Fiber Mediated Receptor Masking in Non-Infected Bystander Cells Restricts Adenovirus Cell Killing Effect but Promotes Adenovirus Host Co-Existence

Abstract

The basic concept of conditionally replicating adenoviruses (CRAD) as oncolytic agents is that progenies generated from each round of infection will disperse, infect and kill new cancer cells. However, CRAD has only inhibited, but not eradicated tumor growth in xenograft tumor therapy, and CRAD therapy has had only marginal clinical benefit to cancer patients. Here, we found that CRAD propagation and cancer cell survival co-existed for long periods of time when infection was initiated at low multiplicity of infection (MOI), and cancer cell killing was inefficient and slow compared to the assumed cell killing effect upon infection at high MOI. Excessive production of fiber molecules from initial CRAD infection of only 1 to 2% cancer cells and their release prior to the viral particle itself caused a tropism-specific receptor masking in both infected and non-infected bystander cells. Consequently, the non-infected bystander cells were inefficiently bound and infected by CRAD progenies. Further, fiber overproduction with concomitant restriction of adenovirus spread was observed in xenograft cancer therapy models. Besides the CAR-binding Ad4, Ad5, and Ad37, infection with CD46-binding Ad35 and Ad11 also caused receptor masking. Fiber overproduction and its resulting receptor masking thus play a key role in limiting CRAD functionality, but potentially promote adenovirus and host cell co-existence. These findings also give important clues for understanding mechanisms underlying the natural infection course of various adenoviruses.

Modeling Adenovirus Latency in Human Lymphocyte Cell Lines

“…8), the apparent loss of CAR on the cell surface may be due to intracellular sequestration or epitope masking. Although it is not known whether fiber protein can bind CAR within the cell and prevent its externalization, Rebetz and associates have recently characterized the disappearance of cell surface CAR and the species B adenovirus receptor, CD46, shortly after infection (28). These investigators suggested that secreted fiber protein from a small fraction of infected cells masks the cognate receptor in neighboring cells.…”

Adenovirus with Hexon Tat-Protein Transduction Domain Modification Exhibits Increased Therapeutic Effect in Experimental Neuroblastoma and Neuroendocrine Tumors

“…Soluble Ad5 fiber molecule was obtained as described previously (31). A549 cells were transduced at 500 evg/cell with Ad5(GFP) or Ad5PTD(GFP) in the presence or absence of fiber molecules (500 l) for 2 h. The cells were then washed once and seeded in a 24-well plate.…”

“…A second limiting factor is fiber masking of receptors. This is caused by overproduction of adenovirus fiber proteins (4,17,31), which are released from the infected cell before cell lysis. The released fibers bind to CAR on noninfected neighboring cells, thereby limiting infection efficiency of progeny virus (31).…”

“…This is caused by overproduction of adenovirus fiber proteins (4,17,31), which are released from the infected cell before cell lysis. The released fibers bind to CAR on noninfected neighboring cells, thereby limiting infection efficiency of progeny virus (31). The fiber-masking problem is not limited to the Ad5 fiber but was also observed for the Ad35 fiber, which binds to CD46 (31).…”

“…The released fibers bind to CAR on noninfected neighboring cells, thereby limiting infection efficiency of progeny virus (31). The fiber-masking problem is not limited to the Ad5 fiber but was also observed for the Ad35 fiber, which binds to CD46 (31). These limitations must be overcome to develop successful oncolytic adenovirus agents.…”