Host-derived growth factors drive ERK phosphorylation and MCL1 expression to promote osteosarcoma cell survival during metastatic lung colonization

PURPOSE

For patients with osteosarcoma, disease-related mortality most often results from lung metastasis-a phenomenon shared with many solid tumors. While established metastatic lesions behave aggressively, very few of the tumor cells that reach the lung will survive. By identifying mechanisms that facilitate survival of disseminated tumor cells, we can develop therapeutic strategies that prevent and treat metastasis.

METHODS

We analyzed single cell RNA-sequencing (scRNAseq) data from murine metastasis-bearing lungs to interrogate changes in both host and tumor cells during colonization. We used these data to elucidate pathways that become activated in cells that survive dissemination and identify candidate host-derived signals that drive activation. We validated these findings through live cell reporter systems, immunocytochemistry, and fluorescent immunohistochemistry. We then validated the functional relevance of key candidates using pharmacologic inhibition in models of metastatic osteosarcoma.

RESULTS

Expression patterns suggest that the MAPK pathway is significantly elevated in early and established metastases. MAPK activity correlates with expression of anti-apoptotic genes, especially MCL1. Niche cells produce growth factors that increase ERK phosphorylation and MCL1 expression in tumor cells. Both early and established metastases are vulnerable to MCL1 inhibition, but not MEK inhibition in vivo. Combining MCL1 inhibition with chemotherapy both prevented colonization and eliminated established metastases in murine models of osteosarcoma.

CONCLUSION

Niche-derived growth factors drive MAPK activity and MCL1 expression in osteosarcoma, promoting metastatic colonization. Although later metastases produce less MCL1, they remain dependent on it. MCL1 is a promising target for clinical trials in both human and canine patients.

Tumor resident memory CD8 T cells and concomitant tumor immunity develop independently of CD4 help

Tissue resident memory (Trm) CD8 T cells infiltrating tumors represent an enriched population of tumor antigen-specific T cells, and their presence is associated with improved outcomes in patients. Using genetically engineered mouse pancreatic tumor models we demonstrate that tumor implantation generates a Trm niche that is dependent on direct antigen presentation by cancer cells. However, we observe that initial CCR7-mediated localization of CD8 T cells to tumor draining lymph nodes is required to subsequently generate CD103+ CD8 T cells in tumors. We observe that the formation of CD103+ CD8 T cells in tumors is dependent on CD40L but independent of CD4 T cells, and using mixed chimeras we show that CD8 T cells can provide their own CD40L to permit CD103+ CD8 T cell differentiation. Finally, we show that CD40L is required to provide systemic protection against secondary tumors. These data suggest that CD103+ CD8 T cell formation in tumors can occur independent of the two-factor authentication provided by CD4 T cells and highlight CD103+ CD8 T cells as a distinct differentiation decision from CD4-dependent central memory.

T cell immunotherapies engage neutrophils to eliminate tumor antigen escape variants

Cancer immunotherapies, including adoptive T cell transfer, can be ineffective because tumors evolve to display antigen-loss-variant clones. Therapies that activate multiple branches of the immune system may eliminate escape variants. Here, we show that melanoma-specific CD4+ T cell therapy in combination with OX40 co-stimulation or CTLA-4 blockade can eradicate melanomas containing antigen escape variants. As expected, early on-target recognition of melanoma antigens by tumor-specific CD4+ T cells was required. Surprisingly, complete tumor eradication was dependent on neutrophils and partly dependent on inducible nitric oxide synthase. In support of these findings, extensive neutrophil activation was observed in mouse tumors and in biopsies of melanoma patients treated with immune checkpoint blockade. Transcriptomic and flow cytometry analyses revealed a distinct anti-tumorigenic neutrophil subset present in treated mice. Our findings uncover an interplay between T cells mediating the initial anti-tumor immune response and neutrophils mediating the destruction of tumor antigen loss variants.

