Expression of Malignancy in Interspecies Chinese Hamster × Mouse Cell Hybrids 2

Abstract

Interspecies hybrids of mouse R4/B, bromodeoxyuridine (BUDR)-resistant, malignant cells carrying an overt murine C-type virus infection and Chinese hamster D/AD/Aza, 8-azaguanine-resistant, nonmalignant cells were developed in vitro after elimination of the parent cells in the HAT medium. The hybrid HyCS cells were apparently free of C particles. They presented a wide display of karyologic variants showing a majority of mouse telocentric chromosomes and a minority of chromosomes from the Chinese hamster parent. Most of the hybrid population inherited the hamster cell resistance to actinomycin D (AD). The HyCS cells had both mouse and hamster cell-surface antigens and an “intermediary” morphology, HyCS cells inoculated into cheek pouches of Syrian hamsters or into embryonated chick eggs (chorioallan-toic membrane or brain) produced tumors from which secondary tumorigenic HyCST lines were developed; this showed a further shift toward higher numbers of predominantly telocentric chromosomes and a return to sensitivity to AD. Mice syngeneic to the R4/B parent cells rejected the inoculated HyCS cells, then became resistant to challenge with R4/B malignant cells. The nature of the tumor-specific transplantation antigen characteristic of R4/B cells and expressed in the hybrid cells, despite repression of the murine C-type virus infection, is discussed.