Antibodies targeting the fusion peptide on the HIV envelope provide protection to rhesus macaques against mucosal SHIV challenge

The fusion peptide (FP) on the HIV-1 envelope (Env) trimer can be targeted by broadly neutralizing antibodies (bNAbs). Here, we evaluated the ability of a human FP-directed bNAb, VRC34.01, along with two vaccine-elicited anti-FP rhesus macaque mAbs, DFPH-a.15 and DF1W-a.01, to protect against simian-HIV (SHIV)BG505 challenge. VRC34.01 neutralized SHIVBG505 with a 50% inhibitory concentration (IC50) of 0.58 μg/ml, whereas DF1W-a.01 and DFPH-a.15 were 4- or 30-fold less potent, respectively. VRC34.01 was infused into four rhesus macaques at a dose of 10 mg/kg and four rhesus macaques at a dose of 2.5 mg/kg. The animals were intrarectally challenged 5 days later with SHIVBG505. In comparison with all 12 control animals that became infected, all four animals infused with VRC34.01 (10 mg/kg) and three out of four animals infused with VRC34.01 (2.5 mg/kg) remained uninfected. Because of the lower potency of DF1W-a.01 and DFPH-a.15 against SHIVBG505, we infused both Abs at a higher dose of 100 mg/kg into four rhesus macaques each, followed by SHIVBG505 challenge 5 days later. Three of four animals that received DF1W-a.01 were protected against infection, whereas all animals that received DFPH-a.15 were protected. Overall, the protective serum neutralization titers observed in these animals were similar to what has been observed for other bNAbs in similar SHIV infection models and in human clinical trials. In conclusion, FP-directed mAbs can thus provide dose-dependent in vivo protection against mucosal SHIV challenges, supporting the development of prophylactic vaccines targeting the HIV-1 Env FP.

Trispecific antibody targeting HIV-1 and T cells activates and eliminates latently-infected cells in HIV/SHIV infections

Agents that can simultaneously activate latent HIV, increase immune activation and enhance the killing of latently-infected cells represent promising approaches for HIV cure. Here, we develop and evaluate a trispecific antibody (Ab), N6/αCD3-αCD28, that targets three independent proteins: (1) the HIV envelope via the broadly reactive CD4-binding site Ab, N6; (2) the T cell antigen CD3; and (3) the co-stimulatory molecule CD28. We find that the trispecific significantly increases antigen-specific T-cell activation and cytokine release in both CD4+ and CD8+ T cells. Co-culturing CD4+ with autologous CD8+ T cells from ART-suppressed HIV+ donors with N6/αCD3-αCD28, results in activation of latently-infected cells and their elimination by activated CD8+ T cells. This trispecific antibody mediates CD4+ and CD8+ T-cell activation in non-human primates and is well tolerated in vivo. This HIV-directed antibody therefore merits further development as a potential intervention for the eradication of latent HIV infection.

DPP4 inhibition impairs senohemostasis to improve plaque stability in atherosclerotic mice

Senescent vascular smooth muscle cells (VSMCs) accumulate in the vasculature with age and tissue damage, and secrete factors that promote atherosclerotic plaque vulnerability and disease. Here, we report increased levels and activity of dipeptidyl peptidase 4 (DPP4), a serine protease, in senescent VSMCs. Analysis of the conditioned media from senescent VSMCs revealed a unique senescence-associated secretory phenotype (SASP) signature comprising many complement and coagulation factors; silencing or inhibiting DPP4 reduced these factors and increased cell death. Serum samples from persons with high risk for cardiovascular disease contained high levels of DPP4-regulated complement and coagulation factors. Importantly, DPP4 inhibition reduced senescent cell burden and coagulation and improved plaque stability, while single-cell resolution of senescent VSMCs reflected the senomorphic and senolytic effects of DPP4 inhibition in murine atherosclerosis. We propose that DPP4-regulated factors could be exploited therapeutically to reduce senescent cell function, reverse senohemostasis, and improve vascular disease.

Potent anti-viral activity of a trispecific HIV neutralizing antibody in SHIV-infected monkeys

Broadly neutralizing antibodies (bNAbs) represent an alternative to drug therapy for the treatment of HIV-1 infection. Immunotherapy with single bNAbs often leads to emergence of escape variants, suggesting a potential benefit of combination bNAb therapy. Here, a trispecific bNAb reduces viremia 100- to 1000-fold in viremic SHIV-infected macaques. After treatment discontinuation, viremia rebounds transiently and returns to low levels, through CD8-mediated immune control. These viruses remain sensitive to the trispecific antibody, despite loss of sensitivity to one of the parental bNAbs. Similarly, the trispecific bNAb suppresses the emergence of resistance in viruses derived from HIV-1-infected subjects, in contrast to parental bNAbs. Trispecific HIV-1 neutralizing antibodies, therefore, mediate potent antiviral activity in vivo and may minimize the potential for immune escape.

Fusion peptide priming reduces immune responses to HIV-1 envelope trimer base

Soluble "SOSIP"-stabilized envelope (Env) trimers are promising HIV-vaccine immunogens. However, they induce high-titer responses against the glycan-free trimer base, which is occluded on native virions. To delineate the effect on base responses of priming with immunogens targeting the fusion peptide (FP) site of vulnerability, here, we quantify the prevalence of trimer-base antibody responses in 49 non-human primates immunized with various SOSIP-stabilized Env trimers and FP-carrier conjugates. Trimer-base responses account for ∼90% of the overall trimer response in animals immunized with trimer only, ∼70% in animals immunized with a cocktail of SOSIP trimer and FP conjugate, and ∼30% in animals primed with FP conjugates before trimer immunization. Notably, neutralization breadth in FP-conjugate-primed animals correlates inversely with trimer-base responses. Our data provide methods to quantify the prevalence of trimer-base responses and reveal that FP-conjugate priming, either alone or as part of a cocktail, can reduce the trimer-base response and improve the neutralization outcome.

Anti-HIV-1 Antibodies: An Update

Even after more than 30 years since its discovery, there is no cure for HIV-1 infection. Combination antiretroviral therapy (cART) is currently the only HIV-1 infection management option in clinics. Despite its success in suppressing viral replication and converting HIV-1 from a lethal infection to a chronic and manageable disease, cART treatment is life long and long-term use can result in major drawbacks such as high cost, multiple side effects, and an increase in the development of multidrug-resistant escape mutants. Recently, antibody-based anti-HIV-1 treatment has emerged as a potential alternative therapeutic modality for HIV-1 treatment and cure strategies. These antibody-based anti-HIV-1 treatments comprising either receptor-targeting antibodies or broad neutralizing antibodies (bNAbs) are currently being developed and evaluated in clinical trials. These antibodies have demonstrated potent antiviral effects against multiple strains of HIV-1, and shown promise for prevention, maintenance, and prolonged remission of HIV-1 infection. This review gives an update on the current status of these antibody-based treatments for HIV-1, discusses their mechanism of action and the challenges in developing them, providing insight for their development as novel clinical therapies against HIV-1 infection.