Facile discovery of surrogate cytokine agonists.

Cytokines are powerful immune modulators that initiate signaling through receptor dimerization, but natural cytokines have structural limitations as therapeutics. We present a strategy to discover cytokine surrogate agonists by using modular ligands that exploit induced proximity and receptor dimer geometry as pharmacological metrics amenable to high-throughput screening. Using VHH and scFv to human interleukin-2/15, type-I interferon, and interleukin-10 receptors, we generated combinatorial matrices of single-chain bispecific ligands that exhibited diverse spectrums of functional activities, including potent inhibition of SARS-CoV-2 by surrogate interferons. Crystal structures of IL-2R:VHH complexes revealed that variation in receptor dimer geometries resulted in functionally diverse signaling outputs. This modular platform enabled engineering of surrogate ligands that compelled assembly of an IL-2R/IL-10R heterodimer, which does not naturally exist, that signaled through pSTAT5 on T and natural killer (NK) cells. This "cytokine med-chem" approach, rooted in principles of induced proximity, is generalizable for discovery of diversified agonists for many ligand-receptor systems.

Structure of the interleukin-5 receptor complex exemplifies the organizing principle of common beta cytokine signaling.

Cytokines regulate immune responses by binding to cell surface receptors, including the common subunit beta (ßc), which mediates signaling for GM-CSF, IL-3, and IL-5. Despite known roles in inflammation, the structural basis of IL-5 receptor activation remains unclear. We present the cryo-EM structure of the human IL-5 ternary receptor complex, revealing architectural principles for IL-5, GM-CSF, and IL-3. In mammalian cell culture, single-molecule imaging confirms hexameric IL-5 complex formation on cell surfaces. Engineered chimeric receptors show that IL-5 signaling, as well as IL-3 and GM-CSF, can occur through receptor heterodimerization, obviating the need for higher-order assemblies of ßc dimers. These findings provide insights into IL-5 and ßc receptor family signaling mechanisms, aiding in the development of therapies for diseases involving deranged ßc signaling.

Potentiating adoptive cell therapy using synthetic IL-9 receptors.

Synthetic receptor signalling has the potential to endow adoptively transferred T cells with new functions that overcome major barriers in the treatment of solid tumours, including the need for conditioning chemotherapy1,2. Here we designed chimeric receptors that have an orthogonal IL-2 receptor extracellular domain (ECD) fused with the intracellular domain (ICD) of receptors for common γ-chain (γc) cytokines IL-4, IL-7, IL-9 and IL-21 such that the orthogonal IL-2 cytokine elicits the corresponding γc cytokine signal. Of these, T cells that signal through the chimeric orthogonal IL-2Rß-ECD-IL-9R-ICD (o9R) are distinguished by the concomitant activation of STAT1, STAT3 and STAT5 and assume characteristics of stem cell memory and effector T cells. Compared to o2R T cells, o9R T cells have superior anti-tumour efficacy in two recalcitrant syngeneic mouse solid tumour models of melanoma and pancreatic cancer and are effective even in the absence of conditioning lymphodepletion. Therefore, by repurposing IL-9R signalling using a chimeric orthogonal cytokine receptor, T cells gain new functions, and this results in improved anti-tumour activity for hard-to-treat solid tumours.

Prevention of acute GVHD using an orthogonal IL-2/IL-2Rß system to selectively expand regulatory T cells in vivo.

