Multiploid Inheritance of HIV-1 during Cell-to-Cell Infection

Abstract

During cell-to-cell transmission of human immunodeficiency virus type 1 (HIV-1), many viral particles can be simultaneously transferred from infected to uninfected CD4 T cells through structures called virological synapses (VS). Here we directly examine how cell-free and cell-to-cell infections differ from infections initiated with cell-free virus in the number of genetic copies that are transmitted from one generation to the next, i.e., the genetic inheritance. Following exposure to HIV-1-expressing cells, we show that target cells with high viral uptake are much more likely to become infected. Using T cells that coexpress distinct fluorescent HIV-1 variants, we show that multiple copies of HIV-1 can be cotransmitted across a single VS. In contrast to cell-free HIV-1 infection, which titrates with Poisson statistics, the titration of cell-associated HIV-1 to low rates of overall infection generates a constant fraction of the newly infected cells that are cofluorescent. Triple infection was also readily detected when cells expressing three fluorescent viruses were used as donor cells. A computational model and a statistical model are presented to estimate the degree to which cofluorescence underestimates coinfection frequency. Lastly, direct detection of HIV-1 proviruses using fluorescence in situ hybridization confirmed that significantly more HIV-1 DNA copies are found in primary T cells infected with cell-associated virus than in those infected with cell-free virus. Together, the data suggest that multiploid inheritance is common during cell-to-cell HIV-1 infection. From this study, we suggest that cell-to-cell infection may explain the high copy numbers of proviruses found in infected cells in vivo and may provide a mechanism through which HIV preserves sequence heterogeneity in viral quasispecies through genetic complementation.

Alphaherpesvirus axon-to-cell spread involves limited virion transmission

“…Studies of plant RNA viruses generally report small effective population sizes during transmission, whereas studies with one plant DNA virus reported a large population of virions during spread in single plant (21)(22)(23). The transmission of HIV between T cells involves transmission of a large number of virions across a virological synapse (2,24). The same concept has been suggested for HSV-1 transmission in T cells (25).…”

“…In either case, spread from cell to cell often involves direct transmission of infectious particles with no or limited release of infectious particles into the extracellular milieu (1). Cell-to-cell spread of some infections, such as HIV, involves transfer of many viral particles (2), whereas other infections, such those caused by poliovirus, involve transfer of small numbers of particles (3). Virions of members of the alphaherpesvirinae, including the human pathogens HSV-1 and HSV-2, varicella zoster virus, and the animal pathogen pseudorabies virus (PRV) infect epithelial surfaces and transmit efficiently to innervating axons of the peripheral nervous system (PNS) (4).…”

Improvement of HIV-1 and Human T Cell Lymphotropic Virus Type 1 Replication-Dependent Vectors via Optimization of Reporter Gene Reconstitution and Modification with Intronic Short Hairpin RNA

“…Several different techniques have been used to distinguish target cells from effector cells, such as labeling of cells with fluorescent dyes (21) or mechanical separation of cells by the use of transwells or by continuous shaking of mixed cells (31). However, each of these approaches has its issues.…”

“…Regardless of the precise mechanism, virus transmission and consequent infection are more efficient when the infected cells are in contact with the target cells than when virus is released into body fluids (9,17,18). Furthermore, cell-to-cell infection also alters certain properties of viral infection; for example, it increases the multiplicity of infection (19)(20)(21), enhances the resistance to some antivirals (22,23), allows the virus to bypass potent neutralizing antibodies (24), and contributes to the genetic diversity of HIV (reviewed in reference 25).…”

Antiretroviral Agents Effectively Block HIV Replication after Cell-to-Cell Transfer

“…Cell-to-cell HIV transmission has often been associated with a more efficient mechanism of infection (16,17,32,34,37). Infected cells bind and interact with target CD4 ϩ T cells in manners that promote virus transmission through the so-called "virological synapse" in which the interaction between CD4 and the HIV envelope glycoprotein plays a prominent role (22,31,35).…”