A simple method for unbiased quantitation of adoptively transferred cells in solid tissues

In a mouse model, we demonstrate how to obtain a direct, unbiased estimate of the total number of adoptively transferred cells in a variety of organs at different time points. The estimate is obtained by a straightforward method based on the optical fractionator principle. Specifically, non-stimulated C57BL/6J mouse splenocytes were labelled with carboxyfluorescein diacetate succinimidyl ester (CFSE) and adoptively transferred to normal C57BL/6J mice by intravenous injection. The total number of CFSE-positive cells was subsequently determined in lung, spleen, liver, kidney, and inguinal lymph node at six different time points following adoptive transfer (from 60 s to 1 week), providing a quantitative estimate of the organ distribution of the transferred cells over time. These estimates were obtained by microscopy of uniform samples of thick sections from the respective organs. Importantly, the samples were chosen and prepared in accordance with the optical fractionator principle. We demonstrate that the method is simple, precise, and well suited for quantitative immunological studies.