A Phase 2 Study of Cladribine Add-on to Interferon-beta (IFN-beta) Therapy in Multiple Sclerosis (MS) Subjects With Active Disease (ONWARD)

Be male or female, 18 to 65 years of age (inclusive)

Weigh between 40 to 120 kilogram (kg), (inclusive)

Have definite MS, as confirmed by the revised McDonald criteria 2005, and have relapsing forms of MS, such as relapsing-remitting multiple sclerosis (RRMS) or SPMS with superimposed relapses

Have experienced at least one relapse within 48 weeks prior to Screening, while receiving IFN-beta treatments (Rebif® 44mcg three times a week, subcutaneously; Avonex®30 mcg every week, intramuscular; or Betaseron® 250 mcg every other day, subcutaneously)

Have a minimum time on IFN-beta therapy of 48-consecutive weeks prior to Screening. Participants who switched from one IFN-beta therapy to another in the 48 weeks preceding Screening may be entered into the study if they have been on a stable regimen of their current IFN-beta therapy for a minimum of 3 months prior to Screening

Be clinically stable (other than MS relapse) during the 28 days preceding Screening

The following hematological parameters must be normal (as defined below, inclusively) within 28 days of first dosing of blinded study medication at study day 1 (SD 1)

* Hemoglobin=11.6 to 16.2 gram per deciliter (g/dL)

* Leukocytes (total white blood cells \[WBC\])=4.1 to 12.3\*10\^3 per microliter (/UL)

* Absolute lymphocytes count (ALC)= 1.02 to 3.36\*10\^3/UL

* Absolute neutrophil count (ANC)=2.03 to 8.36\*10\^3/UL

* Platelet count=140 to 450\*10\^3/UL

Have no medical history or evidence of latent tuberculosis infection (LTBI) or active tubercular disease (TB), as evidenced by TB skin test or chest X-ray

Have an expanded disability status scale (EDSS) from 1.0-5.5, inclusive

Have no prior exposure to immunosuppressive or cytotoxic agents (with the exception of steroids for MS flare management, or intravenous immunoglobulin-G \[IVIG\] after allowed wash-out periods

If female, must:

* be neither pregnant nor breast-feeding, nor attempting to conceive, and

* use a highly effective method of contraception throughout the entire duration of the study and for 6 months (6 menstrual cycles) following completion of the last dose of study medication. A highly effective method of contraception is defined as one which result in a low failure rate (that is, less than 1 percent per year) when used consistently and correctly, such as implants, injectables, combined oral contraceptives, some intrauterine devices (IUDs), sexual abstinence or a vasectomized partner. For the purpose of this trial, women of childbearing potential are defined as: All female participants after puberty unless they are post-menopausal for at least 2 years, or are surgically sterile

If male, must be willing to use contraception to avoid pregnancies throughout the entire duration of the study and for 90 days following the last dose of study medication

Be willing and able to comply with study procedures for the duration of the study

What this study is about