FOS and B-cell chronic lymphocytic leukemia: c-fos functions as a subunit of a group of dimeric transcription factors collectively referred to as activating protein 1 (AP-1) that are implicated in a wide range of processes, including proliferation and oncogenic transformation.[41] Hence, we studied the effects of CLL exosomes derived from CLL culture medium and patient plasma on proliferation of HS-5 cells.