Low Ratio of Inter-Follicular CD8/FOXP3-Positive Regulatory T-Cells Is Associated with a favourable Overall Survival in Follicular lymphoma (FL).

Background: By using gene expression profiling, a major role for T-lymphocytes and macrophages (M) have been observed, defining 2 prognostic subgroups. Then, conflicting results were published with both positive and negative impacts of different T-cells subpopulations, particularly for T-regulatory (Tregs) cells. In addition, CD8 and CD4 T-cells were mentioned as key cells in progression and/or transformation process and CD68+ M associated with a poor outcome. Functional studies have suggested that follicular dendritic cells have to be considered as important cells in comprehensive biology of FL, and that the function is probably associated with the proximity of tumour cells, different in intra-or inter-follicular location. We investigate the role CD8+ T cells, FOXP3+ Tregs and M, and calculate in large fields the different numbers of these cells, particularly focusing on their intra-versus inter-follicular localisation. To approach a more dynamical view of the immune response we correlate the ratio CD8+/Treg in these 2 compartments and correlated results with clinical parameters and outcome.

Patients and Methods: Immunochemistry was used to study numbers and distribution of CD8, CD68, and Tregs cells in 89 patients with FL (65 at diagnosis and 24 at relapse). Since it can be expected that overall effect of Tregs depends on their number in relation to CD8+ effectors T cells, we determined the corresponding ratio for each patient and correlated the results with clinical parameters.

Results: The median age of the patients was 58 years (range 23–91 years), and the male/ female ratio was 1.2. There were 67 % of the patients with grade1, 17 % grade 2 and 16 % grade 3a. Advanced stage (Ann Arbor IV) was observed in 24 %. The distribution of the population according to the FLIPI was the following: low risk 36 %, intermediate risk 45 % and high risk, 19 %. The interfollicular CD8/FOXP3+ cell ratio was significantly higher in patients with grade 3 tumours (2.04 versus 1.63) and with a high risk FLIPI index (2.99 versus 1.53) compared with those with grade 1–2 tumours or a low–intermediate FLIPI index. The same results were obtained with the intra-follicular CD8+/FOXP3 + cell ratio. The inter-follicular CD8/FOXP3 ratio was found to have prognostic value for overall survival with a 5-years OS of 82% versus 59% for a ratio of less or more than 1.68. Moreover, an inter-follicular FOXP3+ cell number of more than 86 cells/mm² was correlated with a more favourable outcome (p = 0.03). When comparing the 2 groups at diagnosis and relapse, we observed a significant difference between the number of CD68 cells both in intra-follicular locations (39.23 at diagnosis versus 32 at relapse, p= 0.07) and inter-follicular locations (96 at diagnosis versus 62 at relapse, p=0.05). The CD8/FOXP3 ratio in inter-follicular locations was significantly different (1 .66 at diagnosis versus 2.2 at relapse, p=0.05).

Conclusion: The presence of abundant FOXP3+ cells with a low CD8/FOXP3 ratio is probably the mark of an active immune response during tumour development, with lymphoma cells acting as targets or bystanders.