Prevention of lymphocyte apoptosis in septic mice with cancer increases mortality

Cancer and sepsis

Sepsis is one of the leading causes of death worldwide. While mortality is high regardless of inciting infection or comorbidities, mortality in patients with cancer and sepsis is significantly higher than mortality in patients with sepsis without cancer. Cancer patients are also significantly more likely to develop sepsis than the general population. The mechanisms underlying increased mortality in cancer and sepsis patients are multifactorial. Cancer treatment alters the host immune response and can increase susceptibility to infection. Preclinical data also suggests that cancer, in and of itself, increases mortality from sepsis with dysregulation of the adaptive immune system playing a key role. Further, preclinical data demonstrate that sepsis can alter subsequent tumor growth while tumoral immunity impacts survival from sepsis. Checkpoint inhibition is a well-accepted treatment for many types of cancer, and there is increasing evidence suggesting this may be a useful strategy in sepsis as well. However, preclinical studies of checkpoint inhibition in cancer and sepsis demonstrate results that could not have been predicted by examining either variable in isolation. As sepsis management transitions from a 'one size fits all' model to a more individualized approach, understanding the mechanistic impact of cancer on outcomes from sepsis represents an important strategy towards delivering on the promise of precision medicine in the intensive care unit.

TIGIT modulates sepsis-induced immune dysregulation in mice with preexisting malignancy

TIGIT is a recently identified coinhibitory receptor that is upregulated in the setting of cancer and functionally contributes to the impairment of antitumor immunity. However, its role during sepsis is unknown. Because patients with cancer are 10 times more likely to die of sepsis than previously healthy (PH) patients with sepsis, we interrogated the role of TIGIT during sepsis in the context of preexistent malignancy. PH mice or cancer (CA) mice inoculated with lung carcinoma cells were made septic by cecal ligation and puncture (CLP). We found that sepsis induced TIGIT upregulation predominantly on Tregs and NK cells in both PH and CA mice. Anti-TIGIT Ab improved the 7-d survival of CA septic mice but not PH mice after CLP. Treatment of CA septic animals but not PH septic animals with anti-TIGIT mAb significantly reversed sepsis-induced loss of CD4+ T cells, CD8+ T cells, Foxp3+ Treg, and CD19+ B cells in the spleen, which was the result of decreased caspase-3+ apoptotic cells. In sum, we found that anti-TIGIT Ab reversed sepsis-induced T cell apoptosis in CA septic mice and led to a significant survival benefit, suggesting its use as a potential immunotherapy to improve outcomes in septic patients with cancer.

Sepsis and Cancer: An Interplay of Friends and Foes

Sepsis and cancer share a number of pathophysiological features, and both result from the inability of the host's immune system to cope with the initial insult (tissue invasion by pathogens and malignant cell transformation, respectively). The common coexistence of both disorders and the profound related alterations in immune homeostasis raise the question of their mutual impact on each other's course. This translational review aims to discuss the interactions between cancer and sepsis supported by clinical data and the translation to experimental models. The dramatic improvement in cancer has come at a cost of increased risks of life-threatening infectious complications. Investigating the long-term outcomes of sepsis survivors has revealed an unexpected susceptibility to cancer long after discharge from the ICU. Nonetheless, it is noteworthy that an acute septic episode may harbor antitumoral properties under particular circumstances. Relevant double-hit animal models have provided clues to whether and how bacterial sepsis may impact malignant tumor growth. In sequential sepsis-then-cancer models, postseptic mice exhibited accelerated tumor growth. When using reverse cancer-then-sepsis models, bacterial sepsis applied to mice with cancer conversely resulted in inhibition or even regression of tumor growth. Experimental models thus highlight dual effects of sepsis on tumor growth, mostly depending on the sequence of insults, and allow deciphering the immune mechanisms and their relation with microorganisms.

Murine Pancreatic Cancer Alters T Cell Activation and Apoptosis and Worsens Survival After Cecal Ligation and Puncture

Patients with cancer who develop sepsis have a markedly higher mortality than patients who were healthy prior to the onset of sepsis. Potential mechanisms underlying this difference have previously been examined in two preclinical models of cancer followed by sepsis. Both pancreatic cancer/pneumonia and lung cancer/cecal ligation and puncture (CLP) increase murine mortality, associated with alterations in lymphocyte apoptosis and intestinal integrity. However, pancreatic cancer/pneumonia decreases lymphocyte apoptosis and increases gut apoptosis while lung cancer/CLP increases lymphocyte apoptosis and decreases intestinal proliferation. These results cannot distinguish the individual roles of cancer versus sepsis since different models of each were used. We therefore created a new cancer/sepsis model to standardize each variable. Mice were injected with a pancreatic cancer cell line and 3 weeks later cancer mice and healthy mice were subjected to CLP. Cancer septic mice had a significantly higher 10-day mortality than previously healthy septic mice. Cancer septic mice had increased CD4 T cells and CD8 T cells, associated with decreased CD4 T cell apoptosis 24 h after CLP. Further, splenic CD8+ T cell activation was decreased in cancer septic mice. In contrast, no differences were noted in intestinal apoptosis, proliferation, or permeability, nor were changes noted in local bacterial burden, renal, liver, or pulmonary injury. Cancer septic mice thus have consistently reduced survival compared with previously healthy septic mice, independent of the cancer or sepsis model utilized. Changes in lymphocyte apoptosis are common to cancer model and independent of sepsis model, whereas gut apoptosis is common to sepsis model and independent of cancer model. The host response to the combination of cancer and sepsis is dependent, at least in part, on both chronic comorbidity and acute illness.

