Stem Cells, Cell Therapies and Bioengineering in Lung Biology and Diseases 2023.

Repair and regeneration of a diseased lung using stem cells or bioengineered tissues is an exciting therapeutic approach for a variety of lung diseases and critical illnesses. Over the past decade increasing evidence from preclinical models suggests that cells, which are not normally resident in the lung can be utilized to modulate immune responses after injury, but there have been challenges in translating these promising findings to the clinic. In parallel, there has been a surge in bioengineering studies investigating the use of artificial and acellular lung matrices as scaffolds for three-dimensional lung or airway regeneration, with some recent attempts of transplantation in large animal models. The combination of these studies with those involving stem cells, induced pluripotent stem cell derivatives, and/or cell therapies is a promising and rapidly developing research area. These studies have been further paralleled by significant increases in our understanding of the molecular and cellular events by which endogenous lung stem and/or progenitor cells arise during lung development and participate in normal and pathologic remodeling after lung injury. For the 2023 Stem Cells, Cell Therapies, and Bioengineering in Lung Biology and Diseases Conference, scientific symposia were chosen to reflect the most cutting-edge advances in these fields. Sessions focused on the integration of "-omics" technologies with function, the influence of immune cells on regeneration, and the role of the extracellular matrix in regeneration. The necessity for basic science studies to enhance fundamental understanding of lung regeneration and to design innovative translational studies was reinforced throughout the conference.

Targeted replacement of full-length CFTR in human airway stem cells by CRISPR-Cas9 for pan-mutation correction in the endogenous locus.

Cystic fibrosis (CF) is a monogenic disease caused by impaired production and/or function of the CF transmembrane conductance regulator (CFTR) protein. Although we have previously shown correction of the most common pathogenic mutation, there are many other pathogenic mutations throughout the CF gene. An autologous airway stem cell therapy in which the CFTR cDNA is precisely inserted into the CFTR locus may enable the development of a durable cure for almost all CF patients, irrespective of the causal mutation. Here, we use CRISPR-Cas9 and two adeno-associated viruses (AAVs) carrying the two halves of the CFTR cDNA to sequentially insert the full CFTR cDNA along with a truncated CD19 (tCD19) enrichment tag in upper airway basal stem cells (UABCs) and human bronchial epithelial cells (HBECs). The modified cells were enriched to obtain 60%-80% tCD19+ UABCs and HBECs from 11 different CF donors with a variety of mutations. Differentiated epithelial monolayers cultured at air-liquid interface showed restored CFTR function that was >70% of the CFTR function in non-CF controls. Thus, our study enables the development of a therapy for almost all CF patients, including patients who cannot be treated using recently approved modulator therapies.

CFTR genotype analysis of Asians in international registries highlights disparities in the diagnosis and treatment of Asian patients with cystic fibrosis.

PURPOSE: Cystic fibrosis (CF) is not well-characterized in Asians, potentially resulting in delayed diagnosis and poor prognosis. We characterized CF in Asian subgroups to address these disparities. METHODS: De-identified ethnicity and CFTR variant data were obtained from the United States, United Kingdom, and Canadian CF registries. We measured the prevalence of CF, CFTR variant allele frequencies, effectiveness of screening panels, and eligibility for modulator therapies. RESULTS: The prevalence of CF was 1 in 74,982 people (Canada) to 1 in 13,340 people (United Kingdom) for South Asians and 1 in 256,541 (Canada) to 1 in 52,563 (United Kingdom) for other Asians, suggesting 26,000 to 146,000 patients with CF in South Asia. p.(F508del) variant was markedly less frequent in Asians than in non-Hispanic Whites. Splicing and nonsense variants occurred at high allelic frequencies in Asians, resulting in 41% to 49% of South Asians and 21% to 39% of other Asians being ineligible for CFTR modulator therapies. Hologic/EU2v1 panels failed to identify 37% to 47% of South Asian and 23% to 46% of other Asian patients with CF. CONCLUSIONS: Among Asians, CF appears to be more common in South Asians. A significant CF population may exist in South Asia. CFTR variants in South and other Asians markedly differ from non-Hispanic Whites causing inequities in newborn screening, diagnosis, and treatment. New strategies are necessary to mitigate these health care disparities.

