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Blockade of the co-inhibitory receptor PD-1 enhances antitumor responses by boosting the function of antigen-specific T cells. Although rare, PD-1 blockade in patients with cancer can lead to exacerbation of infection-associated pathology. Here, we detail the case of a 38-year-old man who was enrolled in a clinical trial for assessment of the safety and activity of anti–PD-1 therapy for Kaposi sarcoma in people with HIV well-controlled on antiretroviral therapy. Less than a week after receiving the first dose of anti–PD-1 antibody (pembrolizumab), he presented with severe abdominal pain associated with sudden exacerbations of preexisting cytomegalovirus (CMV) enteritis and nontuberculous mycobacterial mesenteric lymphadenitis. Plasma biomarkers of gastrointestinal tract damage were highly elevated compared with healthy controls, consistent with HIV-associated loss of gut epithelial barrier integrity. Moreover, CMV-specific CD8 T cells expressed high levels of PD-1, and 7 days following PD-1 blockade, there was an increase in the frequency of activated CD38+ Ki67+ CMV-specific CD8 T cells. This case highlights the potential for PD-1 blockade to drive rapid exacerbations of inflammatory symptoms when administered to individuals harboring multiple unresolved infections. [ABSTRACT FROM AUTHOR]

To uncover underlying mechanisms associated with failure of indoleamine 2,3-dioxygenase 1 (IDO1) blockade in clinical trials, we conducted a pilot, window-of-opportunity clinical study in 17 patients with newly diagnosed advanced high-grade serous ovarian cancer before their standard tumor debulking surgery. Patients were treated with the IDO1 inhibitor epacadostat, and immunologic, transcriptomic, and metabolomic characterization of the tumor microenvironment was undertaken in baseline and posttreatment tumor biopsies. IDO1 inhibition resulted in efficient blockade of the kynurenine pathway of tryptophan degradation and was accompanied by a metabolic adaptation that shunted tryptophan catabolism toward the serotonin pathway. This resulted in elevated nicotinamide adenine dinucleotide (NAD+), which reduced T cell proliferation and function. Because NAD+ metabolites could be ligands for purinergic receptors, we investigated the impact of blocking purinergic receptors in the presence or absence of NAD+ on T cell proliferation and function in our mouse model. We demonstrated that A2a and A2b purinergic receptor antagonists, SCH58261 or PSB1115, respectively, rescued NAD+-mediated suppression of T cell proliferation and function. Combining IDO1 inhibition and A2a/A2b receptor blockade improved survival and boosted the antitumor immune signature in mice with IDO1 overexpressing ovarian cancer. These findings elucidate the downstream adaptive metabolic consequences of IDO1 blockade in ovarian cancers that may undermine antitumor T cell responses in the tumor microenvironment. Saying "I DO" to combination therapy: Indoleamine 2,3-dioxygenase 1 (IDO1) drives immunosuppression in high-grade serous ovarian cancer. Inhibition of IDO1 in combination with chemotherapy has shown limited efficacy in clinical trials. Here, Odunsi et al. treated patients with the IDO1 inhibitor epacadostat and studied the effect on the tumor microenvironment (TME) in tumor biopsies. IDO1 inhibition increased nicotinamide adenine dinucleotide (NAD+), which reduced T cell function in the TME. Combining epacadostat with purinergic receptor antagonists rescued T cell proliferation in a mouse model of ovarian cancer. These findings highlight the potential downside of IDO1 inhibition and suggest that IDO1 inhibitor therapy will require combination with NAD+ signaling blockade. [ABSTRACT FROM AUTHOR]

In people living with HIV (PLWH) on antiretroviral therapy (ART), virus persists in a latent form where there is minimal transcription or protein expression. Latently infected cells are a major barrier to curing HIV. Increasing HIV transcription and viral production in latently infected cells could facilitate immune recognition and reduce the pool of infected cells that persist on ART. Given that programmed cell death protein 1 (PD-1) expressing CD4+ T cells are preferentially infected with HIV in PLWH on ART, we aimed to determine whether administration of antibodies targeting PD-1 would reverse HIV latency in vivo. We therefore evaluated the impact of intravenous administration of pembrolizumab every 3 weeks on HIV latency in 32 PLWH and cancer on ART. After the first infusion of anti–PD-1, we observed a median 1.32-fold increase in unspliced HIV RNA and 1.61-fold increase in unspliced RNA:DNA ratio in sorted blood CD4+ T cells compared to baseline. We also observed a 1.65-fold increase in plasma HIV RNA. The frequency of CD4+ T cells with inducible virus evaluated using the tat/rev limiting dilution assay was higher after 6 cycles compared to baseline. Phylogenetic analyses of HIV env sequences in a participant who developed low concentrations of HIV viremia after 6 cycles of pembrolizumab did not demonstrate clonal expansion of HIV-infected cells. These data are consistent with anti–PD-1 being able to reverse HIV latency in vivo and support the rationale for combining anti–PD-1 with other interventions to reduce the HIV reservoir. PD-1 blockade for HIV: Strategies to target and reverse the latent HIV reservoir are required to cure HIV. Because CD4+ T cells expressing programmed cell death protein 1 (PD-1) are preferentially infected with HIV in an individual on antiretroviral therapy, PD-1 is an attractive target to manipulate the latent reservoir. To this end, Uldrick et al. measured the impact of anti–PD-1 treatment with pembrolizumab on the HIV reservoir in 32 individuals living with HIV on suppressive antiretroviral therapy and diagnosed with cancer. They observed evidence of increased unspliced HIV RNA and of the unspliced RNA:DNA ratio, consistent with anti–PD-1 treatment having the potential to reverse HIV latency. Further studies are needed to evaluate the dose and frequency of anti–PD-1 treatment required for latency reversal. [ABSTRACT FROM AUTHOR]

