Development of a whole cell vaccine for acute myeloid leukaemia

We describe the modification of tumour cells to enhance their capacity to act as antigen presenting cells with particular focus on the use of costimulatory molecules to do so. We have been involved in the genetic modification of tumour cells to prepare a whole cell vaccine for nearly a decade and we have a particular interest in acute myeloid leukaemia (AML). AML is an aggressive and difficult to treat disease, especially, for patients for whom haematopoietic stem cell (HSC) transplant is not an option. AML patients who have a suitable donor and meet HSC transplant fitness requirements, have a 5-year survival of 50%; however, for patients with no suitable donor or for who age is a factor, the prognosis is much worse. It is particularly poor prognosis patients, who are not eligible for HSC transplant, who are likely to benefit most from immunotherapy. It would be hoped that immunotherapy would be used to clear residual tumour cells in these patients in the first remission following standard chemotherapy treatments and this will extend the remission and reduce the risk of a second relapse associated with disease progression and poor mortality rates. In this symposia report, we will focus on whole cell vaccines as an immunotherapeutic option with particular reference to their use in the treatment of AML. We will aim to provide a brief overview of the latest data from our group and considerations for the use of this treatment modality in clinical trials for AML. This article is a symposium paper from the conference “Progress in Vaccination against Cancer 2004 (PIVAC 4)”, held in Freudenstadt-Lauterbad, Black Forest, Germany, on 22–25 September 2004     

Imagerie de la néoangiogenèse en médecine nucléaire

The formation of new vessels, a process referred to as neoangiogenesis, is one of the key pathophysiological mechanisms in the development and progression of cancer. It contributes to tumour growth and dissemination of neoplastic cells and can determine response or resistance to anticancer therapies. It involves different signaling pathways including the vascular endothelial growth factor (VEGF) pathway and integrins, which are also preferred targets for the development of antiangiogenic therapies. Changes in the microvasculature induced by antiangiogenic treatments occur before morphological changes can be detected with conventional imaging approaches. The development of molecular tools enabling an assessment of these targets before initiating therapy, or early detection of response or recurrence during or following treatment is essential for the close monitoring of antiangiogenic treatments. These outstanding needs call for the development of specific probes enabling the characterization of the molecules and pathways involved. This review summarizes the major signaling pathway involved in promoting tumor neoangiogenes is, the different radiotracers recently developed in preclinical and clinical settings, as well as their potential use in humans in order to improve the management of patients treated with antiangiogenic treatments.     

Dll4-Notch Signalling Blockade Synergizes Combined Ultrasound-Stimulated Microbubble and Radiation Therapy in Human Colon Cancer Xenografts

Tumour vasculature acts as an essential lifeline for tumour progression and facilitates metastatic spread. Novel vascular targeting strategies aiming to sustain vascular shutdown could potentially induce substantial damage, resulting in a significant tumour growth delay. We investigated the combination of two novel complementary vascular targeting agents with radiation therapy in a strategy aiming to sustain vascular disruption. Experiments were carried out with delta-like ligand 4 (Dll4) blockade (angiogenesis deregulator) treatment administered in combination with a radiation-based vascular destruction treatment in a highly aggressive well-perfused colon cancer tumour line implanted in female athymic nude mice. Tumours were treated with permutations of radiation, ultrasound-stimulated microbubbles (USMB) and Dll4 monoclonal antibody (mAb). Tumour vascular response was assessed with three-dimensional power Doppler ultrasound to measure active flow and immunohistochemistry. Tumour response was assessed with histochemical assays and longitudinal measurements of tumour volume. Our results suggest a significant tumour response in animals treated with USMB combined with radiation, and Dll4 mAb, leading to a synergistic tumour growth delay of up to 24 days. This is likely linked to rapid cell death within the tumour and a sustained tumour vascular shutdown. We conclude that the triple combination treatments cause a vascular shutdown followed by a sustained inhibition of angiogenesis and tumour cell death, leading to a rapid tumour vascular-based ‘collapse’ and a significant tumour growth delay.     

