Polarization states and far-field optical properties in dielectric photonic crystal slabs

We study the role of topological singularities like Bound States in a Continuum (BICs) or Circularly Polarized States (CPSs) in determining ellipticity of the far-field polarization in dielectric metasurfaces. Using finite-difference time-domain as well as rigorous coupled-wave analysis simulations, we determine the behavior of the Stokes parameter S3 in the whole k space above the light cone, with special regard to the region close to the singularities. Moreover, we clarify the relation between the topological singularities and the circular dichroism in reflectivity.

Experimentally realized in situ backpropagation for deep learning in photonic neural networks

Integrated photonic neural networks provide a promising platform for energy-efficient, high-throughput machine learning with extensive scientific and commercial applications. Photonic neural networks efficiently transform optically encoded inputs using Mach-Zehnder interferometer mesh networks interleaved with nonlinearities. We experimentally trained a three-layer, four-port silicon photonic neural network with programmable phase shifters and optical power monitoring to solve classification tasks using "in situ backpropagation," a photonic analog of the most popular method to train conventional neural networks. We measured backpropagated gradients for phase-shifter voltages by interfering forward- and backward-propagating light and simulated in situ backpropagation for 64-port photonic neural networks trained on MNIST image recognition given errors. All experiments performed comparably to digital simulations ([Formula: see text]94% test accuracy), and energy scaling analysis indicated a route to scalable machine learning.

Theory for Twisted Bilayer Photonic Crystal Slabs

We analyze scattering properties of twisted bilayer photonic crystal slabs through a high-dimensional plane wave expansion method. The method is applicable for arbitrary twist angles and does not suffer from the limitations of the commonly used supercell approximation. We show strongly tunable resonance properties of this system which can be accounted for semianalytically from a correspondence relation to a simpler structure. We also observe strongly tunable resonant chiral behavior in this system. Our work provides the theoretical foundation for predicting and understanding the rich optical physics of twisted multilayer photonic crystal systems.

Higher-order topological insulators in synthetic dimensions

Conventional topological insulators support boundary states with dimension one lower than that of the bulk system that hosts them, and these states are topologically protected due to quantized bulk dipole moments. Recently, higher-order topological insulators have been proposed as a way of realizing topological states with dimensions two or more lower than that of the bulk due to the quantization of bulk quadrupole or octupole moments. However, all these proposals as well as experimental realizations have been restricted to real-space dimensions. Here, we construct photonic higher-order topological insulators (PHOTIs) in synthetic dimensions. We show the emergence of a quadrupole PHOTI supporting topologically protected corner modes in an array of modulated photonic molecules with a synthetic frequency dimension, where each photonic molecule comprises two coupled rings. By changing the phase difference of the modulation between adjacent coupled photonic molecules, we predict a dynamical topological phase transition in the PHOTI. Furthermore, we show that the concept of synthetic dimensions can be exploited to realize even higher-order multipole moments such as a fourth-order hexadecapole (16-pole) insulator supporting 0D corner modes in a 4D hypercubic synthetic lattice that cannot be realized in real-space lattices.

PT-Symmetric Topological Edge-Gain Effect

We demonstrate a non-Hermitian topological effect that is characterized by having complex eigenvalues only in the edge states of a topological material, despite the fact that the material is completely uniform. Such an effect can be constructed in any topological structure formed by two gapped subsystems, e.g., a quantum spin-Hall system, with a suitable non-Hermitian coupling between the spins. The resulting complex-eigenvalued edge state is robust against defects due to the topological protection. In photonics, such an effect can be used for the implementation of topological lasers, in which a uniform pumping provides gain only in the edge lasing state. Furthermore, such a topological lasing model is reciprocal and is thus compatible with standard photonic platforms.

Experimental realization of arbitrary activation functions for optical neural networks

We experimentally demonstrate an on-chip electro-optic circuit for realizing arbitrary nonlinear activation functions for optical neural networks (ONNs). The circuit operates by converting a small portion of the input optical signal into an electrical signal and modulating the intensity of the remaining optical signal. Electrical signal processing allows the activation function circuit to realize any optical-to-optical nonlinearity that does not require amplification. Such line shapes are not constrained to those of conventional optical nonlinearities. Through numerical simulations, we demonstrate that the activation function improves the performance of an ONN on the MNIST image classification task. Moreover, the activation circuit allows for the realization of nonlinearities with far lower optical signal attenuation, paving the way for much deeper ONNs.

Absence of unidirectionally propagating surface plasmon-polaritons at nonreciprocal metal-dielectric interfaces

In the presence of an external magnetic field, the surface plasmon polariton that exists at the metal-dielectric interface is believed to support a unidirectional frequency range near the surface plasmon frequency, where the surface plasmon polariton propagates along one but not the opposite direction. Recent works have pointed to some of the paradoxical consequences of such a unidirectional range, including in particular the violation of the time-bandwidth product constraint that should otherwise apply in general in static systems. Here we show that such a unidirectional frequency range is nonphysical using both a general thermodynamic argument and a detailed calculation based on a nonlocal hydrodynamic Drude model for the metal permittivity. Our calculation reveals that the surface plasmon-polariton at metal-dielectric interfaces remains bidirectional for all frequencies.

