Immunoglobulin-like transcript 2 blockade restores antitumor immune responses in glioblastoma.

Glioblastoma stands as the most frequent primary brain tumor. Despite the multimodal therapy for glioblastoma patients, the survival rate is very low, highlighting the need for novel therapies that improve patient outcomes. Immune checkpoint blockade strategies are achieving promising results in a myriad of tumors and several studies have reported its efficacy in glioblastoma at a preclinical level. ILT2 is a novel immune checkpoint that exerts an inhibitory effect via the interaction with classical and non-classical HLA class-I molecules. Herein, we report that ILT2 blockade promotes antitumor responses against glioblastoma. In silico and immunohistochemical analyses revealed that the expression of ILT2 and its ligands HLA-A, -B, -C, and -E are highly expressed in patients with glioblastoma. Disruption of ILT2 with blocking monoclonal antibodies increased natural killer cell-mediated IFN-γ production and cytotoxicity against glioblastoma, partially reverting the immunosuppression linked to this malignancy. In addition, co-treatment with temozolomide strengthened the antitumor capacity of anti-ILT2-treated immune cells. Collectively, our results establish the basis for future studies regarding the clinical potential of ILT2 blockade alone or in combination regimens in glioblastoma.

HLA-G-ILT2 interaction contributes to suppression of bone marrow B cell proliferation in acquired aplastic anemia.

Acquired aplastic anemia (AA) is an autoimmune disease characterized by hematopoietic stem and progenitor cell destruction in bone marrow. The non-classic human leukocyte class I antigen (HLA-) G interacts with multiple cell subsets, such as T cells and B cells. HLA-G exerts powerful immune suppression by binding with its receptors, immunoglobulin-like transcripts (ILTs). Here, we compared 46 AA patients and 28 healthy controls. Soluble HLA-G levels in bone marrow supernatants from AA patients were higher than controls. The proportion of bone marrow B cells was decreased and the ILT2-expressing cells among CD19+ cells were increased in AA patients. In addition, the percentage of mature B cells among marrow B cells was increased in AA patient, while the percentage of pro-B plus pre-B cells was decreased. More immature B cells and pro-B plus pre-B cells expressed ILT2 in AA patients than in controls, while mature B cells expressing ILT2 did not differ significantly. Functional studies demonstrated that high-level soluble HLA-G inhibited bone marrow B cell proliferation by interacting with ILT2 in AA, and was blocked by anti-HLA-G and anti-ILT2 monoclonal antibodies. Together, these results suggest that the abnormal decrease of pro-B plus pre-B cells in AA patients was related to the enhanced suppression by the excess HLA-G and ILT2 proteins. Therapeutic blockade of the HLA-G-ILT2 interaction may help to normalize bone marrow B cell proliferation.

Markers of systemic inflammation are positively associated with influenza vaccine antibody responses with a possible role for ILT2(+)CD57(+) NK-cells.

BACKGROUND: With increasing age, overall health declines while systemic levels of inflammatory mediators tend to increase. Although the underlying mechanisms are poorly understood, there is a wealth of data suggesting that this so-called "inflammaging" contributes to the risk of adverse outcomes in older adults. We sought to determine whether markers of systemic inflammation were associated with antibody responses to the seasonal influenza vaccine. RESULTS: Over four seasons, hemagglutination inhibition antibody titres and ex vivo bulk peripheral blood mononuclear cell (PBMC) responses to live influenza viruses assessed via interferon (IFN)-γ/interleukin (IL)-10 production, were measured pre- and 4-weeks post-vaccination in young adults (n = 79) and older adults randomized to standard- or high-dose inactivated vaccine (n = 612). Circulating tumour necrosis factor (TNF), interleukin (IL)-6 and C-reactive protein (CRP) were also measured pre-vaccination. Post-vaccination antibody titres were significantly associated with systemic inflammatory levels; specifically, IL-6 was positively associated with A/H3N2 titres in young adults (Cohen's d = 0.36), and in older high-dose, but not standard-dose recipients, all systemic inflammatory mediators were positively associated with A/H1N1, A/H3N2 and B titres (d = 0.10-0.45). We further show that the frequency of ILT2(+)CD57(+) CD56-Dim natural killer (NK)-cells was positively associated with both plasma IL-6 and post-vaccination A/H3N2 titres in a follow-up cohort of older high-dose recipients (n = 63). Pathway analysis suggested that ILT2(+)CD57(+) Dim NK-cells mediated 40% of the association between IL-6 and A/H3N2 titres, which may be related to underlying participant frailty. CONCLUSIONS: In summary, our data suggest a complex relationship amongst influenza vaccine responses, systemic inflammation and NK-cell phenotype in older adults, which depends heavily on age, vaccine dose and possibly overall health status. While our results suggest that "inflammaging" may increase vaccine immunogenicity in older adults, it is yet to be determined whether this enhancement contributes to improved protection against influenza disease.

