This study is a 96-week study designed to evaluate the safety and efficacy of GW873140 in combination with Kaletra in HIV infected, untreated subjects.

A Phase IIb, 96 week, randomized, open-label, multicenter, parallel group, repeat dose study to evaluate the safety, tolerability, pharmacokinetics and antiviral effect of different doses and regimens of GW873140 in combination with Kaletra (lopinavir and ritonavir) in HIV-1 infected antiretroviral therapy naive subjects

Inclusion criteria:

• HIV infected, therapy-naive subjects.
• Females must be of either non-childbearing age, or have a negative pregnancy test.
• All subjects participating in this study should be counseled on the practice of safe sex using a proven double barrier method of contraception throughout the study.
• Screening lab result of plasma HIV-1 RNA greater than or equal to 50,000 copies/mL and CD4 cell count greater than or equal to 100 cells/mm3.
• Have CC Chemokine Receptor5-tropic (R5-tropic) or CC Chemokine Receptor5/CXC Chemokine Receptor4-tropic (R5/X4-tropic) virus based on viral tropism test at screening visit.
• Be treatment-naive, defined as less than or equal to 2 weeks of treatment with a protease inhibitor (PI) or an nucleoside reverse transcriptase inhibitor/nucleotide reverse transcriptase inhibitor (NRTI/ NtRTI), or less than or equal to 7 days of therapy with a non-nucleoside reverse transcriptase inhibitor (NNRTI).
• Prior treatment with any entry inhibitor, attachment inhibitor, or fusion inhibitor (experimental or approved) is not allowed.
• Be able to understand and follow with protocol requirements, instructions and protocol-stated restrictions.
• Signed and dated written informed consent prior to study entry.

Exclusion criteria:

• No detection of CXC Receptor4-tropic (X4-tropic) virus only, based on viral tropism test at screening.
• No active Class C AIDS-defining illness.
• No laboratory abnormalities at screen.
• No significant blood loss prior to study start.
• No pregnant or breastfeeding women.
• Additional qualifying criteria to be determined by the physician.