Separation of populations of sensitized lymphoid cells into fractions inhibiting and fractions enhancing syngeneic tumor growth in vivo.

Separation of subpopulations of lymphoid cells sensitized against a syngeneic tumor was attempted by means of velocity sedimentation and the fractions were injected together with tumor cells into syngeneic hosts. Spleen cells from tumor-bearing mice or spleen cells sensitized on tumor cell monolayers could be fractionated into a subpopulation capable of inhibiting growth of the same tumor and a separable fraction which enhanced tumor growth. Activity of the tumor-inhibiting lymphocytes was not apparent in the presence of the tumor-enhancing cells. The former activity was associated with small lymphocytes and the latter with injection of larger cells. Preliminary experiments investigated the developmental relation between the cells responsible for these opposing activities.