Effects of dose rates on radiation-induced replenishment of intestinal stem cells determined by Lgr5 lineage tracing

An understanding of the dynamics of intestinal Lgr5⁺ stem cells is important for elucidating the mechanism of colonic cancer development. We previously established a method for evaluating Lgr5⁺ stem cells by tamoxifen-dependent Lgr5-lineage tracing and showed that high-dose-rate radiation stimulated replenishment of colonic stem cells. In this study, we evaluated the effects of low-dose-rate radiation on stem cell maintenance. Tamoxifen (4OHT)-injected Lgr5-EGFP-IRES-Cre^ERT2 × ROSA-LSL-LacZ mice were used, LacZ-labeled colonic crypts were enumerated, and the loss of LacZ⁺ crypts under low-dose-rate radiation was estimated. After 4OHT treatment, the number of LacZ-labeled Lgr5⁺ stem cells was higher in the colon of infant mice than in adult mice. The percentage of LacZ-labeled crypts in infant mice rapidly decreased after 4OHT treatment. However, the percentage of labeled crypts plateaued at ∼2% at 4 weeks post-treatment and remained unchanged for up to 7 months. Thus, it will be advantageous to evaluate the long-term effects of low-dose-rate radiation. Next, we determined the percentages of LacZ-labeled crypts irradiated with 1 Gy administered at different dose rates. As reported in our previous study, mice exposed to high-dose-rate radiation (30 Gy/h) showed a marked replenishment (P = 0.04). However, mice exposed to low-dose-rate radiation (0.003 Gy/h) did not exhibit accelerated stem-cell replenishment (P = 0.47). These findings suggest the percentage of labeled crypts can serve as a useful indicator of the effects of dose rate on the stem cell pool.     

A novel in vitro survival assay of small intestinal stem cells after exposure to ionizing radiation

The microcolony assay developed by Withers and Elkind has been a gold standard to assess the surviving fraction of small intestinal stem cells after exposure to high (≥8 Gy) doses of ionizing radiation (IR), but is not applicable in cases of exposure to lower doses. Here, we developed a novel in vitro assay that enables assessment of the surviving fraction of small intestinal stem cells after exposure to lower IR doses. The assay includes in vitro culture of small intestinal stem cells, which allows the stem cells to develop into epithelial organoids containing all four differentiated cell types of the small intestine. We used Lgr5-EGFP-IRES-CreERT2/ROSA26-tdTomato mice to identify Lgr5⁺ stem cells and their progeny. Enzymatically dissociated single crypt cells from the duodenum and jejunum of mice were irradiated with 7.25, 29, 101, 304, 1000, 2000 and 4000 mGy of X-rays immediately after plating, and the number of organoids was counted on Day 12. Organoid-forming efficiency of irradiated cells relative to that of unirradiated controls was defined as the surviving fraction of stem cells. We observed a significant decrease in the surviving fraction of stem cells at ≥1000 mGy. Moreover, fluorescence-activated cell sorting analyses and passage of the organoids revealed that proliferation of stem cells surviving IR is significantly potentiated. Together, the present study demonstrates that the in vitro assay is useful for quantitatively assessing the surviving fraction of small intestinal stem cells after exposure to lower doses of IR as compared with previous examinations using the microcolony assay.     

A comparison of the dose distributions between the brachytherapy 125I source models,STM1251 and Oncoseed 6711, in a geometry lacking radiation equilibrium scatter conditions

