TNF-inhibitors or bisphosphonates in chronic nonbacterial osteomyelitis? - Results of an international retrospective multicenter study.

Chronic nonbacterial osteomyelitis (CNO) can cause significant morbidity, including bone pain and damage. In the absence of clinical trials, treatments include non-steroidal anti-inflammatory drugs, corticosteroids, TNF-inhibitors (TNFi) and/or bisphosphonates. In a retrospective chart review in the United Kingdom and Germany, we investigated response to TNFi and/or pamidronate. Ninety-one patients were included, receiving pamidronate (n = 47), TNFi (n = 22) or both sequentially (n = 22). Patients with fatigue [p = 0.003] and/or arthritis [p = 0.002] were more frequently treated with TNFi than pamidronate. Both therapies were associated with clinical remission at 6 months, and reduction of bone lesions on MRI at 12 months. While not reaching statistical significance, pamidronate resulted in faster resolution of MRI lesions. Fewer flares were observed with TNFi. Failure to respond to pamidronate was associated with female sex [p = 0.027], more lesions on MRI [p = 0.01] and higher CRP levels [p = 0.03]. Randomized clinical trials are needed to confirm observations and generate evidence.

Cryopreserved bone marrow aspirate concentrate as a cell source for the colony-forming unit fibroblast assay.

PURPOSE: The prevalence of connective tissue progenitor cells within a cell-based therapy is often quantified using the colony-forming unit fibroblast (CFU-F) assay. The present study investigates the feasibility of using cryopreserved bone marrow aspirate concentrate (BMAC) as an alternative cell source to fresh BMAC for CFU-F quantification. METHODS: Freshly prepared and corresponding cryopreserved BMAC samples from patients receiving autologous cell therapy (n = 98) were analyzed using the CFU-F assay for comparison. Cultures were established by directly plating BMAC at low cell densities and maintained for a 2-week growth period. Colonies were enumerated to determine CFU-F frequency, and a subset of cultures was imaged and analyzed to quantify colony area and density. RESULTS: A nonlinear relationship was observed between plating density and CFU-F frequency over a wide range in plating densities (~30-fold). Cryopreserved BMAC yielded recoverable (77 ± 23%) and viable (73 ± 9%) nucleated cells upon thawing. After cryopreservation, CFU-F frequencies were found to be significantly lower (56.6 ± 34.8 vs. 50.3 ± 31.7 colonies per million nucleated cells). Yet the number of CFU-F in fresh and cryopreserved BMAC were strongly correlated (r = 0.87) and had similar area and densities. Further, moderate correlations were observed between the number of CFU-F and nucleated cells, and both the mean colony area and density were negatively correlated with patient age. Notably, no relationship was found between CFU-F frequency and age, regardless of whether fresh or cryopreserved BMAC was used. CONCLUSIONS: Freshly prepared and cryopreserved BMAC yielded correlated results when analyzed using the CFU-F assay. Our findings support the cryogenic storage of patient BMAC samples for retrospective CFU-F analyses, offering a potential alternative for characterizing BMAC and furthering our understanding of progenitor cells in relation to clinical outcome.

Modulation of human allogeneic and syngeneic pluripotent stem cells and immunological implications for transplantation.

Tissues derived from induced pluripotent stem cells (iPSCs) are a promising source of cells for building various regenerative medicine therapies; from simply transplanting cells to reseeding decellularized organs to reconstructing multicellular tissues. Although reprogramming strategies for producing iPSCs have improved, the clinical use of iPSCs is limited by the presence of unique human leukocyte antigen (HLA) genes, the main immunologic barrier to transplantation. In order to overcome the immunological hurdles associated with allogeneic tissues and organs, the generation of patient-histocompatible iPSCs (autologous or HLA-matched cells) provides an attractive platform for personalized medicine. However, concerns have been raised as to the fitness, safety and immunogenicity of iPSC derivatives because of variable differentiation potential of different lines and the identification of genetic and epigenetic aberrations that can occur during the reprogramming process. In addition, significant cost and regulatory barriers may deter commercialization of patient specific therapies in the short-term. Nonetheless, recent studies provide some evidence of immunological benefit for using autologous iPSCs. Yet, more studies are needed to evaluate the immunogenicity of various autologous and allogeneic human iPSC-derived cell types as well as test various methods to abrogate rejection. Here, we present perspectives of using allogeneic vs. autologous iPSCs for transplantation therapies and the advantages and disadvantages of each related to differentiation potential, immunogenicity, genetic stability and tumorigenicity. We also review the current literature on the immunogenicity of syngeneic iPSCs and discuss evidence that questions the feasibility of HLA-matched iPSC banks. Finally, we will discuss emerging methods of abrogating or reducing host immune responses to PSC derivatives.

