Certain experimental tumours have been reported to be characterised by specific tumour antigens, and it has been suggested that it should therefore be possible to influence the growth of such tumours by immunological methods. Immuno- logical pretreatment of the host before tumour challenge, or admixing tumour cells with immune lymphoid cells prior to transplantation, results in inhibition of tumour characterised by strong specific antigens. Established tumours have, however, been found resistant to immunological influence.
This work concerns the investigation of adoptive transfer of immunity and non -specific reticuloendothelial stimulation as means of inhibiting the growth of established tumours. Two tumours, the mouse mammary carcinoma and Methylcholanthrene induced sarcoma, transplanted within their strain of origin or pl hybrids of that strain, have been studied. Tumours were transplanted by injecting suspensions of tumour cells and an efficient method of preparing viable cell suspensions by the enzymatic digestion of tumour fragments was evolved.
Adoptive immunity was passaged by the transplantation of spleen cell or thoracic duct lymphocyte suspensions. A technique for the cannulation of the mouse thoracic duct and the collection of pure lymphocytes was perfected, and is described in detail.
Significant inhibition of established transplants of mouse mammary carcinoma in syngeneic A- strain female hosts was obtained following whole body irradiation (400r) and the injection of allogeneic spleen cells or thoracic duct lympho- cytes. It was possible to completely destroy the tumour in situ only at the expense of the host succumbing to graft - versus -host syndrome.
Men the mouse mammary carcinoma was transplanted into (CBA/Á)F1 hybrids, significant inhibition of growth was obtained following the injection of immune lymphoid cells. It was possible in this situation to destroy the tumour in situ without killing the host.
The growth of mammary carcinoma transplants was also inhibited when the recipients were treated either two days before, or several days after tumour transplantation, by the injection of a killed suspension of Corynebacterium pa.rvum, a powerful reticuloendothelial stimulant.
Established transplants of Methylcholanthrene induced sarcoma were not sensitive to the adoptive transfer of immunity. A__1.e"sser degree of inhibition than that obtained with mouse mammary carcinoma was noted when recipients were treated with Corznebacterium parvum suspensions.
The Methylcholanthrene induced sarcoma is widely accepted as possessing strong specific tumour antigens yet established transplants of this tumour appear resistant to immunological treatment. The specific antigenicity of the mouse mammary carcinoma is less certain and, at best, this tumour is thought to be characterised by weak specific antigens. In spite of this, these studies show that established transplants of mouse mammary carcinoma can be inhibited by immunological methods. It is suggested that specific tumour antigens may favour the growth of established tumour protecting it from the host's own, or adoptively transferred reaction, by a process of enhancement. The marked inhibition of the mouse mammary carcinoma by immunological methods may be due to lymphoid cells exerting a direct attack on tumour cells or, in part, due to the abolition of tolerance to the Bittner virus.
The need for further laboratory investigation of the many problems relating to specific tumour antigens and the transplantation of lymphoid cells is stressed and suggestions for the possible future application of immunotherapeutic procedures in the treatment of cancer are made.