Total Body Irradiation Exposure Research Articles

Assessment of Micronuclei Frequency in the Peripheral Blood of Adult and Pediatric Patients Receiving Fractionated Total Body Irradiation

The cytokinesis-block micronucleus (CBMN) assay is an established method for assessing chromosome damage in human peripheral blood lymphocytes resulting from exposure to genotoxic agents such as ionizing radiation. The objective of this study was to measure cytogenetic DNA damage and hematology parameters in vivo based on MN frequency in peripheral blood lymphocytes (PBLs) from adult and pediatric leukemia patients undergoing hematopoietic stem cell transplantation preceded by total body irradiation (TBI) as part of the conditioning regimen. CBMN assay cultures were prepared from fresh blood samples collected before and at 4 and 24 h after the start of TBI, corresponding to doses of 1.25 Gy and 3.75 Gy, respectively. For both age groups, there was a significant increase in MN yields with increasing dose (p < 0.05) and dose-dependent decrease in the nuclear division index (NDI; p < 0.0001). In the pre-radiotherapy samples, there was a significantly higher NDI measured in the pediatric cohort compared to the adult due to an increase in the percentage of tri- and quadri-nucleated cells scored. Complete blood counts with differential recorded before and after TBI at the 24-h time point showed a rapid increase in neutrophil (p = 0.0001) and decrease in lymphocyte (p = 0.0006) counts, resulting in a highly elevated neutrophil-to-lymphocyte ratio (NLR) of 14.45 ± 1.85 after 3.75 Gy TBI (pre-exposure = 4.62 ± 0.49), indicating a strong systemic inflammatory response. Correlation of the hematological cell subset counts with cytogenetic damage, indicated that only the lymphocyte subset survival fraction (after TBI compared with before TBI) showed a negative correlation with increasing MN frequency from 0 to 1.25 Gy (r = −0.931; p = 0.007). Further, the data presented here indicate that the combination of CBMN assay endpoints (MN frequency and NDI values) and hematology parameters could be used to assess cytogenetic damage and early hematopoietic injury in the peripheral blood of leukemia patients, 24 h after TBI exposure.

Longitudinal multi-omic changes in the transcriptome and proteome of peripheral blood cells after a 4 Gy total body radiation dose to Rhesus macaques

BackgroundNon-human primates, such as Rhesus macaques, are a powerful model for studies of the cellular and physiological effects of radiation, development of radiation biodosimetry, and for understanding the impact of radiation on human health. Here, we study the effects of 4 Gy total body irradiation (TBI) at the molecular level out to 28 days and at the cytogenetic level out to 56 days after exposure. We combine the global transcriptomic and proteomic responses in peripheral whole blood to assess the impact of acute TBI exposure at extended times post irradiation.ResultsThe overall mRNA response in the first week reflects a strong inflammatory reaction, infection response with neutrophil and platelet activation. At 1 week, cell cycle arrest and re-entry processes were enriched among mRNA changes, oncogene-induced senescence and MAPK signaling among the proteome changes. Influenza life cycle and infection pathways initiated earlier in mRNA and are reflected among the proteomic changes during the first week. Transcription factor proteins SRC, TGFβ and NFATC2 were immediately induced at 1 day after irradiation with increased transcriptional activity as predicted by mRNA changes persisting up to 1 week. Cell counts revealed a mild / moderate hematopoietic acute radiation syndrome (H-ARS) reaction to irradiation with expected lymphopenia, neutropenia and thrombocytopenia that resolved within 30 days. Measurements of micronuclei per binucleated cell levels in cytokinesis-blocked T-lymphocytes remained high in the range 0.27–0.33 up to 28 days and declined to 0.1 by day 56.ConclusionsOverall, we show that the TBI 4 Gy dose in NHPs induces many cellular changes that persist up to 1 month after exposure, consistent with damage, death, and repopulation of blood cells.

Organ-Specific Endothelial Dysfunction Following Total Body Irradiation Exposure.

