Background: The advances of HIV research and especially the advent of antiretroviral therapy (ART)
led to strong and long-lasting viral suppression in peripheral blood of most treated individuals. Despite
the efficacy of ART, treatment interruption results in vial rebound and disease progression due to the
persistence of HIV in reservoirs that cannot be reached by ART. Recent studies have shown that
PD-1+CD4 T cells serve as a major cellular reservoir for HIV-1 replication and production, thus providing
a strong rationale for developing therapeutic strategies targeting the elimination of PD-1+CD4 T cells.
Aim: The current project aims at killing HIV infected cells based on PD-1 as a marker for HIV cellular
reservoir using the antibody-dependent cellular cytotoxic activity (ADCC) of humanized IgG1 antibodies
or antibody-drug conjugates (ADC).
Methods: Humanized anti-human PD-1 antibodies (hPD-1 IgG1/IgG4) were developed to evaluate
ADCC activity. In parallel, mouse or humanized anti-PD-1 antibodies (mPD-1 or hPD-1 Ab) were
conjugated with an anthracycline toxin to produce an antibody-drug conjugate (ADC). ADCC and ADCs
were evaluated on blood mononuclear cells and isolated CD4+ T cells, respectively, isolated from viremic
untreated or ART suppressed HIV infected donors in 5-day assays. Cells undergoing apoptosis and cell
death were assessed by flow cytometry and culture supernatants were analyzed for viral p24 (ECL
COBAS HIV Ag) or HIV RNA (COBAS AmpliPrep/TaqMan HIV-1) production. Cells from ART treated
donors were tested in a quantitative viral outgrowth assay (QVOA) to evaluate the frequency of cells
harboring replication competent and infectious viruses following Ab or ADC treatment.
Results: In HIV viremic donors, hPD-1 IgG1 lead to the targeted depletion of PD-1+CD4 T cells, which
was associated with 59% and 43% reduction of HIV RNA and p24 production from infected cells,
respectively (n=4). Similarly, m/hPD-1 ADCs efficiently depleted PD-1+CD4 T cells as indicated by the
increased frequencies of apoptotic and dead cells compared to unconjugated m/hPD-1 Ab (n=7 and
n=5, respectively). Targeted cytotoxicity was associated with 80% and 83% reduced viral p24 production
in the culture supernatants compared to unconjugated m/hPD-1 Ab, respectively. In ART suppressed
individuals, increased frequencies of apoptotic cells and cell death after incubation with hPD-1 IgG1
treatment reduced the frequency of infected cells harboring replication competent viruses by 66% (n=4).
Similarly, mPD-1 ADC was associated with 88% reduction of infected cells harboring replication
competent viruses and cells harboring infectious viruses were undetectable (n=5; n=4).
Discussion: These results indicate that the depletion of PD-1+CD4 T cells by hPD-1 IgG1 or m/hPD-1
ADC strongly reduces HIV-1 infected cells capable to produce infectious viruses. In these proof of
concept studies, hPD-1 IgG1 or anti-PD-1 ADC represent novel interventions that could contribute to a
functional cure for HIV-1 infected individuals.