The future of bladder control-intravesical drug delivery, a pinch of pepper, and gene therapy

The incidence of urinary incontinence and overactive bladder problems will continue to grow as the population ages. Future treatments are likely to include an implantable drug delivery system, gene therapy, and the intravesical use of the vallinoids capsaicin and resiniferatoxin (RTX). An understanding of the urothelium is essential for effective design of these therapies. Intravesical anticholinergic drug treatment is currently not widely used, but intravesical pumps are under development to provide less cumbersome treatment methods and will provide nonsurgical options for patients who cannot tolerate oral anticholinergic agents. Research on the use of capsaicin as an intravesicular drug has had limited success, but trials have confirmed the efficacy of intravesical capsaicin for detrusor hyperreflexia. RTX is as effective as capsaicin but without side effects, such as pain and inflammatory neuropeptide release. RTX treatment may eliminate the need for surgical and other drug treatments of lower urinary tract dysfunction in patients with spinal cord injuries. Gene therapy will change the practice of urology by addressing the deficiencies that cause symptoms rather than attacking the symptoms themselves.     

An efficient targeted radiotherapy/gene therapy strategy utilising human telomerase promoters and radioastatine and harnessing radiation-mediated bystander effects

BACKGROUND: Targeted radiotherapy achieves malignant cell-specific concentration of radiation dosage by tumour-affinic molecules conjugated to radioactive atoms. Combining gene therapy with targeted radiotherapy is attractive because the associated cross-fire irradiation of the latter induces biological bystander effects upon neighbouring cells overcoming low gene transfer efficiency. METHODS: We sought to maximise the tumour specificity and efficacy of noradrenaline transporter (NAT) gene transfer combined with treatment using the radiopharmaceutical meta-[(131)I]iodobenzylguanidine ([(131)I]MIBG). Cell-kill was achieved by treatment with the beta-decay particle emitter [(131)I]MIBG or the alpha-particle emitter [(211)At]MABG. We utilised our novel transfected mosaic spheroid model (TMS) to determine whether this treatment strategy could result in sterilisation of spheroids containing only a small proportion of NAT-expressing cells. RESULTS: The concentrations of [(131)I]MIBG and [(211)At]MABG required to reduce to 0.1% the survival of clonogens derived from the TMS composed of 100% of NAT gene-transfected cells were 1.5 and 0.004 MBq/ml (RSV promoter), 8.5 and 0.0075 MBq/ml (hTR promoter), and 9.0 and 0.008 MBq/ml (hTERT promoter), respectively. The concentrations of radiopharmaceutical required to reduce to 0.1% the survival of clonogens derived from 5% RSV/NAT and 5% hTERT/NAT TMS were 14 and 23 MBq/ml, respectively, for treatment with [(131)I]MIBG and 0.018 and 0.028 MBq/ml, respectively, for treatment with [(211)At]MABG. CONCLUSIONS: These results indicate that the telomerase promoters have the capacity to drive the expression of the NAT. The potency of [(211)At]MABG is approximately three orders of magnitude greater than that of [(131)I]MIBG. Spheroids composed of only 5% of cells expressing NAT under the control of the RSV or hTERT promoter were sterilised by radiopharmaceutical treatment. This observation is indicative of bystander cell-kill.     

MIBG, an inhibitor of arginine-dependent mono(ADP-ribosyl)ation, prevents differentiation of L6 skeletal myoblasts by inhibiting expression of myogenin and p21(cip1)

The development of skeletal muscle is controlled by a highly synchronized series of cellular events, and various signals from both inside and outside the cell play a role in the switch from multipotential mesodermal stem cells to muscle fibers. Meta-iodobenzylguanidine (MIBG), an inhibitor of mono(ADP-ribosyl)ation, has been shown to prevent terminal differentiation of skeletal myoblasts; however, its mechanism of action has not been established. We recently reported that MIBG is capable of preventing phenotypic modulation of smooth muscle cells by interfering with specific trans-acting factors [L. Yau, B. Litchie, S. Thomas, B. Storie, N. Yurkova, P. Zahradka, Endogenous mono-ADP-ribosylation mediates smooth muscle cell proliferation and migration via protein kinase N-dependent induction of c-fos expression. Eur. J. Biochem. 270 (2003) 101-110.]. We therefore examined the effect of MIBG on select myogenic regulatory factors known to control terminal differentiation. It was confirmed that MIBG, but not inhibitors of poly-ADP-ribose polymerase (3-aminobenzamide, PD128763), inhibits fusion of L6 skeletal myoblasts in a concentration-dependent manner. Moreover, inhibition by MIBG correlated with a failure to induce expression of myogenin and p21(cip1), while levels of MyoD and MEF2 were unaffected. Time-of-addition studies revealed that MIBG also affected a late event possibly linked to cell fusion. Finally, arginine-dependent mono(ADP-ribosyl)transferase activity increased over the first 24 h of the differentiation period. These data support a role for arginine-dependent mono(ADP-ribosyl)transferase as an essential positive regulator of differentiation in skeletal muscle cells that operates by modulating the expression of specific myogenic factors.     

