Objectives: The eradication of leukemia cells while sparing hematopoietic stem cells in the graft before autologous hematopoietic stem cell transplant is critical to prevention of leukemia relapse. Proliferating cells have been shown to be more prone to apoptosis than differentiated cells in response to ultraviolet radiation; however, whether leukemia cells are more sensitive to ultraviolet LED radiation than hemato-poietic stem cells remains unclear.
Materials and Methods: We compared the in vitro responses between murine leukemia L1210 cells and murine hematopoietic stem cells to 280-nm ultraviolet LED radiation. We also investigated the effects of ultraviolet LED radiation on the tumorigenic and metastatic capacity of L1210 cells and hematopoietic stem cell hematopoiesis in a mouse model of hematopoietic stem cell transplant.
Results: L1210 cells were more sensitive to ultraviolet LED radiation than hematopoietic stem cells in vitro, as evidenced by significantly reduced colony formation rates and cell proliferation rates, along with remarkably increased apoptosis rates in L1210 cells. Compared with corresponding unirradiated cells, ultraviolet LED-irradiated L1210 cells failed to generate palpable tumors in mice, whereas ultraviolet LED-irradiated bone marrow cells restored hema-topoiesis in vivo. Furthermore, transplant with an irradiated mixture of L1210 cells and bone marrow cells showed later onset of leukemia, milder leukemic infiltration, and prolonged survival in mice, compared with unirradiated cell transplant.
Conclusions: Our results suggest that ultraviolet
LED radiation can suppress the proliferative and tumorigenic abilities of leukemia cells without reducing the hematopoietic reconstitution capacity of hematopoietic stem cells, serving as a promising approach to kill leukemia cells in autograft before autologous hematopoietic stem cell transplant.

Key words : Apoptosis, Hematopoietic stem cell transplantation, Leukemia L1210 cells

Introduction

Hematopoietic stem cells (HSCs) are adult stem cells that can self-renew and differentiate into specialized, mature blood cells. Hematopoietic stem cell transplant (HSCT), including allogeneic, autologous, and syngeneic HSCT, has been widely used in patients with blood disorders.¹ Autologous HSCT is performed using the patient’s HSCs, which are procured before transplant and reinfused after myeloablation. Compared with allogeneic HSCT, autologous HSCT has important advantages, inclu-ding no need to identify a human leukocyte antigen-matched donor and no risk of graft-versus-host disease.^2,3 However, the relapse resulting from clonogenic leukemia cells transfused with the graft becomes a major concern of autologous HSCT.⁴ Therefore, eradicating leukemia cells residing in the graft before transplant is crucial to prevent cancer relapse.

Ultraviolet (UV) radiation induces apoptosis in different cell types, such as cancer cells, skin fibroblasts, and retinal pigment epithelium cells.^5-7 Studies have shown that UV radiation triggers rapid apoptosis in human leukemia cell lines, such as HL-60 myeloid leukemia cells, Molt-4 T-lymphoblastoid cells, and U937 myelomonocytic leukemia cells, possibly by inducing membrane lipid rearrangement, DNA cleavage, or reactive oxygen species production.^7-9 Interestingly, the differentiation status of the cells is associated with their sensitivity to UV radiation. It has been reported that UV radiation-induced apoptosis occurs less frequently in differentiated leukemia cells than in proliferating cells.¹⁰ Human and murine HSCs are less sensitive to UV-B radiation than lymphocytes.¹¹ Based on these reports, we hypothesized that leukemia cells might be more sensitive to UV radiation than HSCs. In addition, questions remain on whether HSCs can preserve differentiation potential to blood cells after UV radiation.

Recently, UV light-emitting diodes (LEDs) have emerged as a substitute for traditional mercury lamps in numerous applications, such as UV therapy, decontamination, and phototherapy, owing to the advantages, which include nontoxicity, higher energy efficiency, greater operational flexibility, shorter set-up time, and longer lifetime, compared with traditional UV lamps.^12-14 An application of 280-nm UV LED has a strong killing effect because of a wavelength close to the UV absorption peak of DNA and nucleoprotein. We previously showed that 280-nm UV LED suppresses Bcl-2 mRNA expression and induces apoptosis and cell cycle arrest of human leukemia HL-60 cells.¹⁵ However, the differential effects of UV LED radiation on cell proliferation and apoptosis in leukemia cells and HSCs remain unexplored.

