The expanding role of aerosols in systemic drug delivery, gene therapy and vaccination: an update
© Laube; licensee Springer. 2014
Received: 17 September 2013
Accepted: 23 October 2013
Published: 13 January 2014
Until the late 1990s, aerosol therapy consisted of beta2-adrenergic agonists, anti-cholinergics, steroidal and non-steroidal agents, mucolytics and antibiotics that were used to treat patients with asthma, COPD and cystic fibrosis. Since then, inhalation therapy has matured to include drugs that: (1) are designed to treat diseases outside the lung and whose target is the systemic circulation (systemic drug delivery); (2) deliver nucleic acids that lead to permanent expression of a gene construct, or protein coding sequence, in a population of cells (gene therapy); and (3) provide needle-free immunization against disease (aerosolized vaccination). During the evolution of these advanced applications, it was also necessary to develop new devices that provided increased dosing efficiency and less loss during delivery. This review will present an update on the success of each of these new applications and their devices. The early promise of aerosolized systemic drug delivery and its outlook for future success will be highlighted. In addition, the challenges to aerosolized gene therapy and the need for appropriate gene vectors will be discussed. Finally, progress in the development of aerosolized vaccination will be presented. The continued expansion of the role of aerosol therapy in the future will depend on: (1) improving the bioavailability of systemically delivered drugs; (2) developing gene therapy vectors that can efficiently penetrate the mucus barrier and cell membrane, navigate the cell cytoplasm and efficiently transfer DNA material to the cell nucleus; (3) improving delivery of gene vectors and vaccines to infants; and (4) developing formulations that are safe for acute and chronic administrations.
KeywordsSystemic drug delivery by inhalation Aerosolized gene therapy Vaccination by inhalation
There are many advantages to administering medications to the lung as an aerosol. These include: a more rapid onset of action for short-acting bronchodilators, compared to oral therapy; high local concentration by delivery directly to the airways; needle-free systemic delivery of drugs with poor oral bioavailability; and pain- and needle-free delivery for drugs that require subcutaneous or intravenous injection. Traditional aerosol therapies with the lung as the target consist of short-acting β2-adrenergic agonists and long-acting β2-adrenergic agonists (LABA), anticholinergics, inhaled corticosteroids (ICSs), nonsteroidal anti-inflammatories, antibiotics and mucolytics. Devices that are available to deliver these drugs include pressurized metered-dose inhalers (pMDIs), used either alone, or attached to spacers, or valved holding chambers (VHCs), breathactuated (BA)-pMDIs, dry powder inhalers (DPIs), jet nebulizers, vibrating mesh nebulizers and soft mist inhalers. Well-established treatment guidelines for the management of asthma  and chronic obstructive pulmonary disease (COPD)  each recommend inhaled therapy as the primary route to administer these medications. Treatment guidelines for cystic fibrosis (CF) also include recommendations for inhalation of aerosolized medications [3, 4]. Guidelines for inhalation therapy to treat these diseases will not be covered in this review. A comprehensive presentation of old and newly-approved devices and their correct use in treating these diseases has also been published  and will not be included in this review. This review will focus on the newest applications for aerosol therapy by oral inhalation. When possible, results from clinical studies, rather than preclinical studies, will be highlighted and delivery devices will be included if they are a new design and critical to the success of the application. Updates on new applications for intranasal therapy are beyond the scope of this review and can be found in several referenced articles [6–14].
New applications for oral inhalation now include drugs that: (1) target the systemic circulation as a means to treat disorders unrelated to the lung (systemic drug delivery by inhalation); (2) deliver nucleic acids that lead to permanent expression of a gene construct, or protein coding sequence, in a population of cells within the lung, thereby reversing or preventing a disease process (aerosolized gene therapy); and (3) provide needle-free immunization and prevention against infectious diseases (vaccination by inhalation). Since first reviewing this subject in 2005 , each of these new applications has met with varying degrees of success in terms of achieving clinical efficacy and commercialization. This brief review provides an update on the status and challenges facing each of these new applications and focuses on an example that is furthest along in development and/or affects the most people. Within each example are success stories, failures and lessons to be learned. Addressing those lessons will enhance these applications in the future.
Systemic drug delivery by inhalation
Because of the many advantages to aerosol therapy mentioned above, a number of systemically active drugs have been developed as possible candidates for aerosol delivery through the lung into the systemic circulation. For these drugs, it is important that delivery lead to adequate systemic absorption with no irritability, or damage, to the airways or alveoli. Drugs that have been tested include opioids for pre- and post-operative analgesia, dihydroergotamine (DHE) for acute treatment of migraine, interferon β to treat multiple sclerosis, leuprolide acetate to treat prostatic cancer, infertility and post-menopausal breast cancer, calcitonin to treat postmenopausal osteoporosis, growth hormone releasing factor to treat pituitary dwarfism and insulin to treat diabetes.
A few of these drugs have shown promise in human trials and some have been commercialized. Opioids such as morphine and fentanyl have been tested as a liquid aerosol generated by traditional jet nebulizers  and by the AERx® vibrating mesh prototype nebulizer . The usefulness of inhaled opioids lies in the elimination of an intravenous catheter with the potential of providing rapid-onset, patient-controlled analgesia. A large variability in absorption was reported with jet nebulizer administration , which likely will limit acceptance as a method for pre- or post-operative pain control with these devices. Pain management was more predictable with the AERx® device (Aradigm Corp., Hayward, CA, USA) . Another pain management drug, DHE, has proven superior to placebo for the acute treatment of migraine in a phase 3, double-blinded, multicenter study . In that study, a novel formulation of DHE (LEVADEX™, MAP Pharmaceuticals, Mountain View, CA, USA) was delivered to the systemic circulation using the TEMPO® pMDI (MAP Pharmaceuticals). Calcitonin has been successfully delivered to the systemic circulation intranasally [7, 8] and is now available as Miacalcin® (Novartis Pharmaceuticals Corp, East Hanover, NJ, USA) nasal spray to treat postmenopausal osteoporosis in females greater than 5 years post menopause.
Best example of systemic drug delivery by aerosolization: treating diabetes with oral inhalation of insulin
Although there are several other successful drugs that have been administered to the systemic circulation by inhalation, the best example of the expanding role of aerosol therapy into systemic drug delivery is treating diabetes with oral inhalation of insulin. This is because this route of administration has the potential to eliminate subcutaneous (SC) injection of insulin for a significantly large patient population. An estimated 370 million people worldwide have diabetes  and the majority of these have non-insulin dependent diabetes mellitus (NIDDM), or type-2 diabetes. The goal for the treatment of type-2 diabetes is to maintain glucose control in the normal range to prevent long-term complications. Typically, the first line of treatment is oral anti-diabetic medications. Eventually, anti-diabetic medications fail and type-2 patients need to administer insulin SC four times/day (i.e. before meals and at bedtime) to achieve good control. Because injection hurts, compliance with treatment is often reduced. More importantly, patients who would benefit from early intervention with insulin treatment decline treatment because of the pain and inconvenience associated with injection.
