Purpose is to identify whether immune markerscan predict success of salvage anti-retroviral therapy.

Over the last several years two markers of disease have been utilized to determine if antiretroviral therapy has been successful, one is a CD4 cell count (reflects the immunocompetence of an infected individual) and a HIV viral load (a blood test used to determine the amount of HIV in the infected individual). However in patients who fail their first line of therapythe likelihood of extended resuppressing viral replication with subsequent therapies may be as low as 25-50%. This information may take several months to determine the new therapies possible continuing success. It would be preferable to have additional markers that respond to therapies in the first several weeks to such therapies, therfore possibly offering patients alternate treatment earlier without potentiatinglong term side effects and possible further drug resistance.

Inclusion Criteria:

• Patient must be HIV infected
• must be ≥18 years old
• must have been taking the same combination ARV regimen (≥3 drugs) for at least 3 months.
• Must be experiencing virologic failure (viral load ≥50 copies/mL on two occasions at least 2 weeks apart).
• must be changed to a salvage antiretroviral regimen
• Patient has to have signed and dated a full infomred consent.

Exclusion Criteria:

• Patient with any of the following abnormal laboratory test results in the previous 3 months:
• Hemaglobin <100 g/L
• Platelet count <20,000 cells/L
• INR ≥3.5 IU
• PTT ≥60 IU
• Patient with other significant underlying disease (non-HIV) that might impact immune markers ( eg. advanced liver disease, malignancy).