Venom immunotherapy: an updated review.

Venom immunotherapy (VIT) is the most effective form of specific immunotherapy to date. Hitherto, several relevant queries remain unanswered, namely optimal doses, duration, and means of assessment. Important progress has been lately made in terms of diagnosis by means of component-resolved diagnosis. Moreover, basophil activation test results in patients with negative serum immunoglobulin E (IgE) and skin prick test confer this technique a promising future, although these outcomes shall be considered with caution. This review aims to unravel the important advances made on diagnosis, management, and prognosis and also focuses on several undetermined aspects of VIT.

Nonaggressive systemic mastocytosis (SM) without skin lesions associated with insect-induced anaphylaxis shows unique features versus other indolent SM.

BACKGROUND: Indolent systemic mastocytosis (ISM) without skin lesions (ISMs(-)) shows a higher prevalence in males, lower serum baseline tryptase levels, and KIT mutation more frequently restricted to bone marrow (BM) mast cells (MCs) than ISM with skin lesions (ISMs(+)). Interestingly, in almost one-half of ISMs(-) patients, MC-mediator release episodes are triggered exclusively by insects. OBJECTIVE: We aimed to determine the clinical and laboratory features of ISMs(-) associated with insect-induced anaphylaxis (insectISMs(-)) versus other patients with ISM. METHODS: A total of 335 patients presenting with MC activation syndrome, including 143 insectISMs(-), 72 ISMs(-) triggered by other factors (otherISMs(-)), 56 ISMs(+), and 64 nonclonal MC activation syndrome, were studied. RESULTS: Compared with otherISMs(-) and ISMs(+) patients, insectISMs(-) cases showed marked male predominance (78% vs 53% and 46%; P < .001), a distinct pattern of MC-related symptoms, and significantly lower median serum baseline tryptase levels (22.4 vs 28.7 and 45.8 µg/L; P ≤ .009). Moreover, insectISMs(-) less frequently presented BM MC aggregates (46% vs 70% and 81%; P ≤ .001), and they systematically showed MC-restricted KIT mutation. CONCLUSIONS: ISMs(-) patients with anaphylaxis triggered exclusively by insects display clinical and laboratory features that are significantly different from other ISM cases, including other ISMs(-) and ISMs(+) patients, suggesting that they represent a unique subgroup of ISM with a particularly low BM MC burden in the absence of adverse prognostic factors.

Venom immunotherapy in patients with clonal mast cell disorders: efficacy, safety, and practical considerations.

BACKGROUND: A preferential association between systemic mastocytosis (SM) and hymenoptera allergy (HVA) has been observed. Patients with both diseases are at risk for more severe reactions, and venom immunotherapy (VIT) may represent a life-saving treatment, but the use of VIT in such patients raised concerns about its safety. OBJECTIVE: We evaluated a large population of patients with SM and HVA who received VIT. METHODS: This prospective study was performed in Italy and Spain. A diagnosis of SM and HVA and a VIT prescription were made according to international recommendations. The patients were carefully followed up during VIT, with special attention to field stings. RESULTS: A total of 84 patients (70 men, 14 women; mean age 52.1 years) were included, 81% with grade IV reaction, 91% with indolent SM. No difference was seen between the Italian and Spanish patients. There were 10 adverse reactions during the induction phase: 3 with the conventional induction and 7 with the rush-modified induction, none resulted in epinephrine administration and/or hospitalization. Fifty patients had one or more field re-sting (95 episodes), none during induction. The time elapsed from starting VIT and first re-sting was 2 months to 7 years, and the number of re-stings per patient was 1-6. Of the 50 patients who were re-stung, 43 (86%) resulted in being fully protected. Seven patients had reactions, and the maintenance dose was safely increased to 200 mcg. The maintenance dose interval was not different between patients with and those without reactions at re-stings. CONCLUSION: VIT is well tolerated, safe, and effective in patients with SM.

Venom immunotherapy in patients with mastocytosis and hymenoptera venom anaphylaxis.