As the single cell lining of the heart and all blood vessels, the vascular endothelium serves a critical role in maintaining homeostasis via control of vascular tone, immune cell recruitment, and macromolecular transit. For victims of acute high-dose radiation exposure, damage to the vascular endothelium may exacerbate the pathogenesis of acute and delayed multi-organ radiation toxicities. While commonalities exist between radiation-induced endothelial dysfunction in radiosensitive organs, the vascular endothelium is known to be highly heterogeneous as it is required to serve tissue and organ specific roles. In keeping with its organ and tissue specific functionality, the molecular and cellular response of the endothelium to radiation injury varies by organ. Therefore, in the development of medical countermeasures for multi-organ injury, it is necessary to consider organ and tissue-specific endothelial responses to both injury and candidate mitigators. The purpose of this review is to summarize the pathogenesis of endothelial dysfunction following total or near total body irradiation exposure at the level of individual radiosensitive organs.

Mitigation of total body irradiation-induced mortality and hematopoietic injury of mice by a thrombopoietin mimetic (JNJ-26366821)

The threat of a nuclear attack has increased in recent years highlighting the benefit of developing additional therapies for the treatment of victims suffering from Acute Radiation Syndrome (ARS). In this work, we evaluated the impact of a PEGylated thrombopoietin mimetic peptide, JNJ-26366821, on the mortality and hematopoietic effects associated with ARS in mice exposed to lethal doses of total body irradiation (TBI). JNJ-26366821 was efficacious as a mitigator of mortality and thrombocytopenia associated with ARS in both CD2F1 and C57BL/6 mice exposed to TBI from a cobalt-60 gamma-ray source. Single administration of doses ranging from 0.3 to 1 mg/kg, given 4, 8, 12 or 24 h post-TBI (LD70 dose) increased survival by 30–90% as compared to saline control treatment. At the conclusion of the 30-day study, significant increases in bone marrow colony forming units and megakaryocytes were observed in animals administered JNJ-26366821 compared to those administered saline. In addition, enhanced recovery of FLT3-L levels was observed in JNJ-26366821-treated animals. Probit analysis of survival in the JNJ-26366821- and saline-treated cohorts revealed a dose reduction factor of 1.113 and significant increases in survival for up to 6 months following irradiation. These results support the potential use of JNJ-26366821 as a medical countermeasure for treatment of acute TBI exposure in case of a radiological/nuclear event when administered from 4 to 24 h post-TBI.

Residual effects of busulfan and irradiation on murine hematopoietic stem and progenitor cells

Exposure of young C57BL/6 (B6) mice to two courses of busulfan (BSF) injections or two rounds of sublethal total-body irradiation (TBI) induced significant damage to the function of hematopoietic stem and progenitor cells (HSPCs). Fifteen weeks after treatment, BSF- and TBI-treated mice had reduced white blood cells without significant change in red blood cells or platelets, indicating that BSF and TBI hematotoxicity was chronic, with leukocytes being the major targets. Hematopoietic damage induced by BSF or TBI persisted long term. Residual adverse effects were reflected by significantly decreased CD45R B cells and reduced recovery of total bone marrow cells, especially HSPCs carrying markers for KSL (Kit+Sca-1+Lin-) cells, multipotent progenitor (MPP) cells (KSLCD34+CD135+), myeloid progenitor (MP) cells (Kit+Sca-1-Lin-), and common lymphoid progenitor (CLP) cells 62 wk posttreatment. Transplantation of bone marrow (BM) cells from BSF and TBI donors at 49 weeks after treatment into lethally irradiated hosts resulted in decreased engraftment of CD45R B cells in blood and reduced reconstitution of BM HSPCs including KSL cells, short-term hematopoietic stem cells (KSLCD34+CD135-), MPP cells, and MP cell subsets. TBI donor had better reconstitution of CLP cells in recipients posttransplantation than did BSF donor, suggesting an impact of TBI and BSF on B cells at different development stages. In summary, BSF and TBI exposure produced long-lasting adverse effects on hematopoiesis with pronounced effects on mature B cells, immature ST-HSCs, and hematopoietic progenitor cells. Our results may have implications for therapy of human diseases.

Exosomes are involved in total body irradiation-induced intestinal injury in mice.

