Biodistribution of radiolabeled lymphocytes.

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Abstract
Factors that might affect the biodistribution and clinical utility of radiolabeled lymphocytes were evaluated in experimental animals. 111In labeled lymphocytes (107-109 syngeneic or allogeneic cells; 1-10 .mu.Ci [.037-.37 MBq]/108 cells) obtained from peripheral blood, lymph node or spleen were found in significant amounts in the lymphoid tissues of Lewis rats as early as 3 h after infusion. A progressive increase in nodal activity with concomitant fall of activity in other organs followed, indicating active recirculation of the lymphocytes. However, 111In labeled thymocytes or xenogeneic lymphocytes failed to accumulate in lymphoid tissue. In vitro irradiation of the 111In labeled lymphocytes (100-400 rads [1-4 Gy [grays]]) before in vivo administration and increase of the 111In to 40 .mu.Ci [1.48 MBq]/108 lymphocytes resulted in no detectable lymphocyte recirculation and/or reduced localization in lymphoid tissue. Splenectomized animals and those sensitized to an organ allograft before cell infusion showed increased activity in their bone marrow. The source of the injected cells, cell irradiation dose level and host sensitization evidently should be considered when radiolabeled lymphocytes are being prepared for use in clinical diagnosis and therapy.