Discarded Human Thymus Is a Novel Source of Stable and Long-Lived Therapeutic Regulatory T Cells.

Regulatory T cell (Treg)-based therapy is a promising approach to treat many immune-mediated disorders such as autoimmune diseases, organ transplant rejection, and graft-versus-host disease (GVHD). Challenges to successful clinical implementation of adoptive Treg therapy include difficulties isolating homogeneous cell populations and developing expansion protocols that result in adequate numbers of cells that remain stable, even under inflammatory conditions. We investigated the potential of discarded human thymuses, routinely removed during pediatric cardiac surgery, to be used as a novel source of therapeutic Tregs. Here, we show that large numbers of FOXP3(+) Tregs can be isolated and expanded from a single thymus. Expanded thymic Tregs had stable FOXP3 expression and long telomeres, and suppressed proliferation and cytokine production of activated allogeneic T cells in vitro. Moreover, expanded thymic Tregs delayed development of xenogeneic GVHD in vivo more effectively than expanded Tregs isolated based on CD25 expression from peripheral blood. Importantly, in contrast to expanded blood Tregs, expanded thymic Tregs remained stable under inflammatory conditions. Our results demonstrate that discarded pediatric thymuses are an excellent source of therapeutic Tregs, having the potential to overcome limitations currently hindering the use of Tregs derived from peripheral or cord blood.

Out-of-season production of 17,20ß-dihydroxypregn-4-en-3-one in the roach Rutilus rutilus.

In this study, although the highest production of two physiologically significant progestins in teleosts [17,20ß-dihydroxypregn-4-en-3-one (17,20ß-P) and 17,20ß,21-trihydroxypregn-4-en-3-one (17,20ß,21-P)] was observed in the period just prior to spawning in both male and female roach Rutilus rutilus, there was also a substantial production (mean levels of 5-10 ng ml(-1) in blood; and a rate of release of 5-20 ng fish(-1) h(-1) into the water) in males and females in the late summer and early autumn (at least 7 months prior to spawning). During this period, the ovaries were increasing rapidly in size and histological sections were dominated by oocytes in the secondary growth phase [i.e. incorporation of vitellogenin (VTG)]. At the same time, the testes were also increasing rapidly in size and histological sections were dominated by cysts containing mainly spermatogonia type B. Measurements were also made of 11-ketotestosterone (11-KT) in males and 17ß-oestradiol and VTG in females. The 3 months with the highest production of 11-KT coincided with the period that spermatozoa were present in the testes. In females, the first sign of a rise in 17ß-oestradiol concentrations coincided with the time of the first appearance of yolk globules in the oocytes (in August). The role of the progestins during the late summer and autumn has not been established.

Efficacy of surgery for internal snapping hip.

Our purpose was to evaluate evidence regarding the effectiveness of open iliopsoas release and lengthening with arthroscopic approaches, which combine iliopsoas release with the treatment of intra-articular pathology as treatments for internal snapping hip syndrome. Searches were performed of 4 databases and 12 reports on the surgical treatment of internal snapping hip were reviewed. The authors tabulated data according to year of study, journal, study type, level of evidence, patient demographics, procedure, and outcomes. We found that surgical treatment of internal snapping hip improves patient symptoms in the majority of patients. Endoscopic release is associated with fewer reported complications compared with open release. All studies of endoscopic treatment of internal snapping hip syndrome also performed intra-articular examination and treatment of intra-articular pathology. The incidence of associated intra-articular pathology was reported in 5 of 6 studies. These results suggest that a painful snapping iliopsoas tendon in many cases may be a result of intra-articular hip pathology rather than an independent entity. Early studies suggest no difference in efficacy or associated complications rate when comparing extracapsular to transcapsular iliopsoas tendon release. Further studies are needed comparing operative to nonoperative treatment and methods of determining patients likely to benefit from operative intervention.

Direct effects of Bmi1 on p53 protein stability inactivates oncoprotein stress responses in embryonal cancer precursor cells at tumor initiation.

