Adoptive immunotherapy and combined chemo-immunotherapy in transplantable leukaemia of AKR mice (TAL); occurrence of natural killers.

Allo- and syngeneic lymphoid effector cells were injected I. P. into transplantable leukaemia (TAL)-bearing AKR recipients. Effector cells were collected from the peritoneal cavity, lymph nodes, spleen, or thymus, of either non-immunized donors or of donors previously immunized with TAL cells. The ratio, injected number of effector cells divided by injected number of TAL target cells varied in individual experiments from 10:1 to 10 000 : 1. Some AKR recipients were given prior to the leukaemia inoculation a whole-body sublethal X-ray irradiation and/or an I.P. injection of cyclophosphamide. Mean survival of TAL leukaemia was most often prolonged in recipients given viable allogeneic thymocytes derived from non-immunized donors. In some leukaemia-bearing mice treated with chemo-immunotherapy, permanent survival (greater than 70 days) could be observed. As a rule, effector cells derived from non-immunized allogeneic donors were more effective than effector cells from the immunized areas. Syngeneic effectors were ineffective. The occurrence of natural killers (NK cells) to Gross virus-infected cells in the lymphoid organs of low-leukaemic inbred mouse strains is postulated. These NK cells are lacking in high-leukaemic AKR mice.