In order to search the influence of Ⅰ-A^k_αβ gene transfer on the growth of the transferred mouse tumor cells in vivo, the α and β chain cDNA were synthesized, and inserted into a retroviral vector, to construct two Ⅰ-A^k expressing recombinant plasmids pLSXN-A^k_α and pLSXN-A^k_β. By means of a liposome-mediated gene transfer procedure, these two recombinant plasmids together were introduced into mouse lymphoma EL4 cells and mastocytoma P815 cells. The expression of the Ⅰ-A^k_αβ protein on the surface of the transconducted tumor cells was tested by FACS using Anti-A^k-FITC. Afterwards these tumor cells were injected subcutaneously into autologous mice C57BL/6(H-2^b) and DBA/2(H-2^d) respectively. It was observed that tumors developed at the beginning within the mouse bodies, and disappeared after a few weeks with injection. While the nontransferred tumor cells grew continuously. These results show that the tumor immune response can be stimulated by the tumor cells transferred with allogenic MHC class Ⅱ gene, in the absence of B7 co-stimulatory signals.