A second reason why treating diabetes with oral inhalation of insulin is the best example of the expanding role of aerosol therapy into systemic drug delivery is because what we now know about systemic drug delivery of peptides by inhalation was learned during the development of inhaled insulin and the study of its success and early failure continues to inform future development of systemic drug delivery by inhalation, as well as other new applications of aerosol therapy.
The notion that insulin could be administered through the lung to the systemic circulation by inhalation was investigated in the 1970s [20, 21]. From those early trials, several challenges were identified that needed to be overcome. These included: (1) determining the appropriate lung target; (2) determining the inhaled dose that controls blood glucose levels; and (3) developing new devices that deliver the dose to the target. By the early 1990’s, several pharmaceutical companies and device manufacturers began to address these challenges. Work in animals showed that the appropriate target for aerosolized insulin and other drugs delivered through the lung for systemic administration is the alveolar region . This is because the alveolar region comprises a resorptive surface of 50-75 m2, which provides a surface area for drug absorption that is the size of a tennis court. In addition, mucociliary clearance is minimal in the alveolar region. Once drug deposits in the alveolar region, the residence time is long, enhancing the probability of absorption. Finally, the cell barrier to absorption is extremely thin (0.1 mm) in the alveolar region, thereby enhancing the possibility for absorption from the epithelial layer to the lung vasculature.
By the late 1990s, results from several studies [23–26] showed that a dose of 1.0 U/kg body weight human regular insulin aerosol controlled fasting glucose levels and a dose of 1.5 U/kg body weight controlled postprandial glucose levels. However, this dose posed an early limitation to this route of administration, since it was approximately 10 times the dose given subcutaneously (i.e. ~0.1 U/kg body weight).
Nevertheless, the Exubera® Pulmonary Insulin Delivery System (Pfizer Pharmaceuticals, New York, NY; and Nektar Therapeutics, San Carlos, CA), was approved by the U.S. Food and Drug Administration in 2006 for use in adults with both type 1 and type 2 diabetes and became commercially available soon thereafter [27, 28]. By early 2007, two additional devices and formulations were in Phase III testing. These included the AERx® Insulin Diabetes Management System (Novo-Nordisk A/S, Bagsverd, Denmark; and Aradigm Corp., Hayward, CA) and the AIR® Inhaled Insulin System (Eli Lilly and Co., Indianapolis, IN; and Alkermes Inc., Cambridge, MA) [29–31]. However, between October, 2007 and May, 2008, production of all three products had been discontinued.
What went wrong?
The cost of inhaled insulin was higher than injectable insulin. One analysis demonstrated that Exubera®’s inhaled insulin cost about $5 per day, compared to $2-3 per day by injection . The higher cost was due in part to the lower bioavailability of Exubera® inhaled insulin compared to SC. The bioavailability of Exubera was only 10-15% of the SC dose .
Safety became an issue. Studies with Exubera® that lasted 6 months, showed increased insulin binding antibodies, coughing and a reduction in diffusing capacity, compared to injected insulin . However, longer-term studies showed that reductions in lung function parameters were small, non-progressive and reversible with discontinuation of treatment .
Sales in the U.S. of Exubera® were lower than expected, perhaps because of the cost, or safety issues, or because few patients, or care givers, realized the advantages of this route of administration compared to injection therapy.
Second generation delivery system for inhaled insulin
To insure satisfactory outcomes and patient acceptability of systemic drug delivery by aerosolization in the future, it is clear that the bioavailability of expensive drugs like insulin with relatively low bioavailability needs to be improved. Suggestions for improving bioavailability include: better targeting of the alveolar region with nanoparticle (<0.1 μm in diameter) formulations, or formulations containing porous particles that have aerodynamic characteristics similar to extrafine particles (~1.0 μm in diameter); and enhancing absorption by adding absorption enhancers that do not damage lung tissue. Several additives that have been tested in rats appear to enhance absorption and permeation and may be appropriate to improve absorption in future pulmonary protein formulations. These include endogenous surfactants such as DPPC [38, 39], citric acid , and hydroxypropylcellulose .
It is also clear that: (1) formulations are needed that do not produce cough, or changes in lung function, and are safe for acute and chronic administrations; (2) the device should be small, portable and easy to use; (3) the total cost of the device and formulation should be similar in cost to the injection product; and (4) patients and physicians should be well-educated in terms of the advantages of this route of a dministration compared to injection therapy to ensure compliance.
Aerosolized gene therapy
The lung is an important target organ for gene therapy. This is because there are a number of lung diseases that could benefit from this type of treatment. These include: lung cancer, asthma, cystic fibrosis and alpha-1-antitrypsin deficiency. The goal of aerosolized gene therapy is to correct the lung disorder with delivery of a functional copy of the aberrant gene to the appropriate target within the lung.
Viral vectors versus non-viral vectors for gene therapy
As with systemic drug delivery by aerosolization, aerosolized gene therapy will likely require repeat dosing. In order to avoid lung damage as a result of repeat therapy, it is important that the vector that is selected to deliver the functional genetic material does not cause immune responses from the host, or lead to mutagenesis over time. Although there are a number of viral and non-viral vectors that are available for aerosolization that can deliver the functional genetic material, the identification of safe vectors has been one of the major challenges to the development of aerosolized gene therapy [42, 43]. Viral vectors include retroviruses, lentiviruses, adenoviruses (Ad) and adeno-associated viruses (AAV). Retroviruses are capable of long-term gene expression following genomic integration but only in non-dividing cells, whereas, lentiviruses are capable of long-term gene expression in both non-dividing and dividing cells. However, both types of viruses present a high risk of insertional mutation leading to oncogenesis. Adenoviruses infect non-replicating cells, show potential for persistent expression and present low risk of insertional mutagenesis. However, they can trigger a strong immune response by the host. Unlike adenoviruses, AAV do not trigger a strong immune response by the host, but they have a small packaging capability (~4.7 kb), so they are limited in the amount of genetic material they can carry, and they have reduced efficacy with repeat-administration.
