A bimodal burst energy distribution of a repeating fast radio burst source.

The event rate, energy distribution and time-domain behaviour of repeating fast radio bursts (FRBs) contain essential information regarding their physical nature and central engine, which are as yet unknown1,2. As the first precisely localized source, FRB 121102 (refs. 3-5) has been extensively observed and shows non-Poisson clustering of bursts over time and a power-law energy distribution6-8. However, the extent of the energy distribution towards the fainter end was not known. Here we report the detection of 1,652 independent bursts with a peak burst rate of 122 h-1, in 59.5 hours spanning 47 days. A peak in the isotropic equivalent energy distribution is found to be approximately 4.8 × 1037 erg at 1.25 GHz, below which the detection of bursts is suppressed. The burst energy distribution is bimodal, and well characterized by a combination of a log-normal function and a generalized Cauchy function. The large number of bursts in hour-long spans allows sensitive periodicity searches between 1 ms and 1,000 s. The non-detection of any periodicity or quasi-periodicity poses challenges for models involving a single rotating compact object. The high burst rate also implies that FRBs must be generated with a high radiative efficiency, disfavouring emission mechanisms with large energy requirements or contrived triggering conditions.

An extreme magneto-ionic environment associated with the fast radio burst source FRB 121102.

Fast radio bursts are millisecond-duration, extragalactic radio flashes of unknown physical origin. The only known repeating fast radio burst source-FRB 121102-has been localized to a star-forming region in a dwarf galaxy at redshift 0.193 and is spatially coincident with a compact, persistent radio source. The origin of the bursts, the nature of the persistent source and the properties of the local environment are still unclear. Here we report observations of FRB 121102 that show almost 100 per cent linearly polarized emission at a very high and variable Faraday rotation measure in the source frame (varying from +1.46 × 105 radians per square metre to +1.33 × 105 radians per square metre at epochs separated by seven months) and narrow (below 30 microseconds) temporal structure. The large and variable rotation measure demonstrates that FRB 121102 is in an extreme and dynamic magneto-ionic environment, and the short durations of the bursts suggest a neutron star origin. Such large rotation measures have hitherto been observed only in the vicinities of massive black holes (larger than about 10,000 solar masses). Indeed, the properties of the persistent radio source are compatible with those of a low-luminosity, accreting massive black hole. The bursts may therefore come from a neutron star in such an environment or could be explained by other models, such as a highly magnetized wind nebula or supernova remnant surrounding a young neutron star.

A direct localization of a fast radio burst and its host.

Fast radio bursts are astronomical radio flashes of unknown physical nature with durations of milliseconds. Their dispersive arrival times suggest an extragalactic origin and imply radio luminosities that are orders of magnitude larger than those of all known short-duration radio transients. So far all fast radio bursts have been detected with large single-dish telescopes with arcminute localizations, and attempts to identify their counterparts (source or host galaxy) have relied on the contemporaneous variability of field sources or the presence of peculiar field stars or galaxies. These attempts have not resulted in an unambiguous association with a host or multi-wavelength counterpart. Here we report the subarcsecond localization of the fast radio burst FRB 121102, the only known repeating burst source, using high-time-resolution radio interferometric observations that directly image the bursts. Our precise localization reveals that FRB 121102 originates within 100 milliarcseconds of a faint 180-microJansky persistent radio source with a continuum spectrum that is consistent with non-thermal emission, and a faint (twenty-fifth magnitude) optical counterpart. The flux density of the persistent radio source varies by around ten per cent on day timescales, and very long baseline radio interferometry yields an angular size of less than 1.7 milliarcseconds. Our observations are inconsistent with the fast radio burst having a Galactic origin or its source being located within a prominent star-forming galaxy. Instead, the source appears to be co-located with a low-luminosity active galactic nucleus or a previously unknown type of extragalactic source. Localization and identification of a host or counterpart has been essential to understanding the origins and physics of other kinds of transient events, including gamma-ray bursts and tidal disruption events. However, if other fast radio bursts have similarly faint radio and optical counterparts, our findings imply that direct subarcsecond localizations may be the only way to provide reliable associations.