Systemic mastocytosis (SM) is typically suspected in patients with cutaneous mastocytosis (CM). In recent years, the presence of clonal mast cells (MCs) in a subset of patients with systemic symptoms associated with MC activation in the absence of CM has been reported and termed monoclonal MC activation syndromes or clonal systemic MC activation syndromes. In these cases, bone marrow (BM) MC numbers are usually lower than in SM with CM, there are no detectable BM MC aggregates, and serum baseline tryptase is often <20 µg/l; thus, diagnosis of SM in these patients should be based on careful evaluation of other minor WHO criteria for SM in reference centers, where highly sensitive techniques for immunophenotypic analysis and investigation of KIT mutations on fluorescence-activated cell sorter-purified BM MCs are routinely performed. The prevalence of hymenoptera venom anaphylaxis (HVA) among SM patients is higher than among the normal population and it has been reported to be approximately 5%. In SM patients with IgE-mediated HVA, venom immunotherapy is safe and effective and it should be prescribed lifelong. Severe adverse reactions to hymenoptera stings or venom immunotherapy have been associated with increased serum baseline tryptase; however, presence of clonal MC has not been ruled out in most reports and thus both SM and clonal MC activation syndrome might be underdiagnosed in such patients. In fact, clonal BM MC appears to be a relevant risk factor for both HVA and severe reactions to venom immunotherapy, while the increase in serum baseline tryptase by itself should be considered as a powerful surrogate marker for anaphylaxis. The Spanish Network on Mastocytosis has developed a scoring system based on patient gender, the clinical symptoms observed during anaphylaxis and serum baseline tryptase to predict for the presence of both MC clonality and SM among individuals who suffer from anaphylaxis.

Clinical, biological, and molecular characteristics of clonal mast cell disorders presenting with systemic mast cell activation symptoms.

BACKGROUND: Systemic mast cell activation disorders (MCADs) are characterized by severe and systemic mast cell (MC) mediators-related symptoms frequently associated with increased serum baseline tryptase (sBt). OBJECTIVE: To analyze the clinical, biological, and molecular characteristics of adult patients presenting with systemic MC activation symptoms/anaphylaxis in the absence of skin mastocytosis who showed clonal (c) versus nonclonal (nc) MCs and to provide indication criteria for bone marrow (BM) studies. METHODS: Eighty-three patients were studied. Patients showing clonal BM MCs were grouped into indolent systemic mastocytosis without skin lesions (ISMs(-); n = 48) and other c-MCADs (n = 3)-both with CD25(++) BM MCs and either positive mast/stem cell growth factor receptor gene (KIT) mutation or clonal human androgen receptor assay (HUMARA) tests-and nc-MCAD (CD25-negative BM MCs in the absence of KIT mutation; n = 32) and compared for their clinical, biological, and molecular characteristics. RESULTS: Most clonal patients (48/51; 94%) met the World Health Organization criteria for systemic mastocytosis and were classified as ISMs(-), whereas the other 3 c-MCAD and all nc-MCAD patients did not. In addition, although both patients with ISMs(-) and patients with nc-MCAD presented with idiopathic and allergen-induced anaphylaxis, the former showed a higher frequency of men, cardiovascular symptoms, and insect bite as a trigger, together with greater sBt. Based on a multivariate analysis, a highly efficient model to predict clonality before BM sampling was built that includes male sex (P = .01), presyncopal and/or syncopal episodes (P = .009) in the absence of urticaria and angioedema (P = .003), and sBt >25 microg/L (P = .006) as independent predictive factors. CONCLUSIONS: Patients with c-MCAD and ISMs(-) display unique clinical and laboratory features different from nc-MCAD patients. A significant percentage of c-MCAD patients can be considered as true ISMs(-) diagnosed at early phases of the disease.

Safety and effectiveness of immunotherapy in patients with indolent systemic mastocytosis presenting with Hymenoptera venom anaphylaxis.

BACKGROUND: Anaphylaxis after Hymenoptera sting has been described in patients with mastocytosis. Venom immunotherapy (VIT) is a safe and effective way to treat patients with Hymenoptera anaphylaxis, but few studies have addressed its usefulness in patients with systemic mastocytosis. OBJECTIVE: To study the effectiveness and safety of VIT in patients with systemic mastocytosis having anaphylaxis after Hymenoptera sting. METHODS: A total of 21 mastocytosis patients-4 women (19%) and 17 men (81%) with a median age of 50 years (range, 29-74 years)-with Hymenoptera sting anaphylaxis who were treated with VIT and followed for a median of 52 months (range, 2-250 months) were studied. RESULTS: In 18 of 21 patients-16 of them lacking skin involvement-anaphylaxis was the presenting symptom. Six patients (29%) experienced adverse reactions during VIT, 3 during initiation and 3 during maintenance. Twelve patients (57%) were resting while undergoing VIT; 9 (75%) presented local reactions and 3 (25%) systemic reactions, 1 of which required intubation. The Hymenoptera specific IgE decreased from 4.15 kU/L (range, 0.44-100 kU/L) before immunotherapy to 1.2 kU/L (range, 0.34-69.4 kU/L) after 4 years (P < .003). CONCLUSION: Venom immunotherapy is effective to treat IgE-mediated Hymenoptera anaphylaxis in patients with mastocytosis. Its use is recommended despite a relatively high risk of adverse reactions during the build-up phase because it provides protection from anaphylaxis in around 3/4 of the patients.