Correction of recessive dystrophic epidermolysis bullosa by homology-directed repair-mediated genome editing.

Genome-editing technologies that enable the introduction of precise changes in DNA sequences have the potential to lead to a new class of treatments for genetic diseases. Epidermolysis bullosa (EB) is a group of rare genetic disorders characterized by extreme skin fragility. The recessive dystrophic subtype of EB (RDEB), which has one of the most severe phenotypes, is caused by mutations in COL7A1. In this study, we report a gene-editing approach for ex vivo homology-directed repair (HDR)-based gene correction that uses the CRISPR-Cas9 system delivered as a ribonucleoprotein (RNP) complex in combination with donor DNA templates delivered by adeno-associated viral vectors (AAVs). We demonstrate sufficient mutation correction frequencies to achieve therapeutic benefit in primary RDEB keratinocytes containing different COL7A1 mutations as well as efficient HDR-mediated COL7A1 modification in healthy cord blood-derived CD34+ cells and mesenchymal stem cells (MSCs). These results are a proof of concept for HDR-mediated gene correction in different cell types with therapeutic potential for RDEB.

Second-look PET-CT following an initial incomplete PET-CT response to (chemo)radiotherapy for head and neck squamous cell carcinoma.

OBJECTIVES: The limited positive predictive value of an incomplete response on PET-CT following (chemo)radiotherapy for head and neck squamous cell carcinoma (HNSCC) means that the optimal management strategy remains uncertain. The aim of the study is to assess the utility of a 'second-look' interval PET-CT. METHODS: Patients with HNSCC who were treated with (chemo)radiotherapy between 2008 and 2017 and underwent (i) baseline and (ii) response assessment PET-CT and (iii) second-look PET-CT following incomplete (positive or equivocal scan) response were included. Endpoints were conversion rate to complete response (CR) and test characteristics of the second-look PET-CT. RESULTS: Five hundred sixty-two patients with HNSCC underwent response assessment PET-CT at a median of 17 weeks post-radiotherapy. Following an incomplete response on PET-CT, 40 patients underwent a second-look PET-CT at a median of 13 weeks (range 6-25) from the first response PET-CT. Thirty-four out of 40 (85%) patients had oropharyngeal carcinoma. Twenty-four out of 40 (60%) second-look PET-CT scans converted to a complete locoregional response. The primary tumour conversion rate was 15/27 (56%) and the lymph node conversion rate was 14/19 (74%). The sensitivity, specificity, positive predictive value and negative predictive value (NPV) of the second-look PET-CT were 75%, 75%, 25% and 96% for the primary tumour and 100%, 92%, 40% and 100% for lymph nodes. There were no cases of progression following conversion to CR in the primary site or lymph nodes. CONCLUSIONS: The majority of patients who undergo a second-look PET-CT convert to a CR. The NPV of a second-look PET-CT is high, suggesting the potential to avoid surgical intervention. KEY POINTS: • PET-CT is a useful tool for response assessment following (chemo)radiotherapy for head and neck squamous cell carcinoma. • An incomplete response on PET-CT has a limited positive predictive value and optimal management is uncertain. • These data show that with a 'second-look' interval PET-CT, the majority of patients convert to a complete metabolic response. When there is doubt about clinical and radiological response, a 'second-look' PET-CT can be used to spare patients unnecessary surgical intervention.

Global Transcriptional Response to CRISPR/Cas9-AAV6-Based Genome Editing in CD34+ Hematopoietic Stem and Progenitor Cells.

