Immune checkpoint blockade provokes resident memory T cells to eliminate head and neck cancer.

Immune checkpoint blockade is effective in treating many human cancers. In this issue of Cell, Luoma et al. show that tissue-resident memory T cells in head and neck cancers rapidly respond to immune checkpoint blockade, and they identify specific CD8+ T cells in pretreatment blood that predict pathologic tumor regression.

Dual checkpoint T(h1)eamwork makes the anti-cancer dream work.

Combined anti-PD-L1+anti-CTLA-4 therapy has shown benefits over anti-PD-L1 monotherapy as a neoadjuvant treatment in head and neck cancer. In this issue of Immunity, Franken et al. report that CD4+ T cell trafficking from lymph nodes to tumors and expansion toward T helper 1 cells are features specific to combination therapy.

CD4+ T cell activation distinguishes response to anti-PD-L1+anti-CTLA4 therapy from anti-PD-L1 monotherapy.

Cancer patients often receive a combination of antibodies targeting programmed death-ligand 1 (PD-L1) and cytotoxic T lymphocyte antigen-4 (CTLA4). We conducted a window-of-opportunity study in head and neck squamous cell carcinoma (HNSCC) to examine the contribution of anti-CTLA4 to anti-PD-L1 therapy. Single-cell profiling of on- versus pre-treatment biopsies identified T cell expansion as an early response marker. In tumors, anti-PD-L1 triggered the expansion of mostly CD8+ T cells, whereas combination therapy expanded both CD4+ and CD8+ T cells. Such CD4+ T cells exhibited an activated T helper 1 (Th1) phenotype. CD4+ and CD8+ T cells co-localized with and were surrounded by dendritic cells expressing T cell homing factors or antibody-producing plasma cells. T cell receptor tracing suggests that anti-CTLA4, but not anti-PD-L1, triggers the trafficking of CD4+ naive/central-memory T cells from tumor-draining lymph nodes (tdLNs), via blood, to the tumor wherein T cells acquire a Th1 phenotype. Thus, CD4+ T cell activation and recruitment from tdLNs are hallmarks of early response to anti-PD-L1 plus anti-CTLA4 in HNSCC.

Single-Cell Transcriptomic Analysis of Primary and Metastatic Tumor Ecosystems in Head and Neck Cancer.

The diverse malignant, stromal, and immune cells in tumors affect growth, metastasis, and response to therapy. We profiled transcriptomes of ∼6,000 single cells from 18 head and neck squamous cell carcinoma (HNSCC) patients, including five matched pairs of primary tumors and lymph node metastases. Stromal and immune cells had consistent expression programs across patients. Conversely, malignant cells varied within and between tumors in their expression of signatures related to cell cycle, stress, hypoxia, epithelial differentiation, and partial epithelial-to-mesenchymal transition (p-EMT). Cells expressing the p-EMT program spatially localized to the leading edge of primary tumors. By integrating single-cell transcriptomes with bulk expression profiles for hundreds of tumors, we refined HNSCC subtypes by their malignant and stromal composition and established p-EMT as an independent predictor of nodal metastasis, grade, and adverse pathologic features. Our results provide insight into the HNSCC ecosystem and define stromal interactions and a p-EMT program associated with metastasis.

Interferon-γ Drives Treg Fragility to Promote Anti-tumor Immunity.

Regulatory T cells (Tregs) are a barrier to anti-tumor immunity. Neuropilin-1 (Nrp1) is required to maintain intratumoral Treg stability and function but is dispensable for peripheral immune tolerance. Treg-restricted Nrp1 deletion results in profound tumor resistance due to Treg functional fragility. Thus, identifying the basis for Nrp1 dependency and the key drivers of Treg fragility could help to improve immunotherapy for human cancer. We show that a high percentage of intratumoral NRP1+ Tregs correlates with poor prognosis in melanoma and head and neck squamous cell carcinoma. Using a mouse model of melanoma where Nrp1-deficient (Nrp1-/-) and wild-type (Nrp1+/+) Tregs can be assessed in a competitive environment, we find that a high proportion of intratumoral Nrp1-/- Tregs produce interferon-γ (IFNγ), which drives the fragility of surrounding wild-type Tregs, boosts anti-tumor immunity, and facilitates tumor clearance. We also show that IFNγ-induced Treg fragility is required for response to anti-PD1, suggesting that cancer therapies promoting Treg fragility may be efficacious.