A repeating fast radio burst.

Fast radio bursts are millisecond-duration astronomical radio pulses of unknown physical origin that appear to come from extragalactic distances. Previous follow-up observations have failed to find additional bursts at the same dispersion measure (that is, the integrated column density of free electrons between source and telescope) and sky position as the original detections. The apparent non-repeating nature of these bursts has led to the suggestion that they originate in cataclysmic events. Here we report observations of ten additional bursts from the direction of the fast radio burst FRB 121102. These bursts have dispersion measures and sky positions consistent with the original burst. This unambiguously identifies FRB 121102 as repeating and demonstrates that its source survives the energetic events that cause the bursts. Additionally, the bursts from FRB 121102 show a wide range of spectral shapes that appear to be predominantly intrinsic to the source and which vary on timescales of minutes or less. Although there may be multiple physical origins for the population of fast radio bursts, these repeat bursts with high dispersion measure and variable spectra specifically seen from the direction of FRB 121102 support an origin in a young, highly magnetized, extragalactic neutron star.

A strong magnetic field around the supermassive black hole at the centre of the Galaxy.

Earth's nearest candidate supermassive black hole lies at the centre of the Milky Way. Its electromagnetic emission is thought to be powered by radiatively inefficient accretion of gas from its environment, which is a standard mode of energy supply for most galactic nuclei. X-ray measurements have already resolved a tenuous hot gas component from which the black hole can be fed. The magnetization of the gas, however, which is a crucial parameter determining the structure of the accretion flow, remains unknown. Strong magnetic fields can influence the dynamics of accretion, remove angular momentum from the infalling gas, expel matter through relativistic jets and lead to synchrotron emission such as that previously observed. Here we report multi-frequency radio measurements of a newly discovered pulsar close to the Galactic Centre and show that the pulsar's unusually large Faraday rotation (the rotation of the plane of polarization of the emission in the presence of an external magnetic field) indicates that there is a dynamically important magnetic field near the black hole. If this field is accreted down to the event horizon it provides enough magnetic flux to explain the observed emission--from radio to X-ray wavelengths--from the black hole.

Transformation of a star into a planet in a millisecond pulsar binary.

Millisecond pulsars are thought to be neutron stars that have been spun-up by accretion of matter from a binary companion. Although most are in binary systems, some 30% are solitary, and their origin is therefore mysterious. PSR J1719-1438, a 5.7-millisecond pulsar, was detected in a recent survey with the Parkes 64-meter radio telescope. We show that this pulsar is in a binary system with an orbital period of 2.2 hours. The mass of its companion is near that of Jupiter, but its minimum density of 23 grams per cubic centimeter suggests that it may be an ultralow-mass carbon white dwarf. This system may thus have once been an ultracompact low-mass x-ray binary, where the companion narrowly avoided complete destruction.

Recovery of zeta-chain expression and changes in spontaneous IL-10 production after PSA-based vaccines in patients with prostate cancer.

Circulating T lymphocytes of patients with prostate cancer have been reported to have functional deficits, including low or absent zeta-chain expression. To determine whether these functional impairments could be reversed by prostate specific antigen-based vaccination therapy, 10 patients treated with recombinant human prostate specific antigen plus GM-CSF and eight others receiving prostate specific antigen plus oil emulsion in two pilot clinical trials were evaluated prior to and after vaccination for several immunologic end points, including zeta-chain expression and cytokine production by circulating T cells as well as the frequency of T cells able to respond to prostate specific antigen in ELISPOT assays. The flow cytometry assay for zeta-chain expression was standardized to allow for a reliable comparison of pre- vs post-vaccination samples. Prior to therapy, the patients were found to have significantly lower zeta-chain expression in circulating CD3(+) cells and a higher percentage of zeta-chain negative CD3(+) and CD4(+) cells than normal donors. The patients' peripheral blood mononuclear cells spontaneously produced more IL-10 ex vivo than those of normal controls. After vaccination, recovery of zeta-chain expression was observed in 50% of patients in both clinical trials. Also, spontaneous IL-10 secretion by peripheral blood mononuclear cells decreased following immunotherapy in patients treated with prostate specific antigen and GM-CSF. The frequency of prostate specific antigen-reactive T cells was detectable in 7 out of 18 patients vs 4 out of 18 patients prior to vaccination. Only one of 18 patients was a clinical responder. The vaccine had stimulatory effects on the patients' immune system, but post-vaccine immune recovery could not be correlated to progression-free survival in this small cohort of patients with prostate cancer.

