Chelate conjugates of monoclonal antibodies for imaging lymphoid structures in the mouse

Radiolabeling of a mouse monoclonal antibody (MoAb) specific for the mouse histocompatibility alloantigen IA(k) expressed by the B lymphocytes of BALB/k and C3H mice but not BALB/c mice was performed by mixing the chelate-labeled anti (α) IA(k) MoAb with purified, no-carrier-added ¹¹¹In citrate. Labeling efficiency was 85-95%, and the labeled αIA(k) MoAb retained its antigen binding properties in vitro and in vivo. The organ, spleen, and lymph node distribution of intravenously and subcutaneously administered ¹¹¹InαIA(k) MoAb was compared in mice, two IA(k) positive and one Ia(k) negative strains, and to ¹²⁵IαIA(k) MoAb in one IA(k) positive strain. The ¹¹¹InαIA(k) MoAb was more stable in vivo compared to ¹²⁵IαIA(k) MoAb, as shown by a much slower excretion and a higher absolute uptake in lymph nodes and spleen. Lymph node to blood ratio was increased twofold by intravenous anti-EDTA MoAb. Subcutaneous injection permitted clear images of the tiny lymph nodes in the mouse. Potential clinical applications of ¹¹¹Inα lymphocyte MoAb include localization of normal lymph nodes and T & B cell leukemias and lymphomas, as well as detecting lymphatic metastases of other cancers. Therapy may also be possible using MoAbs labeled with beta-emitting metal ions such as yttrium-90.