- Email: [email protected]
New Job for NK Cells: Architects of the Tumor Microenvironment
Immunity
Previews New Job for NK Cells: Architects of the Tumor Microenvironment Lydia Dyck1 and Lydia Lynch1,2,3,* 1School
of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland Medical School, Boston, MA, USA 3Brigham and Women’s Hospital, Boston, MA, USA *Correspondence: [email protected] https://doi.org/10.1016/j.immuni.2018.01.001 2Harvard
NK cells control tumor growth directly through targeted cytotoxic granule release or cytokine secretion and indirectly by orchestrating anti-tumor immune responses. In this issue of Immunity, Glasner et al. (2018) now reveal a new role for NK cells in preventing metastatic spread through controlling tumor architecture. Natural killer (NK) cells are innate lymphoid cells that are potent killers of malignant cells and they are particularly important in limiting tumor metastasis (Glasner et al., 2012; Guillerey et al., 2016). NK cells can dampen tumor growth by direct cytotoxicity through the release of cytolytic granules, by secretion of cytokines like IFN-g, or indirectly by the orchestration of anti-tumor immune responses (Morvan and Lanier, 2016). In this issue of Immunity, Glasner et al. (2018) reveal a new role for NK cells in preventing metastatic spread through controlling tumor architecture. NK cells can be activated by multiple mechanisms, including cytokine stimulation (IL-2, IL-12, IL-15, IL-18) or ligation of activating receptors, such as natural cytotoxicity receptors (Ncrs) (Morvan and Lanier, 2016). The natural ability of NK cells to kill cancer cells is also under investigation for cancer immunotherapy strategies (Guillerey et al., 2016). In this issue, Glasner et al. (2018) discovered a new anti-tumor axis by which NK cells suppress cancer metastasis following engagement of the activating receptor NKp46. The authors show that NKp46 ligation induces IFN-g production by NK cells, which in turn signals the expression of fibronectin 1 (FN1) on tumor cells, inhibiting metastatic spread (Figure 1; Glasner et al., 2018). Thus, a new anti-tumor role is revealed for the usual suspects in cytotoxicity—Ncr1 (NKp46) and IFN-g—that not only involves direct cytotoxicity but also regulates the tumor structure. NKp46 (human) or Ncr1 (mouse) is a conserved activating receptor on NK cells with several pathogen-derived ligands,
but specific ligands expressed on tumor cells are yet to be identified (Morvan and Lanier, 2016). Triggering of NKp46 has been shown to promote NK cell cytotoxicity and cytokine secretion (Sivori et al., 1997). Its functional importance has been demonstrated in several in vivo mice, which studies using Ncr1 / showed enhanced tumor growth when Ncr1 was absent (Glasner et al., 2012; Halfteck et al., 2009). In the present study, Glasner et al. (2018) used transgenic mice in which Ncr1 is replaced with the GFP gene (Ncr1gfp/gfp) and immunocompetent Ncr1+/gfp mice as controls to decipher the role of Ncr1 in the control of tumor growth by NK cells. Using the subcutaneous B16 melanoma model, the authors found that Ncr1 deficiency increased spontaneous metastasis formation in the peritoneum of the mice. Interestingly, Ncr1 deficiency had no effect on the primary tumor growth, and so to investigate the mechanism by which Ncr1 expression prevents metastatic tumor spread, the authors sought to determine the key NK cell factors that were involved. First, using Ncr1 Ig fusion protein, the authors detected unknown Ncr1 ligands on tumor cells, which were not altered by Ncr1 depletion. In addition, the frequency of infiltrating immune cells and NK cell degranulation were not affected in primary tumors of Ncr1gfp/gfp mice. However, the ability of NK cells to secrete IFN-g was impaired in Ncr1gfp/gfp mice or when Ncr1 was blocked during NK cellB16 co-culture. Next, the authors found that the formation of metastases was also increased in Ifng / mice, similar to Ncr1gfp/gfp mice, suggesting that the loss of NK cell-derived IFN-g in Ncr1gfp/gfp