Human Leukocyte Antigen-G Inhibits the Anti-Tumor Effect of Natural Killer Cells via Immunoglobulin-Like Transcript 2 in Gastric Cancer.

BACKGROUND/AIMS: Human leukocyte antigen-G (HLA-G) plays an important role in inhibiting natural killer (NK) cell function and promoting immune escape. However, the specific mechanism of HLA-G on NK in gastric cancer (GC) remains not well understood. This study investigated the expression of HLA-G in GC and the role of HLA-G-effected NK cells in GC progression. METHODS: HLA-G expression in GC tissues obtained from 49 patients with GC was analyzed by immunohistochemistry and western blot. The number of tumor-infiltrating NK cells and the expression of their surface receptors were analyzed by immunohistochemistry and flow cytometry, respectively. The effect of HLA-G on NK cell proliferation was examined by Cell Counting Kit-8 (CCK8) assay. LDH release assay was used to evaluate the effect of HLA-G on the cytotoxic activity of NK cells, and the levels of IFN-γ and TNF-α in the co-cultured supernatant were detected by ELISA. Mice bearing a xenograft tumor model were used to examine the effect of HLA-G on the anti-tumor effect of NK cells. RESULTS: HLA-G positive expression was detected in most of the GC tissues, and was correlated with the adverse prognosis of the disease. The expression of HLA-G was negatively associated with the number of tumor-infiltrating NK cells. Furthermore, GC cell lines with overexpressed HLA-G revealed their ability to inhibit the cell proliferation and cytotoxic activity of NK-92MI cells, and reduce the secretion of IFN-γ and TNF-α through immunoglobulin-like transcript 2 (ILT2). Finally, this in vivo experiment was able to prove that HLA-G can inhibit the anti-tumor effect of NK cells through ILT2. CONCLUSION: The expression of HLA-G was strongly correlated with the adverse prognosis of GC. The reason may be that it inhibits the proliferation and cytotoxic activity of infiltrating NK cells through ILT2.

Immunoglobulin-like transcript 2 as an impaired anti-tumor cytotoxicity marker of natural killer cells in patients with hepatocellular carcinoma.

Introduction: Natural killer (NK) cells play a pivotal role in immune surveillance in the liver. We aimed to identify potential targets for NK cell-mediated immune intervention by revealing the functional molecules on NK cells in HCC patients. Methods: To evaluate the impact of aging on NK cell phenotypes, we examined NK cells from healthy volunteers (HVs) of various ages. Because ILT2 expression on CD56dim NK cells increased with increasing age, we enrolled age-matched HCC patients and HVs. We determined the NK cell phenotypes in blood mononuclear cells (PBMCs) and intrahepatic lymphocytes (IHLs) from cancerous and non-cancerous tissues. We evaluated cytotoxicity and antibody-dependent cellular cytotoxicity (ADCC) of NK cells in vitro. Results: ILT2-positive CD56dim NK cells in PBMCs were increased in HCC patients compared with HVs. In HCC patients, ILT2-positive CD56dim NK cells were increased in cancerous IHLs compared with non-cancerous IHLs and PBMCs. We examined the impact of macrophage migration inhibitory factor (MIF) on ILT2 expression in co-cultures of HCC cells and NK cells. The enhanced expression of ILT2 on CD56dim NK cells from HCC patients was inhibited by masking antibodies against MIF and CXCR4. ILT2-positive CD56dim NK cells exhibited lower capacities for cytotoxicity and ADCC than ILT2-negative cells, which were partially restored by ILT2 blockade. Conclusions: In HCC patients, ILT2 is a signature molecule for cancerous CD56dim NK cells with impaired cytolytic capacity. The MIF-CXCR4 interaction is associated with ILT2 induction on CD56dim NK cells and ILT2 serves as a target for functional NK cell restoration.

Increased ILT2+ natural killer T cells correlate with disease activity in systemic lupus erythematosus.

