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Antibiotic therapy and outcome from immune-checkpoint inhibitors
  1. David J. Pinato1,2,a,
  2. Daria Gramenitskaya1,
  3. Daniel M. Altmann3,
  4. Rosemary J. Boyton4,5,
  5. Benjamin H. Mullish1,
  6. Julian R. Marchesi1 and
  7. Mark Bower6
  1. 1 0000 0001 2113 8111grid.7445.2Department of Surgery and CancerImperial College London, Faculty of Medicine, Hammersmith Hospital Du Cane Road W120NN London UK
  2. 2 0000 0001 2113 8111grid.7445.2Imperial College London Hammersmith Campus Du Cane Road W12 0HS London UK
  3. 3 0000 0001 2113 8111grid.7445.2Department of Immunology and Inflammation, Faculty of MedicineImperial College London W12 0NN London UK
  4. 4 0000 0001 2113 8111grid.7445.2Lung Immunology Group, Department of Infectious Disease, Faculty of MedicineImperial College London W12 0NN London UK
  5. 5 0000 0000 9216 5443grid.421662.5Department of Respiratory MedicineRoyal Brompton & Harefield NHS Foundation Trust SW3 6NP London UK
  6. 6 grid.439369.2National Centre for HIV Malignancy, Department of OncologyChelsea & Westminster Hospital Fulham Road SW10 9NH London UK
  1. a +44 0207 5942799 david.pinato{at}imperial.ac.uk
  • Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Abstract

Sensitivity to immune checkpoint inhibitor (ICPI) therapy is governed by a complex interplay of tumor and host-related determinants. Epidemiological studies have highlighted that exposure to antibiotic therapy influences the probability of response to ICPI and predict for shorter patient survival across malignancies. Whilst a number of studies have reproducibly documented the detrimental effect of broad-spectrum antibiotics, the immune-biologic mechanisms underlying the association with outcome are poorly understood. Perturbation of the gut microbiota, an increasingly well-characterized factor capable of influencing ICPI-mediated immune reconstitution, has been indicated as a putative mechanism to explain the adverse effects attributed to antibiotic exposure in the context of ICPI therapy. Prospective studies are required to validate antibiotic-mediated gut perturbations as a mechanism of ICPI refractoriness and guide the development of strategies to overcome this barrier to an effective delivery of anti-cancer immunotherapy.

  • Antibiotics
  • Immune checkpoint inhibitors
  • Survival
  • Abbreviations:
    ATB
    Antibiotic
    cATB
    Concurrent antibiotic treatment
    CD
    Cluster of Differentiation
    CTLA-4
    Cyotoxic T-Lymphocyte Associated Protein 4
    DCR
    Disease control rate
    EIOP
    Early Immunotherapy Period
    GI
    Gastrointestinal
    HR
    Hazard Ratio
    ICPI
    Immune-checkpoint inhibitors
    LPS
    Lipopolysaccharide
    MHC
    Major Histocompatibility Complex
    NOD1
    Nucleotide-binding oligomerization domain-containing protein 1
    NSCLC
    Non-small Cell Lung Cancer
    ORR
    Overall response rate
    OS
    Overall Survival
    pATB
    Prior antibiotic treatment
    PD
    Progressive Disease
    PD-1
    Programmed Cell-Death 1
    PD-L1
    Programmed Cell-Death Ligand 1
    PFS
    Progression-free survival
    RCC
    Renal Cell Carcinoma
    RR
    Response rate
    TH
    T-Helper cell
    TLR
    Toll-like receptors
    WIOP
    Whole immunotherapy Period
  • Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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    Introduction

    Antibiotic therapy has produced unquestionable advances in the management of patients with cancer, a population with intrinsically higher risk of bacterial infection as a result of malignancy or treatment-related immune suppression.

    While antimicrobial therapy has markedly reduced morbidity and mortality stemming from infection, the effects of broad-spectrum antibiotics on commensal, non-pathogenic bacterial species have remained for a long time an under-appreciated effect of this therapeutic class of drugs.

    The gut microbiota, source of over 100 trillion bacteria, exists in a condition of mutually beneficial relationship with the host. Commensal bacteria are provided with a niche to colonise the host in return for their participation in the digestion of nutrients and xenobiotics, protection from pathogens and shaping of the host’s immune system subsets. Derangement of this delicate relationship has been increasingly well-characterised in the context of tumour-specific immune tolerogenesis [1].