In this study, we investigated whether pretrans-plant UV LED radiation at 280 nm could eradicate leukemia cells in the graft without affecting the capacity of normal HSCs.

Materials and Methods

Animals and bone marrow cell isolation
We purchased DBA/2 mice from The Jackson Laboratory. Mice aged 6 to 12 weeks were raised in a specific pathogen-free environment with sterilized food, water, and bedding. All animal protocols were approved by the Committee for Ethics of Animal Experimentation at Qingdao University (AHQU20161013; Shandong, China). For isolation of bone marrow cells (BMCs), we first euthanized DBA/2 mice aged 6 to 12 weeks by CO₂ inhalation. We then obtained the femur and tibia, which we placed in cold phosphate-buffered saline (PBS) containing 2% fetal bovine serum (FBS; Gibco). We trimmed the ends of the long bones to expose the interior marrow shaft. We repeatedly flushed the bone marrow with 3 mL of cold PBS containing 2% FBS using a syringe with a 21-gauge needle until the bone appeared white. A single-BMC suspension was obtained by pipetting up and down using the syringe and filtering through a 40-μm mesh nylon strainer (BD Falcon). We adjusted the BMC suspension to 1 × 10⁸ cells/mL in Iscove modified Dulbecco’s medium (IMDM; Gibco) supplemented with 10% FBS.

Cell lines and cell culture
To isolate HSCs, we selected stem cell antigen 1 (SCA1)-positive HSCs using the EasySep mouse SCA1 positive selection kits (catalog no. 18756 and 18856; StemCell Technologies), according to the manufacturer’s protocol. The purity of cells labeled with phycoerythrin (catalog no. 18756) was assessed using a flow cytometer (BD Biosciences) at 488-nm excitation and 578-nm emission.

We obtained the mouse lymphocytic leukemia L1210 cell line from the American Type Culture Collection; we cultured cells in IMDM supplemented with 10% FBS at 37 °C in a humidified atmosphere of 5% CO₂. We used the exponentially growing cells for the experiments.

Animal models
For subcutaneous transplant with L1210 cells, we used twelve 4-week-old DBA/2 female mice, which we randomly divided into 2 groups (n = 6/group). We irradiated 2 × 10⁵ L1210 cells with 280-nm UV LED at 0 or 224 J/m², followed by subcutaneous injection of cells into the left forelimb armpit of each mouse (day 0). The length and width of the tumor were measured using a vernier caliper every other day. The volume of the tumor was calculated as length × width²/2. Mice were observed for 90 days after injection. We prepared mouse tissue sections of the tumor, liver, spleen, lung, kidney, and bone. We examined survival rate, tumor growth curve, and histological morphology.

For intravenous transplant with BMCs, we used twelve 7-week-old DBA/2 female mice, which we randomly divided into 2 groups (n = 6/group). Mice received 9 Gy of radiographic total body irradiation (TBI; Varian-23EX) for myeloablative conditioning to destroy hematopoiesis (day 1).¹⁶ We irradiated 2 × 10⁷ BMCs from 8-week-old DBA/2 male mice with 280-nm UV LED at 0 or 9.6 J/m², followed by tail vein injection into the female mice (day 0). On days 7, 14, 21, 42, and 60, mice were anesthetized with 4.9% sevoflurane.17 Blood samples (0.1 mL) of 3 mice in each group were obtained from the angular vein for blood tests. Genomic DNA was isolated from the peripheral blood (<100 μL), BMCs (5 × 10⁶), and spleen tissue (10 mg) of recipient mice on day 60, as well as from the peripheral blood (<100 μL) of control mice using a DNeasy Blood and Tissue Kit (catalog no. 69506; Qiagen). Mice were observed for 90 days after transplant. We examined survival rate, white blood cell (WBC), red blood cell (RBC), hemoglobin, and platelet counts, and sry gene expression in the recipient mice. We obtained peripheral blood from wild-type mice aged 8, 9, 10, 13 and 15 weeks for routine tests.