Cutaneous T cell lymphomas (CTCL) are rare but aggressive cancers without effective treatments. While a subset of patients derive benefit from PD-1 blockade, there is a critically unmet need for predictive biomarkers of response. Herein, we perform CODEX multiplexed tissue imaging and RNA sequencing on 70 tumor regions from 14 advanced CTCL patients enrolled in a pembrolizumab clinical trial (NCT02243579). We find no differences in the frequencies of immune or tumor cells between responders and non-responders. Instead, we identify topographical differences between effector PD-1+ CD4+ T cells, tumor cells, and immunosuppressive Tregs, from which we derive a spatial biomarker, termed the SpatialScore, that correlates strongly with pembrolizumab response in CTCL. The SpatialScore coincides with differences in the functional immune state of the tumor microenvironment, T cell function, and tumor cell-specific chemokine recruitment and is validated using a simplified, clinically accessible tissue imaging platform. Collectively, these results provide a paradigm for investigating the spatial balance of effector and suppressive T cell activity and broadly leveraging this biomarker approach to inform the clinical use of immunotherapies. PD-1 blockade is effective for only a subset of patients with cutaneous T cell lymphomas. Here, the authors report a spatial biomarker that uses immune and cancer cell topography to predict response to PD-1 blockade in this disease. [ABSTRACT FROM AUTHOR]

Increased Mtb-specific TH1 responses precede tuberculosis associated with PD-1 blockade. Preaching caution with PD-1 blockade for TB: Scientists are interested in leveraging PD-1 blockade for diseases other than cancer, such as tuberculosis (TB). Barber et al. studied two patients with cancer who developed active TB during PD-1 blockade. Analysis of longitudinal samples available from one of the patients revealed the presence of TB-specific TH1 cells before presentation of TB. These results are in line with previous work in mouse TB models, which showed that PD-1 deficiency exacerbated disease. This report indicates that PD-1 blockade for treating tuberculosis in humans may instead worsen the disease. Because of the well-established therapeutic benefit of boosting antitumor responses through blockade of the T cell inhibitory receptor PD-1, it has been proposed that PD-1 blockade could also be useful in infectious disease settings, including Mycobacterium tuberculosis (Mtb) infection. However, in preclinical models, Mtb-infected PD-1−/− mice mount exaggerated TH1 responses that drive lethal immunopathology. Multiple cases of tuberculosis during PD-1 blockade have been observed in patients with cancer, but in humans little is understood about Mtb-specific immune responses during checkpoint blockade–associated tuberculosis. Here, we report two more cases. We describe a patient who succumbed to disseminated tuberculosis after PD-1 blockade for treatment of nasopharyngeal carcinoma, and we examine Mtb-specific immune responses in a patient with Merkel cell carcinoma who developed checkpoint blockade–associated tuberculosis and was successfully treated for the infection. After anti–PD-1 administration, interferon-γ–producing Mtb-specific CD4 T cells became more prevalent in the blood, and a tuberculoma developed a few months thereafter. Mtb-specific TH17 cells, CD8 T cells, regulatory T cells, and antibody abundance did not change before the appearance of the granuloma. These results are consistent with the murine model data and suggest that boosting TH1 function with PD-1 blockade may increase the risk or severity of tuberculosis in humans. [ABSTRACT FROM AUTHOR]

Merkel cell carcinoma (MCC) is a highly immunogenic skin cancer primarily induced by Merkel cell polyomavirus, which is driven by the expression of the oncogenic T antigens (T-Ags). Blockade of the programmed cell death protein-1 (PD-1) pathway has shown remarkable response rates, but evidence for therapy-associated T-Ag-specific immune response and therapeutic strategies for the nonresponding fraction are both limited. We tracked T-Ag-reactive CD8+ T cells in peripheral blood of 26 MCC patients under anti-PD1 therapy, using DNA-barcoded pMHC multimers, displaying all peptides from the predicted HLA ligandome of the oncoproteins, covering 33 class I haplotypes. We observed a broad T cell recognition of T-Ags, including identification of 20 T-Ag-derived epitopes we believe to be novel. Broadening of the T-Ag recognition profile and increased T cell frequencies during therapy were strongly associated with clinical response and prolonged progression-free survival. T-Ag-specific T cells could be further boosted and expanded directly from peripheral blood using artificial antigen-presenting scaffolds, even in patients with no detectable T-Ag-specific T cells. These T cells provided strong tumor-rejection capacity while retaining a favorable phenotype for adoptive cell transfer. These findings demonstrate that T-Ag-specific T cells are associated with the clinical outcome to PD-1 blockade and that Ag-presenting scaffolds can be used to boost such responses. [ABSTRACT FROM AUTHOR]