Background: Immunotherapy is emerging as a promising cure for cancer. However, a severe problem in this area is the immune tolerance to tumor cells and tumor-associated antigens, as evidenced by the ability of cancer to escape immune surveillance. To overcome this problem this work examined the potential of improving the antigenicity of myeloma by metabolic engineering of its cell surface carbohydrate antigens (i.e., glycoengineering) and presentation of the modified tumor antigens by dendritic cells (DCs) to generate cytotoxic T-lymphocytes (CTLs).
Methods: CD138+ myeloma cells were isolated from 11 multipe myeloma (MM) patients by the immunomagnetic bead method. The MM cells were treated with N-propionyl-D-mannosamine (ManNPr), a synthetic analog of N-acetyl-D-mannosamine (ManNAc), the natural biosynthetic precursor of N-acetyl sialic acid (NeuNAc), to express unnatural N-propionylated sialoglycans. The glycoengineered cells were then induced to apoptosis, and the apoptotic products were added to cultured functional DCs that could present the unnatural carbohydrate antigens to autologous T-lymphocytes.
Results: It was found that the resultant DCs could activate CD4+ and CD8+ T-lymphocytes, resulting in increased expression of T cell surface markers, including CD8CD28 and CD4CD29. Moreover, upon stimulation by glycoengineered MM cells, these DC-activated T-lymphocytes could release significantly higher levels of IFN-gamma (P < 0.05). Lactate dehydrogenase (LDH) assays further showed that the stimulated T-lymphocytes were cytotoxic to glycoengineered MM cells.
Conclusions: This work demonstrated that glycoengineered myeloma cells were highly antigenic and the CTLs induced by the DCs loaded with the unnatural myeloma antigens were specifically cytotoxic to the glycoengineered myeloma. This may provide a new strategy for overcoming the problem of immune tolerance for the development of effective immunotherapies for MM.