Scalable, Continuous Evolution of Genes at Mutation Rates above Genomic Error Thresholds.

Directed evolution is a powerful approach for engineering biomolecules and understanding adaptation. However, experimental strategies for directed evolution are notoriously labor intensive and low throughput, limiting access to demanding functions, multiple functions in parallel, and the study of molecular evolution in replicate. We report OrthoRep, an orthogonal DNA polymerase-plasmid pair in yeast that stably mutates ∼100,000-fold faster than the host genome in vivo, exceeding the error threshold of genomic replication that causes single-generation extinction. User-defined genes in OrthoRep continuously and rapidly evolve through serial passaging, a highly straightforward and scalable process. Using OrthoRep, we evolved drug-resistant malarial dihydrofolate reductases (DHFRs) in 90 independent replicates. We uncovered a more complex fitness landscape than previously realized, including common adaptive trajectories constrained by epistasis, rare outcomes that avoid a frequent early adaptive mutation, and a suboptimal fitness peak that occasionally traps evolving populations. OrthoRep enables a new paradigm of routine, high-throughput evolution of biomolecular and cellular function.

Discovery of VH domains that allosterically inhibit ENPP1.

Ectodomain phosphatase/phosphodiesterase-1 (ENPP1) is overexpressed on cancer cells and functions as an innate immune checkpoint by hydrolyzing extracellular cyclic guanosine monophosphate adenosine monophosphate (cGAMP). Biologic inhibitors have not yet been reported and could have substantial therapeutic advantages over current small molecules because they can be recombinantly engineered into multifunctional formats and immunotherapies. Here we used phage and yeast display coupled with in cellulo evolution to generate variable heavy (VH) single-domain antibodies against ENPP1 and discovered a VH domain that allosterically inhibited the hydrolysis of cGAMP and adenosine triphosphate (ATP). We solved a 3.2 Å-resolution cryo-electron microscopy structure for the VH inhibitor complexed with ENPP1 that confirmed its new allosteric binding pose. Finally, we engineered the VH domain into multispecific formats and immunotherapies, including a bispecific fusion with an anti-PD-L1 checkpoint inhibitor that showed potent cellular activity.

Adding new chemistries to the genetic code.

The development of new orthogonal aminoacyl-tRNA synthetase/tRNA pairs has led to the addition of approximately 70 unnatural amino acids (UAAs) to the genetic codes of Escherichia coli, yeast, and mammalian cells. These UAAs represent a wide range of structures and functions not found in the canonical 20 amino acids and thus provide new opportunities to generate proteins with enhanced or novel properties and probes of protein structure and function.

The Impact of Nanobodies on G Protein-Coupled Receptor Structural Biology and Their Potential as Therapeutic Agents.

The family of human G protein-coupled receptors (GPCRs) comprises about 800 different members, with about 35% of current pharmaceutical drugs targeting GPCRs. However, GPCR structural biology, necessary for structure-guided drug design, has lagged behind that of other membrane proteins, and it was not until the year 2000 when the first crystal structure of a GPCR (rhodopsin) was solved. Starting in 2007, the determination of additional GPCR structures was facilitated by protein engineering, new crystallization techniques, complexation with antibody fragments, and other strategies. More recently, the use of camelid heavy-chain-only antibody fragments (nanobodies) as crystallographic chaperones has revolutionized the field of GPCR structural biology, aiding in the determination of more than 340 GPCR structures to date. In most cases, the GPCR structures solved as complexes with nanobodies (Nbs) have revealed the binding mode of cognate or non-natural ligands; in a few cases, the same Nb has acted as an orthosteric or allosteric modulator of GPCR signaling. In this review, we summarize the multiple ingenious strategies that have been conceived and implemented in the last decade to capitalize on the discovery of nanobodies to study GPCRs from a structural perspective. SIGNIFICANCE STATEMENT: G protein-coupled receptors (GPCRs) are major pharmacological targets, and the determination of their structures at high resolution has been essential for structure-guided drug design and for insights about their functions. Single-domain antibodies (nanobodies) have greatly facilitated the structural determination of GPCRs by forming complexes directly with the receptors or indirectly through protein partners.

