Impact Of The Number Of Prior Treatment Lines Received On The Distribution Of Peripheral Blood Leukocyte Subsets In Advanced-Stage B-Cell Chronic Lymphocytic Leukemia (CLL)

It is currently well-known that B-cell chronic lymphocytic leukemia (CLL) patients have an impaired immune function -particularly in advanced disease-, which significantly contributes to a higher risk of infections. The introduction of new effective therapeutic agents, such as the purine analogues (or alkylating agents with concomitant properties of purine analogues) plusanti-CD20 monoclonal antibodies, have significantly increased the rate of complete responses in CLL, but so far their impact on the overall immune function and the spectrum of infections occurring in CLL patients after therapy, remains to be fully understood.

To evaluate the effect of the number of treatment lines received on the different normal circulating leucocyte cell populations, including normal B-cell subsets, in advanced-stage treated CLL.

The distribution of peripheral blood (PB) leukocytes was analyzed in 85 untreated CLL patients, and compared to that of 63 patients who had previously been treated with 1 line of treatment (n=39) or >1 line of treatment (n=24), and who failed to respond. Analysis was performed by 8-color flow cytometry with monoclonal antibodies against CD3, CD4, CD5, CD8, TCRgd, CD19, CD20, CD27, CD38, CD45, CD56, sIgM, sIgA, sIgG, sIgLambda and sIgKappa.

The absolute count of circulating malignant B cells was not significantly different (p>0.05) in the untreated vs. previously treated patients who received 1 or >1 line of treatment (77,627±84,211 vs 67,994±72,087 vs 59,282±74,206 cells/uL; respectively). In contrast, as compared to untreated patients, PB normal B cells were found to be reduced in patients who had received either 1 line or >1 line of treatment (89±142 vs 36±57 and 23±32 cells/uL, p=0.004 and p<0.001, respectively), but at similar levels between the two groups of previously treated patients (p>0.05). When dissecting the normal B-cell subsets, therapy-related decreased B-cell numbers were mostly due to a reduced number of circulating memory B cells (67±98 vs 21±45 and 15±26 cells/uL; p=0.001 and p<0.001, respectively), including all memory isotypes: IgM (24±31 vs 5±13 and 5±6 cells/uL, p<0.001), IgG (25±59 vs 10±32 and 6±13 cells/uL; p=0.008) and IgA (18±30 vs 5±10 and 6±12 cells/uL; p=0.001 and p=0.003). No significant differences were found as regards the absolute count of immature (5±11 vs 8±26 and 3±11 cells/uL; p>0.05) and naïve (16±55 vs 6±18 and 4±8 cells/uL; p>0.05) B cells, nor for circulating plasma cells (3±18 vs 5±21 and 2±6 cells/uL; p>0.05), regardless of the therapy status.

As compared to untreated patients, the absolute count of CD4+ T cells and CD4/CD8 double negative TCRαβ cells were significantly lower in patients with >1 line of treatment (1,836±1,340 vs 1,256±1,027 and 131±165 vs 56±97 cells/uL, p=0.03 and p=0.007 respectively) but not in those who had received only 1 line (1,477±1,349 and 201±747 cells/uL; p>0.05). In contrast, therapy did not show a significant impact on the absolute count of PB T CD8+ and TCRgd cells. No statistically significant differences were observed in the number of PB innate immune subpopulations including, neutrophils, eosinophils, basophils, monocytes, NK cells and dendritic cells.

While there are no differences regarding the number of leukemic cells, previously treated patients have significantly reduced counts of total and memory (all isotypes) normal B-cell subsets when compared to untreated patients. Together with this, CD4+ helper T cells could also be compromised after more than 1 line of treatment. Monitoring of these therapy-related immune defects could contribute to a better management of infectious complications in advanced-stage CLL patients.

No relevant conflicts of interest to declare.