Clinical and genomic features of classical and basal transcriptional subtypes in pancreatic cancer.

PURPOSE: Transcriptional profiling of pancreatic cancers (PC) has defined two main transcriptional subtypes, classical and basal. Initial data suggest shorter survival for patients with basal tumors and differing treatment sensitivity to FOLFIRINOX (FFX) and gemcitabine nab-Paclitaxel (GnP) by transcriptional subtype. EXPERIMENTAL DESIGN: We examined 8,743 patients with RNA sequencing from PCs performed at Caris Life Sciences (Phoenix, AZ). Classical and basal subtypes were identified using PurIST algorithm on RNA-sequencing and two cohorts were analyzed: (1) Biomarker cohort included patients with complete molecular profiling data (n = 7,250); (2) Outcomes cohort included patients with metastatic disease with available survival outcomes (n=5,335). RESULTS: In the biomarker cohort, 3,063 tumors (42.2%) were strongly classical (SC), and 2,015 tumors (27.8%) were strongly basal (SB). SC and SB tumors showed strong associations with histologic phenotypes and biopsy site. SB tumors had higher rates of KRAS, TP53, and ARID1A mutations, lower rates of SMAD4 mutation, and transcriptional evidence of epithelial mesenchymal transition. Sixty of 77 cases (78%) maintained their transcriptional subtype between temporally and/or spatially disparate lesions. In the outcomes cohort, SB subtype was associated with shorter overall survival time, regardless of whether they received FFX or GnP as first line chemotherapy. Mutant KRAS allele type was prognostic of outcomes, however this impact was restricted to SC tumors, whereas all mutant KRAS alleles had similarly poor outcomes in SB tumors. CONCLUSIONS: SB subtype is a strong independent predictor of worse outcomes, irrespective of upfront chemotherapy regimen. Clinical trials should investigate PC transcriptional subtypes as a biomarker.

Blockade of IL1ß and PD1 with Combination Chemotherapy Reduces Systemic Myeloid Suppression in Metastatic Pancreatic Cancer with Heterogeneous Effects in the Tumor.

Innate inflammation promotes tumor development, although the role of innate inflammatory cytokines in established human tumors is unclear. Herein, we report clinical and translational results from a phase Ib trial testing whether IL1ß blockade in human pancreatic cancer would alleviate myeloid immunosuppression and reveal antitumor T-cell responses to PD1 blockade. Patients with treatment-naïve advanced pancreatic ductal adenocarcinoma (n = 10) were treated with canakinumab, a high-affinity monoclonal human antiinterleukin-1ß (IL1ß), the PD1 blocking antibody spartalizumab, and gemcitabine/n(ab)paclitaxel. Analysis of paired peripheral blood from patients in the trial versus patients receiving multiagent chemotherapy showed a modest increase in HLA-DR+CD38+ activated CD8+ T cells and a decrease in circulating monocytic myeloid-derived suppressor cells (MDSC) by flow cytometry for patients in the trial but not in controls. Similarly, we used patient serum to differentiate monocytic MDSCs in vitro and showed that functional inhibition of T-cell proliferation was reduced when using on-treatment serum samples from patients in the trial but not when using serum from patients treated with chemotherapy alone. Within the tumor, we observed few changes in suppressive myeloid-cell populations or activated T cells as assessed by single-cell transcriptional profiling or multiplex immunofluorescence, although increases in CD8+ T cells suggest that improvements in the tumor immune microenvironment might be revealed by a larger study. Overall, the data indicate that exposure to PD1 and IL1ß blockade induced a modest reactivation of peripheral CD8+ T cells and decreased circulating monocytic MDSCs; however, these changes did not lead to similarly uniform alterations in the tumor microenvironment.

Oncogenic Drivers and Therapeutic Vulnerabilities in KRAS Wild-Type Pancreatic Cancer.

