Adoptive T cell immunotherapy of MSV-induced tumours in nude mice. Part I. Biology of tumour regression and recurrence.

The induction of immunity to progressively growing murine sarcoma virus (MSV) tumours in nude (nu/nu) mice by reconstitution with immune T cells from syngeneic (+/+) donors has been studied. Whole spleen cell preparations served as the source of immune T cells. Transfer of immune, but not of normal, spleen cells resulted in partial or apparently complete regression of primary tumours and a related moderate to considerable extension of survival time. The dose, the time in days between immunization and transfer, as well as timing of the spleen cells in relation to tumour cell challenge, were all factors which influenced the effectiveness of the protective inocula. An unexpected consequence of even the very effective primary immunotherapy regimens, was secondary tumour development after varying tumour-free intervals. This was most frequently manifest as tumour recurrences at the original injection site either on their own or in combination with distant metastases. Such a relatively high frequency of tumour reappearance and metastatic spread contrasts markedly with the rare instances of secondary regrowth in normal immunocompetent mice. The present reconstitution system may therefore provide a new model for studying the inhibitory or stimulatory properties of T cells with respect to tumour regression and dissemination.