Genome-editing technologies are currently being translated to the clinic. However, cellular effects of the editing machinery have yet to be fully elucidated. Here, we performed global microarray-based gene expression measurements on human CD34+ hematopoietic stem and progenitor cells that underwent editing. We probed effects of the entire editing process as well as each component individually, including electroporation, Cas9 (mRNA or protein) with chemically modified sgRNA, and AAV6 transduction. We identified differentially expressed genes relative to control treatments, which displayed enrichment for particular biological processes. All editing machinery components elicited immune, stress, and apoptotic responses. Cas9 mRNA invoked the greatest amount of transcriptional change, eliciting a distinct viral response and global transcriptional downregulation, particularly of metabolic and cell cycle processes. Electroporation also induced significant transcriptional change, with notable downregulation of metabolic processes. Surprisingly, AAV6 evoked no detectable viral response. We also found Cas9/sgRNA ribonucleoprotein treatment to be well tolerated, in spite of eliciting a DNA damage signature. Overall, this data establishes a benchmark for cellular tolerance of CRISPR/Cas9-AAV6-based genome editing, ensuring that the clinical protocol is as safe and efficient as possible.

Can MR textural analysis improve the prediction of extracapsular nodal spread in patients with oral cavity cancer?

OBJECTIVE: To explore the utility of MR texture analysis (MRTA) for detection of nodal extracapsular spread (ECS) in oral cavity squamous cell carcinoma (SCC). METHODS: 115 patients with oral cavity SCC treated with surgery and adjuvant (chemo)radiotherapy were identified retrospectively. First-order texture parameters (entropy, skewness and kurtosis) were extracted from tumour and nodal regions of interest (ROIs) using proprietary software (TexRAD). Nodal MR features associated with ECS (flare sign, irregular capsular contour; local infiltration; nodal necrosis) were reviewed and agreed in consensus by two experienced radiologists. Diagnostic performance characteristics of MR features of ECS were compared with primary tumour and nodal MRTA prediction using histology as the gold standard. Receiver operating characteristic (ROC) and regression analyses were also performed. RESULTS: Nodal entropy derived from contrast-enhanced T1-weighted images was significant in predicting ECS (p = 0.018). MR features had varying accuracy: flare sign (70%); irregular contour (71%); local infiltration (66%); and nodal necrosis (64%). Nodal entropy combined with irregular contour was the best predictor of ECS (p = 0.004, accuracy 79%). CONCLUSION: First-order nodal MRTA combined with imaging features may improve ECS prediction in oral cavity SCC. KEY POINTS: • Nodal MR textural analysis can aid in predicting extracapsular spread (ECS). • Medium filter contrast-enhanced T1 nodal entropy was strongly significant in predicting ECS. • Combining nodal entropy with irregular nodal contour improves predictive accuracy.

Role of Cell Membrane-Vector Interactions in Successful Gene Delivery.

Cationic polymers have been investigated as nonviral vectors for gene delivery due to their favorable safety profile when compared to viral vectors. However, nonviral vectors are limited by poor efficacy in inducing gene expression. The physicochemical properties of cationic polymers enabling successful gene expression have been investigated in order to improve expression efficiency and safety. Studies over the past several years have focused on five possible rate-limiting processes to explain the differences in gene expression: (1) endosomal release, (2) transport within specific intracellular pathways, (3) protection of DNA from nucleases, (4) transport into the nucleus, and (5) DNA release from vectors. However, determining the relative importance of these processes and the vector properties necessary for optimization remain a challenge to the field. In this Account, we describe over a decade of studies focused on understanding the interaction of cationic polymer and cationic polymer/oligonucleotide (polyplex) interactions with model lipid membranes, cell membranes, and cells in culture. In particular, we have been interested in how the interaction between cationic polymers and the membrane influences the intracellular transport of intact DNA to the nucleus. Recent advances in microfluidic patch clamp techniques enabled us to quantify polyplex cell membrane interactions at the cellular level with precise control over material concentrations and exposure times. In attempting to relate these findings to subsequent intracellular transport of DNA and expression of protein, we needed to develop an approach that could distinguish DNA that was intact and potentially functional for gene expression from the much larger pool of degraded, nonfunctional DNA within the cell. We addressed this need by developing a FRET oligonucleotide molecular beacon (OMB) to monitor intact DNA transport. The research highlighted in this Account builds to the conclusion that polyplex transported DNA is released from endosomes by free cationic polymer intercalated into the endosomal membrane. This cationic polymer initially interacts with the cell plasma membrane and appears to reach the endosome by lipid cycling mechanisms. The fraction of cells displaying release of intact DNA from endosomes quantitatively predicts the fraction of cells displaying gene expression for both linear poly(ethylenimine) (L-PEI; an effective vector) and generation five poly(amidoamine) dendrimer (G5 PAMAM; an ineffective vector). Moreover, intact OMB delivered with G5 PAMAM, which normally is confined to endosomes, was released by the subsequent addition of L-PEI with a corresponding 10-fold increase in transgene expression. These observations are consistent with experiments demonstrating that cationic polymer/membrane partition coefficients, not polyplex/membrane partition coefficients, predict successful gene expression. Interestingly, a similar partitioning of cationic polymers into the mitochondrial membranes has been proposed to explain the cytotoxicity of these materials. Thus, the proposed model indicates the same physicochemical property (partitioning into lipid bilayers) is linked to release from endosomes, giving protein expression, and to cytotoxicity.

