[Recent progress of aptasensors for tumor exosome-associated protein detection]

Exosomes are phospholipid bilayer membrane-enclosed vesicles released from cells with diameters of 30-150 nm, exosomes can directly reflect the physiological and functional state of secretory cells, participate in material transport and information communication between cells, which are of great significance as biomarkers for early tumor diagnosis and treatment evaluation. There are many detection methods for exosomes, among which aptasensor technology with the properties of low price and easy operation, fast response, high sensitivity, remarkable specificity helps tumor patients to find, diagnose and treat early, improve the survival rate, and provide important basis for the evaluation of the prognosis. There are seven types of common aptasensors: fluorescent, electrochemical, colorimetric, luminescence, lateral flow strips, surface-enhanced Raman scattering and surface plasmon resonance sensors. Different aptasensors have different characteristics, this article focuses on the research progress of several common aptasensor for tumor exosomes detection.

Demethylation and reactivation of the fibrosis-suppressor gene Rasal1 is initiated by R-loop formation which facilitates recruitment of TET3 and GADD45g

Background

Silencing of fibrosis suppressor genes through DNA methylation has been shown to contribute to fibrosis progression in the heart and in other organs. Growth Arrest and DNA Damage 45-(GADD45) and Ten-Eleven-Translocation (TET) proteins are involved in active DNA demethylation, but how they are recruited to the promoter of fibrosis suppressor genes has not yet been understood.

Purpose

To identify the mechanisms involved in site-specific demethylation of the promoter region of the cardiac fibrosis suppressor gene Rasal1.

Methods

We previously identified lncRNA Gm15749 located within the Rasal1 promoter region. Using DRIP qRT-PCR, we demonstrated an enrichment of R-loops at the Rasal1 promoter in non-fibrotic mouse cardiac fibroblasts. Such enrichment of R-loops was lost upon TGF-beta-treatment in activated “fibrotic” fibroblasts, and also upon Gm15749 knockdown in untreated non-fibrotic fibroblasts. ChIP qRT-PCR further revealed binding of GADD45g to the Rasal1 promoter and Co-IP experiments confirmed a physical interaction of TET3 and GADD45g.

Results

Studying the RAS Protein Activator Like 1 (Rasal1), which has been shown to be silenced in fibrosis of the heart due to promoter hypermethylation, we find that the lncRNA Gm15749 within the promoter region of Rasal1 is protective by forming an R-loop at the Rasal1 promoter. Gm15749 mediates the recruitment and binding of GADD45g, which then triggers the demethylation process by recruiting TET3 specifically to the Rasal1 promoter region. During cardiac fibrosis, all three factors; Gm15749, TET3, and GADD45g are significantly downregulated and the protection of Rasal1 is lost due to the failure of the formation of the demethylation complex.

Conclusions

Our results suggest a complex involving an R-loop forming lncRNA termed Gm15749, which interacts with the demethylation complex consisting of GADD45g and TET3 to perform site-specific demethylation at the Rasal1 promoter. Such R-loop formation may counteract fibrogenesis through reactivation of fibrosis-suppressor genes silenced by hypermethylation.

Funding Acknowledgement

Type of funding sources: None.

[Association of nutritional status with clinical outcomes of stroke patients with acute anterior circulation large vessel occlusion after emergency endovascular treatment]

OBJECTIVE

To explore the influence of nutritional status on 90-day functional outcomes of stroke patients with acute large vessel occlusion in the anterior circulation after endovascular treatment (EVT).

METHODS

We retrospectively analyzed the baseline, laboratory, surgical and 90-day follow-up data of patients with stroke resulting from acute large vessel occlusion in the anterior circulation, who underwent emergency endovascular treatment in our hospital from July, 2015 to December, 2020. A favorable outcome was defined as a modified Rankin scale score ≤2 at 90 days. Univariate and multivariate regression analyses were performed to explore the relationship between nutritional status and 90-day functional outcomes of the patients.