Embryonal cancer can arise from postnatally persistent embryonal remnant or rest cells, which are uniquely characterized by the absence of p53 mutations. Perinatal overexpression of the MycN oncoprotein in embryonal cancer precursor cells causes postnatal rests, and later tumor formation through unknown mechanisms. However, overexpression of Myc in adult tissues normally activates apoptosis and/or senescence signals as an organismal defense mechanism against cancer. Here, we show that perinatal neuroblastoma precursor cells exhibited a transiently diminished p53 response to MycN oncoprotein stress and resistance to trophic factor withdrawal, compared with their adult counterpart cells from the TH-MYCN(+/+) transgenic mouse model of neuroblastoma. The adult stem cell maintenance factor and Polycomb group protein, Bmi1 (B-cell-specific Moloney murine leukemia virus integration site), had a critical role at neuroblastoma initiation in the model, by repressing p53 responses in precursor cells. We further show in neuroblastoma tumor cells that Bmi1 could directly bind p53 in a complex with other Polycomb complex proteins, Ring1A or Ring1B, leading to increased p53 ubiquitination and degradation. Repressed p53 signal responses were also seen in precursor cells for other embryonal cancer types, medulloblastoma and acute lymphoblastic leukemia. Collectively, these date indicate a general mechanism for p53 inactivation in some embryonal cell types and consequent susceptibility to MycN oncogenesis at the point of embryonal tumor initiation.

Does MR perfusion imaging impact management decisions for patients with brain tumors? A prospective study.

BACKGROUND AND PURPOSE: MR perfusion imaging can be used to help predict glial tumor grade and disease progression. Our purpose was to evaluate whether perfusion imaging has a diagnostic or therapeutic impact on clinical management planning in patients with glioma. MATERIALS AND METHODS: Standard MR imaging protocols were interpreted by a group of 3 NRs in consensus, with each case being interpreted twice: first, including routine sequences; and second, with the addition of perfusion imaging. A multidisciplinary team of treating physicians assessed tumor status and created hypothetical management plans, on the basis of clinical presentation and routine MR imaging and then routine MR imaging plus perfusion MR imaging. Physicians' confidence in the tumor status assessment and management plan was measured by using Likert-type items. RESULTS: Fifty-nine consecutive subjects with glial tumors were evaluated; 50 had known pathologic diagnoses. NRs and the treatment team agreed on tumor status in 45/50 cases (κ = 0.81). With the addition of perfusion, confidence in status assessment increased in 20 (40%) for NRs and in 28 (56%) for the treatment team. Of the 59 patient-care episodes, the addition of perfusion was associated with a change in management plan in 5 (8.5%) and an increase in the treatment team's confidence in their management plan in 34 (57.6%). NRs and the treatment team found perfusion useful in most episodes of care and wanted perfusion included in future MR images for >80% of these subjects. CONCLUSIONS: Perfusion imaging appears to have a significant impact on clinical decision-making and subspecialist physicians' confidence in management plans for patients with brain tumor.

Carcinoid tumor of the lung metastatic to a previously identified pituitary adenoma.

The authors present the case of a 58-year-old gentleman presenting with atypical carcinoid tumor of primary lung origin metastasizing to a previously identified pituitary macroadenoma. The patient presented with symptoms of headache and visual disturbance. Imaging revealed enlargement of a known sellar mass as well as three separate enhancing lesions in the brain parenchyma. Resection was accomplished via a transnasal transshpenoidal approach without complication. Immunoreactivity was demonstrated to synaptophysin, chromogranin, CD56, epithelial membrane antigen, and thyroid transcription factor-1. The specimen was also marked by negative staining for pituitary hormones. This case demonstrates a rare occurrence of metastastic spread of tumor to a previously identified pituitary macroadenoma.

Extending the clinical research network approach to all of healthcare.

The development of Clinical Research Networks (CRN) has been central to the work conducted by Health Departments and research funders to promote and support clinical research within the NHS in the UK. In England, the National Institute for Health Research has supported the delivery of clinical research within the NHS primarily through CRN. CRN provide the essential infrastructure within the NHS for the set up and delivery of clinical research within a high-quality peer-reviewed portfolio of studies. The success of the National Cancer Research Network is summarized in Chapter 5. In this chapter progress in five other topics, and more recently in primary care and comprehensively across the NHS, is summarized. In each of the 'topic-specific' networks (Dementias and Neurodegenerative Diseases, Diabetes, Medicines for Children, Mental Health, Stroke) there has been a rapid and substantial increase in portfolios and in the recruitment of patients into studies in these portfolios. The processes and the key success factors are described. The CRN have worked to support research supported by pharmaceutical, biotechnology and medical device companies and there has been substantial progress in improving the speed, cost and delivery of these 'industry' studies. In particular, work to support the increased speed of set up and delivery of industry studies, and to embed this firmly in the NHS, was explored in the North West of England in an Exemplar Programme which showed substantial reductions in study set-up times and improved recruitment into studies and showed how healthcare (NHS) organizations can overcome delays in set up times when they actively manage the process. Seven out of 20 international studies reported that the first patient to be entered anywhere in the world was from the UK. In addition, the CRN have supported research management and governance, workforce development and clinical trials unit collaboration and coordination. International peer reviews of all of the CRN have been positive and resulted in the continuation of the system for a further 5 years in all cases.