OBJECTIVE: Numerous immune cell types, such as B and T lymphocytes, natural killer cells (NK), and NKT cells, are related to the pathogenesis of diseases in systemic lupus erythematosus (SLE). Our goal in this investigation is to examine the phenotype of NK cells and NKT cells alterations in individuals with SLE. METHODS: Typically, 50 SLE patients and 24 age-matched healthy people had their PBMCs obtained. Employing flow cytometry, the phenotype of NK and NKT cells and immunoglobulin-like transcript 2 (ILT2) expressions were identified. ELISA was utilized to evaluate the amounts of interleukin-15 (IL-15) and sHLA-G in the serum. RESULTS: The frequencies of the circulating NK and NKT cells in individuals with SLE were decreased compared to healthy controls. Furthermore, ILT2 expression was significantly increased in NKT cells, but showed no obvious change in NK cells. Clinical severity and active nephritis were substantially associated with ILT2+ NKT cell frequencies. The correlation study showed that the upregulation of ILT2 expression was related to sHLA-G in plasma but not to IL-15. CONCLUSIONS: ILT2+ NKT cells have a vital function in the immune abnormalities of SLE, which can also supply a viable goal for therapeutic intervention. Key Points •ILT2 expression was significantly increased in NKT cells in SLE patients. •ILT2+ NKT cell frequencies were associated with clinical severity which may be used as an indicator for evaluating disease activity in patients with SLE.

Evidence for Epistatic Interaction between HLA-G and LILRB1 in the Pathogenesis of Nonsegmental Vitiligo.

Vitiligo is the most frequent cause of depigmentation worldwide. Genetic association studies have discovered about 50 loci associated with disease, many with immunological functions. Among them is HLA-G, which modulates immunity by interacting with specific inhibitory receptors, mainly LILRB1 and LILRB2. Here we investigated the LILRB1 and LILRB2 association with vitiligo risk and evaluated the possible role of interactions between HLA-G and its receptors in this pathogenesis. We tested the association of the polymorphisms of HLA-G, LILRB1, and LILRB2 with vitiligo using logistic regression along with adjustment by ancestry. Further, methods based on the multifactor dimensionality reduction (MDR) approach (MDR v.3.0.2, GMDR v.0.9, and MB-MDR) were used to detect potential epistatic interactions between polymorphisms from the three genes. An interaction involving rs9380142 and rs2114511 polymorphisms was identified by all methods used. The polymorphism rs9380142 is an HLA-G 3'UTR variant (+3187) with a well-established role in mRNA stability. The polymorphism rs2114511 is located in the exonic region of LILRB1. Although no association involving this SNP has been reported, ChIP-Seq experiments have identified this position as an EBF1 binding site. These results highlight the role of an epistatic interaction between HLA-G and LILRB1 in vitiligo pathogenesis.

Peripheral HLA-G/ILT-2 immune checkpoint axis in acute and convalescent COVID-19 patients.

The immunosuppressive non-classical human leukocyte antigen-G (HLA-G) can elicits pro-viral activities by down-modulating immune responses. We analysed soluble forms of HLA-G, IL-6 and IL-10 as well as on immune effector cell expression of HLA-G and its cognate ILT-2 receptor in peripheral blood obtained from hospitalised and convalescent COVID-19 patients. Compared with convalescents (N = 202), circulating soluble HLA-G levels (total and vesicular-bound molecules) were significantly increased in hospitalised patients (N = 93) irrespective of the disease severity. During COVID-19, IL-6 and IL-10 levels were also elevated. Regarding the immune checkpoint expression of HLA-G/ILT-2 on peripheral immune effector cells, the frequencies of membrane-bound HLA-G on CD3+ and CD14+ cells were almost identical in patients during and post COVID-19, while the frequency of ILT-2 receptor on CD3+ and CD14+ cells was increased during acute infection. A multi-parametric correlation analysis of soluble HLA-G forms with IL-6, IL-10, activation markers CD25 and CD154, HLA-G, and ILT-2 expression on immune cells revealed a strong positive correlation of soluble HLA-G forms with membrane-bound HLA-G molecules on CD3+/CD14+ cells only in convalescents. During COVID-19, only vesicular-bound HLA-G were positively correlated with the activation marker CD25 on T cells. Thus, our data suggest that the elevated levels of soluble HLA-G in COVID-19 are due to increased expression in organ tissues other than circulating immune effector cells. The concomitant increased expression of soluble HLA-G and ILT-2 receptor frequencies supports the concept that the immune checkpoint HLA-G/ILT-2 plays a role in the immune-pathogenesis of COVID-19.