For intravenous transplant with mixed L1210 cells and BMCs, we used twelve 7-week-old DBA/2 female mice, which we randomly divided into 2 groups (n = 6/group). For nonmyeloablative conditioning, we injected mice intraperitoneally with 200 mg/kg cyclophosphamide (Baxter Oncology) on day -3, irradiated BMCs with 2 Gy TBI on day -1, and injected mice intraperitoneally with 200 mg/kg cyclophosphamide again on day 3.¹⁸ A mixture of 2 × 10⁵ L1210 cells and 2 × 10⁷ BMCs from 8-week-old DBA/2 female mice was irradiated with 280-nm UV LED at 0 or 9.6 J/m², followed by tail vein injection into the female mice (day 0). The mental status, activity, feeding, hair, and other body changes of recipient mice were observed every day after transplant. Body weight was measured every 2 days. Mice were euthanized at 90 days after implantation. We prepared tissue sections of mouse liver, spleen, lung, kidney, gastrointestinal tract, muscle, bone, vertebra, spinal cord, and brain. We examined survival rate and histological morphology.

Colony formation assay
We seeded BMCs (2 × 10⁵ cells/mL) or L1210 cells (1 × 10³ cells/mL) in 24-well plates at 500 μL/well and irradiated cells with 280-nm UV LED (Qingdao Ziyuan Photoelectronic) at 0, 2.4, 4.8, 7.2, 9.6, 12, 14.4, 16.8, or 19.2 J/m². After irradiation, cells were mixed with methylcellulose medium (Methocult M3434; StemCell Technologies) at a ratio of 1:10. The mixture (940 μL/well for BMCs and 720 μL/well for L1210 cells) was loaded into 12-well plates and incubated for 8 days (L1210 cells) or 12 days (BMCs). The colonies containing ≥30 cells were counted by the same researcher using an inverted microscope (Eclipse TS100; Nikon). Experiments for all groups were performed in triplicate.

Cell proliferation assay
We seeded HSCs or L1210 cells (2 × 10⁶ cells/mL) in 24-well plates at 500 μL/well and irradiated cells with 280-nm UV LED at 0, 28, 56, 112, or 224 J/m². Cells were then harvested, centrifuged, and resuspended in HSC serum-free medium (StemCell Technologies) or IMDM and cultured for 3, 6, 12, or 24 hours at 37 ?. We then seeded 100 μL cells in a 96-well plate. Unirradiated, cell-free medium was used as a blank control. After incubation of 10 μL cells in counting kit-8 solution (catalog no. CK04; Dojindo Molecular Technologies) for 3 hours, we measured optical density (OD) at a wavelength of 450 nm using a microplate reader (Multiskan FC; Thermo Fisher Scientific). We calculated cell proliferation rate (%) as (OD_test - OD_blank)/(OD_control - OD_blank) × 100%. Three replicates were made for each dose of UV LED radiation.

Apoptosis assay
We seeded L1210 cells or SCA1-positive HSCs (2 × 106 cells/mL) in 24-well plates at 500 μL/well. After irradiation with 280-nm UV LED at 0, 28, 56, 112, or 224 J/m², L1210 cells were cultured for 3, 6, 12, or 24 hours, whereas HSCs were cultured in fresh HSC serum-free medium for 24 hours. Cells were harvested, washed twice with cold PBS, and resuspended in 100 μL of 1× annexin-binding buffer (Invitrogen), followed by mixing with 5 μL of annexin V-fluorescein isothiocyanate (FITC) and 1 μL of 100 μg/mL propidium iodide working solution (Invitrogen). Unstained, unirradiated cells and the cells stained with annexin V-FITC or propidium iodide alone were used as controls. All samples were incubated at room temperature for 15 minutes before they were mixed with 100 μL of 1× annexin-binding buffer. The proportions of Q1 (annexin V-FITC negative/propidium iodide positive), Q2 (double positive), Q3 (annexin V-FITC positive/propidium iodide negative), and Q4 (double negative) quadrant cells were measured at 530 nm and 575 nm excited at 488 nm using a flow cytometer. Cell apoptosis rate was the percentages of cells in Q2 and Q3. The experiment was performed in quadruplicate.

Agarose gel electrophoresis
The expression of the male-specific sry gene was detected using polymerase chain reaction and agarose gel electrophoresis. The primers are 5'-TTTATGGTGTGGTCCCGTGG-3′ (forward) and 5′-GGTGTGCAGCTCTACTCCAG-3′ (reverse).

Hematoxylin and eosin staining
The tissue samples were fixed, embedded in paraffin, cut into 4-μm-thick sections, and subjected to hematoxylin and eosin staining following a standard protocol. Images were acquired using an inverted microscope (CKX41; Olympus Corporation) at ×100 or ×400 magnification.