mice may contribute, at least in parts, to their increased metastatic potential (Glasner et al., 2018). As loss of IFN-g or Ncr1 didn’t affect primary tumor growth, but were key to inhibiting metastatic spread, the authors looked closer at the primary tumor structure using reflectance confocal microscopy (RCM). RCM is a non-invasive live imaging technique that allows the characterization of the architecture of skin lesions at a resolution similar to conventional histology and is typically used to study nevi and human melanomas (Pellacani et al., 2007). Here, RCM was elegantly adapted to mouse studies, which allowed the authors to characterize the tumors according to features of epidermal disarray, epidermal cellular atypia, dermal-epidermal junction cellular atypia, and nests. Glasner et al. (2018) demonstrated in several experiments using RCM that IFN-g secretion by NK cells alters structural features of primary B16 tumors. Both Ncr1gfp/gfp and Ifng / mice displayed worse tumor structural properties compared to control mice, which the authors confirmed were a direct result of IFN-g signaling. Here the authors isolated B16 tumor cell clones that expressed or lacked the IFN-g receptor (IFN-gR) and implanted them into Ncr1gfp/gfp and Ncr1+/gfp control mice. Indeed, the structural differences observed between Ncr1gfp/gfp and Ncr1+/gfp control mice were diminished when IFN-gR was absent on tumor cells, suggesting that NK cell-derived IFN-g is, at least in part, responsible for the structural changes on B16 primary in tumors in vivo (Glasner et al., 2018). It remains to be seen whether a functional NK-tumor
Immunity 48, January 16, 2018 ª 2018 Published by Elsevier Inc. 9
Immunity
Previews Ncr1+/gfp
Ncr1gfp/gfp
Ncr1 Ncr1 ligand
Ncr1 Tumor cell
NK cell IFN-γ
IFN-γR IFN-γ
FN1
FN1
Figure 1. Control of Tumor Metastasis Formation by NK Cells through the Ncr1-IFN-gFN1 Axis Left: In immunocompetent mice (Ncr1+/gfp), Ncr1 ligation with a yet unknown ligand on tumor cells promotes IFN-g secretion by NK cells. IFN-g binds to the IFN-gR on tumor cells, leading to increased FN1 expression on tumor cells. Right: In mice where Ncr1 is depleted (Ncr1gfp/gfp), IFN-g secretion by NK cells and consequently FN1 expression on tumor cells are reduced. This leads to structural changes of the primary tumor architecture and increased metastatic spread of the tumor.
synapse is also important for these regulatory effects on the tumor architecture. The authors next used RNA sequencing data from IFN-g-treated B16 cells to identify potential target genes that were altered by IFN-g and could potentially affect the architectural structure of the primary tumors. Interestingly, the RNA sequencing data revealed that IFN-g upregulates the mesenchymal gene fibronectin 1 (FN1) (Glasner et al., 2018). FN1 is an adhesive extracellular matrix protein that is a component of the tumor stroma of many cancers (Wang and Hielscher, 2017). Both tumor-promoting and tumorsuppressing properties have been attributed to FN1 in the past (Liu et al., 2008; Wang and Hielscher, 2017). To investigate the role of FN1 in the context of metastatic spread of B16 tumors, the authors depleted Fn1 in B16 tumor cells, which consequently worsened the RCM scores and increased metastatic spread. Depletion of Ncr1 or Ifng had similar effects to Fn1 depletion on the RCM scores (Glasner et al., 2018). Conversely, Fn1 overexpression reduced the number of metastases. Glasner et al. (2018) next highlighted the importance of NK cell-derived IFN-g in this model, as depletion of NK cells but not T cells increased metastasis formation and worsened the tumor architecture in control mice, similar to Ifng / mice and 10 Immunity 48, January 16, 2018
