A male patient presents to the clinic with a history of recurrent infections and unexplained weight loss over the past few months. He reports having unprotected sexual intercourse witl multiple partners in the past and a history of intravenous drug use. Physical examination reveals oral thrush, generalized lymphadenopathy, and a low-grade fever. An infectious agent is believed to be the cause of his symptoms. Which is the key cell that is killed by this infectious agent?
a. Neutrophil precursor cells
b. CD4 T-cells
c. B-cells
d. Macrophages