Non-viral vectors are carrier molecules that are either cationic lipids, or cationic polymers, that bind to negatively charged plasmid DNA and either encapsulate or condense the DNA to generate lipoplexes and polyplexes. Non-viral vectors are generally less efficient than viral vectors because they lack specific components that could help with endosomal escape, movement through the cytoplasm and nuclear uptake. The simpler composition of non-viral vectors, however, may have an advantage over viral vectors, since they are free of non-human components, making re-administration potentially more successful [44, 45].
Of the vectors available for delivering genetic material for gene therapy, AAV vectors have been the most utilized in terms of animal experiments and clinical trials. Currently, the most common carrier is the viral vector AAV2, but recent studies suggest that AAV2 with capsids from serotypes 1, 5 and 6 may be more efficient in transducing airway epithelial cells than AAV2 [46, 47]. Some progress has been made in improving non-viral gene transfer , but more safety data is needed before they can be safely administered to humans on a chronic basis. There are currently no dry-powder, or metered-dose inhaler formulations for any vector-drug combination. Therefore, the field is further limited by delivery in a liquid formulation using a nebulizer.
Best example of aerosolized gene therapy: treating cystic fibrosis (CF)
Development of aerosolized gene therapy for lung cancer and alpha-1-antitrypsin deficiency has not progressed beyond the preclinical stage. Results from clinical trials with early therapies have not shown efficacy. On the other hand, aerosolized gene therapy for treating cystic fibrosis has had some success in clinical trials and details of those efforts are reported here. Approximately 70,000 people worldwide have cystic fibrosis (CF), an inherited, autosomal recessive disease. Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene lead to loss of chloride, sodium and water transport, impaired mucus removal, obstructed airways, chronic infection and end stage lung disease. The goal of aerosolized gene therapy in treating cystic fibrosis is to restore CFTR function and normal chloride channel function in the lungs.
Over the years, there have been a number of challenges to aerosol delivery of vectors carrying intact CFTR complementary DNA (cDNA). First, there has been the challenge of delivering an adequate dose to infants, who are an important target population. This is because identification of infants who are afflicted with CF is now possible at birth and early gene therapy holds the promise of correcting the abnormality before irreversible lung damage can occur. However, due to anatomic, physiologic and behavioral factors, delivery of aerosols to infants is challenging and highly variable. Gene transfer therapy is likely to be extremely expensive, so improving delivery efficiency and reducing variability of delivery to small children will result in less waste and help insure the desired effect.
Additional challenges to aerosolized gene therapy for CF that likely apply to aerosolized gene therapy for other lung diseases include delivery of DNA through the mucus barrier. The mucus barrier is thick and viscous in patients with CF, and in patients with chronic obstructive lung disease (COPD), there is excess mucus production. Gene vectors whose target is the airway epithelial cell must be able to penetrate beyond the mucus barrier to reach their cell target. Another challenge is the need for vectors that recognize receptors on the apical surface of airway epithelial cells. Many vectors only recognize receptors on the basal-lateral surfaces, which are very difficult to access. The gene vector must deliver DNA to the cell nucleus. To do this, the vector must penetrate the cytoplasmic membrane, overcome cytoplasmic proteases and penetrate the nuclear membrane.
To date, 24 clinical trials with aerosolized gene vectors have been carried out since the cloning of the CF gene in 1989. Nine Ad CF gene therapy trials were carried out in the upper and lower airways of CF patients between 1993 and 2001 . These trials showed that low level gene transfer can be achieved in some patients, but administration resulted in lung inflammation and induced humoral and cellular immune responses, affecting the efficacy of re-administration. These shortcomings have not been overcome .
Between 1999 and 2007, six clinical trials were carried out with the AAV2 serotype . Acute administration appeared to be safe, but assessment of the efficiency of vector-specific expression was lacking and in another large trial there was no improvement in lung function . Moreover, repeat dosing with the AAV2 serotype does not appear to be possible due to the development of an anti-viral immune response.
Nine clinical trials have evaluated non-viral gene transfer to the upper and lower airways of CF patients . For the most part these were proof of principle and Phase I safety studies. None of the trials were designed to assess clinical efficacy. A recent review article provides detailed information about these clinical trials, what vectors were used and their drawbacks .
Recent developments in the UK hold new promise for improving CF lung disease through gene therapy . The UK CF Gene Therapy Consortium (http://www.cfgenetherapy.org.uk) is currently conducting the only active CF gene therapy clinical trial. This will be a multi-dose clinical trial using the non-viral cationic lipid formulation GL67A (Genzyme, Cambridge, MA, USA) with certain modifications, including CpG-depletion and the incorporation of an hCEFI promoter called pGM169 . CpG-free plasmids reduce inflammation and lead to long-acting gene expression when administered to the mouse lung [45, 53]. The hCEFI promoter also prolongs gene expression in mice . A safe dose for a multi-dose double-blinded placebo-controlled trial of this new formulation has been determined and trial participants have been recruited . Participants will be treated with 12 monthly doses delivered by the AeroEclipseII Breath-Actuated Nebulizer (Trudell Medical Instruments, London, Canada) over a year period .
Successful correction of lung diseases with inhaled gene therapy remains elusive. A number of challenges must be overcome before pulmonary gene therapy becomes a reality. These include: (1) developing gene vectors that can more efficiently penetrate the mucus barrier and cell membrane, navigate the cell cytoplasm and transfer DNA material to the cell nucleus; (2) improving delivery of gene vectors to infants; and (3) developing formulations that are safe and effective for acute and chronic administrations.
Vaccination by inhalation
The rationale for aerosolized vaccination is based on the following advantages over injection therapy, particularly in developing countries. First, vaccination by inhalation avoids the need for disposal strategies for the large number of needles that are used in mass campaigns in developing countries. Secondly, it prevents the spread of blood borne diseases such as hepatitis B and HIV, which can be transmitted by improper use and handling of used sharps. Thirdly, administration of a vaccine via the aerosol route has less need for medical personnel, or a medical setting, compared to administration by injection, and should facilitate vaccination implementation in developing countries. Another rationale for aerosolized vaccination is that it induces protection by exposure of the airway mucosa to agents that directly affect the lungs and cause diseases such as tuberculosis, diphtheria, pneumococcal pneumonia, measles, mumps and rubella. Airway mucosal vaccination may also represent a potential approach for immunizing against agents that do not directly affect the lungs such as human papilloma virus, or hepatitis B virus, by inducing relevant antibodies in the serum.
