Is CD94/NKG2A a Novel Target for Lymphoid Malignancies Immunotherapy?.

Background: Natural killer (NK)-cell receptors (NKRs) on CD8+ T cells can modulate antigen-specific T cell activity but their function and rules that govern their expression remain unclear. Among NKRs heterodimers CD94-NKG2 form either an inhibitory or an activating receptor, depending on whether CD94 associates with NKG2A or NKG2C, E or H, respectively. NKG2D is expressed on all naïve and activated CD8+ T cells. NKG2D ligands are distantly related to HLA class I molecules and up-regulated in virally infected cells, tumour cells or otherwise stressed cells. The expression of NKG2D ligands by target cells potently induces NK cells cytotoxicity.

Although specific immunity mediated by cytolitic T-lymphocytes might have an anti-cancer role, tumours escape from T-cell-based immune surveillance using various mechanisms, such as downregulation, mutation, or loss of HLA class I molecules.

Aims: In this study we tried to establish the expression significance of molecules stimulating (NKG2D) and inhibiting (CD94/NKG2A) NK cells cytotoxicity in lymphoid malignancies. Our aim was also to explore whether any influence of this expression on treatment response exists. It could be useful as remission predictive factor or a future target for therapeutic approaches.

Patients: 23 patients (F/M -13/10, median age 57) with lymphoid malignancies (Non-Hodgkin Lymphoma (NHL), Myeloma multiplex (MM) and Hodgkin disease (HD) in 19, 3 and 1 case respectively) diagnosed in our unit in two recent years and 8 healthy volunteers were included. Eight patients were still untreated while involved into the study. In the previously treated group 4 of 15 patients achieved complete remission (CR), 5-partial remission (PR) and in 6 cases there were no response (NR) for chemotherapy. In all cases first line treatment was used.

Methods: Mononuclear cells (MNC) were isolated from blood samples in Ficoll gradient. All used antibodies were conjugated: CD8 (DAKO Cytomation), CD94/NKG2A PE (Becton Dickinson) and NKG2D PE (Immunotech). MNC were stained for co-expression of CD8/NKG2D and CD8/CD94/NKG2A populations and then performed for flow cytometry.

Results: We evaluated the diffreneces in CD94/NKG2A and NKG2D expression in blood deriving CD8+ population between lymphoid malignancies patients and healthy volunteers. There were no statistically significant difference in CD94/NKG2A and NKG2D expression between treated and untreated patients. CD94/NKG2A expression was significantly higher in the treated group than in healthy controls (p=0,01). In reverse, NKG2D expression was significantly higher in previously untreated group than in healthy controls (p=0,04). The only significant correlation we found was positive CD94/NKG2A and NKG2D correlation among the whole group of patients (r=0,57, p=0,004).

Conclusions: As the expression of NKG2D ligands by target cells potently induces NK cells cytotoxicity and we have found NKG2D to be overexpressed in lymphoid malignancies comparing to healthy controls it may be just another proof for a natural anti tumour surveillance. On the other hand the opposite role of CD94/NKG2A heterodimer may be a premise for antiNKG2A immunotherapy of lymphoid malignancies to support the natural surveillance especially in the light of our results: CD94/NKG2A expression was significantly higher in the treated group than in healthy controls.