The purpose of this study was to estimate the uncertainty in the dose distribution for the ¹²⁵I source STM1251, as measured with a radiophotoluminescent glass rod dosimeter and calculated using the Monte Carlo code EGS5 in geometry that included the source structure reported by Kirov et al. This was performed at a range of positions in and on a water phantom 18 cm in diameter and 16 cm in length. Some dosimetry positions were so close to the surface that the backscatter margin was insufficient for photons. Consequently, the combined standard uncertainty (CSU) at the coverage factor k of 1 was 11.0–11.2% for the measurement and 1.8–3.6% for the calculation. The calculation successfully reproduced the measured dose distribution within 13%, with CSU at k ≤ 1.6 (P > 0.3). Dose distributions were then compared with those for the ¹²⁵I source Oncoseed 6711. Our results supported the American Association of Physicists in Medicine Task Group No. 43 Updated Protocol (TG43U1) formalism, in which STM1251 dose distributions were more penetrating than those of Oncoseed 6711. This trend was also observed in the region near the phantom surface lacking the equilibrium radiation scatter conditions. In this region, the difference between the TG43U1 formalism and the measurement and calculation performed in the present study was not significant (P > 0.3) for either of the source models. Selection of the source model based on the treatment plans according to the TG43U1 formalism will be practical.     

Wnt-3a/eGFP双表达基因慢病毒载体的构建及其在大鼠骨髓间充质干细胞中的表达

目的构建双表达基因慢病毒载体pLV.EX3d.P/puro-EF1A>Wnt-3a>IRES/eGFP,用携带目的基因Wnt-3a及示踪基因增强型绿色荧光蛋白(eGFP)的慢病毒转导大鼠骨髓间充质干细胞(rat bone marrow mesenchymal stem cells,rBMSCs),建立能够持续激活Wnt信号通路的体外细胞模型。方法基于GatewayTM技术构建双表达基因慢病毒载体,经293FT包装并释放出病毒转导rBMSCs,检测Wnt-3a以及β-catenin的表达水平。结果经测序证实目的基因Wnt-3a及示踪基因eGFP片段按正确方向重组入目的载体中。用含Wnt-3a/eGFP的病毒上清转导rBMSCs,转导率超过85%。RT-PCR证实rBMSCs-Wnt3a过表达wnt-3a和β-catenin。结论携带目的基因Wnt-3a及示踪基因eGFP的慢病毒可以稳定转染rBMSCs,构建了能够持续激活Wnt信号通路的体外细胞模型。     

Tumor-specific peptide-based vaccines containing the conformationally biased, response-selective C5a agonists EP54 and EP67 protect against aggressive large B cell lymphoma in a syngeneic murine model

Vaccines to large B cell lymphoma were made by the covalent attachment of an epitope from the gp70 glycoprotein (SSWDFITV) to the N-termini of the conformationally biased, response-selective C5a agonists EP54 (YSFKPMPLaR) and EP67 (YSFKDMP(MeL)aR). Syngeneic Balb/c mice were immunized with these EP54/EP67-containing vaccines and challenged with a lethal dose of the highly liver metastatic and gp70-expressing lymphoma cell line RAW117-H10 to evaluate the ability of these vaccines to induce protective immune outcomes. All mice immunized with SSWDFITVRRYSFKPMPLaR (Vaccine 2) and SSWDFITVRRYSFKDMP(MeL)aR (Vaccine 3) were protected to a lethal challenge of RAW117-H10 lymphoma (>170 days survival) and exhibited no lymphoma infiltration or solid tumor nodules in the liver relative to unvaccinated controls (<18 days survival). Vaccines 2 and 3 contained the protease-sensitive double-Arg (RR) linker sequence between the epitope and the EP54/EP67 moieties in order to provide a site for intracellular proteases to separate the epitope from the EP54/EP67 moieties once internalized by the APC and, consequently, enhance epitope presentation in the context of MHC I/II. These protected mice exhibited an immune outcome consistent with increased involvement of CD8⁺ and/or CD4⁺ T lymphocytes relative to controls and mice that did not survive or showed low survival rates as with Vaccines 1 and 4, which lacked the RR linker sequence. CD8⁺ T lymphocytes activated in response to Vaccines 2 and 3 express cytotoxic specificity for gp70-expressing RAW117-H10 lymphoma cells, but not antigen-irrelevant MDA-MB231A human breast cancer cells. Results are discussed against the backdrop of the ability of EP54/EP67 to selectively target antigens to and activate C5a receptor-bearing antigen presenting cells and the prospects of using such vaccines therapeutically against lymphoma and other cancers.