Short-term autologous tumor cell lines for the active specific immunotherapy of patients with metastatic melanoma.

We established short-term cell lines for 108/170 (64%) patients with metastatic melanoma. Tumor cell numbers were expanded to 10(8), then cells were irradiated, aliquoted, and cryopreserved for clinical use. Vaccines have been used to treat 69 patients with clinical follow up for 33 who had measurable metastatic disease at the time vaccine therapy was initiated (METS), and 33 who had no evidence of disease (NED) at the time of vaccine therapy following surgical resection of metastases. The protocol called for a baseline test of delayed tumor hypersensitivity (DTH), three weekly injections, a repeat of the DTH test, then monthly injections for an additional 5 months. Objective tumor responses were noted in 3/26 (12%) patients who received a minimum of three vaccinations, one complete, and two partial, with survivals of 36, 46+, and 78+ months. Only 6/64 (9.4%) had a positive DTH (>10 mm) at baseline, including three METS, all of whom progressed within 4 months and died within a year, and three who are still NED after more than 5 years. Conversion of DTH from negative to positive was documented in 18/44 (41%) patients who were tested at week 0 and 4. At a median follow up of greater than 5 years, the median overall survival (OS) was 40 months for "NED" with a 5-year survival rate of 39%, and 8.6 months with a 5-year survival rate of 10% for "METS" The 18 patients who had conversion of their DTH had a median event-free survival (EFS) of 15.8 months and 5-year EFS of 32% compared to 4.2 months and 9% for the 26 non-converters (P=0.012, two-tailed, log-rank test). Among patients who were NED when treatment started, the 12 patients whose DTH converted had a median overall survival of 61.4 months with 5-year survival of 63% compared to 9.7 months and 0% for the 13 non-converters (P=0.0026). This treatment approach is feasible, produces minimal toxicity, and is associated with long-term survival in a significant subset of patients.

Adjuvant therapy of stage III and IV malignant melanoma using granulocyte-macrophage colony-stimulating factor.

PURPOSE: To evaluate granulocyte-macrophage colony-stimulating factor (GM-CSF) as surgical adjuvant therapy in patients with malignant melanoma who are at high risk of recurrence. PATIENTS AND METHODS: Forty-eight assessable patients with stage III or IV melanoma were treated in a phase II trial with long-term, chronic, intermittent GM-CSF after surgical resection of disease. Patients with stage III disease were required to have more than four positive nodes or a more than 3-cm mass. All patients were rendered clinically disease-free by surgery before enrollment. The GM-CSF was administered subcutaneously in 28-day cycles, such that a dose of 125 microg/m(2) was delivered daily for 14 days followed by 14 days of rest. Treatment cycles continued for 1 year or until disease recurrence. Patients were evaluated for toxicity and disease-free and overall survival. RESULTS: Overall and disease-free survival were significantly prolonged in patients who received GM-CSF compared with matched historical controls. The median survival duration was 37.5 months in the study patients versus 12.2 months in the matched controls (P <.001). GM-CSF was well tolerated; only one subject discontinued drug due to an adverse event (grade 2 injection site reaction). CONCLUSION: GM-CSF may provide an antitumor effect that prolongs survival and disease-free survival in patients with stage III and IV melanoma who are clinically disease-free. These results support institution of a prospective, randomized clinical trial to definitively determine the value of surgical adjuvant therapy with GM-CSF in such patients.

