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Longitudinal sampling of tumor tissue from patients with solid cancers, aside from melanoma and a few other cases, is often unfeasible, and thus may not capture the plasticity of interactions between the tumor and immune system under selective pressure of a given therapy. Peripheral blood analyses provide salient information about the human peripheral immunome while offering technical and practical advantages over traditional tumor biopsies, and should be utilized where possible alongside interrogation of the tumor. Some common blood-based biomarkers used to study the immune response include immune cell subsets, circulating tumor DNA, and protein analytes such as cytokines. With the recent explosion of immune checkpoint inhibitors (ICI) as a modality of treatment in multiple cancer types, soluble immune checkpoints have become a relevant area of investigation for peripheral immune-based biomarkers. However, the exact functions of soluble immune checkpoints and their roles in cancer for the most part remain unclear. This review discusses current literature on the production, function, and expression of nine soluble immune checkpoints - sPD-L1, sPD-1, sCTLA4, sCD80, sTIM3, sLAG3, sB7-H3, sBTLA, and sHVEM - in patients with solid tumors, and explores their role as biomarkers of response to ICI as well as to conventional therapies (chemotherapy, radiotherapy, targeted therapy, and surgery) in cancer patients.

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BACKGROUND: Immune checkpoint inhibitors (ICIs), administered alone or combined with chemotherapy, are the standard of care in advanced non-oncogene addicted Non-Small Cell Lung Cancer (NSCLC). Despite these treatments' success, most long-term survival benefit is restricted to approximately 20% of patients, highlighting the need to identify novel biomarkers to optimize treatment strategies. In several solid tumors, immune soluble factors, the activatory CD137+ Tcells, and the immunosuppressive cell subsets Tregs and MDSCs (PMN(Lox1+)-MDSC and M-MDSCs) correlated with responses to ICIs and clinical outcomes thus becoming appealing predictive and prognostic factors. This study investigated the role of distinct CD137+ Tcell subsets, Tregs, MDSCs, and immune-soluble factors in NSCLC patients as possible biomarkers. METHODS: The levels of T cells, MDSCs and soluble factors were evaluated in 89 metastatic NSCLC patients who underwent ICIs as first- or second-line treatment. T cell analysis was performed by cytoflurimetry evaluating Tregs and different CD137+ Tcell subsets also combined with CD3+, CD8+, PD1+, and Ki67+ markers. Circulating cytokines and immune checkpoints were also evaluated by Luminex analysis. All these parameters were correlated with several clinical factors (age, sex, smoking status, PS and TPS), response to therapy, PFS , and OS . The analyses were conducted in the overall population and in patients treated with ICIs as first-line (naïve patients). RESULTS: In both groups of patients, high levels of circulating CD137+ and CD137+PD1+ T cells (total, CD4 and CD8) and the soluble factor LAG3 positively correlated with response to therapy. In naïve patients, PMN(Lox1+)-MDSCs negatively correlated with clinical response, and a high percentage of Tregs was associated with favorable survival. Moreover, the balance between Treg/CD137+ Tcells or PMN(Lox1+)-MDSC/CD137+ Tcells was higher in non-responding patients and was associated with poor survival. CD137+ Tcells and Tregs resulted as two positive independent prognostic factors. CONCLUSION: High levels of CD137+, CD137+PD1+ Tcells and sLAG3 could predict the response to ICIs in NSCLC patients independently by previous therapy. Combining the evaluation of CD137+ Tcells and Tregs also as Treg/CD137+ T cells ratio it is possible to identify naive patients with longer survival.