99mTc-labeled MIBG derivatives: novel 99mTc complexes as myocardial imaging agents for sympathetic neurons

Radioactive-iodine-labeled meta-iodobenzylguanidine (MIBG) is currently being used as an in vivo imaging agent to evaluate neuroendocrine tumors as well as the myocardial sympathetic nervous system in patients with myocardial infarct and cardiomyopathy. It is generally accepted that MIBG is an analogue of norepinephrine and its uptake in the heart corresponds to the distribution of norepinephrine and the density of sympathetic neurons. A series of MIBG derivatives containing suitable chelating functional groups N2S2 for the formation of [TcvO]3+N2S2 complex was successfully synthesized, and the 99mTc-labeled complexes were prepared and tested in rats. One of the compounds, [99mTc]2, tested showed significant, albeit lower, heart uptakes post iv injection in rats (0.21% dose/g at 4 h) as compared to [125I]MIBG (1.7% dose/g at 4 h). The heart uptake of the 99mTc-labeled complex appears to be specific and can be reduced by co-injection with nonradioactive MIBG or by pretreatment with desipramine, a selective norepinephrine transporter inhibitor. Further evaluation of the in vitro uptake of [99mTc]2 in cultured neuroblastoma cells displayed consistently lower, but measurable uptake (approximately 10% of that for [125I]MIBG). These preliminary results suggested that the mechanisms of heart uptake of [99mTc]2 may be related to those for [125I]MIBG uptake. If suitable 99mTc-labeled MIBG derivatives can be further developed, the prevalent availability of 99mTc in nuclear medicine clinics will allow them to be readily available for widespread application.     

Traitements à visée palliative ou curative : la radiothérapie vectorisée des tumeurs endocrines

Internal targeted radiotherapy (ITR), which consists in irradiation of small disseminated tumour lesions using injected radiopharmaceuticals has been for a long time successfully used for differentiated thyroid carcinoma treatment, as an adjuvant treatment after surgery, but as an efficient treatment of metastatic disease (especially lung involvement) as well. New efficient radiopharmaceuticals for tumour targeting become available, making feasible such successful ITR treatment for other endocrine tumours (ET). Malignant phaeochromocytomas have firstly been treated with ¹³¹I-metaiodobenzyguanidine (MIBG) and more recently radiolabeled ligands of somatostatine receptors (SSR) which are overexpressed by most of ET have been proved to be an effective treatment of these tumours. Moreover, radiolabelled antibodies, which have been used successfully in malignant lymphoma treatment, could have an interest in ET, mainly medullary thyroid carcinoma. Using ITR for ET treatment suppose clinical indications are well defined, according to the new WHO classification of ET: only non-differentiated not eradicable and/or metastatic progressive tumours should be treated. Furthermore, efficiency of ITR is greater than could be thought as minor responses and even prolonged stabilizations are now considered as positive responses. Randomized studies are still necessary, however, in order to demonstrate, beyond its efficiency, a clinical impact of ITR on quality of life and survival, and to determine the right place of ITR in the global therapeutic management of ET.     

Angiogenic and anti-angiogenic factors in adrenal tumours

It appears that neoangiogenesis is an important factor in tumour invasion and the formation of metastases in several human cancers, and studies on pro-angiogenic and antiangiogenic factors are therefore of considerable interest to researchers. In this review we present pro-angiogenic and anti-angiogenic factors and other growth factors and their role in the formation of new blood vessels in adrenal tumours. Assessment of the angiogenic status of adrenal tumours and their vascular pattern may be useful for discriminating benign from malignant lesions and knowledge of their angiogenesis may be essential to the drawing up of promising treatment strategies for patients with malignant tumours.     