IFN-g neutralization studies. This phenotype was rescued by administration of recombinant IFN-g or by overexpression of Ncr1. These findings implicate Ncr1dependent NK cell-derived IFN-g as a major inhibitor of metastatic tumor spread (Glasner et al., 2018). It will be interesting to see whether other IFN-g-producing cells, such as MAIT cells, that can express activatory receptors which may have tumor ligands can also modulate the tumor architecture. Lastly, the authors investigated whether this model had translational potential. IFN-gR and NKp46 ligand expression was detected in a range of patient cancer biopsies, including melanoma and carcinoma. Interestingly, while Ncr1, Ifng, Ifngr, and Fn1 expression alone had little or insignificant association with patient survival, the combined expression of these genes in primary tumors correlated with a significant increase in recurrence-free survival (Glasner et al., 2018). This suggests that the Ncr1-IFN-g-FN1 axis may also play a role in the control of human metastases. The authors investigated a possible mechanism by which FN1 could suppress metastasis formation, namely the modulation of epithelial to mesenchymal transition (EMT). EMT promotes metastatic spread of tumors (Kalluri and Weinberg, 2009) and the authors found that several EMT-
associated genes (Keratin, N-Cadherin, Twist, Vimentin) were upregulated in tumors of Ncr1gfp/gfp mice (Glasner et al., 2018). It will be interesting to decipher how exactly FN1 expression by tumor cells re-structures the tumor architecture and whether it is through control of EMT, and whether this could be a key target of future therapeutic potential to contain tumors and prevent metastatic spread. Although NK cells are often sparse in the tumor, their presence, as well as other NK cell-associated receptors like KLRB1, have been associated with good prognosis in many human cancers (Gentles et al., 2015). However, little is known about the impact of NCR stimulation on NK cell activity and function in vivo. In the current study, the authors shed light on a novel axis by which NKp46 (Ncr1) ligation induces IFN-g secretion by NK cells which in turn enhances FN1 expression on tumor cells. FN1 expression prevented metastasis-promoting structural changes of the tumor architecture, thereby preventing metastatic spread (Glasner et al., 2018). The current study emphasizes that it is not only secreted factors or the cellular and molecular composition of the tumor microenvironment, but also the architecture of the tumor itself, that are crucial factors affecting metastasis formation. The findings that NKp46 ligation controls metastatic spread of tumor cells reveal a novel non-cytotoxic mechanism of NK cell antitumor control and could help to advance the development of potent NK cell immunotherapy strategies. It would be exciting to see whether modulation of NK cells ex vivo, such as enhancing NKp46 activity or IFN-g production, could improve their anti-tumor activity upon adoptive transfer. Moreover, targeting the tumor architecture could represent a novel cancer therapy target. Overall, these findings highlight the importance of activating receptors for potent NK cell-mediated anti-tumor immunity which could pave the way for novel therapies. REFERENCES Gentles, A.J., Newman, A.M., Liu, C.L., Bratman, S.V., Feng, W., Kim, D., Nair, V.S., Xu, Y., Khuong, A., Hoang, C.D., et al. (2015). The prognostic landscape of genes and infiltrating immune cells across human cancers. Nat. Med. 21, 938–945. Glasner, A., Ghadially, H., Gur, C., Stanietsky, N., Tsukerman, P., Enk, J., and Mandelboim, O. (2012). Recognition and prevention of tumor
Immunity
Previews metastasis by the NK receptor NKp46/NCR1. J. Immunol. 188, 2509–2515. Glasner, A., Levi, A., Enk, J., Isaacson, B., Viukov, S., Orlanski, S., Scope, A., Neuman, T., Enk, C.D., Hanna, J.H., et al. (2018). NKp46 receptor-mediated interferon-g production by natural killer cells increases fibronectin 1 to alter tumor architecture and control metastasis. Immunity 48, this issue, 107–119. Guillerey, C., Huntington, N.D., and Smyth, M.J. (2016). Targeting natural killer cells in cancer immunotherapy. Nat. Immunol. 17, 1025–1036. Halfteck, G.G., Elboim, M., Gur, C., Achdout, H., Ghadially, H., and Mandelboim, O. (2009).
Enhanced in vivo growth of lymphoma tumors in the absence of the NK-activating receptor NKp46/NCR1. J. Immunol. 182, 2221–2230. Kalluri, R., and Weinberg, R.A. (2009). The basics of epithelial-mesenchymal transition. J. Clin. Invest. 119, 1420–1428.
Pellacani, G., Guitera, P., Longo, C., Avramidis, M., Seidenari, S., and Menzies, S. (2007). The impact of in vivo reflectance confocal microscopy for the diagnostic accuracy of melanoma and equivocal melanocytic lesions. J. Invest. Dermatol. 127, 2759–2765.