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative option for patients with hematological disorders and bone marrow (BM) failure syndromes. Graft-versus-host disease (GVHD) remains a leading cause of morbidity posttransplant. Regulatory T cell (Treg) therapies are efficacious in ameliorating GVHD but limited by variable suppressive capacities and the need for a high therapeutic dose. Here, we sought to expand Treg in vivo by expressing an orthogonal interleukin 2 receptor ß (oIL-2Rß) that would selectively interact with oIL-2 cytokine and not wild-type (WT) IL-2. To test whether the orthogonal system would preferentially drive donor Treg expansion, we used a murine major histocompatibility complex-disparate GVHD model of lethally irradiated BALB/c mice given T cell-depleted BM from C57BL/6 (B6) mice alone or together with B6Foxp3+GFP+ Treg or oIL-2Rß-transduced Treg at low cell numbers that typically do not control GVHD with WT Treg. On day 2, B6 activated T cells (Tcons) were injected to induce GVHD. Recipients were treated with phosphate-buffered saline (PBS) or oIL-2 daily for 14 days, then 3 times weekly for an additional 14 days. Mice treated with oIL-2Rß Treg and oIL-2 compared with those treated with PBS had enhanced GVHD survival, in vivo selective expansion of Tregs, and greater suppression of Tcon expansion in secondary lymphoid organs and intestines. Importantly, oIL-2Rß Treg maintained graft-versus-tumor (GVT) responses in 2 distinct tumor models (A20 and MLL-AF9). These data demonstrate a novel approach to enhance the efficacy of Treg therapy in allo-HSCT using an oIL-2/oIL-2Rß system that allows for selective in vivo expansion of Treg leading to GVHD protection and GVT maintenance.

IL-2 receptor engineering enhances regulatory T cell function suppressed by calcineurin inhibitor.

Clinical trials utilizing regulatory T cell (Treg) therapy in organ transplantation have shown promising results, however, the choice of a standard immunosuppressive regimen is still controversial. Calcineurin inhibitors (CNIs) are one of the most common immunosuppressants for organ transplantation, although they may negatively affect Tregs by inhibiting IL-2 production by conventional T cells. As a strategy to replace IL-2 signaling selectively in Tregs, we have introduced an engineered orthogonal IL-2 (ortho IL-2) cytokine/cytokine receptor (R) pair that specifically binds with each other but does not bind with their wild-type counterparts. Murine Tregs were isolated from recipients and retrovirally transduced with ortho IL-2Rß during ex vivo expansion. Transduced Tregs (ortho Tregs) were transferred into recipient mice in a mixed hematopoietic chimerism model with tacrolimus administration. Ortho IL-2 treatment significantly increased the ortho IL-2Rß(+) Treg population in the presence of tacrolimus without stimulating other T cell subsets. All the mice treated with tacrolimus plus ortho IL-2 achieved heart allograft tolerance, even after tacrolimus cessation, whereas those receiving tacrolimus treatment alone did not. These data demonstrate that Treg therapy can be adopted into a CNI-based regimen by utilizing cytokine receptor engineering.

Lack of defined apheresis collection criteria in publicly available CAR-T cell clinical trial descriptions: Comprehensive review of over 600 studies.

BACKGROUND: Chimeric antigen receptor T (CAR-T) cell successes have encouraged continued clinical study. Apheresis collection of starting material for CAR-T cell therapy product manufacturing is critical but described approaches suggest variability and clinical guidelines are currently lacking. The goal of this study was to gather and assess variability in apheresis collection descriptions in publicly available CAR T-cell therapy clinical trials. STUDY DESIGN: We searched clinicaltrials.gov (a publicly available clinical trial database) for "chimeric antigen receptor T cells" on July 01, 2020 and studies accessed July 30, 2020-August 15, 2020. Data collected included date posted, study characteristics, apheresis mentions (number, location, and context), laboratory parameters and transfusion allowances. Apheresis context was analyzed using a qualitative inductive approach of grounded theory method with open coding. Text was classified into 37 context codes, grouped into 12 categories, and then consolidated into patient, procedure, product, and miscellaneous themes. RESULTS: Apheresis was mentioned 1044 times in 322 (51.9%) of 621 total studies. Laboratory parameters mentioned included white blood cells (100 studies), absolute neutrophil count (220 studies), absolute lymphocyte count (102 studies), CD3+ cell (38 studies), hemoglobin (233 studies, 54 studies specified transfusion allowance), and platelet (269 studies, 48 studies specified transfusion allowance). CONCLUSIONS: Apheresis collection of CAR-T cell products is not well-defined in clinical study descriptions and the context is inconsistent. Laboratory parameters useful for apheresis collection are variably present and do not consistently align with current practices. Further exploration, and clinical guideline development will encourage alignment of apheresis collections for CAR-T cell products.