Colonisation of Clostridium in the body is restricted to hypoxic and necrotic areas of tumours

The use of gene therapy is one of the most recent molecular strategies for the treatment of cancer. It is essential, however, to have an efficient transfer system by which the desired gene can be delivered to the correct environment. The experiments described in this report investigate apathogenic Clostridium as a possible vector to transfer a specific gene product into the extracellular microenvironment of the tumour which is hypoxic/necrotic in parts, using WAG/Rij rats with transplantable rhabdomyosarcomas as a model. Our data show that Clostridium, after systemic administration of at least 10(7) spores, specifically colonises the hypoxic/necrotic areas of our tumour model, the most efficient species being C. acetobutylicum (NI-4082) and C. oncolyticum. Although spores were also detected in normal tissues for up to 4 weeks, they did not germinate in these tissues. We conclude that it seems likely that these bacteria can be used as a selective transfer system into the extracellular environment of tumours which have hypoxic regions. This strategy would be more tumour-specific than various other strategies that are currently being investigated in anti-cancer gene therapy.     

Efficacy and safety of [131I]metaiodobenzylguanidine therapy for patients with refractory neuroblastoma.

Metaiodobenzylguanidine (MIBG) is a guanethidine derivative that is selectively concentrated in sympathetic nervous tissue. MIBG labeled with 123I or 131I has proven to be a specific and sensitive tool for detection of primary and metastatic pheochromocytoma and neuroblastoma. Eleven patients, with refractory stage IV neuroblastoma were treated with a total of 23 courses of 131I-MIBG, 100-400 mCi/m2/course. Total activity administered per course ranged from 90-550 mCi; maximum cumulative radioactivity per patient was 1356 mCi. The 131I-MIBG was given as a 2 hour infusion. Total body dose was calculated from whole body activity measurements, ranging from 73-250 cGy. The main toxicity was thrombocytopenia, with platelet nadirs to less than 25,000/microL in 5/23 courses (5 patients), all occurring in patients with greater than 25% replacement by tumor in the bone marrow. Neutropenia to a nadir of less than 500/microL was seen in only 2 patients, both with greater than 50% bone marrow replacement after 2 and 4 courses of 131I-MIBG, respectively. Tumor doses were calculated in patients with an evaluable measurable lesion, and ranged from 312-6329 cGy per course. Two of the eleven patients had partial responses, with one long-term survivor with stage IV neuroblastoma with no evidence of active disease now 4 years off treatment. Two other patients survive with stable disease after 3 treatments, at 3+ and 5+ months. Seven patients died with progressive disease. This study shows that treatment with 131I-MIBG is safe and can be effective in refractory neuroblastoma, particularly in patients who do not have extensive bone and bone marrow involvement.     

Evolutionary game theory elucidates the role of glycolysis in glioma progression and invasion

Abstract. Objectives: Tumour progression has been described as a sequence of traits or phenotypes that cells have to acquire if the neoplasm is to become an invasive and malignant cancer. Although genetic mutations that lead to these phenotypes are random, the process by which some of these mutations become successful and cells spread is influenced by tumour microenvironment and the presence of other cell phenotypes. It is thus likely that some phenotypes that are essential in tumour progression will emerge in the tumour population only with prior presence of other different phenotypes. Materials and methods: In this study, we use evolutionary game theory to analyse the interactions between three different tumour cell phenotypes defined by autonomous growth, anaerobic glycolysis, and cancer cell invasion. The model allows us to understand certain specific aspects of glioma progression such as the emergence of diffuse tumour cell invasion in low‐grade tumours. Results: We have found that the invasive phenotype is more likely to evolve after appearance of the glycolytic phenotype which would explain the ubiquitous presence of invasive growth in malignant tumours. Conclusions: The result suggests that therapies, which increase the fitness cost of switching to anaerobic glycolysis, might decrease probability of the emergence of more invasive phenotypes.     

Tumour suppressor genes in chemotherapeutic drug response

Since cancer is one of the leading causes of death worldwide, there is an urgent need to find better treatments. Currently, the use of chemotherapeutics remains the predominant option for cancer therapy. However, one of the major obstacles for successful cancer therapy using these chemotherapeutics is that patients often do not respond or eventually develop resistance after initial treatment. Therefore identification of genes involved in chemotherapeutic response is critical for predicting tumour response and treating drug-resistant cancer patients. A group of genes commonly lost or inactivated are tumour suppressor genes, which can promote the initiation and progression of cancer through regulation of various biological processes such as cell proliferation, cell death and cell migration/invasion. Recently, mounting evidence suggests that these tumour suppressor genes also play a very important role in the response of cancers to a variety of chemotherapeutic drugs. In the present review, we will provide a comprehensive overview on how major tumour suppressor genes [Rb (retinoblastoma), p53 family, cyclin-dependent kinase inhibitors, BRCA1 (breast-cancer susceptibility gene 1), PTEN (phosphatase and tensin homologue deleted on chromosome 10), Hippo pathway, etc.] are involved in chemotherapeutic drug response and discuss their applications in predicting the clinical outcome of chemotherapy for cancer patients. We also propose that tumour suppressor genes are critical chemotherapeutic targets for the successful treatment of drug-resistant cancer patients in future applications.     