PURPOSE: Approximately 8% to 10% of pancreatic ductal adenocarcinomas (PDAC) do not harbor mutations in KRAS. Understanding the unique molecular and clinical features of this subset of pancreatic cancer is important to guide patient stratification for clinical trials of molecularly targeted agents. EXPERIMENTAL DESIGN: We analyzed a single-institution cohort of 795 exocrine pancreatic cancer cases (including 785 PDAC cases) with a targeted multigene sequencing panel and identified 73 patients (9.2%) with KRAS wild-type (WT) pancreatic cancer. RESULTS: Overall, 43.8% (32/73) of KRAS WT cases had evidence of an alternative driver of the MAPK pathway, including BRAF mutations and in-frame deletions and receptor tyrosine kinase fusions. Conversely, 56.2% of cases did not harbor a clear MAPK driver alteration, but 29.3% of these MAPK-negative KRAS WT cases (12/41) demonstrated activating alterations in other oncogenic drivers, such as GNAS, MYC, PIK3CA, and CTNNB1. We demonstrate potent efficacy of pan-RAF and MEK inhibition in patient-derived organoid models carrying BRAF in-frame deletions. Moreover, we demonstrate durable clinical benefit of targeted therapy in a patient harboring a KRAS WT tumor with a ROS1 fusion. Clinically, patients with KRAS WT tumors were significantly younger in age of onset (median age: 62.6 vs. 65.7 years; P = 0.037). SMAD4 mutations were associated with a particularly poor prognosis in KRAS WT cases. CONCLUSIONS: This study defines the genomic underpinnings of KRAS WT pancreatic cancer and highlights potential therapeutic avenues for future investigation in molecularly directed clinical trials. See related commentary by Kato et al., p. 4527.

Utility of Established Prognostic Scoring Systems for Patients with Advanced Pancreatic Adenocarcinoma Enrolled in Immunotherapy-Based Early-Phase Clinical Trials.

BACKGROUND: Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy for which multiagent chemotherapy is the mainstay of treatment resulting in limited survival and symptomatic benefit. Treatment with immune checkpoint inhibitors (ICI) has proven effective in a growing number of solid tumors but has yet to show clinical benefit in patients with PDAC. Given the growing number of ICI-based clinical trials in development for patients with PDAC and lack of clinical benefit thus far with ICI-based therapies in these patients, we sought to (1) determine the outcomes of patients with PDAC treated with ICI-based therapies as part of an early phase clinical trial, (2) validate the utility of established prognostic scoring systems, and (3) identify novel prognostic factors in an attempt to better identify patients that would benefit from enrollment onto an ICI-based early phase clinical trial. METHODS: We conducted a single-center retrospective analysis of patients with advanced PDAC who were treated with ICI-based therapy as part of an early-phase clinical trial. RESULTS: Patients were only able to stay on study for a limited time due to disease progression and/or a change in performance status and had a poor overall survival. Established prognostic scoring systems were not effective in predicting outcomes in this patient population, but factors such as pre-treatment albumin neutrophil to lymphocyte ratio (NLC) may be helpful in patient selection. CONCLUSIONS: This study underscores the need for larger studies to help identify patient and tumor intrinsic factors that predict response to ICI-based therapies in patients with PDAC.

Emerging Role of Targeted Therapy in Metastatic Pancreatic Adenocarcinoma.

The aggressive biology of pancreatic ductal adenocarcinoma (PDAC), along with its limited sensitivity to many systemic therapies, presents a major challenge in the management of patients with metastatic PDAC. Over the past decade, the incorporation of combinatorial cytotoxic chemotherapy regimens has improved patient outcomes. Despite these advances, resistance to cytotoxic chemotherapy inevitably occurs, and there is a great need for effective therapies. A major focus of research has been to identify molecularly defined subpopulations of patients with PDAC who may benefit from targeted therapies that are matched to their molecular profile. Recent successes include the demonstration of the efficacy of maintenance PARP inhibition in PDAC tumors harboring deleterious BRCA1, BRCA2, and PALB2 alterations. In addition, while therapeutic targeting of KRAS was long thought to be infeasible, emerging data on the efficacy of KRAS G12C inhibitors have increased optimism about next-generation KRAS-directed therapies in PDAC. Meanwhile, KRAS wild-type PDAC encompasses a unique molecular subpopulation of PDAC that is enriched for targetable genetic alterations, such as oncogenic BRAF alterations, mismatch repair deficiency, and FGFR2, ALK, NTRK, ROS1, NRG1, and RET rearrangements. As more molecularly targeted therapies are developed, precision medicine has the potential to revolutionize the treatment of patients with metastatic PDAC.