Because of the advantages to aerosolized immunization, a number of vaccines are being tested for feasibility and efficacy via the pulmonary route. Many of these are still in preclinical stages and have not progressed to clinical trials. Brief descriptions of results from these early studies are described here. Hepatitis B virus infection remains an important global health concern despite effective vaccines that are available by injection. But, for reasons mentioned above, injection therapy for hepatitis B is restricted in the developing world. Although inhalation therapy is of interest, it is unknown if immunization is possible by inhalation of hepatitis vaccine. A few animal studies have begun to investigate the effects of particle size and formulation on this route of administration. A liquid suspension of hepatitis B vaccine PLGA (poly-D,L-lactide-co-glycolide) or PLA (poly-lactic acid), nanoparticles of different sizes administered to rats using a Microsprayer® (Penn-Century, Inc., Wyndmoor, PA, USA) resulted in humoral and mucosal immune responses that varied with particle size and hydrophobicity of the polymers used . A dry powder of hepatitis B vaccine nanoparticles administered by the Insufflator® (Penn-Century, Inc.) led to lower IgG and higher IgA in guinea pigs, compared to intramuscular injection . A liquid suspension of PLGA microspheres of hepatitis B vaccine, administered by Microsprayer®, showed that immunogenicity in rats was a function of particle size .
Safety and tolerance of intranasal administration of hepatitis B vaccine (NASVAC), comprised of hepatitis B virus (HBV) surface (HBsAg) and core antigens (HBcAg), with Accuspray® (Becton Dickinson and Company, Franklin Lakes NJ, USA) has been demonstrated in a small group of healthy volunteers . However, large, randomized controlled clinical trials with this inhaled hepatitis B vaccine are needed to show efficacy.
Administration of diphtheria vaccine by inhalation is of interest because it would avoid the high probability of a local reaction that occurs at the site of vaccination with intramuscular injection. It would be a safer route of administration in developing countries and might induce mucosal IgA antibody which could bind to the exotoxin released by Cornyebacterium diphtheriae, preventing it from entering and colonizing the airway mucosal membrane . Inhaled diphtheria vaccine is in early stages of development, but a dry powder formulation of diphtheria CRM-197 antigen with PLGA as an adjuvant, administered using the Insufflator®, resulted in lower IgG in the sera and higher IgA in the BAL of guinea pigs, compared to intramuscular injection .
The urgency to address drug-resistant TB has led to a resurgence in interest in inhalation as a route of administration for anti-TB drugs to treat TB as well as vaccines to prevent TB. A recent review of the status of anti-TB drugs is provided by Hickey et al. . Small clinical trials suggest that immunotherapy with inhaled interferon-gamma , or inhalation of a dry powder formulation of the antibiotic capreomycin with a hand-held inhaler (Cyclohaler®, Plastiape, Italy), might be beneficial to TB patients . However, large, randomized controlled clinical trials are needed to further evaluate efficacy and safety.
Mucosal immunity for protection against TB has been theorized, but is yet unproven in clinical trials. Nevertheless, a number of novel formulations including nanoparticles and dry powders of antigen/adjuvant combinations are being evaluated in animal models . Two examples are provided here. A suspension of nanoparticles (i.e. particles <0.1 μm in diameter) conjugated with Ag85B tuberculosis antigen and delivered through the nostrils of mice showed better protection against subsequent challenge, compared to intradermal delivery . A dry powder of live- attenuated tuberculosis vaccine bacille Calmette-Guerin (BCG), administered by an Insufflator®, resulted in a significantly reduced bacterial burden and lung pathology in guinea pigs subsequently challenged with virulent Mycobacterium tuberculosis, compared to untreated animals and control animals immunized with the standard parenteral BCG . Further investigation is needed to bring these products forward.
Immunization against the human papilloma virus by inhalation has been tested in a small clinical trial by Nardelli-Haefliger and colleagues . This was a dose escalation study of intranasal and oral inhalation of a human papilloma virus-like particle (HPV16 VLP) vaccine aerosol. Nasal administration was via a Devilbiss® nebulizer sprayed into each nostril. Pulmonary administration was achieved using a sonication-type nebulizer and mouthpiece. Healthy adult female volunteers inhaled two doses of the vaccine on day 0 and day 2 by nose, or mouth. Doses escalated from 2 μg to 50 μg and 250 μg. Volunteers who inhaled 250 μg by mouth seroconverted (an indicator of vaccination) and the magnitude of their serum IgG and IgA responses was similar to that seen with an historically-treated group that was administered 50 μg by intramuscular injection. Lower doses by oral inhalation were less effective and intranasal vaccination was poorly immunogenic for most volunteers. These data raise the possibility that administration of the VLP vaccine via oral inhalation may offer an alternative to systemic immunization. More trials are needed to confirm that aerosol vaccination is safe, immunogenic and protective against genital HPV infection.
Gordon et al.  compared the effect of intramuscular vs. inhaled 23-valent pneumococcal capsular polysaccharide vaccine (23-PPV) on pulmonary mucosal immunoglobulin levels. Vaccine was delivered by jet nebulizer (Sidestream®, Respironics, Murrysville, PA, USA). Bronchoalveolar lavage (BAL) and serum were collected from 33 adults before and 1 month after injected (n=16) or inhaled (n=17) 23-PPV. Levels of pneumococcal capsule-specific IgG and IgA to types 1, 9V and 14 were measured in each sample. Injected 23-PPV produced a significant increase in types 1, 9V and 14 capsule-specific IgG and type 1 IgA in both serum and BAL. Inhaled vaccine produced no response in either BAL or serum.
Best example of vaccination by inhalation: preventing measles with inhaled measles vaccine
Inhaled measles vaccine is furthest along in drug development, compared to the other inhaled vaccine candidates mentioned above and is, therefore, the best example of vaccination by inhalation. Its development has also been greatly influenced by lessons learned from the Exubera® inhaled insulin experience. The worldwide incidence of measles has been declining for the last ten years. However, populations in some countries remain unprotected. For example, an estimated 20 million children worldwide were under-vaccinated in 2012 . If infants are not adequately immunized against measles, the entire community will be at risk for measles epidemics.
Over three decades ago, Dr. Albert Sabin and colleagues proved the feasibility of vaccination by aerosolized measles vaccine [70, 71]. Since then, other trials have demonstrated that measles vaccine administered by aerosol provides a superior boosting response compared to vaccination by injection in school-age children [72, 73]. However, studies performed in infants younger than 10 months of age showed that seroconversion rates were lower with aerosolized than subcutaneous vaccine . This may have been due to an inadequate dose delivered to the lungs of these infants, since an inefficient nebulizer and face mask was used in those trials. Thus, a major challenge to developing an aerosolized vaccine for preventing measles in the developing world is to deliver an adequate dose to infants.
