IDO1 and B-cell chronic lymphocytic leukemia: IDO+ myeloid cells could be detected in CLL lymph nodes, but the concentrations of tryptophan and its key degradation products in serum specimens from patients with the highest frequency (MDSChi (n = 10)) and the lowest frequency (MDSClo (n = 10)) of aberrant monocytes, did not detect any difference, suggesting that the comprehension of clinical impact of mo-MDSCs in CLL is still largely unknown [52].