Alemtuzumab (ATM) is a lymphocyte-depleting humanized anti-CD52 monoclonal antibody used for the treatment of multiple malignancies and licensed for relapsing-remitting multiple sclerosis. Here, we evaluated whether ATM can deplete long-lived latently infected CD4+ memory T cells in SIV-infected rhesus macaques (RM) on suppressive combination antiretroviral therapy (cART). We hypothesized that ATM-induced depletion and reconstitution in the presence of cART may significantly reduce SIV persistence.
RM were initially screened for CD52 expression on erythrocytes using an agglutination assay to minimize any risk of hemolysis. Nine RM were intravenously inoculated with SIVmac239 and after 12 days received cART (tenofovir/emtricitabine/dolutegravir). Once sustained virus suppression (<15 RNA copies/ml) was achieved, 6 RM received intravenous doses of ATM at 5mg/Kg on days 0, 7, 14 and 29. Three RM did not receive ATM (controls). Lymph node (LN) and gastrointestinal tract (GIT) tissue was collected at 10 and 20 weeks. SIV DNA and RNA were quantified by qPCR/qRT-PCR and markers of immune activation by flow cytometry.
ATM induced a rapid and profound depletion in circulating lymphocyte populations, including T cells, NK cells, B cells and monocytes, including a significant depletion in CD4+ memory and naive T cells in the blood (>95%) and some depletion in LN (~50%). CD4+ T regulatory cells were also significantly depleted (>90%). T cell reconstitution was associated with a massive burst in memory T cell proliferation as measured by Ki67, which peaked around 3-4 weeks post-ATM and followed by a gradual recovery of all T cell subsets in blood. After 7 months, naïve, central, and effector memory CD4+ T cell subsets were 51%, 60% and 100% of pre-ATM levels, respectively. Post-ATM, but while still on cART, plasma SIV RNA remained detectable but below 15 copies/ml with only 1 of 6 RM showing blips above 100 SIV RNA copies/ml. At 10 weeks post-ATM, total SIV DNA in peripheral blood mononuclear cells (PBMC) decreased from a mean of 2.4 to 1.4 log copies per 10e6 cells (p=0.03); however, SIV DNA in peripheral LN and GIT remained unchanged.
Although ATM can significantly reduce SIV DNA levels in the PBMC of SIV-infected RM on cART, low level viremia persists. The minimal effect on SIV DNA in LN and GIT suggests either limited depletion in those tissues or a rapid reconstitution at those sites post-ATM, perhaps by expanded clones.