Chordoid meningioma of the third ventricle: a case report and review of the literature.

Chordoid meningioma is a rare variant of meningioma with histologic features that mimic chordoma and other chordoid neoplasms. This tumor is important to recognize, as there is a well-documented propensity for local recurrence and aggressive behavior. Most cases occur around the cerebral convexities, in locations that are similar to classical forms of meningioma. Intraventricular forms of chordoid meningioma are rare, with most reported cases arising in the lateral ventricles. We present a case of a chordoid meningioma that presented in the third ventricle of a 63-year-old female. This represents only the second documented case of a third ventricular chordoid meningioma and the first case in an adult. The distinction from other chordoid neoplasms can be challenging, particularly chordoid gliomas, which classically occur in this location. Herein, we compare and contrast chordoid meningioma with chordoid glioma and provide a review of the relevant literature.

Non-thermal irreversible electroporation (N-TIRE) and adjuvant fractionated radiotherapeutic multimodal therapy for intracranial malignant glioma in a canine patient.

Non-thermal irreversible electroporation (N-TIRE) has shown promise as an ablative therapy for a variety of soft-tissue neoplasms. Here we describe the therapeutic planning aspects and first clinical application of N-TIRE for the treatment of an inoperable, spontaneous malignant intracranial glioma in a canine patient. The N-TIRE ablation was performed safely, effectively reduced the tumor volume and associated intracranial hypertension, and provided sufficient improvement in neurological function of the patient to safely undergo adjunctive fractionated radiotherapy (RT) according to current standards of care. Complete remission was achieved based on serial magnetic resonance imaging examinations of the brain, although progressive radiation encephalopathy resulted in the death of the dog 149 days after N-TIRE therapy. The length of survival of this patient was comparable to dogs with intracranial tumors treated via standard excisional surgery and adjunctive fractionated external beam RT. Our results illustrate the potential benefits of N-TIRE for in vivo ablation of undesirable brain tissue, especially when traditional methods of cytoreductive surgery are not possible or ideal, and highlight the potential radiosensitizing effects of N-TIRE on the brain.

Monophyly of terrestrial adephagan beetles as indicated by three nuclear genes (Coleoptera: Carabidae and Trachypachidae).

The beetle suborder Adephaga is traditionally divided into two sections on the basis of habitat, terrestrial Geadephaga and aquatic Hydradephaga. Monophyly of both groups is uncertain, and the relationship of the two groups has implications for inferring habitat transitions within Adephaga. Here we examine phylogenetic relationships of these groups using evidence provided by DNA sequences from all four suborders of beetles, including 60 species of Adephaga, four Archostemata, three Myxophaga, and ten Polyphaga. We studied 18S ribosomal DNA and 28S ribosomal DNA, aligned with consideration of secondary structure, as well as the nuclear protein-coding gene wingless. Independent and combined Bayesian, likelihood, and parsimony analyses of all three genes supported placement of Trachypachidae in a monophyletic Geadephaga, although for analyses of 28S rDNA and some parsimony analyses only if Coleoptera is constrained to be monophyletic. Most analyses showed limited support for the monophyly of Hydradephaga. Outside of Adephaga, there is support from the ribosomal genes for a sister group relationship between Adephaga and Polyphaga. Within the small number of sampled Polyphaga, analyses of 18S rDNA, wingless, and the combined matrix supports monophyly of Polyphaga exclusive of Scirtoidea. Unconstrained analyses of the evolution of habitat suggest that Adephaga was ancestrally aquatic with one transition to terrestrial. However, in analyses constrained to disallow changes from aquatic to terrestrial habitat, the phylogenies imply two origins of aquatic habit within Adephaga.

Patched1 deletion increases N-Myc protein stability as a mechanism of medulloblastoma initiation and progression.

