Tfr Cells and IgA Join Forces to Diversify the Microbiota

Immunity

Previews employing either naturally occurring or gene-engineered tumor-reactive T cells (Gattinoni et al., 2012). However, cell products currently employed in adoptive immunotherapy studies predominantly comprise Teff and Tem cells, which have a limited life span. Adoptive transfer of long-lived, multipotent CD62L+ memory T cells might significantly improve persistence and potentiate the therapeutic efficacy of adoptive immunotherapies. New clinical trials employing Tcm or CD62L+derived T cells have been initiated and hopefully will translate into increased tumor response rates. Finally, the experimental demonstration that tiny numbers of CD62L+ memory cells can fully reconstitute immunocompetence emphasizes the idea that large numbers of cells are not necessary for therapeutic success

when memory stem cell populations are employed. The use of small numbers of CD62L+ memory cells might reduce the cost and complexity of the treatment and, ultimately, allow the widespread application of adoptive immunotherapies.

Graef, P., Buchholz, V.R., Stemberger, C., Flossdorf, M., Henkel, L., Schiemann, M., Drexler, I., Ho¨fer, T., Riddell, S.R., and Busch, D.H. (2014). Immunity 41, this issue, 116–126.

REFERENCES

Osawa, M., Hanada, K., Hamada, H., and Nakauchi, H. (1996). Science 273, 242–245.

Cartwright, E.K., McGary, C.S., Cervasi, B., Micci, L., Lawson, B., Elliott, S.T., Collman, R.G., Bosinger, S.E., Paiardini, M., Vanderford, T.H., et al. (2014). J. Immunol. 192, 4666–4673. Fearon, D.T., Manders, P., and Wagner, S.D. (2001). Science 293, 248–250. Gattinoni, L., Lugli, E., Ji, Y., Pos, Z., Paulos, C.M., Quigley, M.F., Almeida, J.R., Gostick, E., Yu, Z., Carpenito, C., et al. (2011). Nat. Med. 17, 1290–1297. Gattinoni, L., Klebanoff, C.A., and Restifo, N.P. (2012). Nat. Rev. Cancer 12, 671–684.

Lugli, E., Dominguez, M.H., Gattinoni, L., Chattopadhyay, P.K., Bolton, D.L., Song, K., Klatt, N.R., Brenchley, J.M., Vaccari, M., Gostick, E., et al. (2013). J. Clin. Invest. 123, 594–599.

Simons, B.D., and Clevers, H. (2011). Cell 145, 851–862. Sung, J.H., Zhang, H., Moseman, E.A., Alvarez, D., Iannacone, M., Henrickson, S.E., de la Torre, J.C., Groom, J.R., Luster, A.D., and von Andrian, U.H. (2012). Cell 150, 1249–1263. Wherry, E.J., Teichgra¨ber, V., Becker, T.C., Masopust, D., Kaech, S.M., Antia, R., von Andrian, U.H., and Ahmed, R. (2003). Nat. Immunol. 4, 225–234.

Tfr Cells and IgA Join Forces to Diversify the Microbiota Maria Rescigno1,* 1Department of Experimental Oncology, European Institute of Oncology, 20139 Milan, Italy *Correspondence: [email protected] http://dx.doi.org/10.1016/j.immuni.2014.06.012

How diversity of the microbiota is generated and maintained is an open question. In this issue of Immunity, Kawamoto et al. show that T follicular regulatory cells foster microbiota diversity via the regulation of IgA selection. The microbiota participates in several physiological functions, including the function and maturation of the immune system (Hooper et al., 2012). It is so important for our well being that the immune system has found ways to nourish it in a symbiotic relationship that only recently has started to be unraveled. How the immune system shapes the composition of the microbiota is not completely understood. In this issue of Immunity, Kawamoto et al. (2014) show a role for T regulatory cells in promoting microbiota diversity via the regulation of immunoglobulin A (IgA) selection. IgA is the most abundant immunoglobulin and is released in body secretions (Macpherson et al., 2012). IgAs are pro-

duced by plasma cells in the lamina propria of the gut and are transported across epithelial cells by the polymeric immunoglobulin receptor (pIgR) into the intestinal secretion (Kaetzel, 2014). Mice lacking activation-induced cytidine deaminase (AID) that cannot carry out class switch recombination or somatic hypermutation of IgA, or lacking pIgR that cannot release IgAs in the intestinal lumen, display a modified microbiota composition (Kaetzel, 2014). However, this is not simply due to the absence of IgAs; mice with a mutation in AID (AIDG23S) that allows class switch recombination but not somatic hypermutation also display an imbalance in gut bacterial communities (Wei et al., 2011). Thus, affinity maturation of IgAs

plays a crucial role in selecting the microbiota. How are IgAs selected? Germlineencoded IgAs have low affinity and are polyreactive, i.e., they can bind to common microbial antigens. After specific challenge, B cells enter the germinal centers (GC) of Peyer’s patches where T-celldependent affinity maturation of IgAs can occur (Kato et al., 2014). Two types of CD4+ T cells are found in the GCs: T follicular helper (Tfh) cells and T follicular regulatory (Tfr) cells (Kato et al., 2014). Tfh cells provide help to B cell proliferation, selection, and affinity maturation, but Tfh cells hardly proliferate. This is because their growth is controlled by Tfr cells (Linterman et al., 2011). Tfr cells are

