Succinate dehydrogenase mutations: paraganglioma imaging and at-risk population screening

Paragangliomas are rare vascular tumours of the autonomic nervous system. They can be classified as sympathetic or parasympathetic. Sympathetic paragangliomas, which include phaeochromocytomas, tend to be functional and symptomatic. Parasympathetic paragangliomas are usually non-functional and may present with mass effect. Forty percent of paragangliomas are linked to genetic syndromes, most commonly due to mutations of the succinate dehydrogenase (SDH) enzyme complex and are collectively known as paraganglioma syndromes, of which five are described. Genetic testing is recommended for all patients, and their first-degree relatives, diagnosed with paragangliomas. When SDH mutations are discovered, biochemical screening and imaging surveillance is indicated. There is currently no consensus on imaging surveillance protocols. Most advocate full-body imaging, but the choice of technique and frequency varies. If paragangliomas are demonstrated, functional imaging to look for synchronous tumours or metastases is indicated. 2-[¹⁸F]-fluoro-2-deoxy-d-glucose (¹⁸F-FDG) positron-emission tomography (PET)-computed tomography (CT) is the technique of choice for metastatic evaluation, but [¹²³I]-metaiodobenzylguanidine or [¹¹¹In]-DTPA-octreotide scintigraphy are also utilised. Current research into emerging positron-emitting radiolabelled somatostatin analogues have yielded promising results, which is likely to be reflected in future guidelines. As genetic testing becomes increasingly prevalent, the need to answer the remaining questions regarding surveillance imaging is paramount.

Rationale for a Community Strategy in the Field of Information and Communications Technologies Applied to Health Care

The challenge for Europe in the field of information and communications technologies applied to health care is that of addressing positively the problem of the widening gap between the expectations of the citizens of the type of care that can be made available and the limited resources to provide that care. If the expectations of the population are to be fulfilled, it will be necessary to find innovative ways of delivering health services and to do it more efficiently than has yet been the case. Advanced information and communications technologies will be important tools for Member States to achieve the levels of efficiency required. Based on the results of the Community AIM Exploratory Action, further collaborative work is required at EEC level to create an Integrated Health Information Environment (lHE) allowing essentially for integration, modularity and security.

Proposal for Prevention or Alleviation of Protein/Lymph-Losing Enteropathy (PLE/LLE) After Fontan Circulation Treatment of Univentricular Hearts: Restoration of Lymph Balance With a "Lymphatic Right-to-Left Shunt."

In Fontan circulations created for univentricular hearts, systemic venous return is diverted to the lungs before returning to the heart. The Total Cavopulmonary Connection (TCPC) is often the preferred surgical procedure whereby a 4-way anastomosis is created with inflow from the superior vena cava (SVC) and inferior vena cava (IVC) and outflow to the right and left branches of the pulmonary artery. In this arrangement, the systemic venous pressure must be elevated sufficiently to perfuse the lungs passively without the normal boost of the right ventricle. Hence, unlike surgical corrections for other congenital heart conditions, the systemic venous pressures in a Fontan circuit must be elevated to make the circulation work. It is proposed here that the incidence of PLE/LLE is directly related to elevated venous and lymphatic pressures, which cause leakage of proteins/lymph into the gastrointestinal tract (GIT) and expulsion from the body. It is commonly held that elevated venous pressures are relatively better tolerated in the upper body, but much less so in the heptatosplanchnic circulation and the lower body. It is also well established that elevated venous pressure increases lymph formation, most of which is produced in the hepatosplanchnic region (liver and intestine). It is further argued here that the increase in lymph filling pressure arising from the higher lymph flow, in association with the backpressure exerted by elevated venous pressure at the main drainage point into the venous system, results in a substantial increase in pressure in the thoracic duct. This pressure is transmitted back to the intestinal lymphatics, causing dilatation with lacteal rupture and protein or bulk lymph leakage into the intestine. We propose in this paper a new approach, based on experimental evidence, to prevent and/or alleviate this condition by draining or redirecting the thoracic duct (or, alternatively, a more localized intestinal lymphatic vessel) into one of the pulmonary veins or the left atrium, which are typically at near-normal pressure in a Fontan circulation. This “lymphatic-venous right-to-left” shunt maneuver would significantly reduce the venous backpressure on the lymphatics as well as improve lymph circulation, resulting in a decrease in the intestinal lymphatic pressure and thereby prevent or alleviate protein/lymph loss, i.e. lymph balance would be restored. Moreover, the greatly facilitated lymphatic flow would encourage further capillary filtration to relieve excessive venous pressure in the hepatosplanchnic region and protect the liver and kidneys. This paper is intended as a discussion document for elicitation of comments on the soundness and viability of this proposal as well as on technical challenges and steps to explore and advance it.