Liu, W., Cheng, S., Asa, S.L., and Ezzat, S. (2008). The melanoma-associated antigen A3 mediates fibronectin-controlled cancer progression and metastasis. Cancer Res. 68, 8104–8112.
Sivori, S., Vitale, M., Morelli, L., Sanseverino, L., Augugliaro, R., Bottino, C., Moretta, L., and Moretta, A. (1997). p46, a novel natural killer cell-specific surface molecule that mediates cell activation. J. Exp. Med. 186, 1129–1136.
Morvan, M.G., and Lanier, L.L. (2016). NK cells and cancer: you can teach innate cells new tricks. Nat. Rev. Cancer 16, 7–19.
Wang, J.P., and Hielscher, A. (2017). Fibronectin: how its aberrant expression in tumors may improve therapeutic targeting. J. Cancer 8, 674–682.
HIV Immunogens: Affinity Is Key Savit Prabhu,1 Ian A. Cockburn,1 and Carola G. Vinuesa1,* 1Department of Immunology and Infectious Disease, The John Curtin School of Medical Research, Australian National University, Canberra, Australia *Correspondence: [email protected] https://doi.org/10.1016/j.immuni.2018.01.002
Generation of broadly neutralizing antibodies is a key aim of HIV vaccine design, but the precursor B cells are rare. Abbott et al. (2018) report that high affinity and avidity immunogens are required to promote maturation of low frequency B cells in germinal centers. HIV infection is notorious for the host’s poor ability to generate specific neutralizing antibodies against the rapidly mutating virus epitopes. However, some HIV-infected individuals do generate broadly neutralizing antibodies (bNAbs) capable of neutralizing broad strains of HIV virus as a result of a time-consuming process of multiple rounds of somatic hypermutation (SHM) of B cells in germinal centers (Scheid et al., 2011). Significant efforts in the search for effective vaccines are focusing on using immunogens specifically designed to target the precursor unmutated B cells (also known as ‘‘germline-targeting’’) so that upon SHM they can ultimately develop into bNAb producers. A notable attempt at this comes from the recent finding that immunogens such as engineered outer domain germline-targeting version 8 (eOD-GT8) are capable of expanding endogenous precursor naive B cells that can generate VRC01 bNAbs through the process of SHM (Briney et al., 2016; Jardine et al., 2016a); these VRC01 bNAbs are capable of binding crucial epitopes of the HIV
envelope. However, such precursor VRC01-B cells have been found to be rare in healthy individuals, usually at a frequency of 1 in 400,000 (Jardine et al., 2016b). This raises the question of whether rare VRC01 B cells are able to out-compete other non-VRC01 B cell clones and generate good germinal center responses. Moreover, it would be desirable to know what is the effect of immunogen epitope affinity and avidity when responding B cells are present in low numbers. Abbott et al. now show that only immunogens above a certain affinity and in multimeric form are capable of inducing VRC01 B cell-dominated germinal centers from a starting low VRC01 B cell precursor frequency. Furthermore, these B cells achieve extensive somatic hypermutation after a single immunization. Abbott et al. (2018) developed a controlled adoptive cell transfer model, in which different numbers of B cells from germline VRC01 heavy and light chain B cell receptor knockin mice (VRC01gHL) are transferred into congenic
hosts that are subsequently vaccinated with monomeric or multimeric immunogens of defined affinities for VRC01gHL B cells (0.5 mM, 14 mM, and 40 mM) (Jardine et al., 2013), representative of the range of BCR affinities of naı¨ve VRC01class precursor B cells in humans that ranges from 0.1 mM to > 100 mM KD (Jardine et al., 2016b). The starting transferred VRC01gHL B cell precursor frequency of 1 in a million was just below the physiological frequency reported in humans (Jardine et al., 2016b). This transfer model allows the rare B cell populations to be tracked so their participation in germinal center and memory responses can be quantified. When germinal center responses were evaluated against a range of immunogen affinities and precursor frequencies, physiological frequencies of precursor B cells generated a poor response, unless the immunogen was of high affinity. Avidity mattered as well, since immunogen monomers elicited several hundred-fold lower responses in comparison to multimers. When physiologically low frequencies of B cells were