Outcomes of patients with metastatic pancreatic cancer who progress on first restaging imaging.

BACKGROUND: Objective responses to first-line systemic chemotherapy in metastatic pancreatic cancer patients are seen in less than one third of cases. Unfortunately, a significant amount will have disease progression (PD) on their first restaging imaging. With patients' short life expectancy, it is crucial for clinicians to be prudent when deciding whom and when to treat. Our study aimed to evaluate outcomes of patients that progressed on their first restaging imaging on 1st line therapy. METHODS: We retrospectively analyzed patients diagnosed between 2010-2017 whose first restaging imaging demonstrated PD. The primary outcome was overall survival (OS) from metastatic diagnosis date to death. Patients who were lost to follow-up were excluded. RESULTS: Out of 262 total patients reviewed, 98 patients (37%) were included. Sixty-five (66%) received 2nd line therapy, and 33 (34%) did not. Reasons patients did not pursue 2nd line therapy were performance status (PS) decline, organ dysfunction, or patient choice for alternative therapy. Median ages for patients who did and did not receive 2nd line therapy were 61 and 67, respectively (P<0.001). More patients had a poor PS at the time of initial diagnosis in the non-2nd line therapy group (7.5% vs. 31.0%, P=0.021). Median OS for those receiving 2nd line therapy was 9 months (95% CI: 7-11 months) compared to 4 months (95% CI: 3-5 months) for those not receiving 2nd-line therapy (P<0.001). CONCLUSIONS: Although likely biased due to better performance status and younger age, our patients who progressed rapidly on 1st line therapy showed an OS benefit if they received 2nd line therapy. These results suggest that patients maintaining a good PS after immediate progression on 1st line therapy should be offered 2nd line therapy.

Immunotherapy in Gastrointestinal Malignancies.

Gastrointestinal (GI) cancers represent a heterogeneous group of malignancies, each with a unique tumor biology that in turn affects response to treatment and subsequent prognosis. The interplay between tumor cells and the local immune microenvironment also varies within each GI malignancy and can portend prognosis and response to therapy. Treatment with immune checkpoint inhibitors has changed the treatment landscape of various solid tumors including (but not limited to) renal cell carcinoma, melanoma, and lung cancer. Advances in the understanding between the interplay between the immune system and tumors cells have led to the integration of immunotherapy as standard of care in various GI malignancies. For example, immunotherapy is now a mainstay of treatment for tumors harboring defects in DNA mismatch repair proteins and tumors harboring a high mutational load, regardless of primary site of origin. Data from recent clinical trials have led to the integration of immunotherapy as standard of care for a subset of gastroesophageal cancers and hepatocellular carcinoma. Here, we outline the current landscape of immunotherapy in GI malignancies and highlight ongoing clinical trials that will likely help to further our understanding of how and when to integrate immunotherapy into the treatment of various GI malignancies.

Phase II Study of Ipilimumab in Men With Metastatic Prostate Cancer With an Incomplete Response to Androgen Deprivation Therapy.

Background: Phase 3 studies of immune checkpoint inhibitors have not shown a survival benefit in prostate cancer, but some patients have a profound anticancer response. Patients and Methods: We evaluated the efficacy of the CTLA-4 targeted agent, ipilimumab, in metastatic prostate cancer patients who had an incomplete biochemical response to initial androgen deprivation therapy (ADT) alone. Ten patients were enrolled, each treated with ipilimumab 10 mg/kg (every 3 weeks for up to 4 doses) with maintenance ipilimumab every 12 weeks for non-progressing patients. The primary endpoint was proportion of patients with an undetectable PSA. The total sample size was 30 patients, but there was an interim analysis planned at 10 for futility. If none of the 10 patients achieved an undetectable PSA, the study would be halted. Results: The study was halted at the interim analysis as none of the 10 patients achieved the primary endpoint, but 30% of patients demonstrated a >50% reduction in PSA, with one patient achieving a >90% reduction in PSA. Peripheral blood mononuclear cells (PBMC) examined by mass cytometry showed that patients with clinical responses had an increase in effector memory T-cell subsets as well as an increase in T-cell expression of T-bet, suggesting induction of a Th1 response. Conclusions: This study provides further evidence that ipilimumab has activity in some patients with prostate cancer and provides further rationale for the development of future studies aimed at identifying a subset of patients with CPRC that are more likely to derive a benefit from treatment with ipilimumab. Implications for Practice: There is insufficient evidence to use ipilimumab in prostate cancer in routine practice. Trial Registration: ClinicalTrials.gov, NCT01498978. Registered 26 December 2011. https://www.clinicaltrials.gov/ct2/show/NCT01498978?term=julie+graff&rank=3.