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Immunity

Previews Secreted IgA

Bacteria Clostridia IV, XIVa

LP B cell

Peyer’s patch

PC

Tfh cell ? Tfr cell GC Foxp3+ CD4+ T cell

Figure 1. Symbiotic Feedback Loop of IgA Selection and Microbiota Diversification Foxp3+CD4+ T cells (lower left) give rise to T follicular regulatory (Tfr) cells that control Tfh cell proliferation and the germinal center (GC) reaction. Tfh cells mediate class switch recombination and somatic hypermutation. In the absence of Tfr cells, Tfh cells are uncontrolled and can also induce the proliferation of B cells carrying polyreactive IgA. IgA-B cells proliferate and migrate to the lamina propria (LP) of intestinal villi where they become plasma cells (PCs). Plasma cells release dimeric IgAs that are translocated across epithelial cells through the pIgR. Affinity-matured IgAs foster microbiota diversity, and in particular the expansion of firmicutes (Clostridia cluster IV and XIVa) that in turn drive the development of Foxp3+ T cells, thus initiating a mutualistic feedback loop.

distinct from Tfh or T regulatory cells, because they express CXCR5, PD1, and the transcription factor Bcl6 like Tfh cells, but also Foxp3, GITR, and CTLA4 like Treg cells. Kawamoto et al. (2014) found that mice lacking B or T cells had a reduced diversity and different phylogenetic structure of bacterial communities. Then they asked which subset of T cells contributed to increased bacterial diversity. They used mice lacking T cells (Cd3e / ) and reconstituted them with naive or Foxp3+ T cells from different genetically modified mice. Unexpectedly, they found that naive T cell reconstitution led to even more decreased microbiota complexity even when inflammation was exogenously controlled. By contrast, the reconstitution of T-cell-deficient mice with naive T cells plus Foxp3+ T cells or with Foxp3+ T cells alone increased bacterial diversity almost to the degree of wild-type mice. Foxp3+ T cells alone were capable of reestablishing the diversification of Firmicutes, including Clostridia belonging to clusters IV and XIVa that are strong inducers of T regulatory cell differentiation (Atarashi et al., 2011). Hence, Foxp3+

Treg cells induce the expansion of those bacteria that in turn promote their own differentiation in a symbiotic feedback loop. This effect was dependent on the presence of class-switched antibodies; as in mice deficient for AID and T cells, the transfer of Foxp3+ cells did not impact microbiota composition. More interestingly, the effect of Foxp3+ cells was dependent on their capacity to give rise to GC T cells, as indicated by the fact that the transfer of CD25+ T cells lacking the expression of Bcl6, which is required to produce GC T cells, together with naive T cells did not lead to increased microbiota diversity nor to inflammation. This indicates that transferred Foxp3+ cells were capable of controlling inflammation, but not of restoring microbiota composition. Interestingly, in this context, GCs were still formed, but they contained more Tfh and fewer Tfr cells. This led to a skewing of the response toward IgG1 production and a decrease in frequency and number of IgA-producing plasma cells as well as a reduced affinity maturation index of the produced IgAs. Hence the authors confirmed previous observations that Foxp3+ T cells give rise to Tfr cells

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(Linterman et al., 2011), but they also showed that Tfr cells are fundamental to control the quality of the IgA response and this then results in increased microbial diversity. An elegant sorting strategy was then used to assess the composition of IgAbound bacteria, based on the intensity of IgA staining. In the absence of GCcompetent Foxp3+ T cells, there was an increase of high IgA-bound bacteria; however, there was no clear distinction in microbial composition among the high, intermediate, and negative IgA binding groups. By contrast, in mice transferred with GC-competent Foxp3+ T cells, there was a clear difference in microbiota composition among the three groups and an increased affinity selection index for IgAs. Thus, when IgA undergo affinity maturation, the microbiota composition is more diverse. Along the same lines, it has been shown that during lactation, mother-derived IgAs shape the composition of offspring microbiota that makes them more resistant to colitis in the adult life (Rogier et al., 2014), suggesting that early exposure to affinity-matured IgAs is fundamental for selecting a protective microbiota. Finally, Kawamoto et al. (2014) demonstrated a mutual relationship between the adaptive immune response and the microbiota. Colonization of germ-free mice with microbiota obtained from mice that had been transferred with Foxp3+ T cells resulted in the induction of more Tfh cells and greater class-switch to IgAs, as compared to mice colonized with microbiota obtained from mice that had been transferred with naive T cells. Hence, the adaptive response selects a microbiota that then, in a mutualistic loop, fosters the development of a selective IgA response (Figure 1). This is consistent with recent findings that the microbiota and its metabolic products can drive the development of immune cells (reviewed in Rescigno, 2014). These findings have important consequences in disease, because they suggest that individuals with mutations or polymorphisms in the genes encoding Foxp3, Bcl6, or GC-related transcription factors or with defects in IgA production or release may present a less diverse microbiota. This could then contribute to metabolic and inflammatory disorders, such as autoimmune diseases, diabetes,

Immunity

Previews and inflammatory bowel disease. It remains to be established how IgAs are selecting the microbiota. One speculation is that IgAs allow the microbiota to attach to the mucus layer, thus avoiding bacterial wash out in the intestinal bolus and allowing access to the nutrients released by the epithelium. Hence, IgAs play a major role in shaping rather than in eliminating the microbiota.