Statistical analyses
Data are shown as mean ± SD. We used SPSS software (SPSS Inc) for statistical analyses. One-way analysis of variance (ANOVA) was used to compare single factors between groups, followed by least significant difference (LSD) t test. We used ANOVA for factorial designed data to compare 2 factors, such as dose and time, between groups. We used ANOVA for repeated measures to analyze blood test results at different time points. We used the Kaplan-Meier method to assess and compare survival rates between the 2 groups using the log-rank test. P < .05 was considered significant.

Results

L1210 cells are more sensitive to ultraviolet LED radiation than hematopoietic stem cells in vitro
To investigate whether L1210 cells are more sensitive to UV LED radiation than HSCs, we compared the proliferative abilities between L1210 cells and BMCs/HSCs in response to UV LED radiation. As shown in Figure 1a, UV LED radiation inhibited colony formation in both L1210 cells and BMCs in a dose-dependent manner (all P < .01). Of note, colony formation rates for L1210 cells were significantly lower than rates for BMCs in response to UV LED radiation ranging from 2.4 to 14.4 J/m² (all P < .05), with the most significant difference at 9.6 J/m². The colony morphology results for L1210 cells and BMCs are shown in Figure 2.

We isolated HSCs from BMCs to compare cell proliferation and apoptosis between L1210 cells and HSCs in response to UV LED radiation. The purity of SCA1-positive HSCs reached 97.1% (Figure 3). As shown in Figure 1, b to go, UV LED radiation ranging from 28 to 224 J/m² significantly inhibited cell prolife-ration of both L1210 cells and HSCs in dose- and time-dependent manners (Figure 1, b and c), with more potent inhibitory effects on L1210 cell proliferation compared with those on HSC proliferation (all P < .05; Figure 1, d-g).

Flow cytometry analysis consistently showed that UV LED radiation ranging from 28 to 224 J/m² significantly promoted apoptosis of L1210 cells in dose- and time-dependent manners starting 12 hours after treatment (all P < .05; Figure 4, a-d, f). The use of UV LED radiation also induced apoptosis of HSCs at 24 hours after treatment, with radiation at 112 J/m² exhibiting the maximum effect (Figure 4, e and g). Of note, 24 hours after UV LED radiation ranging from 28 to 224 J/m², greater enhancive effects were shown regarding L1210 cell apoptosis than HSC apoptosis, which occurred in a dose-dependent manner (P < .01; Figure 4h). Together, these results suggest that L1210 cells are more sensitive to UV LED radiation than HSCs in vitro.

Pretransplant ultraviolet LED radiation suppresses in vivo tumorigenicity of L1210 cells
In our investigation of whether UV LED radiation affects the tumorigenicity of L1210 cells in vivo, we found that all mice inoculated with unirradiated L1210 cells developed palpable tumors starting on day 8 after inoculation (Figure 5a, Figure 6a), whereas mice inoculated with irradiated L1210 cells did not develop palpable tumors. The mice inoculated with unirradiated L1210 cells had remarkably shorter survival than those inoculated with irradiated L1210 cells (χ2 = 11.76, P < .001) (Figure 5b). Hematoxylin and eosin staining showed that unirradiated L1210 cell-generated tumor tissue exhibited cellular atypia, including pleomorphism, multinuclear cells, tumor giant cells, singular nuclei, pathological mitotic figures, and high nucleus-to-cytoplasm ratio (Figure 5c). Tumor cells infiltrated into the spleens of mice in the unirradiated group (66.67%), whereas no infiltration was observed in the spleens of mice in the irradiated group (Figure 5, d and e). No infiltration was observed in other organs in either group. These results suggest that UV LED radiation results in a loss of in vivo tumorigenicity of L1210 cells.

Ultraviolet LED irradiation of hematopoietic stem cells preserves hematopoiesis in vivo
To explore whether UV LED radiation affects the hematopoiesis of HSCs, we transplanted unirradiated or irradiated BMCs from male mice into female recipient mice. No significant differences were observed in survival rates (100% vs 83.33%, χ2 = 1.00, P = .32) or in the numbers of WBC, RBC, hemoglobin, and platelets at different time points between the mice transplanted with irradiated and unirradiated BMCs (all P > .05).