RESULTS

A total of 459 patients (mean age of 68.29±11.21 years, including 260 males) were enrolled in this study. According to their prognostic nutritional index (PNI), the patients were divided into normal nutrition group (392 cases, 85.4%), moderate malnutrition group (44 cases, 9.6%), and severe malnutrition group (23 cases, 5.0%). Univariate analysis showed that the patients with good clinical outcomes had a lower proportion of malnutrition with a younger age, a lower rate of diabetes, lower baseline blood pressure, lower baseline NIHSS score, higher baseline ASPECT score, and higher rates of good collateral circulation and complete vascular recanalization. Multivariate analysis showed that in addition to age, diabetes, baseline systolic blood pressure, successful recanalization, baseline ASPECT score, baseline NIHSS score and collateral circulation, a greater PNI was a protective factor for a good 90-day outcome of patients after EVT (moderate vs severe: OR=0.245, 95% CI: 0.066-0.908, P=0.035; normal vs severe: OR=0.185, 95% CI: 0.059-0.581, P=0.004).

CONCLUSION

Nutritional status an important factor affecting the 90-day outcomes after EVT of stroke patients with acute large vessel occlusion in the anterior circulation.

OpenKBP-Opt: an international and reproducible evaluation of 76 knowledge-based planning pipelines

Objective.To establish an open framework for developing plan optimization models for knowledge-based planning (KBP).Approach.Our framework includes radiotherapy treatment data (i.e. reference plans) for 100 patients with head-and-neck cancer who were treated with intensity-modulated radiotherapy. That data also includes high-quality dose predictions from 19 KBP models that were developed by different research groups using out-of-sample data during the OpenKBP Grand Challenge. The dose predictions were input to four fluence-based dose mimicking models to form 76 unique KBP pipelines that generated 7600 plans (76 pipelines × 100 patients). The predictions and KBP-generated plans were compared to the reference plans via: the dose score, which is the average mean absolute voxel-by-voxel difference in dose; the deviation in dose-volume histogram (DVH) points; and the frequency of clinical planning criteria satisfaction. We also performed a theoretical investigation to justify our dose mimicking models.Main results.The range in rank order correlation of the dose score between predictions and their KBP pipelines was 0.50-0.62, which indicates that the quality of the predictions was generally positively correlated with the quality of the plans. Additionally, compared to the input predictions, the KBP-generated plans performed significantly better (P< 0.05; one-sided Wilcoxon test) on 18 of 23 DVH points. Similarly, each optimization model generated plans that satisfied a higher percentage of criteria than the reference plans, which satisfied 3.5% more criteria than the set of all dose predictions. Lastly, our theoretical investigation demonstrated that the dose mimicking models generated plans that are also optimal for an inverse planning model.Significance.This was the largest international effort to date for evaluating the combination of KBP prediction and optimization models. We found that the best performing models significantly outperformed the reference dose and dose predictions. In the interest of reproducibility, our data and code is freely available.

[Clinicopathological features and HER2 expression of metaplastic squamous cell carcinoma of the breast]

Objective: To investigate the clinicopathological features and HER2 expression of metaplastic squamous cell carcinoma (MSCC) of the breast. Methods: A total of 47 MSCC cases diagnosed in the Wuhan Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China from January 2010 to December 2021 were reviewed. The clinical information (including the follow-up data of HER2 positive patients) and pathological features were collected and analyzed. Results: All of the patients were female. Among the 47 cases, 25 were pure squamous cell carcinoma (PSCC) and 22 were mixed metaplastic carcinoma with squamous cell component (MMSC). The median age of the patients was 54 years (range, 29-84 years). The maximum diameter of the mass ranged from 0.8 to 10.0 cm, with a mean value of 3.3 cm, 85.7% (24/28) of the cases were smaller than 5 cm, and only 4 cases were larger than or equal to 5 cm. 89.5% of the MMSC presented with a solid mass. Cystic changes were more commonly found in the PSCC group (50%, P<0.05) than the MMSC group. 36.7% (11/30) of the patients had lymph node metastasis at the time of diagnosis. The squamous cell carcinoma component in all cases showed diffuse or patchy expression of p63, p40 and CK5/6. 55.3% (26/47) of the cases showed triple-negative phenotype. Among the 7 HER2-positive patients, 6 were MMSC group, which had a significantly higher rate of HER2-positivity than that in the PSCC group (1 case). In 1 MMSC case, immunohistochemistry showed HER2 2+in the invasive ductal carcinoma component and HER2 negativity (0) in the squamous cell carcinoma component, but HER2 FISH was negative in invasive ductal carcinoma and positive in squamous cell carcinoma component. Six HER2-positive MSCC patients received anti-HER2-targeted therapy, including two patients who received neoadjuvant chemotherapy combined with anti-HER2-targeted therapy before surgery. One patient achieved pathological complete remission, while the other achieved partial remission (the residual tumors were squamous cell carcinoma components). After 9-26 months of follow-up, four patients had no disease progression, two patients developed pulmonary metastases, and one patient showed local recurrence. Conclusions: MSCC is a group of heterogeneous diseases. PSCC and MMSC may be two different entities. Most of the MSCC are triple-negative and HER2 positivity is more commonly seen in MMSC with invasive ductal carcinoma component. Some HER2-positive MSCC patients can achieve complete remission or long-term progression-free survival after receiving anti-HER2 targeted therapy, but the squamous cell carcinoma component may be less sensitive to targeted therapy than the invasive ductal carcinoma component.

