Background: Breast cancer is the most common cancer in women but fortunately 80% of those diagnosed with early disease survive without recurrence and those with advanced disease are living longer. It is now suspected that immune editing is a requisite hallmark of cancer but that the ongoing anti-tumour immune response, implied by tumour lymphocyte infiltration, can be a favourable prognostic feature. Little is known however about this equilibrium's impact on or from B Cells either within the tumour or in patient circulation. We therefore aimed to analyse the circulating mature memory B cell compartment in breast cancer patients to identify any changes detectable beyond the tumour environment.

Methods: Between April 2014 and May 2015, 49 healthy volunteers (HVs) and 56 patients with breast cancer were recruited for analysis. Patients were recruited at all stages of disease and the treatment pathway, but none were within 3 weeks of either cytotoxic chemotherapy or radiotherapy. Fresh Peripheral Blood Mononuclear Cells (PBMCs) were extracted and analysed with multi-colour flow cytometry for markers of B lymphocyte differentiation (CD45/19/20/22/23/24/27/38). Subsequent B cell populations were compared between HVs and patients and also across recognised clinico-pathological parameters.

Results: While patients were significantly older than HVs (mean age, 55.7 vs 44.4, p<0.0001), there was no correlation between age and the total B Cell proportion (r=-0.2642, p=0.07) or between age and the subset of greatest interest, memory B Cells (r= 0.1246, p=0.3938) amongst HVs. Patients predominantly were within a year of diagnosis (n=29, 51.8%), had early stage (stage 4, n=18, 32.1%), higher grade (grade 3, n=31, 55.4%), ER+ (n=41, 73.2%), breast cancer and the majority (n=42, 75%) had received cytotoxic chemotherapy. There was no significant difference between HVs and patients in the overall CD19+CD20+ B cell proportion of the CD45+ lymphocytes in blood (mean 6.32% vs 6.151%, p= 0.8269). Of the overall CD19+CD20+ B cell compartment, there were no significant differences in CD23+CD24+/- naive B cells (mean, 62.3% vs 61.05%, p=0.7419), or CD24+CD38++ regulatory B cells (mean, 2.33% vs 2.02%, p=0.6606) between patients and HVs. There was however a substantial depletion of the CD22+CD27+ memory B Cell compartment in patients (mean, 6.31% vs 12.6%, p<0.0001). This difference was apparent both at early (stage 2/3), advanced (stage 4), Grade 2 or 3, ER negative and positive breast cancer groups and, also, for those with early disease, both within a year and longer since their diagnosis. Whilst non-significant, there was a strong suggestion that patients who had received cytotoxic chemotherapy had a smaller memory B cell component than those who did not (mean, 5.90% vs 8.85%, p=0.0531). This effect, if true, seems to be maintained with time, as those who had received chemotherapy less than (mean, 6.56% vs 12.64%, p< 0.0001) as well as those who had received chemotherapy for more than a year (mean, 4.99% vs 12.64%, p<0.0001) prior to analysis had depressed memory B cell components when compared with HVs.

Conclusions: Breast cancer patients, across pathological subtypes, seem to have a preserved total B cell count as a proportion of total peripheral blood mononuclear cells, but have a selectively depleted circulating memory B cell compartment when compared with the equivalent memory B cell compartment of healthy volunteers. Whether this effect is part of an immuno-editing phenomenon or the result of cancer treatment remains uncertain but warrants further investigation. Analysing the antigen reactivity and clonal expansion or function of this memory B cell compartment may yield insights into whether a normal immune, or even anti-tumour, memory response is retained in breast cancer.

Citation Format: Matthew W. Fittall, Dina Levi, Angela Clifford, Vandna Shah, Anthony Cheung, Andrew Tutt, Sophia N. Karagiannis. The circulating memory B cell compartment of breast cancer patients is depleted in comparison with healthy volunteers. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A089.