Chronic Lymphocytic Leukemia (CLL)/Small Lymphocytic Leukemia (SLL) Exhibit Altered Cytokine Protein Levels in Peripheral Blood Serum

Chronic lymphocytic leukemia (CLL)/Small lymphocytic leukemia (SLL) is one of the most common forms of indolent lymphomas in elderly adults. Currently, CLL is not treated until it develops into later stage disease. An increase in the knowledge of the biology of CLL could aid in the development of new treatment strategies for early stage CLL, thus positively impacting disease progression. We therefore investigated the cytokine levels present in peripheral blood (PB) serum of CLL patients and compared them to levels in healthy donors. Methods: PB was obtained from 25 untreated CLL and 3 untreated SLL patients and 29 normal healthy donors under an IRB approved protocol. Serum was stored at −80°C until analyzed. 86% of the patients were Rai 0/1, 3.5% Rai stage 2, and 10.5% unknown at diagnosis. Risk stratification based on cytogenetics and FISH found of the enrolled patients, 47% good, 25% intermediate, and 14% poor risk. The risk factor was unknown in 14%. β-2 microglobulin and 54 cytokine protein levels in 2 different serum samples per patient (collected at least one year post diagnosis) were measured in duplicate using MILLIPLEX™, a multiplex Luminex based technology. Genespring 11.5.1 software was used to convert the data into base-2 logarithmic values and then apply a median baseline transformation across all samples. Data is grouped according to the source of the sample (CLL or normal PB serum). A Filter on Volcano Plot analysis is then done. This filter analysis performs an unpaired t-test, which yields a p-value as well as computes the fold change of each cytokine. Results: As expected, β-2 microglobulin was significantly higher in CLL patients compared to normal samples (p=5.17×10⁻⁷, 1.79 fold). Using a minimum of a 1.5 fold change and p-value≤0.05, 16 cytokines had significantly higher expression and 9 cytokines had significantly lower expression in CLL samples compared to normal samples (see Table 1). Conclusion: These changes in cytokine levels help provide insight to the peripheral blood microenvironment, in which circulating CLL cells reside. Some cytokines were substantially higher in CLL patients; soluble IL-2 receptor alpha (sIL-2Rα) and stem cell factor (SCF). The substantially higher levels of sIL-2Rα have also been observed in follicular lymphoma (FL) and appear to predict which FL patients will have a reduced survival (Yang et al., Blood 2011). Levels of sIL-2Rα correlating to survival may be a phenomenon seen in all B-cell lymphomas. SCF is thought to be important in early B-cell development but its receptor c-kit (CD117) has not been reported to be expressed on B-CLL cells. The chemokine receptors CXCR4, CXCR5 and CCR7 are expressed on B-CLL cells. Interestingly, their corresponding ligands, CXCL12, CXCL13, and CCL21 are significantly higher (Table 1) in the PB serum of CLL patients. It is likely that existing immunomodulatory therapies, such as IMiDs, lenalidomide or thalidomide alter the PB levels of the cytokine milieau. Other successful hematological malignancy therapies involve targeted monoclonal antibodies. Therefore, a deeper understanding of the cytokine microenvironment will provide guidance in the development of future targeted therapies or highlight current therapies for other malignancies that could be promising for CLL.

No relevant conflicts of interest to declare.