A next generation mathematical model for the in vitro to clinical translation of T-cell engagers.

T-cell engager (TCE) molecules activate the immune system and direct it to kill tumor cells. The key mechanism of action of TCEs is to crosslink CD3 on T cells and tumor associated antigens (TAAs) on tumor cells. The formation of this trimolecular complex (i.e. trimer) mimics the immune synapse, leading to therapeutic-dependent T-cell activation and killing of tumor cells. Computational models supporting TCE development must predict trimer formation accurately. Here, we present a next-generation two-step binding mathematical model for TCEs to describe trimer formation. Specifically, we propose to model the second binding step with trans-avidity and as a two-dimensional (2D) process where the reactants are modeled as the cell-surface density. Compared to the 3D binding model where the reactants are described in terms of concentration, the 2D model predicts less sensitivity of trimer formation to varying cell densities, which better matches changes in EC50 from in vitro cytotoxicity assay data with varying E:T ratios. In addition, when translating in vitro cytotoxicity data to predict in vivo active clinical dose for blinatumomab, the choice of model leads to a notable difference in dose prediction. The dose predicted by the 2D model aligns better with the approved clinical dose and the prediction is robust under variations in the in vitro to in vivo translation assumptions. In conclusion, the 2D model with trans-avidity to describe trimer formation is an improved approach for TCEs and is likely to produce more accurate predictions to support TCE development.

SIRT1 is dispensable for function of hematopoietic stem cells in adult mice.

SIRT1 is an NAD(+)-dependent histone deacetylase implicated in the establishment of the primitive hematopoietic system during mouse embryonic development. However, investigation of the role of SIRT1 in adult hematopoiesis has been complicated by the high perinatal mortality of SIRT1-deficient mice (SIRT1(-/-)). We performed a comprehensive in vivo study of the hematopoietic stem cell (HSC) compartment in adult SIRT1(-/-) mice and show that, apart from anemia and leukocytosis in older mice, the production of mature blood cells, lineage distribution within hematopoietic organs, and frequencies of the most primitive HSC populations are comparable to those of wild-type littermate controls. Furthermore, we show that SIRT1-deficient BM cells confer stable long-term reconstitution in competitive repopulation and serial transplantation experiments. The results of the present study rule out an essential physiologic role for cell-autonomous SIRT1 signaling in the maintenance of the adult HSC compartment in mice.

Respiratory Syncytial Virus in a Child With Dravet Syndrome: A Case Report.

The objective of this case report is to describe and document a case of respiratory syncytial virus (RSV) in a pediatric patient with Dravet syndrome (DS), also known as severe myoclonic epilepsy of infancy. Febrile seizures are often a complication in a patient with DS and can lead to status epilepticus, necessitating measures to prevent triggers such as fever, electrolyte imbalance, or dehydration. An increased awareness and understanding of DS can facilitate the identification of warning signs. A two-year-old female with a past medical history of DS with focal and generalized features presented to the pediatric emergency department (ED) with a five-day history of cough, fever, and decreased oral intake. The patient's parents accompanied her and expressed concerns regarding the risk of seizures associated with a rise in body temperature, as they had been alternating between acetaminophen and ibuprofen to manage her fever with a maximum recorded temperature of 101.5℉. She exhibited signs of increased work of breathing, necessitating the administration of supplemental oxygen via nasal cannula. Blood samples were obtained and resulted in the development of metabolic acidosis. A respiratory panel confirmed the presence of an RSV infection, promoting the administration of breathing treatment with albuterol and ipratropium bromide. The patient was admitted for dehydration and was started on ½ normal saline/potassium chloride 20 mEq at 40 mL/hr. Additionally, her home medication regimen was resumed to minimize the risk of seizures. Given the patient's complications and increased risk of seizure, she was transferred to higher-level care where her status improved after the placement of a percutaneous endoscopic gastrostomy (PEG). This case underscores the complexities involved in managing patients with DS, particularly when complicated by respiratory illness and electrolyte imbalances that can lower the seizure threshold. This patient received a combination of diet and medications to prevent seizures, as well as allow for recovery and correction of the underlying metabolic acidosis. The transfer to a higher level of care in this case was necessary to allow for the specialized resources and expertise needed to handle this case.