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There is an urgent need to better understand the impact of different severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants on immune response and disease dynamics to facilitate better intervention strategies. Here, we show that SARS-CoV-2 variants differentially affect host immune responses. The magnitude and quantity of cytokines and chemokines were comparable in those infected with the Wuhan strain and the Delta variant. However, individuals infected with the Omicron variant had significantly lower levels of these mediators. We also found an elevation of plasma galectins (Gal-3, Gal-8, and Gal-9) in infected individuals, in particular, in those with the original strain. Soluble galectins exert a proinflammatory role in COVID-19 pathogenesis. This was illustrated by their correlation with the plasma levels of sCD14, sCD163, enhanced TNF-α/IL-6 secretion, and increased SARS-CoV-2 infectivity in vitro. Moreover, we observed enhanced CD4+ and CD8+ T cell activation in Wuhan strain-infected individuals. Surprisingly, there was a more pronounced T cell activation in those infected with the Omicron in comparison to the Delta variant. In line with T cell activation status, we observed a more pronounced expansion of T cells expressing different co-inhibitory receptors in patients infected with the Wuhan strain, followed by the Omicron and Delta variants. Individuals infected with the Wuhan strain or the Omicron variant had a similar pattern of plasma soluble immune checkpoints. Our results imply that a milder innate immune response might be beneficial and protective in those infected with the Omicron variant. Our results provide a novel insight into the differential impact of SARS-CoV-2 variants on host immunity. IMPORTANCE There is a need to better understand how different SARS-CoV-2 variants influence the immune system and disease dynamics to facilitate the development of better vaccines and therapies. We compared immune responses in 140 SARS-CoV-2-infected individuals with the Wuhan strain, the Delta variant, or the Omicron variant. All these patients were admitted to the intensive care unit and were SARS-CoV-2 vaccination naïve. We found that SARS-CoV-2 variants differentially affect the host immune response. This was done by measuring soluble biomarkers in their plasma and examining different immune cells. Overall, we found that the magnitude of cytokine storm in individuals infected with the Wuhan strain or the Delta variant was greater than in those infected with the Omicron variant. In light of enhanced cytokine release syndrome in individuals infected with the Wuhan strain or the Delta variant, we believe that a milder innate immune response might be beneficial and protective in those infected with the Omicron variant.

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Background: The immune profile of each patient could be considered as a portrait of the fitness of his/her own immune system. The predictive role of the immune profile in immune-related toxicities (irAEs) development and tumour response to treatment was investigated. Methods: A prospective, multicenter study evaluating, through a multiplex assay, the soluble immune profile at the baseline of 53 patients with advanced cancer, treated with immunotherapy as single agent was performed. Four connectivity heat maps and networks were obtained by calculating the Spearman correlation coefficients for each group: responder patients who developed cumulative toxicity (R-T), responders who did not develop cumulative toxicity (R-NT), non-responders who developed cumulative toxicity (NR-T), non-responders who did not develop cumulative toxicity (NR-NT). Results: A statistically significant up-regulation of IL-17A, sCTLA4, sCD80, I-CAM-1, sP-Selectin and sEselectin in NR-T was detected. A clear loss of connectivity of most of the soluble immune checkpoints and cytokines characterized the immune profile of patients with toxicity, while an inversion of the correlation for ICAM-1 and sP-selectin was observed in NR-T. Four connectivity networks were built for each group. The highest number of connections characterized the NR-T. Conclusions: A connectivity network of immune dysregulation was defined for each subgroup of patients, regardless of tumor type. In patients with the worst prognosis (NR-T) the peculiar connectivity model could facilitate their early and timely identification, as well as the design of a personalized treatment approach to improve outcomes or prevent irAEs.

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Individual response to immune checkpoint inhibitors (ICIs) is currently unpredictable in patients with melanoma. Recent findings highlight a striking improvement in the clinical outcomes of overweight/obese patients treated with ICIs, which seems driven, at least in part, by programmed cell death protein 1 (PD-1)-mediated T-cell dysfunction. A putative role of butyrophilins (BTNs) is under investigation as a novel mechanism of cancer immune evasion and obesity-associated inflammation. This study investigates the role of baseline plasma levels of soluble PD-1 (sPD-1), soluble programmed cell death ligand 1 (sPD-L1), BTN2A1 (sBTN2A1), BTN3A1 (sBTN3A1), along with body mass index (BMI), as predictive biomarkers of immunotherapy response in metastatic melanoma patients treated with nivolumab or pembrolizumab as first-line treatment. In all, 41 patients were included in the study. The baseline plasma level of sPD-1 was significantly lower, and the sBTN2A1 was significantly higher, in long-responder patients to nivolumab or pembrolizumab (median sPD-1: 10.3 ng/ml versus 16.6 ng/ml, p = 0.001; median sBTN2A1: 4.4 ng/ml versus 3.77 ng/ml, p = 0.004). Lower levels of sPD-1 and higher levels of sBTN2A1 were also significantly associated with better overall response rate. Notably, when we further stratified the study cohort using BMI along with sPD-1, patients with BMI ⩾ 25 and sPD-1 < 11.24 ng/ml had longer time to treatment failure after PD-1 inhibitor than other subgroups of patients (p < 0.001). Circulating sPD-1 and sBTN2A1 detection, along with BMI, could give more insights into the immune-metabolic interactions underlying the benefit observed in overweight/obese patients, improving the use of dynamic, noninvasive, biomarkers for patient selection.

