Comparative abilities of athymic nude mice and severe combined immune deficient (SCID) mice to accept transplants of induced rat mammary carcinomas: enhanced transplantation efficiency of those rat mammary carcinomas that have elevated expression of neu oncogene.

Grafts of primary carcinogen (DMBA)-induced mammary carcinomas from Sprague-Dawley rats have a poor transplantation efficiency in athymic nude mice. Further compromising these mice immunologically via whole-body irradiation and/or splenectomy, or the administration of hormonal growth factors (estrogen and progesterone) to these mice, did not significantly alter transplantation efficiency. Use of strains of mice that are more immune-impaired than the athymic nude mouse, i.e., the athymic nude-beige-XID mouse (T-cell and LAK-cell deficient) or mice with severe combined immune deficiency (SCID) (which lack functional T cells and B cells) also failed to improve transplantation efficiency. In contrast, transplantation efficiency was sharply increased when primary neu-induced rat mammary carcinomas from female Sprague-Dawley rats were used. These mammary carcinomas, unlike the DMBA-induced rat mammary carcinomas, have a very high level of expression of neu; transplantation of these tumors to either athymic nude mice or SCID mice was considerably more efficient. Thus, these data provide evidence that enhanced expression of neu confers heightened efficiency in the transplantation of primary rat mammary carcinomas to immune-deficient mice (athymic-nude or SCID). Increased neu expression was a greater determinant than more compromised immune states in the transplantation of these rat mammary carcinomas. This biological characteristic of neu expression in mammary carcinomas provides new, additional insight into the importance of this oncogene in mammary tumorigenic processes and may explain, at least in part, the reported inverse relationship between human breast carcinoma neu expression and patient prognosis.