Perspectives of targeting LILRB1 in innate and adaptive immune checkpoint therapy of cancer.

Immune checkpoint blockade is a compelling approach in tumor immunotherapy. Blocking inhibitory pathways in T cells has demonstrated clinical efficacy in different types of cancer and may hold potential to also stimulate innate immune responses. A novel emerging potential target for immune checkpoint therapy is leukocyte immunoglobulin-like receptor subfamily B member 1 (LILRB1). LILRB1 belongs to the superfamily of leukocyte immunoglobulin-like receptors and exerts inhibitory functions. The receptor is expressed by a variety of immune cells including macrophages as well as certain cytotoxic lymphocytes and contributes to the regulation of different immune responses by interaction with classical as well as non-classical human leukocyte antigen (HLA) class I molecules. LILRB1 has gained increasing attention as it has been demonstrated to function as a phagocytosis checkpoint on macrophages by recognizing HLA class I, which represents a 'Don't Eat Me!' signal that impairs phagocytic uptake of cancer cells, similar to CD47. The specific blockade of the HLA class I:LILRB1 axis may provide an option to promote phagocytosis by macrophages and also to enhance cytotoxic functions of T cells and natural killer (NK) cells. Currently, LILRB1 specific antibodies are in different stages of pre-clinical and clinical development. In this review, we introduce LILRB1 and highlight the features that make this immune checkpoint a promising target for cancer immunotherapy.

Elevated sHLA-G plasma levels post chemotherapy combined with ILT-2 rs10416697C allele status of the sHLA-G-related receptor predict poorest disease outcome in early triple-negative breast cancer patients.

Introduction: Triple negative breast cancer (TNBC) shows an aggressive growing and spreading behavior and has limited treatment options, often leading to inferior disease outcome. Therefore, surrogate markers are urgently needed to identify patients at high risk of recurrence and more importantly, to identify additional therapeutic targets enabling further treatment options. Based on the key role of the non-classical human leukocyte antigen G (HLA-G) and its related receptor immunoglobulin-like transcript receptor-2 (ILT-2) in immune evasion mechanisms of tumors, members of this ligand-receptor axis appear to be promising tool for both, defining risk groups and potential therapeutic targets. Materials and methods: To follow this, sHLA-G levels before and after chemotherapy (CT), HLA-G 3' UTR haplotypes, and allele variations rs10416697 at the distal gene promoter region of ILT-2 were defined in healthy female controls and early TNBC patients. The results obtained were associated with clinical status, presence of circulating tumor cell (CTC) subtypes, and disease outcome of patients in terms of progression-free or overall survival. Results: sHLA-G plasma levels were increased in TNBC patients post-CT compared to levels of patients pre-CT or controls. High post-CT sHLA-G levels were associated with the development of distant metastases, the presence of ERCC1 or PIK3CA-CTC subtypes post-CT, and poorer disease outcome in uni- or multivariate analysis. HLA-G 3' UTR genotypes did not influence disease outcome but ILT-2 rs10416697C allele was associated with AURKA-positive CTC and with adverse disease outcome by uni- and multivariate analysis. The prognostic value of the combined risk factors (high sHLA-G levels post-CT and ILT-2 rs10416697C allele carrier status) was an even better independent indicator for disease outcome in TNBC than the lymph nodal status pre-CT. This combination allowed the identification of patients with high risk of early progression/death with positive nodal status pre-CT or with non-pathological complete therapy response. Conclusion: The results of this study highlight for the first time that the combination of high levels of sHLA-G post-CT with ILT-2 rs10416697C allele receptor status is a promising tool for the risk assessment of TNBC patients and support the concept to use HLA-G/ILT-2 ligand-receptor axis as therapeutic targets.

HLA-G: Too Much or Too Little? Role in Cancer and Autoimmune Disease.