Compared with findings in wild-type mice (WBC: 4-9 × 10⁹/L; RBC: 9.5-11.5 × 10¹²/L; hemoglobin: 125-155 g/L; platelet: 450-850 × 10⁹/L), the WBC and platelet counts, but not the hemoglobin and RBC counts, of recipient mice in both groups were significantly decreased on day 7 after transplant, possibly due to high-dose TBI-induced hematopoietic failure. However, the WBC and platelet counts of the recipient mice in both groups rebounded to normal levels on day 14 after transplant (Figures 7a-d). Agarose gel electrophoresis showed that male-specific sry gene was detectable in the peripheral blood cells, BMCs, and spleen tissue of recipient mice in both groups, suggesting stable donor chimerism is achieved after transplant (Figure 7e). Together, these results suggest that UV LED-irradiated HSCs could restore hematopoiesis in vivo.

Pretransplant ultraviolet LED radiation reduces in vivo tumorigenic and metastatic capacity of L1210 cells
Minimum residual disease (MRD) represents a risk factor for leukemia relapse and an indicator for allogeneic HSCT.¹⁹ To mimic MRD and explore whether pretransplant UV LED radiation could prevent MRD relapse, we transplanted a mixture of BMCs and L1210 cells into mice (Figure 6b). We found that mice transplanted with the irradiated cell mixture showed a later onset of weight loss (day 28 vs day 21 posttransplant), greater body weight (starting on day 28 posttransplant), and longer survival (84 days vs 56 days; χ2 = 12.02, P < .001) than those transplanted with unirradiated cell mixture (Figure 6c, Figure 8a). Hematoxylin and eosin staining showed that mice transplanted with irradiated cells displayed milder leukemia cell infiltration in various tissue samples, including the femoral and vertebral bone marrow, spinal cord, epidural space, spleen, liver, and muscle, compared with those transplanted with unirradiated cells (Figures 8, b-o). These results collectively suggest that pretransplant UV LED radiation suppresses tumorigenic and metastatic capacity of leukemia cells in the graft and may prevent MRD relapse in acute leukemia.

Discussion

In this study, we demonstrated that mice transplanted with irradiated cell mixture had a later onset of weight loss, greater body weight, longer survival, and milder leukemia cell infiltration in multiple tissue samples than those transplanted with unirradiated cell mixture, suggesting that pret-ransplant UV LED radiation suppresses tumorigenic and metastatic capacity of leukemia cells in the graft and may prevent MRD relapse in acute leukemia.

Leukemia lymphocytes are hypersensitive to UV radiation compared with healthy cells, partially because of their inability to repair UV-induced DNA damage.²⁰ Therefore, we hypothesized that the highly proliferative leukemia cells might be more sensitive to UV radiation than HSCs, which are normally in a quiescent or dormant state.²¹ To test our hypothesis, we compared colony formation, proliferation, and apoptosis between L1210 cells and normal BMCs/HSCs in response to different doses of UV LED radiation at different time points. Consistent with previous reports, our results suggest that L1210 cells are more sensitive to UV LED radiation than HSCs, as evidenced by significantly lower colony formation rates and cell proliferation rates, along with remarkably higher apoptosis rates, of L1210 cells compared with those in HSCs. Thus, UV LED radiation may serve as a potential approach to eradicate leukemia cells in the autograft before HSCT.

In acute leukemia, MRD negativity in the graft or the patient bone marrow represents an essential prerequisite for autologous HSCT.²² To investigate whether pretransplant UV LED radiation could prevent relapse by killing leukemia cells without affecting HSC hematopoiesis, we established HSCT mouse models by transplanting unirradiated or irradiated L1210 cells, BMCs, or a mixture of L1210 cells and BMCs into mice. In the L1210 cell transplant model, unirradiated L1210 cells generated visible and rapidly growing tumors in 100% of mice starting on day 8 after inoculation. By day 19, the tumor volumes of all mice reached 9600 mm3. Anatomical examination revealed that the tumor mass wrapped around the left upper limb and grew into the thoracic cavity, resulting in dyspnea and death in mice (Figure 6a). In contrast, the irradiated L1210 cells failed to develop measurable tumors in mice, suggesting that pretransplant UV LED radiation results in a loss of in vivo tumorigenicity of L1210 cells.