Necrotizing Enterocolitis in an Infant With a History of Twin-Twin Transfusion Syndrome: A Case Report.

This case report describes necrotizing enterocolitis (NEC) in an infant with a history of twin-twin transfusion syndrome (TTTS). TTTS is a volume imbalance where the anastomosis at the vascular equator between the two placentae shifts from the donor to the recipient twin. This causes a higher risk for NEC, a marked inflammation caused by bacterial infection into the intestinal wall, from prematurity and intestinal hypoperfusion. Complications include sepsis, bowel necrosis, perforation, peritonitis, and death. NEC is a leading cause of morbidity in preterm infants. A 3-month-old female with a history of TTTS and prematurity presented with her mother to the pediatric emergency department (ED) for bloody diarrhea, emesis, lack of appetite, and lethargy for 4 days. The pediatrician changed the formula due to a possible milk allergy, however, she continued to have bloody diarrhea. Over the 2 days, the patient had nonbilious and non-bloody emesis and couldn't tolerate oral intake. In the ED, labs showed neutropenia and sepsis. She had a positive fecal occult blood test (FOBT) and an abdominal x-ray that revealed dilated loops of bowel and pneumatosis intestinalis. She was started on intravenous (IV) fluids for maintenance of hydration. She was started on broad-spectrum antibiotics including intravenous (IV) vancomycin and meropenem, and had her feedings temporarily stopped. The patient was transferred to the pediatric intensive care unit (PICU) at a tertiary care/children's hospital that evening where she had a laparotomy performed to resect the diseased intestine. She was discharged 10 days after the surgery for home recovery with clinical follow-up.

Comparison of dose selection based on target engagement versus inhibition of receptor-ligand interaction for checkpoint inhibitors.

Immune checkpoint inhibitors block the interaction between a receptor on one cell and its ligand on another cell, thus preventing the transduction of an immunosuppressive signal. While inhibition of the receptor-ligand interaction is key to the pharmacological activity of these drugs, it can be technically challenging to measure these intercellular interactions directly. Instead, target engagement (or receptor occupancy) is commonly measured, but may not always be an accurate predictor of receptor-ligand inhibition, and can be misleading when used to inform clinical dose projections for this class of drugs. In this study, a mathematical model explicitly representing the intercellular receptor-ligand interaction is used to compare dose prediction based on target engagement or receptor-ligand inhibition for two checkpoint inhibitors, atezolizumab and magrolimab. For atezolizumab, there is little difference between target engagement and receptor-ligand inhibition, but for magrolimab, the model predicts that receptor-ligand inhibition is significantly less than target engagement. The key variables explaining the difference between these two drugs are the relative concentrations of the target receptors and their ligands. Drug-target affinity and receptor-ligand affinity can also have divergent effects on target engagement and inhibition. These results suggest that it is important to consider ligand-receptor inhibition in addition to target engagement and demonstrate the impact of using modeling for efficacious dose estimation.

ATG-101 Is a Tetravalent PD-L1×4-1BB Bispecific Antibody That Stimulates Antitumor Immunity through PD-L1 Blockade and PD-L1-Directed 4-1BB Activation.

