Safety and Immunological Evaluation of Interleukin-21 Plus Anti-α4β7 mAb Combination Therapy in Rhesus Macaques

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infections compromise gut immunological barriers, inducing high levels of inflammation and a severe depletion of intestinal CD4(+)T cells. Expression of alpha 4 beta 7 integrin promotes homing of activated T cells to intestinal sites where they become preferentially infected; blockade of alpha 4 beta 7 with an anti-alpha 4 beta 7 monoclonal antibody (mAb) prior to infection has been reported to reduce gut SIV viremia in rhesus macaques (RMs). Interleukin-21 (IL-21) administration in antiretroviral therapy-treated, SIV-infected RMs reduces gut inflammation and improves gut integrity. We therefore hypothesized that the combination of IL-21 and anti-alpha 4 beta 7 mAb therapies could synergize to reduce inflammation and HIV persistence. We co-administered two intravenous doses of rhesus anti-alpha 4 beta 7 mAb (50 mg/kg) combined with seven weekly subcutaneous infusions of IL-21-IgFc (100 mu g/kg) in four healthy, SIV-uninfected RMs to evaluate the safety and immunological profiles of this intervention in blood and gut. Co-administration of IL-21 and anti-alpha 4 beta 7 mAb showed no toxicity at the given dosages as assessed by multiple hematological and chemical parameters and did not alter the bioavailability of the therapeutics or result in the generation of antibodies against the anti-alpha 4 beta 7 mAb or IL-21-IgFc. Upon treatment, the frequency of CD4 memory T cells expressing beta 7 increased in blood and decreased in gut, consistent with an inhibition of activated CD4 T-cell homing to the gut. Furthermore, the frequency of T cells expressing proliferation and immune activation markers decreased in blood and, more profoundly, in gut. The combined IL-21 plus anti-alpha 4 beta 7 mAb therapy is well-tolerated in SIV-uninfected RMs and reduces the gut homing of alpha 4 beta 7(+)CD4 T cells as well as the levels of gut immune activation.