Thursday, March 23, 2017
Food allergy is the leading cause of anaphylaxis, a serious and life-threatening systemic allergic reaction, among American children today. Although it can be managed by avoidance and supportive management, there are few options for disease modification. Oral immunotherapy (OIT) whereby increasing doses of an allergen are given, has been a promising investigational treatment, but the high rates of adverse reactions and intolerance of symptoms lead to high drop-out rates. In this month’s issue of JACI, MacGinnitie et al look at the use of omalizumab, an anti-IgE medication used in asthma, in helping to facilitate OIT (J Allergy Clin Immunol 2017; 139(3): 873-881).
To do this, they randomized 37 participants to receive either omalizumab or a placebo for 19 weeks, in addition to oral immunotherapy. Neither the patients nor the researchers knew the assignment of the groups. 6 weeks after stopping the omalizumab, it was found that a majority (79%) of the omalizumab group was able to achieve the 2000-mg maintenance dose. Even 12 weeks after stopping the omalizumab, 76% were able to tolerate even higher doses of peanut protein (4000mg). Even though the reaction rates were not statistically different between the two groups, the omalizumab group was also exposed to higher doses of peanut proteins.
Despite the small number of participants, this is encouraging news for the use of omalizumab as an adjunct for peanut oral desensitization. The authors suggest that the benefits of omalizumab-enabled OIT may outweigh the downsides of its expense, repeat injections, and risk of hypersensitivity reactions.
Body fat mass distribution and interrupter resistance, fractional exhaled nitric oxide, and asthma at school-age
Obesity and asthma are two of the most common childhood chronic diseases, seen in 25% and 10% of children, respectively. There are increasing lines of evidence suggesting that they may be inter-dependent : fat may be the source of proinflammatory mediators and may change the mechanics of lung function.
However, not all fat is considered equal. The android distribution of fat along the abdomen, compared to gynoid distribution along the hips, is more closely associated with a variety of cardiometabolic diseases. Similarly, visceral fat, situated just above the guts in the belly, is considered a marker of inflammatory status, compared to more superficial subcutaneous fat deposits. In this month’s issue of JACI, den Dekker and colleagues discuss the effect of body fat mass distribution on asthma and airway function in children (J Allergy Clin Immunol 2017; 139(3): 810-816).
To do this, they looked at the medical histories and physical characteristics of 6178 children. They focused on body-mass index (BMI), total and abdominal fat measures using ultrasonography and dual energy x-ray absorptiometry (DEXA), respiratory resistance (Rint), fractional exhaled nitric oxide (FENO), wheezing, and asthma. They found that a higher BMI was associated with increased respiratory resistance and current wheezing. They also noted that more visceral fat was associated with a higher FENO, while a higher android (belly)/gynoid (hip) ratio was associated with a lower FENO.
Altogether, these results suggest that local fat deposition, especially visceral fat, is more closely related to asthma. Even though the reasons for this are unclear, the authors speculate that maybe the different metabolic profiles of visceral vs. subcutaneous fat and the mechanical effects may be responsible for these differences. Regardless, understanding the finer details of fat composition and distribution may help to explain part of the increased prevalence of childhood asthma.
Novel baseline predictors of adverse events during oral immunotherapy in children with peanut allergy
Food allergy is a huge problem affecting 3 to 8% of school-age children. So far, avoidance and supportive management have been the mainstays of therapy, but this is rapidly changing with studies showing the efficacy of oral immunotherapy (OIT), especially for peanut allergies. In peanut OIT, gradually increasing doses of peanut are given as part of the buildup, with steady doses given during maintenance. The hope is to desensitize the immune system so that reactions are not as severe. In this month’s issue of JACI, Virkud and colleagues discuss the safety of oral immunotherapy to peanut by examining 104 patients from 3 peanut OIT trials (J Allergy Clin Immunol 2017; 139(3): 882-888). They look at the past medical history, parental reports, daily symptom diaries, and relationship to dose escalations to determine the risks and predictors of adverse effects (AEs).
The rate of AEs was high, with 80% experiencing at least 1 episode, and over 90% of these occurring at home. 42% of AEs were systemic reactions, but fewer than 50% received epinephrine, indicating a need for better patient education. About half of these AEs were gastrointestinal, and half of the patients who dropped out did so due to these gastrointestinal AEs; this amounted to 10% of all enrolled patients.
Overall, allergic rhinitis and the wheal size on peanut skin prick testing (SPT) were significant predictors of AEs. Allergic rhinitis approximately doubled the likelihood of having an AE, and seemed to explain why there was a higher rate of AEs during the spring and the fall. Asthma was also predictive of AEs during maintenance, but not in the buildup phase. Gastrointestinal AEs, like abdominal pain, nausea, vomiting, difficulty swallowing, and diarrhea, were also associated with the peanut SPT wheal size.
While there remains a lot to be learned about oral immunotherapy, this study helps to determine who would be the best candidates for this promising means of treating food allergies. Virkud and colleagues conclude that until there are rigorous well-designed and controlled trials, avoidance should remain the current standard of care.
Treatment of infants identified as having severe combined immunodeficiency by means of newborn screening
Severe Combined Immunodeficiency (SCID) is a set of fatal immune disorders in which infants are born without proper functioning immune systems needed to fight off infections. Fortunately, in recent years, there has been a push in several states for newborn screening (NBS) for early identification and life-saving treatment of these children. In this month’s issue of JACI, Dorsey and colleagues describe the protocol that they use in California, which has successfully identified 32 SCID patients and 46 non-SCID patients with decreased levels of T-cells (J Allergy Clin Immunol 2017; 139(3): 733-742).
Newborn screening is performed by measuring TRECs (T-cell receptor excision circles) which are formed upon gene rearrangement of the T-cell receptor. Peripheral blood count with differential and flow cytometry is the first follow up testing to determine the number of lymphocytes. This is followed by functional lymphocyte testing. If SCID is suspected, then children are placed in protective isolation and aggressively treated with antibiotics if needed. A SCID social worker coordinates with family in order to manage workup and identify needs for support, including emotional support.
Because allogenic and autologous hematopoietic stem cell (HSC) transplant is life-saving, Dorsey and colleagues relay that they apply three principles: (1) use of a donor with the least likelihood of graft-versus-host disease (GVHD), (2) minimize the duration of waiting for the SCT, and (3) use the least amount of chemotherapy necessary. Adherence to these principles has led to good outcomes: among the 32 that underwent transplant, 29 (94%) are alive and well.
Among the non-SCID patients, the protocol is more reliant on the degree of immunodeficiency, but nevertheless, they are followed up very closely by immunologists in the coming years to identify the status of their immune dysfunction. There remains a lot of work to be done in order to find out the best way to identify and treat SCID, but nationwide screening promises to accelerate our reaching that goal.