Immune checkpoint inhibitors (ICI) have transformed cancer treatment. However, only a minority of patients achieve a profound response. Many patients are innately resistant while others acquire resistance to ICIs. Furthermore, hepatotoxicity and suboptimal efficacy have hampered the clinical development of agonists of 4-1BB, a promising immune-stimulating target. To effectively target 4-1BB and treat diseases resistant to ICIs, we engineered ATG-101, a tetravalent "2+2″ PD-L1×4-1BB bispecific antibody. ATG-101 bound PD-L1 and 4-1BB concurrently, with a greater affinity for PD-L1, and potently activated 4-1BB+ T cells when cross-linked with PD-L1-positive cells. ATG-101 activated exhausted T cells upon PD-L1 binding, indicating a possible role in reversing T-cell dysfunction. ATG-101 displayed potent antitumor activity in numerous in vivo tumor models, including those resistant or refractory to ICIs. ATG-101 greatly increased the proliferation of CD8+ T cells, the infiltration of effector memory T cells, and the ratio of CD8+ T/regulatory T cells in the tumor microenvironment (TME), rendering an immunologically "cold" tumor "hot." Comprehensive characterization of the TME after ATG-101 treatment using single-cell RNA sequencing further revealed an altered immune landscape that reflected increased antitumor immunity. ATG-101 was well tolerated and did not induce hepatotoxicity in non-human primates. According to computational semimechanistic pharmacology modeling, 4-1BB/ATG-101/PD-L1 trimer formation and PD-L1 receptor occupancy were both maximized at around 2 mg/kg of ATG-101, providing guidance regarding the optimal biological dose for clinical trials. In summary, by localizing to PD-L1-rich microenvironments and activating 4-1BB+ immune cells in a PD-L1 cross-linking-dependent manner, ATG-101 safely inhibits growth of ICI resistant and refractory tumors. SIGNIFICANCE: The tetravalent PD-L1×4-1BB bispecific antibody ATG-101 activates 4-1BB+ T cells in a PD-L1 cross-linking-dependent manner, minimizing the hepatotoxicity of existing 4-1BB agonists and suppressing growth of ICI-resistant tumors. See related commentary by Ha et al., p. 1546.

Utilizing Infantile Spasm Seizure Activity as a Baseline Vital in the Setting of Acute Pseudomonas aeruginosa Pneumonia.

The objective of this case report is to describe and document a decrease in seizure activity in a 16-year-old female with a past medical history of Aicardi syndrome (AS) and infantile spasms (IS) while being treated for acute Pseudomonas aeruginosa pneumonia with pleural effusion. This patient presented to the pediatric emergency department with a chief complaint of fever, tachycardia, increased nasal secretions, and oxygen requirement at home. She was admitted to the general pediatric medical floor for treatment of an adenovirus infection due to her having a complex medical history and her being medically unstable. On hospital admission day 1, she developed post-viral P. aeruginosa pneumonia. She subsequently had three days of complete clinical seizure cessation without changing her anti-epileptic medications. It was not until the symptomatology related to her pneumonia improved that her seizure activity returned to its baseline frequency. The treating team discovered that the decrease in her frequency of seizure activity related to periods of increased physiologic stress was not new. Her mother reported that she has used the relationship between her daughter's seizures and any acute illness to gauge how her daughter was "feeling" medically. Three weeks prior to this hospital admission, her mother reported that her daughter's seizures ceased for two days during a period in which it was determined that the patient was having renal colic and passed a renal stone. This phenomenon, the decrease in the frequency of seizure activity related to periods of increased physiologic stress, could help primary caretakers assess when significant, new comorbid conditions are present and could aid in the primary assessment of physical health in a particular patient population who are unable to verbalize their current medical status. Utilizing seizure activity as an at-home vital sign could help caretakers recognize when their patient is under an elevated physiologic stress condition. Recognizing the relationship between seizure frequency and acute illness could also help diagnostically, as ISs are difficult to both diagnose and manage. Also, future research on this possible association could explore more understanding of IS and pathophysiology of such phenomenon.

Pulsatile tinnitus as a presenting symptom of central venous stenosis secondary to an ipsilateral upper arm arteriovenous PTFE graft.

A 51-year-old man presented with a swollen left arm and unilateral pulsatile tinnitus 2 weeks after a left upper arm polytetrafluoroethylene graft was created for haemodialysis access. A fistulogram of the left upper arm showed a central venous stenosis and significant retrograde flow up the left internal jugular vein. Percutaneous transluminal angioplasty was attempted unsuccessfully and fistula ligation was subsequently performed. This led to immediate resolution of the tinnitus. The venous stenosis was likely secondary to a cardiac resynchronisation therapy defibrillator, which had been removed 1 year previously. Central venous stenosis is a common but often asymptomatic complication of a cardiac device, with the exception of patients with upper extremity arteriovenous fistulas, who frequently develop symptomatic venous hypertension. This generally presents with ipsilateral arm swelling and/or high venous pressures during dialysis. To our knowledge, this is the first report of pulsatile tinnitus arising in this context.