Pediatric Chronic Myeloid Leukemia Presenting With Extreme Thrombocytosis Simulating Essential Thrombocythemia.

A 10-year-old boy presented with spontaneous bruising and was found to have extreme thrombocytosis without neutrophilia/shift to immaturity, basophilia or eosinophilia. While the peripheral blood and bone marrow findings initially suggested essential thrombocythemia, BCR-ABL1 translocation was detected and chronic myeloid leukemia, chronic phase, was diagnosed. Apheresis for platelet depletion was performed as a bridge given the delayed effects of medical therapy.

The Role of Thromboelastography in Pediatric Patients with Sinusoidal Obstructive Syndrome Receiving Defibrotide.

Sinusoidal obstructive syndrome (SOS) is a potentially fatal form of hepatic injury after hematopoietic stem cell transplantation. Patients can develop liver dysfunction, portal hypertension, ascites, coagulopathies, and multisystem organ failure. The mortality rate of severe SOS has been reported as high as 98% by day 100 after transplantation. Defibrotide, which is now approved for the treatment of SOS, has significantly decreased mortality. Defibrotide is a polynucleotide with profibrinolytic, anti-ischemic, and anti-inflammatory activity. These properties can increase the risk of life-threatening bleeding in this patient population. Previous protocols have suggested maintaining international normalized ratio ≤ 1.5, platelets > 30 k/uL, and fibrinogen ≥ 150 mg/dL to minimize this risk of bleeding. However, this can be challenging in fluid-sensitive patients with SOS. Thromboelastography (TEG) is a functional assay that evaluates the balance of procoagulant and anticoagulant proteins. In this series, TEG was used to guide defibrotide therapy as well as blood product transfusions in SOS patients with abnormal coagulation studies. Each patient recovered from SOS and had no bleeding complications. A randomized clinical trial is the next step in supporting the use of TEG in SOS patients with abnormal coagulation studies receiving defibrotide therapy.

Extracorporeal photopheresis practice patterns: An international survey by the ASFA ECP subcommittee.

BACKGROUND: Although many apheresis centers offer extracorporeal photopheresis (ECP), little is known about current treatment practices. METHODS: An electronic survey was distributed to assess ECP practice internationally. RESULTS: Of 251 responses, 137 met criteria for analysis. Most respondents were from North America (80%). Nurses perform ECP at most centers (84%) and the majority of centers treat adults only (52%). Most centers treat fewer than 50 patients/year (83%) and perform fewer than 300 procedures/year (70%). Closed system devices (XTS and/or Cellex) are used to perform ECP at most centers (96%). The most common indications for ECP are acute/chronic skin graft versus host disease (89%) and cutaneous T-cell lymphoma (63%). The typical wait time for ECP treatment is less than 2 weeks (91%). Most centers do not routinely perform quality control assessment of the collected product (66%). There are device-specific differences in treatment parameters. For example, XTS users more frequently have a minimum weight limit (P = 0.003) and use laboratory parameters to determine eligibility for treatment (P = 0.03). Regardless of device used, the majority of centers assess the clinical status of the patient before each procedure. Greater than 50% of respondents would defer treatment for hemodynamic instability due to active sepsis or heart failure, positive blood culture in the past 24 h or current fever. CONCLUSION: This survey based study describes current ECP practices. Further research to provide evidence for optimal standardization of patient qualifications, procedure parameters and product quality assessment is recommended.

A structural blueprint for interleukin-21 signal modulation.

Interleukin-21 (IL-21) plays a critical role in generating immunological memory by promoting the germinal center reaction, yet clinical use of IL-21 remains challenging because of its pleiotropy and association with autoimmune disease. To better understand the structural basis of IL-21 signaling, we determine the structure of the IL-21-IL-21R-γc ternary signaling complex by X-ray crystallography and a structure of a dimer of trimeric complexes using cryo-electron microscopy. Guided by the structure, we design analogs of IL-21 by introducing substitutions to the IL-21-γc interface. These IL-21 analogs act as partial agonists that modulate downstream activation of pS6, pSTAT3, and pSTAT1. These analogs exhibit differential activity on T and B cell subsets and modulate antibody production in human tonsil organoids. These results clarify the structural basis of IL-21 signaling and offer a potential strategy for tunable manipulation of humoral immunity.