A second challenge to the development of an inhalable measles vaccine is the need for new delivery devices. Such delivery devices need to be efficient, portable and battery operated, since electricity is not readily available in villages in developing countries. New, efficient, portable devices that are battery-operated are now available for liquid aerosol deliver (i.e. vibrating mesh devices) and for dry powder delivery. Details about how these devices operate and their proper use can be found elsewhere . However, it is only within the last 4–5 years that these devices have been incorporated into clinical trials that are testing the efficacy of inhalable measles vaccine. Unfortunately, many of these trials have only recently been completed, or are being completed, and results are not yet published. An update of the status of those trials, the formulation of measles vaccine being tested and the devices that are being used to deliver the vaccine is provided below.
The possibility of delivering a combination aerosol vaccine to protect against measles, mumps and rubella with the AeronebGo® device has also being conducted . This was an exploratory study to evaluate the safety and antibody responses to each component of MMR II (Attenuvax measles live-attenuated vaccine, Jeryl Lynn mumps live-attenuated vaccine and L-Zagreb mumps live-attenuated vaccine) in healthy adults 21–38 years of age. The investigators chose to use the AeronebGo® device because previous studies with aerosolized Schwarz measles vaccine (similar to the Attenuvax base sequence) showed rapid degradation of vaccine potency using a jet nebulizer and compressed air system. Results from the more recent study showed that aerosolization of the three components of MMRII vaccine was safe and produced secondary immune responses in healthy adults. Similar safety studies need to be performed in children.
Unlike aerosol applications for systemic drug delivery and gene therapy, immunization by inhalation does not require chronic repeat dosing for efficacy. For many vaccines, immunization may be achieved with 1–2 aerosol treatments followed by a booster treatment. Thus, there is less concern about the safety of repeated lung dosing with immunization by inhalation, compared to systemic drug delivery and gene therapy by inhalation. Nevertheless, safety remains an issue with inhaled vaccines because some patient populations (e.g. patients with allergic asthma) may be more sensitive to excipients in the formulations and care-givers who are immunosuppressed may be more vulnerable to vaccine exposure than non-immunosuppressed individuals.
Vaccination by inhalation is a promising new method for immunization. It has already been used in large populations and appears to be a feasible method for mass vaccinations. Recent developments in device innovation have made reliable, portable aerosol dosing in mass campaigns possible. Improvements in delivery to infants and in the development of vaccines that do not require refrigeration (i.e. powders) and are stable at the ambient temperatures of the tropics could make this the preferred route of administration for a number of vaccines in the future.
The role of aerosol therapy has changed over the years to now include systemic drug delivery by inhalation, inhaled gene therapy and vaccination by inhalation. Each of these new applications has led to the development of new delivery devices and achieved varying degrees of success in treating their disease targets. The continued expansion of the role of aerosol therapy in the future will depend on: (1) improving the bioavailability of systemically delivered drugs; (2) developing gene therapy vectors that can efficiently penetrate the airway mucus barrier and cell membrane, navigate the cell cytoplasm and efficiently transfer DNA material to the cell nucleus; (3) improving delivery of gene vectors and vaccines to infants; and (4) developing formulations that are safe for acute and chronic administrations.
- Global Initiative for Asthma (GINA), National Heart Lung and Blood Institute, National Institutes of Health: GINA report. Global strategy for asthma management and prevention. Bethesda: National Institutes of Health; 2006.Google Scholar
- Global Initiative for Obstructive Lung Disease (GOLD), National Heart Lung and Blood Institute, National Institutes of Health: GOLD report. Global strategy for diagnosis, management and prevention of COPD. Bethesda: National Institutes of Health; 2009.Google Scholar
- Flume PA, O’Sullivan BP, Robinson KA, Goss CH, Mogayzel PJ Jr, Willey-Courand DB, Bujan J, Finder J, Lester M, Quittell L, Rosenblatt R, Vender RL, Hazle L, Sabadosa K, Marshall B: Cystic fibrosis pulmonary guidelines: chronic medications for maintenance of lung health. Am J Respir Crit Care Med 2007, 176: 957–969. 10.1164/rccm.200705-664OCView ArticleGoogle Scholar
- Heijerman H, Westerman E, Conway S, Touw D, Döring G, consensus working group: Inhaled medication and inhalation devices for lung disease in patients with cystic fibrosis: a European consensus. J Cyst Fibros 2009, 8: 295–315. 10.1016/j.jcf.2009.04.005View ArticleGoogle Scholar
- Laube BL, Janssens HM, de Jongh FH, Devadason SG, Dhand R, Diot P, Everard ML, Horvath I, Navalesi P, Voshaar T, Chrystyn H: What the pulmonary specialist should know about the new inhalation therapies. Eur Respir J 2011, 37: 1308–1331. 10.1183/09031936.00166410View ArticleGoogle Scholar
- Carter NJ, Curran MP: Live attenuated influenza vaccine (FluMist ® ; Fluenz™): a review of its use in the prevention of seasonal influenza in children and adults. Drugs 2011, 71: 1591–1622. 10.2165/11206860-000000000-00000View ArticleGoogle Scholar
- Drugs for postmenopausal osteoporosis Treat Guidel Med Lett 2008, 6: 67–74.
