (TAA) for the treatment of myeloma. BCMA has been targeted by both CD3 bispecific antibody and antibody-drug conjugate (ADC) modalities, but a true comparison of modalities has yet to be performed. Here we utilized a single BCMA antibody to develop and characterize both a CD3 bispecific and 2 ADC formats (cleavable and noncleavable) and compared activity both in vitro and in vivo with the aim of generating an optimal therapeutic. Antibody affinity, but not epitope was influential in drug activity and hence a high-affinity BCMA antibody was selected. Both the bispecific and ADCs were potent in vitro and in vivo, causing dose-dependent cell killing of myeloma cell lines and tumor regression in orthotopic myeloma xenograft models. Primary patient cells were effectively lysed by both CD3 bispecific and ADCs, with the bispecific demonstrating improved potency, maximal cell killing, and consistency across patients. Safety was evaluated in cynomolgus monkey toxicity studies and both modalities were active based on on-target elimination of B lineage cells. Distinct nonclinical toxicity profiles were seen for the bispecific and ADC modalities. When taken together, results from this comparison of BCMA CD3 bispecific and ADC modalities suggest better efficacy and an improved toxicity profile might be achieved with the bispecific modality. This led to the advancement of a bispecific candidate into phase I clinical trials.

bisFabs: Tools for rapidly screening hybridoma IgGs for their activities as bispecific antibodies.

Bispecific antibodies are a growing class of therapeutic molecules. Many of the current bispecific formats require DNA engineering to convert the parental monoclonal antibodies into the final bispecific molecules. We describe here a method to generate bispecific molecules from hybridoma IgGs in 3-4 d using chemical conjugation of antigen-binding fragments (Fabs) (bisFabs). Proteolytic digestion conditions for each IgG isotype were analyzed to optimize the yield and quality of the final conjugates. The resulting bisFabs showed no significant amounts of homodimers or aggregates. The predictive value of murine bisFabs was tested by comparing the T-cell redirected cytotoxic activity of a panel of antibodies in either the bisFab or full-length IgG formats. A variety of antigens with different structures and expression levels was used to extend the comparison to a wide range of binding geometries and antigen densities. The activity observed for different murine bisFabs correlated with those observed for the full-length IgG format across multiple different antigen targets, supporting the use of bisFabs as a screening tool. Our method may also be used for the screening of bispecific antibodies with other mechanisms of action, allowing for a more rapid selection of lead therapeutic candidates.

Correction: Intestinal Autophagy Improves Healthspan and Longevity in C. elegans During Dietary Restriction.

[This corrects the article DOI: 10.1371/journal.pgen.1006135.].

Intestinal Autophagy Improves Healthspan and Longevity in C. elegans during Dietary Restriction.

Dietary restriction (DR) is a dietary regimen that extends lifespan in many organisms. One mechanism contributing to the conserved effect of DR on longevity is the cellular recycling process autophagy, which is induced in response to nutrient scarcity and increases sequestration of cytosolic material into double-membrane autophagosomes for degradation in the lysosome. Although autophagy plays a direct role in DR-mediated lifespan extension in the nematode Caenorhabditis elegans, the contribution of autophagy in individual tissues remains unclear. In this study, we show a critical role for autophagy in the intestine, a major metabolic tissue, to ensure lifespan extension of dietary-restricted eat-2 mutants. The intestine of eat-2 mutants has an enlarged lysosomal compartment and flux assays indicate increased turnover of autophagosomes, consistent with an induction of autophagy in this tissue. This increase in intestinal autophagy may underlie the improved intestinal integrity we observe in eat-2 mutants, since whole-body and intestinal-specific inhibition of autophagy in eat-2 mutants greatly impairs the intestinal barrier function. Interestingly, intestinal-specific inhibition of autophagy in eat-2 mutants leads to a decrease in motility with age, alluding to a potential cell non-autonomous role for autophagy in the intestine. Collectively, these results highlight important functions for autophagy in the intestine of dietary-restricted C. elegans.

Site-specific antibody drug conjugates for cancer therapy.

Antibody therapeutics have revolutionized the treatment of cancer over the past two decades. Antibodies that specifically bind tumor surface antigens can be effective therapeutics; however, many unmodified antibodies lack therapeutic activity. These antibodies can instead be applied successfully as guided missiles to deliver potent cytotoxic drugs in the form of antibody drug conjugates (ADCs). The success of ADCs is dependent on four factors--target antigen, antibody, linker, and payload. The field has made great progress in these areas, marked by the recent approval by the US Food and Drug Administration of two ADCs, brentuximab vedotin (Adcetris) and ado-trastuzumab emtansine (Kadcyla). However, the therapeutic window for many ADCs that are currently in pre-clinical or clinical development remains narrow and further improvements may be required to enhance the therapeutic potential of these ADCs. Production of ADCs is an area where improvement is needed because current methods yield heterogeneous mixtures that may include 0-8 drug species per antibody molecule. Site-specific conjugation has been recently shown to eliminate heterogeneity, improve conjugate stability, and increase the therapeutic window. Here, we review and describe various site-specific conjugation strategies that are currently used for the production of ADCs, including use of engineered cysteine residues, unnatural amino acids, and enzymatic conjugation through glycotransferases and transglutaminases. In addition, we also summarize differences among these methods and highlight critical considerations when building next-generation ADC therapeutics.