The local Drude model predicts that, under certain conditions, surface plasmon polaritons at a metal-dielectric surface have a frequency range where only unidirectional propagation is supported. Here, the authors show that in more realistic non-local models surface plasmon polaritons exhibit bidirectional propagation for all frequencies.

Wave physics as an analog recurrent neural network

Analog machine learning hardware platforms promise to be faster and more energy efficient than their digital counterparts. Wave physics, as found in acoustics and optics, is a natural candidate for building analog processors for time-varying signals. Here, we identify a mapping between the dynamics of wave physics and the computation in recurrent neural networks. This mapping indicates that physical wave systems can be trained to learn complex features in temporal data, using standard training techniques for neural networks. As a demonstration, we show that an inverse-designed inhomogeneous medium can perform vowel classification on raw audio signals as their waveforms scatter and propagate through it, achieving performance comparable to a standard digital implementation of a recurrent neural network. These findings pave the way for a new class of analog machine learning platforms, capable of fast and efficient processing of information in its native domain.

A single photonic cavity with two independent physical synthetic dimensions

The concept of synthetic dimensions has generated interest in many branches of science, ranging from ultracold atomic physics to photonics, as it provides a versatile platform for realizing effective gauge potentials and topological physics. Previous experiments have augmented the real-space dimensionality by one additional physical synthetic dimension. In this study, we endow a single ring resonator with two independent physical synthetic dimensions. Our system consists of a temporally modulated ring resonator with spatial coupling between the clockwise and counterclockwise modes, creating a synthetic Hall ladder along the frequency and pseudospin degrees of freedom for photons propagating in the ring. We observe a wide variety of physics, including effective spin-orbit coupling, magnetic fields, spin-momentum locking, a Meissner-to-vortex phase transition, and signatures of topological chiral one-way edge currents, completely in synthetic dimensions. Our experiments demonstrate that higher-dimensional physics can be studied in simple systems by leveraging the concept of multiple simultaneous synthetic dimensions.

Experimental band structure spectroscopy along a synthetic dimension

There has been significant recent interest in synthetic dimensions, where internal degrees of freedom of a particle are coupled to form higher-dimensional lattices in lower-dimensional physical structures. For these systems, the concept of band structure along the synthetic dimension plays a central role in their theoretical description. Here we provide a direct experimental measurement of the band structure along the synthetic dimension. By dynamically modulating a resonator at frequencies commensurate with its mode spacing, we create a periodically driven lattice of coupled modes in the frequency dimension. The strength and range of couplings can be dynamically reconfigured by changing the modulation amplitude and frequency. We show theoretically and demonstrate experimentally that time-resolved transmission measurements of this system provide a direct readout of its band structure. We also realize long-range coupling, gauge potentials and nonreciprocal bands by simply incorporating additional frequency drives, enabling great flexibility in band structure engineering.

Zero-Index Bound States in the Continuum

Metamaterials with an effective zero refractive index associated with their electromagnetic response are sought for a number of applications in communications and nonlinear optics. A promising way that this can be achieved in all-dielectric photonic crystals is through the design of a Dirac cone at zero Bloch wave vector in the photonic band structure. In the optical frequency range, the natural way to implement this design is through the use of a photonic crystal slab. In the existing implementation, however, the zero-index photonic modes also radiate strongly into the environment due to intrinsic symmetry properties. This has resulted in large losses in recent experimental realizations of this zero-index paradigm. Here, we propose a photonic crystal slab with zero-index modes which are also symmetry-protected bound states in the continuum. Our approach thus eliminates the associated radiation loss. This could enable, for the first time, large-scale integration of zero-index materials in photonic devices.

Ultra-wide-band structural slow light

The ability of using integrated photonics to scale multiple optical components on a single monolithic chip offers key advantages to create miniature light-controlling chips. Numerous scaled optical components have been already demonstrated. However, present integrated photonic circuits are still rudimentary compared to the complexity of today’s electronic circuits. Slow light propagation in nanostructured materials is a key component for realizing chip-integrated photonic devices controlling the relative phase of light and enhancing optical nonlinearities. We present an experimental record high group-index-bandwidth product (GBP) of 0.47 over a 17.7 nm bandwidth in genetically optimized coupled-cavity-waveguides (CCWs) formed by L3 photonic crystal cavities. Our structures were realized in silicon-on-insulator slabs integrating up to 800 coupled cavities, and characterized by transmission, Fourier-space imaging of mode dispersion, and Mach-Zehnder interferometry.

Isotropic wavevector domain image filters by a photonic crystal slab device

We show that several types of isotropic image filters in the wavevector domain can be implemented with a single photonic crystal slab device. Such a slab is designed so that the guided resonance near the Γ point exhibits an isotropic band structure. Depending on the light frequency and the choice of transmission or reflection mode, the device realizes isotropic high-pass, low-pass, band-reject, and band-pass filtering in wavevector space. These filter functions are important for various image processing tasks, including edge detection, smoothing, white noise suppression, and suppression or extraction of periodic noises. We numerically demonstrate these filter functionalities by simulations of a slab structure that is designed to operate in the visible wavelength range. Our work expands the application of nanophotonics-based optical analog computing for image processing.