TALEN-Mediated Gene Editing of HBG in Human Hematopoietic Stem Cells Leads to Therapeutic Fetal Hemoglobin Induction.

Elements within the γ-hemoglobin promoters (HBG1 and HBG2) function to bind transcription complexes that mediate repression of fetal hemoglobin expression. Sickle cell disease (SCD) subjects with a 13-bp deletion in the HBG1 promoter exhibit a clinically favorable hereditary persistence of fetal hemoglobin (HPFH) phenotype. We developed TALENs targeting the homologous HBG promoters to de-repress fetal hemoglobin. Transfection of human CD34+ cells with TALEN mRNA resulted in indel generation in HBG1 (43%) and HBG2 (74%) including the 13-bp HPFH deletion (∼6%). Erythroid differentiation of edited cells revealed a 4.6-fold increase in γ-hemoglobin expression as detected by HPLC. Assessment of TALEN-edited CD34+ cells in vivo in a humanized mouse model demonstrated sustained presence of indels in hematopoietic cells up to 24 weeks. Indel rates remained unchanged following secondary transplantation consistent with editing of long-term repopulating stem cells (LT-HSCs). Human γ-hemoglobin expressing F cells were detected by flow cytometry approximately 50% more frequently in edited animals compared to mock. Together, these findings demonstrate that TALEN-mediated indel generation in the γ-hemoglobin promoter leads to high levels of fetal hemoglobin expression in vitro and in vivo, suggesting that this approach can provide therapeutic benefit in patients with SCD or ß-thalassemia.

Clonal Analysis of Embryonic Hematopoietic Stem Cell Precursors Using Single Cell Index Sorting Combined with Endothelial Cell Niche Co-culture.

The ability to study hematopoietic stem cell (HSC) genesis during embryonic development has been limited by the rarity of HSC precursors in the early embryo and the lack of assays that functionally identify the long-term multilineage engraftment potential of individual putative HSC precursors. Here, we describe methodology that enables the isolation and characterization of functionally validated HSC precursors at the single cell level. First, we utilize index sorting to catalog the precise phenotypic parameter of each individually sorted cell, using a combination of phenotypic markers to enrich for HSC precursors with additional markers for experimental analysis. Second, each index-sorted cell is co-cultured with vascular niche stroma from the aorta-gonad-mesonephros (AGM) region, which supports the maturation of non-engrafting HSC precursors to functional HSC with multilineage, long-term engraftment potential in transplantation assays. This methodology enables correlation of phenotypic properties of clonal hemogenic precursors with their functional engraftment potential or other properties such as transcriptional profile, providing a means for the detailed analysis of HSC precursor development at the single cell level.

Laparoscopic liver resection for lesions adjacent to major vasculature: feasibility, safety and oncological efficiency.

BACKGROUND AND OBJECTIVES: Laparoscopic liver resection for lesions adjacent to major vasculature can be challenging, and many would consider it a contraindication. Recently, however, laparoscopic liver surgeons have been pushing boundaries and approached some of these lesions laparoscopically. We assessed feasibility, safety and oncological efficiency of this laparoscopic approach for these lesions. METHODS: This is a monocenter study (2003-2013) describing technique and outcomes of laparoscopic liver resection for lesions adjacent to major vasculature: <2 cm from the portal vein (main trunk and first division), hepatic arteries or inferior vena cava. RESULTS: Thirty-seven patients underwent laparoscopic liver resection (LLR) for a lesion adjacent to major vasculature. Twenty-four (65%) resections were for malignant disease and 92% R0 resections. Conversion occurred in three patients (8%). Mean operative time was 313 min (standard deviation (SD) ± 101) and intraoperative blood loss 400 ml (IQR 213-700). Clavien-Dindo complications > II occurred in two cases (5%), with no mortality. Lesions at <1 cm were larger (7.2 cm (2.7-14) vs. 3 cm (2.5-5), p = 0.03) and operation time was longer (344 ± 94 vs. 262 ± 92 min, p = 0.01) than lesions at 1-2 cm from major vasculature. CONCLUSIONS: Lesions <2 cm from major hepatic vasculature do not represent an absolute contraindication for LLR when performed by experienced laparoscopic liver surgeons in selected patients.