CD103 and CD39 coexpression identifies neoantigen-specific cytotoxic T cells in colorectal cancers with low mutation burden

BACKGROUND

Expression of CD103 and CD39 has been found to pinpoint tumor-reactive CD8⁺ T cells in a variety of solid cancers. We aimed to investigate whether these markers specifically identify neoantigen-specific T cells in colorectal cancers (CRCs) with low mutation burden.

EXPERIMENTAL DESIGN

Whole-exome and RNA sequencing of 11 mismatch repair-proficient (MMR-proficient) CRCs and corresponding healthy tissues were performed to determine the presence of putative neoantigens. In parallel, tumor-infiltrating lymphocytes (TILs) were cultured from the tumor fragments and, in parallel, CD8⁺ T cells were flow-sorted from their respective tumor digests based on single or combined expression of CD103 and CD39. Each subset was expanded and subsequently interrogated for neoantigen-directed reactivity with synthetic peptides. Neoantigen-directed reactivity was determined by flow cytometric analyses of T cell activation markers and ELISA-based detection of IFN-γ and granzyme B release. Additionally, imaging mass cytometry was applied to investigate the localization of CD103⁺CD39⁺ cytotoxic T cells in tumors.

RESULTS

Neoantigen-directed reactivity was only encountered in bulk TIL populations and CD103⁺CD39⁺ (double positive, DP) CD8⁺ T cell subsets but never in double-negative or single-positive subsets. Neoantigen-reactivity detected in bulk TIL but not in DP CD8⁺ T cells could be attributed to CD4⁺ T cells. CD8⁺ T cells that were located in direct contact with cancer cells in tumor tissues were enriched for CD103 and CD39 expression.

CONCLUSION

Coexpression of CD103 and CD39 is characteristic of neoantigen-specific CD8⁺ T cells in MMR-proficient CRCs with low mutation burden. The exploitation of these subsets in the context of adoptive T cell transfer or engineered T cell receptor therapies is a promising avenue to extend the benefits of immunotherapy to an increasing number of CRC patients.

OX40 agonist stimulation increases and sustains humoral and cell-mediated responses to SARS-CoV-2 protein and saRNA vaccines

To prevent SARS-CoV-2 infections and generate long-lasting immunity, vaccines need to generate strong viral-specific B and T cell responses. Previous results from our lab and others have shown that immunizations in the presence of an OX40 agonist antibody lead to higher antibody titers and increased numbers of long-lived antigen-specific CD4 and CD8 T cells. Using a similar strategy, we explored the effect of OX40 co-stimulation in a prime and boost vaccination scheme using an adjuvanted SARS-CoV-2 spike protein vaccine in C57BL/6 mice. Our results show that OX40 engagement during vaccination significantly increases long-lived antibody responses to the spike protein. In addition, after immunization spike protein-specific proliferation was greatly increased for both CD4 and CD8 T cells, with enhanced, spike-specific secretion of IFN-γ and IL-2. Booster (3^rd injection) immunizations combined with an OX40 agonist (7 months post-prime) further increased vaccine-specific antibody and T cell responses. Initial experiments assessing a self-amplifying mRNA (saRNA) vaccine encoding the spike protein antigen show a robust antigen-specific CD8 T cell response. The saRNA spike-specific CD8 T cells express high levels of GrzmB, IFN-γ and TNF-α which was not observed with protein immunization and this response was further increased by the OX40 agonist. Similar to protein immunizations the OX40 agonist also increased vaccine-specific CD4 T cell responses. In summary, this study compares and contrasts the effects and benefits of both protein and saRNA vaccination and the extent to which an OX40 agonist enhances and sustains the immune response against the SARS-CoV-2 spike protein.