Differential mTOR and ERK pathway utilization by effector CD4 T cells suggests combinatorial drug therapy of arthritis.

The signaling pathways utilized by naïve and experienced effector CD4 T cells during activation and proliferation were evaluated. While inhibition of either mTOR or MAPK alone was able to inhibit naïve T cell proliferation, both mTOR and MAPK (ERK) pathway inhibition was required to efficiently block experienced, effector CD4 T cell proliferation. This was demonstrated both in vitro, and in vivo by treating mice with collagen-induced arthritis using mTOR and/or ERK inhibitors. The combination of mTOR and ERK inhibition prevented or treated disease more efficiently than either agent alone. These data illustrate the different requirements of naïve and experienced effector CD4 T cells in the use of the mTOR and MAPK pathways in proliferation, and suggest that therapies targeting both the mTOR and MAPK pathways may be more effective than targeting either pathway alone in the treatment of CD4 T cell-mediated autoimmunity.

Improving the performance of culture-based bacterial screening by increasing the sample volume from 4 mL to 8 mL in aerobic culture bottles.

BACKGROUND: In the setting of bacterial detection of apheresis platelets (PLTs), the manufacturer recommended PLT inoculation volume for BacT/ALERT culture bottles (bioMérieux) ranges from 4 to 10 mL. This study compares the rate of capture of true-positive (TP) contaminations between aerobic culture bottles inoculated with either 4 or 8 mL of sample and assesses if a larger sample volume reduces time to detection. STUDY DESIGN AND METHODS: Detection of TP samples and mean time to detection were compared for 4- and 8-mL samples collected between September 1, 2003, and May 2, 2011. RESULTS: A total of 180,263 and 283,114 PLT collections were tested with an 8- and 4-mL sample, respectively. Analysis of TP rates by volume sampled show an increase in the rate of detection of TP with the 8-mL sample relative to the 4-mL sample (139 vs. 106 per million events; odds ratio, 1.31; 95% confidence interval, 0.77-2.23). Comparison of mean time to detection for TP shows a decrease in mean time to detection using 8 mL compared with 4 mL (12.36 ± 3.7 hr to 15.97 ± 6.3 hr, p = 0.012). CONCLUSION: Doubling the sample volume to 8 mL showed a trend in improvement for the rate of detection of TP and shortened the mean time of detection for TP by 23% when compared to a sample volume of 4 mL. The decrease in mean time to detection using a larger sample volume suggests that a shorter release time after inoculation could be achieved without significantly increasing patient risk.

Induced CD45 Proximity Potentiates Natural Killer Cell Receptor Antagonism.

Natural killer (NK) cells are a major subset of innate immune cells that are essential for host defense against pathogens and cancer. Two main classes of inhibitory NK receptors (NKR), KIR and CD94/NKG2A, play a key role in suppressing NK activity upon engagement with tumor cells or virus-infected cells, limiting their antitumor and antiviral activities. Here, we find that single-chain NKR antagonists linked to a VHH that binds the cell surface phosphatase CD45 potentiate NK and T activities to a greater extent than NKR blocking antibodies alone in vitro. We also uncovered crosstalk between NKG2A and Ly49 that collectively inhibit NK cell activation, such that CD45-NKG2A and CD45-Ly49 bispecific molecules show synergistic effects in their ability to enhance NK cell activation. The basis of the activity enhancement by CD45 ligation may reflect greater antagonism of inhibitory signaling from engagement of MHC I on target cells, combined with other mechanisms, including avidity effects, tonic signaling, antagonism of weak inhibition from engagement of MHC I on non-target cells, and possible CD45 segregation within the NK cell-target cell synapse. These results uncover a strategy for enhancing the activity of NK and T cells that may improve cancer immunotherapies.

The transmembrane E3 ligase GRAIL ubiquitinates and degrades CD83 on CD4 T cells.