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Immune checkpoints (ICPs) serve as regulatory switches on immune-competent cells. Soluble ICPs consist of fragments derived from ICP molecules typically located on cell membranes. Research has demonstrated that they perform similar functions to their membrane-bound counterparts but are directly present in the bloodstream. Effective control of the maternal immune system is vital for a successful pregnancy due to genetic differences between the mother and fetus. Abnormalities in the immune response are widely acknowledged as the primary cause of spontaneous abortions. In our research, we introduce a novel approach to understanding the immune-mediated mechanisms underlying recurrent miscarriages and explore new possibilities for diagnosing and preventing pregnancy loss. The female participants in the study were divided into three groups: RSA (recurrent spontaneous abortion), pregnant, and non-pregnant women. The analysis of soluble forms of immune checkpoints and their ligands in the serum of the study groups was conducted using the Luminex method Statistically significant differences in the concentrations of (ICPs) were observed between physiological pregnancies and the RSA group. Among patients with RSA, we noted reduced concentrations of sGalectin-9, sTIM-3, and sCD155, along with elevated concentrations of LAG-3, sCD80, and sCD86 ICPs, in comparison to physiological pregnancies. Our study indicates that sGalectin-9, TIM-3, sLAG-3, sCD80, sCD86, sVISTA, sNectin-2, and sCD155 could potentially serve as biological markers of a healthy, physiological pregnancy. These findings suggest that changes in the concentrations of soluble immune checkpoints may have the potential to act as markers for early pregnancy loss.

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Background: Despite the efficacy of immunotherapy, only a small percentage of patients achieves a long-term benefit in terms of overall survival. The aim of this study was to define an immune profile predicting the response to immune checkpoint inhibitors (ICIs). Methods: Patients with advanced solid tumors, who underwent ICI treatment were enrolled in this prospective study. Blood samples were collected at the baseline. Thirteen soluble immune checkpoints, 3 soluble adhesion molecules, 5 chemokines and 11 cytokines were analyzed. The results were associated with oncological outcomes. Results: Regardless of tumor type, patients with values of sTIM3, IFNα, IFNγ, IL1ß, IL1α, IL12p70, MIP1ß, IL13, sCD28, sGITR, sPDL1, IL10 and TNFα below the median had longer overall survival (p<0.05). By using cluster analysis and grouping the patients according to the trend of the molecules, two clusters were found. Cluster A had a significantly higher mean progression free survival (Cluster A=11.9 months vs Cluster B=3.5 months, p<0.01), a higher percentage of disease stability (Cluster A=34.5% vs. Cluster B=0%, p<0.05) and a lower percentage of disease progression (Cluster A=55.2% vs. Cluster B = 94.4%, p=0.04). Conclusion: The combined evaluation of soluble molecules, rather than a single circulating factor, may be more suitable to represent the fitness of the immune system status in each patient and could allow to identify two different prognostic and predictive outcome profiles.