Unmet clinical needs in the management of advanced melanoma: findings from a survey of oncologists

Advanced melanoma is a life-threatening cancer with limited life expectancy. The recent introduction of new targeted systemic therapies has provided clinicians with the means to potentially extend survival for the first time. However, the chance of cure remains very low and treatment-induced toxicity is well described. This qualitative study was undertaken to evaluate clinicians' assessment regarding the key concerns in managing advanced melanoma following the introduction of these new treatments. Three hundred and forty-three oncologists were surveyed online between August and November 2012 (in 11 countries) and March and April 2013 (in an additional country). Analysis of free-text responses identified 23 clinical issues of concern across all countries. Of these, the most common clinical concerns were drug toxicity and tolerability, followed by limited treatment effectiveness and limited treatment options. These results suggest that despite the promise of the two new agents in the field, clinicians are still concerned about the limitations of current treatment options, recognising that there remains a significant unmet need in the treatment of advanced melanoma.

Treatment patterns in advanced melanoma: findings from a survey of European oncologists

With the emergence of new therapies, established patterns of treating advanced melanoma are changing. The aim of this study was to understand how advanced melanoma is treated in clinical practice in Europe following the introduction of ipilimumab and vemurafenib. An online survey was conducted between August and November 2012 with 150 oncologists and dermatologists, from France, Germany, Italy, Spain and the U.K.; respondents reported treating the majority of patients with one or two lines of therapy. For BRAF mutant melanoma, the most frequently used first-line treatments were vemurafenib and dacarbazine. For BRAF wild-type melanoma, the most frequently used first-line treatment was dacarbazine. There was no single preferred agent for the second-line treatment of BRAF mutant or BRAF wild-type disease. Most sequencing from first- to second-line was from conventional dacarbazine to newer agents such as ipilimumab and vemurafenib. The treatment of advanced melanoma is rapidly evolving due to the introduction of new agents. This study presents an early insight into access to the new agents, ipilimumab and vemurafenib, and clinical practice in several European countries.

Health-related quality of life in patients with metastatic colorectal cancer treated with panitumumab in first- or second-line treatment

Background:

Panitumumab in combination with chemotherapy was evaluated in two pivotal clinical trials in first- and second-line treatment of metastatic colorectal cancer (mCRC), respectively. This analysis compared the health-related quality of life (HRQoL) of patients with or without panitumumab in the two trials.

Methods:

Patients with mCRC were randomised to FOLFOX (first-line trial) or FOLFIRI (second-line trial)±panitumumab. The EuroQoL 5-Dimensions Health State Index (EQ-5D HSI) and Visual Analogue Scale (EQ-5D VAS) were assessed at baseline and monthly follow-up until disease progression. Patients with wild-type KRAS mCRC with baseline and post-baseline HRQoL scores were included. Difference in change from baseline between treatment groups was evaluated using linear mixed and pattern-mixture models.

Results:

In the first-line trial, 576 patients with wild-type KRAS mCRC (284 panitumumab+FOLFOX4 and 292 FOLFOX4 alone) were included in the HRQoL analyses. In the second-line trial, 530 patients with wild-type KRAS mCRC were included in these analyses (263 panitumumab+FOLFIRI and 267 FOLFIRI alone). There was no significant difference in the change in EQ-5D HSI and VAS scores between treatment groups in either trial.

Conclusion:

The addition of panitumumab to FOLFOX4 or FOLFIRI in first- or second-line treatment of wild-type KRAS mCRC significantly improved progression-free survival without compromising HRQoL.

A Q-TWiST analysis comparing panitumumab plus best supportive care (BSC) with BSC alone in patients with wild-type KRAS metastatic colorectal cancer

Background:

Panitumumab+best supportive care (BSC) significantly improved progression-free survival (PFS) vs BSC alone in patients with chemo-refractory wild-type KRAS metastatic colorectal cancer (mCRC). We applied the quality-adjusted time without symptoms of disease or toxicity (Q-TWiST) analysis to provide an integrated measure of clinical benefit, with the objective of comparing quality-adjusted survival between the two arms. As the trial design allowed patients on BSC alone to receive panitumumab after disease progression, which confounded overall survival (OS), the focus of this analysis was on PFS.