Immunity 48, January 16, 2018 ª 2018 Published by Elsevier Inc. 11
Previews New Job for NK Cells: Architects of the Tumor Microenvironment Lydia Dyck1 and Lydia Lynch1,2,3,* 1School
of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland Medical School, Boston, MA, USA 3Brigham and Women’s Hospital, Boston, MA, USA *Correspondence: [email protected] https://doi.org/10.1016/j.immuni.2018.01.001 2Harvard
NK cells control tumor growth directly through targeted cytotoxic granule release or cytokine secretion and indirectly by orchestrating anti-tumor immune responses. In this issue of Immunity, Glasner et al. (2018) now reveal a new role for NK cells in preventing metastatic spread through controlling tumor architecture. Natural killer (NK) cells are innate lymphoid cells that are potent killers of malignant cells and they are particularly important in limiting tumor metastasis (Glasner et al., 2012; Guillerey et al., 2016). NK cells can dampen tumor growth by direct cytotoxicity through the release of cytolytic granules, by secretion of cytokines like IFN-g, or indirectly by the orchestration of anti-tumor immune responses (Morvan and Lanier, 2016). In this issue of Immunity, Glasner et al. (2018) reveal a new role for NK cells in preventing metastatic spread through controlling tumor architecture. NK cells can be activated by multiple mechanisms, including cytokine stimulation (IL-2, IL-12, IL-15, IL-18) or ligation of activating receptors, such as natural cytotoxicity receptors (Ncrs) (Morvan and Lanier, 2016). The natural ability of NK cells to kill cancer cells is also under investigation for cancer immunotherapy strategies (Guillerey et al., 2016). In this issue, Glasner et al. (2018) discovered a new anti-tumor axis by which NK cells suppress cancer metastasis following engagement of the activating receptor NKp46. The authors show that NKp46 ligation induces IFN-g production by NK cells, which in turn signals the expression of fibronectin 1 (FN1) on tumor cells, inhibiting metastatic spread (Figure 1; Glasner et al., 2018). Thus, a new anti-tumor role is revealed for the usual suspects in cytotoxicity—Ncr1 (NKp46) and IFN-g—that not only involves direct cytotoxicity but also regulates the tumor structure. NKp46 (human) or Ncr1 (mouse) is a conserved activating receptor on NK cells with several pathogen-derived ligands,
but specific ligands expressed on tumor cells are yet to be identified (Morvan and Lanier, 2016). Triggering of NKp46 has been shown to promote NK cell cytotoxicity and cytokine secretion (Sivori et al., 1997). Its functional importance has been demonstrated in several in vivo mice, which studies using Ncr1 / showed enhanced tumor growth when Ncr1 was absent (Glasner et al., 2012; Halfteck et al., 2009). In the present study, Glasner et al. (2018) used transgenic mice in which Ncr1 is replaced with the GFP gene (Ncr1gfp/gfp) and immunocompetent Ncr1+/gfp mice as controls to decipher the role of Ncr1 in the control of tumor growth by NK cells. Using the subcutaneous B16 melanoma model, the authors found that Ncr1 deficiency increased spontaneous metastasis formation in the peritoneum of the mice. Interestingly, Ncr1 deficiency had no effect on the primary tumor growth, and so to investigate the mechanism by which Ncr1 expression prevents metastatic tumor spread, the authors sought to determine the key NK cell factors that were involved. First, using Ncr1 Ig fusion protein, the authors detected unknown Ncr1 ligands on tumor cells, which were not altered by Ncr1 depletion. In addition, the frequency of infiltrating immune cells and NK cell degranulation were not affected in primary tumors of Ncr1gfp/gfp mice. However, the ability of NK cells to secrete IFN-g was impaired in Ncr1gfp/gfp mice or when Ncr1 was blocked during NK cellB16 co-culture. Next, the authors found that the formation of metastases was also increased in Ifng / mice, similar to Ncr1gfp/gfp mice, suggesting that the loss of NK cell-derived IFN-g in Ncr1gfp/gfp
