Srinivasula Sharat, Kim Insook, Jang Hyukjin, Degrange Paula, Brown Heather, Dalton Viviana, Badralmaa Yunden, Natarajan Ven, Long Brad, Carrasquillo Jorge A, Di Mascio Michele
AIDS Imaging Research Section, Clinical Monitoring Research Program Directorate, Frederick National Laboratory for Cancer Research, Frederick, MD, USA.
AIDS Imaging Research Section, Applied/Developmental Research Directorate, Frederick National Laboratory for Cancer Research, Frederick, MD, USA.
Eur J Nucl Med Mol Imaging. 2025 Jun;52(7):2645-2657. doi: 10.1007/s00259-025-07110-8. Epub 2025 Jan 31.
Following the initial reports demonstrating the feasibility of immunoPET imaging of simian immunodeficiency virus (SIV) using gp120-targeting monoclonal antibodies in non-human primates, replication efforts of the imaging system in human immunodeficiency virus (HIV)-infected individuals have yielded conflicting results. Herein, we used two anti-gp120 antibodies, 7D3 and ITS103.01LS-F(ab'), to interrogate the reproducibility of gp120-targeting probes for immunoPET imaging of SIV in rhesus macaques.
The binding affinity estimates of Zr radiolabeled 7D3 and ITS103.01LS-F(ab') to SIV gp120, and the in-vitro and ex-vivo binding specificities of [Zr]Zr-7D3 and [Zr]Zr-ITS103.01LS-F(ab') to SIV Env expressing cells, primary cells, and tissue sections from uninfected and SIV-infected macaques were obtained through competition assays. The biodistributions of [Zr]Zr-7D3 and [Zr]Zr-ITS103.01LS-F(ab') were performed with static PET scans up to 6 days post-injection in 20 rhesus macaques and the standardized uptake values in various tissues were compared between SIV-infected and uninfected controls.
Despite the demonstrated nanomolar affinity of [Zr]Zr-7D3 and [Zr]Zr-ITS103.01LS-F(ab') to SIV gp120, and strong binding specificity to SIV gp120 cell lines, we observed no discernible differences in their binding in primary cells, tissue sections of secondary lymphoid organs, in-vivo probe uptake between SIV-infected and uninfected macaques, or ex-vivo validation necropsies. While the probes remained stable in-vivo, only [Zr]Zr-ITS103.01LS-F(ab') in chronic plasma retained its binding specificity to SIV gp120, with [Zr]Zr-7D3 experiencing a > 97% reduction in binding to gp120 due to competition from endogenous antibodies at the 7D3 binding site.
The overall absence of specific uptake suggests inadequate binding potential (ligand affinity x target molarity) for these probes to effectively image SIV or HIV in-vivo, warranting further investigation into the lack of reproducibility observed with earlier non-human primate SIV imaging and conflicting human studies.
在最初的报告证明使用靶向gp120的单克隆抗体在非人类灵长类动物中对猿猴免疫缺陷病毒（SIV）进行免疫正电子发射断层扫描（immunoPET）成像的可行性之后，该成像系统在人类免疫缺陷病毒（HIV）感染个体中的复制研究产生了相互矛盾的结果。在此，我们使用两种抗gp120抗体7D3和ITS103.01LS - F(ab')，来探究用于恒河猴SIV免疫正电子发射断层扫描成像的靶向gp120探针的可重复性。
通过竞争试验获得锆放射性标记的7D3和ITS103.01LS - F(ab')与SIV gp120的结合亲和力估计值，以及[Zr]Zr - 7D3和[Zr]Zr - ITS103.01LS - F(ab')对表达SIV包膜蛋白（Env）的细胞、原代细胞以及未感染和感染SIV的猕猴的组织切片的体外和离体结合特异性。对20只恒河猴进行注射后长达6天的静态正电子发射断层扫描，以测定[Zr]Zr - 7D3和[Zr]Zr - ITS103.01LS - F(ab')的生物分布，并比较SIV感染组和未感染对照组各种组织中的标准化摄取值。
尽管已证明[Zr]Zr - 7D3和[Zr]Zr - ITS103.01LS - F(ab')对SIV gp120具有纳摩尔亲和力，且对SIV gp120细胞系具有强结合特异性，但我们观察到它们在原代细胞、次级淋巴器官组织切片中的结合、SIV感染和未感染猕猴之间的体内探针摄取或离体验证尸检中均无明显差异。虽然探针在体内保持稳定，但只有慢性血浆中的[Zr]Zr - ITS103.01LS - F(ab')保留了对SIV gp120的结合特异性，由于7D3结合位点处内源性抗体的竞争，[Zr]Zr - 7D3与gp120的结合减少了>97%。
总体上缺乏特异性摄取表明这些探针的结合潜力（配体亲和力×靶标摩尔浓度）不足以在体内有效成像SIV或HIV，这需要对早期非人类灵长类动物SIV成像中观察到的可重复性缺乏以及人类研究中的矛盾结果进行进一步研究。