Mainstream Germline Genetic Testing with Expanded Eligibility for Early Breast Cancer Patients in a Large Integrated Health System.

BACKGROUND: This study evaluated a new mainstream genetic testing pathway for hereditary cancer, with expanded eligibility for early-stage breast cancer patients. METHODS: The study compared multigene panel (62 genes) germline testing uptake and results for breast cancer patients at 4 pilot sites (n = 502 patients) and 10 non-pilot sites (n = 1792 patients) within Kaiser Permanente Northern California from December 2020, to June 2021. At the pilot sites, breast care coordinators (BCCs) offered and consented patients for testing, with eligibility expanded to include all patients age 65 years or younger. At the non-pilot sites, eligible patients were referred to genetics for pre-test counseling, ordering, and follow-up evaluation with the standard guideline that included all patients age 45 years or younger. RESULTS: Demographic and disease characteristics were similar at the pilot and non-pilot sites. At the pilot verses non-pilot sites, a higher percentage of patients was tested overall (61.6% vs 31.7%) and across all age groups. The median time from breast biopsy to test result also was reduced (22 vs 33 days, respectively). A higher percentage of patients at the pilot sites was identified as having a pathogenic/likely pathogenic variant (PV/LPV) in a breast cancer-related gene (3.6% vs 1.6%). Although the percentage of total patients tested was nearly twofold higher at the pilot sites than at the non-pilot sites, the percentage of total patients seen by genetics was estimated to be similar (33.7% vs 31.7%). CONCLUSION: Mainstream genetic testing of breast cancer patients facilitated by BCCs makes it feasible for a large health care system to expand germline genetic testing to early breast cancer patients age 65 years or younger.

Intrinsic Toroidal Rotation Driven by Turbulent and Neoclassical Processes in Tokamak Plasmas from Global Gyrokinetic Simulations.

Gyrokinetic tokamak plasmas can exhibit intrinsic toroidal rotation driven by the residual stress. While most studies have attributed the residual stress to the parallel-momentum flux from the turbulent E×B motion, the parallel-momentum flux from the drift-orbit motion (denoted Π_{∥}^{D}) and the E×B-momentum flux from the E×B motion (denoted Π_{E×B}) are often neglected. Here, we use the global total-f gyrokinetic code XGC to study the residual stress in the core and the edge of a DIII-D H-mode plasma. Numerical results show that both Π_{∥}^{D} and Π_{E×B} make up a significant portion of the residual stress. In particular, Π_{∥}^{D} in the core is higher than the collisional neoclassical level in the presence of turbulence, while in the edge it represents an outflux of countercurrent momentum even without turbulence. Using a recently developed "orbit-flux" formulation, we show that the higher-than-neoclassical-level Π_{∥}^{D} in the core is driven by turbulence, while the outflux of countercurrent momentum from the edge is mainly due to collisional ion orbit loss. These results suggest that Π_{∥}^{D} and Π_{E×B} can be important for the study of intrinsic toroidal rotation.

Broadening of the Divertor Heat Flux Profile in High Confinement Tokamak Fusion Plasmas with Edge Pedestals Limited by Turbulence in DIII-D.

Multimachine empirical scaling predicts an extremely narrow heat exhaust layer in future high magnetic field tokamaks, producing high power densities that require mitigation. In the experiments presented, the width of this exhaust layer is nearly doubled using actuators to increase turbulent transport in the plasma edge. This is achieved in low collisionality, high confinement edge pedestals with their gradients limited by turbulent transport instead of large-scale, coherent instabilities. The exhaust heat flux profile width and divertor leg diffusive spreading both double as a high frequency band of turbulent fluctuations propagating in the electron diamagnetic direction doubles in amplitude. The results are quantitatively reproduced in electromagnetic XGC particle-in-cell simulations which show the heat flux carried by electrons emerges to broaden the heat flux profile, directly supported by Langmuir probe measurements.

A per-cent-level determination of the nucleon axial coupling from quantum chromodynamics.