We next mimicked MRD by transplanting an unirradiated or UV LED-irradiated mixture of L1210 cells and BMCs into mice. In this model, mice in the unirradiated group exhibited a continuous decline in body weight since day 21 after transplant. Mental malaise, poor diet, bow back, dull fur, hair loss, dyspnea, and lower limb paralysis were observed. Starting on day 52, the mice progressed to cachexia and death (Figure 6b). Histologically, leukemia cells infiltrated into multiple organs and tissues, including the femoral and vertebral bone marrow, spinal cord, and epidural space, which may possibly cause limb paralysis.²³ On the other hand, results showing later onset of leukemia, milder degree of leukemic infiltration, and prolonged survival in mice transplanted with irradiated cell mixture, suggesting the important role of UV LED radiation in preventing leukemia relapse.

To investigate whether HSCs preserve the potential to differentiate into blood cells after UV LED radiation, we transplanted unirradiated or irradiated BMCs from male mice into female mice. Agarose gel electrophoresis showed male-specific sry gene expression in the peripheral blood cells, BMCs, and spleen tissue of recipient mice in both groups, suggesting stable donor chimerism is achieved after transplant. In this model, we used high-dose TBI for myeloablative conditioning to destroy the immune system of the recipient mice. In the preliminary experiment, we found that mice without bone marrow transplant died 5 to 8 days after myeloablative conditioning. Hematoxylin and eosin staining showed a significantly reduced number of hematopoietic cells in the bone marrow (Figure 6d), suggesting that high-dose TBI destroys the hematopoietic system of recipient mice. On the other hand, in recipient mice transplanted with irradiated or unirradiated BMCs, high-dose TBI-induced hematopoietic failure resulted in significant decreases in WBC and platelet counts on day 7 posttransplant. However, WBC and platelet counts of recipient mice in both groups rebounded to normal levels on day 14 posttransplant, suggesting that UV LED-irradiated HSCs preserve the potential to differentiate into blood cells in vivo.

Conclusions

Mouse L1210 leukemia cells are more sensitive to UV LED radiation than normal HSCs. Pretransplant UV LED radiation suppressed in vivo tumorigenicity of L1210 cells without affecting the differentiation potential of HSCs.

References:

1. Galgano L, Hutt, D. How does it work? In: Kenyon M, Babic A, ed. The European Blood and Marrow Transplantation Textbook for Nurses: Under the Auspices of EBMT. Springer; 2018:23-36.
   CrossRef - PubMed
   
2. Cornelissen JJ, Blaise D. Hematopoietic stem cell transplantation for patients with AML in first complete remission. Blood. 2016;127(1):62-70. doi:10.1182/blood-2015-07-604546
   CrossRef - PubMed
   
3. Mizutani M, Hara M, Fujita H, et al. Comparable outcomes between autologous and allogeneic transplant for adult acute myeloid leukemia in first CR. Bone marrow transplantation. 2016;51(5):645-653.
   CrossRef - PubMed
   
4. Khaddour K, Hana, CK, Mewawalla, P. Hematopoietic stem cell transplantation. StatPearls. StatPearls Publishing; 2023.
   CrossRef - PubMed
   
5. Penna I, Albanesi E, Bertorelli R, Bandiera T, Russo D. Cytoprotective, anti-inflammatory, and antioxidant properties of high-molecular-weight hyaluronan enriched with red orange extract in human fibroblasts exposed to ultra violet light B irradiation. Biotechnol Appl Biochem. 2019;66(3):273-280. doi:10.1002/bab.1722
   CrossRef - PubMed
   
6. Li KR, Yang SQ, Gong YQ, et al. 3H-1,2-dithiole-3-thione protects retinal pigment epithelium cells against ultra-violet radiation via activation of Akt-mTORC1-dependent Nrf2-HO-1 signaling. Sci Rep. 2016;6:25525. doi:10.1038/srep25525
   CrossRef - PubMed
   
7. Salucci S, Burattini S, Battistelli M, Baldassarri V, Maltarello MC, Falcieri E. Ultraviolet B (UVB) irradiation-induced apoptosis in various cell lineages in vitro. Int J Mol Sci. 2012;14(1):532-546. doi:10.3390/ijms14010532
   CrossRef - PubMed
   
8. Luchetti F, Canonico B, Mannello F, et al. Melatonin reduces early changes in intramitochondrial cardiolipin during apoptosis in U937 cell line. Toxicol In Vitro. 2007;21(2):293-301. doi:10.1016/j.tiv.2006.08.003
   CrossRef - PubMed
   
9. Burattini S, Ferri P, Battistelli M, et al. Apoptotic DNA fragmentation can be revealed in situ: an ultrastructural approach. Microsc Res Tech. 2009;72(12):913-923. doi:10.1002/jemt.20735
   CrossRef - PubMed
   