SMET: systematic multiple enzyme targeting - a method to rationally design optimal strains for target chemical overproduction.

Identifying multiple enzyme targets for metabolic engineering is very critical for redirecting cellular metabolism to achieve desirable phenotypes, e.g., overproduction of a target chemical. The challenge is to determine which enzymes and how much of these enzymes should be manipulated by adding, deleting, under-, and/or over-expressing associated genes. In this study, we report the development of a systematic multiple enzyme targeting method (SMET), to rationally design optimal strains for target chemical overproduction. The SMET method combines both elementary mode analysis and ensemble metabolic modeling to derive SMET metrics including l-values and c-values that can identify rate-limiting reaction steps and suggest which enzymes and how much of these enzymes to manipulate to enhance product yields, titers, and productivities. We illustrated, tested, and validated the SMET method by analyzing two networks, a simple network for concept demonstration and an Escherichia coli metabolic network for aromatic amino acid overproduction. The SMET method could systematically predict simultaneous multiple enzyme targets and their optimized expression levels, consistent with experimental data from the literature, without performing an iterative sequence of single-enzyme perturbation. The SMET method was much more efficient and effective than single-enzyme perturbation in terms of computation time and finding improved solutions.

CD33 expression and P-glycoprotein-mediated drug efflux inversely correlate and predict clinical outcome in patients with acute myeloid leukemia treated with gemtuzumab ozogamicin monotherapy.

Gemtuzumab ozogamicin (GO) contains an anti-CD33 antibody to facilitate uptake of a toxic calicheamicin-gamma(1) derivative. While recent in vitro data demonstrated a quantitative relationship between CD33 expression and GO cytotoxicity, previous correlative studies failed to identify a significant association between CD33 expression and clinical outcome. Studying patients undergoing GO monotherapy for relapsed acute myeloid leukemia (AML), we now find that AML blasts of responders have a significantly higher mean CD33 level and lower P-glycoprotein (Pgp) activity compared with nonresponders. CD33 expression and Pgp activity are inversely correlated. While both variables are associated with outcome, Pgp remains significantly associated with outcome even after adjusting for CD33, whereas CD33 does not show such an association after adjusting for Pgp. The inverse relationship between CD33 and Pgp suggests a maturation-stage-dependent expression of both proteins, and offers the rationale for using cell differentiation-promoting agents to enhance GO-induced cytotoxicity.

Safety and efficacy of gemtuzumab ozogamicin in pediatric patients with advanced CD33+ acute myeloid leukemia.

This open-label, dose-escalation study evaluated the safety and efficacy of single-agent gemtuzumab ozogamicin, a humanized anti-CD33 antibody-targeted chemotherapeutic agent, for pediatric patients with multiple relapsed or primary refractory acute myeloid leukemia (AML). Twenty-nine children 1 to 16 years of age (relapsed disease, 19; refractory disease, 10) received gemtuzumab ozogamicin ranging from 6 to 9 mg/m2 per dose for 2 doses (separated by 2 weeks) infused over 2 hours. All patients had anticipated myelosuppression. Other toxicities included grade 3/4 hyperbilirubinemia (7%) and elevated hepatic transaminase levels (21%); the incidence of grade 3/4 mucositis (3%) or sepsis (24%) was relatively low. One patient treated at 9 mg/m2 developed veno-occlusive disease (VOD) of the liver and defined the dose-limiting toxicity. Thirteen patients underwent hematopoietic stem-cell transplantation less than 3.5 months after the last dose of gemtuzumab ozogamicin; 6 (40%) developed VOD. Eight of 29 (28%) patients achieved overall remission. Remissions were comparable in patients with refractory (30%) and relapsed (26%) disease. Mean multidrug resistance-protein-mediated drug efflux was significantly lower in the leukemic blasts of patients achieving remission (P < .005). Gemtuzumab ozogamicin was relatively well tolerated at 6 mg/m2 for 2 doses and was equally effective in patients with refractory and relapsed disease. Further studies in combination with standard induction therapy for childhood AML are warranted.

