Effects Of Bendamustine Plus Rituximab On The Distribution Of Normal Peripheral Blood Leucocyte Populations In Advanced-Stage Chronic Lymphocytic Leukemia (CLL)

Management of B-cell chronic lymphocytic leukemia (CLL) is currently undergoing profound changes. Accordingly, new treatment options with an expected less toxicity than standard regimens are been explored. Recent results show that chemoimmunotherapy may improve the life expectancy of CLLpatients and has proven to be more efficient than chemotherapy alone in depleting malignant cells. Despite its efficacy, little is known about its precise immunomodulatory effects.

To evaluate the effects of chemoimmunotherapy with bendamustine plusrituximab (BR) on the distribution of normal residual leucocyte populations in peripheral blood (PB) from advanced-stage CLL patients, with special emphasis on maturation-associated B-cell subsets (immature, naïve, memory IgM/IgG/IgA and plasma cells).

Distribution of PB neoplastic cells and residual normal immune cell subpopulations were analyzed in 72 CLL patients with advanced disease (Binet B/C), before therapy (M0) and after 1 course of BR (M1). The same analysis was repeated 3 months after completing treatment (M3) in 31/72 patients. PB leucocyte cell subsets were identified at each time-point by 8-color flow cytometry with monoclonal antibody reagents against CD3, CD4, CD5, CD8, TCRgd, CD19, CD20, CD27, CD38, CD45, CD56, sIgM, sIgA, sIgG, sIgLambda and sIgKappa.

After the first BR course, absolute counts of all PB myeloid subsets were significantly decreased as compared to time M0, including neutrophils (2,744±1,830 vs 4,764±2,906 cells/uL, p<0.001), eosinophils (132±185 vs 215±245 cells/uL; p<0.001), basophils (37±28 vs 59±47 cells/uL, p<0.001), monocytes (334±280 vs 504±424 cells/uL, p=0.001) and dendritic cells (DCs, 41±40 vs 89±168 cells/uL, p=0.02), as well as NK cells (120±147 vs 550±599 cells/uL, p<0.001). At M3, all these populations remained decreased when compared to M0, but at similar levels to M1 (except for the absolute number of DCs, found to be increased vs. M1 -74±46 vs 41±40 cells/uL, p=0.008- and closer to M0).

In turn, total T cells were reduced in M1 as compared to M0 values (818±655 vs 3,905±2,375 cells/uL, p<0.001), due to decreased numbers of CD4+ (424±376 vs 1,573±1,204 cells/uL, p<0.001), CD8+ (342±330 vs 1,334±1,218 cells/uL, p<0.001) and TCRgd (21±28 vs 141±289 cells/uL, p=0.001) T cells, leading to an increased CD4/CD8 ratio (1.8±1.3 vs 1.4±0.8, p=0.004). Also, decreased levels of CD4 (222±156 cells/uL), CD8 (501±544 cells/uL) and TCRgd (21±40 cells/uL) T cells were observed at time M3 vs. baseline values. No changes (p>0.05) were observed for CD8 and TCRgd for M3 vs. M1, while CD4+ T-cell numbers were significantly reduced (p=0.006), resulting in an inverted CD4/CD8 ratio (0.9±1.0 vs. 1.8±1.3, p=0.005) at the M3 time-point.

As regards B cells, the absolute count of both neoplastic and normal B lymphocytes were significantly decreased at time M1 vs. M0 (3,363±9,353 vs 53,521±56,602 CLL cells/uL and 2±6 vs 58±107 normal B-cells/uL, p=0.006 and p<0.001, respectively). Within the normal residual B-cell compartment, we found significantly decreased numbers of immature (0.07±0.22 vs 6.55±21.64 cells/uL, p=0.01) and memory (1.3±14.7 vs 35.1±43.6 cells/uL, p<0.001) B cells -including sIgM (0.5±2.3 vs 14.5±24.8 cells/uL, p<0.001), sIgG (0.2±1.0 vs 11.5±17.2 cells/uL; p<0.001) and sIgA (0.6±3.1 vs 9.5±12.5 cells/uL, p<0.001) memory B cells-. At time M3, decreased (p<0.01) naïve (0.46±2.58 cells/uL) and memory B-cells (1.34±6.75 cells/uL), including IgM (0.46±2.58 cells/uL), IgG (0.34±1.69 cells/uL) and IgA (0.09±0.31 cells/uL), but not immature cells (2.28±8.84 cells/uL, p=0.9), were observed as compared to time M0. Differences did not reach statistical significance when comparing M3 vs. M1. The number of circulating plasma cells did not significantly vary during treatment.

All PB leucocyte subsets are affected by BR treatment in advanced-stage CLL. Interestingly, at time M3 the CD4+ T-cell subset continues to be decreased, while the other T-cell compartments seem to remain stable. Also, normal B cells are affected by BR treatment, and the depletion induced after one course therapy is maintained even three months after finishing BR therapy, except for immature B cells, that seem to be the first to recover in PB. Further studies will offer a more accurate insight into the biology of cell recovery during and after BR therapy in CLL patients.

No relevant conflicts of interest to declare.