10. Ueno E, Tanigawa T, Osaki M, Ito H. Apoptosis induced by ultraviolet B irradiation of leukemia cells and macrophages. Oncol Rep. 1997;4(3):531-533. doi:10.3892/or.4.3.531
    CrossRef - PubMed
    
11. Azuma H, Ikebuchi K, Yamaguchi M, et al. Comparison of sensitivity to ultraviolet B irradiation between human lymphocytes and hematopoietic stem cells. Blood. 2000;96(7):2632-2634.
    CrossRef - PubMed
    
12. Song K, Mohseni M, Taghipour F. Application of ultraviolet light-emitting diodes (UV-LEDs) for water disinfection: A review. Water Res. 2016;94:341-349. doi:10.1016/j.watres.2016.03.003
    CrossRef - PubMed
    
13. Kwon TR, Oh CT, Choi EJ, et al. Ultraviolet light-emitting-diode irradiation inhibits TNF-alpha and IFN-gamma-induced expression of ICAM-1 and STAT1 phosphorylation in human keratinocytes. Lasers Surg Med. 2015;47(10):824-832. doi:10.1002/lsm.22425
    CrossRef - PubMed
    
14. Ibrahim MA, MacAdam J, Autin O, Jefferson B. Evaluating the impact of LED bulb development on the economic viability of ultraviolet technology for disinfection. Environ Technol. 2014;35(1-4):400-406. doi:10.1080/09593330.2013.829858
    CrossRef - PubMed
    
15. Xie D, Sun Y, Wang L, et al. Ultraviolet light-emitting diode irradiation-induced cell death in HL-60 human leukemia cells in vitro. Mol Med Rep. 2016;13(3):2506-2510. doi:10.3892/mmr.2016.4812
    CrossRef - PubMed
    
16. Ueha S, Yokochi S, Ishiwata Y, et al. Combination of anti-CD4 antibody treatment and donor lymphocyte infusion ameliorates graft-versus-host disease while preserving graft-versus-tumor effects in murine allogeneic hematopoietic stem cell transplantation. Cancer Sci. 2017;108(10):1967-1973. doi:10.1111/cas.13346
    CrossRef - PubMed
    
17. Cesarovic N, Nicholls F, Rettich A, et al. Isoflurane and sevoflurane provide equally effective anaesthesia in laboratory mice. Lab Anim. 2010;44(4):329-336. doi:10.1258/la.2010.009085
    CrossRef - PubMed
    
18. Luznik L, Jalla S, Engstrom LW, Iannone R, Fuchs EJ. Durable engraftment of major histocompatibility complex-incompatible cells after nonmyeloablative conditioning with fludarabine, low-dose total body irradiation, and posttransplantation cyclophosphamide. Blood. 2001;98(12):3456-3464. doi:10.1182/blood.v98.12.3456
    CrossRef - PubMed
    
19. Czyz A, Nagler A. The Role of Measurable Residual Disease (MRD) in Hematopoietic Stem Cell Transplantation for Hematological Malignancies Focusing on Acute Leukemia. Int J Mol Sci. 2019;20(21):5362. doi:10.3390/ijms20215362
    CrossRef - PubMed
    
20. Tuck A, Smith S, Larcom L. Chronic lymphocytic leukemia lymphocytes lack the capacity to repair UVC-induced lesions. Mutat Res. 2000;459(1):73-80. doi:10.1016/s0921-8777(99)00060-9
    CrossRef - PubMed
    
21. Grinenko T, Eugster A, Thielecke L, et al. Hematopoietic stem cells can differentiate into restricted myeloid progenitors before cell division in mice. Nat Commun. 2018;9(1):1898. doi:10.1038/s41467-018-04188-7
    CrossRef: https://doi.org/10.1038/s41467-018-04188-7
    PubMed
    
22. Ferrara F, Picardi A. Is there still a role for autologous stem cell transplantation for the treatment of acute myeloid leukemia? Cancers (Basel). 2019;12(1):59. doi:10.3390/cancers12010059
    CrossRef - PubMed
    
23. Chen JJ, Zhou W, Cai N, Chang G. In vivo murine model of leukemia cell-induced spinal bone destruction. Biomed Res Int. 2017;2017:3521481. doi:10.1155/2017/3521481
    CrossRef - PubMed