A short course of treatment with an investigational synthetic cat-peptide antigen desensitizing vaccine, or Cat-PAD, results in a substantial and persistent reduction in cat allergy symptom scores, according to two-year findings from a randomized, placebo-controlled phase II clinical study involving 202 adult patients.
Study participants were initially randomized to receive either eight 3-nmol intradermal doses at 2-week intervals, four 6 nmol-doses at 4-week intervals, or placebo. At 1-year follow-up, the improvement in Total Rhinoconjunctivitis Symptom Score (TRSS) was significantly greater in the patients who received four doses of Cat-PAD (ToleroMune Cat, Circassia Limited, Oxford, England), compared with those who received placebo (–7.1 points vs. –2.99 points), according to findings published online in the Journal of Allergy and Clinical Immunology (doi:10.1016/j.jaci.2012.12.1185).
Courtesy Kate Fulton
Data from a 2-year follow-up study were reported by Rod P. Hafner, Ph.D., and his colleagues in a poster at the annual meeting of the American Academy of Allergy, Asthma, and Immunology.
Of 89 patients enrolled into the follow-up study, 50 returned at 2-years after the start of treatment, having received no additional treatment, for an environmental exposure chamber challenge. The magnitude of difference from baseline in TRSS seen at 1 year in those who received 4 doses and those who received placebo was maintained at 2 years (–5.87 vs. –2.02) among those who initially received the 4-dose regimen.
"Cat-PAD is the first in a new class of synthetic peptide immune-regulatory epitopes. The results from this study provide the first evidence that four doses of 6 nmol Cat-PAD over a 12-week period has a disease-modifying effect with subjects showing sustained improvement at 2 years," the investigators wrote.
Study participants were adults aged 18-65 years with cat allergy who underwent a baseline environmental exposure chamber (EEC) challenge, as well as follow-up EEC challenges at 18-22 weeks and at 100-104 weeks.
"Cat allergen was dispersed into the EEC to achieve a consistent mean level of approx. 50 ng Fel d1/m3, using a validated method," they explained, noting that TRSS was calculated at each EEC challenge based on self-scoring of four nasal symptoms (running nose, sneezing, blocked nose, itchy nose), and four ocular symptoms (itchy eyes, watery eyes, red eyes, sore eyes) on a scale of 0-3, every 30 minutes during the challenge.
Cat-PAD is a "potentially exciting new approach to cat allergy immunotherapy," the investigators said, noting that improvements in the TRSS seen in the initial phase II study and follow-up study represent a substantial improvement over numerous therapies investigated in the past, in some cases reaching a threefold improvement in symptom reduction.
"For example, studies of similar design in an EEC reported TRSS changes of approximately –1.5 units after 16 weeks treatment with a sublingual cat allergy tablet, while a single 180-mg dose of the antihistamine fexofenadine achieved a mean difference in TRSS of –1.3 in a cat allergen study. Moreover, the change in TRSS of –3.8 units reported here was observed after four administrations of Cat-PAD over a 12-week period and persisted 21 months after the end of treatment," they concluded.
In late 2012 the investigators began enrolling a phase III study, which will include individuals aged 12-65 years.
This study was funded by Circassia Limited. Dr. Hafner is employed by Circassia.