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INTRODUCTION: Only a minority of patients with platinum refractory head and neck squamous cell carcinoma (PR/HNSCC) gain some lasting benefit from immunotherapy. METHODS: The combined role of the comprehensive genomic (through the FoundationOne Cdx test) and immune profiles of 10 PR/HNSCC patients treated with the anti-PD-1 nivolumab was evaluated. The immune profiles were studied both at baseline and at the second cycle of immunotherapy, weighing 20 circulating cytokines/chemokines, adhesion molecules, and 14 soluble immune checkpoints dosed through a multiplex assay. A connectivity map was obtained by calculating the Spearman correlation between the expression profiles of circulating molecules. RESULTS: Early progression occurred in five patients, each of them showing TP53 alteration and three of them showing a mutation/loss/amplification of genes involved in the cyclin-dependent kinase pathway. In addition, ERB2 amplification (1 patient), BRCA1 mutation (1 patient), and NOTCH1 genes alteration (3 patients) occurred. Five patients achieved either stable disease or partial response. Four of them carried mutations in PI3K/AKT/PTEN pathways. In the only two patients, with a long response to immunotherapy, the tumor mutational burden (TMB) was high. Moreover, a distinct signature, in terms of network connectivity of the circulating soluble molecules, characterizing responder and non-responder patients, was evidenced. Moreover, a strong negative and statistically significant (p-value ≤ 0.05) correlation with alive status was evidenced for sE-selectin at T1. CONCLUSIONS: Our results highlighted the complexity and heterogeneity of HNSCCs, even though it was in a small cohort. Molecular and immune approaches, combined in a single profile, could represent a promising strategy, in the context of precision immunotherapy.

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Chronic lymphocytic leukemia (CLL) is a lymphoid neoplasm characterized by the accumulation of mature B cells. The diagnosis is established by the detection of monoclonal B lymphocytes in peripheral blood, even in early stages [monoclonal B-cell lymphocytosis (MBLhi)], and its clinical course is highly heterogeneous. In fact, there are well-characterized multiple prognostic factors that are also related to the observed genetic heterogenicity, such as immunoglobulin heavy chain variable region (IGHV) mutational status, del17p, and TP53 mutations, among others. Moreover, a dysregulation of the immune system (innate and adaptive immunity) has been observed in CLL patients, with strong impact on immune surveillance and consequently on the onset, evolution, and therapy response. In addition, the tumor microenvironment is highly complex and heterogeneous (i.e., matrix, fibroblast, endothelial cells, and immune cells), playing a critical role in the evolution of CLL. In this study, a quantitative profile of 103 proteins (cytokines, chemokines, growth/regulatory factors, immune checkpoints, and soluble receptors) in 67 serum samples (57 CLL and 10 MBLhi) has been systematically evaluated. Also, differential profiles of soluble immune factors that discriminate between MBLhi and CLL (sCD47, sCD27, sTIMD-4, sIL-2R, and sULBP-1), disease progression (sCD48, sCD27, sArginase-1, sLAG-3, IL-4, and sIL-2R), or among profiles correlated with other prognostic factors, such as IGHV mutational status (CXCL11/I-TAC, CXCL10/IP-10, sHEVM, and sLAG-3), were deciphered. These results pave the way to explore the role of soluble immune checkpoints as a promising source of biomarkers in CLL, to provide novel insights into the immune suppression process and/or dysfunction, mostly on T cells, in combination with cellular balance disruption and microenvironment polarization leading to tumor escape.

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During SARS-CoV-2 infection, an effective immune response provides the first line of defense; however, excessive inflammatory innate immunity and impaired adaptive immunity may harm tissues. Soluble immune mediators are involved in the dynamic interaction of ligands with membrane-bound receptors to maintain and restore health after pathological events. In some cases, the dysregulation of their expression can lead to disease pathology. In this literature review, we described current knowledge of the basic features of soluble immune mediators and their dysregulation during SARS-CoV-2 infections and highlighted their contribution to disease severity and mortality. Video Abstract.

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Coronavirus disease 2019 (COVID-19) is a contagious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a highly pathogenic infection responsible for the world pandemic in 2020. COVID-19 is characterized by an increased number of critically ill patients with a high risk of health care system collapse. Therefore, the search for severity biomarkers and potential therapies is crucial. In this study, we evaluated SARS-CoV-2 -induced cytokines, cytokines receptors and growth factors profile, in critical COVID-19 patients admitted in intensive care unit (ICU) aiming to identify potential biomarkers and therapeutic targets. We designed a prospective study enrolling 62 adults with severe COVID-19 during the first two Brazilian COVID-19 waves (from May to July 2020 and December 2020 to May 2021), convenience samples recruitment in first 24 hours and then, every 4 days until day 20 of ICU admission from a tertiary hospital in São Paulo, Brazil. Controls were healthy blood donors. Whole blood was used to evaluate 17 cytokines, cytokines receptors and growth factors. Due to low mortality rate, we used the need of mechanical ventilation as primary endpoint. In our analysis, we found a different pattern in soluble CD137 (sCD137) in critically ill patients with COVID-19, with a direct relationship between increased levels and worse clinical outcome. sCD137 was related with increased risk of mechanical ventilation and World Health Organization (WHO) clinical score for disease severity. CD137 is a tumor necrosis factor receptor (TNF) family member, mainly responsible for T-cell activation. Soluble isoforms of immune checkpoints competitively regulate function of their membrane-bound counterparts. Our study demonstrated the onward increase in sCD137 levels during severe SARS-CoV-2 infection and its correlation with worse outcomes, suggesting sCD137 as a potential reliable severity biomarker.

