Randomised, Placebo Controlled, Phase IV, Safety and Exploratory Immunogenicity Study on Maraviroc, an Oral ART CCR5 Inhibitor, on the Intensification of Immune Function in HIV-1 Infected Subjects Receiving Immunisation With Novel Antigens

Maraviroc is a CCR5 antagonist with potent anti-HIV-1 activity, demonstrated in both treatment naïve and experienced settings. Binding of maraviroc to CCR5 leads to the loss of receptor function. Individuals with non-functioning CCR5 due to a 32 base pair deletion in the encoding gene are observed at a 1% frequency in the northern European Caucasian population. These individuals have near normal immune function, although differential response to renal transplant and West Nile virus have been reported relative to individuals with functional CCR5. The modest impact on immune function is indicative of a functional overlap between CCR5 and other CC chemokine receptors. While the precise role of CCR5 has not been established, data suggest a role in chemotaxis and inflammation.

An excess of clinical events, infective, inflammatory or malignant, have not been reported in persons receiving maraviroc relative to placebo or to efavirenz-based antiretroviral therapy over 48 weeks follow-up. Indeed, individuals randomized to maraviroc were noted in these studies to have modestly greater increases in CD4 T-cell numbers, not accounted for by changes in lymphocyte counts or rates of viral suppression.

The impact of inclusion of maraviroc in an antiretroviral treatment regimen on immune function has not been reported.

In chronically infected HIV-1+ individuals who progress to AIDS, the full functionality of the anti-HIV-1 CD8+ cytotoxic T lymphocyte response is progressively lost. This is accompanied by diminished responses to neo- and recall antigens and skin anergy (loss of DTH response). This is likely dependent on the loss of function and numbers of HIV-1-specific CD4+ helper T lymphocytes (Appay and Sauce 2008). This process is apparently, at least partially, irreversible despite otherwise successful, currently used antiretroviral drug regimens. Accumulation of functionally inert ('anergic') HIV-1-specific CD4+ and CD8+ CD28- CTLA-4hi T cells is observed, which lack proliferative and IL-2 producing ability and cytolytic function despite maintaining the capacity to produce IFN-γ (Deeks and Walker 2007). A balanced response in which the host responds appropriately to prevalent antigen, such as HIV-1 Gag, yet remains relatively quiescent, may prove to be the strongest functional correlate of virologic control (Imami et al. 2002; Imami et al. 2007).

Recent work has shown that tetanus antibody responses are significantly impaired in HIV patients on successful ART (Hart et al. 2007). A recently identified CD4 T-cell subset, known as follicular T cells (TFH) plays a crucial role in the development of humoral immune responses to protein antigens such as tetanus toxoid (King et al. 2008). Follicular CD4 T cells express a chemokine receptor called CXCR5, a protein called inducible co-stimulatory factor (ICOS) and are readily identified in peripheral blood. Follicular CD4 T cells are prone to activation induced cell death which is believed to be a major mechanism of CD4 T-cell depletion in chronic HIV-1 infection and therefore could be a vulnerable target in retroviral disease. A reduction in circulating CD4 TFH numbers and/or function may account for the failure of HIV-1 patients to respond to tetanus vaccination.