PD-1 and ICOS coexpression identifies tumor-reactive CD4+ T cells in human solid tumors

CD4⁺ Th cells play a key role in orchestrating immune responses, but the identity of the CD4⁺ Th cells involved in the antitumor immune response remains to be defined. We analyzed the immune cell infiltrates of head and neck squamous cell carcinoma and colorectal cancers and identified a subset of CD4⁺ Th cells distinct from FOXP3⁺ Tregs that coexpressed programmed cell death 1 (PD-1) and ICOS. These tumor-infiltrating lymphocyte CD4⁺ Th cells (CD4⁺ Th TILs) had a tissue-resident memory phenotype, were present in MHC class II–rich areas, and proliferated in the tumor, suggesting local antigen recognition. The T cell receptor repertoire of the PD-1⁺ICOS⁺ CD4⁺ Th TILs was oligoclonal, with T cell clones expanded in the tumor, but present at low frequencies in the periphery. Finally, these PD-1⁺ICOS⁺ CD4⁺ Th TILs were shown to recognize both tumor-associated antigens and tumor-specific neoantigens. Our findings provide an approach for isolating tumor-reactive CD4⁺ Th TILs directly ex vivo that will help define their role in the antitumor immune response and potentially improve future adoptive T cell therapy approaches.

PD-1 and ICOS co-expression identifies tumor-reactive CD4 Th cells in human solid tumors

CD4 T helper (Th) cells play a key role in orchestrating immune responses, but the identity of the CD4 Th cells involved in the immune response against cancer remains to be defined. We analyzed the immune cell infiltrates of head and neck squamous cell carcinoma and microsatellite stable colorectal cancers and identified a subset of CD4 Th cells distinct from FOXP3+ regulatory T cells that co-express PD-1 and ICOS. This cell population, which was present in the tumor but absent in the periphery, features of chronic stimulation and displays characteristics of tissue-resident memory T cells. PD-1+ICOS+ tumor-infiltrating (TIL) CD4 Th cells are located primarily in the tumor stroma in proximity to MHC class II+ cells and are proliferating, suggesting local antigen recognition. The T-cell receptor repertoire of the PD-1+ICOS+ CD4 Th TIL is oligoclonal, with T-cell clones expanded in the tumor, but present at low frequencies in the periphery. Finally, these PD-1+ICOS+ CD4 Th TIL were shown to recognize both tumor-associated antigens and tumor-specific neoantigens, which were distinct from the epitopes recognized by the CD8 T cells from the same patients. Our findings provide an approach for isolating tumor-reactive CD4 Th TIL directly ex vivo and imply that harnessing the cooperation between CD4 and CD8 T cells might lead to more efficient tumor recognition and control in cancer patients.

Supported by the Providence Portland Medical Foundation and the Developmental Research Program for Head and Neck Cancer.

Tumor resident memory CD8 T cell formation and concomitant tumor immunity is CD40L dependent and CD4 independent

The implantation of cancer cell lines into immunocompetent mice acts as a vaccination event, resulting in T cell immunity that impacts both tumor progression and the response to subsequent therapy. We have previously shown that blocking immunity at tumor implantation using anti-CD40L antibodies blocks development of an intratumoral antigen-specific CD8 T cell population with tissue resident memory (Trm) phenotypes, and also limits responsiveness to radiation therapy and immunotherapy combinations. Using pancreatic tumors derived from Pdx1-Cre and Pdx1-Cre /R26LSL-LSIY mice crossed with KrasLSL-G12D/+Tp53LSL-R172H/+ mice, we explored the role of CD4 T cells in providing CD40-CD40L help to generate Trm and conventional T central memory CD8 T cells (Tcm) cells in the tumor and systemically. Using depleting antibodies, we identified that Trm cells in the tumor could form independently of CD4 T cells but were lost following CD40L blockade. By contrast, systemically circulating Tcm cells that could re-expand after antigen-specific challenge were dependent on both CD4 T cells and CD40-CD40L interactions. Notably, concomitant immunity generated by tumor implantation that can prevent tumor growth on the opposite flank could also occur independently of CD4 T cells, but was lost on CD40L blockade. Systemic vaccination with Listeria monocytogenes expressing SIY efficiently induced the formation of SIY-specific Tcm cells but did not impact tumor implantation. These data suggest that tumor implantation generates Trm cells independently of CD4 T cells, and that these cells, not Tcm cells, sustain concomitant immunity. These data may impact immune therapies designed to control metastatic seeding in patients.

Supported by grants from NIH (R01CA182311,  R01CA244142, R01CA208644).