The axial coupling of the nucleon, gA, is the strength of its coupling to the weak axial current of the standard model of particle physics, in much the same way as the electric charge is the strength of the coupling to the electromagnetic current. This axial coupling dictates the rate at which neutrons decay to protons, the strength of the attractive long-range force between nucleons and other features of nuclear physics. Precision tests of the standard model in nuclear environments require a quantitative understanding of nuclear physics that is rooted in quantum chromodynamics, a pillar of the standard model. The importance of gA makes it a benchmark quantity to determine theoretically-a difficult task because quantum chromodynamics is non-perturbative, precluding known analytical methods. Lattice quantum chromodynamics provides a rigorous, non-perturbative definition of quantum chromodynamics that can be implemented numerically. It has been estimated that a precision of two per cent would be possible by 2020 if two challenges are overcome1,2: contamination of gA from excited states must be controlled in the calculations and statistical precision must be improved markedly2-10. Here we use an unconventional method 11 inspired by the Feynman-Hellmann theorem that overcomes these challenges. We calculate a gA value of 1.271 ± 0.013, which has a precision of about one per cent.

Orychophragmus violaceus and/or chicory forage affects performance, egg quality, sensory evaluation and antioxidative properties in native laying hens.

Orychophragmus violaceus (OV) and chicory (Cichorium intybus L., CC) can be used as fresh or dry forage for animals. To determine whether OV and/or CC have beneficial effects on performance and egg quality, a total of 1212 28-wk-old Beijing You Chicken (BYC) laying hens with similar performance were randomly allocated to 4 groups with 3 replicate pens per group, and 101 birds per pen. The birds were fed a basal diet (control), the basal diet + OV (3.507 kg/d/pen), the basal diet + CC (2.525 kg/d/pen), and the basal diet + OV + CC (OVC, 1.7535 kg/d/pen OV + 1.2625 kg/d/pen CC) for 3 wks after one wk of adaptation. The results showed that egg-laying rate was not affected by OV, CC and OVC (p > 0.05), but weekly average egg mass was significantly increased by OV and CC (p < 0.05). The feed egg ratio in the CC group (2.82) was significantly lower than that in the other three groups (p < 0.05). The eggshell thickness (EST), albumen height (AH) and Haugh unit (HU) were decreased by OV and CC (p < 0.05); while yolk color (YC) was increased in the CC and OVC groups (p < 0.05). Egg grade was decreased by OV (p < 0.05). Sensory evaluation showed that there was a trend for increased YC in OV, CC and OVC (p = 0.089). Serum total protein was significantly lower in OV group than those in the control and CC group (p < 0.05); serum albumin content was significantly decreased in OV, CC and OVC groups (p = 0.006). Serum glutathione peroxidase activity in CC and OVC groups was significantly higher than that in the control group (p < 0.05). In conclusion, the present study suggests that CC had a better effect on the performance of the native laying hens than OV. The OV and CC affected egg quality, while YC was increased in CC and OVC groups. The OVC improved YC and serum antioxidative properties of native laying hens without affecting the performance.

Association between workplace health promotion service utilisation and depressive symptoms among workers: a nationwide survey.

OBJECTIVES: Workplace-related factors are associated with the risk of depression. Despite implementation of workplace health promotion (WHP) programmes in China to promote the physical and mental well-being of workers, the relationship between WHP and depression has received limited attention. This study investigated the association between WHP service utilisation and depressive symptoms among workers. STUDY DESIGN: This was a cross-sectional survey. METHODS: A researcher-designed questionnaire was used to collect information on socio-demographic and occupational characteristics, WHP service utilisation, and mental health status. The Lasso method was used for variable selection to achieve dimension reduction, and logistic regression was used to assess the association between WHP service utilisation and depressive symptoms. RESULTS: The analysis included 11,710 workers, of whom 17.0% had depressive symptoms. Lasso regression resulted in 6 of 18 WHP services showing significant negative associations with depressive symptoms, including occupational safety training, mental health services, health check-ups, sports activities, fitness rooms, and healthy canteens. The logistic regression results showed that, after adjusting for sociodemographic and occupational factors, utilisation of these six services was associated with a decreased likelihood of depressive symptoms. The adjusted odds ratio (aOR) was 0.84 (95% confidence interval [CI]: 0.73-0.96) for occupational safety training, aOR: 0.82 (95% CI: 0.68-0.99) for mental health services, aOR: 0.80 (95% CI: 0.71-0.90) for health check-ups, aOR: 0.68 (95% CI: 0.57-0.80) for sports activities, aOR: 0.59 (95% CI: 0.47-0.74) for fitness rooms and aOR: 0.72 (95% CI: 0.59-0.87) for healthy canteens. CONCLUSIONS: Utilisation of WHP services was associated with a lower prevalence of depressive symptoms. Implementation of WHP services and the provision of a supportive workplace environment should be prioritised to benefit the mental health of workers.