Methylation of histone H3 lysine 36 is a barrier for therapeutic interventions of head and neck squamous cell carcinoma.

Approximately 20% of head and neck squamous cell carcinomas (HNSCCs) exhibit reduced methylation on lysine 36 of histone H3 (H3K36me) due to mutations in histone methylase NSD1 or a lysine-to-methionine mutation in histone H3 (H3K36M). Whether such alterations of H3K36me can be exploited for therapeutic interventions is still unknown. Here, we show that HNSCC models expressing H3K36M can be divided into two groups: those that display aberrant accumulation of H3K27me3 and those that maintain steady levels of H3K27me3. The former group exhibits reduced proliferation, genome instability, and heightened sensitivity to genotoxic agents like PARP1/2 inhibitors. Conversely, H3K36M HNSCC models with constant H3K27me3 levels lack these characteristics unless H3K27me3 is elevated by DNA hypomethylating agents or inhibiting H3K27me3 demethylases KDM6A/B. Mechanistically, H3K36M reduces H3K36me by directly impeding the activities of the histone methyltransferase NSD3 and the histone demethylase LSD2. Notably, aberrant H3K27me3 levels induced by H3K36M expression are not a bona fide epigenetic mark because they require continuous expression of H3K36M to be inherited. Moreover, increased sensitivity to PARP1/2 inhibitors in H3K36M HNSCC models depends solely on elevated H3K27me3 levels and diminishing BRCA1- and FANCD2-dependent DNA repair. Finally, a PARP1/2 inhibitor alone reduces tumor burden in a H3K36M HNSCC xenograft model with elevated H3K27me3, whereas in a model with consistent H3K27me3, a combination of PARP1/2 inhibitors and agents that up-regulate H3K27me3 proves to be successful. These findings underscore the crucial balance between H3K36 and H3K27 methylation in maintaining genome instability, offering new therapeutic options for patients with H3K36me-deficient tumors.

RBM33 is a unique m6A RNA-binding protein that regulates ALKBH5 demethylase activity and substrate selectivity.

Regulation of RNA substrate selectivity of m6A demethylase ALKBH5 remains elusive. Here, we identify RNA-binding motif protein 33 (RBM33) as a previously unrecognized m6A-binding protein that plays a critical role in ALKBH5-mediated mRNA m6A demethylation of a subset of mRNA transcripts by forming a complex with ALKBH5. RBM33 recruits ALKBH5 to its m6A-marked substrate and activates ALKBH5 demethylase activity through the removal of its SUMOylation. We further demonstrate that RBM33 is critical for the tumorigenesis of head-neck squamous cell carcinoma (HNSCC). RBM33 promotes autophagy by recruiting ALKBH5 to demethylate and stabilize DDIT4 mRNA, which is responsible for the oncogenic function of RBM33 in HNSCC cells. Altogether, our study uncovers the mechanism of selectively demethylate m6A methylation of a subset of transcripts during tumorigenesis that may explain demethylation selectivity in other cellular processes, and we showed its importance in the maintenance of tumorigenesis of HNSCC.

TGF-ß promotes heterogeneity and drug resistance in squamous cell carcinoma.

Subsets of long-lived, tumor-initiating stem cells often escape cancer therapies. However, sources and mechanisms that generate tumor heterogeneity and drug-resistant cell population are still unfolding. Here, we devise a functional reporter system to lineage trace and/or genetic ablate signaling in TGF-ß-activated squamous cell carcinoma stem cells (SCC-SCs). Dissecting TGF-ß's impact on malignant progression, we demonstrate that TGF-ß concentrating near tumor-vasculature generates heterogeneity in TGF-ß signaling at tumor-stroma interface and bestows slower-cycling properties to neighboring SCC-SCs. While non-responding progenies proliferate faster and accelerate tumor growth, TGF-ß-responding progenies invade, aberrantly differentiate, and affect gene expression. Intriguingly, TGF-ß-responding SCC-SCs show increased protection against anti-cancer drugs, but slower-cycling alone does not confer survival. Rather, TGF-ß transcriptionally activates p21, which stabilizes NRF2, thereby markedly enhancing glutathione metabolism and diminishing effectiveness of anti-cancer therapeutics. Together, these findings establish a surprising non-genetic paradigm for TGF-ß signaling in fueling heterogeneity in SCC-SCs, tumor characteristics, and drug resistance.