S., Saito, T., Ohba, Y., et al. (2011). Science 331, 337–341. Hooper, L.V., Littman, D.R., and Macpherson, A.J. (2012). Science 336, 1268–1273.

kar, D.P., Beaton, L., Hogan, J.J., et al. (2011). Nat. Med. 17, 975–982. Macpherson, A.J., Geuking, M.B., and McCoy, K.D. (2012). Trends Immunol. 33, 160–167.

Kaetzel, C.S. (2014). Immunol. Lett. Kato, L.M., Kawamoto, S., Maruya, M., and Fagarasan, S. (2014). Immunol. Cell Biol. 92, 49–56.

REFERENCES

Kawamoto, S., Maruya, M., Kato, L.M., Suda, W., Atarashi, K., Doi, Y., Tsutsui, Y., Qin, H., Honda, K., Okada, T., et al. (2014). Immunity 41, this issue, 152–165.

Atarashi, K., Tanoue, T., Shima, T., Imaoka, A., Kuwahara, T., Momose, Y., Cheng, G., Yamasaki,

Linterman, M.A., Pierson, W., Lee, S.K., Kallies, A., Kawamoto, S., Rayner, T.F., Srivastava, M., Dive-

Rescigno, M. (2014). Cell. Microbiol. 16, 1004– 1013. Rogier, E.W., Frantz, A.L., Bruno, M.E., Wedlund, L., Cohen, D.A., Stromberg, A.J., and Kaetzel, C.S. (2014). Proc. Natl. Acad. Sci. USA 111, 3074–3079. Wei, M., Shinkura, R., Doi, Y., Maruya, M., Fagarasan, S., and Honjo, T. (2011). Nat. Immunol. 12, 264–270.

Macrophages Have a Grip on the Gut Massimo Locati1,* 1Department of Medical Biotechnologies and Translational Medicine, University of Milan, Italy, and Humanitas Clinical and Research Center, Italy *Correspondence: [email protected] http://dx.doi.org/10.1016/j.immuni.2014.07.002

We host a world inside, and every day, new evidence reveals how relevant our microbiota is for daily living. In the most recent issue of Cell, Muller and colleagues demonstrate that microbiota commensals also influence colon peristalsis via a direct effect of muscolaris externae macrophages (Muller et al., 2014). Influence of inflammatory reactions on gut peristalsis is common knowledge. A dramatic example of this is represented by ileus, a well-known dangerous complication of abdominal surgery. Muscularis externa-residing macrophages have been recognized as key players in the second long-lasting phase of this phenomenon, and pharmacological or genetic depletion of resident macrophages results in a decrease of inflammatory mediators and normalized muscle function and gastrointestinal transit in the wake of surgical manipulation (Kalff et al., 1999; Wehner et al., 2007). Under these inflammatory conditions, several mechanisms have been implicated in macrophage activation, including sensing of danger-associated or pathogen-associated molecular patterns, inflammatory cytokines, and direct translocation of bacteria or their products (Boeckxstaens and de Jonge, 2009). Interestingly, ileus hypomotility is a generalized functional reaction involv-

ing areas of the intestine not directly affected by the inflammatory reaction, and evidence indicates that this generalized paralysis is sustained by neural pathways activated by immune cells (de Jonge et al., 2003). It is also common knowledge that intestine peristalsis is influenced by physiological parameters, including diet and luminal microbiota, and evidence in germ-free and gene-targeted animals indicates that gut-flora sensing by the immune system has profound effects on gastrointestinal motility (Anitha et al., 2012). However, aside from controlling gastrointestinal motility under pathologic conditions, the cellular and molecular mechanisms involved in physiological effects of microbiota on gastrointestinal transit are far less understood. Muller and colleagues now provide a first key element in this setting by showing that gastrointestinal peristaltic activity is regulated by muscularis externa macrophages, which represent a distinct

macrophage population organized in layers between the serosa and the longitudinal muscle, the longitudinal and circular muscles, and the outer and the inner circular muscles, and extending from the stomach to distal colon both in humans and mice (Mikkelsen, 2010) (Figure 1). These macrophages are known to contribute to ileus by releasing inflammatory mediators, but their role in physiological conditions is unknown. Muller et al. (2014) have shown that under homeostatic conditions, this macrophage population stimulated enteric neuronal activity via release of bone morphogenetic protein 2 (BMP2). They have also provided evidence that BMP2 expression is reduced following antibiotic treatment, thus suggesting that muscularis externa macrophages tune intestinal motility as a function of luminal microbiota content. Though the authors have not provided information on the molecular mechanisms allowing microbiota sensing by the muscularis externa macrophages,

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