2B4 but not PD-1 blockade improves mortality in septic animals with preexisting malignancy

In addition to its well-known beneficial effects for the treatment of several types of cancer, PD-1 blockade has shown encouraging results in preclinical models of sepsis and in a recent clinical trial in sepsis. Because cancer is the most common comorbidity in septic patients, here we aimed to determine the efficacy of PD-1 checkpoint blockade in the setting of sepsis complicated with preexisting malignancy. In a model of established lung cancer followed by cecal ligation and puncture-induced (CLP-induced) sepsis, PD-1 blockade exhibited no therapeutic effect on sepsis survival. This diminished efficacy of PD-1 blockade in cancer septic animals (septic animals with cancer) was characterized by a reduction in both the quality and quantity of PD-1+ responder cells. Specifically, CD8+ T cells isolated from cancer septic animals exhibited decreased CD28 expression and a reduction in the CXCR5+PD-1+ subset. In addition, flow cytometric analysis of T cells isolated from cancer septic animals revealed 2B4 as another possible checkpoint under these conditions. Administration of anti-2B4 to cancer septic animals significantly improved sepsis survival and was associated with increased T cell costimulatory receptor expression and decreased coinhibitory receptor expression. These results illustrate functions of coinhibitory receptors in the setting of sepsis complicated with cancer.

Apoptosis-induced lymphopenia in sepsis and other severe injuries

Sepsis and other acute injuries such as severe trauma, extensive burns, or major surgeries, are usually followed by a period of marked immunosuppression. In particular, while lymphocytes play a pivotal role in immune response, their functions and numbers are profoundly altered after severe injuries. Apoptosis plays a central role in this process by affecting immune response at various levels. Indeed, apoptosis-induced lymphopenia duration and depth have been associated with higher risk of infection and mortality in various clinical settings. Therapies modulating apoptosis represent an interesting approach to restore immune competence after acute injury, although their use in clinical practice still presents several limitations. After briefly describing the apoptosis process in physiology and during severe injuries, we will explore the immunological consequences of injury-induced lymphocyte apoptosis, and describe associations with clinically relevant outcomes in patients. Therapeutic perspectives targeting apoptosis will also be discussed.

Mechanisms of Intestinal Barrier Dysfunction in Sepsis

Intestinal barrier dysfunction is thought to contribute to the development of multiple organ dysfunction syndrome in sepsis. Although there are similarities in clinical course following sepsis, there are significant differences in the host response depending on the initiating organism and time course of the disease, and pathways of gut injury vary widely in different preclinical models of sepsis. The purpose of this study was to determine whether the timecourse and mechanisms of intestinal barrier dysfunction are similar in disparate mouse models of sepsis with similar mortalities. FVB/N mice were randomized to receive cecal ligation and puncture (CLP) or sham laparotomy, and permeability was measured to fluoresceinisothiocyanate conjugated-dextran (FD-4) six to 48 h later. Intestinal permeability was elevated following CLP at all timepoints measured, peaking at 6 to 12 h. Tight junction proteins claudin 1, 2, 3, 4, 5, 7, 8, 13, and 15, Junctional Adhesion Molecule-A (JAM-A), occludin, and ZO-1 were than assayed by Western blot, real-time polymerase chain reaction, and immunohistochemistry 12 h after CLP to determine potential mechanisms underlying increases in intestinal permeability. Claudin 2 and JAM-A were increased by sepsis, whereas claudin-5 and occludin were decreased by sepsis. All other tight junction proteins were unchanged. A further timecourse experiment demonstrated that alterations in claudin-2 and occludin were detectable as early as 1 h after the onset of sepsis. Similar experiments were then performed in a different group of mice subjected to Pseudomonas aeruginosa pneumonia. Mice with pneumonia had an increase in intestinal permeability similar in timecourse and magnitude to that seen in CLP. Similar changes in tight junction proteins were seen in both models of sepsis although mice subjected to pneumonia also had a marked decrease in ZO-1 not seen in CLP. These results indicate that two disparate, clinically relevant models of sepsis induce a significant increase in intestinal permeability mediated through a common pathway involving alterations in claudin 2, claudin 5, JAM-A, and occludin although model-specific differences in ZO-1 were also identified.