Neuropeptide Y immunoreactivity in the cat claustrum: A light- and electron-microscopic investigation

The claustrum is a telencephalic nucleus located ventrolateral to the basal ganglia in the mammalian brain. It has an extensive reciprocal connectivity with most if not all of the cerebral cortex, in particular, primary sensory areas. However, despite renewed and growing interest amongst investigators, there remains a paucity of data concerning its peptidergic profile. The aim of the present study was to examine the presence, morphology, distribution and ultrastructure of neuropeptide Y-immunoreactive (NPY-ir) neurons and fibers in the claustrum of the cat. Ten adult healthy cats from both sexes were used. All animals received human and ethical treatment in accordance with the Principles of Laboratory Animal Care. Subjects were irreversibly anesthetized and transcardially perfused with fixative solution containing glutaraldehyde and paraformaldehyde. Brains were promptly removed, postfixed and sectioned. Slices were incubated with polyclonal anti-NPY antibodies according to the standard avidin-biotin-peroxidase complex method adopted by our Department of Anatomy, Histology and Embryology. NPY-ir neurons and fibers were found to be diffusely distributed throughout the claustrum, with no obvious topographic or functional patterning other than larger numbers in its central/broadest part (stereotaxic planes A12-A16). Neurons were generally classified by diameter into three sizes: small (under 17 μm), medium (17-25 μm) and large (over 25 μm). Staining density is varied with some neurons appearing darker than others. At the electron-microscopic level NPY immunoproduct was observed within neurons, dendrites and terminal boutons, each differing relative to their ultrastructural attributes. Two types of NPY-ir synaptic boutons were found. Lastly, it is of interest to note that gender-specific differences were not observed.

Statistics of the disorder-induced losses of high-Q photonic crystal cavities

We analyze and compare the effect of fabrication disorder on the quality factor of six well-known high-index photonic crystal cavity designs. The theoretical quality factors for the different nominal structures span more than three orders of magnitude, ranging from 5.4 × 10(4) to 7.5 × 10(7), and the defect responsible for confining light is introduced in a different way for each structure. Nevertheless, among the different designs we observe similar behavior of the statistics of the disorder-induced light losses. In particular, we show that for high enough disorder, such that the quality factor is mainly determined by the disorder-induced losses, the measured quality factors differ marginally - not only on average as commonly acknowledged, but also in their full statistical distributions. This notably shows that optimizing the theoretical quality factor brings little practical improvement if its value is already much larger than what is typically measured, and if this is the case, there is no way to choose an alternative design more robust to disorder.

Effect of hole-shape irregularities on photonic crystal waveguides

The effect of irregular hole shape on the spectrum and radiation losses of a photonic crystal waveguide is studied using Bloch-mode expansion. Deviations from a circular hole are characterized by a radius fluctuation amplitude and correlation angle. It is found that the parameter that determines the magnitude of the effect of disorder is the standard deviation of the hole areas. Hence, for a fixed amplitude of the radius fluctuation around the hole, those effects are strongly dependent on the correlation angle of the irregular shape, which suggests how to potentially improve the quality of photonic crystal structures.

Evaluating bleeding severity in children with newly diagnosed immune thrombocytopenia: a pilot study

BACKGROUND

Childhood immune thrombocytopenia (ITP) is a bleeding disorder characterized by decreased platelet counts. Assessment of the individual bleeding risk during the course of the disease would allow more accurately guiding treatment-related decisions in these patients.

PATIENTS AND METHODS

We conducted a pilot study and prospectively evaluated platelet counts and bleeding signs using an established bleeding (Buchanan) score in 30 patients with newly diagnosed ITP at 3 different time points (at diagnosis [TP1], on day 2-3 [TP2], and on day 5-8 [TP3]) during the first week after diagnosis. 15 patients received immune modulatory therapy.

RESULTS

Median platelet counts at the 3 different time points were 13, 19, 32×10 (9)/L (untreated patients) and 2, 7, 37×10 (9)/L (treated patients). Corresponding median cumulative bleeding scores were 5, 2, 0 (untreated patients) and 7, 6, 2 (treated patients). Cumulative median bleeding scores and platelet counts were inversely correlated in treated and untreated patients at all 3 time points. Cumulative median bleeding scores significantly decreased in both groups.

CONCLUSIONS

Bleeding signs in children with newly diagnosed ITP rapidly improve within one week after diagnosis. Serial grading of bleeding severity seems to be useful to comprehensively assess and monitor the individual bleeding risk in these patients, but has to be evaluated and validated in a larger cohort.

