Mouse transgenesis has proven invaluable for analysis of gene function and generation of human disease models. We describe here the development of a pronuclear injection-based targeted transgenesis (PITT) system, involving site-specific integration in fertilized eggs. The system was applied to two different genomic target loci to generate a series of transgenic lines including fluorescent mice, which reproducibly displayed strong, ubiquitous and stable transgene expression. We also demonstrated that knockdown mice could be readily generated by PITT by taking advantage of the reproducible and highly efficient expression system. The PITT system, which circumvents the problem of unpredictable and unstable transgene expression of conventional random-integration transgenic mice, reduces the time, cost and effort needed to generate transgenic mice, and is potentially applicable to both in vivo ‘gain-of-function’ and ‘loss-of-function’ studies.

The role of T helper type 1 (Th1) and Th2 cells in tumor immunity was investigated using Th cells induced from ovalbumin (OVA)-specific T cell receptor transgenic mice. Although Th1 cells exhibited stronger cytotoxicity than Th2 cells, both cell types completely eradicated tumors when transferred into mice bearing A20 tumor cells transfected with the OVA gene (A20-OVA). Th1 cells eradicated the tumor mass by inducing cellular immunity, whereas Th2 cells destroyed the tumor by inducing tumor necrosis. Both Th1 and Th2 cells required CD8+ T cells to eliminate tumors, and neither of these cells were able to completely eliminate A20-OVA tumors from T and B cell–deficient RAG2−/− mice. Mice cured from tumors by Th1 and Th2 cell therapy rejected A20-OVA upon rechallenge, but CD8+ cytotoxic T lymphocytes were induced only from spleen cells prepared from cured mice by Th1 cell therapy. Moreover, we demonstrated that Th1 and Th2 cells used distinct adhesion mechanisms during tumor eradication: the leukocyte function-associated antigen (LFA)-1–dependent cell–cell adhesion step was essential for Th1 cell therapy, but not for Th2 cell therapy. These findings demonstrated for the first time the distinct role of antigen-specific Th1 and Th2 cells during eradication of established tumors in vivo.