[Association between metabolic risk factors and the hepatitis B reactivation of inactive HBsAg carriers in Jiangsu province: a cohort study]

Objective: To analyze the impact of metabolic risk factors on the epidemiological characteristics of the reactivation of inactive HBsAg carriers (IHC) and provide effective intervention measures to standardize the management of chronic hepatitis B infections. Methods: Based on the chronic hepatitis B infection cohort established in 2010 in Jiangsu province, six follow-up visits from 2012 to 2020 were conducted to analyze the characteristics and influencing factors of the hepatitis B reactivation of IHC and the impact of metabolic risk factors, including obesity, high blood pressure, diabetes and hyperglycemia. Results: From 2012 to 2020, 2 527 IHC and 17 730 person-years were observed during a median follow-up period of 7.0 person-years. Ninety-eight cases of hepatitis B reactivation, with a cumulative reaction rate, was 3.9%, and the incidence density was 5.53/1 000 person-years. Multivariate Cox proportional risk regression analysis showed that age and baseline HBV DNA were independent risk factors of HBV reactivation. Compared with the patients ≥60 years, 40-49 age group (aHR=2.16, 95%CI:1.20-3.90) and 20-29 age group (aHR=5.48, 95%CI:2.07-14.48) were significantly associated with hepatitis B reactivation. Compared with the HBV DNA negative patients at baseline, the risk of hepatitis B reactivation was higher in the group with low HBV DNA level 100-1 999 IU/ml (aHR=1.67, 95%CI:1.11-2.52). Stratification analysis results showed that compared with those without metabolic risk factors, in the ≥50 age group, patients with ≥2 metabolic risk factors showed adjusted HR of 2.73 (95%CI:1.08-6.96). Conclusions: The risk of hepatitis B being reactive is the persistent existence of IHC in communities in Jiangsu province, especially young adults, low-level HBV DNA carriers, and IHC with ≥2 metabolic risk factors. Follow-up for these IHC should be strengthened to reduce the risk of disease progression by antiviral treatment at the right time.

Effect of induction of labor on maternal and perinatal outcomes in low-risk singleton pregnancies: a retrospective case-control study

OBJECTIVE

The aim of the study was to investigate the effect of induction of labor on maternal and fetal outcomes.

PATIENTS AND METHODS

This retrospective case-control study included 4386 pregnant women with low-risk singleton pregnancies who underwent regular prenatal examination and successful vaginal delivery at ≥41 weeks and 0 days of gestation in Fujian Maternal and Child Health Hospital between January 2014 and December 2018. Clinical data of women were retrospectively divided into the induction of labor group (2007 cases) and spontaneous onset of labor group (2361 cases) based on the mode of labor initiation. Two-sample independent t-test and χ2 tests were used to analyze the differences in clinical characteristics, such as maternal age and parity between the two groups.

RESULTS

The induction of the labor group had a significantly longer total duration of labor (9.37±5.37 vs. 8.82±5.13 h; p<0.001), more postpartum blood loss (219.18±188.32 vs. 199.95±124.69 mL; p=0.01) and a significantly higher incidence of severe postpartum hemorrhage (PPH) comparing to the spontaneous onset of labor group [0.8% (16/2007) vs. 0.33% (8/2361); p=0.041]. However, no significant difference was found in the neonatal outcomes. After adjusting for age, induction of labor in nulliparous women was more likely to lead to PPH than the spontaneous onset of labor [2.74% (55/2007) vs. 1.65% (39/2361); odds ratio=1.557; 95% confidence interval: 1.039-2.332; p<0.05].

