CD69, a New Potential Clinical Marker in Multiple Myeloma

CD69 is a type II membrane protein. T cells express CD69 rapidly upon stimulation of the T-cell receptor (TCR), which is why CD69 has been mostly regarded as an activation marker. The precise role of CD69 in immunity has not been determined because its ligand is unknown, but an emerging role of CD69 in Multiple Myeloma (MM) has been postulated. Previous data, using tumor lines derived from murine model with genotypic and immunophenotypic features of resistance to bortezomib, showed that as the neoplastic plasma cells (PC) develop bortezomib resistance, they have a germinal center B cell like immunophenotype, including decreased to absent expression of CD69. CD69 has not been yet studied in human multiple myeloma, though it has been shown that human chronic lymphocytic lymphoma cells, when induced toward a plasma cell phenotype with tetradecanoyl phorbol acetate (TPA) have increased CD69 expression. Interestingly the activation antigen CD69 associates with and inhibits the function of Sphingosine 1-phosphate (S1P). S1P is a bioactive lysophospholipid which is known to induce diverse cellular responses through at least five G-protein-coupled receptors on various cell types. Other data showed that MM cells express the S1P receptors, S1P1, S1P2 and S1P3. Furthermore, S1P protects MM cells against dexametason-induced apoptosis. Importantly, S1P upregulates Mcl-1 expression in a time and concentration-dependent manner in human MM cell lines. Therefore, we analyzed the CD69 expression on pathological PCs, from bone marrow samples of 43 patients, by flow cytometry with two aims: to evaluate the real expression of CD69 on pathological PCs and to determine the clinico-pathological significance of this molecule. Immunophenotyping was carried out by a 6-color method, using a FacsCanto II cytometer and the FacsDiva software. PCs were identified as CD138+/CD38+ events after an initial gate which included events with low SSC in the CD45/SSC cytogram. The MoAb panel also included CD19, CD20, CD117, CD56, cytoplasmic light chains K and Lambda. PerCP-Cy5.5-conjugated CD69 was evaluated on phenotypically abnormal plasma cells (i.e. CD19-, CD45- or dim), which were resulted to be clonally restricted. Results were considered positive when the percentage of positive cells was > 20%. 22 of 43 pts (see table I, group A) were MM resistant/refractory to at least two different chemotherapy regimens (including bortezomib in all patients). 21 patients (table I, group B) were smouldering multiple myeloma (SMM) or MM in at least very good partial response (VGPR) after first line treatment. CD69 was detected on bone marrow PCs in 19 of the 43 patients evaluated (44%). Of the 19 patients with CD69+ (see table II) only 6 (27%) were in the group of refractory/resistant MM, while the majority of these advanced patients, 16/22 (73%), had an absent expression of CD69. On the contrary in the group of SMM/VGPR/CR MM 13 patients (62%) were CD69+ (p=0.04, using a Chi squared test with Yates correction). At the best of our Knowledge this is the first clinical report that confirms CD69 expression on pathological PCs of MM patients. Our preliminary data also suggest an intriguing role of CD69, this molecule could represent an emerging clinical factor to identify different outcomes in patients affected by MM and treated with the modern drugs.