Ionizing radiation-induced intestinal injury is a catastrophic complication in patients receiving radiotherapy. Circulating exosomes from patients undergoing radiotherapy can mediate communication between cells and facilitate a variety of pathological processes in vivo, but its effects on ionizing radiation-induced intestinal damage are undetermined. In this study we investigated the roles of exosomes during total body irradiation (TBI)-induced intestinal injury in vivo and in vitro. We isolated exosomes from serum of donor mice 24 h after lethal dose (9 Gy) TBI (Exo-IR-24h), then intravenously injected the exosomes into receipt mice, and found that Exo-IR-24h injection not only exacerbated 9 Gy TBI-induced lethality and weight loss, but also promoted crypt-villus structural and functional injury of the small intestine in receipt mice. Moreover, Exo-IR-24h injection significantly enhanced the apoptosis and DNA damage of small intestine in receipt mice following TBI exposure. In murine intestinal epithelial MODE-K cells, treatment with Exo-IR-24h significantly promoted 4 Gy ionizing radiation-induced apoptosis, resulting in decreased cell vitality. We further demonstrated that Exo-IR-24h promoted the IR-induced injury in receipt mice partially through its DNA damage-promoting effects and attenuating Nrf2 antioxidant response in irradiated MODE-K cells. In addition, TBI-related miRNAs and their targets in the exosomes of mice were enriched functionally using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. Finally, injection of GW4869 (an inhibitor of exosome biogenesis and release, 1.25 mg·kg-1·d-1, ip, for 5 consecutive days starting 3 days before radiation exposure) was able to rescue mice against 9 Gy TBI-induced lethality and intestinal damage. Collectively, this study reveals that exosomes are involved in TBI-induced intestinal injury in mice and provides a new target to protect patients against irradiation-induced intestinal injury during radiotherapy.

2672. Clostridioides difficile Infection Among Bone Marrow Transplant Recipients: Findings From a Single Institution

Background Clostridioides difficile infection (CDI) is increasingly common among hematopoietic stem cell transplantation (HSCT) recipients and efforts to define CDI risk have shown variable results. The primary objective of this study was to further characterize CDI incidence and risk factors in HSCT recipients.MethodsAll allogeneic and autologous HSCT recipients at Loyola University Chicago between January 2011 and May 2017 were retrospectively reviewed for development of CDI within 6 months prior to 2 years following HSCT. Collected data include comorbid conditions, statin or proton pump inhibitor (PPI), and antimicrobial use. HSCT baseline information was also obtained and include underlying malignancy, prior chemotherapy, graft type, conditioning regimen consisting of total body irradiation (TBI) use, and donor source (matched related or unrelated and umbilical cord blood). Among those with diagnosed CDI, data pertaining to CDI severity, treatment, and recurrence was collected. Logistic regression analyses were performed to estimate odds ratios for factors associated with development of CDI.ResultsSix hundred eighty-nine patients met our inclusion criteria. Of these, 367 (53%) underwent autologous HSCT and 322 (47%) allogeneic HSCT. Among all patients, 132 (19.1%) had CDI of which 26 (19.7%) had recurrence within 60 days. In univariable analysis, any type of leukemia was associated with increased odds of CDI compared with lymphoma (OR = 2.44, 95% CI: 1.49- 4.00, P < 0.01) as was allogeneic HSCT compared with autologous (OR = 2.51, 95% CI: 1.63–3.88, P < 0.01 for matched and OR = 3.96, 95% CI: 2.31–6.79, P < 0.01 for cord blood) and use of TBI (OR = 1.63, 95% CI: 1.10 – 2.40, P < 0.05). Exposure to any cephalosporin or intravenous vancomycin within 100 days of HSCT was associated with CDI (OR = 1.55, 95% CI: 1.03–2.32, P < 0.05 and OR = 1.75, 95% CI: 1.19–2.58, P < 0.01 respectively). No significant differences in the odds of developing CDI were identified by patient comorbidities, statin or PPI use.ConclusionIn our population there was a 19% incidence of CDI. Underlying leukemia, TBI exposure, and allogeneic HSCT appear to be risk factors for CDI and further research is needed to evaluate whether exposure to cephalosporin or vancomycin may be modifiable risk factors. Disclosures All authors: No reported disclosures.

