Serum Proteomic Analyses Suggest That the HMGB1 and Other Inflammatory Pathways Are Operational in MBL and Are Less in Overt CLL

Background. CLL-like monoclonal B-ceII lymphocytosis (MBL) is considered a requisite precursor of CLL, with 1-2% of subjects annually progressing to CLL requiring therapy. The role of immune alterations leading to and operating in MBL and controlling progression to CLL is not well characterized. Since an increased frequency of immune-related conditions associated with immune dysfunction exists prior to CLL diagnosis (Landgren et al, Br J Haematol 2007 and Blood 2007; Andersen et al, Leukemia 2020), immune alterations likely exist in MBL. We have examined the serum protein profiles of MBL and CLL in search of clues linking immune dysfunction with malignant transformation.

Objectives. 1. Characterize the serum proteomic profiles of MBL individuals, IGHV-mutated CLL (M-CLL) and IGHV-unmutated CLL (U-CLL) patients, and age-matched healthy controls (HC). 2. Compare the serum proteomic profiles between the groups. 3. Assess the effect of IGHV mutation status on serum proteomic profiles in CLL.

Methods. A total of 12 MBL, 12 M-CLL, 12 U-CLL and 12 age-matched HC were studied. Patients were cared for at Northwell Health, New York (n=25) and Hospital del Mar, Barcelona (n=11). All patients were treatment naive except for one U-CLL patient who was treated one year beforehand. Serum samples were collected, and their protein levels measured employing SOMAmers (modified single-stranded DNA aptamers; SomaLogic) to quantify relative levels of 1,310 proteins. P-values <0.05 were used to define significantly different protein levels between groups. Ingenuity Pathway Analysis (IPA; QIAGEN) was employed to evaluate potential protein interactions and pathways. IPA pathways with P-value <0.05 and Z-score ≥2 or ≤-2 were considered to be activated or inhibited, respectively.

Results. Overall, the levels of 862 proteins differed significantly between groups: MBL vs. HC: 10 downregulated (d) and 24 upregulated (u); M-CLL vs. HC: 206d and 6u; U-CLL vs. HC: 54d and 40u; M-CLL vs. MBL: 384d and 5u; U-CLL vs. MBL: 74d and 24u; and M-CLL vs. U-CLL: 35d and 0u. IPA highlighted a role for the pro-inflammatory HMGB1 pathway in several comparisons. First, an activated HMGB1 pathway was predicted in MBL compared to HC, together with activation of phagocytes, and an inhibition of the systemic immune suppressor TGF-β. Second and consistent with the former, U-CLL patients displayed an activated HMGB1 pathway compared to HC, along with other signs of immune stimulation (activated NFkB and Th1 pathways, maturation of dendritic cells, and inhibition of TGF-β) and leukemic progression (activated progression of tumor, and leukocyte extravasation). Third and contrary to the above, the HMGB1 pathway was inhibited when comparing M-CLL to HC, in line with a global immune suppression signature (inhibited PRR, GM-CSF, FcεRI, IL1, IL8, TNF, Th1, STAT3 and NFkB pathways, in addition to inhibited cell movement, viability and activation). Notably, inhibition of immune pathways was predicted for both M-CLL and U-CLL compared to MBL (diminished TNF and IL6 signaling, and reduced cell movement), although the greatest differences were seen for M-CLL vs. MBL comparison, including blockade of the HMGB1 pathway in M-CLL. Finally, the M-CLL vs. U-CLL comparison suggested inhibited INFγ, IL2, IL3, IL4, NFkB, and decreased T lymphocyte stimulation and movement of tumor cells in M-CLL patients.

Conclusions. An increased pro-inflammatory signature with involvement of the HMGB1 pathway was identified in MBL and U-CLL compared with HC, whereas the opposite was seen for M-CLL. Since MBL most often exhibit mutated IGHV (91% of cases in our cohort), these findings suggest immune stimulation as a characteristic feature in the pre-leukemic and U-CLL leukemic stage that surprisingly is not operative in M-CLL. Consistent with this, M-CLL displayed a global immune suppression (HMGB1 pathway inhibition), whereas U-CLL exhibited signs of immune stimulation (HMGB1 pathway activation) compared to HC which may relate to distinct capabilities of the two subtypes to interact with the microenvironment. Lastly, the increased inflammatory signature identified in MBL, which are mainly IGHV-mutated, was lessened in CLL, mainly in M-CLL patients. This is consistent with a decreased influence of immune imbalance and the HMGB1 pathway associated with IGHV-mutated clonal expansions.

Acknowledgments. GB is supported by a grant from Fundación Alfonso Martín Escudero.