Myeloid Cells Exert Immunosuppressive Activity and Have Prognostic Value In Hodgkin Lymphoma

Inflammation dominates both the histological and the clinical pictures of Hodgkin’s Lymphoma (HL) and there are several clues that accessory cells such as neutrophils and macrophages have an important role in the development and progression of the disease and are well recognized negative prognostic factors.

In order to identify an additional HD marker with prognostic significance, we evaluated 70 HL patients for circulating levels of Myeloid Derived Suppress Cells (MDSC), identified as CD34⁺, CD45⁺, CD11b⁺, CD33⁺, CD14^- in peripheral blood by flow cytometry at diagnosis. All patients were treated with ABVD but those patients who showed an interim-PET (PET-2) positivity were switched to BEACOPP followed by autologous transplant.

In addition, neutrophils (N) obtained from 15 HL patients we tested for phagocytic activity, enzymatic activity of arginase (ARG-1) (a molecule able to suppress T-lymphocytes activity), expression of ARG-1 and pro-angiogenic factor PROK-2, and suppression of healthy T-lymphocytes activation in co-culture experiments.

In HL patients the mean absolute count of MDSC at diagnosis was higher than healthy controls (2.7±0.2 cells/uL versus 1.6±0.1 cells/uL), correlated with PET-2 positivity and identified all except one (3 out of 4) patients with relapse/progression despite a PET2-oriented therapy. MDSC count at diagnosis added further prognostic information to PET-2 since, among the 62 PET-2 negative patients, 4 relapsed, all of them with high MDSC count at diagnosis. On the whole,13 patients out of 70 (19%) presented with MDSC count higher than 4.5 cells/uL (cut off identified by ROC analysis) at diagnosis and 9 (69%) of them had a negative event: 5 were PET-2 positive and 4 relapsed within 18 months. On the contrary, only one patient with low MDSC count at diagnosis had progression of disease. In term of PFS, MDSC count and PET-2 had a similar predictive value (respectively p=<0.0001 and p=0.048, Fischer exact test). Combining the information given by MDSC count and PET2, we found that after a median follow up of 24 months no progression occurred in patients with a low MDSC count at diagnosis and a negative PET-2. On the contrary, patients with either high MDSC or PET-2 positivity or both have a median PFS of 14.6 months (p<0.0001).

In vitro studies showed an increase of ARG-1 expression in N-HL up to 100 folds and of PROK-2 up to 36 folds compared to healthy subjects matched for age and sex (p=0.001), independently from tumor load and other well-known prognostic factors.

N-HL exhibited a reduced phagocytosis (73.1 ± 3.7 vs 93.2 ±1.9 %, p=0.0008) and an increased arginase activity up to 15 times compared to healthy subjects matched for age and sex.

Finally, we co-cultured lymphocytes isolated from healthy subjects (h-Ly) with neutrophils isolated from fresh peripheral blood of HL patients (HL-N) or healthy subjects (h-Ne). After PHA-P stimulation, the activation markers CD69, CD25 and CD71 were increased in h-Ly while their expression was down-regulated by co-culture with HL-N (but not h-Ne) at ratio 1:4 and 1:8 at all tested time-points.

MDSC are increased in peripheral blood of HL patients at diagnosis, correlate with interim PET, and have a strong prognostic value, earlier and more easily accessible than interim PET. Neutrophils isolated from HD patients have a reduced phagocytic activity, produce an angiogenic factor (PROK-2) and high amount of arginase and are able to reduce normal lymphocytes activation. These findings represent a paradigma of how a myeloid compartment may favor the development of a lymphoid neoplasia through T-cell impairment and encompasses a prognostic significance.

No relevant conflicts of interest to declare.