Three-dimensional semiquantitative analysis of SPECT images and ex vivo biodistribution study. Monkeys were grouped in high (blue bars), intermediate (red bars), and low (black bars) peripheral blood CD4 T-cell counts. The radiotracer retention from imaging data was calculated. For each VOI, the maximum pixel activity of radiotracer uptake was obtained and values were normalized on the maximum activity in the liver. (A) Mean (± SE) of normalized maximal counts in spleen, lymph nodes, and tonsils. (B) Mean (± SE) of normalized max counts in heart, kidney, bone marrow, and testes. (C) Relationship between CD4 T-cell counts in the peripheral blood and retention of ¹¹¹In-DTPA-OKT4A/hIgG4 estimated from imaging data in tonsils and spleen VOIs. R² for the fit of the exponential model to the data observed in the tonsils (R² = 0.77, P < .001, n = 11); in the spleen (R² = 0.56, P = .008, n = 11). (D) The radiotracer retention from organs collected from 6 monkeys was derived from the counts per minute normalized on the mass (cpm/g) of each organ divided by the cpm/g of the liver, for both lymphoid organs and (E) for lung, kidney, blood, and subcompartments of small and large intestine (radiotracer retention for kidney and blood of RH4001 (CD4⁺ T cells = 39/μL), not available). (F) Relationship between CD4 T-cell counts in the peripheral blood and retention of ¹¹¹In-DTPA-OKT4A/hIgG4 estimated from ex vivo data in tonsils and mean value of all lymphoid organs analyzed (spleen, tonsils, submandibular, axillary, inguinal, and mesenteric lymph nodes).