Pre-existing malignancy results in increased prevalence of distinct populations of CD4+ T cells during sepsis

The presence of pre-existing malignancy in murine hosts results in increased immune dysregulation and risk of mortality following a septic insult. Based on the known systemic immunologic changes that occur in cancer hosts, we hypothesized that the presence of pre-existing malignancy would result in phenotypic and functional changes in CD4⁺ T cell responses following sepsis. In order to conduct a non-biased, unsupervised analysis of phenotypic differences between CD4⁺ T cell compartments, cohorts of mice were injected with LLC1 tumor cells and tumors were allowed to grow for 3 weeks. These cancer hosts and age-matched non-cancer controls were then subjected to CLP. Splenocytes were harvested at 24h post CLP and flow cytometry and SPADE (Spanning-tree Progression Analysis of Density-normalized Events) were used to analyze populations of CD4⁺ cells most different between the two groups. Results indicated that relative to non-cancer controls, cancer mice contained more resting memory CD4⁺ T cells, more activated CD4⁺ effectors, and fewer naïve CD4⁺ T cells during sepsis, suggesting that the CD4⁺ T cell compartment in cancer septic hosts is one of increased activation and differentiation. Moreover, cancer septic animals exhibited expansion of two distinct subsets of CD4⁺ T cells relative to previously healthy septic controls. Specifically, we identified increases in both a PD-1^hi population and a distinct 2B4^hi BTLA^hi LAG-3^hi population in cancer septic animals. By combining phenotypic analysis of exhaustion markers with functional analysis of cytokine production, we found that PD-1⁺ CD4⁺ cells in cancer hosts failed to make any cytokines following CLP, while the 2B4⁺ PD-1^lo cells in cancer mice secreted increased TNF during sepsis. In sum, the immunophenotypic landscape of cancer septic animals is characterized by both increased CD4⁺ T cell activation and exhaustion, findings that may underlie the observed increased mortality in mice with pre-existing malignancy following sepsis.

Murine Lung Cancer Increases CD4+ T Cell Apoptosis and Decreases Gut Proliferative Capacity in Sepsis

BACKGROUND

Mortality is significantly higher in septic patients with cancer than in septic patients without a history of cancer. We have previously described a model of pancreatic cancer followed by sepsis from Pseudomonas aeruginosa pneumonia in which cancer septic mice have higher mortality than previously healthy septic mice, associated with increased gut epithelial apoptosis and decreased T cell apoptosis. The purpose of this study was to determine whether this represents a common host response by creating a new model in which both the type of cancer and the model of sepsis are altered.

METHODS

C57Bl/6 mice received an injection of 250,000 cells of the lung cancer line LLC-1 into their right thigh and were followed three weeks for development of palpable tumors. Mice with cancer and mice without cancer were then subjected to cecal ligation and puncture and sacrificed 24 hours after the onset of sepsis or followed 7 days for survival.

RESULTS

Cancer septic mice had a higher mortality than previously healthy septic mice (60% vs. 18%, p = 0.003). Cancer septic mice had decreased number and frequency of splenic CD4+ lymphocytes secondary to increased apoptosis without changes in splenic CD8+ numbers. Intestinal proliferation was also decreased in cancer septic mice. Cancer septic mice had a higher bacterial burden in the peritoneal cavity, but this was not associated with alterations in local cytokine, neutrophil or dendritic cell responses. Cancer septic mice had biochemical evidence of worsened renal function, but there was no histologic evidence of renal injury.

CONCLUSIONS

Animals with cancer have a significantly higher mortality than previously healthy animals following sepsis. The potential mechanisms associated with this elevated mortality differ significantly based upon the model of cancer and sepsis utilized. While lymphocyte apoptosis and intestinal integrity are both altered by the combination of cancer and sepsis, the patterns of these alterations vary greatly depending on the models used.

The Gut as the Motor of Multiple Organ Dysfunction in Critical Illness

All elements of the gut - the epithelium, the immune system, and the microbiome - are impacted by critical illness and can, in turn, propagate a pathologic host response leading to multiple organ dysfunction syndrome. Preclinical studies have demonstrated that this can occur by release of toxic gut-derived substances into the mesenteric lymph where they can cause distant damage. Further, intestinal integrity is compromised in critical illness with increases in apoptosis and permeability. There is also increasing recognition that microbes alter their behavior and can become virulent based upon host environmental cues. Gut failure is common in critically ill patients; however, therapeutics targeting the gut have proven to be challenging to implement at the bedside. Numerous strategies to manipulate the microbiome have recently been used with varying success in the ICU.

