parental tumor cell line (44) . Expression of IL-4 by 
plasmacytoma or mammary adenocarcinoma cells induced a potent 
anti-tumor effect mediated by infiltration of eosinophils and 
macrophages (45) . These studies demonstrate that cytokines, 
expressed at high local concentrations, are effective anti-tumor 
agents . 
We propose an alternative approach to stimulate an anti- 
tumor response, through the introduction of an allogeneic class I 
MHC gene into human tumor cells. The antigenicity of tumor cells 
has been altered previously by the expression of viral antigens 
through infection of tumor cells (46-50) , or expression of 
allogeneic antigens introduced by somatic cell hybridization 
(51,52). Allogeneic class I MHC genes have been introduced into 
tumor cells by transfection and subsequent selection in vitro . 
These experiments have produced some conflicting results. In one 
case, transfection of an allogeneic class I MHC gene (H-2L^) into 
an H-2 b tumor resulted in immunologic rejection of the transduced 
cells and also produced transplantation resistance against the 
parent tumor cells (53) . In another instance, transfection of H- 
2 b melanoma cells with the H-2D d gene did not lead to rejection 
(54) , however increased differential expression of H-2D products 
relative to H-2K may have affected the metastatic potential and 
immunogenicity of tumor cells (55) . The effects of allogeneic H- 
2K gene expression in tumor cells was examined in another study 
(56) . Several subclones which were selected in vitro and 
expressed an allogeneic gene were rejected in mice syngeneic for 
the parental tumor line, however, other subclones did not differ 
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Recombinant DNA Research, Volume 15 