Methods:

For each treatment group, the time spent in the toxicity (grade 3 or 4 adverse events; TOX), time without symptoms of disease or toxicity (TWiST), and relapse (after disease progression; REL) states were estimated by the product-limit method, and adjusted using utility weights derived from patient-reported EuroQoL 5-dimensions measures. Sensitivity analyses were performed in which utility weights (varying from 0 to 1) were applied to time in the TOX and REL health states.

Results:

There was a significant difference between groups favouring panitumumab+BSC in quality-adjusted PFS (12.3 weeks vs 5.8 weeks, respectively, P<0.0001) and quality-adjusted OS (P=0.0303).

Conclusion:

In patients with chemo-refractory wild-type KRAS mCRC, panitumumab+BSC significantly improved quality-adjusted survival compared with BSC alone.

Abstract P1-09-02: Health Care Costs Incurred by Post-Menopausal Women with Hormone-Positive Breast Cancer Following the Initial Diagnosis of Metastasis

Objectives: Estimate the healthcare costs before and after progression to chemotherapy in a population of post-menopausal hormone-receptor positive (HR+) metastatic breast cancer (mBC) patients. Methods:

This retrospective cohort study used claims from a large national US health plan. Females age 55 to 63 were selected if they were diagnosed with metastatic breast cancer between 7/1/01 and 12/31/07, and initiated hormonal therapy before progressing to chemotherapy. Incident metastatic patients were followed until the earliest of disenrollment from the health plan, death, or 12/31/08. The pre-chemotherapy period was defined as the period between the incident diagnosis of metastases and the earlier of the initiation of chemotherapy and the end of the study period. Among the subset of patients with use of chemotherapy, the post-chemotherapy period was defined as the time following chemotherapy initiation until the end of the study. Inflation-adjusted costs were examined during the pre-and post-chemotherapy periods. Descriptive analyses were supplemented with Kaplan-Meier sample-average to adjust for variable follow-up time and censoring. Results:

A total of 1,202 patients were identified, 366 (30.4%) of whom progressed to chemotherapy following the onset of metastases. The mean age ± SD was 58.9 ± 2.6 years.

On average, patients incurred $79,139 (SD± $121,489) per year in total health care costs before the initiation of chemotherapy and $132,786 (SD± $117,635) after the initiation of chemotherapy. In the pre-chemotherapy and post-chemotherapy phases, medical expenses were $74,149 (SD± $119,838) and $120,942 (SD± $116,225) per patient-year, respectively, while outpatient medications filled at a retail pharmacy or through a mail system pharmacy cost $4,990 (SD± $5033) and $11,843 (SD± $14,431) per patient-year, respectively. On average, most of the observed medical expenses were incurred during outpatient visits with $44,405 (SD± $55,710) and $87,299 (SD± $75,360) per patient-year in the pre-and post-chemotherapy phases respectively. Inpatient stays accounted for $27,147 (SD± $101,405) and $30,118 (SD± $73,216) per patient-year during the pre-and post-chemotherapy periods, respectively. ER visits cost an average of $424 (SD± $1,871) per patient-year during the pre-chemotherapy period and $1,274 (SD± $5,686) per patient-year during the post chemotherapy period, on average. During the post-chemotherapy period, combined costs for both inpatient and outpatient chemotherapy were $33,559 (SD± $38,692) per patient-year on average, and costs for services associated with supportive care for chemotherapy during the same time period accounted for an additional $18,676 (SD± $30,281) per patient-year on average. After adjusting for variable follow-up times, cumulative total healthcare costs were $54,725, $73,107, and $84,200 for years one, two, and three of the pre-chemotherapy period, respectively, and were $92,639, $148,228, and $176,163 during the same portions of the post-chemotherapy period. Conclusions:

Post-menopausal HR+ mBC patients incur significant healthcare costs both before and after progressing to chemotherapy. The main cost driver was medical costs in both the pre-and post-chemotherapy periods.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P1-09-02.

