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HIV-1 entry into host cells is mediated by the sequential binding of the envelope glycoprotein gp120 to CD4 and a chemokine receptor. Antibodies binding to epitopes overlapping the CD4-binding site on gp120 are potent inhibitors of HIV entry, such as the llama heavy chain antibody fragment V(HH) D7, which has cross-clade neutralizing properties and competes with CD4 and mAb b12 for high affinity binding to gp120. We report the crystal structure of the D7 V(HH) at 1.5 A resolution, which reveals the molecular details of the complementarity determining regions (CDR) and substantial flexibility of CDR3 that could facilitate an induced fit interaction with gp120. Structural comparison of CDRs from other CD4 binding site antibodies suggests diverse modes of interaction. Mutational analysis identified CDR3 as a key component of gp120 interaction as determined by surface plasmon resonance. A decrease in affinity is directly coupled to the neutralization efficiency since mutations that decrease gp120 interaction increase the IC50 required for HIV-1 IIIB neutralization. Thus the structural study identifies the long CDR3 of D7 as the key determinant of interaction and HIV-1 neutralization. Furthermore, our data confirm that the structural plasticity of gp120 can accommodate multiple modes of antibody binding within the CD4 binding site.

Background: Vγ9Vδ2 T-cells are antitumor immune effector cells that can detect metabolic dysregulation in cancer cells through phosphoantigen-induced conformational changes in the butyrophilin (BTN) 2A1/3A1 complex. In order to clinically exploit the anticancer properties of Vγ9Vδ2 T-cells, various approaches have been studied including phosphoantigen stimulation, agonistic BTN3A-specific antibodies, adoptive transfer of expanded Vγ9Vδ2 T-cells, and more recently bispecific antibodies. While Vγ9Vδ2 T-cells constitute a sizeable population, typically making up ~1-10% of the total T cell population, lower numbers have been observed with increasing age and in the context of disease., Methods: We evaluated whether bivalent single domain antibodies (VHHs) that link Vδ2-TCR specific VHHs with different affinities could support Vγ9Vδ2 T-cell expansion and could be incorporated in a bispecific engager format when additionally linked to a tumor antigen specific VHH., Results: Bivalent VHHs that link a high and low affinity Vδ2-TCR specific VHH can support Vγ9Vδ2 T-cell expansion. The majority of Vγ9Vδ2 T-cells that expanded following exposure to these bivalent VHHs had an effector or central memory phenotype and expressed relatively low levels of PD-1. Bispecific engagers that incorporated the bivalent Vδ2-TCR specific VHH as well as a tumor antigen specific VHH triggered antitumor effector functions and supported expansion of Vγ9Vδ2 T-cells in vitro and in an in vivo model in NOG-hIL-15 mice., Conclusion: By enhancing the number of Vγ9Vδ2 T-cells available to exert antitumor effector functions, these novel Vδ2-bivalent bispecific T cell engagers may promote the overall efficacy of bispecific Vγ9Vδ2 T-cell engagement, particularly in patients with relatively low levels of Vγ9Vδ2 T-cells., Competing Interests: NV. TG and HV own LAVA Therapeutics NV shares. DH, PY, VI-G, PH and HV are/were employed by LAVA Therapeutics NV. TG is scientific advisor to LAVA Therapeutics NV. The authors declare that this study received funding from Lava Therapeutics NV. LK, MJ and MV were funded by LAVA Therapeutics NV., (Copyright © 2024 King, de Jong, Veth, Lutje Hulsik, Yousefi, Iglesias-Guimarais, van Helden, de Gruijl and van der Vliet.)

Background: CD1d is a monomorphic major histocompatibility complex class I-like molecule that presents lipid antigens to distinct T-cell subsets and can be expressed by various malignancies. Antibody-mediated targeting of CD1d on multiple myeloma cells was reported to induce apoptosis and could therefore constitute a novel therapeutic approach., Methods: To determine how a CD1d-specific single-domain antibody (VHH) enhances binding of the early apoptosis marker annexin V to CD1d + tumor cells we use in vitro cell-based assays and CRISPR-Cas9-mediated gene editing, and to determine the structure of the VHH1D17-CD1d(endogenous lipid) complex we use X-ray crystallography., Results: Anti-CD1d VHH1D17 strongly enhances annexin V binding to CD1d + tumor cells but this does not reflect induction of apoptosis. Instead, we show that VHH1D17 enhances presentation of phosphatidylserine (PS) in CD1d and that this is saposin dependent. The crystal structure of the VHH1D17-CD1d(endogenous lipid) complex demonstrates that VHH1D17 binds the A'-pocket of CD1d, leaving the lipid headgroup solvent exposed, and has an electro-negatively charged patch which could be involved in the enhanced PS presentation by CD1d. Presentation of PS in CD1d does not trigger phagocytosis but leads to greatly enhanced binding of T-cell immunoglobulin and mucin domain containing molecules (TIM)-1 to TIM-3, TIM-4 and induces TIM-3 signaling., Conclusion: Our findings reveal the existence of an immune modulatory CD1d(PS)-TIM axis with potentially unexpected implications for immune regulation in both physiological and pathological conditions., Competing Interests: Competing interests: DLH, PB and HJvdV are employees of LAVA Therapeutics, a company that develops bispecific gamma-delta T-cell engagers, and own LAVA Therapeutics shares and/or stock options. RL, TDdG and HJvdV are named inventors on international patent application WO 2016/122320 Al (‘Single domain antibodies targeting CD1d’) which partially relates to the work described in this paper. TDdG is a consultant for and a shareholder of LAVA Therapeutics. RL and MV were funded by a LAVA Therapeutics grant to Amsterdam UMC. JR has received funding from LAVA Therapeutics. DIG is a member of the scientific advisory board and a shareholder of Avalia Immunotherapies, a company working on NKT cell-based vaccines and is an inventor on patent applications WO 2021/127745 and WO 2021/127744 that describe effects of cross-linking CD1 molecules and WO2020/231274 that describes CD1d-dependent glycopeptide vaccines., (© Author(s) (or their employer(s)) 2023. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)