The transfer of transplantation immunity by lymph node cells has been the subject of investigation. Transplantable tumors have been used to provoke and to measure transplantation immunity. Cells from the lymph nodes draining a tumor homograft were transferred as mince or in suspension into the peritoneum of a secondary host to confer immunity. These cells could confer immunity while the immunizing graft was undergoing breakdown during the primary, and also during the more rapid secondary, response. Cells from other nodes and from the spleen, and also whole blood or serum failed in these experiments to transfer immunity. In one combination of tumor and host, serum from immunized donors enhanced tumor growth.

Evidence has been presented favoring the hypothesis that the lymph node cells were immunologically activated before transfer, and that they conferred immunity by continuing to function in their host. Immunization by tumor cells transferred along with the cells of the nodes could not account for the failure of lymph node transferred into susceptible animals to give rise to tumors; nor for the failure of tumor cells to give rise to immunity as rapidly as transferred lymph node cells. Freezing and thawing of the transferred cells prevented transfer of immunity. Cells from donors immunized against an isoantigen failed to confer immunity on hosts which carried that isoantigen, offering evidence of absorption of antibody. The duration of immunity transferred within an inbred strain was shorter than actively induced immunity, but longer than could have been expected of passively transferred immunity. After transfer of cells into foreign hosts, immunity declined more rapidly, as if the transferred cells were destroyed by the homograft reaction of the host.

The possibility that cells of the host were activated has also been discussed. A brief review showed that similar problems are raised in other systems of transfer of immunity by cells.