Histone methylation antagonism drives tumor immune evasion in squamous cell carcinomas.

How cancer-associated chromatin abnormalities shape tumor-immune interaction remains incompletely understood. Recent studies have linked DNA hypomethylation and de-repression of retrotransposons to anti-tumor immunity through the induction of interferon response. Here, we report that inactivation of the histone H3K36 methyltransferase NSD1, which is frequently found in squamous cell carcinomas (SCCs) and induces DNA hypomethylation, unexpectedly results in diminished tumor immune infiltration. In syngeneic and genetically engineered mouse models of head and neck SCCs, NSD1-deficient tumors exhibit immune exclusion and reduced interferon response despite high retrotransposon expression. Mechanistically, NSD1 loss results in silencing of innate immunity genes, including the type III interferon receptor IFNLR1, through depletion of H3K36 di-methylation (H3K36me2) and gain of H3K27 tri-methylation (H3K27me3). Inhibition of EZH2 restores immune infiltration and impairs the growth of Nsd1-mutant tumors. Thus, our work uncovers a druggable chromatin cross talk that regulates the viral mimicry response and enables immune evasion of DNA hypomethylated tumors.

Tissue-resident memory features are linked to the magnitude of cytotoxic T cell responses in human lung cancer.

Therapies that boost the anti-tumor responses of cytotoxic T lymphocytes (CTLs) have shown promise; however, clinical responses to the immunotherapeutic agents currently available vary considerably, and the molecular basis of this is unclear. We performed transcriptomic profiling of tumor-infiltrating CTLs from treatment-naive patients with lung cancer to define the molecular features associated with the robustness of anti-tumor immune responses. We observed considerable heterogeneity in the expression of molecules associated with activation of the T cell antigen receptor (TCR) and of immunological-checkpoint molecules such as 4-1BB, PD-1 and TIM-3. Tumors with a high density of CTLs showed enrichment for transcripts linked to tissue-resident memory cells (TRM cells), such as CD103, and CTLs from CD103hi tumors displayed features of enhanced cytotoxicity. A greater density of TRM cells in tumors was predictive of a better survival outcome in lung cancer, and this effect was independent of that conferred by CTL density. Here we define the 'molecular fingerprint' of tumor-infiltrating CTLs and identify potentially new targets for immunotherapy.

Immune Landscape of Viral- and Carcinogen-Driven Head and Neck Cancer.

Head and neck squamous cell carcinoma (HNSCC) arises through exposure to environmental carcinogens or malignant transformation by human papillomavirus (HPV). Here, we assessed the transcriptional profiles of 131,224 single cells from peripheral and intra-tumoral immune populations from patients with HPV- and HPV+ HNSCC and healthy donors. Immune cells within tumors of HPV- and HPV+ HNSCC displayed a spectrum of transcriptional signatures, with helper CD4+ T cells and B cells being relatively divergent and CD8+ T cells and CD4+ regulatory T cells being relatively similar. Transcriptional results were contextualized through multispectral immunofluorescence analyses and evaluating putative cell-cell communication based on spatial proximity. These analyses defined a gene expression signature associated with CD4+ T follicular helper cells that is associated with longer progression-free survival in HNSCC patients. The datasets and analytical approaches herein provide a resource for the further study of the impact of immune cells on viral- and carcinogen-induced cancers.

Genomic signature of Fanconi anaemia DNA repair pathway deficiency in cancer.

Fanconi anaemia (FA), a model syndrome of genome instability, is caused by a deficiency in DNA interstrand crosslink repair resulting in chromosome breakage1-3. The FA repair pathway protects against endogenous and exogenous carcinogenic aldehydes4-7. Individuals with FA are hundreds to thousands fold more likely to develop head and neck (HNSCC), oesophageal and anogenital squamous cell carcinomas8 (SCCs). Molecular studies of SCCs from individuals with FA (FA SCCs) are limited, and it is unclear how FA SCCs relate to sporadic HNSCCs primarily driven by tobacco and alcohol exposure or infection with human papillomavirus9 (HPV). Here, by sequencing genomes and exomes of FA SCCs, we demonstrate that the primary genomic signature of FA repair deficiency is the presence of high numbers of structural variants. Structural variants are enriched for small deletions, unbalanced translocations and fold-back inversions, and are often connected, thereby forming complex rearrangements. They arise in the context of TP53 loss, but not in the context of HPV infection, and lead to somatic copy-number alterations of HNSCC driver genes. We further show that FA pathway deficiency may lead to epithelial-to-mesenchymal transition and enhanced keratinocyte-intrinsic inflammatory signalling, which would contribute to the aggressive nature of FA SCCs. We propose that the genomic instability in sporadic HPV-negative HNSCC may arise as a result of the FA repair pathway being overwhelmed by DNA interstrand crosslink damage caused by alcohol and tobacco-derived aldehydes, making FA SCC a powerful model to study tumorigenesis resulting from DNA-crosslinking damage.