Clinical and immunological overlap between autoimmune lymphoproliferative syndrome and common variable immunodeficiency

Autoimmune lymphoproliferative syndrome (ALPS) is mainly caused by defects in the CD95 pathway. Raised CD3+TCRαβ+CD4-CD8- double negative T cells and impaired T cell apoptosis are hallmarks of the disease. In contrast, the B cell compartment has been less well studied. We found an altered distribution of B cell subsets with raised transitional B cells and reduced marginal zone B cells, switched memory B cells and plasma blasts in most of 22 analyzed ALPS patients. Moreover, 5 out of 66 ALPS patients presented with low IgG and susceptibility to infection revealing a significant overlap between ALPS and common variable immunodeficiency (CVID). In patients presenting with lymphoproliferation, cytopenia, hypogammaglobulinemia and impaired B cell differentiation, serum biomarkers were helpful in addition to apoptosis tests for the identification of ALPS patients. Our observations may indicate a role for apoptosis defects in some diseases currently classified as CVID.

Importance of allogeneic T-cells for disease control after stem cell transplantation for high-risk Langerhans cell histiocytosis

Reduced intensity conditioning followed by allogeneic SCT (RIC-SCT) has recently emerged as promising new salvage option for children suffering from Langerhans cell histiocytosis (LCH) with risk organ involvement and failure to conventional therapy. We report on the posttransplant course of female toddler with high-risk LCH, who achieved complete remission after RIC-SCT, despite a posttransplant chimerism constellation, in which only the T-cell subset proved to be of donor origin in the long-term. We therefore suggest that allogeneic T-cells have played a crucial role in controlling disease activity in this patient and may exert the major curative effect after RIC-SCT for LCH.

Risk factors for diabetes insipidus in langerhans cell histiocytosis

BACKGROUND

Diabetes insipidus (DI) is the most frequent central nervous system (CNS)-related permanent consequence in Langerhans cell histiocytosis (LCH), which mostly requires life-long hormone replacement therapy. In an attempt to define the population at risk for DI, 1,741 patients with LCH registered on the trials DALHX 83 and DALHX 90, LCH I and LCH II were studied.

RESULTS

Overall 212 of 1,741 patients (12%) was reported to have DI. In 102 of 1,741 patients (6%) DI was present at diagnosis of LCH. One thousand one hundred eighty three of 1,539 patients without DI at diagnosis had follow up information. One hundred ten of these (9%) later developed DI. The risk of developing DI was 20% at 15 years after diagnosis. Multisystem disease patients at diagnosis carried a 4.6-fold risk for DI compared to single system patients. Craniofacial lesions, in particular in the "ear," "eye," and oral region were associated with a significantly increased risk for DI (relative hazard rate, RHR 1.7), independent of the extent of disease. No influence of the duration of therapy could be determined, but the duration of initial disease activity (RHR 1.5) and the occurrence of reactivations (RHR 3.5) significantly increased the risk for DI.

CONCLUSIONS

Patients with multisystem disease and craniofacial involvement at diagnosis, in particular of the "ear," "eye," and the oral region carry a significantly increased risk to develop DI during their course. This risk is augmented when the disease remains active for a longer period or reactivates.

Langerhans cell histiocytosis in neonates

BACKGROUND

To study the incidence, clinical patterns, course, and outcome of neonatal Langerhans cell histiocytosis (LCH).

PROCEDURE

Retrospective analysis of the data of the Austrian/German/Swiss/Netherlands LCH Study Group. The incidence of neonatal LCH was estimated with the data from the population-based German Childhood Cancer Registry.

RESULTS

The estimated incidence of neonatal LCH (LCH diagnosed within 28 days after birth) in the population-based registry was 1-2/1,000,000. In 61/1,069 trial patients (6%), the first disease manifestations were observed in the neonatal period. However, in only 20 of them, the diagnosis was established within this period. There was a preponderance of multisystem (MS)-LCH 36/61 (59%). Cutaneous changes were the most common initial manifestation in both, single-system (SS)-LCH (92%), and MS-LCH (86%). In 72% of the MS-LCH patients, risk organs (ROs) were involved at diagnosis as well. The probability of survival at 5 years was 94% in SS-LCH and 57% in MS-LCH, which is significantly lower than in older age groups.

CONCLUSIONS

In contrast to the available literature, neonatal LCH is characterized by a clear predominance of MS-LCH. Cutaneous changes are the most common initial manifestation in neonates with both SS-LCH and MS-LCH. Prompt evaluation of disease extent upon diagnosis is mandatory for risk-adapted treatment. The disease course is unpredictable upon diagnosis. Close monitoring for disease progression is mandatory if isolated cutaneous LCH is managed by the "wait and see" approach. Neonates with MS-LCH, especially those with RO involvement at diagnosis, have less favorable prognosis compared to infants and older children, and need systemic therapy.

Improved outcome of treatment-resistant high-risk Langerhans cell histiocytosis after allogeneic stem cell transplantation with reduced-intensity conditioning

Children with multisystem Langerhans cell histiocytosis (LCH) and risk organ involvement who fail to respond to conventional chemotherapy have an extremely poor prognosis. Myeloablative stem cell transplantation (SCT) as a possible salvage approach for these patients has been associated with a high risk of transplant-related mortality. Therefore, allogeneic stem cell transplantation following a reduced-intensity conditioning regimen (RIC-SCT) has recently been performed as an alternative salvage approach. We report on the experience with allogeneic RIC-SCT in nine pediatric high-risk LCH patients. Conditioning regimen included fludarabine in all patients, melphalan in eight patients, total lymphoid irradiation in six patients, total body irradiation in two, antithymocyte globulin in five, and Campath in four patients. RIC-SCT was well tolerated with regard to common procedure-related complications. Two patients died 50 and 69 days after RIC-SCT, respectively. Seven out of the nine patients survived and showed no signs of disease activity (including one with nonengraftment and full autologous hematopoietic recovery) after median follow-up of 390 days post-SCT. Based on this observation, we conclude that RIC-SCT is a feasible procedure with low transplant-related morbidity and mortality and a promising new salvage approach for high-risk LCH patients with resistant risk organ involvement.