[Clinicopathological features of BAP1 mutated clear cell renal cell carcinoma].

Objective: To investigate the clinicopathological characteristics, immunophenotypes, molecular features, and differential diagnosis of BAP1 mutated clear cell renal cell carcinoma (CCRCC) for better understanding this entity. Methods: Clinical data, histological morphology, immunophenotypes and molecular characteristics of 18 BAP1 mutated CCRCC cases diagnosed at the Department of Pathology, the First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China from January 2020 to December 2022 were analyzed. The patients were followed up. Results: There were 17 males and 1 female patients, aged from 39 to 72 years, with an average age of 56.3 years. Sixteen patients with primary CCRCC were followed up for an average of 24 months, 7 patients had metastases occurred from 4 to 22 months postoperatively. Thirteen of the 16 patients were alive at the time of the last follow-up while 3 patients died 12, 15, and 20 months after the surgery, respectively. One patient underwent retroperitoneal mass resection, but had lung metastasis 32 months after surgery. One case received cervical tumor resection and died at 22 months after the surgery. Characteristic CCRCC regions were identified in 11 of the 18 cases. The tumor cells were arranged in papillary, alveolar, and large nest patterns. Abundant lymphoid tissue, necrosis, and psammoma bodies were seen. Tumor cells showed abundant eosinophilic cytoplasm, and sometimes exhibited rhabdoid differentiation. Round eosinophilic globules were located in the cytoplasm and extracellular matrix. There were 9 cases with WHO/International Society of Urological Pathology grade 3, and 9 cases with grade 4. PAX8 (18/18), carbonic anhydrase 9 (CA9, 16/18), CD10 (18/18), and vimentin (18/18) were positive in the vast majority of tumors.TFE3 was expressed in 5 cases, with strong expression in only 1 case. Eighteen cases were all positive for P504s. Twelve cases harbored a BAP1 mutation combined with von Hippel-Lindau (VHL) mutation, and 2 cases had mutations in BAP1, VHL and PBRM1 simultaneously. SETD2 mutation was not found in any of the cases. Conclusions: BAP1 mutated CCRCC contained papillary, alveolar, and large nest patterns, eosinophilic cytoplasm, high-grade nucleoli, and collagen globules, with P504s positivity. In practical work, when encountering CCRCC containing these features, pathologists should consider the possibility of BAP1 mutations and conduct related molecular tests.

Liquid-like atoms in dense-packed solid glasses.

Revealing the microscopic structural and dynamic pictures of glasses is a long-standing challenge for scientists1,2. Extensive studies on the structure and relaxation dynamics of glasses have constructed the current classical picture3-5: glasses consist of some 'soft zones' of loosely bound atoms embedded in a tightly bound atomic matrix. Recent experiments have found an additional fast process in the relaxation spectra6-9, but the underlying physics of this process remains unclear. Here, combining extensive dynamic experiments and computer simulations, we reveal that this fast relaxation is associated with string-like diffusion of liquid-like atoms, which are inherited from the high-temperature liquids. Even at room temperature, some atoms in dense-packed metallic glasses can diffuse just as easily as they would in liquid states, with an experimentally determined viscosity as low as 107 Pa·s. This finding extends our current microscopic picture of glass solids and might help establish the dynamics-property relationship of glasses4.