- Vestergaard P, Mosekilde L, Langdahl B: Fracture prevention in postmenopausal women. Clin Evid 2011, 05: 1109.Google Scholar
- Pillow JJ, Minocchieri S: Innovation in surfactant therapy II: surfactant administration by aerosolization. Neonatology 2012, 101: 337–344.Google Scholar
- Möller W, Lübbers C, Münzing W, Canis M: Pulsating airflow and drug delivery to paranasal sinuses. Curr Opin Otolaryngol Head Neck Surg 2011, 19: 48–53. 10.1097/MOO.0b013e3283420f39View ArticleGoogle Scholar
- Durand M, Le Guellec S, Pourchez J, Dubois F, Aubert G, Chantrel G, Vecellio L, Hupin C, De Gersem R, Reychler G, Pitance L, Diot P, Jamar F: Sonic aerosol therapy to target maxillary sinuses. Eur Ann Otorhinolaryngol Head Neck Dis 2012, 129: 244–250. 10.1016/j.anorl.2011.09.002View ArticleGoogle Scholar
- Silberstein SD, Kori SH: Dihydroergotamine: a review of formulation approaches for the acute treatment of migraine. CNS Drugs 2013, 27: 385–394. 10.1007/s40263-013-0061-2View ArticleGoogle Scholar
- Carr WW: New therapeutic options for allergic rhinitis: back to the future with intranasal corticosteroid aerosols. Am J Rhinol Allergy 2013, 27: 309–313. 10.2500/ajra.2013.27.3946View ArticleGoogle Scholar
- Podolska K, Stachurska A, Hajdukiewicz K, Małecki M: Gene therapy prospects–intranasal delivery of therapeutic genes. Adv Clin Exp Med 2012, 21: 525–534.Google Scholar
- Laube BL: The expanding role of aerosols in systemic drug delivery, gene therapy, and vaccination. Respir Care 2005, 50: 1161–1174.Google Scholar
- Alexander-Williams JM, Rowbotham DJ: Novel routes of opioid administration. Br J Anaesth 1998, 81: 3–7. 10.1093/bja/81.1.3View ArticleGoogle Scholar
- Thipphawong J, Babul N, Morishige R, Morishige RJ, Findlay HK, Reber KR, Millward GJ, Otulana BA: Analgesic efficacy of inhaled morphine in patients after bunionectomy surgery. Anesthesiology 2003, 99: 693–700. 10.1097/00000542-200309000-00026View ArticleGoogle Scholar
- Aurora SK, Silberstein SD, Kori SH, Tepper SJ, Borland SW, Wang M, Dodick DW: MAP0004, orally inhaled DHE: a randomized, controlled study in the acute treatment of migraine. Headache 2011, 51: 507–517. 10.1111/j.1526-4610.2011.01869.xView ArticleGoogle Scholar
- International Diabetes Federation Diabetes Atlas: International Diabetes Federation Diabetes Atlas. 5th edition. http://www.idf.org/diabetesatlas/5e/the-global-burden
- Wigley FM, Londono JH, Wood SH, Shipp JC, Waldman RH: Insulin across respiratory mucosae by aerosol delivery. Diabetes 1971, 20: 552–556.View ArticleGoogle Scholar
- Elliott RB, Edgar BW, Pilcher CC, Quested C, McMaster J: Parenteral absorption of insulin from the lung in diabetic children. Aust Paediatr J 1987, 23: 293–297.Google Scholar
- Adjei AL, Fu Lu M-Y: LH-RH Analogs. In Inhalation delivery of therapeutic peptides and proteins. Edited by: Adjei AL, Gupta PK. New York: Marcel Dekker; 1997:389–412.Google Scholar
- Laube BL, Georgopoulos A, Adams GK 3rd: Preliminary study of the efficacy of insulin aerosol delivered by oral inhalation in diabetic subjects. JAMA 1993, 269: 2106–2109. 10.1001/jama.1993.03500160076035View ArticleGoogle Scholar
- Laube BL, Benedict GW, Dobs AS: Time to peak insulin level, relative bioavailability, and effect of site of deposition of nebulized insulin in patients with noninsulin-dependent diabetes mellitus. J Aerosol Med 1998, 11: 153–173. 10.1089/jam.1998.11.153View ArticleGoogle Scholar
- Cefalu WT, Skyler JS, Kourides IA, Landschulz WH, Balagtas CC, Cheng S, Gelfand RA, Inhaled Insulin Study Group: Inhaled human insulin treatment in patients with type 2 diabetes mellitus. Ann Intern Med 2001, 134: 203–207. 10.7326/0003-4819-134-3-200102060-00011View ArticleGoogle Scholar
- Skyler JS, Cefalu WT, Kourides IA, Landschulz WH, Balagtas CC, Cheng SL, Gelfand RA: Efficacy of inhaled human insulin in type 1 diabetes mellitus: a randomized proof-of-concept study. Lancet 2001, 357: 331–335. 10.1016/S0140-6736(00)03638-2View ArticleGoogle Scholar
- Harper NJ, Gray S, de Groot J, Parker JM, Sadrzadeh N, Schuler C, Schumacher JD, Seshadri S, Smith AE, Steeno GS, Stevenson CL, Taniare R, Wang M, Bennett DB: The design and performance of the Exubera ® pulmonary insulin delivery system. Diabetes Technol Ther 2007, 9(Suppl 1):S16-S27.Google Scholar
- Cefalu WT, Wang ZQ: Clinical research obsevations with use of Exubera ® in patients with type 1 and type 2 diabetes. Diabetes Technol Ther 2007, 9(Suppl 1):S28-S40.Google Scholar
- Wollmer P, Pieber TR, Gall M-A, Brunton S: Delivering needle-free insulin using the AERx ® IDMS (insulin diabetes management system) technology. Diabetes Techol Ther 2007, 9(Suppl 1):S57-S64.Google Scholar
- Muchmore DB, Silverman B, de la Pena A, Tobian J: The Air ® inhaled insulin system: system components and pharmacokinetic/glucodynamic data. Diabetes Technol Ther 2007, 9(Suppl 1):S41-S47.Google Scholar
- Ellis SL, Gemperline KA, Garg S: Review of phase 2 studies utilizing the Air ® particle technology in the delivery of human insulin inhalation powder versus subcutaneous regular or lispro insulin in subjects with type 1 or type 2 diabetes. Diabetes Technol Ther 2007, 9(Suppl 1):S48-S56.Google Scholar
- Wall Street Journal On-Line . http://online.wsj.com/article/SB119269071993163273.html
- Skyler JS, Jovanovic L, Klioze S, Reis J, Duggan W, Inhaled Human Insulin Type 1 Diabetes Study Group: Two-year safety and efficacy of inhaled human insulin (Exubera) in adult patients with type 1 diabetes. Diabetes Care 2007, 30: 579–585. 10.2337/dc06-1863View ArticleGoogle Scholar
- MannKind Corporation. http://www.mannkindcorp.com/product-pipeline-diabetes-afrezza.htm