Pancreatic cancer.

Pancreatic cancer is a highly fatal disease with a 5-year survival rate of approximately 10% in the USA, and it is becoming an increasingly common cause of cancer mortality. Risk factors for developing pancreatic cancer include family history, obesity, type 2 diabetes, and tobacco use. Patients typically present with advanced disease due to lack of or vague symptoms when the cancer is still localised. High quality computed tomography with intravenous contrast using a dual phase pancreatic protocol is typically the best method to detect a pancreatic tumour and to determine surgical resectability. Endoscopic ultrasound is an increasingly used complementary staging modality which also allows for diagnostic confirmation when combined with fine needle aspiration. Patients with pancreatic cancer are often divided into one of four categories based on extent of disease: resectable, borderline resectable, locally advanced, and metastatic; patient condition is also an important consideration. Surgical resection represents the only chance for cure, and advancements in adjuvant chemotherapy have improved long-term outcomes in these patients. Systemic chemotherapy combinations including FOLFIRINOX (5-fluorouracil, folinic acid [leucovorin], irinotecan, and oxaliplatin) and gemcitabine plus nab-paclitaxel remain the mainstay of treatment for patients with advanced disease. Data on the benefit of PARP inhibition as maintenance therapy in patients with germline BRCA1 or BRACA2 mutations might prove to be a harbinger of advancement in targeted therapy. Additional research efforts are focusing on modulating the pancreatic tumour microenvironment to enhance the efficacy of the immunotherapeutic strategies.

RNA interference screening methods to identify proliferation determinants and mechanisms of resistance to immune attack.

We have used RNA interference (RNAi) screening technology to reveal unknown components of biological signaling pathways including survival mechanisms of estrogen-independent breast cancer cell growth and cancer cell resistance to immune attack. In this chapter, a detailed protocol describing the use of RNAi screening to identify factors important for the proliferation of estrogen-independent MCF7 breast cancer cells will be described. Resistance to therapies that target the estrogen pathway remains a challenge in the treatment of estrogen receptor-positive breast cancer. To address this challenge, small interfering-RNA (siRNA)-based libraries targeting an estrogen receptor (ER)- and aromatase-centered network, including 631 genes relevant to estrogen signaling, was designed and constructed for RNAi screening. This protocol will include the following parts: (1) selection of RNAi transfection reagent for specific cells; (2) optimization of RNAi screening conditions using Z'-factor; (3) procedure of ER-network gene siRNA library screening using automated machines under optimized experimental conditions; and (4) method of analysis for RNAi screening data to identify specific determinants important for cell proliferation. 46 genes were found to be selectively required for the survival of estrogen-independent MCF7-derived cells.

RNA Interference Screening to Identify Proliferation Determinants in Breast Cancer Cells.

RNAi screening technology has revealed unknown determinants of various biological signaling pathways in biomedical studies. This protocol provided detailed information about how to use RNAi screening to identify proliferation determinants in breast tumor cells. siRNA-based libraries targeting against Estrogen receptor (ER)-network, including 631 genes relevant to estrogen signaling, was constructed for screening in breast cancer cells. Briefly, reverse transfection of siRNA induced transient gene knockdown in MCF7 cells. First, the transfection reagent for MCF7 cells was selected. Next, the Z'-score assay was used to monitor if screening conditions yielded efficiently. Then, the ER-network siRNA library screening was preceded by automatic machines under optimized experimental conditions.