Phenotypic T cell exhaustion in a murine model of bacterial infection in the setting of pre-existing malignancy

While much of cancer immunology research has focused on anti-tumor immunity both systemically and within the tumor microenvironment, little is known about the impact of pre-existing malignancy on pathogen-specific immune responses. Here, we sought to characterize the antigen-specific CD8⁺ T cell response following a bacterial infection in the setting of pre-existing pancreatic adenocarcinoma. Mice with established subcutaneous pancreatic adenocarcinomas were infected with Listeria monocytogenes, and antigen-specific CD8⁺ T cell responses were compared to those in control mice without cancer. While the kinetics and magnitude of antigen-specific CD8⁺ T cell expansion and accumulation was comparable between the cancer and non-cancer groups, bacterial antigen-specific CD8⁺ T cells and total CD4⁺ and CD8⁺ T cells in cancer mice exhibited increased expression of the coinhibitory receptors BTLA, PD-1, and 2B4. Furthermore, increased inhibitory receptor expression was associated with reduced IFN-γ and increased IL-2 production by bacterial antigen-specific CD8⁺ T cells in the cancer group. Taken together, these data suggest that cancer's immune suppressive effects are not limited to the tumor microenvironment, but that pre-existing malignancy induces phenotypic exhaustion in T cells by increasing expression of coinhibitory receptors and may impair pathogen-specific CD8⁺ T cell functionality and differentiation.

The endogenous bacteria alter gut epithelial apoptosis and decrease mortality following Pseudomonas aeruginosa pneumonia

The endogenous bacteria have been hypothesized to play a significant role in the pathophysiology of critical illness, although their role in sepsis is poorly understood. The purpose of this study was to determine how commensal bacteria alter the host response to sepsis. Conventional and germ-free (GF) C57Bl/6 mice were subjected to Pseudomonas aeruginosa pneumonia. All GF mice died within 2 days, whereas 44% of conventional mice survived for 7 days (P = 0.001). Diluting the dose of bacteria 10-fold in GF mice led to similar survival in GF and conventional mice. When animals with similar mortality were assayed for intestinal integrity, GF mice had lower levels of intestinal epithelial apoptosis but similar levels of proliferation and intestinal permeability. Germ-free mice had significantly lower levels of tumor necrosis factor and interleukin 1β in bronchoalveolar lavage fluid compared with conventional mice without changes in systemic cytokine production. Under conventional conditions, sepsis unmasks lymphocyte control of intestinal epithelial apoptosis, because sepsis induces a greater increase in gut apoptosis in Rag-1 mice than in wild-type mice. However, in a separate set of experiments, gut apoptosis was similar between septic GF Rag-1 mice and septic GF wild-type mice. These data demonstrate that the endogenous bacteria play a protective role in mediating mortality from pneumonia-induced sepsis, potentially mediated through altered intestinal apoptosis and the local proinflammatory response. In addition, sepsis-induced lymphocyte-dependent increases in gut epithelial apoptosis appear to be mediated by the endogenous bacteria.

Mechanisms of methicillin-resistant Staphylococcus aureus pneumonia-induced intestinal epithelial apoptosis

Methicillin-resistant Staphylococcus aureus (MRSA) pneumonia-induced sepsis is a common cause of morbidity in the intensive care unit. Although pneumonia is initiated in the lungs, extrapulmonary manifestations occur commonly. In light of the key role the intestine plays in the pathophysiology of sepsis, we sought to determine whether MRSA pneumonia induces intestinal injury. FVB/N mice were subjected to MRSA or sham pneumonia and killed 24 h later. Septic animals had a marked increase in intestinal epithelial apoptosis by both hematoxylin-eosin and active caspase 3 staining. Methicillin-resistant S. aureus-induced intestinal apoptosis was associated with an increase in the expression of the proapoptotic proteins Bid and Bax and the antiapoptotic protein Bcl-xL in the mitochondrial pathway. In the receptor-mediated pathway, MRSA pneumonia induced an increase in Fas ligand but decreased protein levels of Fas, FADD, pFADD, TNF-R1, and TRADD. To assess the functional significance of these changes, MRSA pneumonia was induced in mice with genetic manipulations in proteins in either the mitochondrial or receptor-mediated pathways. Both Bid-/- mice and animals with intestine-specific overexpression of Bcl-2 had decreased intestinal apoptosis compared with wild-type animals. In contrast, Fas ligand-/- mice had no alterations in apoptosis. To determine if these findings were organism-specific, similar experiments were performed in mice subjected to Pseudomonas aeruginosa pneumonia. Pseudomonas aeruginosa induced gut apoptosis, but unlike MRSA, this was associated with increased Bcl-2 and TNF-R1 and decreased Fas. Methicillin-resistant S. aureus pneumonia thus induces organism-specific changes in intestinal apoptosis via changes in both the mitochondrial and receptor-mediated pathways, although the former may be more functionally significant.