Trends in chemotherapy and biologic treatment of U.S. metastatic colorectal cancer patients

6553

Background: Several long-standing chemotherapy regimens are available to treat metastatic colorectal cancer (mCRC) including: oxaliplatin plus 5-fluorouracil (5-FU) and leucovorin (FOLFOX); and Irinotecan plus 5-FU and leucovorin (FOLFIRI). More recently, new biologic therapies were approved for use in mCRC. This cohort study examines trends in first-line chemotherapy treatments for newly diagnosed mCRC patients after the introduction of capecitabine (CAP) in 2001 and the biologic therapies in 2004. Methods: Using a large, US-based administrative medical claims database of a national commercially insured population, patients with newly diagnosed mCRC were identified from 2001 to 2005. At least 6-months of patient history prior to mCRC diagnosis were required to confirm patients were newly diagnosed. Patients were followed from initial mCRC diagnosis to death, disenrollment, or 12/31/2006. Results: Total of 3,781 newly diagnosed mCRC patients were identified between 2001–2005. On average over the 5 years, 58% of patients (with annual variation ± 4% points) received chemotherapy/biologic treatment in the year following their mCRC diagnosis; mean days to initiation of chemotherapy treatment decreased from 135 to 62 between 2001–2005. In 2001, FOLFIRI (40%), 5-FU (30%), and CAP (20%) were the most prevalent first-line treatments. In 2005, first-line treatment regimens were more diverse: FOLFOX plus bevacizumab (35%), FOLFOX alone (15%), 5-FU (15%), and CAP (15%) were the most prevalent, while 33% of patients used other treatment combinations. Among mCRC patients diagnosed in 2005, 63% were treated with at least one biologic therapy in the first year after diagnosis (57% received bevacizumab; 26% received cetuximab). Conclusions: While rates of chemotherapy use remained relatively constant between 2001–2005, patients initiated chemotherapy treatment sooner after their initial diagnosis and the standard course of therapy shifted from being FOLFIRI-based to FOLFOX-based. A rapid uptake in biologic therapies occurred. The majority of newly diagnosed mCRC patients were users of biologic therapy within one year following their introduction.

[Table: see text]

Metastatic colorectal cancer (mCRC): Recent patterns of chemotherapy and monoclonal antibody (MoAb) therapy in clinical practice

4120

Background: New systemic chemotherapies, particularly the MoAbs, bevacizumab (BMab), cetuximab (CMab), and panitumumab (PMab) have advanced therapy for mCRC. However, the optimal combination and sequencing of these and other chemotherapies are not established, and little is known about their patterns of use in clinical practice. We examined the frequency, patterns of use, and dosing changes of MoAbs across lines of therapy. Methods: The dataset consists of Varian and Impac electronic medical records for 304,654 cancer patients from 91 practice sites across 19 states. Inclusion/exclusion criteria were applied: ≥18 years old, newly diagnosed with mCRC or developed metastases during 1/1/2004 - 1/31/2008, and could be observed ≥3 months beyond their dates of metastases. Patients on a clinical trial at any time during the analysis were excluded. Results: The study sample included 1,655 patients (52% male, mean age 61.9 years). 11% received all five therapeutic classes: fluoropyrimidines, irinotecan, oxaliplatin, EGFR MoAbs (PMab and CMab), and VEGF MoAb (BMab). 19% received at least 3 treatment classes. BMab, fluorouracil, leucovorin, oxaliplatin (BMab+FOLFOX) was the most frequently observed 1st line regimen in 26% of patients. Across the study period more patients received BMab than PMab or CMab (69%, 7%, and 22%, respectively, for any exposure); 55% received BMab for 1st-line therapy. A BMab dose increase within a line of therapy was recorded in 22% of patients for 1st-line, 21% for 2nd-line, and 15% for 3rd-line. Among patients who continued BMab from 1st to 2nd line (N=239) and 2nd to 3rd line (N=88), 44% and 39%, respectively had a dose increase (mean/month 890mg to 1078mg, and 844mg to 1053mg). Conclusions: The most frequent 1st-line chemo regimen was FOLFOX. BMab was the most commonly administrated MoAb. Trends toward dose-escalation of BMab were observed both within lines of therapy and across lines of therapy.

[Table: see text]

Burden of hospitalizations associated with skeletal related events in patients with breast cancer or lung cancer and bone metastases or multiple myeloma