HLA-G is a non-classical HLA class I molecule with immunomodulatory properties. It was initially described at the maternal-fetal interface, and it was later found that this molecule was constitutively expressed on certain immuneprivileged tissues, such as cornea, endothelial and erythroid precursors, and thymus. The immunosuppressive effect of HLA-G is exerted through the interaction with its cognate receptors, expressed on immunocompetent cells, like ILT2, expressed on NK, B, T cells and APCs; ILT4, on APCs; KIR, found on the surface of NK cells; and finally, the co-receptor CD8. Because of these immunomodulatory functions, HLA-G has been involved in several processes, amongst which organ transplantation, viral infections, cancer progression, and autoimmunity. HLA-G neo-expression on tumors has been recently described in several types of malignancies. In fact, tumor progression is tightly linked to the presence of the molecule, as it exerts its tolerogenic function, inhibiting the cells of the immune system and favoring tumor escape. Several polymorphisms in the 3'UTR region condition changes in HLA-G expression (14bp and +3142C/G, among others), which have been associated with both the development and outcome of patients with different tumor types. Also, in recent years, several studies have shown that HLA-G plays an important role in the control of autoimmune diseases. The ability of HLA-G to limit the progression of these diseases has been confirmed and, in fact, levels of the molecule and several of its polymorphisms have been associated with increased susceptibility to the development of autoimmune diseases, as well as increased disease severity. Thus, modulating HLA-G expression in target tissues of oncology patients or patients with autoimmune diseases may be potential therapeutic approaches to treat these pathological conditions.

Increased ILT2 expression contributes to dysfunction of CD56dimCD16+NK cells in chronic hepatitis B virus infection.

Natural killer (NK) cells play a crucial role in the control of human viral infections but their activity is significantly impaired in patients infected with chronic hepatitis B (CHB). The mechanism that contributes to NK cell dysfunction in CHB needs further elucidation. In this study, we analyzed the expression and function of the novel inhibitory receptor immunoglobulin-like transcript-2 (ILT2) on NK cells from 131 CHB patients and 36 healthy controls. We observed that ILT2 expression on circulating CD56dimCD16+NK cells was increased in immune-tolerant, immune-active and HBeAg-negative hepatitis patients compared with inactive carriers and controls. The frequency of ILT2+CD56dimNK cells was positively correlated with serum viral load in immune-tolerant patients. The percentage of ILT2+CD56dimNK cells decreased along with HBV load in CHB patients who received antiviral therapy. Functional analysis showed that ILT2+CD56dimNK cells in CHB patients had significantly reduced degranulation and IFN-γ production. Upregulation of ILT2 was associated with high levels of apoptosis in CD56dimCD16+NK cells from CHB patients. ILT2 blockade was shown to increase the cytotoxicity and IFN-γ production of CD56dimNK cells in some CHB patients. Finally, ILT2 was found to be moderately upregulated by TGF-ß1, which was increased in immune-tolerant, immune-active and HBeAg-negative hepatitis patients. Our results show that chronic HBV infection increases the levels of the inhibitory receptor ILT2 on CD56dimNK cells and inhibits their functions, providing a new mechanism of NK-cell disability in CHB patients.

Chronic lung allograft dysfunction is associated with an early increase of circulating cytotoxic CD4+CD57+ILT2+ T cells, selectively inhibited by the immune check-point HLA-G.

BACKGROUND: Survival after lung transplantation (LTx) still remains limited by chronic lung allograft dysfunction (CLAD), thought to represent a form of chronic rejection. We investigated whether the immune checkpoint HLA-G/ILT2 expressed by peripheral T-cell subpopulations could predict CLAD. METHODS: We used data for 150 LTx recipients from COLT (Cohort-For-Lung-Transplantation) cohort with ≥1 available blood sample at 1-, 6-, or 12-months post-Tx. Analysis of T cells by flow cytometry focused on the ILT2 receptor of HLA-G and other markers (CD57, CD25, CD127). T-cell subset analyses compared stable patients and those with CLAD at 3 years post-LTx. RESULTS: With data for 78 stable and 72 CLAD patients, among 21 T-cell subsets expressing ILT2, only CD4+CD57+ILT2+ T cells were associated with outcome. At 1-month post-Tx, low proportion of CD4+CD57+ILT2+ T cells was associated with reduced 3-year incidence of CLAD (CD4+CD57+ILT2+ T cells ≤ first IQR [25%] vs > first IQR, log-rank test, p = 0.028). Furthermore, the incidence of CLAD was higher with >2.6- vs ≤2.6-fold increased proportion of CD4+CD57+ILT2+ T cells over the first year post-LTx (3-year freedom frequencies: 27% [95%CI: 8-50] vs 64% [95%CI: 48-77] (log-rank test, p = 0.014). On multivariable analysis, increased proportion of CD4+CD57+ILT2+ T cells over the first year predicted CLAD (hazard ratio 1.25; 95%CI: 1.09-1.44; p = 0.001). Focusing on CD4+CD57+ILT2+ T cells, we demonstrated ex vivo that they are cytotoxic CD4+ T cells, selectively inhibited by HLA-G. CONCLUSIONS: Our data suggest that an early increase of CD4+CD57+ILT2+ T cells after LTx may be associated with CLAD onset.