Long‐term outcomes among 2‐year survivors of autologous hematopoietic cell transplantation for Hodgkin and diffuse large b‐cell lymphoma

Autologous hematopoietic cell transplantation (auto-HCT) is a standard therapy for relapsed classic Hodgkin lymphoma (cHL) and diffuse large B-cell lymphoma (DLBCL); however, long-term outcomes are not well described. This study analyzed survival, nonrelapse mortality, late effects, and subsequent malignant neoplasms (SMNs) in 1617 patients who survived progression-free for ≥2 years after auto-HCT for cHL or DLBCL between 1990 and 2008. The median age at auto-HCT was 40 years; the median follow-up was 10.6 years. The 5-year overall survival rate was 90% (95% confidence interval [CI], 87%-92%) for patients with cHL and 89% (95% CI, 87%-91%) for patients with DLBCL. The risk of late mortality in comparison with the general population was 9.6-fold higher for patients with cHL (standardized mortality ratio [SMR], 9.6) and 3.4-fold higher for patients with DLBCL (SMR, 3.4). Relapse accounted for 44% of late deaths. At least 1 late effect was reported for 9% of the patients. A total of 105 SMNs were confirmed: 44 in the cHL group and 61 in the DLBCL group. According to a multivariate analysis, older age, male sex, a Karnofsky score < 90, total body irradiation (TBI) exposure, and a higher number of lines of chemotherapy before auto-HCT were risk factors for overall mortality in cHL. Risk factors in DLBCL were older age and TBI exposure. A subanalysis of 798 adolescent and young adult patients mirrored the outcomes of the overall study population. Despite generally favorable outcomes, 2-year survivors of auto-HCT for cHL or DLBCL have an excess late-mortality risk in comparison with the general population and experience an assortment of late complications. Cancer 2018;124:816-25. © 2017 American Cancer Society.

Childhood cancer survivors exposed to total body irradiation are at significant risk for slipped capital femoral epiphysis during recombinant growth hormone therapy

Childhood cancer survivors treated with cranial or total body irradiation (TBI) are at risk for growth hormone deficiency (GHD). Recombinant growth hormone (rhGH) therapy is associated with slipped capital femoral epiphysis (SCFE). We compared the incidence of SCFE after TBI versus cranial irradiation (CI) in childhood cancer survivors treated with rhGH. Retrospective cohort study (1980-2010) of 119 survivors treated with rhGH for irradiation-induced GHD (56 TBI; 63 CI). SCFE incidence rates were compared in CI and TBI recipients, and compared with national registry SCFE rates in children treated with rhGH for idiopathic GHD. Median survivor follow-up since rhGH initiation was 4.8 (range 0.2-18.3) years. SCFE was diagnosed in 10 subjects post-TBI and none after CI (P < 0.001). All 10 subjects had atypical valgus SCFE, and 7 were bilateral at presentation. Within TBI recipients, age at cancer diagnosis, sex, race, underlying malignancy, age at radiation, and age at initiation of rhGH did not differ significantly between those with versus without SCFE. The mean (SD) age at SCFE diagnosis was 12.3 (2.7) years and median duration of rhGH therapy to SCFE was 1.8 years. The SCFE incidence rate after TBI exposure was 35.9 per 1,000 person years, representing a 211-fold greater rate than reported in children treated with rhGH for idiopathic GH deficiency. The markedly greater SCFE incidence rate in childhood cancer survivors with TBI-associated GHD, compared with rates in children with idiopathic GHD, suggests that cancer treatment effects to the proximal femoral physis may contribute to SCFE.

Total Body Irradiation (TBI) Increases Cardio-Metabolic Risk and Induces Carotid Vascular Stiffness in Survivors After Hematopoietic Cell Transplant (HCT) for Childhood Hematologic Malignancies.