Medulloblastoma tumorigenesis caused by inactivating mutations in the PATCHED1 (PTCH1) gene is initiated by persistently activated Sonic Hedgehog (Shh) signaling in granule neuron precursors (GNPs) during the late stages of cerebellar development. Both normal cerebellar development and Shh-driven medulloblastoma tumorigenesis require N-Myc expression. However, the mechanisms by which N-Myc affects the stages of medulloblastoma initiation and progression are unknown. Here we used a mouse model of Ptch1 heterozygosity and medulloblastoma to show that increased N-Myc expression characterized the earliest selection of focal GNP hyperplasia destined for later tumor progression. Step-wise loss of Ptch1 expression, from tumor initiation to progression, led to incremental increases in N-Myc protein, rather than mRNA, expression. Increased N-Myc resulted in enhanced proliferation and death resistance of perinatal GNPs at tumor initiation. Sequential N-Myc protein phosphorylation at serine-62 and serine-62/threonine-58 characterized the early and late stages of medulloblastoma tumorigenesis, respectively. Shh pathway activation led to increased Myc protein stability and reduced expression of key regulatory factors. Taken together our data identify N-Myc protein stability as the result of loss of Ptch1, which distinguishes normal cerebellar development from medulloblastoma tumorigenesis.

Australian breast cancer specialists' involvement in multidisciplinary treatment planning meetings.

Australian breast cancer specialists' involvement in multidisciplinary team (MDT) treatment planning meetings was ascertained in a cross sectional survey. The format of MDT meetings was also investigated. Medical specialists were regular attendees (>or=78%) compared to allied health staff and psychologists (or=50 new cases a year (AOR 7.34; 95%CI: 3.38-15.96) were more likely to attend. Over 69% reported that the proportion of time devoted to case discussions was >or=75%. Topics always discussed were pathology, extent of disease, surgery performed and a treatment plan (>or=83%). The majority of respondents stated that MDT meetings were effective and improved referrals. Suggested improvements included that all key personnel attend, meetings are structured and that the views of all be heard. Work is needed to ensure MDT's function and co-operate as intended in treatment planning meetings.

Clinical and radiological grading of superior vena cava obstruction.

BACKGROUND: Superior vena cava obstruction (SVCO) is commonly caused by neoplastic venous compression and presents with typical symptoms and signs. Its clinical severity presumably depends on the degree of obstruction and the adequacy of venous collateral formation. OBJECTIVES: The development of novel clinical and radiological scoring systems based on the postulate that a reproducible relationship exists between the degree of SVCO, the presence of collateral circulation and the extent of clinical symptoms. METHODS: We prospectively evaluated consecutive cases of acute and subacute SVCO with a newly developed clinical scoring system, which is based on easily detectable clinical symptoms and signs of SVCO. In parallel, we recorded and scored the degree of SVCO and the extent of collaterals visible on contrast-enhanced computed tomography (CT). RESULTS: Thirty-four cases of SVCO were evaluated: 8 (23.5%) were clinically mild, 16 (47%) moderate and 10 (29.5%) severe. Lung cancer was the underlying histological diagnosis in 94% of cases. Radiologically, 53% had complete SVCO. A well-developed collateral system was found in 14 (41%). A scoring system subtracting a 'collateral score' from an 'obstruction score' showed a significant correlation with the clinical score (r = 0.75, p < 0.01). CONCLUSIONS: Clinical severity of SVCO depends upon the degree of SVCO and is ameliorated by collateral formation. The novel clinical scoring system can predict the underlying CT features in SVCO and may be valuable in the bedside assessment of SVCO severity.

Health professional and consumer views on involving breast cancer patients in the multidisciplinary discussion of their disease and treatment plan.

BACKGROUND: The aim was to obtain the views of health professionals and patients about the concept of involving breast cancer patients in the multidisciplinary (MD) treatment planning meeting. METHODS: Breast cancer surgeons, nurses, oncologists, and patient advocates completed a mailed questionnaire. RESULTS: The majority of breast cancer health professionals and patient advocates support shared decision-making (58%-62%). However, less than a third of surgeons (32%), medical (25%), and radiation oncologists (24%) were supportive of involving women in the MD treatment planning meeting. In contrast, 93% of breast cancer advocates and 73% of breast cancer nurses were supportive of this approach. Patient advocates were significantly more in favor than all other groups (chi(2) = 148.8, df = 4, P < .001). The common reasons for supporting patient involvement included that it would lead to patients being more informed and empowered, provide them with an opportunity to ask questions, facilitate decision-making, and improve communication between the patient and the medical team. Health professionals stated that attendance would make patients anxious and that they would have to modify their medical language. Suggestions about how to manage patient involvement included the patient being supported by a breast nurse and pre-education before the meeting. Patient advocates were significantly more willing to participate in a randomized controlled trial of this process compared with all other groups. (chi(2) = 155.15, df = 4, P < .001). CONCLUSIONS: Despite health professional's reservations, patient advocates were highly supportive of including women in the MD meeting. Such a high demand justifies consideration of this option.

