Cell-cell interactions and subcellular protein dynamics during retrovirus cell-to-cell transmission
Final Report Abstract
Other studies have visualized stable cell-cell contacts in MLV- and HIV-infected lymphoid tissues, indicating that retrovirus-presenting cells locally spread the infection through cell contacts called virological synapses. Contacts were retrovirus induced and/or stabilized since they decreased after infection with mutant retroviruses lacking the Env glycoprotein or Env with reduced receptor-binding capacity. However, the functional link that the observed cell-cell contacts contribute to the spread of the infection is difficult because of the use of non-infectious retrovirus mutants. In our project, we used a different approach by removing host cell adhesion proteins, known to mediate cell-cell contacts of leukocytes, in the context of WT retrovirus infection. Infection experiments in LFA1- and ICAM1-deficient mice with WT MLV clearly demonstrate a role of cell adhesion in the local dissemination of MLV in vivo. MLV infection spread by a factor of ~5 within 3 days, i.e., an estimated doubling time of 1.69 per day, in WT mice. In the absence of LFA1 or ICAM1, we observe a significant reduction inMLV spread (factor ~2) that corresponds to a doubling time of 1.24 and 1.28 per day, respectively. In summary, these data demonstrate that the cell adhesion proteins LFA1 and ICAM1 are critical host factors for the efficient spread of MLV in vivo and thereby support the concept that cell-cell contacts drive retrovirus infection. We have further established in vitro co-cultures with relevant primary cell types to demonstrate that the polarity in the LFA1-ICAM1 interaction is relevant for MLV transmission. Whereas ICAM1 was critical on the MLV-presenting donor cells, LFA1 was important on the target cell during trans- and cis-infection. Establishing infection within the host by targeting specific cell subsets within local tissues is considered a bottleneck for retroviruses in vivo. Thereby, the low frequency of MLV target cells at the time point of infection might be a limiting factor for the productive infection of cells. Alternatively, an additional bottleneck might exist at the level of retroviral particle fusion with target cells. Applying a BlaM-based VLP fusion assay in vivo, we were able to demonstrate that fusion is not the limiting step for MLV to establish infection in lymphoid tissue in vivo. Despite the high fusion rate of MLV with the naive CD4+ T cell population most cells are not permissive to MLV, possibly because of restriction factors that block infection before integration. Whether these cells, however, play a role in the immune response to MLV through innate sensing of the infection or indirectly support MLV spread by creating an activating tissue environment needs to be determined.
Publications
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LFA1 and ICAM1 are critical for fusion and spread of murine leukemia virus in vivo. Cell Reports, 2022 Jan, 18;38(3):110279
Engels R, Falk L, Albanese M, Keppler OT, Sewald X
