After the first chemotherapy session for CLL, my dad has a persistent fever. Why?

Hello doctor,

I would like to enquire about my dad's health. He is 82 years old and has been having chronic lymphocytic leukemia for the past seven years. He had no symptoms other than the high blood cell count and was doing regular checkups every six months. Recently, his hemoglobin level dropped a lot (around 3 to 4 g/dL), white blood cell count was very high, he also had a high percentage of antibodies in his blood. I was also told the red cells were being destroyed. He was admitted to the hospital and was given Mabthera, after which he got better and went back home. His oncologist prescribed him a chemotherapy treatment of Mabtehra and something else. After the first chemotherapy session, he got a fever spell that has been persisting till today. It has been two weeks, and he still has a high fever, around 102.2 to 104 degrees Fahrenheit once every 24 hours.

He was admitted to the hospital the day he had the first fever peak and all tests have been run to try to identify an infection or a cause for the fever. He underwent blood tests, X-rays, scans, hemoculture, etc. Nothing seems to show what the reason for the fever is. We were told it could be a symptom of the CLL itself. What do you think? I would like to seek a second opinion.

Thanks in advance.