Immune Response to Recombinant Capsid Proteins of Adenovirus in Humans: Antifiber and Anti-Penton Base Antibodies Have a Synergistic Effect on Neutralizing Activity

Abstract

Replication-deficient adenovirus used in humans for gene therapy induces a strong immune response to the vector, resulting in transient recombinant protein expression and the blocking of gene transfer upon a second administration. Therefore, in this study we examined in detail the capsid-specific humoral immune response in sera of patients with lung cancer who had been given one dose of a replication-defective adenovirus. We analyzed the immune response to the three major components of the viral capsid, hexon (Hx), penton base (Pb), and fiber (Fi). A longitudinal study of the humoral response assayed on adenovirus particle-coated enzyme-linked immunosorbent assay plates showed that patients had preexisting immunity to adenovirus prior to the administration of adenovirus–β-gal. The level of the response increased in three patients after adenovirus administration and remained at a maximum after three months. One patient had a strong immune response to adenovirus prior to treatment, and this response was unaffected by adenovirus administration. Sera collected from the patients were assayed for recognition of each individual viral capsid protein to determine more precisely the molecular basis of the humoral immune response. Clear differences existed in the humoral response to the three major components of the viral capsid in serum from humans. Sequential appearance of these antibodies was observed: anti-Fi antibodies appeared first, followed by anti-Pb antibodies and then by anti-Hx antibodies. Moreover, anti-Fi antibodies preferentially recognized the native trimeric form of Fi protein, suggesting that they recognized conformational epitopes. Our results showed that sera with no neutralizing activity contained only anti-Fi antibodies. In contrast, neutralizing activity was only obtained with sera containing anti-Fi and anti-Pb antibodies. More importantly, we showed that anti-native Fi and anti-Pb antibodies had a synergistic effect on neutralization. The application of these conclusions to human gene therapy with recombinant adenovirus should lead to the development of strategies to overcome the formation of such neutralization antibodies, which have been shown to limit the efficacy of gene transfer in humans.

Pre-existing immunity against Ad vectors

“…15,16 Depletion of Ab against the three main Ad capsid proteins (fiber, penton, hexon) by affinity chromatography in Ad immune serum, greatly reduces the inhibitory effect of these sera on vaccine vector efficacy, as demonstrated by an almost complete restoration of transgene expression level. 15 Although nAbs targeting the main 3 capsid proteins have been detected in vitro, 15,[17][18][19] they do not equally contribute to Ad vector neutralization in vivo. The relative contribution of each subset of nAbs has been teased apart by vaccinating Ad preimmuned animals with capsid chimeric Ad vectors.…”

Strategies to overcome host immunity to adenovirus vectors in vaccine development

“…In addition to Ad-specific T cells, Ad-specific neutralizing antibodies (NAbs), predominately directed against hexon, fiber and penton base, are generated following the first exposure to Ad, whether naturally occurring or after one immunization with an Ad vector [51,91,92]. These NAbs inhibit Ad transduction of cells by a variety of methods, including prevention of cell attachment or facilitation of virus aggregation and clearance [51].…”

“…Further studies indicated that HD-Ad vectors delivered systemically induce early, capsid-dependent inflammatory cytokines similar to those induced by Ad5 vectors, although the induced cytokine release is short-lived in comparison and adaptive immune responses are not induced [154]. The discovery that the majority of anti-Ad immune responses are produced against capsid proteins further emphasizes that, similar to unmodified Ad vectors, systemically delivered HD-Ad vectors must evade capsid-specific PEI to provide optimal efficacy in humans [51,81,82,91,92].…”

Xenogenic Adenoviral Vectors

“…The humoral immune response to HAdVs consists of both neutralizing and nonneutralizing antibodies. 20 Although the anti-HAdV-neutralizing antibodies (nAbs) targeting the three major capsid proteins, hexon, penton, and fiber, have been confirmed, 21,22 the anti-hexon nAbs are the most significant in vector neutralization. The major epitopes for anti-hexon nAbs are located in the exposed loops, also known as hypervariable regions, located on the surface of the virus particle.…”