key: cord-0925803-7qz1o6aa
authors: Jackson, Laurelle; Rodel, Hylton; Hwa, Shi-Hsia; Cele, Sandile; Ganga, Yashica; Tegally, Houriiyah; Bernstein, Mallory; Giandhari, Jennifer; Gosnell, Bernadett I.; Khan, Khadija; Hanekom, Willem; Karim, Farina; de Oliveira, Tulio; Moosa, Mahomed-Yunus S.; Sigal, Alex
title: SARS-CoV-2 cell-to-cell spread occurs rapidly and is insensitive to antibody neutralization
date: 2021-06-01
journal: bioRxiv
DOI: 10.1101/2021.06.01.446516
sha: 209a8b2929f5389fad71ed8ca1161927771db6a6
doc_id: 925803
cord_uid: 7qz1o6aa

Viruses increase the efficiency of close-range transmission between cells by manipulating cellular physiology and behavior, and SARS-CoV-2 uses cell fusion as one mechanism for cell-to-cell spread. Here we visualized infection using time-lapse microscopy of a human lung cell line and used live virus neutralization to determine the sensitivity of SARS-CoV-2 cell-to-cell spread to neutralizing antibodies. SARS-CoV-2 infection rapidly led to cell fusion, forming multinucleated cells with clustered nuclei which started to be detected at 6h post-infection. To compare sensitivity of cell-to-cell spread to neutralization, we infected either with cell-free virus or with single infected cells expressing on their surface the SARS-CoV-2 spike protein. We tested two variants of SARS-CoV-2: B.1.117 containing only the D614G substitution, and the escape variant B.1.351. We used the much smaller area of single infected cells relative to infection foci to exclude any input infected cells which did not lead to transmission. The monoclonal antibody and convalescent plasma we tested neutralized cell-free SARS-CoV-2, with the exception of B.1.351 virus, which was poorly neutralized with plasma from non-B.1.351 infections. In contrast, cell-to-cell spread of SARS-CoV-2 showed no sensitivity to monoclonal antibody or convalescent plasma neutralization. These observations suggest that, once cells are infected, SARS-CoV-2 may be more difficult to neutralize in cell types and anatomical compartments permissive for cell-to-cell spread.

which contains the D614G substitution [20] and is referred to here as D614G.

For cell-to-cell spread, cells were infected by cell-free virus for 16 hours before they were used as the 89 infecting donor cells (Materials and Methods). We validated that spike was expressed on the cell surface Visual inspection showed that while cell-free infection was sensitive to neutralization by the mAb, 110 cell-to-cell spread was not ( Figure 2C ). We normalized the number of foci to the number of foci in the 111 absence of plasma on the same plate to obtain the transmission index (Tx, [4, 20] cell-to-cell spread ( Figure 2D ).

SARS-CoV-2 cell-to-cell spread is not neutralized by convalescent plasma 119 We next proceeded to test neutralization of virus from plasma of convalescent participants. When cell-free D614G virus was used as the infection source, the P RN T 50 combined across partici-135 pants was 328.4 (95% CI 290.6-377.4). In contrast, the P RN T 50 for cell-to-cell spread was 3.6 with 95% 136 CI of 2.2-8.7 ( Figure 3A , left plot). The value for cell-to-cell spread is an extrapolation, given that our 137 most concentrated plasma dilution was 1:25. 

Cell-to-cell spread reduced P RN T 50 to undetectable ( Figure 3B , left plot). 

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