17083

Background: Patients with bone metastases secondary to cancer often experience skeletal related events (SREs) including pathological fracture, spinal cord compression, hypercalcemia, bone surgery or radiotherapy, or initiation of opioid analgesic use. These SREs result in major morbidity and reduced quality of life. This research examines hospitalizations associated with SREs. Methods: Data for this study were obtained from i3 LabRx Database (05/01/2000 to 03/31/2005). Individuals were included in the analyses if they had at least two diagnoses of breast cancer (based upon an ICD-9 code of 174.xx), lung cancer (162.xx), or multiple myeloma (203.0x) and had at least two diagnoses of bone metastases (198.5x) after the first diagnosis of cancer. In addition, individuals were required to have at least one SRE (based upon a previously published algorithm) on or after their initial diagnosis of bone metastases (their index date). Individuals were required to be continuously insured for at least 6 months prior to, and at least one month post their index date. Data were analyzed until 03/31/2005 or until the end of their continuous coverage, whichever occurred first. Descriptive statistics for each of these cohorts are provided. Results: A total of 1,204 individuals with breast cancer, 1,094 with lung cancer, and 258 with multiple myeloma were included in the study. The vast majority of individuals with breast cancer (96.5%), lung cancer (95.9%), or multiple myeloma (96.8%) were hospitalized. All three patient groups were likely to have SRE-related hospitalizations; multiple myeloma 43.4%, breast cancer 36.2% and lung cancer 35.6%. The average number of days per patient year that patients were hospitalized related to a diagnosis or procedure for a SRE was 6.75 days for patients with lung cancer, 6.56 days for patients with multiple myeloma, and 3.75 days for patients with breast cancer. Conclusion: Hospitalizations related to SREs are common and the number of days per year is substantial.

No significant financial relationships to disclose.

Cost effectiveness of drotrecogin alfa (activated) for the treatment of severe sepsis in the United Kingdom*

Drotrecogin alfa (activated) is licensed in Europe for the treatment of severe sepsis in patients with multiple organ failure. We constructed a model to assess the cost effectiveness of drotrecogin alfa (activated) from the perspective of the UK National Health Service when used in adult intensive care units. Patient outcomes from a 28-day international clinical trial (PROWESS) and a subsequent follow-up study (EVBI) were supplemented with UK data. Cost effectiveness was assessed as incremental cost per life year and per quality adjusted life year saved compared to placebo alongside best usual care. Applying the 28-day mortality outcomes of the PROWESS study, the model produced a cost per life year saved of 4608 UK pounds and cost per quality adjusted life year saved of 6679 UK pounds. Equivalent results using actual hospital outcomes were 7625 UK pounds per life year and 11,051 UK pounds per quality adjusted life year. Drotrecogin alfa (activated) appears cost effective in treating severe sepsis in UK intensive care units.

Info-vigilance or safety in health information systems

The paper examines the issues of security and safety in Health Information Systems and focuses the need for the development of appropriate Guidelines for the effective use of IEC 61508 standard.

Therapeutic vaccines against melanoma and colorectal cancer

Our overall strategy is to develop multivalent recombinant vaccines capable of eliciting broad immune responses in patients with malignant melanoma or colorectal cancer. We report herein results from initial studies conducted in cancer patients to evaluate the effect of intratumoral administration of recombinant canarypox viruses carrying cytokine genes. Our current focus is on the induction of tumor-specific T-cell responses using a prime/boost immunization schedule with a unique vector system derived from the canary pox virus called ALVAC, in which we incorporate genes encoding Tumor Associated Antigens (TAAs) of interest. Clinical studies in colorectal cancer evaluating an ALVAC CEA candidate vaccine have shown that this approach is safe and can induce tumor-specific T cell responses. Additional clinical studies evaluating candidate vaccines against melanoma and colorectal cancer, targeting either the gp100, Mage 1, Mage 3 or p53 molecules are ongoing.

Law and standards

A comparison is made between the widely different processes of creating legislation and that of developing standards. Despite their very different origins, in practical terms standards can influence the development of legislation as well as demonstrating compliance with legislative requirements.

Neurocardiovascular instability, hypotensive episodes, and MRI lesions in neurodegenerative dementia

We investigated whether carotid sinus hypersensitivity (CSH) and orthostatic hypotension (OH) were associated with a greater severity of hyperintensities on MRI scan in 30 patients with neurodegenerative dementia (17 dementia with Lewy bodies, 13 Alzheimer's disease), who had a detailed evaluation of OH and CSH during active standing and head-up tilt. Patients also underwent a 1.0 Tesla MRI scan, from which hyperintensities were rated on a standardized scale. A blood pressure (BP) drop > 30 mm Hg during carotid sinus massage or active standing was significantly associated with the severity of MRI hyperintensities in the deep white matter (OR 10.0, 95%; CI 1.8-55.7) and in the basal ganglia (OR 11.0, 95%; CI 1.2-99.5) but not in periventricular areas (OR 1.4, 95%; CI 0.3-1.8). Patients with the cardio-inhibitory form of CSH with the largest BP drops were the most at risk. Further longitudinal studies need to investigate the direction of causality to determine whether CSH or OH predispose to MRI hyperintensities and accelerate cognitive decline.