Immune responses of pigs to commercialized emulsion FMD vaccines and live virus challenge.

The immune response to structural and non-structural proteins (NSPs) was studied on sequential serum samples in swine from O/Taiwan/97 FMDV challenge studies, outbreaks and after vaccination. The results showed that pigs vaccinated with a commercial vaccine prior to or after infection maintained high neutralizing antibody titers with gradual decline from peak titers over the duration of this study. However, neutralizing antibody titers in non-vaccinated pigs only reached moderate levels 2-4 weeks post infection and remained low thereafter. For the 3B and 3ABC NSP antibody ELISA responses, there were gradually decreasing levels of NSP antibody over time. In multiple vaccinations, all pigs showed significant increases in neutralizing antibodies after booster vaccination. For the 3B NSP antibody ELISA after vaccination, the mean S/P ratios for pigs vaccinated with all three FMD vaccines were all below the 0.23 cut-off value set by the manufacture, but some sera from individual vaccinated pigs gave results above this cut-off after primary or secondary vaccination. However, with the 3ABC NSP antibody ELISA, all sera from vaccinated pigs had negative results for NSP antibody for all time points.

Radial forearm osteocutaneous free flap in maxillofacial and oromandibular reconstructions.

OBJECTIVES/HYPOTHESIS: The radial forearm osteocutaneous free flap is an excellent reconstructive modality for oromandibular and maxillofacial reconstruction in certain well-defined circumstances. The initial concern over donor site morbidity and the ability of the bone to reconstruct mandibular defects have led to only a few published series. STUDY DESIGN: Retrospective study of the experience of two tertiary medical centers with radial forearm osteocutaneous free flap. METHODS: Retrospectively, 52 patients were studied who underwent radial forearm osteocutaneous free flap reconstruction for cancer (49 cases) and trauma (3 cases). Bone length and skin paddle harvested, general morbidity (hematoma, wound infection, and dehiscence), recipient site morbidity (nonunion of neomandible, flap failure, and bone or plate exposure), and donor site morbidity (radius bone fracture, plate exposure, and skin graft failure) were reviewed. RESULTS: The average skin paddle size was 55.1 cm (range, 15-112 cm). The average radius bone harvest length was 6.3 cm (range, 2.5-11 cm). Donor site complications included tendon exposure (3 cases), radius bone fracture (1 case), and exposure of the plate (0). Recipient site complications included nonunion of the mandible (4), exposed mandible (1), exposed mandibular plates (2), exposed maxillary plates or bone (0), venous compromise (1), and flap failure (1). Two patients had perioperative deaths. CONCLUSION: Radial forearm osteocutaneous free flap is a valuable and viable option for oromandibular and maxillofacial reconstruction.

H5N1 influenza: a protean pandemic threat.

Infection with avian influenza A virus of the H5N1 subtype (isolates A/HK/212/03 and A/HK/213/03) was fatal to one of two members of a family in southern China in 2003. This incident was preceded by lethal outbreaks of H5N1 influenza in waterfowl, which are the natural hosts of these viruses and, therefore, normally have asymptomatic infection. The hemagglutinin genes of the A/HK/212/03-like viruses isolated from humans and waterfowl share the lineage of the H5N1 viruses that caused the first known cases of human disease in Hong Kong in 1997, but their internal protein genes originated elsewhere. The hemagglutinin of the recent human isolates has undergone significant antigenic drift. Like the 1997 human H5N1 isolates, the 2003 human H5N1 isolates induced the overproduction of proinflammatory cytokines by primary human macrophages in vitro, whereas the precursor H5N1 viruses and other H5N1 reassortants isolated in 2001 did not. The acquisition by the viruses of characteristics that enhance virulence in humans and waterfowl and their potential for wider distribution by infected migrating birds are causes for renewed pandemic concern.