CONCLUSIONS

Induction of labor increases the duration of labor and postpartum blood loss, especially in primary parturient, leading to an increased risk of PPH. This increase may be related to the overall higher duration of labor, associated with IOL. Therefore, low-risk nulliparous women should try to avoid induction of labor without medical indications.

Novel MSH6 mutation predicted metastasis in eyelid and periocular squamous cell carcinoma

BACKGROUND

Our previous research revealed the relative local aggressiveness of eyelid and periocular squamous cell carcinoma (EPSCC), but its distinct genetic characteristics involved remain unknown.

OBJECTIVES

We conducted this study based on next-generation sequencing to identify the genetic distinctiveness of EPSCC and damaging mutations for possible etiology and poor prognosis.

METHODS

We performed sequencing using a 556-gene panel (smartonco) in 48 EPSCCs. Cox hazards model was applied to explore mutated genes that increase risk of metastasis and death. Pathogenesis of the mutations was predicted by sequence alignment algorithms.

RESULTS

The most commonly mutated genes were KMT2C (N=17, 35%), LRP1B (N=14, 29%), KMT2D (N=12, 25%), PTCH1(N=10, 21%) and TP53(N=10, 21%). DNA mismatch repair (MMR) genes (42%) like MSH6(19%) and MLH3(12%) were among the most frequently mutated genes. Cell cycle regulators including TP53(21%) and CDKN2A (10%) were less frequently mutated than in other squamous cell carcinomas (SCCs). Ultra violet exposure, MMR deficiency and aging were the main etiology. Of note, KMT2C has a deleterious mutation hotspot. Patients burdened with MSH6 mutation has a higher risk of overall metastasis (P=0.045, HR=5.165) and nodal metastasis (P=0.022, HR=14.038). Moreover, a hotspot mutation MSH6^E52A brought an even higher risk of nodal metastasis (P=0.011, HR=18.745).

CONCLUSIONS

EPSCCs displayed a unique mutation profile from cutaneous SCCs and mucosal SCCs. We have identified novel damaging mutations in epigenetic regulators like KMT2C boosted early onset of EPSCCs in addition to UVR, aging or MMR deficiency. And malfunction of MMR genes worsened prognosis.

3D-Stacked Multistage Inertial Microfluidic Chip for High-Throughput Enrichment of Circulating Tumor Cells

Whether for cancer diagnosis or single-cell analysis, it remains a major challenge to isolate the target sample cells from a large background cell for high-efficiency downstream detection and analysis in an integrated chip. Therefore, in this paper, we propose a 3D-stacked multistage inertial microfluidic sorting chip for high-throughput enrichment of circulating tumor cells (CTCs) and convenient downstream analysis. In this chip, the first stage is a spiral channel with a trapezoidal cross-section, which has better separation performance than a spiral channel with a rectangular cross-section. The second and third stages adopt symmetrical square serpentine channels with different rectangular cross-section widths for further separation and enrichment of sample cells reducing the outlet flow rate for easier downstream detection and analysis. The multistage channel can separate 5 μm and 15 μm particles with a separation efficiency of 92.37% and purity of 98.10% at a high inlet flow rate of 1.3 mL/min. Meanwhile, it can separate tumor cells (SW480, A549, and Caki-1) from massive red blood cells (RBCs) with a separation efficiency of >80%, separation purity of >90%, and a concentration fold of ~20. The proposed work is aimed at providing a high-throughput sample processing system that can be easily integrated with flowing sample detection methods for rapid CTC analysis.

Long-distance polarizing microscope system combined with solenoid-type magnet for microscopy and simultaneous measurement of physical parameters

We have developed a long-distance polarizing microscope system combined with a solenoid-type superconducting magnet. By inserting an infinity-corrected objective lens into the magnet, direct or polarizing microscope images are observed in magnetic fields of up to 12 T at various temperatures down to 2 K. Through magneto-optical measurements in the transmission geometry, the local magnetization process of a transparent magnet is evaluated in areas of 10 × 10 µm². This system enables simultaneous measurements of other physical properties over a wide range of temperatures and magnetic fields. The basic principle of the proposed long-distance microscopy can be applied to imaging experiments in various research fields, particularly biology and chemistry.