Abstract A186: A new strategy to identify and expand tumor-reactive CD8 TILs in human solid tumors

The immune system can recognize and destroy tumor cells through T-cell mediated mechanisms. Hence, identifying tumor antigen-specific T-cells from cancer patients and expanding them in large numbers in vitro has important implications for immunotherapy diagnostics and therapeutics. Here we show that tumor-reactive T-cells are enriched in a subset of tumor-infiltrating CD8 T-cells (CD8 TILs) identified by co-expression of CD103 and CD39 both in primary and metastatic tumors. The CD103+CD39+ CD8 TILs are present at high frequencies in melanoma and mismatch repair-deficient colon cancer but at low frequencies in microsatellite stable (MSS) colon cancer and colorectal liver metastasis. This cell population displays a distinct T-cell receptor (TCR) repertoire, with T-cell clones expanded in the tumor but present at low frequencies in the periphery. Importantly, we show in a MSS colon cancer patient that a very low number of CD103+CD39+ CD8 TILs can be expanded in vitro and that those cells recognize tumor-specific neoantigens. Finally, patients with head and neck cancer whose CD8 TILs contained a higher frequency of CD103+CD39+ cells experienced a greater overall survival. Our work suggests that CD103+CD39+ CD8 TILs are key players in the patient’s antitumor response and describe an approach for detecting and expanding those cells, which will help improve adoptive TIL therapy for cancer patients.

Citation Format: Thomas Duhen, Rebekka Duhen, Ryan Montler, Tarsem Moudgil, Jitske van den Bulk, Bernard A. Fox, Shu-Ching Chang, Gary Grunkemeier, Els M.E. Verdegaal, Noel F. de Miranda, Rom Leidner, Richard B. Bell, Andrew D. Weinberg. A new strategy to identify and expand tumor-reactive CD8 TILs in human solid tumors [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A186.

Abstract B094: Successful identification of neoantigen-specific T-cell responses in low mutation burden colorectal cancers for personalized cancer vaccine development

Innovative treatment options are required to improve cure rates in advanced colorectal cancer patients. Immune checkpoint blockade therapy (anti-PD-1) was shown to be effective in colorectal cancers with high mutation burden (e.g., mismatch repair deficient) as antitumor reactivity is largely explained by the recognition of somatically mutated antigens (neoantigens). No immunotherapeutic strategies are currently available for patients diagnosed with low mutation burden colorectal cancer. We hypothesized that if neoantigen-reactive T-cells are present in low mutation burden patients, the latter could benefit from immunotherapeutic interventions that stimulate neoantigen recognition and the onset of a robust antitumor immune response.In order to detect neoantigens, whole exome and RNA next-generation sequencing analyses were performed in cancer and healthy tissues from five colorectal cancer patients. Corresponding neoepitopes were synthesized and tested for their ability to induce immune cell activation in T-cells isolated from the tumor tissue (TIL) and from peripheral blood. Neoantigen-specific T-cell responses were identified in the majority of patients that presented with tumors carrying 25 to 36 transcribed, non-synonymous variants. Up to six different neoantigens were recognized per tumor, which resulted in a higher detection rate than anticipated based on published data. Moreover, we discovered the merits of isolating CD39+CD103+CD8+ T-cells for detection of a broad recognition of HLA class I-restricted neoantigens. This CD39+CD103+CD8+ T-cell subset comprises the majority and a broader repertoire of neoantigen-specific T-cells compared to bulk TIL populations or lymphocytes derived from peripheral blood. In conclusion, we developed a neoantigen screening pipeline to unlock the immunogenic potential of colorectal cancers with low mutation burden. We have detected a relatively high number of neoantigens that are recognized by tumor- and/or PBMC-derived T-cells in mismatch repair proficient, low mutation burden colorectal cancer patients, and show the importance of the CD39+CD103+CD8+ T-cell subset for neoantigen-based immunotherapies. These findings warrant the further exploration of the potential to employ neoantigen-targeted therapies to improve clinical outcomes of colorectal cancer patients.