Prognostic significance of the immune checkpoint HLA-G/ILT-4 in the survival of patients with gastric cancer.

OBJECTIVE: Human leukocyte antigen-G (HLA-G) and its receptors, including immunoglobulin-like transcripts (ILT)-2 and ILT-4, are closely associated with cancer development and clinical outcomes of patients. However, the clinical significance of HLA-G and ILT-2/-4 in gastric cancer (GC) is limited. METHODS: In this study, the percentage of HLA-G-, ILT-2 and ILT-4 positive tumor cells in 127 GC lesion suspensions of tumor cells gated for epithelialcelladhesionmolecule(EpCAM) was determined using multicolor flow cytometry and their clinical significance was evaluated. RESULTS: Our data showed that the median percentages of HLA-G-, ILT-2, and ILT-4 expressing GC cells were 18.0%, 67.80%, and 1.42%, respectively, and co-expression of HLA-G/ILT-2, HLA-G/ILT-4, and ILT-2/ILT-4 was 16.9%, 1.42%, and 1.70%, respectively. Kaplan-Meier survival results revealed that besides post-operation N status (p = 0.006), M status (p = 0.001), and AJCC clinical stage (p < 0.001), only high percentage of ILT-4+ GC cells was a significant factor for worse survival of patients with GC (overall survival [OS]: 42.9 months vs. 84.5 months; p = 0.031). However, among female patients with GC (n = 31), high percentage of either HLA-G+ (OS: 18.5 months vs. 89.3 months; p = 0.001) or ILT-4+ (OS: 17.9 months vs. 85.8 months; p = 0.002) GC cells was markedly associated with a poor prognosis. CONCLUSION: Our findings revealed that among HLA-G, ILT-2, and ILT-4, only a high percentage of ILT-4+ GC cells was significantly related to poor prognosis in the entire cohort of patients with GC. However, high percentage of HLA-G+ and ILT-4+ GC cells is associated with poor clinical outcome among female patients with GC.

Dual checkpoint blockade of CD47 and LILRB1 enhances CD20 antibody-dependent phagocytosis of lymphoma cells by macrophages.

Antibody-dependent cellular phagocytosis (ADCP) by macrophages, an important effector function of tumor targeting antibodies, is hampered by 'Don´t Eat Me!' signals such as CD47 expressed by cancer cells. Yet, human leukocyte antigen (HLA) class I expression may also impair ADCP by engaging leukocyte immunoglobulin-like receptor subfamily B (LILRB) member 1 (LILRB1) or LILRB2. Analysis of different lymphoma cell lines revealed that the ratio of CD20 to HLA class I cell surface molecules determined the sensitivity to ADCP by the combination of rituximab and an Fc-silent variant of the CD47 antibody magrolimab (CD47-IgGσ). To boost ADCP, Fc-silent antibodies against LILRB1 and LILRB2 were generated (LILRB1-IgGσ and LILRB2-IgGσ, respectively). While LILRB2-IgGσ was not effective, LILRB1-IgGσ significantly enhanced ADCP of lymphoma cell lines when combined with both rituximab and CD47-IgGσ. LILRB1-IgGσ promoted serial engulfment of lymphoma cells and potentiated ADCP by non-polarized M0 as well as polarized M1 and M2 macrophages, but required CD47 co-blockade and the presence of the CD20 antibody. Importantly, complementing rituximab and CD47-IgGσ, LILRB1-IgGσ increased ADCP of chronic lymphocytic leukemia (CLL) or lymphoma cells isolated from patients. Thus, dual checkpoint blockade of CD47 and LILRB1 may be promising to improve antibody therapy of CLL and lymphomas through enhancing ADCP by macrophages.

Tumor infiltrating and peripheral CD4+ILT2+ T cells are a cytotoxic subset selectively inhibited by HLA-G in clear cell renal cell carcinoma patients.

