Antibody-Nanoparticle Conjugates in Therapy: Combining the Best of Two Worlds

Abstract

Monoclonal antibodies (mAbs) and antibody fragments have revolutionized medicine as highly specific binding agents and inhibitors. At the same time, several types of nanomaterials, including liposomes, lipid nanoparticles (NPs), polymersomes, metal and metal oxide NPs, and protein nanostructures, are increasingly utilized and explored for therapeutic potential due to their versatility, chemical and physical properties, and tunability. However, nanomaterials alone often lack specificity, leading to relatively low efficacy and/or high toxicity. To address this problem, a rapidly emerging area is antibody-nanomaterial conjugates (ANCs), which combine the precise targeting specificity of antibodies with the effector functionality of the nanomaterial. In this review, we give a brief introduction to mAbs and major conjugation techniques, describe major classes of nanomaterials being studied for therapeutic potential, and review the literature on ANCs of each class. Special focus is given to emerging applications including ANCs addressing the blood-brain barrier, ANCs delivering nucleic acids, and light-activated ANCs. While many disease targets are related to cancer, ANCs are also under development to address autoimmune, neurological, and infectious diseases. While important challenges remain, ANCs are poised to become a next-generation therapeutic technology.

Keywords: antibody; bioconjugation; liposome; mAb; nanoparticle.

Figure 1

Monoclonal antibody (mAb) structures. a) IgG structure consists of two heavy (H) chains and two light (L) chains linked with disulfide bonds. Each heavy chain contains three constant domains (C_H1, C_H2, and C_H3) and one variable domain (V_H), while each light chain consists of one constant (C_L) and one variable (V_L) domain. V_L, C_L, C_H1, and V_H together form the Fab region, enabling specific antigen binding. The binding of antigen is specifically mediated by six loops, known as complementarity‐determining regions (CDRs), with three loops located in each of the V_H and V_L domains. The remaining constant regions (C_H2 and C_H3) form the Fc domain that regulates effector functions, subcellular transport, and clearance. The N‐linked glycan (modulates effector function and pharmacokinetics, PK) attached to the conserved asparagine (Asn) residue at position 297 consists of a core structure of N‐acetylglucosamine and mannose. ADCC: Antibody‐dependent cell‐mediated cytotoxicity; ADCP: Antibody‐dependent cellular phagocytosis; CDC: Complement‐dependent cytotoxicity. b) Types of mAbs to reduce immunogenicity, from murine mAbs, to chimeric mAbs (murine variable (V) regions grafted onto human constant (C) regions), to humanized mAbs (human immunoglobulin scaffold and murine‐derived CDRs), to human mAbs. c) mAb fragments used in therapeutics. Fab (Fragment antigen‐binding): monovalent fragment with antigen‐binding capability but lacking immune effector functions. scFv (Single‐chain variable fragment): monovalent fragment engineered as a single‐chain made of fused variable regions, retaining antigen binding without an Fc region. scFvC (single‐chain variable fragment with truncated Fc): mAb fragment combining scFv domains with the Fc region, enabling antigen binding along with Fc‐mediated immune effector functions. Diabody: bivalent antibody fragment consisting of two scFv units. Bis‐scFv: engineered fragment capable of binding two distinct antigens, for dual targeting. F(ab’)₂: bivalent antibody fragment composed of two Fab units, with bivalent antigen binding without immune effector regions. Nanobody (V_HH): minimal antibody fragment derived from camelid antibodies, which have a single variable region.