Efficacy of qualitative response assessment interpretation criteria at 18F-FDG PET-CT for predicting outcome in locally advanced cervical carcinoma treated with chemoradiotherapy.

OBJECTIVES: To evaluate the utility of a standardized qualitative scoring system for treatment response assessment at 18F-FDG PET-CT in patients undergoing chemoradiotherapy for locally advanced cervical carcinoma and correlate this with subsequent patient outcome. METHODS: Ninety-six consecutive patients with locally advanced cervical carcinoma treated with radical chemoradiotherapy (CRT) in a single centre between 2011 and 2014 underwent 18F-FDG PET-CT approximately 3 months post-treatment. Tumour metabolic response was assessed qualitatively using a 5-point scale ranging from background level activity only through to progressive metabolic disease. Clinical and radiological (MRI pelvis) follow-up was performed in all patients. Progression-free (PFS) and overall survival (OS) was calculated using the Kaplan-Meier method (Mantel-Cox log-rank) and correlated with qualitative score using Chi-squared test. RESULTS: Forty patients (41.7 %) demonstrated complete metabolic response (CMR) on post-treatment PET-CT (Score 1/2) with 38 patients (95.0 %) remaining disease free after a minimum follow-up period of 18 months. Twenty-four patients (25.0 %) had indeterminate residual uptake (ID, Score 3) at primary or nodal sites after treatment, of these eight patients (33.3 %) relapsed on follow-up, including all patients with residual nodal uptake (n = 4Eleven11 of 17 patients (64.7 %) with significant residual uptake (partial metabolic response, PMR, Score 4) subsequently relapsed. In 15 patients (15.6 %) PET-CT demonstrated progressive disease (PD, Score 5) following treatment. Kaplan-Meier analysis showed a highly statistically significant difference in PFS and OS between patients with CMR, indeterminate uptake, PMR and PD (Log-rank, P < 0.0001). Chi-squared test demonstrated a highly statistically significant association between increasing qualitative score and risk of recurrence or death (P < 0.001). CONCLUSION: Use of a 5-point qualitative scoring system to assess metabolic response to CRT in locally advanced cervical carcinoma predicts survival outcome and this prognostic information may help guide further patient management.

Cationic Polymer Intercalation into the Lipid Membrane Enables Intact Polyplex DNA Escape from Endosomes for Gene Delivery.

Developing improved cationic polymer-DNA polyplexes for gene delivery requires improved understanding of DNA transport from endosomes into the nucleus. Using a FRET-capable oligonucleotide molecular beacon (OMB), we monitored the transport of intact DNA to cell organelles. We observed that for effective (jetPEI) and ineffective (G5 PAMAM) vectors, the fraction of cells displaying intact OMB in the cytosol (jetPEI ≫ G5 PAMAM) quantitatively predicted the fraction expressing transgene (jetPEI ≫ G5 PAMAM). Intact OMB delivered with PAMAM and confined to endosomes could be released to the cytosol by the subsequent addition of L-PEI, with a corresponding 10-fold increase in transgene expression. These results suggest that future vector development should optimize vectors for intercalation into, and destabilization of, the endosomal membrane. Finally, the study highlights a two-step strategy in which the pDNA is loaded in cells using one vector and endosomal release is mediated by a second agent.