Enhanced critical currents of superconducting ErNi2B2C in the ferromagnetically ordered state

We report on transport and magnetization studies of the critical current in single crystal ErNi2B2C for applied fields below 4 kG. Below T approximately 2.5 K superconductivity coexists with weak ferromagnetism. We find that the critical currents are strongly enhanced for all field orientations in this ferromagnetic regime, corresponding to a threefold increase of the pinning force of the flux line lattice. We speculate that this increase is due to strong pair breaking by the ferromagnetism.

The Night Vision Threshold Test (NVTT): a simple instrument for testing dark adaptation in young children

It is estimated that 41 per cent of the population aged under 5 in the developing world has an inadequate vitamin A dietary intake resulting in increased morbidity and mortality. Half a million children go blind each year as a result of vitamin A deficiency. Thirteen and a half million have night blindness, the first sign of vitamin A deficiency. Unfortunately, there is no simple, sensitive and inexpensive means to identify the child who has marginal levels of vitamin A and thus institute means to prevent their development of severe deficiency. A low cost, simple, easy-to-use instrument designed to detect a young child's ability to adapt to darkness was tested in children admitted to the Mwanamugimu Nutrition Unit at Makerere Medical School in Kampala, Uganda. Despite the severe degree of malnutrition found in these children, Night Vision Threshold Test results and serum retinol levels were related (r = 0.41, p < 0.05). Further efficacy trials for this instrument are planned at community sites in Nepal.

Rates of tuberculosis infection in healthcare workers providing services to HIV-infected populations. Terry Beirn Community Programs for Clinical Research on AIDS

OBJECTIVE

To assess the prevalence of tuberculosis (TB) or a positive skin test in healthcare workers (HCWs) providing services to human immunodeficiency virus (HIV)-infected individuals and to determine prospectively the incidence of new infections in this population.

DESIGN

This prospective cohort study enrolled 1,014 HCWs working with HIV-infected populations from 10 metropolitan areas. Purified protein derivative (PPD) tuberculin skin tests were placed at baseline and every 6 months afterwards on those without a history of TB or a positive PPD. Demographic, occupational, and TB exposure data also were collected.

SETTING

Outpatient clinics, hospitals, private practice offices, and drug treatment programs providing HIV-related healthcare and research programs.

PARTICIPANTS

A voluntary sample of staff and volunteers from 16 Community Programs for Clinical Research on AIDS units.

RESULTS

Factors related to prior TB or a positive skin test at baseline included being foreign-born, increased length of time in health care, living in New York City, or previous bacille Calmette-Guerin vaccination. The rate of PPD conversion was 1.8 per 100 person years of follow-up. No independent relation was found between the amount or type of contact with HIV-infected populations and the risk of TB infection.

CONCLUSION

These data provide some reassurance that caring for HIV-infected patients is not related to an increased rate of TB infection among HCWs in these settings.

Introduction: Emerging vaccine strategies

No abstractCopyright 1997 Academic Press Limited Copyright 1997Academic Press Limited

Murine antibody responses to the verotoxin 1 B subunit: demonstration of major histocompatibility complex dependence and an immunodominant epitope involving phenylalanine 30

Structurally conserved verotoxin 1 (VT1) mutant derivatives, showing reduced receptor binding and cytotoxicity, may serve as natural toxoids to protect against VT-mediated disease. In this study, the antibody responses to the wild-type VT1 B subunit, a B-subunit mutant (Phe30Ala B), and the corresponding holotoxin (Phe30Ala HT) were examined in three inbred mouse strains. BALB/c (H-2d) and CBA (H-2k) mice produced strong antibody responses to both wild-type and mutant B subunits. VT1 B-raised sera reacted more strongly with VT1 B than with Phe30Ala B in enzyme-linked immunosorbent assays, while Phe30Ala B-raised sera reacted equally with VT1 B and Phe30Ala B. C57BL/6 (H-2b) and congenic BALB/c (BALB x B [H-2b]) mice produced no detectable antibody response to either VT1 B or Phe30Ala B. However, an anti-VT1 B antibody response was detected in H-2b mice immunized with biologically active Phe30Ala HT. Based on these observations, we conclude that the VT1 B subunit possesses a B-cell immunodominant epitope formed partly by phenylalanine 30 and that the B-subunit antibody response is dependent on the H-2 haplotype of the mouse strain. Our results also support a potential role for the A subunit in providing the T-cell help necessary to overcome a deficient B-subunit antibody response in H-2b mice.