A Study to Examine the Efficacy and Safety of Anti-Fel d 1 Antibodies Injections in Cat-allergic Adolescent and Adult Patients With Allergic Rhinitis Who Live With a Cat

The primary objective of the study is to determine the efficacy of REGN1908-1909, as compared to placebo, to reduce allergic rhinitis/conjunctivitis symptoms and allergy rescue medication use during natural cat exposure.

The Secondary Objectives are:

* To assess the reduction of allergic symptoms and use of allergy rescue medications after treatment with REGN1908-1909 versus placebo, as measured by the individual components of the CSMS
* To assess health-related quality of life (HRQoL) as measured by the Rhinoconjunctivitis Quality of Life Questionnaire (RQLQ\[S\])
* To determine the efficacy of REGN1908-1909, as compared to placebo, to inhibit a wheal-and-flare response to a skin prick test with cat allergen
* To assess the durability of effect in allergic rhinitis and conjunctivitis symptom and medication scores after multiple doses of REGN1908-1909 compared to placebo given every 12 weeks (Q12W)
* To determine the efficacy following multiple doses of REGN1908-1909 compared to placebo at inhibiting a wheal-and-flare response to a skin prick test with cat allergen
* To estimate the effect of REGN1908-1909 on lung function, as compared to placebo, in patients with asthma
* To determine the efficacy of REGN1908-1909 as compared to placebo to reduce asthma symptoms in patients with asthma
* To assess whether there is a difference in asthma rescue medication use in patients with asthma who are treated with REGN1908-1909 compared to placebo
* To assess whether there is a difference in nighttime awakenings in patients with asthma treated with REGN1908-1909 compared to placebo
* To evaluate the short-term and long-term safety and tolerability of REGN1908-1909, including the incidence of hypersensitivity reactions, local injection site reactions, and asthma exacerbations
* To determine systemic exposure of total (free and antigen-bound) antibodies as measured by concentration of REGN1908 and REGN1909
* To assess the immunogenicity of REGN1908 and REGN1909


Eligibility Criteria:
Key Inclusion Criteria:

1. Generally healthy males and females who are 12 years and older at the time of screening.
2. Weight must be ≥40 kg at the time of screening
3. Documented or patient reported history (for at least 2 years) of symptomatic cat allergen-triggered allergic rhinitis with or without conjunctivitis and with or without asthma as defined by all of the following criteria:

   1. Positive skin prick test (SPT) with cat hair extract (mean wheal diameter at least 5 mm greater than a negative control) at screening
   2. Positive allergen-specific IgE (sIgE) tests for cat and Fel d 1 (both ≥0.7 kUa/L at screening)
   3. Documented or patient reported history of nasal and/or ocular symptoms upon cat exposure
   4. Symptomatic despite the use of medications to treat their nasal and/or ocular symptoms
4. At least 1 generally healthy cat (that is unlikely to die during the study) living in the home resulting in regular exposure
5. A daily total rhinitis/conjunctivitis symptom score (total symptom score \[TSS\]) of at least 8 of 18 during at least 8 days of the 15-day baseline assessment period and use of standard, therapeutic doses of pharmacotherapy for the treatment of allergic rhinoconjunctivitis on at least 8 days of the 15-day baseline assessment period.

Key Exclusion Criteria:

1. History of significant multiple and/or severe allergies, as assessed by the investigator, that would potentially interfere with the assessments during the baseline and 12-week efficacy assessment periods or confound results, per investigator discretion, including significant rhinitis or sinusitis due to daily contact with other allergens causing symptoms that are expected to coincide with the baseline period or any of the efficacy assessment periods
2. Received REGN1908-1909 in a prior REGN1908-1909 clinical trial (receipt of placebo in a previous trial is allowed)
3. Active lung disease other than asthma
4. FEV1 less than 70% of predicted at screening or randomization
5. Treatment with an investigational drug within 2 months or within 5 half-lives (if known), whichever is longer, prior to screening
6. Persistent chronic or recurring acute infection requiring treatment with antibiotics, antivirals, or antifungals, or any untreated respiratory infections within 4 weeks prior to screening. Patients may be re-evaluated after resolution of symptoms and specified time duration

NOTE: Other protocol-defined Inclusion/ Exclusion Criteria apply