Synergistic innate and adaptive immune response to combination immunotherapy with anti-tumor antigen antibodies and extended serum half-life IL-2.

Cancer immunotherapies under development have generally focused on either stimulating T cell immunity or driving antibody-directed effector functions of the innate immune system such as antibody-dependent cell-mediated cytotoxicity (ADCC). We find that a combination of an anti-tumor antigen antibody and an untargeted IL-2 fusion protein with delayed systemic clearance induces significant tumor control in aggressive isogenic tumor models via a concerted innate and adaptive response involving neutrophils, NK cells, macrophages, and CD8(+) T cells. This combination therapy induces an intratumoral "cytokine storm" and extensive lymphocyte infiltration. Adoptive transfer of anti-tumor T cells together with this combination therapy leads to robust cures of established tumors and development of immunological memory.

IL4 limits the efficacy of tumor-targeted antibody therapy in a murine model.

Tumor-targeted antibody therapy has had a major impact on reducing morbidity and mortality in a wide range of cancers. Antibodies mediate their antitumor activity in part by activating immune effector cells; however, the tumor microenvironment (TME) is enriched with cellular and soluble mediators that actively suppress generation of antitumor immunity. Here, we investigate the potential of prospectively identifying and neutralizing an immunomodulatory soluble mediator within the TME to enhance therapeutic efficacy of the HER2-directed antibody trastuzumab. Using the D5-HER2 cell line and an immunocompetent human HER2 transgenic animal (hmHER2Tg) in which human HER2 is a self-antigen, we determined that IL4 was present in the TME and produced by both tumor and stromal cells. A siRNA-based screening approach identified STAT5A as a novel negative regulator of IL4 production by D5-HER2 tumor cells. Furthermore, IL4 neutralization using the anti-IL4 antibody 11B11 enhanced the efficacy of trastuzumab and modulated the TME. For example, IL4 neutralization resulted in reduced levels of myeloid chemoattractants CCL2, CCL11, and CXCL5 in the TME. Combination therapy with 11B11 and trastuzumab resulted in a reduction of tumor-infiltrating CD11b(+)CD206(+) myeloid cells compared with monotherapy. These data suggest that IL4 neutralization enhances the efficacy of trastuzumab by influencing the phenotype of myeloid cells within the TME and provide further rationale for combining tumor-targeted antibody therapy with agents that neutralize factors in the TME that suppress generation of productive antitumor immune responses.

Monoclonal antibodies for the treatment of cancer.

Over the past decade, the clinical utility of monoclonal antibodies has been realized and antibodies are now a mainstay for the treatment of cancer. Antibodies have the unique capacity to target and kill tumor cells while simultaneously activating immune effectors to kill tumor cells through the complement cascade or antibody-dependent cellular cytotoxicity (ADCC). This multifaceted mechanism of action combined with target specificity underlies the capacity of antibodies to elicit anti-tumor responses while minimizing the frequency and magnitude of adverse events. This review will focus on mechanisms of action, clinical applications and putative mechanisms of resistance to monoclonal antibody therapy in the context of cancer.

Monoclonal antibodies: versatile platforms for cancer immunotherapy.

Antibodies are important therapeutic agents for cancer. Recently, it has become clear that antibodies possess several clinically relevant mechanisms of action. Many clinically useful antibodies can manipulate tumour-related signalling. In addition, antibodies exhibit various immunomodulatory properties and, by directly activating or inhibiting molecules of the immune system, antibodies can promote the induction of antitumour immune responses. These immunomodulatory properties can form the basis for new cancer treatment strategies.

Vaccine prevention of cancer: can endogenous antigens be targeted?

This perspective on the report by Beatty et al. in this issue of the journal (beginning on page 438) discusses the prevention of cancer through vaccination strategies that target antigens associated with tumor promotion and progression. Such approaches were first developed for treating cancer. We address cancer vaccination in the context of a mouse model of inflammatory bowel disease expressing MUC1, an epithelial mucin aberrantly expressed during chronic inflammation and in colorectal carcinogenesis, and in a broader context that includes the potential of targeting the tumor microenvironment for immunoprevention in humans. Obstacles in developing effective cancer vaccines, including antigen selection, immunoediting, and tumor-mediated immunosuppression, are also discussed.

