ИСТИНА

HIV-1 restriction factors are cellular proteins that inhibit viral replication at post-entry stage of virus life cycle. The dozens of cellular factors with antiviral activities have been described. However, only six main protein families, i.e. APOBEC, TRIM, Tetherin, SAMHD, and MX2, specifically restrict the replication of HIV. The mechanisms of restriction are specific for each factor, and affect different stages of viral replication that overall makes cells highly resistant to virus. Nevertheless, HIV has evolved its own proteins Vif, Vpr, Vpu, Vpx, Nef, which efficiently counteract restriction factors and abolish their protective effects. The role of restriction factors in HIV-1 replication has been studied extensively upon infection with cell free virus. However, an HIV-1 restriction during cell-to-cell mode of virus transmission, which dominates at the early stages of infection in vivo, is not studied comprehensively. In this work, we have constructed HIV-1 packaging plasmids with deletions in Vif, Vpu, Vpr or Nef gene, and determined the levels of defective virus replication at the different settings including various types of producer and target cells, and modes of transmission. To quantify the levels of cell-to-cell infection, the improved replication dependent vectors were used (Shunaeva A et al. J Virol. 2015 Oct 15;89(20):10591-601). The effect of accessory gene deletion on HIV-1 infectivity was dependent on cell type and mode of transmission. Particularly, the differences between wild type and mutated HIV-1 replication levels were significant in lymphoid cells and neglectable in HEK 293T cells. This suggests that lymphoid cells express a wide gamma of HIV-1 restriction factors in the response to infection. When comparing cell-free infection with cell-coclulture infection, the defect in the expression of one of accessory proteins resulted in ten fold and more decrease in infectivity with cell-free virus derived from Jurkat T cells. In contrast, the levels of replication of defective virus in coculture of lymphoid cells were reduced less than 1.5-2 times in comparison to replication of wild type virus, indicating that cell-to-cell transmission overcomes the restriction imposed by deletion of HIV-1 accessory genes. Interestingly, the replication of Vpu-defective HIV-1 was even 3-5 fold more efficient in cell cocultures than infectivity of wild type virus, whilst under cell-free mode of infection the deletion of Vpu decreased the HIV infectivity. Overall, our data suggest that hijacking cell-to-cell mode of transmission can be an additional mechanism that HIV-1 uses to counteract cellular restriction.