Abstract 3329Poster Board III-217▪▪This icon denotes an abstract that is clinically relevant. BackgroundCardiovascular disease, hypertension and diabetes all contribute to the increased risk of late non-relapse mortality after HCT and lead to diminished life expectancy compared to the general population. An association between TBI exposure and cardio-metabolic (C-M) risk factors in adult HCT survivors has been described but this association has not been well characterized in children. MethodsMeasures of insulin resistance (euglycemic hyperinsulinemic clamp adjusted for lean body mass [Mlbm], low Mlbm represents insulin resistance), fasting glucose, insulin, lipids, anthropometry, blood pressure (BP), and carotid artery compliance and distensibility (lower values represent arterial stiffness) were determined in 106 children and young adults (current age 26.6 yr, 60.4% male) who had received HCT for hematologic malignancy during childhood (mean age at HCT 9.9 yr) and 72 healthy sibling controls (current age 23.7 yr, 51.4% male). Subjects were compared in 3 radiation exposure groups, all received myeloablative preparative regimens; 79 received allogeneic HCT and 27 received autologous HCT. Diagnoses included AML (n=50), ALL (n=30), myelodysplastic syndrome, n=8, Hodgkin's (n=10) and non-Hodgkin's lymphoma (n=8). Sixty two (58.5%) received TBI, 20 (18.9%) received cranial radiation (CRT) prior to TBI (TBI+CRT), and 24 (22.6%) received no TBI or cranial radiation (noXRT) before or during HCT. Linear regression models were used to evaluate risk factors between groups after adjusting for age, gender, pubertal stage, body mass index (BMI), and carotid lumen diameter (stiffness measures only). ResultsMetabolic syndrome (MS) (ATP III criteria for adults, modified criteria for children) was present in 15 (15.6%) HCT survivors and 4 (5.6%) controls (OR 2.3, 95% CI 0.7-7.7, p=0.16). Two or more components of the MS were present in 39 (37.1%) survivors and 10 (14.5%) controls (OR, 2.7, 95% CI 1.2-5.9, p=0.015). Compared to siblings, there were no differences between groups for glucose, BMI, waist circumference, percent body fat, or BP. However, HCT survivors who had TBI or TBI+CRT all had significantly higher cholesterol, LDL cholesterol, triglycerides and insulin. Those who received TBI+CRT had significantly lower HDL cholesterol and were also more insulin resistant (Table). However, for the noXRT group there were no differences in any of the C-M risk factors compared to controls. Carotid artery distensibility was decreased in survivors who received TBI compared to controls with even greater negative impact in those who received TBI+CRT. There was not a significant difference in distensibility in the noXRT group compared to controls. Only the TBI+CRT group had lower compliance compared to controls. ConclusionsEven at a relatively young age, and independent of obesity, HCT survivors of childhood hematologic malignancies have increased C-M risk factors present as well as adverse vascular changes, which are associated with exposure to TBI +/- CRT. These abnormalities may ultimately contribute to a higher risk of early cardiovascular morbidity and mortality thus early screening and management of modifiable C-M risk factors should be considered in HCT survivors.Cardiometabolic Risk FactorsControlTreatment Groups, mean (SD)P-values(A) TBI(B) TBI +CRT(C) noXRTA vs. controlB vs. controlC vs. controlBMI (kg/m2)22.9(1.2)21.5(1.1)21.1(1.4)23.4(1.4)0.150.170.71Waist circumference (cm)78.9(1.2)78.6(1.1)79.4(1.4)80.3(1.5)0.690.70.3Systolic BP (mmHG)113.4(2.7)112.9(2.5)119.0(3.2)110.4(3.3)0.850.060.29Fasting glucose (mg/dL)88.5(2.3)91.5(2.1)92.3(2.7)87.3(2.8)0.110.140.62Fasting insulin (mU/L)13.9(2.4)21.1(2.2)26.1(2.8)16.2(2.9)<0.001<0.0010.38Total cholesterol (md/dL)155.5(7.8)176.2(7.2)199.8(9.4)157.7(9.6)0.001<0.0010.78LDL-cholesterol (mg/dL)89.1(6.7)98.6(6.1)114.6(8.6)92.5(7.9)0.07<0.0010.61HDL-cholesterol (md/dL)45.3(2.5)43.8(2.3)38.3(2.9)44.2(3.0)0.440.010.67Triglyderides (md/dL)113(26.3)172(23.7)266(30.9)114(31.5)0.006<0.0010.98Insulin resistance [Mlbm]12.2(1.1)10.5(1.0)8.0(1.4)10.5(1.4)0.070.0020.17Carotid distensibility (%)12.1(0.6)10.2(0.6)8.5(0.7)10.9(0.8)<0.001<0.0010.14Carotid compliance (mm2/mmHg)0.14(0.009)0.13(0.008)0.10(0.01)0.14(0.01)0.15<0.0010.85 DisclosuresNo relevant conflicts of interest to declare.