Intermittent PI3Kδ inhibition sustains anti-tumour immunity and curbs irAEs.

Phosphoinositide 3-kinase δ (PI3Kδ) has a key role in lymphocytes, and inhibitors that target this PI3K have been approved for treatment of B cell malignancies1-3. Although studies in mouse models of solid tumours have demonstrated that PI3Kδ inhibitors (PI3Kδi) can induce anti-tumour immunity4,5, its effect on solid tumours in humans remains unclear. Here we assessed the effects of the PI3Kδi AMG319 in human patients with head and neck cancer in a neoadjuvant, double-blind, placebo-controlled randomized phase II trial (EudraCT no. 2014-004388-20). PI3Kδ inhibition decreased the number of tumour-infiltrating regulatory T (Treg) cells and enhanced the cytotoxic potential of tumour-infiltrating T cells. At the tested doses of AMG319, immune-related adverse events (irAEs) required treatment to be discontinued in 12 out of 21 of patients treated with AMG319, suggestive of systemic effects on Treg cells. Accordingly, in mouse models, PI3Kδi decreased the number of Treg cells systemically and caused colitis. Single-cell RNA-sequencing analysis revealed a PI3Kδi-driven loss of tissue-resident colonic ST2 Treg cells, accompanied by expansion of pathogenic T helper 17 (TH17) and type 17 CD8+ T (TC17) cells, which probably contributed to toxicity; this points towards a specific mode of action for the emergence of irAEs. A modified treatment regimen with intermittent dosing of PI3Kδi in mouse models led to a significant decrease in tumour growth without inducing pathogenic T cells in colonic tissue, indicating that alternative dosing regimens might limit toxicity.

METTL3 and N6-Methyladenosine Promote Homologous Recombination-Mediated Repair of DSBs by Modulating DNA-RNA Hybrid Accumulation.

Double-strand breaks (DSBs) are the most deleterious DNA lesions, which, if left unrepaired, may lead to genome instability or cell death. Here, we report that, in response to DSBs, the RNA methyltransferase METTL3 is activated by ATM-mediated phosphorylation at S43. Phosphorylated METTL3 is then localized to DNA damage sites, where it methylates the N6 position of adenosine (m6A) in DNA damage-associated RNAs, which recruits the m6A reader protein YTHDC1 for protection. In this way, the METTL3-m6A-YTHDC1 axis modulates accumulation of DNA-RNA hybrids at DSBs sites, which then recruit RAD51 and BRCA1 for homologous recombination (HR)-mediated repair. METTL3-deficient cells display defective HR, accumulation of unrepaired DSBs, and genome instability. Accordingly, depletion of METTL3 significantly enhances the sensitivity of cancer cells and murine xenografts to DNA damage-based therapy. These findings uncover the function of METTL3 and YTHDC1 in HR-mediated DSB repair, which may have implications for cancer therapy.

An update on the immune landscape in lung and head and neck cancers.

Immunotherapy has dramatically changed the treatment landscape for patients with cancer. Programmed death-ligand 1/programmed death-1 checkpoint inhibitors have been in the forefront of this clinical revolution. Currently, there are 6 US Food and Drug Administration-approved checkpoint inhibitors for approximately 18 different histologic types of cancer. Lung cancer and head and neck squamous cell carcinoma (HNSCC) are 2 diseases that have led the way in the development of immunotherapy. Atezolizumab, durvalumab, nivolumab, and pembrolizumab are all currently used as part of standard-of-care treatment for different stages of lung cancer. Similarly, nivolumab and pembrolizumab have US regulatory approval as treatment for advanced metastatic HNSCC. This is significant because lung cancer represents the most common and most fatal cancer globally, and HNSCC is the sixth most common. Currently, most of the approvals for the use of immunotherapy agents are for patients diagnosed in the metastatic setting. However, research is ongoing to evaluate these drugs in earlier stage disease. There is plausible biological rationale to expect that pharmacologic activation of the immune system will be effective for early-stage and smaller tumors. In addition, selecting patients who are more likely to respond to immunotherapy and understanding why resistance develops are crucial areas of ongoing research. The objective of this review was to provide an overview of the current immune landscape and future directions in lung cancer and HNSCC.