[Early outcomes of excimer laser atherectomy for below-the-knee lesions in patients with diabetic foot]

Objective: To evaluate the clinical outcomes of excimer laser atherectomy (ELA) in the treatment of diabetic foot with below-the-knee(BTK) lesions. Methods: The clinical data of 11 patients with diabetic foot with BTK lesions who underwent ELA at Department of Vascular Surgery,Zhongshan Hospital of Fudan University and Department of Vascular and Wound Treatment Center,Jinshan Hospital of Fudan University from September 2019 to May 2021 were retrospectively analyzed.There were 10 males and 1 female,aged 70.5 years(range:41 to 83 years).There were 20 lesions in 12 limbs,including 19 chronic total occlusion.All of the limbs were classified as Rutherford class 5 and suffered ulceration.The surgical efficacy,complications and ankle brachial index(ABI) after operation were record. Results: All patients underwent the operation successfully,the technical success rate was 12/12.No distal embolization,flow-limiting dissection,perforation or bailout stenting was occurred.The follow-up period was 8.2 months(range:3 to 13 months).The ABI increased from 0.58(range:0.24 to 1.57) before operation to 0.88(range:0.68 to 1.05) after operation.At 3 months after the operation,1 limb (1/12) underwent endovascular operation again due to restenosis,ulcers were healed in 5 limbs(5/12),and no amputation (limb/toe),death or loss of follow-up patients.Six months after the operation,2 patients were lost to follow-up and 2 died,ulcers were healed in 6 limbs(6/8),1 limb (1/8) underwent toe amputation due to prolonged healing of ulcers of toe. Conclusion: ELA is feasible and effective in the treatment of DF with BTK lesions,providing a new option of debulking atherectomy in such a group of patients.

Shadow-Consistent Semi-Supervised Learning for Prostate Ultrasound Segmentation

Prostate segmentation in transrectal ultrasound (TRUS) image is an essential prerequisite for many prostate-related clinical procedures, which, however, is also a long-standing problem due to the challenges caused by the low image quality and shadow artifacts. In this paper, we propose a Shadow-consistent Semi-supervised Learning (SCO-SSL) method with two novel mechanisms, namely shadow augmentation (Shadow-AUG) and shadow dropout (Shadow-DROP), to tackle this challenging problem. Specifically, Shadow-AUG enriches training samples by adding simulated shadow artifacts to the images to make the network robust to the shadow patterns. Shadow-DROP enforces the segmentation network to infer the prostate boundary using the neighboring shadow-free pixels. Extensive experiments are conducted on two large clinical datasets (a public dataset containing 1,761 TRUS volumes and an in-house dataset containing 662 TRUS volumes). In the fully-supervised setting, a vanilla U-Net equipped with our Shadow-AUG&Shadow-DROP outperforms the state-of-the-arts with statistical significance. In the semi-supervised setting, even with only 20% labeled training data, our SCO-SSL method still achieves highly competitive performance, suggesting great clinical value in relieving the labor of data annotation. Source code is released at https://github.com/DIAL-RPI/SCO-SSL.

Dietary amylose and amylopectin ratio changes starch digestion and intestinal microbiota diversity in goslings

1. Research has confirmed that amylopectin (AP) is more easily digested than amylose (AM) because AP polymers have more intramolecular hydrogen bonds and less surface area. Studying the relationship between the amylose:amylopectin (AM:AP) ratio and intestine digestion in goslings can provide useful information for effective utilisation of starch.2. A total of 288 healthy male Jiangnan White Goslings, aged three days old, were randomly allotted to four groups, which included six pen replicates per treatment with 12 goslings per replicate. Four diets were formulated with maize, long-grained rice and glutinous rice as starch sources, with AM:AP ratios of 0.12, 0.23, 0.34, and 0.45. In vitro starch digestion of the four diets was measured, as well as the effect of AM:AP ratio on growth performance, serum amino-acid concentration and intestinal microbiota diversity of goslings.3. In terms of in vitro starch digestion, the increase in dietary AM:AP ratio resulted in a decrease followed by an increase in both rapidly and slowly digestible starch. The glucose release rate at an AM:AP ratio of 0.34 showed a steady upward trend.4. The in vivo study showed that increasing the AM:AP ratio resulted in a quadratic increase in body weight (BW) and average daily feed intake (ADFI; P<0.05). Goslings fed diets with an AM:AP ratio of 0.34 had lower (P<0.05) histidine and valine serum concentrations compared with the other three starch sources. Higher AM was beneficial to jejunal microbial and diversity. The species colonisation level of the jejunum microbiota samples at an AM:AP ratio of 0.34 was higher than that in the other groups.5. The results indicated that diets with an AM:AP ratio of 0.34 improved the growth performance and intestinal microbiota diversity of goslings. This may have been due to the higher level of resistant starch in amylose, which resulted in a slow release of intestinal glucose that acted as a substrate for the microbial species, thus providing conditions that were more conducive to growth.