Decline in Sexual Functioning Over a 3-Year Period after Hematopoietic Cell Transplantation (HCT): Gender-Specific Impact of Total Body Irradiation (TBI) and Chronic Graft-Versus-Host Disease (cGvHD)

Sexual dysfunction is a multidimensional problem caused by both physiologic and psychosocial factors. Yet little is known about the longitudinal trends of sexual functioning in HCT survivors, or the clinical or psychosocial factors associated with decline. Using a longitudinal study design, we administered the Derogatis Interview for Sexual Functioning (DISF-SR), the Global Sexual Satisfaction Index (GSSI), and the City of Hope-QOL instrument at 5 time points to a large cohort of patients undergoing HCT at City of Hope (COH): prior to HCT, at 6m, 1y-, 2y-, and 3y-post-HCT. DISF-SR assessed 5 domains of sexual functioning (Cognition/Fantasy, Arousal, Behavior/Experiences, Orgasm, and Drive/Relationship), and a Total score. GSSI elicited patients' subjective appraisal of sexual satisfaction. The COH-QOL instrument was used to obtain self-reported levels of anxiety, distress, depression, pain, physical strength, and sleep changes, which were converted to composite scores of mental and physical stress. Long-term trends of sexual functions were estimated using the Generalized Estimating Equation. We examined the effects of sociodemographic factors, primary diagnosis, HCT conditioning regimens, disease status at HCT, presence of cGvHD, and composite mental and physical stress levels on the longitudinal trends of DISF-SR, the Total score, and GSSI. The cohort included 312 adults (median age at HCT 48y; 56% males) undergoing autologous (n=175) or allogeneic (n=137) HCT for hematologic malignancies or severe aplastic anemia; 144 patients completed the 3y sexual survey (participation rate at 3 years=75%). GSSI (general sexual satisfaction) declined significantly after HCT (p=0.001) for both men and women, and remained depressed over the 3-y study period, with 40% reporting poor or worse sexual satisfaction level at 3y. There were no significant differences between men and women in terms of general sexual satisfaction level. However, the degree of sexual dysfunction as measured by DISF-SR was worse in women than in men for all domains, and for Total score (p<.001) at all post-HCT time points (Fig. 1A). Furthermore, assessment of DISF-SR scores revealed that while men experienced a persistent decline in satisfaction with Orgasm and Drive/Relationship (p<0.05), women did not demonstrate a significant decline in sexual function in any of the domains post-HCT. Gender-specific multivariate analyses revealed certain subgroups that were more vulnerable to a decline in sexual functions after HCT. Notably, older age (≥40y) (Fig. 1B), being married, and TBI exposure in men (Fig. 1C), and older age (≥30y) (Fig. 1D), being overweight, and greater mental and/or physical stress in women were factors identified as significantly associated with decreased sexual functioning following HCT. Although cGvHD was not directly related to DISF-SR or GSSI, presence of cGvHD was accompanied by worse mental and physical composite scores (p<0.0001). Lower mental and/or physical composite scores in turn were significantly related to lower sexual functions for all domains of DISF-SR, the Total score (Fig. 1E) and GSSI in women (p<0.05). Thus, women may be vulnerable to the effects of cGvHD mediated through mental and/or physical stress, in turn resulting in compromised sexual functions and satisfaction after HCT. This study should inform healthcare providers that patients undergoing HCT require more attention to their sexual QOL within the first year after HCT. Routine inquiry of patients' sexual health should be included in follow-up exams after HCT, especially for those at high risk (i.e. TBI-exposed men and those with cGvHD), with the ability to offer a multidisciplinary approach to managing this distressing complication. [Display omitted]

Intensive Supportive Care and Cytokines Promote Recovery of Hematopoiesis after Total Body Irradiation (TBI) without Hematopoietic Stem Cell Support.