mice may contribute, at least in parts, to their increased metastatic potential (Glasner et al., 2018). As loss of IFN-g or Ncr1 didn’t affect primary tumor growth, but were key to inhibiting metastatic spread, the authors looked closer at the primary tumor structure using reflectance confocal microscopy (RCM). RCM is a non-invasive live imaging technique that allows the characterization of the architecture of skin lesions at a resolution similar to conventional histology and is typically used to study nevi and human melanomas (Pellacani et al., 2007). Here, RCM was elegantly adapted to mouse studies, which allowed the authors to characterize the tumors according to features of epidermal disarray, epidermal cellular atypia, dermal-epidermal junction cellular atypia, and nests. Glasner et al. (2018) demonstrated in several experiments using RCM that IFN-g secretion by NK cells alters structural features of primary B16 tumors. Both Ncr1gfp/gfp and Ifng / mice displayed worse tumor structural properties compared to control mice, which the authors confirmed were a direct result of IFN-g signaling. Here the authors isolated B16 tumor cell clones that expressed or lacked the IFN-g receptor (IFN-gR) and implanted them into Ncr1gfp/gfp and Ncr1+/gfp control mice. Indeed, the structural differences observed between Ncr1gfp/gfp and Ncr1+/gfp control mice were diminished when IFN-gR was absent on tumor cells, suggesting that NK cell-derived IFN-g is, at least in part, responsible for the structural changes on B16 primary in tumors in vivo (Glasner et al., 2018). It remains to be seen whether a functional NK-tumor
Immunity 48, January 16, 2018 ª 2018 Published by Elsevier Inc. 9
Immunity
Previews Ncr1+/gfp
Ncr1gfp/gfp
Ncr1 Ncr1 ligand
Ncr1 Tumor cell
NK cell IFN-γ
IFN-γR IFN-γ
FN1
FN1
Figure 1. Control of Tumor Metastasis Formation by NK Cells through the Ncr1-IFN-gFN1 Axis Left: In immunocompetent mice (Ncr1+/gfp), Ncr1 ligation with a yet unknown ligand on tumor cells promotes IFN-g secretion by NK cells. IFN-g binds to the IFN-gR on tumor cells, leading to increased FN1 expression on tumor cells. Right: In mice where Ncr1 is depleted (Ncr1gfp/gfp), IFN-g secretion by NK cells and consequently FN1 expression on tumor cells are reduced. This leads to structural changes of the primary tumor architecture and increased metastatic spread of the tumor.
synapse is also important for these regulatory effects on the tumor architecture. The authors next used RNA sequencing data from IFN-g-treated B16 cells to identify potential target genes that were altered by IFN-g and could potentially affect the architectural structure of the primary tumors. Interestingly, the RNA sequencing data revealed that IFN-g upregulates the mesenchymal gene fibronectin 1 (FN1) (Glasner et al., 2018). FN1 is an adhesive extracellular matrix protein that is a component of the tumor stroma of many cancers (Wang and Hielscher, 2017). Both tumor-promoting and tumorsuppressing properties have been attributed to FN1 in the past (Liu et al., 2008; Wang and Hielscher, 2017). To investigate the role of FN1 in the context of metastatic spread of B16 tumors, the authors depleted Fn1 in B16 tumor cells, which consequently worsened the RCM scores and increased metastatic spread. Depletion of Ncr1 or Ifng had similar effects to Fn1 depletion on the RCM scores (Glasner et al., 2018). Conversely, Fn1 overexpression reduced the number of metastases. Glasner et al. (2018) next highlighted the importance of NK cell-derived IFN-g in this model, as depletion of NK cells but not T cells increased metastasis formation and worsened the tumor architecture in control mice, similar to Ifng / mice and 10 Immunity 48, January 16, 2018