Citation Format: Jitske van den Bulk, Dina Ruano, Marieke E. Ijsselsteijn, Marten Visser, Ruud van der Breggen, Koen C.M.J. Peeters, Thomas Duhen, Rebekka Duhen, Andrew D Weinberg, Sjoerd S.H. van der Burg, Els M.E. Verdegaal, Noel F. de Miranda. Successful identification of neoantigen-specific T-cell responses in low mutation burden colorectal cancers for personalized cancer vaccine development [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B094.

Co-expression of CD39 and CD103 identifies tumor-reactive CD8 T cells in human solid tumors

Identifying tumor antigen-specific T cells from cancer patients has important implications for immunotherapy diagnostics and therapeutics. Here, we show that CD103⁺CD39⁺ tumor-infiltrating CD8 T cells (CD8 TIL) are enriched for tumor-reactive cells both in primary and metastatic tumors. This CD8 TIL subset is found across six different malignancies and displays an exhausted tissue-resident memory phenotype. CD103⁺CD39⁺ CD8 TILs have a distinct T-cell receptor (TCR) repertoire, with T-cell clones expanded in the tumor but present at low frequencies in the periphery. CD103⁺CD39⁺ CD8 TILs also efficiently kill autologous tumor cells in a MHC-class I-dependent manner. Finally, higher frequencies of CD103⁺CD39⁺ CD8 TILs in patients with head and neck cancer are associated with better overall survival. Our data thus describe an approach for detecting tumor-reactive CD8 TILs that will help define mechanisms of existing immunotherapy treatments, and may lead to future adoptive T-cell cancer therapies.

Identifying and enumerating tumor-specific CD8 T cells are important for assessing cancer prognosis and therapy efficacy. Here the authors show that CD39 and CD103 mark a subset of tumor-infiltrating CD8 T cells that are tumor-reactive and exhibit characteristics of exhausted or tissue-resident memory T cells.

S1P1 deletion differentially affects TH17 and Regulatory T cells

Sphingosine-1 phosphate receptor 1 (S1P₁) is critical for the egress of T and B cells out of lymphoid organs. Although S1P₁ agonist fingolimod is currently used for the treatment of multiple sclerosis (MS) little is known how S1P₁ signaling regulates Th17 and T_reg cell homeostasis. To study the impact of S1P₁ signaling on Th17 and T_reg cell biology, we specifically deleted S1P₁ in Th17 and T_reg cells using IL-17A^Cre and Foxp3^Cre mice, respectively. Deletion of S1P₁ in Th17 cells conferred resistance to experimental autoimmune encephalomyelitis (EAE). On the other hand, permanent deletion of S1P₁ in T_reg cells resulted in autoimmunity and acute deletion rendered mice more susceptible to EAE. Importantly, our study revealed that S1P₁ not only regulated the egress of T_reg cells out of lymphoid organs and subsequent non-lymphoid tissue distribution but also their phenotypic diversity. Most of the T_reg cells found in S1P₁-deficient mice as well as MS patients on fingolimod therapy had an activated phenotype and were more prone to apoptosis, thus converted to effector T_reg. Our results provide novel insight into the functions of S1P₁ and potential impact of long term fingolimod use on Th17 and T_reg cell biology and general health in MS patients.

S1P1 deletion differentially affects TH17 and Regulatory T cells

Sphingosine-1 phosphate receptor 1 (S1P1) is a G-protein coupled receptor critical for the egress of T and B cells out of lymphoid organs. Although S1P1 agonists (such as fingolimod) are currently used for the treatment of multiple sclerosis (MS) little is known how S1P1 signaling regulates Th17 and Treg cell homeostasis. To study the impact of S1P1 signaling on Th17 and Treg biology, we specifically deleted S1P1 in Th17 and Treg cells using IL-17ACre and Foxp3Cremice, respectively. Deletion of S1P1 in Th17 cells conferred resistance to experimental autoimmune encephalomyelitis (EAE) characterized by reduced Th17 cell distribution across peripheral organs and diminished Th17 cell generation. On the other hand, permanent deletion of S1P1 in Treg cells resulted in autoimmunity and acute deletion rendered mice more susceptible to EAE. Importantly, our study revealed that S1P1 not only regulated the egress of Treg cells out of lymphoid organs and subsequent non-lymphoid tissue distribution but also their phenotypic diversity. Most of the Treg cells found in S1P1-deficient mice had an activated phenotype and were more prone to apoptosis, thus converted to effector Treg. The comparison of Treg cells obtained from MS patients treated with fingolimod to those treated with other oral drugs confirmed the switch of Treg cells into effector memory phenotype. Our results provide novel insight into the functions of S1P1 and potential impact of long term fingolimod use on Th17 and Treg cell biology and general health in MS patients.