Fluorophore:dendrimer ratio impacts cellular uptake and intracellular fluorescence lifetime.

G5-NH2-TAMRAn (n = 1-4, 5+, and 1.5(avg)) were prepared with n = 1-4 as a precise dye:dendrimer ratio, 5+ as a mixture of dendrimers with 5 or more dye per dendrimer, and 1.5(avg) as a Poisson distribution of dye:dendrimer ratios with a mean of 1.5 dye per dendrimer. The absorption intensity increased sublinearly with n whereas the fluorescence emission and lifetime decreased with an increasing number of dyes per dendrimer. Flow cytometry was employed to quantify uptake into HEK293A cells. Dendrimers with 2-4 dyes were found to have greater uptake than dendrimer with a single dye. Fluorescence lifetime imaging microscopy (FLIM) showed that the different dye:dendrimer ratio alone was sufficient to change the fluorescence lifetime of the material observed inside cells. We also observed that the lifetime of G5-NH2-TAMRA5+ increased when present in the cell as compared to solution. However, cells treated with G5-NH2-TAMRA1.5(avg) did not exhibit the high lifetime components present in G5-NH2-TAMRA1 and G5-NH2-TAMRA5+. In general, the effects of the dye:dendrimer ratio on fluorescence lifetime were of similar magnitude to environmentally induced lifetime shifts.

Investigating adverse genomic and regulatory changes caused by replacement of the full-length CFTR cDNA using Cas9 and AAV.

A "universal strategy" replacing the full-length CFTR cDNA may treat >99% of people with cystic fibrosis (pwCF), regardless of their specific mutations. Cas9-based gene editing was used to insert the CFTR cDNA and a truncated CD19 (tCD19) enrichment tag at the CFTR locus in airway basal stem cells. This strategy restores CFTR function to non-CF levels. Here, we investigate the safety of this approach by assessing genomic and regulatory changes after CFTR cDNA insertion. Safety was first assessed by quantifying genetic rearrangements using CAST-seq. After validating restored CFTR function in edited and enriched airway cells, the CFTR locus open chromatin profile was characterized using ATAC-seq. The regenerative potential and differential gene expression in edited cells was assessed using scRNA-seq. CAST-seq revealed a translocation in ∼0.01% of alleles primarily occurring at a nononcogenic off-target site and large indels in 1% of alleles. The open chromatin profile of differentiated airway epithelial cells showed no appreciable changes, except in the region corresponding to the CFTR cDNA and tCD19 cassette, indicating no detectable changes in gene regulation. Edited stem cells produced the same types of airway cells as controls with minimal alternations in gene expression. Overall, the universal strategy showed minor undesirable genomic changes.

Single-Stranded DNA with Internal Base Modifications Mediates Highly Efficient Gene Insertion in Primary Cells.

Single-stranded DNA (ssDNA) templates along with Cas9 have been used for gene insertion but suffer from low efficiency. Here, we show that ssDNA with chemical modifications in 10-17% of internal bases (eDNA) is compatible with the homologous recombination machinery. Moreover, eDNA templates improve gene insertion by 2-3 fold compared to unmodified and end-modified ssDNA in airway basal stem cells (ABCs), hematopoietic stem and progenitor cells (HSPCs), T-cells and endothelial cells. Over 50% of alleles showed gene insertion in three clinically relevant loci (CFTR, HBB, and CCR5) in ABCs using eDNA and up to 70% of alleles showed gene insertion in the HBB locus in HSPCs. This level of correction is therapeutically relevant and is comparable to adeno-associated virus-based templates. Knocking out TREX1 nuclease improved gene insertion using unmodified ssDNA but not eDNA suggesting that chemical modifications inhibit TREX1. This approach can be used for therapeutic applications and biological modeling.