Generation of PSA-reactive effector cells after vaccination with a PSA-based vaccine in patients with prostate cancer.

BACKGROUND: JBT 1001 is a vaccine used for therapy of prostate cancer (CA), which consists of recombinant prostate-specific antigen (PSA) with lipid A formulated in liposomes. Patients with prostate CA were vaccinated with JBT 1001 emulsified in mineral oil (n = 5) or with the vaccine in combination with granulocyte-macrophage colony-stimulating factor (GM-CSF) administered locally at the site of vaccination (n = 5). Frequency of PSA-reactive T cells was measured in peripheral blood mononuclear cells (PBMC) before and after immunization, using an interferon-gamma (IFN-gamma) enzyme-linked immunospot (ELISPOT) assay with autologous dendritic cells (DC) as antigen-presenting cells. The hypothesis tested was that PSA-based vaccines induce T cell responses to human PSA. METHODS: In order to expand precursor cells, in vitro sensitization (IVS) was performed. Microcultures of peripheral blood lymphocytes (PBL) (1 x 10(5)/well) in medium supplemented with interleukin-2 (IL-2) (10 IU/ml) and interleukin-7 (IL-7) (10 ng/ml) were stimulated twice (day 0 and day 7) with monocyte-derived autologous DC, generated by culture with interleukin-4 (IL-4) and GM-CSF and pulsed with PSA (10 microg/ml) at an effector to stimulator ratio of 10:1. ELISPOT assays were performed on day 14 of culture. In addition, PBMC were separated on immunobeads into CD4(+) and CD8(+) subsets for ELISPOT assays performed without IVS. RESULTS: Two patients had PSA-reactive responses before vaccination (frequency range, 1/700-1/4,400). After vaccination, 8/10 patients had measurable PSA-reactive T-cell frequencies, ranging from 1/200-1/1900, using IVS. In contrast, without IVS, but after immunoselection to enrich in CD8(+) and CD4(+) T cells, only 2/10 patients had detectable PSA-reactive T cells after vaccination, at a frequency ranging from 1/2,600-1/4,000. CONCLUSIONS: Vaccination with PSA formulated into liposomes induced T-cell responses in 8/10 patients with prostate carcinoma. The frequency of PSA-reactive precursor T cells was relatively low in the blood of these patients, and IVS, leading to amplification of the precursor cells prior to ELISPOT, was necessary for quantification of the PSA-responding T cells. Cellular responses to PSA were predominantly mediated by CD4(+) T lymphocytes.

Oil-in-water liposomal emulsions: characterization and potential use in vaccine delivery.

Emulsification of mineral oil by phospholipids donated by liposomes composed of dimyristoyl phosphatidylcholine, dimyristoyl phosphatidylglycerol, cholesterol, and lipid A by extrusion resulted in the formation of oil-in-water liposomal emulsions containing a substantial number of intact liposomes. Increasing the proportion of liposomes from 25 mM to 150 mM phospholipid and increasing the oil content from 2.5% (v/v) to 42.5% (v/v) changed the flow characteristics of the emulsions from fluid liquid-like to viscous. Likewise, the degree of stability of the emulsions was liposomal phospholipid concentration-dependent, ranging from partial emulsification in the range 25-100 mM to complete stabilization in the range 125-150 mM. Despite some loss of liposome integrity, as evidenced by the release of liposomal trapped glucose, emulsification of liposomes containing encapsulated prostate-specific antigen (PSA) exhibited antigen-specific immunostimulation in mice. These results suggest that liposomes containing encapsulated antigen can serve as constituents for the formulation of oil-in-water vaccines.

Immunologic approaches to the treatment of prostate cancer.

