The purpose of this study is to examine the safety, reactogenicity and immunogenicity of the GlaxoSmithKline (GSK) Biologicals candidate pneumococcal vaccine containing PhtD in healthy elderly population aged 18-45 years of age.

The safety profile of the PhtD vaccine will be assessed in comparison to a comparator vaccine (Pneumovax 23TM). In order to further increase the immune response to vaccination, a novel adjuvant system will also be examined.

Inclusion Criteria:

• Subjects who the investigator believes will comply with the requirements of the protocol should be enrolled in the study.
• A male or female between, and including, 18 and 45 years at the time of the first vaccination.
• Written informed consent obtained from the subject.
• Free of obvious health problems as established by medical history and clinical examination before entering into the study.
• If the subject is female, she must be of non-childbearing potential, i.e., either surgically sterilized or one year post-menopausal; or, if of childbearing potential, she must be abstinent or have used adequate contraceptive precautions for 30 days prior to vaccination, have a negative pregnancy test and must agree to continue such precautions for two months after completion of the vaccination series.

Exclusion Criteria:

• Use of any investigational or non-registered product other than the study vaccine(s) within 30 days preceding the first dose of study vaccine, or planned use during the study period or participation to another pharmaceutical/vaccine study.
• Chronic administration of immunosuppressants or other immune-modifying drugs within six months prior to the first vaccine dose.
• Use of any anticoagulants.
• Planned administration/ administration of a vaccine not foreseen by the study protocol within 2 weeks of the first dose of vaccines.
• Previous vaccination against Streptococcus pneumoniae.
• Bacterial pneumonia within 3 years prior to 1st vaccination.
• Any confirmed or suspected immunosuppressive or immunodeficient condition, including human immunodeficiency virus (HIV) infection.
• History of allergic disease or reactions likely to be exacerbated by any component of the vaccine.
• Current serious neurologic or mental disorders.
• Inflammatory processes such as known chronic active infections.
• All malignancies (excluding non-melanic skin cancer) and lymphoproliferative disorders diagnosed or treated actively during the past 5 years.
• History of administration of an experimental vaccine containing 3-deacylated Monophosphoryl Lipid A (MPL) or Quillaja saponaria 21 (QS21).
• Acute disease at the time of enrolment. All vaccines can be administered to persons with a minor illness such as diarrhea, mild upper respiratory infection with or without low-grade febrile illness, i.e., Oral temperature <37.5°C or Axillary temperature <37.5°C.
• Acute or chronic, clinically significant pulmonary, cardiovascular, hepatic or renal functional abnormality, as determined by physical examination or laboratory screening tests, at the discretion of the investigator.
• Pregnant or lactating female.
• History of chronic alcohol consumption and/or intravenous drug abuse.