Defining HPV-specific B cell responses in patients with head and neck cancer.

Tumours often contain B cells and plasma cells but the antigen specificity of these intratumoral B cells is not well understood1-8. Here we show that human papillomavirus (HPV)-specific B cell responses are detectable in samples from patients with HPV-positive head and neck cancers, with active production of HPV-specific IgG antibodies in situ. HPV-specific antibody secreting cells (ASCs) were present in the tumour microenvironment, with minimal bystander recruitment of influenza-specific cells, suggesting a localized and antigen-specific ASC response. HPV-specific ASC responses correlated with titres of plasma IgG and were directed against the HPV proteins E2, E6 and E7, with the most dominant response against E2. Using intratumoral B cells and plasma cells, we generated several HPV-specific human monoclonal antibodies, which exhibited a high degree of somatic hypermutation, consistent with chronic antigen exposure. Single-cell RNA sequencing analyses detected activated B cells, germinal centre B cells and ASCs within the tumour microenvironment. Compared with the tumour parenchyma, B cells and ASCs were preferentially localized in the tumour stroma, with well-formed clusters of activated B cells indicating ongoing germinal centre reactions. Overall, we show that antigen-specific activated and germinal centre B cells as well as plasma cells can be found in the tumour microenvironment. Our findings provide a better understanding of humoral immune responses in human cancer and suggest that tumour-infiltrating B cells could be harnessed for the development of therapeutic agents.

Functional HPV-specific PD-1+ stem-like CD8 T cells in head and neck cancer.

T cells are important in tumour immunity but a better understanding is needed of the differentiation of antigen-specific T cells in human cancer1,2. Here we studied CD8 T cells in patients with human papillomavirus (HPV)-positive head and neck cancer and identified several epitopes derived from HPV E2, E5 and E6 proteins that allowed us to analyse virus-specific CD8 T cells using major histocompatibility complex (MHC) class I tetramers. HPV-specific CD8 T cells expressed PD-1 and were detectable in the tumour at levels that ranged from 0.1% to 10% of tumour-infiltrating CD8 T lymphocytes (TILs) for a given epitope. Single-cell RNA-sequencing analyses of tetramer-sorted HPV-specific PD-1+ CD8 TILs revealed three transcriptionally distinct subsets. One subset expressed TCF7 and other genes associated with PD-1+ stem-like CD8 T cells that are critical for maintaining T cell responses in conditions of antigen persistence. The second subset expressed more effector molecules, representing a transitory cell population, and the third subset was characterized by a terminally differentiated gene signature. T cell receptor clonotypes were shared between the three subsets and pseudotime analysis suggested a hypothetical differentiation trajectory from stem-like to transitory to terminally differentiated cells. More notably, HPV-specific PD-1+TCF-1+ stem-like TILs proliferated and differentiated into more effector-like cells after in vitro stimulation with the cognate HPV peptide, whereas the more terminally differentiated cells did not proliferate. The presence of functional HPV-specific PD-1+TCF-1+CD45RO+ stem-like CD8 T cells with proliferative capacity shows that the cellular machinery to respond to PD-1 blockade exists in HPV-positive head and neck cancer, supporting the further investigation of PD-1 targeted therapies in this malignancy. Furthermore, HPV therapeutic vaccination efforts have focused on E6 and E7 proteins; our results suggest that E2 and E5 should also be considered for inclusion as vaccine antigens to elicit tumour-reactive CD8 T cell responses of maximal breadth.

TM4SF19 controls GABP-dependent YAP transcription in head and neck cancer under oxidative stress conditions.

