Vaccine-Induced Antibodies Mediate Higher Antibody-Dependent Cellular Cytotoxicity After Interleukin-15 Pretreatment of Natural Killer Effector Cells.

Leigh Fisher,Georgia Tomaras,Justin Pollara,Peter B Gilbert,Fatima Laher,Lindsay N Carpp,Zoe Moodie,R Whitney Edwards,Guido Ferrari,Sherry Stanfield-Oakley,Thomas Denny,Melissa Zinter,M Juliana Mcelrath,Linda-Gail Bekker,Lawrence Corey

doi:10.3389/fimmu.2019.02741

Abstract

The secondary analyses for correlates of risk of infection in the RV144 HIV-1 vaccine trial implicated vaccine-induced antibody-dependent cellular cytotoxicity (ADCC) responses in the observed protection, highlighting the importance of assessing such responses in ongoing and future HIV-1 vaccine trials. However, in vitro assays that detect ADCC activity in plasma from HIV-1 infected seropositive individuals are not always effective at detecting ADCC activity in plasma from HIV-1 vaccine recipients. In vivo, ADCC-mediating antibodies must operate at the site of infection, where effector cells are recruited and activated by a local milieu of chemokines and cytokines. Based on previous findings that interleukin 15 (IL-15) secretion increases during acute HIV-1 infection and enhances NK cell-mediated cytotoxicity, we hypothesized that IL-15 pretreatment of NK effector cells could be used to improve killing of infected cells by vaccine-induced antibodies capable of mediating ADCC. Using the HIV-1 infectious molecular clone (IMC)-infected target cell assay along with plasma samples from HIV-1 vaccine recipients, we found that IL-15 treatment of effector cells improved the ability of the vaccine-induced antibodies to recruit effector cells for ADCC. Through immunophenotyping experiments, we showed that this improved killing was likely due to IL-15 mediated activation of NK effector cells and higher intracellular levels of perforin and granzyme B in the IL-15 pretreated NK cells. We also found that using a 4-fold dilution series of plasma and subtraction of pre-vaccination responses resulted in lowest response rates among placebo recipients and significant separation between treatment groups. This represents the first attempt to utilize IL-15-treated effector cells and optimized analytical approaches to improve the detection of HIV-1 vaccine-induced ADCC responses and will inform analyses of future HIV vaccine clinical trials.

Highlights

Antibody-dependent cellular cytotoxicity (ADCC) is an immune mechanism that bridges the adaptive humoral and innate immune responses
We first explored the effect of the IL-15 concentration used to pretreat effector cells in the Luc assay with plasma samples from one HIV-1 infected seropositive and one healthy HIV1 seronegative individual
Effector cells were treated overnight with IL-15 concentrations ranging from 0 to 100 ng/ml IL-15, and used to assay each plasma sample; ADCC activity against IMCCM235-infected target cells detected for the six dilutions of IL-15 is summarized in Figure 1 (Results from additional dilutions and independent replicates are shown in the Supplementary Material)

Summary

Introduction

Antibody-dependent cellular cytotoxicity (ADCC) is an immune mechanism that bridges the adaptive humoral and innate immune responses. ADCC has important applications in cancer treatment, via monoclonal antibody (mAb)-mediated ADCC killing of tumor cells [1], and is involved in host defense from viral infection and control of viremia, via ADCC-mediated killing of virus-infected cells [2]. In the latter, antibodies (Abs) bind pathogen antigens expressed on the membrane of infected cells, which can recruit and activate Fc-gamma receptor (FcγR)-expressing cytotoxic effector cells to kill the infected cells [3]. This finding, combined with later follow up work [11,12,13], supports the hypothesis that the protection afforded by the RV144 vaccine regimen was due in part to ADCC activity of vaccine-induced Abs [14]

Methods

Results

Conclusion