HLA-G: ILT2 has recently been positioned as a major immune checkpoint in urologic cancers. In clear cell renal cell carcinoma (ccRCC), tumor-infiltrating CD8+ T cells expressing ILT2 are a highly cytotoxic cell population, distinct from PD1+ T cells, and whose function is inhibited by HLA-G+ targets. Here we report that ILT2 receptor can also be expressed by CD4+ T cells in urologic cancer patients. In the course of deciphering the role of these ILT2+CD4+ T cells, we found a statistical association between the tumor context and these T cells, and a positive correlation between the levels of peripheral and intra-tumoral CD4+ILT2+ T cells. Phenotypic analyses revealed that CD4+ILT2+ T cells express memory T cell (CD27-CD28-CD57+) and cytotoxicity (Tbet+Perforin+KLRG1+NKp80+GPR56+) markers, consistent with a CD4+CTL phenotype. Functional assays showed that ccRCC-infiltrating CD4+ILT2+ T cells indeed have high cytolytic properties and therefore function as proper CD4+CTLs, but are selectively inhibited by HLA-G+ targets. Clinical relevance was provided by immunohistochemical analyses on ccRCC tumor lesions with HLA-G+ HLA class II+ tumor cells next to CD4+ T cell infiltrates. Our findings provide evidence supporting that ILT2+ T cells constitute a reservoir of intratumor cytotoxic T cells that is not targeted by the current checkpoint inhibitors, but could be by anti-HLA-G/anti-ILT2 antibodies as novel immunotherapy in HLA-G+ tumors.

Prognostic Significance of Immune Checkpoints HLA-G/ILT-2/4 and PD-L1 in Colorectal Cancer.

Immune checkpoint inhibitors (ICIs) have become a promising area of research for cancer treatment. In addition to the well-known ICIs targeting PD-1/PD-L1, HLA-G/ILT-2/-4 is relatively new immune checkpoint that has been evaluated in early clinical trials in patients with advanced solid tumors. In this study, the expression of HLA-G (n=157), ILT-2/4 (n=82), and PD-L1 (n=70) in epithelial cell adhesion molecule (EpCAM)-positive colorectal cancer (CRC) cells was analyzed by multicolor flow cytometry, and the prognostic significance of these molecules was evaluated. In EpCAM+ CRC cells, the median percentages of HLA-G, ILT-2, ILT-4, and PD-L1 were 14.90%, 67.70%, 8.55% and 80.30%, respectively. In addition, a positive correlation was observed between them (all p<0.001). Higher levels of these immune checkpoint proteins are associated with lymph node metastasis. In addition to the AJCC stage (p=0.001), Kaplan-Meier survival analysis showed that higher levels of HLA-G (p=0.041), ILT-2 (p=0.060), ILT-4 (p<0.001), PD-L1 (p=0.012), HLA-GILT4 (p<0.001) and ILT-2ILT-4 (p<0.001) were significantly associated with shorter survival of CRC patients. When CRC patients were stratified by early and advanced AJCC stages, HLA-G levels were only related to the survival among CRC patients with early disease stage (p=0.024), while ILT-4 levels were significant for both CRC patients with early (p=0.001) and advanced (p=0.020) disease stages. Multivariate cox regression analysis revealed that advanced AJCC stage (HR=2.435; p=0.005) and higher ILT-4 levels (HR=2.198; p=0.063) were independent risk factors for poor outcomes in patients with CRC. In summary, among the immune checkpoints, HLA-G/ILT-2/4 and PD-L1, ILT-4 is the most significant prognostic indicator of CRC. This finding indicated that a combination of immunotherapy strategies, such as ILT-4 blockade, could improve the clinical outcomes in patients with cancer. Moreover, multicolor flow cytometry can be employed as a reliable and efficient, alternative to immunohistochemistry, for evaluating the immune checkpoint proteins expressed in tumor lesions.

Cytometry-based analysis of HLA-G functions according to ILT2 expression.

