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Non-invasive in vivo Imaging of CD4 Cells in SHIV-infected Rhesus Monkeys
Michele Di Mascio*1, P Ch2, J Carrasquillo3, J S Maeng2, S Srinivasula4, M Catalfamo1, Y Nishimura1, K Reimann5, M Martin1, and C Lane1
1NIAID, NIH, Bethesda, MD, US; 2Warren G Magnuson Clinical Ctr, NIH, Bethesda, MD, US; 3Memorial Sloan Kettering Cancer Ctr, New York, NY, US; 4SAIC-Frederick, MD, US; and 5Beth Israel Deaconess Med Ctr, Boston, MA, US
Background: Peripheral blood lymphocytes represent
only 2% of total lymphocyte pool. Current methods to monitor changes in CD4 cells
throughout the body require the use of invasive technologies. We here describe
a humanized non-depleting anti-CD4 monoclonal antibody labeled with a gamma
emitter to detect changes in CD4 cell counts in tissues with non-invasive
imaging during SHIV infection
Methods: The humanized CDR-OKT4A/hIgG4 monoclonal
antibody was conjugated with a chelator (CHX-A"-DTPA) and labeled with 111Indium. The specific activity of the labeled
antibody was >11
mCi/mg;
radiochemical purity of >98% was used. The binding affinity of the modified monoclonal antibody and bindability of the labeled monoclonal antibody were tested in MT4 cells in vitro. One
uninfected and 7 simian-human immunodeficiency virus (SHIV) chronically
infected rhesus macaques with CD4 T cell counts ranging from 5 to 2314
CD4 T cells/mL were imaged 48 hours
post radiotracer injection with a SPECT camera. Rhesus macaques received 1.51 (single
dose 0.14) mCi of 111In- OKT4A (250 µg) intravenously. Scans were
acquired from the top of the skull to the inguinal region
Results: Adding the chelator did not change the
binding affinity, kd, of the anti-CD4 monoclonal antibody (kd
= 0.22 vs 0.29 nM, p = 0.41). The 111In-labeled monoclonal
antibody showed a high percentage of binding to MT4 cells. Of the total, 3 rhesus
macaques with high CD4 cell counts (>1400 CD4 T cells/µL) showed greater
uptake of the radiotracer in lymph nodes, tonsils, and spleen; 3 macaques with
low CD4 cell counts (<100) showed little to no uptake in the same regions. The
illustration shows radiotracer uptake in 1 uninfected and 2 infected macaques with
1408 and 50 CD4 T cells/µL. Three-dimensional quantitative analyses of all images
showed a high correlation between the radiotracer uptake in spleen and tonsil regions
of interest and CD4 T cell counts (r = 0.84 and r = 0.91, p
< 0.005).
Conclusions: Non-invasive whole-body imaging of CD4
cells in non-human primates is feasible and might contribute to our
understanding of the immunodeficiency status in HIV-1-infected patients. Potential
areas of clinical investigations that could benefit from such technique are: prognostic
values of CD4 cell counts in anatomic compartments; relative contribution of
trafficking versus depletion of CD4 cells during infection or after HAART, and evaluation
of efficacies of new HAART regimens
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