This is really not good. SARS-infected cells are becoming MHC-negative. This means that chewed up pieces of the virus are not appearing on the cell surface for T cells to be able to recognize.
While innate immune cells (NK cells) actively clear cells that are MHC-, this is a big blow to adaptive immunity, especially when coupled with antibody avoidance techniques the virus has.
“[T]he killer T cells used in the study were not effective at eliminating the virus in infected cells. When the scientists took a closer look they found that a molecule known as major histocompatibility complex, or MHC, was missing.”