Hematopoietic cells are highly sensitive to radiation damage and their loss after radiation exposure results in lethal infections. We asked if intensive supportive care and hematopoietic-specific cytokine treatment after doses of TBI that were previously identified as lethal would permit survival and promote recovery of endogenous hematopoiesis without requiring hematopoietic stem cell support in the well-established dog model. Historical results showed that after 4 Gy TBI and standard supportive care, only 1 of 28 dogs survived with recovery of endogenous hematopoiesis. The intensive supportive care regimen for dogs after irradiation included an antibiotic use algorithm for empiric treatment of prolonged neutropenia and fever. After TBI exposure, dogs were treated with an oral fluoroquinolone. If fever developed or when absolute neutrophil count (ANC) fell below 100/μL, dogs were empirically treated with the combination of intravenous ceftazidime and amikacin. Blood cultures were obtained with fevers, and antibiotics were adjusted based on culture results. If neutropenic fever persisted for 48 hours, additional empiric antibiotic treatment was added. Blood transfusion support included increased volume and frequency of irradiated blood products. Intravenous fluid support (10–30 mL/kg/day Lactated Ringer's solution) was given until full clinical recovery. Intensive supportive care given to 60 dogs resulted in significantly improved survival after TBI compared to limited supportive care. With intensive supportive care, we observed high rates of survival in dogs following exposure of up to 7 Gy TBI with complete endogenous hematopoietic recovery (Table). Cytokine treatment consisting of either granulocyte colony stimulating factor (G-CSF) alone or combined G-CSF and fms-like tyrosine kinase 3 (flt-3) ligand (FL), given after TBI did not significantly improve long term survival compared to recipients of intensive supportive care alone, but it significantly decreased the duration of intensive and expensive supportive care. For all cohorts receiving cytokines after TBI, the recovery of ANC was more rapid compared with supportive care alone (p<0.002). Treatment with the combination of G-CSF (10 μg/kg/day) and FL (100 μg/kg/day), starting 2 hours after TBI and continuing until recovery of ANC>1000/μL resulted in more rapid recovery of ANC and platelets compared to G-CSF alone. Follow-up of all surviving dogs >6 months after irradiation showed sustained hematopoiesis and immune reconstitution. These studies show that in this model, hematopoietic stem cells survive doses of TBI up to 7 and 8 Gy without requiring infusion of either autologous or allogeneic hematopoietic stem cells, that intensive supportive care is sufficient to permit reliable survival after 7 Gy TBI, and that the cytokine combination of G-CSF and FL is more effective than G-CSF in promoting rapid recovery of neutrophils and platelets after moderately high dose TBI. The results are relevant for the treatment of victims of terrorist or accidental radiation exposure.TBI dose (Gy)Cytokine after TBIANC RecoveryPlatelet RecoverySurvival / total # of dogs studiedMedian Days after TBI4no26434/45no27523/65G-CSF20446/66no33845/66G-CSF27645/66G-CSF + FL18535/57no55775/67G-CSF24645/57G-CSF + FL18576/68no*n/an/a0/48G-CSF + FL37991/6survival at > day +120

Total body irradiation in bone marrow transplantation: The influence of fractionation and delay of marrow infusion

Bone marrow transplantation (BMT) after total body irradiation (TBI) and cyclophosphamide is being employed increasingly in the therapy of end stage leukemia. Interstitial pneumonitis (IP) represents a major acute toxicity after allogeneic transplantation. A more rapid reconstitution of lymphoid organs and bone marrow post transplant may result in increased immune competence and hence fewer opportunistic pulmonary infections and IP. By delaying the infusion of marrow to 72 hr after TBI (1250 rod at 7.5 rad/min) instead of the customary 24 hr, we can demonstrate an increase in initial repopulation of thymus, spleen and marrow, with syngeneic transplants in Lewis rats. Interstitial pneumonitis may also be caused, in part, by the pulmonary toxicity of large single exposures of TBI. Clinical and laboratory data suggest that fractionated TBI may be less toxic to the lung. When fractionated TBI (625 rad × 2, 7.5 rad/min) is compared to single dose TBI (1250 rad, 7.5 rad/min), an increased initial repopulation of lymphoid organs is observed when fractionated therapy is employed. Delay in marrow infusion and fractionation of TBI exposure may have clinical advantages in patients who receive BMT.