The Journal of Immunology, 2007, 178: 4706.
Copyright © 2007 by The American Association of Immunologists, Inc.
Response to Comment on "Cutting Edge: Induction of B7-H4 on APCs through IL-10: Novel Suppressive Mode for Regulatory T Cells"
Ilona Kryczek and
Weiping Zou
Department of Surgery, University of Michigan, Ann Arbor, MI 48109
In our recent work (1), we showed that, in an in vitro culture system, human CD4+CD25+FOXP3+ T cells (Treg cells) triggered B7-H4 expression on monocytes and myeloid dendritic cells, human Treg cell-conditioned monocytes suppressed T cell activation, and B7-H4 importantly contributed to T cell suppression mediated by Treg cell-conditioned macrophages. Drs. Mirza and Gabrilovich commented, "... this in vitro experimental system is not adequate to address the question of Treg effect on monocytes and may produce rather misleading conclusions. It is still possible that Tregs can induce monocytes to become suppressive cells but proof of this point in the human system will require a very different experimental approach." We agree with them that in vitro experimental data need to be confirmed by the rigorous in vivo experimental setting. We would like to point out that, when the "very different experimental approach" (the in vivo approach in humans) is not available, the scientific value of the in vitro experiments should not be minimized, as testified by many other outstanding in vitro studies in the field. Furthermore, we observed that B7-H4+ macrophages and Treg cells are localized in human ovarian cancer in vivo. Human tumor-associated B7-H4+ macrophages are functionally suppressive at least partially through B7-H4 in vivo (2). The data suggest that the mechanistic interaction between Treg cells and macrophages may be operative in vivo in patients with ovarian cancer.
Drs. Mirza and Gabrilovich further showed that normal human monocytes induced a dose-dependent T cell suppression. The suppression reached 125% with 20 responder cells to 1 monocyte. It appears that, in their culture system, normal human monocytes are superior to the well-described human Treg cells to mediate T cell suppression (1, 3). It is well known that the phenotype, characteristics, and functions of macrophages are determined by the environmental milieu and its stimulation (4, 5, 6). Our culture system is rather different from the one described by Drs. Mirza and Gabrilovich. We stimulated CD4+CD25– T cells (2 x 105/ml) for 72 h with up to 2 x 105/ml fresh monocytes in the presence of soluble anti-CD3 (2.5 µg/ml) and anti-CD28 (1.2 µg/ml). In this optimized condition, human monocytes are able to stimulate T cell proliferation. In their culture system, they stimulated CD4+CD25– T cells (5 x 105/ml) for 90 h with up to 1 x 106/ml magnetic bead-selected monocytes in the presence of coated anti-CD3 (1 µg/ml) and anti-CD28 (5 µg/ml). One potential possibility is that their T cell concentration is too high (2.5-fold higher than ours) and the stimulation is too strong, and T cells might be overactivated and become apoptotic. Nonetheless, we thank Drs. Mirza and Gabrilovich for their comments. We will confirm our data by in vivo human system once available but are confident that our results will stand the test of time.
References
- Kryczek, I., S. Wei, L. Zou, G. Zhu, P. Mottram, H. Xu, L. Chen, W. Zou. 2006. Cutting edge: induction of B7-H4 on APCs through IL-10: novel suppressive mode for regulatory T cells. J. Immunol. 177: 40-44. [Abstract/Free Full Text]
- Kryczek, I., L. Zou, P. Rodriguez, G. Zhu, S. Wei, P. Mottram, M. Brumlik, P. Cheng, T. Curiel, L. Myers, et al 2006. B7-H4 expression identifies a novel suppressive macrophage population in human ovarian carcinoma. J. Exp. Med. 203: 871-881. [Abstract/Free Full Text]
- Curiel, T. J., G. Coukos, L. Zou, X. Alvarez, P. Cheng, P. Mottram, M. Evdemon-Hogan, J. R. Conejo-Garcia, L. Zhang, M. Burow, et al 2004. Specific recruitment of regulatory T cells in ovarian carcinoma fosters immune privilege and predicts reduced survival. Nat. Med. 10: 942-949. [Medline]
- Gordon, S.. 2003. Alternative activation of macrophages. Nat. Rev. Immunol. 3: 23-35. [Medline]
- Gordon, S., P. R. Taylor. 2005. Monocyte and macrophage heterogeneity. Nat. Rev. Immunol. 5: 953-964. [Medline]
- Mantovani, A., S. Sozzani, M. Locati, P. Allavena, A. Sica. 2002. Macrophage polarization: tumor-associated macrophages as a paradigm for polarized M2 mononuclear phagocytes. Trends Immunol. 23: 549-555. [Medline]
