Answer:
5. Lack of viable T cells
Explanation:
The thymus is a crucial organ for the development and maturation of T cells, a type of lymphocyte involved in cell-mediated immunity. Without a functioning thymus, the production of T cells is impaired or absent, leading to a lack of viable T cells. This deficiency in T cells compromises the body's ability to mount an effective immune response against pathogens and increases the risk of infections and immune-related disorders.