HIV is a chronic active infection of lymphocytes and monocytoid cells resulting in a progressive and profound depletion of T cell subsets and ultimately in acquired immune deficiency syndrome (AIDS). HIV infects cells of the immune system throughout the body and may cause an active cytolytic infection in activated lymphocytes, become dormant as a latent infection in resting lymphocytes, or continue as a chronically active infection in macrophages. Continuous anti-retroviral drug treatment (ART) suppresses virus within the bloodstream and allows some degree of immune healing so as to permit near-normal health and life expectancy. However, interruption of ART is uniformly followed by rebound of viremia as a result of ongoing chronic active infection, and reactivation of latent infection. Successful ART requires daily medications indefinitely. There is an ongoing need for treatments which are more effective in the eradication of HIV. Counter to past expectations for cell-mediated immunity, broadly neutralizing monoclonal antibodies (nmAb) have been developed which show anti-HIV activity in vivo in reducing viremia (plasma virus load, PVL), and in slightly reducing recurrence of lasting PVL following analytical treatment interruption (ATI). Monoclonal antibody therapies against host cellular markers such as HIV co-receptors have been put forward as potential strategy in immunological treatment of HIV infection. If activated lymphocytes could be protected from cytolytic HIV infection in the presence of concurrent active HIV infection of other cells and tissues, then unperturbed potent acquired specific or innate immunity might confer lasting immunological remission of HIV infection.
This year, an unexpected finding of sustained remission of plasma viremia level (PVL) to below quantifiable assay limits in a rhesus macaque SIV infection model of AIDS was reported. The envelope of SIV (and HIV) appears to interact with α4β7 integrin, a lymphocyte homing receptor for trafficking to gut mucosal-associated lymphoid tissue (GALT) that was the target of mAb treatment in this study. This study showed that in animals treated with the mAb while discontinuing ART there was a diminished rebound and sustained remission of PVL, and less GALT associated viral load for a long-lasting period of at least 24 months. The mechanism of this unexpected post-treatment effect is unknown. In humans infected with HIV, such an effect sustained over time with continued remission of progressive immunodeficiency would meet definitional criteria of "functional cure" of HIV/AIDS. The results observed in the SIV model reveal a promising avenue for investigation in this area of research towards control of HIV infection in absence of ART. We propose to assess the safety and tolerability of anti-α4β7 integrin monoclonal antibody in healthy HIV-infected adults on ART, to assess the safety of ATI and whether anti-α4β7 integrin monoclonal antibody treatment can induce sustained virologic remission in the absence of ART.