    Multiple levels of evidence now support the link between sensitivity to immunotherapy, taxonomic diversity and enrichment in specific gut bacterial taxa, suggesting that some species or species consortia provide intrinsic immune-modulating properties. The landmark study by Gopalakrishnan [2] demonstrated how broader stool bacterial diversity and higher representation of Ruminococcaceae communities including Faecalibacterium positively influences patients’ survival following ICPI by promoting a strongly immune-reactive microenvironment and lower systemic release of pro-inflammatory cytokines [3]. Many other commensal bacteria have subsequently been recognised to play a similar role including Bifidobacteria spp., a saccarolytic Gram-positive genus highly represented within the gut that facilitates dendritic cell maturation and increased accumulation of antigen-specific T-cells within the tumour microenvironment [4]. Similarly, the presence of the anaerobic commensal Akkermansia Muciniphila is more common in responders to ICPI, who display higher peripheral CD4 and CD8 memory T-cell responses to this bacterium [5].

    Antibiotic (ATB) therapy imposes profound and protracted changes to the taxonomic diversity of the host microbial ecosystem, affecting the composition of up to 30% of the bacterial species in the gut microbiome [6], consequently leading to loss of microbial functions that are protective for the host. Such changes in gut microbial communities are rapid and pervasive, occurring within days from the first antibiotic dose [7] and persisting for up to several months after completion of therapy [8].

    Mounting evidence from epidemiological studies has underscored the detrimental role of antibiotics in ICPI outcome, with exposure to antibiotics having been linked to shortened progression-free, overall survival and reduced response rates in patients receiving ICPI as part of clinical trials and in routine practice (Table 1). In a previous study, we demonstrated time-dependence of antibiotics exposure as a strong, tumour-agnostic determinant of outcome in ICPI recipients, confirming prior, but not concurrent antibiotic therapy as doubling the risk of primary progression to immunotherapy and leading to a > 20-months shortening in patients’ survival independent of established prognostic factors and corticosteroid use [10]. Whilst mirroring pre-clinical evidence, where antibiotic pre-conditioning ahead of tumour implantation leads to impaired responses to ICPI in mice [26, 27], the expanding body of clinical studies has so far painted an incomplete picture as to the mechanistic foundations underlying the relationship between ATB and immunotherapy, a point of greater consequence given the potential practice-influencing implications of ATB prescribing in the clinic.

    The relationship between antibiotic exposure and outcomes from immune checkpoint inhibitor therapy

    Most of the studies highlighting the importance of a healthy gut microbial environment as a pre-requisite for ICPI response were unfortunately characterised by insufficient data on preceding or concomitant antibiotic exposure, making it impossible to disentangle the role of antibiotic-induced perturbation of the gut ecosystem in influencing clinically meaningful outcomes in these patients [3].

    Mechanistically, the breadth and depth of downstream effects produced by antibiotics within the cancer-immune synapse are an important challenge in studying this prognostically adverse relationship. On one hand, the direct bacteriostatic/bactericidal effect of antibiotics can cause selective pressure within the host microbial ecosystem and instigate an alternative microbiota state characterised, amongst other traits, by downregulation of major histocompatibility complex (MHC) class I/II genes and impaired effector T-cell responses, immunologic traits implicated in reduced responsiveness to ICPI [28].

    ATB-induced depletion of gut bacteria can also shift the repertoire of microbial-associated molecular patterns (MAMPS). These molecules signal through mucosal innate immune cells primarily via toll-like receptors (TLRs) and NOD1 [29] to influence neutrophil priming, reduce local cytokine release and prime adaptive immunity by influencing the expression of MHC genes within the intestinal mucosa and reduce immunoglobulin secretion [30]. Antibiotic treatment impairs TH1/TH17 responses in tumour-bearing mice through direct pre-conditioning of the gut microbiota, reducing the efficacy of cyclophosphamide-mediate immune-rejection of the tumour [31]. In addition, antibiotics can also reduce the capacity of adoptively transferred CD8+ T-cells to mediate a tumour-specific response through altered LPS/TLR4 signaling in lymphodepleted mice [32].

    By disrupting the gut ecosystem, antibiotics instigate downstream metabolic alterations within the microenvironment with complex repercussions to the tumour-host-microbe interface. Amongst them, changes in the availability of short-chain fatty acids produced by Akkermansia, Faecalibacteria and Enterococcus from the catabolism of non-digestible carbohydrates and the conversion of primary bile acids to secondary bile acids (including deoxycholate) mediated by Clostridiales can significantly alter gut homeostasis and lead to profound and clinically meaningful immune-modulatory consequences [33]. The immune-metabolic repercussions secondary to gut dysbiosis, potentially reversible by oral Akkermansia supplementation [34], might explain the influence of body mass index in determining response to ICPI [35, 36].