Pineal gland abnormalities in Langerhans cell histiocytosis

BACKGROUND

The most common types of central nervous system (CNS) disease in Langerhans cell histiocytosis (LCH) comprise involvement of the hypothalamic-pituitary region (HPR) and neurodegenerative changes in the cerebellum, basal ganglia or pons. In the review process of magnetic resonance images (MRI) from 129 LCH patients a high frequency of cysts within or large pineal glands was noted by chance.

PROCEDURE

To prove whether this observation was specific for LCH or not, we compared MRI findings of the HPR in LCH patients with a control group of 55 non-LCH patients with the same age and sex distribution.

RESULTS

In LCH patients, the pineal gland was significantly larger and also the number of pineal cysts was significantly higher as compared to the control group. No difference was found regarding the size or frequency of cystic changes between patients who had received chemotherapy prior to the MRI and untreated patients. In the LCH patients, we further found a significant correlation of pineal gland enlargement with involvement of the HPR, but not with neurodegenerative changes. Analysis of melatonin (the principal hormone of the pineal gland) levels in 24 hr urine in 14 LCH patients did not reveal a melatonin deficiency or overproduction in the LCH group as compared to 6 normal controls.

CONCLUSIONS

The pineal gland is another site of possible CNS involvement in LCH. LCH CNS patients did not show an overt disturbance in melatonin levels. The role of the pineal gland in CNS LCH remains to be defined.

[Associated trauma with urinary tract injuries]

The authors analyze the peculiarities in the diagnostic and curative behavior in cases of associated traumatic injuries with participation of the urinary system in adults and children. A trauma is defined as associated when one kind of traumatic agent affects more then one organ or system. The authors do not discuss the combined trauma where we observed different damaging agents as for example mechanical trauma plus radiation or burn. The experience of the treatment of 64 children and 109 adults suffering from associated traumatic injuries for the period 1981-1997 has been summarized. In cases of associated traumatic injuries the kidneys are the most common participants on the part of the urinary system (70.3% of the children and 51.4% of the adults). On the second place we witness bladder damages in adults and urethra damages in children. The data concerning the combination between urological trauma and other organs traumas are available in details--the most common are: bone fractures, lesions of intraabdominal organs, skull and brain traumas, etc. The three basic problems caused by such kind of trauma are also discussed--organizational, diagnostic and curative. At the end the authors present the most typical characteristics of associated traumatic injuries in children compared to those in adults.

Pattern and course of single-system disease in Langerhans cell histiocytosis data from the DAL-HX 83- and 90-study

BACKGROUND

Single-system (SS) disease is the most common presentation in Langerhans cell histiocytosis (LCH) with a heterogenous clinical picture and course. Mostly bone and rarely skin or lymph nodes are involved.

PROCEDURE

One hundred and seventy patients with SS-LCH were registered in the DAL-HX 83/90 studies. They were diagnosed according to uniform diagnostic criteria and followed by a standardised schedule.

RESULTS

Single bone lesions were most common (68%), followed by multiple bone lesions (19%), isolated skin disease (11%), and isolated lymph node involvement (4 patients). In the detection of bone lesions radiographic skeletal survey proved to be superior to bone scan (97% vs. 82%). Treatment comprised surgery, irradiation and local instillation of steroids, and standardised chemotherapy for multifocal bone disease. After initial therapy 81% of the patients remained disease free. Reactivations restricted to the skeleton occurred in 18% of both unifocal and multifocal bone disease. Two skin patients had a chronic course. Fatality occurred only in one infant with skin disease who progressed to multi-system disease. Twenty-five percent of all patients developed permanent consequences, which were already present at diagnosis in about half of these patients and comprised mainly orthopedic problems related to lesional sites. Diabetes insipidus occurred in 3% and anterior pituitary dysfunction in 2% of the patients.

CONCLUSIONS

The course in SS%LCH was benign. In bone disease reactivations remained restricted to the skeleton and did not influence survival. However, reactivations had an impact on morbidity, as permanent consequences were mostly related to the site of disease activity. Med Pediatr Oncol 2001;37:108-114.