Figure 2

Trends of nanoparticle (NP) size, surface charge, and hydrophobicity on cytotoxicity, blood circulation time, and clearance pathways. Small, positively charged NPs exhibit high cytotoxicity but are rapidly cleared, reducing their systemic efficacy. Larger, neutral or slightly negatively charged NPs generally show lower cytotoxicity and longer circulation times. Positively charged, hydrophobic NPs are usually cytotoxic, and prone to aggregation and immune clearance. NPs with extended circulation times (e.g., hydrophilic, neutral/negatively charged, 50–200 nm) are ideal for exploiting the enhanced permeability and retention (EPR) effect, while short circulation time typically corresponds to rapid clearance by the reticuloendothelial system (RES) or kidneys. Cytotoxicity is based on qualitative biocompatibility trends observed during in vivo screening of ≈130 NPs designed for therapeutic applications.^{[ 57} , ^{58 ]}

Figure 3

Selected conjugation processes and their advantages and limitations. a) Noncovalent binding (physical adsorption and electrostatic interactions); b) carbodiimide chemistry (1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide (EDC)/NHS mediated coupling of −COOH or −NH₂ functionalized nanoparticles (NPs) with antibodies); c) maleimide chemistry; d) Cu‐mediated click chemistry; e) copper‐free click chemistry (azide‐DBCO reaction and inverse electron‐demand Diels‐Alder (iEDDA) reaction).

Figure 4

Lipid nanoparticle (LNP) structure and antibody‐targeted LNP‐mediated nucleic acid delivery. a) Lipid NPs typically consist of an ionizable lipid, a helper lipid, cholesterol and polyethylene glycol (PEG) lipid. b) Upon binding to the target cells, the Ab‐targeted LNPs are internalized by receptor‐mediated endocytosis followed by endosomal escape and payload delivery. c–e) Endosomal escape mechanisms. PEGylated lipids facilitate fusion with endosomes (c); anionic lipids promote endosomal disruption through osmotic destabilization and charge reversal from proton influx (d); cationic lipids promote disruptive colloid osmotic effects (e).^{[ 136} , ^{137 ]}

Figure 5

Schematic of the dually targeted vesicle‐shuttle approach for treating myocardial infarction. Anti‐CD63 antibodies on the vesicle shuttle capture endogenous circulating exosomes. Dual targeting occurs via an external magnet, which directs the magnetic vesicle shuttle to the infarct site, and a conjugated anti‐MLC antibody that targets damaged cardiomyocytes. Exosome release is triggered by the infarct environment, characterized by pH < 6.8, leading to acidosis‐induced cleavage of hydrazone bonds and shedding of the corona for selective exosome delivery.

Figure 6

Structure of blood‐brain‐barrier (BBB) and modes of nanomaterial transport across it. (a) The BBB is formed by capillary endothelial cells, surrounded by basal lamina and astrocytic perivascular end feet. Astrocytes provide a cellular link to the neurons. Magnified view of the contact between two endothelial cells forming adherens junctions and tight junctions that inhibit paracellular permeability. (b) Various endogenous (top three) and exogenous (bottom two) mechanisms of nanoparticle (NP) transport across the BBB. Note that paracellular transport is typically uncommon for NPs. However, ultrasmall NPs can exploit this pathway in areas with compromised tight junctions, such as in a diseased BBB or BBB subjected to focused ultrasound beam (FUS). Similarly, passive transcellular diffusion can take place when assisted by electroporation.

Figure 7

CAR T‐cell therapy and nanoparticle (NP) bispecific T‐cell engager (NBiTE) T‐cell therapy. a) Production of CAR T cells begins with the collection of immune cells from the patient or donor through leukapheresis. T cells are isolated from other blood components and then activated and expanded. Gene transfer (e.g., by viral vector) introduces the chimeric antigen receptor genes (CARs) to the T cells. The modified T cells are further expanded, harvested and infused into the patient. b) An NBiTE contains two distinct scFvs attached to the NP surface: one that binds to a T‐cell specific antigen (i.e., T‐cell receptor) and another that targets a tumor‐specific antigen, enabling cytotoxicity. Multivalent interactions at the NP‐cell interface can increase efficiency in bridging T cells to tumor cells compared to molecular BiTEs.

Figure 8

Modular platform for anchoring antibodies to lipid nanoparticles (LNPs) for gene editing. An LNP containing nucleic acids, such as Cas9 mRNA and sgRNA, is nanoassembled using a microfluidic mixer. Then micelles functionalized with an Fc‐binding protein (green) are fused to the LNPs. LNP targeting is determined by the IgG added (pink) for a particular application.