Immuno-PET identifies the myeloid compartment as a key contributor to the outcome of the antitumor response under PD-1 blockade

Abstract

Immunotherapy using checkpoint-blocking antibodies against PD-1 has produced impressive results in a wide range of cancers. However, the response remains heterogeneous among patients. We used noninvasive immuno-positron emission tomography (PET), using 89Zr-labeled PEGylated single-domain antibody fragments (nanobodies or VHHs), to explore the dynamics and distribution of intratumoral CD8+ T cells and CD11b+ myeloid cells in response to anti–PD-1 treatment in the MC38 colorectal mouse adenocarcinoma model. Responding and nonresponding tumors showed consistent differences in the distribution of CD8+ and CD11b+ cells. Anti–PD-1 treatment mobilized CD8+ T cells from the tumor periphery to a more central location. Only those tumors fully infiltrated by CD8+ T cells went on to complete resolution. All tumors contained CD11b+ myeloid cells from the outset of treatment, with later recruitment of additional CD11b+ cells. As tumors grew, the distribution of intratumoral CD11b+ cells became more heterogeneous. Shrinkage of tumors in responders correlated with an increase in the CD11b+ population in the center of the tumors. The changes in distribution of CD8+ and CD11b+ cells, as assessed by PET, served as biomarkers to gauge the efficacy of anti–PD-1 treatment. Single-cell RNA sequencing of RNA from intratumoral CD45+ cells showed that CD11b+ cells in responders and nonresponders were markedly different. The responders exhibited a dominant population of macrophages with an M1-like signature, while the CD45+ population in the nonresponders displayed an M2-like transcriptional signature. Thus, by using immuno-PET and single-cell RNA sequencing, we show that anti–PD-1 treatment not only affects interactions of CD8+ T cells with the tumor but also impacts the intratumoral myeloid compartment.

Nanobodies as non-invasive imaging tools

“…55 ImmunoPET of CD8 þ T cells in the anti-PD-1-responsive syngeneic MC38 colorectal cancer model showed that successful PD-1 blockade is accompanied by mobilization, expansion and infiltration of cytotoxic CD8 þ T cells from the tumor periphery into the tumor core. 54 CD8 immunostaining on tumor samples confirmed the CD8 PET data. The different distribution patterns of CD8 þ T cells may thus serve as a prognostic indicator of the outcome of checkpoint blockade therapy.…”

“…Data adopted from Rashidian et al (2017Rashidian et al ( , 2019). 54,55 h post injection, and a good signal-to-background ratio in lymphoid organs and tumors 22 h post injection, although kidney retention was relatively high, a rather common feature of immunoPET imaging agents when antibody fragments are used. An anti-human CD8 89 Zr-labeled minibody was used in patients with melanoma, lung and hepatocellular carcinoma, where it was well tolerated with no adverse effects.…”

Current Strategies to Target Tumor-Associated-Macrophages to Improve Anti-Tumor Immune Responses

“…Other studies showed that high expression by TAMs of the leukemia inhibitory factor (LIF), a member of the IL-6 family, triggers the epigenetic silencing of CXCL9, a chemo-attractant for CD8+ T cells, and LIF inhibition improved the efficacy of anti-PD-1 therapy [53]. Finally, several studies have described how TAMs also interfere with the correct recruitment and localization of CD8+ T cells within the tumor, thus precluding the efficacy of ICB therapy [54,55].…”

Spatial Deconvolution of HER2-positive Breast Tumors Reveals Novel Intercellular Relationships

“…[38,39] Tumor-associated myeloid cells expressing CXCL9/10 have been described previously and attributed important immunotherapy-induced anti-tumor functions. [19,[40][41][42] Furthermore, the chemokines CXCL9/10 may be induced by a type I interferon stimuli, also reported to be present in the IFIT1 T-cell subset. [30] Type I interferon activation within tumors can act directly on tumor cells, to inhibit proliferation or stimulate apoptotic processes, or indirectly by activation of anti-tumor immunity.…”