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Tumor Discovery Monocytes from single-cell analysis

used in different laboratories. Information pertaining to and potential side effects of these therapeutic approaches
the surface biomarkers overlapping between subsets and are also important for future clinical applications.
a unifying classification of monocytes, TAMs and moDCs
based on ontogeny, location, function, and phenotype are Funding
urgently needed. Full delineation of the origin and function This study was supported by grants from General Program,
of TAMs, along with new pathways for the differentiation The National Natural Science Foundation of China
of TAMs can provide new insights into strategies of (No. 81874138, 82073020 and 81903222).
tumor immunotherapy [144] . Some concepts, such as TAM
heterogeneity and the nature of the monocytic TAM Conflict of interest
precursors, are speculative and difficult to be unified . The authors declare no conflict of interest.
[22]
Moreover, the ontogeny, transcriptional regulation, and
heterogeneity of MPS remain largely unknown, which Author contribution
hampered their clinical application . Monocytes are
[62]
thought to preferentially generate immunosuppressive Conceptualization: Mingzhu Yin
TAMs in solid tumors, yet the basis for this is largely Data curation: Xin Fu
unknown . Moreover, monocytes can diversify into a Writing - original draft: Xin Fu, Mingzhu Yin
[68]
continuum of states, which may promote or impede tumor
growth. More evidence is needed to determine whether Writing - review & editing: Xin Fu, Mingzhu Yin.
monocytes differentiate with intermediate modes of
functioning. Conventional definitions of monocytes will References
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and intermediate subsets deserve further exploration mononuclear phagocytes. J Exp Med, 128: 415–435.
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immunity and the basis of tumor immune escape still
remain to be elucidated. In addition, the mechanisms of 2. Engblom C, Pfirschke C, Pittet MJ, 2016, The role of myeloid
balancing immune protection and self-tolerance and their cells in cancer therapies. Nat Rev Cancer, 16: 447–462.
correlation with tumor surveillance and escape are still not https://doi.org/10.1038/nrc.2016.54
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well documented . The clinical studies and experiments 3. Pollard JW, 2004, Tumour-educated macrophages promote
in mouse models clearly indicate that TAMs show a pro- tumour progression and metastasis. Nat Rev Cancer,
tumoral phenotype that facilitates tumor cell invasion, 4: 71–78.
motility, and intravasation. Therefore, it is not surprising https://doi.org/10.1038/nrc1256
that extensive TAM infiltration is positively associated with
cancer metastasis and poor clinical prognosis in various 4. Sica A, Schioppa T, Mantovani A, et al., 2006, Tumour-
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immunotherapies are key to be part of prophylactic approach
and effective treatment. One of the future directions is to https://doi.org/10.1016/j.ejca.2006.01.003
unveil the underlying functions of mononuclear phagocytes 5. Yunna C, Mengru H, Lei W, et al., 2020. Macrophage M1/
and their potential as diagnostic and therapeutic targets. M2 polarization. Eur J Pharmacol, 877: 173090.
Besides, combination therapy targeting monocytes and https://doi.org/10.1016/j.ejphar.2020.173090
immune checkpoint therapy may be promising.
6. Krieg C, Nowicka M, Guglietta S, et al., 2018, High-
Most patients do not show durable responses to dimensional Single-cell Analysis Predicts Response to
immunotherapy, especially ICT, despite a dramatic Anti-PD-1 Immunotherapy. Nat Med, 24: 144–153.
increase in progression-free survival. Therefore, more https://doi.org/10.1038/nm.4466
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urgently needed. In addition, it is still not clear how these 7. Roberts SA, Waziri AE, Agrawal N, 2016, Development of
APCs develop and function before and during anti-PD-1 a single-cell migration and extravasation platform through
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are quite promising targets for the diagnosis and treatment migration chip for chemotaxis-based microfluidic selection
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