Clinical Use and Utility of Metaiodobenzylguanidine Scintigraphy in Pheochromocytoma Diagnosis

ObjectiveTo examine the indications for metaiodo- benzylguanidine (MIBG) scintigraphy and to assess its performance in localizing pheochromocytoma in the post- computed tomography and magnetic resonance imaging era.MethodsIn this retrospective study, electronic and paper medical records of patients who underwent MIBG scintigraphy at a large academic hospital in Los Angeles, California, between January 1995 and July 2009 were reviewed for indications for MIBG scintigraphy, clinical history, biochemical test results, findings from imaging studies, and pathologic diagnoses. MIBG score was defined as follows: 3 (or intensive uptake) meant MIBG uptake of adrenal gland or other locus was higher than that of the liver; 2 (or moderate uptake) meant uptake was similar to that of the liver; 1 (or borderline uptake) meant uptake was lower than that of liver; and 0 (or negative uptake) meant background signal.ResultsNinety-eight patients underwent MIBG scintigraphy during the study period; the indica- tion was suspected pheochromocytoma in 75 cases. Pheochromocytoma diagnosis was excluded in 48 and con- firmed in 15. The remaining 12 patients had insufficient information in the medical records to render a diagnosis. Among the 63 patients, 47 received ¹³¹I-MIBG and 16 received ¹²³I-MIBG. Sensitivity was 73% and specificity was 69% if any adrenal uptake was considered positive, but increased to 90% if borderline uptake was considered negative. False results were more common in younger patients, but not correlated with biochemical test results. In patients with pheochromocytoma either excluded or con- firmed, the MIBG scintigraphy results were confirmatory in 63%, but misleading in 37%. MIBG scintigraphy results did not provide additional diagnostic value to any case and contributed to pheochromocytoma overdiagnosis and even unnecessary adrenalectomy.ConclusionsMIBG scintigraphy results are either confirmatory or misleading, and this imaging modal- ity is not necessary formost patients in modern practice.(Endocr Pract. 2010;16:398-407)     

Interferon therapy in neoplastic diseases

Three types of interferon preparation (alpha, beta and gamma) have been used in the treatment of tumours in vivo. At the time of writing no information is available on IFN-gamma treatment of tumour patients. Treatments with IFN-alpha and IFN-beta have been undertaken at many clinical centres. Both types of preparation can exert side effects. Both types have also been able to cause regression of certain tumours in individual patients. At our hospital, IFN-alpha has been given to tumour patients over the last decade. Antitumour effects have been registered on patients with juvenile laryngeal papillomatosis, Hodgkin's disease, myelomatosis, ovarian carcinoma, hypernephroma and glioblastoma. Further study is needed on how therapy with IFN should best be undertaken and also how such treatment compares with other treatments of various tumour diseases. IFN therapy should also be combined with other such treatments.     

A tale of two multi‐focal therapies for glioblastoma: An antibody targeting ELTD1 and nitrone‐based OKN‐007

Glioblastoma (GBM) is the most common primary malignant brain tumour in adults. Despite a multimodal treatment response, survival for GBM patients remains between 12 and 15 months. Anti‐ELTD1 antibody therapy is effective in decreasing tumour volumes and increasing animal survival in an orthotopic GBM xenograft. OKN‐007 is a promising chemotherapeutic agent that is effective in various GBM animal models and is currently in two clinical trials. In this study, we sought to compare anti‐ELTD1 and OKN‐007 therapies, as single agents and combined, against bevacizumab, a commonly used therapeutic agent against GBM, in a human G55 xenograft mouse model. MRI was used to monitor tumour growth, and immunohistochemistry (IHC) was used to assess tumour markers for angiogenesis, cell migration and proliferation in the various treatment groups. OKN and anti‐ELTD1 treatments significantly increased animal survival, reduced tumour volumes and normalized the vasculature. Additionally, anti‐ELTD1 was also shown to significantly affect other pro‐angiogenic factors such as Notch1 and VEGFR2. Unlike bevacizumab, anti‐ELTD1 and OKN treatments did not induce a pro‐migratory phenotype within the tumours. Anti‐ELTD1 treatment was shown to be as effective as OKN therapy. Both OKN and anti‐ELTD1 therapies show promise as potential single‐agent multi‐focal therapies for GBM patients.     