- Rosenstock J, Bergenstal R, DeFronzo RA, Hirsch IB, Klonoff D, Boss AH, Kramer D, Petrucci R, Yu W, Levy B, for the 0008 Study Group: Efficacy and safety of technosphere inhaled insulin compared with technosphere powder placebo in insulin-naïve type 2 diabetes suboptimally contolled with oral agents. Diabetes Care 2008, 31: 2177–2182. 10.2337/dc08-0315View ArticleGoogle Scholar
- Rosenstock J, Lorber DL, Gnudi L, Howard CP, Bilheimer DW, Chang PC, Petrucci RE, Boss AH, Richardson PC: Prandial inhaled insulin plus basal insulin glargine versus twice daily biaspart insulin for type 2 diabetes: a multicentre randomised trial. Lancet 2010, 375: 2244–2253. 10.1016/S0140-6736(10)60632-0View ArticleGoogle Scholar
- Neumiller JJ, Campbell RK, Wood LD: A review of inhaled technosphere insulin. Ann Pharmacother 2010, 44: 1231–1239. 10.1345/aph.1P055View ArticleGoogle Scholar
- Codrons V, Vanderbist F, Ucakar B, Preat V, Vanbever R: Impact of formulation and methods of pulmonary delivery on absorption of parathyroid hormone (1–34) from rat lungs. J Pharm Sci 2004, 93: 1241–1252. 10.1002/jps.20053View ArticleGoogle Scholar
- Bosquillon C, Preat V, Vanbever R: Pulmonary delivery of growth hormone using dry powders and visualization of its local fate in rats. J Control Release 2004, 96: 233–244. 10.1016/j.jconrel.2004.01.027View ArticleGoogle Scholar
- Todo H, Okamoto H, Iida K, Danjo K: Effect of additives on insulin absorption from intratracheally administered dry powders in rats. Int J Pharm 2001, 220: 101–110. 10.1016/S0378-5173(01)00662-7View ArticleGoogle Scholar
- Sakagami M, Sakon K, Kinoshita W, Makino Y: Enhanced pulmonary absorption following aerosol administration of mucoadhesive powder microspheres. J Control Release 2001, 77: 117–129. 10.1016/S0168-3659(01)00475-8View ArticleGoogle Scholar
- Seow Y, Wood MJ: Biological gene delivery vehicles: Beyond viral vectors. Mol Ther 2009, 17: 767–777. 10.1038/mt.2009.41View ArticleGoogle Scholar
- Mali S: Delivery systems for gene therapy. Indian J Hum Genet 2013, 19: 3–8. 10.4103/0971-6866.112870View ArticleGoogle Scholar
- Pichon C, Billiet L, Midoux P: Chemical vectors for gene delivery: uptake and intracellular trafficking. Curr Opin Biotechnol 2010, 21: 640–645. 10.1016/j.copbio.2010.07.003View ArticleGoogle Scholar
- Griesenbach U, Alton EW: Expert opinion in biological therapy: update on developments in lung gene transfer. Expert Opin Biol Ther 2013, 13: 345–360. 10.1517/14712598.2013.735656View ArticleGoogle Scholar
- Virella-Lowell I, Zusman B, Foust K, Loiler S, Conlon T, Song S, Chesnut KA, Ferkol T, Flotte TR: Enhancing rAAV vector expression in the lung. J Gene Med 2005, 7: 842–850. 10.1002/jgm.759View ArticleGoogle Scholar
- Sirninger J, Muller C, Braag S, Tang Q, Yue H, Detrisac C, Ferkol T, Guggino WB, Flotte TR: Functional characterization of a recombinant adeno-associated virus 5-pseudotyped cystic fibrosis transmembrane conductance regulator vector. Hum Gene Ther 2004, 15: 832–841.Google Scholar
- Griesenbach U, Alton EW: Progress in gene and cell therapy for cystic fibrosis lung disease. Curr Pharm Des 2012, 18: 642–662. 10.2174/138161212799315993View ArticleGoogle Scholar
- Cystic Fibrosis Foundation Patient Registry Annual Data Report to the Center Directors. Bethesda, Maryland: Cystic Fibrosis Foundation; 2011. http://www.cff.org/UploadedFiles/Research/ClinicalResearch/2011-Patient-Registry.pdf
- Griesenbach U, Alton EW: Gene transfer to the lung: lessons learned from more than 2 decades of CF gene therapy. Adv Drug Deliv Rev 2009, 61: 128–139. 10.1016/j.addr.2008.09.010View ArticleGoogle Scholar
- Moss RB, Rodman D, Spencer LT, Aitken ML, Zeitlin PL, Waltz D, Milla C, Brody AS, Clancy JP, Ramsey B, Hamblett N, Heald AE: Repeated adeno-associated virus serotype 2 aerosol-mediated cystic fibrosis transmembrane regulator gene transfer to the lungs of patients with cystic fibrosis: a multicenter, double-blind, placebo-controlled trial. Chest 2004, 125: 509–521. 10.1378/chest.125.2.509View ArticleGoogle Scholar
- Moss RB, Milla C, Colombo J, Accurso F, Zeitlin PL, Clancy JP, Spencer LT, Pilewski J, Waltz DA, Dorkin HL, Ferkol T, Pian M, Ramsey B, Carter BJ, Martin DB, Heald AE: Repeated aerosolized AAV-CFTR for treatment of cystic fibrosis: a randomized placebo-controlled phase 2B trial. Hum Gene Ther 2007, 18: 726–732. 10.1089/hum.2007.022View ArticleGoogle Scholar
- Hyde SC, Pringle IA, Abdullah S, Lawton AE, Davies LA, Varathalingam A, Nunez-Alonso G, Green AM, Bazzani RP, Sumner-Jones SG, Chan M, Li H, Yew NS, Cheng SH, Boyd AC, Davies JC, Griesenbach U, Porteous DJ, Sheppard DN, Munkonge FM, Alton EW, Gill DR: CpG-free plasmids confer reduced inflammation and sustained pulmonary gene expression. Nat Biotechnol 2008, 26: 549–551. 10.1038/nbt1399View ArticleGoogle Scholar
- Alton EW, Boyd AC, Cheng SH, Cunningham S, Davies JC, Gill DR, Griesenbach U, Higgins T, Hyde SC, Innes JA, Murray GD, Porteous DJ: A randomised, double-blind, placebo-controlled phase IIB clinical trial of repeated application of gene therapy in patients with cystic fibrosis. Thorax doi:10.1136/thoraxjnl-2013–203309. Epub ahead of print
- Griesenbach U, Alton EW: Moving forward: cystic fibrosis gene therapy. Hum Mol Genet 2013, 22(R1):R52-R58. 10.1093/hmg/ddt372View ArticleGoogle Scholar
- Thomas C, Rawat A, Hope-Weeks L, Ahsan F: Aerosolized PLA and PLGA nanoparticles enhance humoral, mucosal and cytokine responses to hepatitis B vaccine. Mol Pharm 2011, 8: 405–415. 10.1021/mp100255cView ArticleGoogle Scholar