Tobacco and alcohol are risk factors for human papillomavirus-negative head and neck squamous cell carcinoma (HPV- HNSCC), which arises from the mucosal epithelium of the upper aerodigestive tract. Notably, despite the mutagenic potential of smoking, HPV- HNSCC exhibits a low mutational load directly attributed to smoking, which implies an undefined role of smoking in HPV- HNSCC. Elevated YAP (Yes-associated protein) mRNA is prevalent in HPV- HNSCC, irrespective of the YAP gene amplification status, and the mechanism behind this upregulation remains elusive. Here, we report that oxidative stress, induced by major risk factors for HPV- HNSCC such as tobacco and alcohol, promotes YAP transcription via TM4SF19 (transmembrane 4 L six family member 19). TM4SF19 modulates YAP transcription by interacting with the GABP (Guanine and adenine-binding protein) transcription factor complex. Mechanistically, oxidative stress induces TM4SF19 dimerization and topology inversion in the endoplasmic reticulum membrane, which in turn protects the GABPß1 subunit from proteasomal degradation. Conversely, depletion of TM4SF19 impairs the survival, proliferation, and migration of HPV- HNSCC cells, highlighting the potential therapeutic relevance of targeting TM4SF19. Our findings reveal the roles of the key risk factors of HPV- HNSCC in tumor development via oxidative stress, offering implications for upcoming therapeutic approaches in HPV- HNSCC.

A druggable cascade links methionine metabolism to epigenomic reprogramming in squamous cell carcinoma.

Upper aerodigestive squamous cell carcinoma (UASCC) is a common and aggressive malignancy with few effective therapeutic options. Here, we investigate amino acid metabolism in this cancer, surprisingly noting that UASCC exhibits the highest methionine level across all human cancers, driven by its transporter LAT1. We show that LAT1 is also expressed at the highest level in UASCC, transcriptionally activated by UASCC-specific promoter and enhancers, which are directly coregulated by SCC master regulators TP63/KLF5/SREBF1. Unexpectedly, unbiased bioinformatic screen identifies EZH2 as the most significant target downstream of the LAT1-methionine pathway, directly linking methionine metabolism to epigenomic reprogramming. Importantly, this cascade is indispensable for the survival and proliferation of UASCC patient-derived tumor organoids. In addition, LAT1 expression is closely associated with cellular sensitivity to inhibition of the LAT1-methionine-EZH2 axis. Notably, this unique LAT1-methionine-EZH2 cascade can be targeted effectively by either pharmacological approaches or dietary intervention in vivo. In summary, this work maps a unique mechanistic cross talk between epigenomic reprogramming with methionine metabolism, establishes its biological significance in the biology of UASCC, and identifies a unique tumor-specific vulnerability which can be exploited both pharmacologically and dietarily.

Engineering Dimeric EGFR-directed IgA Antibodies Reveals a Central Role of CD147 during Neutrophil-mediated Tumor Cell Killing of Head and Neck Squamous Cancer Cells.

Human IgA Abs engage neutrophils for cancer immunotherapy more effectively than IgG Abs. Previous studies demonstrated that engineering approaches improved biochemical and functional properties. In this study, we report a novel, to our knowledge, IgA2 Ab against the epidermal growth factor receptor generated by protein engineering and polymerization. The resulting molecule demonstrated a covalent linkage of L and H chains and an effective polymerization by the joining chain. The engineered dimer outperformed its monomeric variant in functional experiments on Fab-mediated modes of action and binding to the Fc receptor. The capacity to engage neutrophils for Ab-dependent cell-mediated cytotoxicity (ADCC) of adherent growing target cancer cells was cell line dependent. Although the engineered dimer displayed a long-term efficacy against the vulva carcinoma cell line A431, there was a notable in-efficacy against human papillomavirus (HPV)- head and neck squamous cell carcinoma (HNSCC) cell lines. However, the highly engineered IgA Abs triggered a neutrophil-mediated cytotoxicity against HPV+ HNSCC cell lines. Short-term ADCC efficacy correlated with the target cells' epidermal growth factor receptor expression and the ability of cancer cell-conditioned media to enhance the CD147 surface level on neutrophils. Notably, the HPV+ HNSCC cell lines demonstrated a significant increment in releasing soluble CD147 and a reduced induction of membranous CD147 on neutrophils compared with HPV- cells. Although membranous CD147 on neutrophils may impair proper IgA-Fc receptor binding, soluble CD147 enhanced the IgA-neutrophil-mediated ADCC in a dose-dependent manner. Thus, engineering IgA Abs and impedance-based ADCC assays provided valuable information regarding the target-effector cell interaction and identified CD147 as a putative critical parameter for neutrophil-mediated cytotoxicity.