IFN-g neutralization studies. This phenotype was rescued by administration of recombinant IFN-g or by overexpression of Ncr1. These findings implicate Ncr1dependent NK cell-derived IFN-g as a major inhibitor of metastatic tumor spread (Glasner et al., 2018). It will be interesting to see whether other IFN-g-producing cells, such as MAIT cells, that can express activatory receptors which may have tumor ligands can also modulate the tumor architecture. Lastly, the authors investigated whether this model had translational potential. IFN-gR and NKp46 ligand expression was detected in a range of patient cancer biopsies, including melanoma and carcinoma. Interestingly, while Ncr1, Ifng, Ifngr, and Fn1 expression alone had little or insignificant association with patient survival, the combined expression of these genes in primary tumors correlated with a significant increase in recurrence-free survival (Glasner et al., 2018). This suggests that the Ncr1-IFN-g-FN1 axis may also play a role in the control of human metastases. The authors investigated a possible mechanism by which FN1 could suppress metastasis formation, namely the modulation of epithelial to mesenchymal transition (EMT). EMT promotes metastatic spread of tumors (Kalluri and Weinberg, 2009) and the authors found that several EMT-
associated genes (Keratin, N-Cadherin, Twist, Vimentin) were upregulated in tumors of Ncr1gfp/gfp mice (Glasner et al., 2018). It will be interesting to decipher how exactly FN1 expression by tumor cells re-structures the tumor architecture and whether it is through control of EMT, and whether this could be a key target of future therapeutic potential to contain tumors and prevent metastatic spread. Although NK cells are often sparse in the tumor, their presence, as well as other NK cell-associated receptors like KLRB1, have been associated with good prognosis in many human cancers (Gentles et al., 2015). However, little is known about the impact of NCR stimulation on NK cell activity and function in vivo. In the current study, the authors shed light on a novel axis by which NKp46 (Ncr1) ligation induces IFN-g secretion by NK cells which in turn enhances FN1 expression on tumor cells. FN1 expression prevented metastasis-promoting structural changes of the tumor architecture, thereby preventing metastatic spread (Glasner et al., 2018). The current study emphasizes that it is not only secreted factors or the cellular and molecular composition of the tumor microenvironment, but also the architecture of the tumor itself, that are crucial factors affecting metastasis formation. The findings that NKp46 ligation controls metastatic spread of tumor cells reveal a novel non-cytotoxic mechanism of NK cell antitumor control and could help to advance the development of potent NK cell immunotherapy strategies. It would be exciting to see whether modulation of NK cells ex vivo, such as enhancing NKp46 activity or IFN-g production, could improve their anti-tumor activity upon adoptive transfer. Moreover, targeting the tumor architecture could represent a novel cancer therapy target. Overall, these findings highlight the importance of activating receptors for potent NK cell-mediated anti-tumor immunity which could pave the way for novel therapies. REFERENCES Gentles, A.J., Newman, A.M., Liu, C.L., Bratman, S.V., Feng, W., Kim, D., Nair, V.S., Xu, Y., Khuong, A., Hoang, C.D., et al. (2015). The prognostic landscape of genes and infiltrating immune cells across human cancers. Nat. Med. 21, 938–945. Glasner, A., Ghadially, H., Gur, C., Stanietsky, N., Tsukerman, P., Enk, J., and Mandelboim, O. (2012). Recognition and prevention of tumor
Immunity
Previews metastasis by the NK receptor NKp46/NCR1. J. Immunol. 188, 2509–2515. Glasner, A., Levi, A., Enk, J., Isaacson, B., Viukov, S., Orlanski, S., Scope, A., Neuman, T., Enk, C.D., Hanna, J.H., et al. (2018). NKp46 receptor-mediated interferon-g production by natural killer cells increases fibronectin 1 to alter tumor architecture and control metastasis. Immunity 48, this issue, 107–119. Guillerey, C., Huntington, N.D., and Smyth, M.J. (2016). Targeting natural killer cells in cancer immunotherapy. Nat. Immunol. 17, 1025–1036. Halfteck, G.G., Elboim, M., Gur, C., Achdout, H., Ghadially, H., and Mandelboim, O. (2009).
Enhanced in vivo growth of lymphoma tumors in the absence of the NK-activating receptor NKp46/NCR1. J. Immunol. 182, 2221–2230. Kalluri, R., and Weinberg, R.A. (2009). The basics of epithelial-mesenchymal transition. J. Clin. Invest. 119, 1420–1428.
Pellacani, G., Guitera, P., Longo, C., Avramidis, M., Seidenari, S., and Menzies, S. (2007). The impact of in vivo reflectance confocal microscopy for the diagnostic accuracy of melanoma and equivocal melanocytic lesions. J. Invest. Dermatol. 127, 2759–2765.