Integrin-linked kinase modulates longevity and thermotolerance in C. elegans through neuronal control of HSF-1.

Integrin-signaling complexes play important roles in cytoskeletal organization and cell adhesion in many species. Components of the integrin-signaling complex have been linked to aging in both Caenorhabditis elegans and Drosophila melanogaster, but the mechanism underlying this function is unknown. Here, we investigated the role of integrin-linked kinase (ILK), a key component of the integrin-signaling complex, in lifespan determination. We report that genetic reduction of ILK in both C. elegans and Drosophila increased resistance to heat stress, and led to lifespan extension in C. elegans without majorly affecting cytoskeletal integrity. In C. elegans, longevity and thermotolerance induced by ILK depletion was mediated by heat-shock factor-1 (HSF-1), a major transcriptional regulator of the heat-shock response (HSR). Reduction in ILK levels increased hsf-1 transcription and activation, and led to enhanced expression of a subset of genes with roles in the HSR. Moreover, induction of HSR-related genes, longevity and thermotolerance caused by ILK reduction required the thermosensory neurons AFD and interneurons AIY, which are known to play a critical role in the canonical HSR. Notably, ILK was expressed in neighboring neurons, but not in AFD or AIY, implying that ILK reduction initiates cell nonautonomous signaling through thermosensory neurons to elicit a noncanonical HSR. Our results thus identify HSF-1 as a novel effector of the organismal response to reduced ILK levels and show that ILK inhibition regulates HSF-1 in a cell nonautonomous fashion to enhance stress resistance and lifespan in C. elegans.

Signals of youth: endocrine regulation of aging in Caenorhabditis elegans.

Aging research has advanced greatly in the nematode Caenorhabditis elegans over the past 20 years, and we are now beginning to piece together distinct pathways that impinge on the aging process. The knowledge base that has been obtained through genetic analysis strongly suggests that endocrine signalling has a key role in most, if not all, of the pathways that alter the aging process of multicellular organisms such as the worm. In this review, we provide an overview of two well-studied aging pathways in C. elegans, the insulin/IGF-1 and germline signalling pathways, in which endocrine signalling is clearly important. We also incorporate recent data to create a model of how endocrine signalling in these pathways might occur.

Optimizing dietary restriction for genetic epistasis analysis and gene discovery in C. elegans.

Dietary restriction (DR) increases mammalian lifespan and decreases susceptibility to many age-related diseases. Lifespan extension due to DR is conserved across a wide range of species. Recent research has focused upon genetically tractable model organisms such as C. elegans to uncover the genetic mechanisms that regulate the response to DR, in the hope that this information will provide insight into the mammalian response and yield potential therapeutic targets. However, no consensus exists as to the best protocol to apply DR to C. elegans and potential key regulators of DR are protocol-specific. Here we define a DR method that better fulfills criteria required for an invertebrate DR protocol to mirror mammalian studies. The food intake that maximizes longevity varies for different genotypes and informative epistasis analysis with another intervention is only achievable at this 'optimal DR' level. Importantly therefore, the degree of restriction imposed using our method can easily be adjusted to determine the genotype-specific optimum DR level. We used this protocol to test two previously identified master regulators of DR in the worm. In contrast to previous reports, we find that DR can robustly extend the lifespan of worms lacking the AMP-activated protein kinase catalytic subunit AAK2 or the histone deacetylase SIR-2.1, highlighting the importance of first optimizing DR to identify universal regulators of DR mediated longevity.

Age-dependent deterioration of nuclear pore complexes causes a loss of nuclear integrity in postmitotic cells.

In dividing cells, nuclear pore complexes (NPCs) disassemble during mitosis and reassemble into the newly forming nuclei. However, the fate of nuclear pores in postmitotic cells is unknown. Here, we show that NPCs, unlike other nuclear structures, do not turn over in differentiated cells. While a subset of NPC components, like Nup153 and Nup50, are continuously exchanged, scaffold nucleoporins, like the Nup107/160 complex, are extremely long-lived and remain incorporated in the nuclear membrane during the entire cellular life span. Besides the lack of nucleoporin expression and NPC turnover, we discovered an age-related deterioration of NPCs, leading to an increase in nuclear permeability and the leaking of cytoplasmic proteins into the nucleus. Our finding that nuclear "leakiness" is dramatically accelerated during aging and that a subset of nucleoporins is oxidatively damaged in old cells suggests that the accumulation of damage at the NPC might be a crucial aging event.

PHA-4/Foxa mediates diet-restriction-induced longevity of C. elegans.

Reduced food intake as a result of dietary restriction increases the lifespan of a wide variety of metazoans and delays the onset of multiple age-related pathologies. Dietary restriction elicits a genetically programmed response to nutrient availability that cannot be explained by a simple reduction in metabolism or slower growth of the organism. In the nematode worm Caenorhabditis elegans, the transcription factor PHA-4 has an essential role in the embryonic development of the foregut and is orthologous to genes encoding the mammalian family of Foxa transcription factors, Foxa1, Foxa2 and Foxa3. Foxa family members have important roles during development, but also act later in life to regulate glucagon production and glucose homeostasis, particularly in response to fasting. Here we describe a newly discovered, adult-specific function for PHA-4 in the regulation of diet-restriction-mediated longevity in C. elegans. The role of PHA-4 in lifespan determination is specific for dietary restriction, because it is not required for the increased longevity caused by other genetic pathways that regulate ageing.