Background
Strategies to enhance immune responses towards HIV-infected cells are needed for eliminating HIV reservoirs. Natural killer (NK) cell-mediated antibody-dependent cellular cytotoxicity (ADCC) plays a key role in HIV protection. In cancer, Tri-specific Killer Engagers (TriKEs), consisting of a CD16-binding domain, an antigen-targeting domain, and an IL-15 moiety, enhance NK cell-mediated ADCC by forming immune synapses through CD16 and antigen engagement. Building on this strategy, we developed a gp120-targeting TriKE to activate NK cells toward targeting HIV-infected cells. A version specific for rhesus macaques (RMs) has been generated to conduct an in vivo dose-response study to evaluate TriKE safety and impact on NK cell responses.
Methods
TriKE was administered subcutaneously 5 times per week for 3 weeks in 3 uninfected RMs, with doses from 100 to 300 µg/kg (Figure 1). Complete blood counts and blood chemistry tests were performed; whole blood and lymph nodes (LNs) were collected longitudinally for immunophenotyping.
Results
TriKE treatment, even at the higher dose, was well-tolerated; blood biochemistry parameters remained normal throughout the study, with slight and transient increases in transaminases (AST/ALT) and creatine kinase levels following the first administration of each cycle. TriKe treatment significantly increases NK cell frequencies in blood and LNs. Specifically, CD16+CD56- and CD16+CD56+ NK cell subsets peaked in LNs on day 11, coinciding with the final administration in week 2. NK cell expansion was accompanied by increased NK cell activation (HLA-DR+CD69+) and proliferation (Ki-67+). Following the third week’s dosing (300 µg/kg, day 14), the frequency of NK cells and their activation and proliferation levels decreased. Interestingly, PD-1 expression significantly increased on day 4 (end of the first week’s dosing) in both blood and LNs, normalizing by day 11; this may reflect an immunological response to prevent excessive NK cell activation.
Conclusions
Our study demonstrates, for the first time, that the gp120-targeting TriKE safely and potently engages NK cell responses in RMs, with their substantial activation, proliferation, and expansion in blood and lymphoid tissues. Furthermore, blocking PD-1 upregulation could synergize with TriKE treatment to enhance TriKE-mediated NK cell function. These findings provide strong rationale to further characterize TriKE-based therapies as a strategy for targeting HIV/SIV reservoirs, including in lymphoid tissues.