Ubiquitination of eukaryotic proteins regulates a broad range of cellular processes, including T cell activation and tolerance. We have previously demonstrated that GRAIL (gene related to anergy in lymphocytes), a transmembrane RING finger ubiquitin E3 ligase, initially described as induced during the induction of CD4 T cell anergy, is also expressed in resting CD4 T cells. In this study, we show that GRAIL can down-modulate the expression of CD83 (previously described as a cell surface marker for mature dendritic cells) on CD4 T cells. GRAIL-mediated down-modulation of CD83 is dependent on an intact GRAIL extracellular protease-associated domain and an enzymatically active cytosolic RING domain, and proceeds via the ubiquitin-dependent 26S proteosome pathway. Ubiquitin modification of lysine residues K168 and K183, but not K192, in the cytoplasmic domain of CD83 was shown to be necessary for GRAIL-mediated degradation of CD83. Reduced CD83 surface expression levels were seen both on anergized CD4 T cells and following GRAIL expression by retroviral transduction, whereas GRAIL knock-down by RNA interference in CD4 T cells resulted in elevated CD83 levels. Furthermore, CD83 expression on CD4 T cells contributes to T cell activation as a costimulatory molecule. This study supports the novel mechanism of ubiquitination by GRAIL, identifies CD83 as a substrate of GRAIL, and ascribes a role for CD83 in CD4 T cell activation.

Naive CD4 t cell proliferation is controlled by mammalian target of rapamycin regulation of GRAIL expression.

In this study, we demonstrate that the E3 ubiquitin ligase gene related to anergy in lymphocytes (GRAIL) is expressed in quiescent naive mouse and human CD4 T cells and has a functional role in inhibiting naive T cell proliferation. Following TCR engagement, CD28 costimulation results in the expression of IL-2 whose signaling through its receptor activates the Akt-mammalian target of rapamycin (mTOR) pathway. Activation of mTOR allows selective mRNA translation, including the epistatic regulator of GRAIL, Otubain-1 (Otub1), whose expression results in the degradation of GRAIL and allows T cell proliferation. The activation of mTOR appears to be the critical component of IL-2R signaling regulating GRAIL expression. CTLA4-Ig treatment blocks CD28 costimulation and resultant IL-2 expression, whereas rapamycin and anti-IL-2 treatment block mTOR activation downstream of IL-2R signaling. Thus, all three of these biotherapeutics inhibit mTOR-dependent translation of mRNA transcripts, resulting in blockade of Otub1 expression, maintenance of GRAIL, and inhibition of CD4 T cell proliferation. These observations provide a mechanistic pathway sequentially linking CD28 costimulation, IL-2R signaling, and mTOR activation as important requirements for naive CD4 T cell proliferation through the regulation of Otub1 and GRAIL expression. Our findings also extend the role of GRAIL beyond anergy induction and maintenance, suggesting that endogenous GRAIL regulates general cell cycle and proliferation of primary naive CD4 T cells.

Structure-based decoupling of the pro- and anti-inflammatory functions of interleukin-10.

Interleukin-10 (IL-10) is an immunoregulatory cytokine with both anti-inflammatory and immunostimulatory properties and is frequently dysregulated in disease. We used a structure-based approach to deconvolute IL-10 pleiotropy by determining the structure of the IL-10 receptor (IL-10R) complex by cryo-electron microscopy at a resolution of 3.5 angstroms. The hexameric structure shows how IL-10 and IL-10Rα form a composite surface to engage the shared signaling receptor IL-10Rß, enabling the design of partial agonists. IL-10 variants with a range of IL-10Rß binding strengths uncovered substantial differences in response thresholds across immune cell populations, providing a means of manipulating IL-10 cell type selectivity. Some variants displayed myeloid-biased activity by suppressing macrophage activation without stimulating inflammatory CD8+ T cells, thereby uncoupling the major opposing functions of IL-10. These results provide a mechanistic blueprint for tuning the pleiotropic actions of IL-10.