Relation of BMI and waist circumference with the risk of new-onset hyperuricemia in hypertensive patients

BACKGROUND

We aimed to evaluate the relationship of body mass index (BMI) and waist circumference (WC) with the risk of new-onset hyperuricemia, and examine possible effect modifies in general hypertensive patients.

METHODS

A total of 10 611 hypertensive patients with normal uric acid (UA) concentrations (<357 μmol/l) at baseline were included from the UA sub-study of the China Stroke Primary Prevention Trial. The primary outcome was new-onset hyperuricemia, defined as a UA concentration ≥417 μmol/l in men or ≥357 μmol/l in women at the exit visit.

RESULTS

During a median follow-up duration of 4.4 years, 1663 (15.7%) participants developed new-onset hyperuricemia. When analyzed separately, increased BMI (≥25 kg/m2, quartile 3-4; OR, 1.46; 95% CI: 1.29-1.65), or increased WC (≥85 cm for females, quartile 3-4; OR, 1.24; 95% CI: 1.08-1.42; and ≥84 cm for males, quartile 3-4; OR, 1.30; 95% CI: 1.01-1.67) were each significantly associated with higher risk of new-onset hyperuricemia. When WC was forced into the model with BMI simultaneously, its significant association with new-onset hyperuricemia disappeared in females (<85 vs. ≥85 cm; OR, 0.96, 95% CI: 0.81-1.13) or males (≥84 vs. <84 cm; OR, 1.13; 95% CI: 0.84-1.52); however, BMI was still significantly related with new-onset hyperuricemia (≥25 vs. <25 kg/m2; OR, 1.48; 95% CI: 1.27-1.73). Moreover, the positive BMI & new-onset hyperuricemia association was more pronounced in participants with higher time-averaged on-treatment systolic blood pressure (median: <138.3 vs. ≥138.3 mmHg; P-interaction = 0.041).

CONCLUSIONS

Higher BMI, but not WC, is significantly and independently associated with an increased risk of new-onset hyperuricemia among hypertensive patients.

First live birth in China after cryopreserved ovarian tissue transplantation to prevent premature ovarian insufficiency

OBJECTIVE

This article reports the first live birth after cryopreserved ovarian tissue transplantation to prevent premature ovarian insufficiency in China.

METHODS

A patient with myelodysplastic syndrome received ovarian tissue cryopreservation before hematopoietic stem cell transplantation, and six ovarian cortex strips were thawed and transplanted into her peritoneal pocket 2 years later.

RESULTS

Pregnancy occurred spontaneously 27 months after grafting, and a healthy girl was born at 38 weeks gestation. Until now, the child has developed normally without any major diseases.

CONCLUSIONS

We report the first live birth resulting from ovarian tissue cryopreservation and transplantation in China.

Ultrabright Electron Bunch Injection in a Plasma Wakefield Driven by a Superluminal Flying Focus Electron Beam

We propose a new method for self-injection of high-quality electron bunches in the plasma wakefield structure in the blowout regime utilizing a "flying focus" produced by a drive beam with an energy chirp. In a flying focus the speed of the density centroid of the drive bunch can be superluminal or subluminal by utilizing the chromatic dependence of the focusing optics. We first derive the focal velocity and the characteristic length of the focal spot in terms of the focal length and an energy chirp. We then demonstrate using multidimensional particle-in-cell simulations that a wake driven by a superluminally propagating flying focus of an electron beam can generate GeV-level electron bunches with ultralow normalized slice emittance (∼30  nm rad), high current (∼17  kA), low slice energy spread (∼0.1%), and therefore high normalized brightness (>10^{19}  A/m^{2}/rad^{2}) in a plasma of density ∼10^{19}  cm^{-3}. The injection process is highly controllable and tunable by changing the focal velocity and shaping the drive beam current. Near-term experiments at FACET II where the capabilities to generate tens of kA, <10  fs drivers are planned, could potentially produce beams with brightness near 10^{20}  A/m^{2}/rad^{2}.