Polyplex exposure inhibits cell cycle, increases inflammatory response, and can cause protein expression without cell division.

We sought to evaluate the relationship between cell division and protein expression when using commercial poly(ethylenimine) (PEI)-based polyplexes. The membrane dye PKH26 was used to assess cell division, and cyan fluorescent protein (CFP) was used to monitor protein expression. When analyzed at the whole population level, a greater number of cells divided than expressed protein, regardless of the level of protein expression observed, giving apparent consistency with the hypothesis that protein expression requires cells to pass through mitosis in order for the transgene to overcome the nuclear membrane. However, when the polyplex-exposed population was evaluated for the amount of division in the protein-expressing subpopulation, it was observed that substantial amounts of expression had occurred in the absence of division. Indeed, in HeLa S3 cells, this represented the majority of expressing cells. Of interest, the doubling time for both cell lines was slowed by ~2-fold upon exposure to polyplexes. This change was not altered by the origin of the plasmid DNA (pDNA) transgene promoter (cytomegalovirus (CMV) or elongation factor-1 alpha (EF1α)). Gene expression arrays in polyplex-exposed HeLa S3 cells showed upregulation of cell cycle arrest genes and downregulation of genes related to mitosis. Chemokine, interleukin, and toll-like receptor genes were also upregulated, suggesting activation of proinflammatory pathways. In summary, we find evidence that a cell division-independent expression pathway exists, and that polyplex exposure slows cell division and increases inflammatory response.

Polyplex-induced cytosolic nuclease activation leads to differential transgene expression.

Cytosolic nucleases have been proposed to play an important role in limiting the effectiveness of polyplex-based gene delivery agents. In order to explore the effect of cell membrane disruption on nuclease activation, nuclease activity upon polyplex uptake and localization, and nuclease activity upon gene expression, we employed an oligonucleotide molecular beacon (MB). The MB was incorporated as an integral part of the polymer/DNA polyplex, and two-color flow cytometry experiments were performed to explore the relationship of MB cleavage with propidium iodide (PI) uptake, protein expression, and polyplex uptake. In addition, confocal fluorescence microcopy was performed to examine both polyplex and cleaved MB localization. The impact of cell membrane disruption was also probed using whole-cell patch clamp measurement of the plasma membrane's electrical conductance. Differential activation of cytosolic nuclease was observed with substantial activity for B-PEI and G5 PAMAM dendrimer (G5), less cleavage for jetPEI, and little activity for L-PEI. jetPEI and L-PEI exhibited substantially greater transgene expression, consistent with the lower amounts of MB oligonucleotide cleavage observed. Cytosolic nuclease activity, although dependent on the choice of polymer employed, was not related to the degree of cell plasma membrane disruption that occurred as measured by PI uptake or whole-cell patch clamp.

Inhaled and systemic corticosteroid response in severe asthma assessed by alveolar nitric oxide: a randomized crossover pilot study of add-on therapy.