Statement of current majority practices in graft-versus-host disease prophylaxis and treatment in children

Great variations exist in the prophylaxis and treatment of GVHD in children undergoing allogeneic stem cell transplantation (SCT). The EBMT Working Party Paediatric Diseases (EBMT-WP PD) and the International BFM Study Group--Subcommittee Bone Marrow Transplantation (IBFM-SG), aimed at evaluating current local standards in the prevention and treatment of GVHD and steps which can be taken to achieve a uniform policy for the individual methods. Several conferences with their members assessed practices which are mainly applied or under investigation in children and identified where additional information is needed. For prevention of GVHD, the majority of the paediatric centres prefer CsA +/- MTX. Addition of folinic acid to MTX was considered for reduction of side-effects. During treatment of acute GVHD most centres administer prednisolone and whole blood level-adjusted CsA as medications of first choice. In cases of poor or no response to this therapy, additional immunosuppressive agents such as ATG, mycophenolate-mofetile and tacrolimus are being increasingly used. The treatment of chronic GVHD usually consists of various combinations of prednisolone and CsA. In severe cases, extracorporeal photopheresis, psoralene-UVA (PUVA) and thalidomide are administered.

Treatment of multisystem Langerhans cell histiocytosis. Results of the DAL-HX 83 and DAL-HX 90 studies. DAL-HX Study Group

BACKGROUND

The prognosis of children with multisystem Langerhans cell histiocytosis (LCH) has improved with the application of chemotherapy. However, treatment strategies used varied from conservative approach with treatment only during disease exacerbation to intensive chemotherapy starting immediately after diagnosis. No single drug or regimen has been proven to be superior to the others. Thus, optimal treatment of multisystem LCH remains still an unsolved problem.

PATIENTS

Three hundred and twenty-four patients enrolled in the DAL-HX 83 and DAL-HX 90 studies were retrospectively re-evaluated by using the current definition for disease extent. Sixty-three patients fulfilling the criteria for multisystem LCH (involvement of > or = 2 organ systems) were object of the present study. These were 33 males and 30 females, median age at diagnosis 11.5 months (range, birth-13 years 2 months). The median observation time was 7 years 6 months (4 years-11 years 8 months).

METHODS

All patients had morphologically confirmed diagnosis, which was additionally verified through demonstration of CD1a antigen, presence of Birbeck granules or central pathologic review. Uniform evaluation including a complete medical history and physical examination, laboratory tests (complete blood count, liver function tests, coagulation profile) and radiographic survey (skeletal survey and/or radionuclide bone scan) was performed in all patients. Additional investigations (bone marrow tap, CT, MRI etc.) were performed upon specific indications. The 63 patients with multisystem LCH were evaluated with respect to response to therapy, clinical course, outcome and development of permanent disabilities. The results of the DAL-HX studies were compared with the results of the first randomized international clinical trial on multisystem LCH (LCH-I).

RESULTS

Response to 6 weeks of initial therapy showed a clear discrimination between responders and non-responders, with only 6% of the patients having intermediate response. When correlated to survival response to initial therapy appears to be a powerful prognosticator in multisystem LCH. There were some typical patterns of clinical course. Complete disease resolution at some point of the clinical course was documented in 50 (79%) patients. Thirty-five of them remained disease free, while 15 experienced one or more episodes of disease reactivation. Chronic reactivating course without complete disease resolution was observed in one patient. Deteriorating disease with fatal outcome was shown in 12 (19%) patients. The overall survival after 5 years of observation was 81%. One or more disease-related permanent disabilities were documented in 24 patients, in 4 of them these were shown at diagnosis and in 20 patients these developed after therapy had been commenced. Despite more intensive chemotherapy, the overall survival in DAL-HX 83/90 cohort was comparable with that in LCH-I studies. However, LCH-I compares unfavorably to DAL-HX 83/90 in some very important aspects. With respect to reactivation rate, reactivation free interval and development of permanent disabilities better results were achieved with the more intensive initial and prolonged continuation therapy concept of the DAL-HX studies. Even after extended analysis it remains unclear whether the superiority of the DAL-HX studies has to be attributed to the administration of continuous steroids, to the combination of vinblastine and etoposide, or to the prolonged continuation therapy including mercaptopurine. Answers to these questions are expected from the ongoing international clinical trial LCH-II.

Cyclosporine A therapy for multisystem langerhans cell histiocytosis

BACKGROUND

Treatment of multisystem Langerhans cell histiocytosis (LCH) remains difficult. Various regimens of single and multiagent chemotherapy have been used, but a significant proportion of patients fail to respond to treatment.

PROCEDURE

We have evaluated the use of cyclosporine A (CSA) in a controlled group of patients, who had received a systematic primary therapy (LCH-I). Patients received CSA either as a single agent (10 patients) or in combination with vinblastine, etoposide, prednisolone, and/or antithymocyte globulin (16 patients).

RESULTS

Among the total of 26 patients treated, a single patient developed a complete response and three a partial response, whereas 85% (22 patients) had no response to CSA.

CONCLUSIONS

CSA is at best of limited value in the treatment of patients with multisystem LCH, particularly those who had progressive disease while receiving chemotherapy.