The presence of several organ-specific molecules that could serve as immunogens or targets of an immune attack, the nonessential nature of the prostate gland, the substantial failure rate after treatment of the primary tumor, and the lack of effective chemotherapy for metastatic disease make prostate cancer an ideal candidate for immunotherapy. This report reviews the current status of two novel approaches to the treatment of prostate cancer. The first is an effort to induce antitumor immunity by enriching the cytokine environment within the primary cancer by intraprostatic injection of Leukocyte Interleukin (Cel-Sci Corp, Vienna, VA), a mixture of natural cytokines that includes interleukin-1 beta (IL-1beta), IL-2, granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon gamma (IFN-gamma), and tumor necrosis factor alpha (TNF-alpha). The second approach uses OncoVax-P (Jenner Biotherapies, Inc, San Ramon, CA), a vaccine consisting of liposome-encapsulated recombinant prostate-specific antigen (PSA) and lipid A. When administered as an emulsion or in association with bacillus Calmette-Guérin (BCG)/cyclophosphamide or GM-CSF with or without IL-2/cyclophosphamide, immunologic tolerance is broken as evidenced by the generation of humoral and cellular immunity. Both of these approaches have been shown to be feasible and safe, and are now being tested in patients with less advanced disease to determine if manipulation of the immune system can favorably influence clinical outcome.

Clinical experience with autologous tumor cell lines for patient-specific vaccine therapy in metastatic melanoma.

Because of their patient specificity and proliferative capacity, tumor cell lines established from autologous metastatic melanoma tumor samples may be an excellent immunogen for patient-specific vaccine therapy. Between October 1990 and July 1996, the Hoag Cancer Center cell biology laboratory received 136 fresh metastatic melanoma samples from 122 different patients. Tumor cell lines were successfully established for 92 of 136 samples (68%), for 87 of 122 patients (71%). Successful cultures were expanded to 10(8) cells (total culture time about 8 weeks), confirmed to be sterile, irradiated, and stored frozen in aliquots of 10(7) cells. Vaccines were prepared from 72 lines, and 62 vaccines were used in 57 different patients. Subcutaneous vaccination took place on weeks 1, 2 and 3, and then monthly for a total of 6 months. A delayed tumor hypersensitivity skin test (DTH) was administered at week zero and week 4. Various adjuvants were co-administered including BCG, alpha- or gamma-interferon, and GM-CSF. Patients were monitored for failure-free survival (FFS) and overall survival (OS) from the date of the first vaccination. Follow-up data is available for 52 patients, 27 who had no evident disease (NED) at the time of vaccination and 25 who had metastatic disease at the time of treatment. There were two partial responses which persisted 11.9 and 39.8+ months among the 25 patients who had detectable metastatic disease whün treatment was initiated (8%, 1 to 26%, 95%-Ci). Twenty patients had negative skin tests at week 0 and week 4; six were positive both times, and 13 converted their DTH from negative to positive, for a conversion rate of 13 of 33 (39%). Patients who received interferon-gamma and/or GM-CSF as an adjuvant had a higher rate of DTH conversion compared to patients who received other adjuvants (13 of 20 v 2 of 13, P = 0.003). For patients who were NED, nine of 19 (47%) converted their DTH test compared to four of 14 (29%) patients with metastatic disease (p = 0.33). For patients whose DTH converted from negative to positive after 3 weeks of vaccination, median FFS and OS were superior compared to patients whose DTH remained negative (19.4 v 4.0 months FFS, p = 0.0052 and 39.6 v 18.3 months OS, p = 0.0602). The autologous cell line approach to active specific immunotherapy is feasible for patients who have resectable foci of metastatic disease. Administration of such patient-specific vaccines improves survival for those patients who are NED at the time of vaccination and convert their DTH skin test, compared to those whose DTH test remains negative.

Penetration of anti-melanoma immunotoxin into multicellular tumor spheroids and cell kill effects.