- Muttil P, Prego C, Garcia-Contreras L, Pulliam B, Fallon JK, Wang C, Hickey AJ, Edwards D: Immunization of guinea pigs with novel hepatitis B antigen as nanoparticle aggregate powders administered by the pulmonary route. AAPS J 2010, 12: 330–337. 10.1208/s12248-010-9192-2View ArticleGoogle Scholar
- Thomas C, Gupta V, Ahsan F: Particle size influences the immune response produced by hepatitis B vaccine formulated in inhalable particles. Pharm Res 2010, 27: 905–919. 10.1007/s11095-010-0094-xView ArticleGoogle Scholar
- Betancourt AA, Delgado CA, Estévez ZC, Martínez JC, Ríos GV, Aureoles-Roselló SR, Zaldívar RA, Guzmán MA, Baile NF, Reyes PA, Ruano LO, Fernández AC, Lobaina-Matos Y, Fernández AD, Madrazo AI, Martínez MI, Baños ML, Alvarez NP, Baldo MD, Mestre RE, Pérez MV, Martínez ME, Escobar DA, Guanche MJ, Cáceres LM, Betancourt RS, Rando EH, Nieto GE, González VL, Rubido JC: Phase I clinical trial in healthy adults of a nasal vaccine candidate containing recombinant hepatitis B surface and core antigens. Int J Infect Dis 2007, 11: 394–401. 10.1016/j.ijid.2006.09.010View ArticleGoogle Scholar
- Muttil P, Pulliam B, Garcia-Contreras L, Fallon JK, Wang C, Hickey AJ, Edwards DA: Pulmonary immunization of guinea pigs with diphtheria CRM-197 antigen as nanoparticle aggregate dry powders enhance local and systemic immune responses. AAPS J 2010, 12: 699–707. 10.1208/s12248-010-9229-6View ArticleGoogle Scholar
- Hickey AJ, Misra A, Fourie PB: Dry Powder Antibiotic Aerosol Product Development: Inhaled Therapy for Tuberculosis. J Pharm Sci 2013, 102: 3900–3907.View ArticleGoogle Scholar
- Gao X-F, Yang Z-W, Li J: Adjunctive therapy with interferon-gamma for the treatment of pulmonary tuberculosis: a systematic review. Int J Infect Dis 2011, 15: e594-e600. 10.1016/j.ijid.2011.05.002View ArticleGoogle Scholar
- Dharmadhikari AS, Kabadi M, Gerety B, Hickey AJ, Fourie PB, Nardell E: Phase I, single-dose, resistant tuberculosis. Antimicrob Agents Chemother 2013, 57: 2613–2619. 10.1128/AAC.02346-12View ArticleGoogle Scholar
- Garcia-Contreras L, Awashthi S, Hanif SNM, Hickey AJ: Inhaled vaccines for the prevention of tuberculosis. J Mycobac Dis 2012, S1: 002.Google Scholar
- Ballester M, Nembrini C, Dhar N, de Titta A, de Piano C, Pasquier M, Simeoni E, van der Vlies AJ, McKinney JD, Hubbell JA, Swartz MA: Nanoparticle conjugation and pulmonary delivery enhance the protective efficacy of Ag85B and CpG against tuberculosis. Vaccine 2011, 29: 6959–6966. 10.1016/j.vaccine.2011.07.039View ArticleGoogle Scholar
- Garcia-Contreras L, Wong YL, Muttil P, Padilla D, Sadoff J, Derousse J, Germishuizen WA, Goonesekera S, Elbert K, Bloom BR, Miller R, Fourie PB, Hickey A, Edwards D: Immunization by a bacterial aerosol. Proc Natl Acad Sci USA 2008, 105: 4656–4660. 10.1073/pnas.0800043105View ArticleGoogle Scholar
- Nardelli-Haefliger D, Lurati F, Wirthner D, Spertini F, Schiller JT, Lowy DR, Ponci F, De Grandi P: Immune responses induced by lower airway mucosal immunisation with a human papillomavirus type 16 virus-like particle vaccine. Vaccine 2005, 23: 3634–3641. 10.1016/j.vaccine.2005.02.019View ArticleGoogle Scholar
- Gordon SB, Malamba R, Mthunthama N, Jarman ER, Jambo K, Jere K, Zijlstra EE, Molyneux ME, Dennis J, French N: Inhaled delivery of 23-valent pneumococcal polysaccharide vaccine does not result in enhanced pulmonary mucosal immunoglobulin responses. Vaccine 2008, 26: 5400–5406. 10.1016/j.vaccine.2008.07.082View ArticleGoogle Scholar
- Centers for Disease Control and Prevention. http://www.cdc.gov/globalhealth/measles/challenges/
- Sabin AB, Flores AA, de Castro JF, Sever JL, Madden DL, Shekarchi I, Albrecht P: Successful immunization of children with and without maternal antibody by aerosolized measles vaccine. I. Different results with human diploid cell and chick embryo fibroblast vaccines. JAMA 1983, 249: 2651–2662. 10.1001/jama.1983.03330430027025View ArticleGoogle Scholar
- Sabin AB, Flores AA, de Castro JF, Albrecht P, Sever JL, Shekarchi I: Successful immunization of infants with and without maternal antibody by aerosolized measles vaccine. II. Vaccine comparisons and evidence for multiple antibody response. JAMA 1984, 251: 2363–2371. 10.1001/jama.1984.03340420029022View ArticleGoogle Scholar
- Bennett JV, de Castro JF, Valdespino-Gomez JL, Garcia-Garcia ML, Islas-Romero R, Echaniz-Aviles G, Jimenez-Corona A, Sepulveda-Amor J: Aerosolized measles and measles-rubella vaccines induce better measles antibody booster responses than injected vaccines: randomized trials in Mexican school children. Bull World Health Organ 2002, 80: 806–812.Google Scholar
- Dilraj A, Cutts FT, de Castro JF, Wheeler JG, Brown D, Roth C, Coovadia HM, Bennett JV: Response to different measles vaccine strains given by aerosol and subcutaneous routes to school children: a randomized trial. Lancet 2000, 355: 798–803. 10.1016/S0140-6736(99)95140-1View ArticleGoogle Scholar
- Low N, Kraemer S, Schneider M, Restrepo AMH: Immunogenicity and safety of aerosolized measles vaccine: Systematic review and meta-analysis. Vaccine 2008, 26: 383–398. 10.1016/j.vaccine.2007.11.010View ArticleGoogle Scholar
- Diaz-Ortega J-L, Bennett JV, Castaneda D, Arellano DM, Martinez D, de Castro Fernandez J: Safety and antibody responses to aerosolized MMR II vaccine in adults: An exploratory study. World Journal of Vaccines 2012, 2: 55–60. 10.4236/wjv.2012.22008View ArticleGoogle Scholar
- Lin WH, Griffin DE, Rota PA, Papania M, Cape SP, Bennett D, Quinn B, Sievers RE, Shermer C, Powell K, Adams RJ, Godin S, Winston S: Successful respiratory immunization with dry powder live-attenuated measles virus vaccine in rhesus macaques. Proc Natl Acad Sci USA 2011, 108: 2987–2992. 10.1073/pnas.1017334108View ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.