Using continuous directed evolution to improve enzymes for plant applications.

Continuous directed evolution of enzymes and other proteins in microbial hosts is capable of outperforming classical directed evolution by executing hypermutation and selection concurrently in vivo, at scale, with minimal manual input. Provided that a target enzyme's activity can be coupled to growth of the host cells, the activity can be improved simply by selecting for growth. Like all directed evolution, the continuous version requires no prior mechanistic knowledge of the target. Continuous directed evolution is thus a powerful way to modify plant or non-plant enzymes for use in plant metabolic research and engineering. Here, we first describe the basic features of the yeast (Saccharomyces cerevisiae) OrthoRep system for continuous directed evolution and compare it briefly with other systems. We then give a step-by-step account of three ways in which OrthoRep can be deployed to evolve primary metabolic enzymes, using a THI4 thiazole synthase as an example and illustrating the mutational outcomes obtained. We close by outlining applications of OrthoRep that serve growing demands (i) to change the characteristics of plant enzymes destined for return to plants, and (ii) to adapt ("plantize") enzymes from prokaryotes-especially exotic prokaryotes-to function well in mild, plant-like conditions.

LED-pumped eye-safe pulse laser with an extracavity optical parametric oscillator.

An LED-side-pumped Nd:YAG/Cr4+:YAG passively Q-switched (PQS) laser containing an extracavity optical parametric oscillator (EOPO) is demonstrated. As far as we know, it is the first LED-pumped eye-safe laser. The Nd:YAG pump module is optimized to increase the PQS pulse energy to 24 mJ at 1064 nm. By using a single-pass EOPO design, the output energy of the signal pulse at 1573 nm is 7.44 mJ with a pulse width of 16 ns, the peak power is 434 kW, and the pump-to-signal conversion efficiency is 31%. For double-pass EOPO operation, the pump-to-signal conversion efficiency increases to 45.8%, the output energy of signal pulse is up to 10.98 mJ with a pulse width of 23.5 ns, and the peak power is 459 kW.

Lineage tracing and analog recording in mammalian cells by single-site DNA writing.

Studying cellular and developmental processes in complex multicellular organisms can require the non-destructive observation of thousands to billions of cells deep within an animal. DNA recorders address the staggering difficulty of this task by converting transient cellular experiences into mutations at defined genomic sites that can be sequenced later in high throughput. However, existing recorders act primarily by erasing DNA. This is problematic because, in the limit of progressive erasure, no record remains. We present a DNA recorder called CHYRON (Cell History Recording by Ordered Insertion) that acts primarily by writing new DNA through the repeated insertion of random nucleotides at a single locus in temporal order. To achieve in vivo DNA writing, CHYRON combines Cas9, a homing guide RNA and the template-independent DNA polymerase terminal deoxynucleotidyl transferase. We successfully applied CHYRON as an evolving lineage tracer and as a recorder of user-selected cellular stimuli.

Rapid generation of potent antibodies by autonomous hypermutation in yeast.

The predominant approach for antibody generation remains animal immunization, which can yield exceptionally selective and potent antibody clones owing to the powerful evolutionary process of somatic hypermutation. However, animal immunization is inherently slow, not always accessible and poorly compatible with many antigens. Here, we describe 'autonomous hypermutation yeast surface display' (AHEAD), a synthetic recombinant antibody generation technology that imitates somatic hypermutation inside engineered yeast. By encoding antibody fragments on an error-prone orthogonal DNA replication system, surface-displayed antibody repertoires continuously mutate through simple cycles of yeast culturing and enrichment for antigen binding to produce high-affinity clones in as little as two weeks. We applied AHEAD to generate potent nanobodies against the SARS-CoV-2 S glycoprotein, a G-protein-coupled receptor and other targets, offering a template for streamlined antibody generation at large.

Deficient chaperone-mediated autophagy in macrophage aggravates inflammation of nonalcoholic steatohepatitis by targeting Nup85.