Leucocyte transfusions from rhG-CSF or prednisolone stimulated donors for treatment of severe infections in immunocompromised neutropenic patients

Sepsis in profound neutropenia after chemotherapy is associated with high mortality despite appropriate antibacterial or antifungal treatment. In a prospective phase I/II study we evaluated the feasability and efficacy of leucocyte transfusions (LT) in patients with malignancies or haematological disorders who were suffering from severe bacterial or fungal infection during therapy-related bone marrow aplasia. 30 patients with severe neutropenia and clinical signs of life-threatening sepsis not responding to adequate treatment, received LT from rhG-CSF-stimulated family donors or from prednisolone-primed volunteers. A total of 301 LT were administered. The median number of LT per patient was seven (range three to 65), the median duration of LT treatment was 8 d (range 2-35). The white cell count (WBC), absolute neutrophil count (ANC) and lymphocyte count of the concentrates from rhG-CSF-stimulated donors were significantly higher than those from prednisolone-primed volunteers (P = 0.0001). Despite the critical condition of the patients, LT were generally well tolerated. Only 39 (12.9%) LT were associated with adverse reactions. The transfusion of leucocytes collected by continuous flow leukapheresis from both rhG-CSF and prednisolone stimulated donors resulted in a measurable increment of the peripheral leucocyte and ANC counts in our patients. On day 100 after the first LT, 20/30 patients were alive with complete clearance of the infection.

Occurrence of acute nonlymphoblastic leukemia in two girls after treatment of recurrent, disseminated Langerhans cell histiocytosis

The occurrence of Langerhans cell histiocytosis (LCH) and acute leukemia in one individual has rarely been observed. Despite few exceptions, two distinct patterns of association appear evident: acute lymphoblastic leukemia preceding LCH and LCH preceding acute nonlymphoblastic leukemia (ANLL). The latency of ANLL after the diagnosis of LCH is suggestive of a therapy-related process. This report describes two new cases in whom ANLL was diagnosed 7 years 8 months and 5 years 8 months after the start of initial treatment of disseminated recurrent LCH. Morphology showed blasts from FAB-type M4/M5 in the first patient, who died due to progression of leukemia. The second patient showed myelodysplastic syndrome (refractory anemia with excess of blasts in transformation; RAEB-t) and is now in remission from leukemia 3 years 11 months after allogeneic bone marrow transplantation. The review of a total of 26 patients with ANLL after LCH suggests that the disease has a poor prognosis and allogeneic BMT seems to be the treatment of choice.

Transplantation activities and treatment strategies in paediatric stem cell transplantation centres: a report from the EBMT Working Party on Paediatric Diseases. European Group for Blood and Marrow Transplantation

To determine the current approach to stem cell transplantation (SCT) in centres which treat predominantly paediatric patients, a questionnaire was sent to 67 centres known by the EBMT registry to perform SCT mainly in children. Fifty-five centres from 19 countries responded. Forty centres (75%) started their transplantation activities between 1980 and 1992. Median number of transplants/centre was 95 (range 8-400). Median number of transplants/centre/year was 18 (range 5-85). On average, there was one physician responsible for seven SCT/year while one nurse was involved for a median of 1.7 SCT/year. Median four rooms/centre (range 1-17) were available for paediatric SCT. The most common isolation facilities were rooms with high efficiency particulate air filtration (HEPA). Eighty-two percent (45/55) of the centres performed allogeneic as well as autologous SCT, while 5% (three centres) offered exclusively allogeneic SCT and 13% (seven centres) used only autologous stem cell rescue. Stem cell source for allogeneic SCT was bone marrow in 87%, peripheral blood (PB) in 10% and umbilical cord blood in 3%. Donors were HLA matched related in 57%, mismatched related in 13%, and matched unrelated in 30% of allogeneic SCT. PB was the most commonly used stem cell source for autologous SCT (48%), followed by BM (41%) and the two together (11%). Data analysis revealed substantial differences in protective care, stem cell processing and transplantation procedures within the centres, irrespective of the country, centre size and transplant type.

Proposal for standard recommendations for prophylaxis of graft-versus-host disease in children. European Group for Blood and Marrow Transplantation (EBMT) Working Party Paediatric Diseases and the International Study Committee of the BFM family-subcommittee Bone Marrow Transplantation (IBFM-STG)

Great variations exist in the practices of graft-versus-host disease prophylaxis for children undergoing allogeneic stem cell transplantation. It was the aim of the EBMT Working Party on Paediatric Diseases and the International Study Group of the BFM-Family, subcommittee bone marrow transplantation (IBFM-SG) to define standard recommendation for prevention of GVHD. Thus a survey was carried out among the local representatives of the EBMT WP and IBFM-SG members to define standards for GVHD prophylaxis basing on available literature data, discussion with colleagues and their own experience. Presently the majority of regimen for GVHD prophylaxis are centred on CsA and a short course of MTX with addition of some other immunosuppression (eg ATG or ALG) in patients with high risk for severe GVHD. The proposal defined different category of patients: patients with malignant disease who are either transplanted from HLA matched sibling donors or HLA mismatched family donors (or volunteer unrelated donors) and patients with non malignant disease who might not benefit from graft-versus-leukaemia effect having either an HLA matched sibling donor or an HLA mismatched family donor (or volunteer unrelated donor). Homogeneous GVHD prophylaxis for defined patient groups should provide better information to optimise strategies in reducing treatment related toxicity and incidence of relapse by increasing GVL effect.