Liu, W., Cheng, S., Asa, S.L., and Ezzat, S. (2008). The melanoma-associated antigen A3 mediates fibronectin-controlled cancer progression and metastasis. Cancer Res. 68, 8104–8112.
Sivori, S., Vitale, M., Morelli, L., Sanseverino, L., Augugliaro, R., Bottino, C., Moretta, L., and Moretta, A. (1997). p46, a novel natural killer cell-specific surface molecule that mediates cell activation. J. Exp. Med. 186, 1129–1136.
Morvan, M.G., and Lanier, L.L. (2016). NK cells and cancer: you can teach innate cells new tricks. Nat. Rev. Cancer 16, 7–19.
Wang, J.P., and Hielscher, A. (2017). Fibronectin: how its aberrant expression in tumors may improve therapeutic targeting. J. Cancer 8, 674–682.
HIV Immunogens: Affinity Is Key Savit Prabhu,1 Ian A. Cockburn,1 and Carola G. Vinuesa1,* 1Department of Immunology and Infectious Disease, The John Curtin School of Medical Research, Australian National University, Canberra, Australia *Correspondence: [email protected] https://doi.org/10.1016/j.immuni.2018.01.002
Generation of broadly neutralizing antibodies is a key aim of HIV vaccine design, but the precursor B cells are rare. Abbott et al. (2018) report that high affinity and avidity immunogens are required to promote maturation of low frequency B cells in germinal centers. HIV infection is notorious for the host’s poor ability to generate specific neutralizing antibodies against the rapidly mutating virus epitopes. However, some HIV-infected individuals do generate broadly neutralizing antibodies (bNAbs) capable of neutralizing broad strains of HIV virus as a result of a time-consuming process of multiple rounds of somatic hypermutation (SHM) of B cells in germinal centers (Scheid et al., 2011). Significant efforts in the search for effective vaccines are focusing on using immunogens specifically designed to target the precursor unmutated B cells (also known as ‘‘germline-targeting’’) so that upon SHM they can ultimately develop into bNAb producers. A notable attempt at this comes from the recent finding that immunogens such as engineered outer domain germline-targeting version 8 (eOD-GT8) are capable of expanding endogenous precursor naive B cells that can generate VRC01 bNAbs through the process of SHM (Briney et al., 2016; Jardine et al., 2016a); these VRC01 bNAbs are capable of binding crucial epitopes of the HIV
envelope. However, such precursor VRC01-B cells have been found to be rare in healthy individuals, usually at a frequency of 1 in 400,000 (Jardine et al., 2016b). This raises the question of whether rare VRC01 B cells are able to out-compete other non-VRC01 B cell clones and generate good germinal center responses. Moreover, it would be desirable to know what is the effect of immunogen epitope affinity and avidity when responding B cells are present in low numbers. Abbott et al. now show that only immunogens above a certain affinity and in multimeric form are capable of inducing VRC01 B cell-dominated germinal centers from a starting low VRC01 B cell precursor frequency. Furthermore, these B cells achieve extensive somatic hypermutation after a single immunization. Abbott et al. (2018) developed a controlled adoptive cell transfer model, in which different numbers of B cells from germline VRC01 heavy and light chain B cell receptor knockin mice (VRC01gHL) are transferred into congenic
hosts that are subsequently vaccinated with monomeric or multimeric immunogens of defined affinities for VRC01gHL B cells (0.5 mM, 14 mM, and 40 mM) (Jardine et al., 2013), representative of the range of BCR affinities of naı¨ve VRC01class precursor B cells in humans that ranges from 0.1 mM to > 100 mM KD (Jardine et al., 2016b). The starting transferred VRC01gHL B cell precursor frequency of 1 in a million was just below the physiological frequency reported in humans (Jardine et al., 2016b). This transfer model allows the rare B cell populations to be tracked so their participation in germinal center and memory responses can be quantified. When germinal center responses were evaluated against a range of immunogen affinities and precursor frequencies, physiological frequencies of precursor B cells generated a poor response, unless the immunogen was of high affinity. Avidity mattered as well, since immunogen monomers elicited several hundred-fold lower responses in comparison to multimers. When physiologically low frequencies of B cells were
Immunity 48, January 16, 2018 ª 2018 Published by Elsevier Inc. 11