HLA-G was described as a molecule inhibiting NK and T cells functions through its receptor, ILT2. However, most functional studies of HLA-G were so far performed on heterogeneous immune populations and regardless of ILT2 expression. This may lead to an underestimation of the effect of HLA-G. Thus, considering the immune subpopulations sensitive to HLA-G remained an important issue in the field. Here we present a new cytometry assay to evaluate HLA-G effects on both NK and CD8+ T cell cytotoxic functions. Using flow cytometry allows for the comparison of HLA-G function on multiple subsets and multiple functions in the same time. In particular, we sharpen the analysis by specifically studying the immune subpopulations expressing HLA-G receptor ILT2. We focused our work on: IFN-gamma production and cytotoxicity (CD107a expression) by CD8+ T cells and NK cells expressing or not ILT2. We compared the expression of these markers in presence of target cells, expressing or not HLA-G1, and added a blocking antibody to reverse HLA-G inhibition. This new method allows for the discrimination of cell subsets responding and non-responding to HLA-G1 in one tube. We confirm that HLA-G-specifically inhibits the ILT2+ CD8+ T cell and ILT2+ NK cell subsets but not ILT2-negative ones. By blocking HLA-G/ILT2 interaction using an anti-ILT2 antibody we restored the cytotoxicity level, corroborating the specific inhibition of HLA-G1. We believe that our methodology enables to investigate HLA-G immune functions easily and finely towards other immune cell lineages or expressing other receptors, and might be applied in several pathological contexts, such as cancer and transplantation.

Soluble HLA-G and HLA-G Bearing Extracellular Vesicles Affect ILT-2 Positive and ILT-2 Negative CD8 T Cells Complementary.

Tumor immune escape is associated with both, the expression of immune checkpoint molecules on peripheral immune cells and soluble forms of the human leukocyte antigen-G (HLA-G) in the blood, which are consequently discussed as clinical biomarker for disease status and outcome of cancer patients. HLA-G preferentially interacts with the inhibitory receptor immunoglobulin-like transcript (ILT) receptor-2 in the blood and can be secreted as free soluble molecules (sHLA-G) or via extracellular vesicles (EV). To investigate the contribution of these two forms to the expression of checkpoint molecules in peripheral blood, we primed peripheral blood mononuclear cells with purified soluble sHLA-G1 protein, or EV preparations derived from SUM149 cells transfected with membrane-bound HLA-G1 or control vector prior to anti-CD3/CD28 T cell activation. Our study demonstrated that priming of PBMC with sHLA-G1 protein prior to 48 h activation resulted in enhanced frequencies of ILT-2 expressing CD8+ T cells, and in an upregulation of immune checkpoint molecules CTLA-4, PD-1, TIM-3, and CD95 exclusively on ILT-2 positive CD8+ T cells. In contrast, when PBMC were primed with EV (containing HLA-G1 or not) upregulation of CTLA-4, PD-1, TIM-3, and CD95 occurred exclusively on ILT-2 negative CD8+ T cells. Taken together, our data suggest that priming with sHLA-G forms induces a pronounced immunosuppressive/exhausted phenotype and that priming with sHLA-G1 protein or EV derived from HLA-G1 positive or negative SUM149 cells affects CD8+ T cells complementary by targeting either the ILT-2 positive or negative subpopulation, respectively, after T cell activation.

Inhibition of iNKT Cells by the HLA-G-ILT2 Checkpoint and Poor Stimulation by HLA-G-Expressing Tolerogenic DC.

Invariant Natural Killer T (iNKT) cells are a small and distinct population of T cells crucial in immunomodulation. After activation by alpha-GalactosylCeramide (αGC), an exogenic glycolipid antigen, iNKT cells can rapidly release cytokines to enhance specific anti-tumor activity. Several human clinical trials on iNKT cell-based anti-cancer are ongoing, however results are not as striking as in murine models. Given that iNKT-based immunotherapies are dependent mainly on antigen-presenting cells (APC), a human tolerogenic molecule with no murine homolog, such as Human Leucocyte Antigen G (HLA-G), could contribute to this discrepancy. HLA-G is a well-known immune checkpoint molecule involved in fetal-maternal tolerance and in tumor immune escape. HLA-G exerts its immunomodulatory functions through the interaction with immune inhibitory receptors such as ILT2, differentially expressed on immune cell subsets. We hypothesized that HLA-G might inhibit iNKT function directly or by inducing tolerogenic APC leading to iNKT cell anergy, which could impact the results of current clinical trials. Using an ILT2-transduced murine iNKT cell line and human iNKT cells, we demonstrate that iNKT cells are sensitive to HLA-G, which inhibits their cytokine secretion. Furthermore, human HLA-G+ dendritic cells, called DC-10, failed at inducing iNKT cell activation compared to their autologous HLA-G‒ DCs counterparts. Our data show for the first time that the HLA-G/ILT2 ICP is involved in iNKT cell function modulation.