BACKGROUND & AIMS: Nonalcoholic steatohepatitis (NASH), a more severe subtype of nonalcoholic fatty liver disease, can cause cirrhosis and hepatocellular carcinoma. Macrophages play critical roles in initiating and maintaining NASH-induced liver inflammation and fibrosis. However, the underlying molecular mechanism of macrophage chaperone-mediated autophagy (CMA) in NASH remains unclear. We aimed to investigate the effects of macrophage-specific CMA on liver inflammation and identify a potential therapeutic target for NASH treatment. METHODS: The CMA function of liver macrophages was detected using Western blot, quantitative reverse transcription-polymerase chain reaction (RT-qPCR) and flow cytometry. By constructing myeloid-specific CMA deficiency mice, we evaluated the effects of deficient CMA of macrophages on monocyte recruitment, liver injury, steatosis and fibrosis in NASH mice. A label-free mass spectrometry was utilized to screen the substrates of CMA in macrophages and their mutual interactions. The association between CMA and its substrate was further examined by immunoprecipitation, Western blot and RT-qPCR. RESULTS: A typical hallmark in murine NASH models was impaired CMA function in hepatic macrophages. Monocyte-derived macrophages (MDM) were the dominant macrophage population in NASH, and CMA function was impaired in MDM. CMA dysfunction aggravated liver-targeted recruitment of monocyte and promoted steatosis and fibrosis. Mechanistically, Nup85 functions as a substrate for CMA and its degradation was inhibited in CMA-deficient macrophages. Inhibition of Nup85 attenuated the steatosis and monocyte recruitment caused by CMA deficiency in NASH mice. CONCLUSIONS: We proposed that the impaired CMA-induced Nup85 degradation aggravated monocyte recruitment, promoting liver inflammation and disease progression of NASH.

Prediction of plan adaptation in head and neck cancer proton therapy using clinical, radiographic, and dosimetric features.

PURPOSE: Because proton head and neck (HN) treatments are sensitive to anatomical changes, plan adaptation (re-plan) during the treatment course is needed for a significant portion of patients. We aim to predict re-plan at plan review stage for HN proton therapy with a neural network (NN) model trained with patients' dosimetric and clinical features. The model can serve as a valuable tool for planners to assess the probability of needing to revise the current plan. METHODS AND MATERIALS: Mean beam dose heterogeneity index (BHI), defined as the ratio of the maximum beam dose to the prescription dose, plan robustness features (clinical target volume (CTV), V100 changes, and V100 > 95% passing rates in 21 robust evaluation scenarios), as well as clinical features (e.g., age, tumor site, and surgery/chemotherapy status) were gathered from 171 patients treated at our proton center in 2020, with a median age of 64 and stages from I-IVc across 13 HN sites. Statistical analyses of dosimetric parameters and clinical features were conducted between re-plan and no-replan groups. A NN was trained and tested using these features. Receiver operating characteristic (ROC) analysis was conducted to evaluate the performance of the prediction model. A sensitivity analysis was done to determine feature importance. RESULTS: Mean BHI in the re-plan group was significantly higher than the no-replan group (p < .01). Tumor site (p < .01), chemotherapy status (p < .01), and surgery status (p < .01) were significantly correlated to re-plan. The model had sensitivities/specificities of 75.0%/77.4%, respectively, and an area under the ROC curve of .855. CONCLUSION: There are several dosimetric and clinical features that correlate to re-plans, and NNs trained with these features can be used to predict HN re-plans, which can be used to reduce re-plan rate by improving plan quality.

Helical CT versus intermittent CT fluoroscopic guidance for musculoskeletal needle biopsies: impact on radiation exposure, procedure time, diagnostic yield, and adverse events.