Multidrug resistance protein attenuates gemtuzumab ozogamicin-induced cytotoxicity in acute myeloid leukemia cells.

Gemtuzumab ozogamicin (GO) is a novel immunoconjugate therapy for acute myeloid leukemia (AML). P-glycoprotein (Pgp) confers resistance to GO and is associated with a worse clinical response. To address whether multidrug resistance protein (MRP) affects GO susceptibility, we characterized Pgp, MRP1, and MRP2 expression in CD33+ cell lines and CD33+ AML samples and analyzed the effect of the Pgp inhibitor cyclosporine (CSA) and the MRP inhibitor MK-571 on GO-induced cytotoxicity. MRP1, but not MRP2, expression correlated with MRP activity. MK-571 enhanced GO-induced cytotoxicity in Pgp-negative/MRP-positive NB4 and HL-60 cells. CSA, but not MK-571 alone, restored GO susceptibility in Pgp-positive/MRP-positive TF1 cells; however, MK-571 enhanced cytotoxicity in the presence of CSA. All patient samples exhibited MRP activity, and 17 of 23 exhibited Pgp activity. CSA increased GO-induced cytotoxicity in 12 Pgp-positive samples, whereas MK-571 alone was effective in only one sample with minimal Pgp activity. In 3 Pgp-positive/MRP-positive samples, MK-571 enhanced GO-induced cytotoxicity in the presence of CSA. Thus, MRP1 may attenuate susceptibility to GO. This effect was comparatively less than that for Pgp and required the inhibition of Pgp for detection in cells that coexpressed both transporters. Because MK-571 and CSA failed to affect cytotoxicity in a portion of Pgp-positive/MRP-positive AML samples, additional resistance mechanisms are likely important.

An anti-CD33 antibody-calicheamicin conjugate for treatment of acute myeloid leukemia. Choice of linker.

The anti-CD33 antibody, P67.6, has been chosen to target the potently cytotoxic calicheamicin antitumor antibiotics to acute myeloid leukemia (AML) due to the presence of CD33 on >80% of patient samples and its lack of expression outside the myeloid cell lineages, especially its lack of expression on pluripotent stem cells. Previous calicheamicin conjugates relied on the attachment of a hydrazide derivative to the oxidized carbohydrates that occur naturally on antibodies. This results in a "carbohydrate conjugate" capable of releasing active drug by hydrolysis of a hydrazone bond in the lysozomes where the pH is low. Conjugates have now been made that are formed by reacting a calicheamicin derivative containing an activated ester with the lysines of antibodies. This results in an "amide conjugate" that is stable to hydrolysis, leaving the disulfide that is present in all calicheamicin conjugates as the likely site of drug release from the conjugate. In this article, these two classes of calicheamicin-antibody conjugates are compared for potential use in AML with the anti-CD33 antibody P67.6. Conjugates of P67.6 are shown to require the site of hydrolytic release afforded by the carbohydrate conjugates in order to retain good potency and selectivity in vitro, in vivo, and ex vivo. The P67.6 carbohydrate conjugate of calicheamicin is selectively cytotoxic at <0.006 ng/mL of calicheamicin equivalents (cal equiv) toward HL-60 promyelocytic leukemia cells in tissue culture. Long-term, tumor-free survivors are seen in xenograft models when mice bearing HL-60 subcutaneous tumors are treated with the P67.6 carbohydrate conjugate at a dose of 300 microg/kg cal equiv given three times. This conjugate also selectively inhibits the formation of colonies from AML marrow samples at 2 ng/mL cal equiv. The P67.6 carbohydrate conjugate of calicheamicin therefore appears to have promise as an antibody-targeted chemotherapeutic agent for CD33-positive diseases such as AML.