AIMS: Alveolar nitric oxide (CA(NO)) is a potential biomarker of small airway inflammation. We investigated effects on CA(NO) of the addition of coarse and fine particle inhaled corticosteroids to standard therapy in severe asthma. METHODS: Severe asthmatics taking ≥1600 µg day(-1) budesonide or equivalent performed a randomized open-label crossover study. Subjects with FEV(1) < 80%, gas trapping and CA(NO) ≥2 ppb entered a 6 week dose-ramp run-in of fluticasone/salmeterol(FPSM) 250/50 µg twice daily for 3 weeks, then 500/50 µg twice daily for 3 weeks. Patients then received additional HFA-beclomethasone diproprionate (BDP) 200 µg twice daily or FP 250 µg twice daily for 3 weeks in a crossover. Participants then received prednisolone(PRED) 25 mg day(-1) for 1 week. Nitric oxide, lung function, mannitol challenge, systemic inflammatory markers and urinary cortisol were measured. RESULTS: Fifteen completed per protocol: mean (SD) age 51 (12) years, FEV(1) 58 (13)% predicted, residual volume 193 (100)% predicted and mannitol(PD10) 177 (2.8) µg. There was no significant difference between FPSM and add-on therapy for CA(NO). FPSM/BDP and FPSM/PRED suppressed broncial flux (Jaw(NO)) and FE(NO) compared with FPSM alone, but there was no significant difference between FPSM/BDP and FPSM/FP. ECP, e-selectin and ICAM-1 were suppressed by FPSM/PRED compared with FPSM and FPSM/FP but not FPSM/BDP. Plasma cortisol was significantly suppressed by FPSM/PRED. CONCLUSION: In severe asthma, CA(NO) is insensitive to changes in dose and delivery of inhaled corticosteroids and is not suppressed by systemic corticosteroids. Additional inhaled HFA-BDP reduced FE(NO) and Jaw(NO) without adrenal suppression. There was a trend to reduction in FE(NO) and Jaw(NO) with additional FP but this did not reach statistical significance. PRED reduced FE(NO) and Jaw(NO) with suppression of systemic inflammatory markers and urinary cortisol.

Clinical Utility of Second-Look FDG PET-CT to Stratify Incomplete Metabolic Response Post (Chemo) Radiotherapy in Oropharyngeal Squamous Cell Carcinoma.

BACKGROUND: Incomplete response on FDG PET-CT following (chemo)radiotherapy (CRT) for head and neck squamous cell carcinoma (HNSCC) hinders optimal management. The study assessed the utility of an interval (second look) PET-CT. METHODS: Patients with oropharyngeal squamous cell carcinoma cancer (OPSCC) treated with CRT at a single centre between 2013 and 2020 who underwent baseline, response, and second-look PET-CT were included. Endpoints were conversion rate to complete metabolic response (CMR) and test characteristics of second-look PET-CT. RESULTS: In total, 714 patients with OPSCC underwent PET-CT post-radiotherapy. In total, 88 patients with incomplete response underwent second-look PET-CT a median of 13 weeks (interquartile range 10-15 weeks) after the initial response assessment. In total, 27/88 (31%) second-look PET-CTs showed conversion to CMR, primary tumour CMR in 20/60 (30%), and nodal CMR in 13/37 (35%). In total, 1/34 (3%) with stable tumour/nodal uptake at the second-look PET-CT relapsed. Sensitivity, specificity, positive (PPV), and negative predictive value (NPV) of second-look PET-CT were 95%, 49%, 50%, and 95% for tumour and 92%, 50%, 50%, and 92% for nodes, respectively. Primary tumour progression following CMR occurred in one patient, two patients with residual nodal uptake at second-look PET-CT progressed locoregionally, and one patient developed metastatic disease following CMR in residual nodes. CONCLUSION: Most patients undergoing second-look PET-CT converted to CMR or demonstrated stable PET signal. NPV was high, suggesting the potential to avoid unnecessary surgical intervention.

High-efficiency transgene integration by homology-directed repair in human primary cells using DNA-PKcs inhibition.

Therapeutic applications of nuclease-based genome editing would benefit from improved methods for transgene integration via homology-directed repair (HDR). To improve HDR efficiency, we screened six small-molecule inhibitors of DNA-dependent protein kinase catalytic subunit (DNA-PKcs), a key protein in the alternative repair pathway of non-homologous end joining (NHEJ), which generates genomic insertions/deletions (INDELs). From this screen, we identified AZD7648 as the most potent compound. The use of AZD7648 significantly increased HDR (up to 50-fold) and concomitantly decreased INDELs across different genomic loci in various therapeutically relevant primary human cell types. In all cases, the ratio of HDR to INDELs markedly increased, and, in certain situations, INDEL-free high-frequency (>50%) targeted integration was achieved. This approach has the potential to improve the therapeutic efficacy of cell-based therapies and broaden the use of targeted integration as a research tool.