OBJECTIVE: Image-guided percutaneous needle biopsies are essential in the workup of musculoskeletal (MSK) lesions. While helical CT (HCT) is well established, intermittent CT fluoroscopy (iCTF) is an increasingly used alternative. The purpose of this study is to establish whether differences in subject radiation exposure, procedure time, yield, or adverse events exist between HCT and iCTF guidance. MATERIALS AND METHODS: This retrospective cohort study included consecutive MSK needle biopsies performed on a single-CT scanner over a 12-month period at a tertiary academic center. Subject demographics, radiation dose, and outcomes were abstracted from the medical record. Comparisons between the two cohorts were performed using Student's t-test for continuous data and using Fisher's exact test for categorical data and a two-tailed p value less than 0.05 was considered significant. RESULTS: Two hundred sixteen adults (115 (53.2%) females) with a mean age of 58.8 ± 18.4 years, underwent 216 biopsies (109 (50.5%) HCT guided, 107 (49.5%) iCTF guided) between June 2017 and June 2018. Dose-length product (DLP) and volume CT dose index (CTDIvol) were significantly higher for the HCT cohort (HCT 698.9 ± 400.8 mGycm vs iCTF 312.8 ± 170.8 mGycm; p < 0.005 and HCT 19.1 mGy ± 8.8 vs iCTF 6.9 mGy ± 1.5, p < 0.001). No significant difference in diagnostic yield, procedure time, or adverse event rate was identified. CONCLUSION: For CT-guided MSK needle biopsies, iCTF decreases subject radiation dose compared to HCT without negatively affecting outcomes. iCTF should be strongly considered by radiologists performing MSK biopsies given the reduced patient radiation exposure.

[Discrepancy between behavioral-indicated and perceived candidacy for HIV pre-exposure prophylaxis among men who have sex with men in Chengdu, China].

OBJECTIVE: To explore the discrepancy between behavioral-indicated candidacy and perceived candidacy (behavioral-perceived gap) and its associated factors of human immunodeficiency virus (HIV) pre-exposure prophylaxis (PrEP) among men who have sex with men (MSM), so as to identify the focus population of PrEP interventions and to design and implement targeted interventions. METHODS: We recruited a sample of 622 HIV-negative MSM who were regular clients of a community-based organization located in Chengdu, China, from November to December 2021. A cross-sectional questionnaire was used to collect the participants' information on social demographics, PrEP-related knowledge and cognitions, and risk behaviors. In this study, behaviorally eligible for PrEP was defined as performing at least one type of high-risk behavior in the past six months, including inconsistent condom use, sex with an HIV-positive partner, confirmed sexual transmitted infections (STI) diagnosis, substance use, and post-exposure prophylaxis (PEP) experience. Logistic regression models were fitted, and multivariate analyses were adjusted for social demographics. RESULTS: Among the 622 eligible participants, 52.6% (327/622) were classified as behaviorally eligible for PrEP. Only 37.9% (124/327) of the participants perceived themselves as appropriate candidates for PrEP and 62.1% (203/207) had discrepancy between behavioral-indicated and perceived candidacy. 85.9% (281/327) had heard of PrEP, and 14.2% (40/281) accessed PrEP information through health care providers. Of the 327 participants eligible for behavior-indicated PrEP use, about half (47.1%) knew how to obtain PrEP medication and 33.0% had a professional PrEP counseling experience. The majority (93.3%) had no or few friends using PrEP. 54.1% scored eight or above in PrEP knowledge level. 66.7% reported having two or more sexual partners in the past six months. After adjusting for age and recruitment channel, we found six factors that were associated with perceived candidacy for PrEP, including PEP use [adjusted odds ratio (ORA)=2.20; 95% confidence interval (CI): 1.33-3.63], PrEP availability (ORA=1.69; 95%CI: 1.06-2.68), a greater number of PrEP-using friends (ORA=4.92; 95%CI: 1.77-13.65), PrEP know-ledge (ORA=2.21; 95%CI: 1.38-3.56), multiple sexual partnership (ORA=1.77; 95%CI: 1.07-2.94), and perceiving a higher risk of HIV infection (ORA=4.02; 95%CI: 1.73-9.32). Substance use during sex and PrEP information channel were not statistically associated with this beha-vioral-perceived gap. CONCLUSION: We observed a high discrepancy between behavioral-indicated and perceived candidacy for PrEP among Chengdu MSM in China. Future PrEP implementation efforts should be made in skills training in assessing HIV infection risk, increasing PrEP knowledge, providing professional PrEP counselling, and fostering PrEP support environment.