In order to gain a better understanding of the interaction between immunotoxins and tumor cells at the level of three-dimensional tumor mass, we evaluated the cell kill effects of monoclonal antimelanoma-antibody/ricin-A-chain immunotoxin (ITN) on melanoma cells in multicellular tumor spheroids (MTS) as well as the penetration of ITN into MTS. For Minor melanoma cells in monolayer the ITN exerted cytotoxic effects after as little as 1 h of exposure. Increasing exposure time resulted in progressive increases in cytotoxic activity. In contrast, the cell kill effects of ITN were markedly delayed and reduced when Minor cells were in MTS. The ITN cytotoxic effects on the melanoma MTS were more than 100 fold less than those in monolayer. Patterns of ITN-induced cytotoxicities for Minor and for another melanoma cell line, DND-1A, were comparable. The native ricin A was more active against PC-10 squamous lung cancer cells than Minor cells, whereas the ITN was more cytotoxic against Minor cells than PC-10 cells, thus exhibiting selectivity. An autoradiographic study revealed time-dependent penetration of radiolabeled ITN from the surface of Minor MTS into the core. Incubation for 1 h resulted in the penetration of ITN into only the two or three outer layers of the Minor MTS, and low grain counts. Prolonged exposure resulted in inhomogeneous penetration of ITN into almost the entire melanoma MTS. Penetration of ITN into PC-10 MTS was extremely poor. The reduced cytotoxicity of ITN on melanoma cells in MTS as compared to cells grown in monolayer appears to correlate with its inhomogeneous distribution in the MTS. The delayed cytotoxicity of ITN is also consistent with its slow penetration into the core of the MTS.

Single-dose murine monoclonal antibody ricin A chain immunotoxin in the treatment of metastatic melanoma: a phase I trial.

To determine the maximally tolerated dose of a ricin A chain-conjugated antimelanoma antibody (XomaZyme-Mel), 20 patients with metastatic melanoma were treated with escalating doses of the murine immunotoxin given as single intravenous infusion over 30 minutes. The starting dose was 0.6 mg/kg and was escalated in five groups to a maximum of 1.6 mg/kg. The maximally tolerated dose was 1.25 mg/kg as three of six patients treated at 1.6 mg/kg developed unacceptable toxicity. The dose-limiting toxicity consisted of profound fatigue, myalgias, and arthralgias. These occurred within 4 days and resolved in 7 to 10 days. Other non-dose-limiting toxicities encountered consisted of hypoalbuminemia, weight gain, peripheral edema, mild hypotension, and flu-like syndrome; the severity of these was also dose related. In addition, two allergic reactions occurred, one severe. There was one durable complete response of 12+ months' duration and one brief mixed response lasting 3 months. We conclude that the maximum tolerated single dose of XomaZyme-Mel is 1.25 mg/kg. Phase I studies evaluating 1.25 mg/kg given in multiple doses at 2- to 4-week intervals and phase II studies to determine the response rate of a single 1.25 mg/kg dose are warranted.

Continuous infusion interleukin-2 and tumor-derived activated cells as treatment of advanced solid tumors: a National Biotherapy Study Group Trial.

Metastases from patients with solid tumors were harvested from 196 patients for the purpose of growing tumor-derived activated cells (TDAC). Cells were prepared from autologous tumor cultures by incubation with Interleukin-2 (IL-2) followed by repeated exposure to tumor antigen and/or anti-CD3 monoclonal antibody. Initial growth success was achieved in 66%; 45/56 (80%) of these early cultures were subsequently expanded for in vivo therapy. It took a mean of 69.4 +/- 24.0 days to grow TDAC for treatment. Thirty-eight patients were treated with cyclophosphamide (1 g/m2) on day one followed by a 96-hour continuous infusion of IL-2 (18 x 10(6) IU/m2/day) on days 2-5 and approximately 10(11) TDAC on day 2. Patients subsequently received monthly IL-2 as a 96-hour constant infusion if their cancers were stable or regressing. Median age was 51 yrs; 58% were male. Performance status was 0-1 in 64%, 29% had lung metastases; 34% had liver metastases. The usual IL-2 toxicities were seen. Responses were seen only in 1/38 patients (3%); a partial response in a patient with lymphoma. Forty-two percent were stable 90 days post-treatment, the rest were progressive or inevaluable. We conclude that a treatment plan for IL-2/TDAC is technically difficult, costly, and not practical under these conditions. Clinical results to date are not clearly different than those obtained with other IL-2 regimens.