Significant Expansion of Myeloid Derived Suppressor Cells in Patients with High- Risk Breast Cancer Treated with Dose Dense Adjuvant Chemotherapy

Myeloid derived suppressor cells (MDSCs) have been reported to be expanded in cancer patients, following growth factor administration and after chemotherapy. These cells have been associated with a loss of T-cell number and function and provide one mechanism of immune evasion. We examined the effect of dose dense chemotherapy on immune phenotypes and function in patients with breast cancers 4 cms or larger and/or four or more involved nodes. The adjuvant therapy was dose-dense doxorubicin, cyclophosphamide (AC) followed by paclitaxel (P), then 33 doses of radiation (R). Blood samples were obtained and studied prior to therapy, 1 week post AC and 1, 15 and 21 weeks post P and then 3, 6 and 12 months later. Flow cytometric analyses of cellular phenotypes were done on these blood specimens and compared to the levels prior to therapeutic intervention and to normal age and sex matched donors. Twenty-three pts have been followed a median of 29 months (range 5.5–50.5 months) from study entry. Two patients relapsed 8 and 23 months after diagnosis. T-cell CD-4 numbers declined following AC from an average of 4.9±0.5 ×10⁶/ml to 1.7±0.3×10⁶/ml, but increased to an average of 2.7± 0.3 × 10⁶/ml, 21 weeks after P or 12 weeks after R. In this study the MDSCs were defined as Lin- (CD3, CD19, CD14 and CD13), HLA-DR- and CD33+. The numbers of MDSCs, which in normal donors were 0.62±0.16×10⁶/ml and in the cancer patients at diagnosis were 11.8±9.6×10⁶/ml increased to 58.4±25.9×10⁶/ml 15 weeks after R. They remained significantly elevated through one year after diagnosis when they were 27.3±12.3×10⁶/ml. The majority of the MDSCs had a high side scatter and forward scatter by flow analysis suggesting a granulocytic commitment rather than a monocytic commitment. The increase in MDSC numbers was apparently associated with R as the numbers of MDSCs were not significantly increased by AC (15.7±13.5×10⁶/ml) or P (10.9±6×10⁶/ml) one week following completion of each cycle of dose dense therapy. In association with the increase in MDSCs there was a significant decrease in PHA proliferation by the peripherial blood mononuclear cells (MNCs) and suppressive activity by irradiated MNC for allergenic lymphocytes.