Significance of alteration in biodistribution of labeled lymphocytes exposed to stannous ion

The biodistribution patterns of 99mTc (99mTc-lymph) and 111In-lymphocytes with [111In-(Sn)-lymph] or without (111In-lymph) stannous ion treatment was compared in Lewis rats. Syngeneic lymphocytes were labeled with either 125 μCi (4.63 MBq) 99mTc or 5 uCi (1985 kBq) 111In per 2×107 cells. Mean labeling efficiency for 99mTc and 111In was 68.61%±3.90% (SEM) and 87.22%±2.01% (SEM) respectively. 99mTc-lymph (n=4), 111In-lymph (n=6) and 111In-(Sn)-lymph (n=6) rats received 2x107 cells and were killed 18 h later. While 99mTc-lymph demonstrated significantly less localization in spleen, lymph nodes, and blood (P(F)0.01) as compared with 111In-lymph, 111In-(Sn)lymph also demonstrated a significant difference (P[F]=0.0001) in lymph node accumulation when compared to 111In-lymph. As the activity levels utilized are not associated with cell radiation damage, these alterations in biodistribution do not reflect viability or chromosomal damage, but appear related to stannous ion exposure.