A single centre experience with allogeneic stem cell transplantation for severe aplastic anaemia in childhood

BACKGROUND

Severe aplastic anaemia (SAA) is a rare disorder which has a fatal course when allogeneic stem cell transplantation (SCT) or an immunosuppressive regimen is not applied. Stem cell replacement is the only curative approach for these patients but it is limited by the availability of a compatible donor.

PATIENTS

Between 1982 and 1993, 18 children (15 boys, 3 girls) with SAA and HLA identical, MLC negative donors underwent SCT in our institution. SAA was preceded by viral infection in 8 patients (3x hepatitis, 1x measles, 1x herpes simplex infection and 3x viral upper respiratory tract infections). It was drug-associated in one and idiopathic in the 9 others. The median age at diagnosis was 9.7 years (range, 2 months to 16 years). Pretreatments included corticosteroids in 11/18 patients, androgens in 4 patients in addition, two had received cyclosporin A (CSA). One patient progressing from Diamond- Blackfan anaemia to SAA had multiple immunosuppressive treatment courses over 7 years before his grand-uncle was identified as donor while 4 patients had no treatment prior to SCT.

METHODS

Early SCT (within 90 days after diagnosis) was performed in 9/18 patients and the median interval between diagnosis and SCT was 2.6 months (range, 0.5 to 7 years). The stem cell source was the bone marrow (BM) of a syngeneic twin in 2 patients, the BM (13 patients) or the cord blood (1 patient) of a sibling whilst it was BM from a HLA-phenotypical family donor (1 father, 1 grand-uncle) in two patients. Cyclophosphamide 50 mg/kg on 4 consecutive days was given as preparative regimen to 16 patients but not to the two syngeneic twins. Rejection prophylaxis included total lymphoid irradiation in 5/16 patients while in the other 11 patients donor buffy coat cells were given on days +1 to +4. The syngeneic twins had no need for either approach. Patients received a median number of 3.7 x 10(8)/kg nucleated cells (range, 2.6 to 6.7). Prophylaxis of graft versus host disease (GVHD) was carried out with MTX alone (n = 12), with CSA alone (n = 2) or with both (n = 4). All patients received standard supportive care.

RESULTS

The overall survival is 89% at the median observation time of 100 months. The median time to reach 500 granulocytes was 24 days (range, 15 to 40). Median time to become transfusion independent after BMT was 30 days for platelets (range, 2 to 111) and was 28 days for packed red blood cells (range, 6 to 128). Acute GVHD was observed in 10/18 patients and involved only skin in 6 patients, skin and liver or gut in two patients and all 3 organs in another two patients. Seven of 10 patients had grade 1 to 2 a GVHD toxicity, whereas 3 patients experienced grade 3 to 4 acute GVHD. Chronic GVHD developed in 5 patients. Acute transplant related mortality was 5.5%. Cause of death was persisting non engraftment till day +180 after 2 transplant procedures in a boy with previous platelet transfusions from his mother. Late mortality occurred in 2 patients: one chronic GVHD associated haemorrhage 20 months after SCT and one chronic GVHD associated septicaemia 10 years after SCT.

CONCLUSION

Although this report reflects patients data accumulated over 15 years, results compare favourably with more recent survival data. Acute and late transplant related toxicity was low in patients undergoing early transplantation with adequate prior supportive care. This data confirms that SCT still should be the first treatment choice if an HLA identical sibling is available.

[Integrating demographic and socioeconomic policies]

"The article offers a theoretical model of integration between demographic and socioeconomic policy [in Bulgaria].... The author examines the changes in the population's demographic structures: changes in the sex ratio; ageing; [and] family nuclearisation.... The conclusion is drawn that in order to boost the effectiveness of the demographic policy, social practice and its scientific back-up should be even more fully integrated." (SUMMARY IN ENG)

[Main conclusions and practical tasks in the socio-demographic sphere]

Demographic considerations are explored in relation to developing a social policy for Bulgaria. "Special attention is devoted to those areas of the social sphere, which are connected with the reproduction and realization of human resources, with raising the potential and abilities of the nation, and attaining a high degree of readiness for labour and social activities." (SUMMARY IN ENG AND RUS)

[Migration and migratory behavior]

"The article considers theoretical and methodological peculiarities in studying...migration and migratory behaviour.... The author makes use of the information obtained from [censuses and current demographic statistics for Bulgaria as well as] information from representative sociological studies.... The author uses [a] mathematical model in modelling migration and migratory behaviour, emphasizing the need for a profound sociological study of the main stimuli which influence the migratory processes and the extent of their impact on individuals." (SUMMARY IN ENG AND RUS)

[Marriage rate, divorce rate, and the development of the Bulgarian family]

The author examines the new forms of consensual union that are becoming increasingly prevalent in Europe and their detrimental effects on the reproduction of generations and socialization. "Using data from the sociological study conducted by the Institute of Sociology of the Bulgarian Academy of Sciences in 1977 and the data obtained in the latest population census in 1985, the development of the Bulgarian family and influence of [these] new social relations under socialism are investigated." Particular attention is given to trends in marriage and divorce rates. (SUMMARY IN ENG AND RUS)