PURPOSE Molecular imaging of CD4+ T cells throughout the body has implications for monitoring autoimmune disease and immunotherapy of cancer. expression and T cell proliferation were analyzed with circulation cytometry and cytokines were assayed. RESULTS For immunoPET imaging, the lowest protein dose of 2 g 89Zr-labeled GK1.5 cDb resulted in significantly higher % injected dose/gram in inguinal lymph nodes (ILN) and spleen compared to the 12 g protein dose. administration of GK1.5 cDb at the high dose of 40 g caused a transient decrease in CD4 expression in spleen, blood, lymph nodes, and thymus, which recovered within 3 days post-injection; this effect was reduced, although not abrogated, when 2 g was administered. Proliferation was inhibited in ILN but not the spleen by injection of 40 g GK1.5 cDb. Concentrations of GK1.5 cDb in excess of 25 nM significantly inhibited CD4+ T cell proliferation and interferon- production and radiolabeled autologous lymphocytes and tracking their migration after reinfusion. This is carried out clinically using 111In-oxine or 99mTc-hexamethylpropyleneamine oxime (99mTcHMPAO) to track cells with SPECT [8]; for tracking lymphocytes using PET, 89Zr- and 64Cu-labeled probes are emerging as effective candidates [12, 13]. To image an endogenous subset of cells, the targeting of a biomarker-specific probe is required. Antibody-based Masitinib inhibitor imaging (immunoPET or immunoSPECT) combines the exquisite specificity of antibodies and the sensitivity and tissue penetration of nuclear imaging to noninvasively image and quantitate endogenous cell surface biomarkers. Radiolabeled antibodies have been used Rabbit Polyclonal to EGFR (phospho-Tyr1172) to image CD4+ T cells, mainly in preclinical settings. Rubin et al. utilized 111In-labeled GK1.5 anti-CD4 antibody to assess distribution of murine CD4+ T cells with gamma camera imaging [14]. In a murine model of colitis, 111In-labeled YTS 177 non-depleting anti-CD4 antibody was utilized for SPECT imaging of excess CD4+ T cells in the gut [6]. ImmunoSPECT with 111In-labeled anti-CD4 antibody enabled tracking of CD4+ T cells in simian-HIV-infected rhesus macaques, and biodistribution data was used to revise the proposed quantity of total lymphocytes in the human body [2]. Clinical use of anti-CD4 immunoSPECT has been explored in the context of rheumatoid arthritis with mixed results. Uptake in inflamed joints correlated well with clinical symptoms in one study, which utilized intact 99mTc-labeled anti-CD4 antibody Maximum.16H5 [5], but in a later study, a 99mTc-labeled Fab fragment of the same antibody identified only 68% of clinically affected joints [4]. These results led the authors to suggest that the presence of CD4+ T cells does not usually correlate with pain and swelling in arthritic joints. A major concern Masitinib inhibitor in the development of new PET tracers is the effect on target cells. Ideally, a tracer should have minimal effects on cell viability and function. Intact antibodies mediate effector function via the Fc region and can induce depletion of or functional changes in cells expressing the target antigen. For example, intact rat anti-mouse CD4 antibody GK1.5 depletes CD4+ T cells and can affect induction of proliferation and cytokine release [15C17]. In addition, intact antibodies have a long half-life (serum t1/2 = 1C3 weeks) Masitinib inhibitor due to recycling through the neonatal Fc receptor, and require several days of clearance to acquire a high-contrast image. To address the drawbacks of Fc-mediated effector functions and long half-life, antibodies can be designed into numerous fragments with customized pharmacokinetics, conjugation capabilities, Fc receptor binding ability, and excretion route [18]. We previously developed an anti-CD4 antibody fragment, GK1.5 cys-diabody (cDb), for immunoPET imaging of murine CD4+ T cells and explained its use in monitoring CD4+ T cell reconstitution after hematopoietic stem cell transplantation [19]. GK1.5 cDb lacks the Fc region and clears rapidly though the kidney, enabling same- or next-day imaging. Subsequent studies exhibited that GK1.5 cDb caused decreased surface expression of CD4, which prompted investigation of the potential impact of GK1.5 cDb on CD4+ T cells. Here, the effects of GK1.5 cDb dose on CD4+ T cell biology and immunoPET imaging were explored. A series of protein doses was evaluated for changes on T cell.