Current and future management approaches for rheumatoid arthritis

With the introduction of new disease-modifying antirheumatic drugs (DMARDs) and other therapeutic agents, the management of rheumatoid arthritis (RA) has shifted toward earlier, more aggressive therapy. The ultimate goal is to prevent structural joint damage that leads to pain and functional disability. Early diagnosis of RA is therefore essential, and early DMARD treatment combined with nonsteroidal anti-inflammatory drugs is recommended. Combination DMARD regimens and new biologic agents (anti-tumor necrosis factor [TNF] therapies [infliximab, etanercept] and the interleukin [IL]-1 antagonist [anakinra]) have emerged as viable options for early treatment of RA patients. These new biologic agents and future nonbiologic agents that target proteins in signaling cascades are likely to change the landscape of RA treatments.     

Durable complete clinical responses in a phase I/II trial using an autologous melanoma cell/dendritic cell vaccine

Advanced metastatic melanoma is incurable by standard treatments, but occasionally responds to immunotherapy. Recent trials using dendritic cells (DC) as a cellular adjuvant have concentrated on defined peptides as the source of antigens, and rely on foreign proteins as a source of help to generate a cell-mediated immune response. This approach limits patient accrual, because currently defined, non-mutated epitopes are restricted by a small number of human leucocyte antigens. It also fails to take advantage of mutated epitopes peculiar to the patient's own tumour, and of CD4+ T lymphocytes as potential effectors of anti-tumour immunity. We therefore sought to determine whether a fully autologous DC vaccine is feasible, and of therapeutic benefit. Patients with American Joint Cancer Committee stage IV melanoma were treated with a fully autologous immunotherapy consisting of monocyte-derived DC, matured after culture with irradiated tumour cells. Of 19 patients enrolled into the trial, sufficient tumour was available to make treatments for 17. Of these, 12 received a complete priming phase of six cycles of either 0.9x10(6) or 5x10(6) DC/intradermal injection, at 2-weekly intervals. Where possible, treatment continued with the lower dose at 6-weekly intervals. The remaining five patients could not complete priming, due to progressive disease. Three of the 12 patients who completed priming have durable complete responses (average duration 35 months+), three had partial responses, and the remaining six had progressive disease (WHO criteria). Disease regression was not correlated with dose or with the development of delayed type hypersensitivity responses to intradermal challenge with irradiated, autologous tumour. However, plasma S-100B levels prior to the commencement of treatment correlated with objective clinical response ( P=0.05) and survival (log rank P<0.001). The treatment had minimal side-effects and was well tolerated by all patients. Mature, monocyte-derived DC preparations exposed to appropriate tumour antigen sources can be reliably produced for patients with advanced metastatic melanoma, and in a subset of those patients with lower volume disease their repeated administration results in durable complete responses.     

Effects of various adrenal inhibitors in low-renin essential hypertension

The blood pressures of patients with spironolactone-responsive low-renin essential hypertension were favorably affected by double blind treatment with amino-glutethimide (an inhibitor of conversion of cholesterol to all types of hormonal steroids) and by WIN 24,540 (an inhibitor of the conversion of 5-ene to 4-ene steroids) but were not favorably affected by dexamethasone (an inhibitor of ACTH-dependent steroidogenesis) or metyrapone (an inhibitor of 11-hydroxylation). Patients with primary aldosterone responded similarly except that their blood pressures also responded favorably to metyrapone. Patients with essential hypertension and normal plasma renin activity failed to respond to any of these treatments. It is concluded that in patients with low-renin essential hypertension a mineralocorticoid plays a major role in the maintenance of the hypertension. In the majority of patients a non-ACTH dependent 4-ene steroid appears to be involved. Aldosterone does not appear to play a major pathogenetic role in maintaining the hypertension of patients with the syndrome of low-renin essential hypertension.