Immunization With Dendritic Cells Infected By Adenovirus Vector Encoding Human CD20 Effectively Elicits Immunity Against Mouse Lymphoma

Immunotherapy plays an important role in the treatment of lymphoma. Rituximab has improved the prognosis of the CD20⁺ B cell lymphoma after it was used as a target therapy drug. However, rituximab can only produce passive immunity, active cell immunity is needed in antitumor immunity. It has been indicated that the tumor associated antigens of xenogeneic rather than self-origin can easily break the immune tolerance. Therefore, it may be an effective strategy for inducing the specific antitumor immunity by dendritic cells (DCs) modified with the tumor associated antigens of xenogeneic origin. In this research, we used the DCs infected by adenovirus encoding the human CD20 gene (hCD20) as a vaccine to immunize the mice with CD20⁺ cell lymphoma, and study the immune protection produced by them.Human CD20 gene was cloned from the peripheral blood using reverse transcription polymerase chain reaction (RT-PCR), and then inserted into adenovirus shuttle plasmid. Ad5/35 hCD20 was. constructed by Ad Max^? adenovirus vector packaging system. Meanwhile, B16.F10 cell expressing mouse CD20 (mCD20) was stably constructed as a model of CD20⁺ lymphoma cells. DCs from the C57BL/6 mouse bone marrow were infected by Ad5/35 hCD20, which doses were 100 pfu/DC. Then 5×l0⁵ DCs were subcutaneously injected into per allogenetic mouse by once a week for totally twice, and the same doses of DCs infected by adenovirus dl 70-3 were used as control. Using mCD20⁺B16.F10 cells as target cells, the splenocytes of the immunized mice as effectors, cytotoxicity assay in vitro was carried out via the lactic acid dehydrogenase release method to detect the antigen specific cell immunity, and the immune protection of the DCs with Ad5/35 hCD20 from the mice inoculated with 2×10⁵ mCD20⁺B16.F10 cells per mouse was observed in an ectopic transplanted lymphoma model one week after the last immunization. Cytotoxicity assay in vitro indicated that the DCs with Ad5/35 hCD20 induced production of the CTL. The killing activity of CTL was related to effector/target. At the effector:target ratio of 100:1, 50:1, 25:1, the killing activities of CTL were 73.9%±7.6%,57.7%±8.8% and 26.7%±3.1% in the experimental group, and 17.4%±0.8%,12.8%±2.9% and 9.1%±1.0% in the control group, respectively. All of the mice in the control group had the tumor growth two weeks after the inoculation with 2×10⁵ mCD20⁺B16.F10 cells, however, just 30% of the mice in the experimental group had the tumor growth. Moreover, the size of tumors in the experimental group was much smaller than that in the. control group. The mice with no tumor growth in the experimental group continued to be observed for two months, and there was no more tumors developed. These results suggested that the DCs with Ad5/35 hCD20 could induce the antigen-specific cell immunity against mouse lymphoma expressing CD20.Our results indicates that the DCs infected by the adenovirus vector encoding CD20 of xenogeneic origin (hCD20) can efficiently break the immune tolerance and induce the specific cell immunity against mouse lymphoma expressing CD20, which might provide a new strategy and experimental evidence for immunotherapy for CD20⁺ lymphoma in a clinical setting.