Selective expansion of regulatory T cells using an orthogonal IL-2/IL-2 receptor system facilitates transplantation tolerance.

Adoptive transfer of Tregs has been shown to improve alloengraftment in animal models. However, it is technically challenging to expand Tregs ex vivo for the purpose of infusing large numbers of cells in the clinic. We demonstrate an innovative approach to engineering an orthogonal IL-2/IL-2 receptor (IL-2R) pair, the parts of which selectively interact with each other, transmitting native IL-2 signals, but do not interact with the natural IL-2 or IL-2R counterparts, thereby enabling selective stimulation of target cells in vivo. Here, we introduced this orthogonal IL-2R into Tregs. Upon adoptive transfer in a murine mixed hematopoietic chimerism model, orthogonal IL-2 injection significantly promoted orthogonal IL-2R+Foxp3GFP+CD4+ cell proliferation without increasing other T cell subsets and facilitated donor hematopoietic cell engraftment followed by acceptance of heart allografts. Our data indicate that selective target cell stimulation enabled by the engineered orthogonal cytokine receptor improves Treg potential for the induction of organ transplantation tolerance.

Cutting edge: The transmembrane E3 ligase GRAIL ubiquitinates the costimulatory molecule CD40 ligand during the induction of T cell anergy.

Activation of naive T lymphocytes is regulated through a series of discrete checkpoints that maintain unresponsiveness to self. During this multistep process, costimulatory interactions act as inducible signals that allow APCs to selectively mobilize T cells against foreign Ags. In this study, we provide evidence that the anergy-associated E3 ubiquitin ligase GRAIL (gene related to anergy in lymphocytes) regulates expression of the costimulatory molecule CD40L on CD4 T cells. Using its luminal protease-associated domain, GRAIL binds to the luminal/extracellular portion of CD40L and facilitates transfer of ubiquitin molecules from the intracellular GRAIL RING (really interesting new gene) finger to the small cytosolic portion of CD40L. Down-regulation of CD40L occurred following ectopic expression of GRAIL in naive T cells from CD40(-/-) mice, and expression of GRAIL in bone marrow chimeric mice was associated with diminished lymphoid follicle formation. These data provide a model for intrinsic T cell regulation of costimulatory molecules and a molecular framework for the initiation of clonal T cell anergy.

Bacterial detection in apheresis platelets: blood systems experience with a two-bottle and one-bottle culture system.

BACKGROUND: United Blood Services (UBS) began bacterial testing of platelets (PLTs) using one-bottle cultures in September 2003. Collection of 7-day PLTs using two-bottle cultures began in April 2006. This study compares our experience using both systems. STUDY DESIGN AND METHODS: PLTs from 13 UBS regional centers cultured from September 1, 2003, to September 1, 2007, were included in the analysis. Positive-signal bottles from a commercially available microbial detection system (BacT/ALERT, bioMérieux) were sent, with corresponding PLTs if available, for confirmatory testing using plate culture media. AABB definitions were used with modifications. RESULTS: A total of 51,265 7-day PLT collections and 191,521 5-day PLT collections were tested with bacterial cultures. The overall true-positive (TP) rate for the two-bottle system (1:8544) was comparable to the TP rate with the previous one-bottle system (1:6344). In three of six yield cases, only the anaerobic bottle was positive (two cases of Group D Streptococci, one case of Corynebacterium spp.). The false-positive (FP) and indeterminate (IND) rates in the anaerobic bottle (1:1767 and 1:1830, respectively) were significantly higher than those in the aerobic bottle (1:6408 and 1:17,088, respectively; p < 0.001). One confirmed transfusion-related septic reaction, classified as a late TP after investigation, was reported out of 242,786 tested PLT donations. CONCLUSION: The rate of TP cases by the two-bottle system was not increased over the one-bottle system, although anaerobic-bottle-only positive cases were detected. FP and IND rates were increased in the two-bottle system, attributable to the anaerobic bottle. Observation of only one documented transfusion-related septic reaction in 4 years of bacterial screening at UBS is reassuring, although limitations in passive surveillance and higher rates of reactions reported by others indicate the need for continued vigilance.