IL-7/IL-7 Receptor Signaling Differentially Affects Effector CD4+ T Cell Subsets Involved in Experimental Autoimmune Encephalomyelitis

IL-17-producing CD4(+) T (Th17) cells, along with IFN-γ-expressing Th1 cells, represent two major pathogenic T cell subsets in experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis (MS). The cytokines and transcription factors involved in the development and effector functions of Th1 and Th17 cells have been largely characterized. Among them, IL-23 is essential for the generation of stable and encephalitogenic Th17 cells and for the development of EAE. The IL-7/IL-7R signaling axis participates in cell survival, and perturbation of this pathway has been associated with enhanced susceptibility to MS. A link between IL-23-driven pathogenic T cells and IL-7/IL-7R signaling has previously been proposed, but has not been formally addressed. In the current study, we showed that Th17 cells from mice with EAE express high levels of IL-7Rα compared with Th1 cells. Using mice that constitutively express IL-7Rα on T cells, we determined that sustained IL-7R expression in IL-23R-deficient mice could not drive pathogenic T cells and the development of EAE. IL-7 inhibited the differentiation of Th17 cells, but promoted IFN-γ and GM-CSF secretion in vitro. In vivo IL-7/anti-IL-7 mAb complexes selectively expanded and enhanced the proliferation of CXCR3-expressing Th1 cells, but did not impact Th17 cells and EAE development in wild-type and IL-23R-deficient mice. Importantly, high IL-7 expression was detected in the CNS during EAE and could drive the plasticity of Th17 cells to IFN-γ-producing T cells. Together, these data address the contribution of IL-23/IL-23R and IL-7/IL-7R signaling in Th17 and Th1 cell dynamics during CNS autoimmunity.

Integrin alpha L controls the homing of regulatory T cells during CNS autoimmunity in the absence of integrin alpha 4

Experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis (MS), results from an autoimmune attack of the central nervous system (CNS) by effector T helper (Th) 1 and Th17 cells. Regulatory T cells (Treg) can control effector T cells and limit the progression of CNS autoimmunity. Integrin alpha 4 (Itga4) is critical for the entry of Th1 but not Th17 cells into the CNS during EAE. Whether Itga4 controls the homing of Tregs in the CNS and whether Tregs can limit Th17-mediated EAE has, however, not been addressed. Through selective elimination of Itga4 in Foxp3-expressing cells, we show here that Tregs can suppress Th17-mediated EAE and enter into the CNS independently of Itga4. Furthermore, similarly to Th17 cells and in contrast to Th1 cells, Tregs depend on LFA-1 for their entry into the CNS in the absence of Itga4. Therefore, these data suggest that the efficacy of Itga4 neutralization on MS progression may be associated with the prevention of Th1 cells and the maintenance of Tregs migration into the CNS.

Integrin alpha 4 differentially affect the migration of effector and regulatory T cells (P4113)