    With improved characterization of immune-microbiologic underpinning of the relationship between antibiotics and ICPI outcome, a key question now is whether disruption of a well-equilibrated gut bacterial ecosystem is truly causal in this relationship, and thus whether reversal of antibiotic-mediated gut dysbiosis might prove beneficial in restoring full sensitivity to ICPI. Whether a favourable gut microbiota is a reflection of an otherwise healthy host rather than the primum movens of clinically meaningful anti-cancer immune responses is still the subject of intense debate [13]. To this end, appreciating how antibiotics might dynamically affect such a strong immune-microbiologic correlate of response to checkpoint inhibition is of key importance to pave the way for strategies that could restore or protect the integrity of this important phenotypic correlate of response. To address the multiplicity of mechanisms that are likely to underscore this complex and bi-directional relationship, the coordinated study of a number of fundamental pathophysiologic processes including bacterial translocation, immune-modulation, an altered metabolome, enzymatic degradation and reduced diversity of the gut microbiome has been proposed as an overarching framework [37].

    Gaining sufficient insight as to the mode of action by which bacteria might work as biotherapeutic agents is not just important for patient prognostication, but is in fact key to a successful, rational development of microbiome-modulating therapies which improve patient’s outcome with ICPI. With antibiotic use now having been validated as an important and dynamic factor influencing outcome from immunotherapy, concerted efforts should be aimed at characterizing the candidate taxonomic features in the gut microbiota that are associated with worse outcome from ICPI in the context of preceding and concomitant antibiotic exposure and evaluate them in conjunction with the concomitant prescription of proton pump inhibitors, corticosteroids and vaccines, all of which have been postulated to influence ICPI response [38].

    Recognising these changes is expected to facilitate the clinical development of diverse biotherapeutic approaches to induce microbiome reprogramming including dietary interventions with pre-biotics, therapeutic administration of single or multiple types of bacterial species or their metabolites, selective antibiotic therapy or faecal microbial transplantation, all of which are currently at the focus of intense clinical research efforts [26].

    Funding

    DJP, RJB, BHM, JRM, DMA have received direct project funding by the NIHR Imperial Biomedical Research Centre (BRC), ITMAT Push for Impact Grant Scheme 2019. The views expressed are those of the authors and not necessarily those of the NIHR or the Department of Health and Social Care.

    Acknowledgments

    The authors would like to acknowledge the Imperial College National Institute for Health Research Biomedical Research Centre and Imperial Cancer Research UK centre for infrastructural and grant funding support. DJP is supported by grant funding from the Wellcome Trust Strategic Fund (PS3416). BHM is the recipient of a Medical Research Council (MRC) Clinical Research Training Fellowship (grant MR/R000875/1).

    Authors’ contributions

    DJP, DG, DMA, RJB, BHM, JRM and MB contributed to the writing and editing of this manuscript. All authors read and approved the final version of the manuscript.

    Availability of data and materials

    n/a.

    Notes

    Ethics approval and consent to participate

    n/a.

    Consent for publication

    n/a.

    Competing interests

    Dr. Pinato reports receiving grant funding in support of clinical trials from Merck Sharpe and Dohme and Bristol Myers Squibb and having received speaker/consultancy fees from ViiV Healthcare, Bayer and MiNa therapeutics outside the submitted work. There are no other conflicts of interest to report.

    ATB
    Antibiotic
    cATB
    Concurrent antibiotic treatment
    CD
    Cluster of Differentiation
    CTLA-4
    Cyotoxic T-Lymphocyte Associated Protein 4
    DCR
    Disease control rate
    EIOP
    Early Immunotherapy Period
    GI
    Gastrointestinal
    HR
    Hazard Ratio
    ICPI
    Immune-checkpoint inhibitors
    LPS
    Lipopolysaccharide
    MHC
    Major Histocompatibility Complex
    NOD1
    Nucleotide-binding oligomerization domain-containing protein 1
    NSCLC
    Non-small Cell Lung Cancer
    ORR
    Overall response rate
    OS
    Overall Survival
    pATB
    Prior antibiotic treatment
    PD
    Progressive Disease
    PD-1
    Programmed Cell-Death 1
    PD-L1
    Programmed Cell-Death Ligand 1
    PFS
    Progression-free survival
    RCC
    Renal Cell Carcinoma
    RR
    Response rate
    TH
    T-Helper cell
    TLR
    Toll-like receptors
    WIOP
    Whole immunotherapy Period

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