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Co-inhibitory B7-CD28 family member proteins negatively regulate T cell responses and are extensively involved in tumor immune evasion. Blockade of classical CTLA-4 (cytotoxic T lymphocyte-associated antigen-4) and PD-1 (programmed cell death protein-1) checkpoint pathways have become the cornerstone of anti-cancer immunotherapy. New inhibitory checkpoint proteins such as B7-H3, B7-H4, and BTLA (B and T lymphocyte attenuator) are being discovered and investigated for their potential in anti-cancer immunotherapy. In addition, soluble forms of these molecules also exist in sera of healthy individuals and elevated levels are found in chronic infections, autoimmune diseases, and cancers. Soluble forms are generated by proteolytic shedding or alternative splicing. Elevated circulating levels of these inhibitory soluble checkpoint molecules in cancer have been correlated with advance stage, metastatic status, and prognosis which underscore their broader involvement in immune regulation. In addition to their potential as biomarker, understanding their mechanism of production, biological activity, and pathological interactions may also pave the way for their clinical use as a therapeutic target. Here we review these aspects of soluble checkpoint molecules and elucidate on their potential for anti-cancer immunotherapy.

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Unresectable recurrent and/or metastatic head and neck squamous cell carcinoma (R/M HNSCC) has a very poor prognosis. Soluble immune checkpoints (sICs) are circulating proteins that result from the alternative splicing of membrane proteins and can modulate the immune response to cancer cells. The aim of our pilot study was to determine the possible role of a comprehensive evaluation of sICs in the classification of prognosis and response to treatment in patients with advanced disease. We evaluated several sICs (CD137, CTLA-4, PD-1, PD-L1, PD-L2, TIM3, LAG3, GITR, HVEM, BTLA, IDO, CD80, CD27, and CD28) from peripheral blood at baseline and investigated the association with clinical characteristics and outcomes. A high baseline soluble LAG3 (sLAG3 > 377 pg/mL) resulted in an association with poor PFS and OS (p = 0.047 and p = 0.003, respectively). Moreover, sLAG3 emerged as an independent prognostic factor using an MVA (p = 0.005). The evaluation of sICs, in particular sLAG3, may be relevant for identifying patients with worse prognoses, or resistance to treatments, and may lead to the development of novel targeted strategies.

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Despite a proportion of renal cancer patients can experiment marked and durable responses to immune-checkpoint inhibitors, the treatment efficacy is widely variable and identifying the patient who will benefit from immunotherapy remains an issue. We performed a prospective study to investigate if soluble forms of the immune-checkpoints PD-1 (sPD-1), PD-L1 (sPD-L1), pan-BTN3As, BTN3A1, and BTN2A1, could be candidate to predict the response to immune-checkpoint blockade therapy. We evaluated the plasma levels in a learning cohort of metastatic clear cell renal carcinoma (mccRCC) patients treated with the anti-PD-1 agent nivolumab by ad hoc developed ELISA's. Using specific cut-offs determined through ROC curves, we showed that high baseline levels of sPD-1 (>2.11 ng/ml), sPD-L1 (>0.66 ng/ml), and sBTN3A1 (>6.84 ng/ml) were associated with a longer progression-free survival (PFS) to nivolumab treatment [median PFS, levels above thresholds: sPD-1, 20.7 months (p < .0001); sPD-L1, 19 months (p < .0001); sBTN3A1, 17.5 months (p = .002)]. High sPD-1 and sBTN3A1 levels were also associated with best overall response by RECIST and objective response of >20%. The results were confirmed in a validation cohort of 20 mccRCC patients. The analysis of plasma dynamic changes after nivolumab showed a statistically significant decrease of sPD-1 after 2 cycles (Day 28) in the long-responder patients. Our study revealed that the plasma levels of sPD-1, sPD-L1, and sBTN3A1 can predict response to nivolumab, discriminating responders from non-responders already at therapy baseline, with the advantages of non-invasive sample collection and real-time monitoring that allow to evaluate the dynamic changes during cancer evolution and treatment.