The integrin alpha 4 (Itga4) is expressed on immune cells and is an important molecule for the migration of T cells in various organs. Because of this propriety, a monoclonal antibody specific to Itga4 is used for the treatment of multiple sclerosis (MS). Although effective, anti-Itga4 therapy has been associated with the development of progressive multifocal leukoencephalopathy (PML), a life threatening condition, which results from a rare infection of the central nervous system (CNS) by the JC virus. Despite its use and efficacy in the clinic, it remains unclear how different cells of the adaptive immune system are affected by Itga4 deletion or neutralization. Experimental autoimmune encephalomyelitis (EAE) serves as an animal model of multiple sclerosis (MS). It results from an autoimmune attack by myelin reactive effector T helper (Th) 1 and Th17 cells and progressive demyelination. Foxp3+ regulatory T cells can control effector T cell responses but are not always effective during autoimmune disease progression. Using mice with selective deletion of Itga4 in T cells, we previously reported that Itga4 selectively inhibits the migration of Th 1 cells but not Th17 cells in the CNS. We have now established that Itga4 differentially affect the migration of effector and regulatory T cells during EAE. The implication of our findings for MS therapy will be discussed.

Pathogenicity of IFN-γ+ Th17 cells is independent of T-bet (P4128)

It is now established that T helper (Th) cell subsets, particularly Th17 cells, are more dynamic than originally anticipated and can acquire the expression of other lineage effector cytokines. However, the molecular cues that dictate their plasticity are unknown. We show that IL-23 plays a central role in the plasticity of Th17 cells and is essential for the generation and propagation of IFN-γ-producing Th17 (IL-17+ IFN-γ+) cells. During the development of experimental autoimmune encephalomyelitis (EAE) IL-17+ IFN-γ+ T cells are preferentially expanded in the central nervous system (CNS). Using an IL-17A-IFN-γ double reporter mouse and I-Ab/MOG38-49 tetramer, we determined that they displayed characteristics of pathogenic T cells, such as GM-CSF expression, and contained the highest number of MOG-specific T cells. Interestingly, the Th1-associated transcription factors T-bet, STAT1 and STAT4 were not involved in the induction of IFN-γ by Th17 cells in vitro. Moreover, in contrast to previous studies showing a role for T-bet in Th1 and Th17-mediated EAE, we demonstrate that T-bet expression in T cells is not required for the emergence of CNS-infiltrating IL-17+ IFN-γ+ T cells and the development of Th17-driven EAE. Our results suggest the existence of different epigenetic programs that regulate IFN-γ expression in Th1 and Th17 cells.

Cutting edge: the pathogenicity of IFN-γ-producing Th17 cells is independent of T-bet

During the development of experimental autoimmune encephalomyelitis (EAE), the proportion of pathogenic and myelin-specific cells within CNS-infiltrating cytokine-producing Th cells is unknown. Using an IL-17A/IFN-γ double reporter mouse and I-A(b)/myelin oligodendrocyte glycoprotein 38-49 tetramer, we show in this study that IL-17(+)IFN-γ(+) Th cells, which are expanded in the CNS during EAE, are highly enriched in myelin oligodendrocyte glycoprotein-specific T cells. We further demonstrate that IL-23 is essential for the generation and expansion of IFN-γ-producing Th17 cells independently of the Th1-associated transcription factors T-bet, STAT1, and STAT4. Furthermore, Th17 and IL-17(+)IFN-γ(+) Th cells can induce CNS autoimmunity independently of T-bet. Whereas T-bet is crucial for Th1-mediated EAE, it is dispensable for Th17 cell-mediated autoimmunity. Our results suggest the existence of different epigenetic programs that regulate IFN-γ expression in Th1 and Th17 cells.

Cutting edge: loss of α4 integrin expression differentially affects the homing of Th1 and Th17 cells

The neutralization of α4 integrin is currently used as treatment in several autoimmune diseases and is thought to prevent the entry of most immune cells in target tissues. In this study, we showed that selective deletion of α4 integrin in T cells did not prevent but delayed the development of experimental autoimmune encephalomyelitis. Whereas both Th1 and Th17 cells infiltrate the CNS of wild-type mice, T cells present in the CNS of mice lacking α4 integrin were mainly enriched in Th17 cells, suggesting that this T cell subset uses other integrins to access the CNS. In contrast, α4 integrin expression is important for Th1 cells to enter the CNS and for the stability of their Th1-associated genetic program. Therefore, our data suggest that anti-α4 integrin Ab treatment may be more efficient in the treatment of Th1- rather than Th17-mediated disease.