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Introduction of checkpoint inhibitors resulted in durable responses and improvements in overall survival in advanced RCC patients, but the treatment efficacy is widely variable, and a considerable number of patients are resistant to PD-1/PD-L1 inhibition. This variability of clinical response makes necessary the discovery of predictive biomarkers for patient selection. Previous findings showed that the epigenetic modifications, including an extensive microRNA-mediated regulation of tumor suppressor genes, are key features of RCC. Based on this biological background, we hypothesized that a miRNA expression profile directly identified in the peripheral lymphocytes of the patients before and after the nivolumab administration could represent a step toward a real-time monitoring of the dynamic changes during cancer evolution and treatment. Interestingly, we found a specific subset of miRNAs, called "lymphocyte miRNA signature", specifically induced in long-responder patients (CR, PR, or SD to nivolumab >18 months). Focusing on the clinical translational potential of miRNAs in controlling the expression of immune checkpoints, we identified the association between the plasma levels of soluble PD-1/PD-L1 and expression of some lymphocyte miRNAs. These findings could help the development of novel dynamic predictive biomarkers urgently needed to predict the potential response to immunotherapy and to guide clinical decision-making in RCC patients.

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Patients with non-small cell lung cancer (NSCLC) have been shown to benefit from the introduction of anti-PD1 treatment. However, not all patients experience tumor regression and durable response. The identification of a string of markers that are direct or indirect indicators of the immune system fitness is needed to choose optimal therapeutic schedules in the management of NSCLC patients. We analyzed 34 immuno-related molecules (14 soluble immune checkpoints, 17 cytokines/chemokines, 3 adhesion molecules) released in the serum of 22 NSCLC patients under Nivolumab treatment and the gut metabolomic profile at baseline. These parameters were correlated with performance status (PS) and/or response to treatment. Nivolumab affected the release of soluble immune checkpoints (sICs). Patients with a better clinical outcome and with an optimal PS (PS = 0) showed a decreased level of PD1 and maintained low levels of several sICs at first clinical evaluation. Low levels of PDL1, PDL2, Tim3, CD137 and BTLA4 were also correlated with a long response to treatment. Moreover, responding patients showed a high proportion of eubiosis-associated gut metabolites. In this exploratory study, we propose a combination of immunological and clinical parameters (sICs, PS and gut metabolites) for the identification of patients more suitable for Nivolumab treatment. This string of parameters validated in a network analysis on a larger cohort of patients could help oncologists to improve their decision-making in an NSCLC setting.

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The importance of a balanced TH1/TH2 humoral immune response against the HIV-1 envelope protein (Env) for antibody-mediated HIV-1 control is increasingly recognized. However, there is no defined vaccination strategy to raise it. Since immune checkpoints are involved in the induction of adoptive immunity and their inhibitors (monoclonal antibodies) are licensed for cancer therapy, we investigated the effect of checkpoint blockade after HIV-1 genetic vaccination on enhancement and modulation of antiviral antibody responses. By intraperitoneal administration of checkpoint antibodies in mice we observed an induction of anti-drug antibodies which may interfere with immunomodulation by checkpoint inhibitors. Therefore, we blocked immune checkpoints locally by co-electroporation of DNA vaccines encoding the active soluble ectodomains of programmed cell death protein-1 (PD-1) or its ligand (PD-L1), respectively. Plasmid-encoded immune checkpoints did not elicit a detectable antibody response, suggesting no interference with their immunomodulatory effects. Co-electroporation of a HIV-1 DNA vaccine formulation with soluble PD-L1 ectodomain increased HIV-1 Env-specific TH1 CD4 T cell and IgG2a antibody responses. The overall antibody response was hereby shifted towards a more TH1/TH2 balanced subtype pattern. These findings indicate that co-electroporation of soluble checkpoint ectodomains together with DNA-based vaccines has modulatory effects on vaccine-induced immune responses that could improve vaccine efficacies.