Genetic evidence for the role of Erk activation in a lymphoproliferative disease of mice.

Germline mutation of the linker for activation of T cells (LAT) gene at the phospholipase C-gamma1 (PLC-gamma1)-binding site leads to a fatal lymphoproliferative disease in mice. The hyperactivated T cells that develop in these mice have defective T-cell antigen receptor (TCR)-induced calcium flux but enhanced mitogen-activated protein kinase (MAPK) activation. We used genetic analysis to investigate genes whose products might suppress MAPK activation and lymphoproliferative disease in LAT mutant mice. B-lymphocyte adaptor molecule of 32 kDa (Bam32) is a known mediator of MAPK activation in B cells. We recently reported that in CD4(+) T cells, Bam32 deficiency decreased MAPK activation and specifically extracellular-signal-regulated kinase (Erk) signaling, following TCR stimulation. By crossing the Bam32 null mutation onto the LAT knock-in background, we found that the Bam32 null mutation delayed the onset and decreased the severity of lymphoproliferative disease in LAT knock-in mice. The pulmonary lymphocyte infiltration seen in LAT knock-in mice was also markedly decreased in double-mutant mice. Additionally, Erk activation was diminished in LAT knock-in Bam32 knockout CD4(+) T cells. To more accurately determine the role of Erk in this delay of lymphoproliferative disease, we also bred a transgenic, hypersensitive Erk allele (the Erk2 sevenmaker mutant) onto the LAT knock-in Bam32 knockout double-mutant background. These triple transgenic mice demonstrated a role for Erk activation in lymphoproliferative disease caused by the LAT knock-in mutation.

Cryptococcal urease promotes the accumulation of immature dendritic cells and a non-protective T2 immune response within the lung.

Urease, a major virulence factor for Cryptococcus neoformans, promotes lethal meningitis/encephalitis in mice. The effect of urease within the lung, the primary site of most invasive fungal infections, is unknown. An established model of murine infection that utilizes either urease-producing (wt and ure1::URE1) or urease-deficient (ure1) strains (H99) of C. neoformans was used to characterize fungal clearance and the resultant immune response evoked by these strains within the lung. Results indicate that mice infected with urease-producing strains of C. neoformans demonstrate a 100-fold increase in fungal burden beginning 2 weeks post-infection (as compared with mice infected with urease-deficient organisms). Infection with urease-producing C. neoformans was associated with a highly polarized T2 immune response as evidenced by increases in the following: 1) pulmonary eosinophils, 2) serum IgE levels, 3) T2 cytokines (interleukin-4, -13, and -4 to interferon-gamma ratio), and 4) alternatively activated macrophages. Furthermore, the percentage and total numbers of immature dendritic cells within the lung-associated lymph nodes was markedly increased in mice infected with urease-producing C. neoformans. Collectively, these data define cryptococcal urease as a pulmonary virulence factor that promotes immature dendritic cell accumulation and a potent, yet non-protective, T2 immune response. These findings provide new insights into mechanisms by which microbial factors contribute to the immunopathology associated with invasive fungal disease.

Bam32: a novel mediator of Erk activation in T cells.

Bam32 (B lymphocyte adapter molecule of 32 kDa) is an adapter protein expressed in some hematopoietic cells including B and T lymphocytes. It was previously shown that Bam32-deficient mice have defects in various aspects of B cell activation including B cell receptor (BCR)-induced Erk activation, BCR-induced proliferation and T-independent antibody responses. In this study, we have examined the role of Bam32 in T cell activation using Bam32-deficient mice. By comparing CD4(+) T cells from lymph nodes of wild-type and Bam32-deficient mice, we found that Bam32 was required for optimal TCR-induced Erk activation, cytokine production, proliferation and actin-mediated spreading of CD4(+) T cells. These results indicate a novel pathway to Erk activation in T cells involving the adapter protein Bam32.

Effect of laparotomy on clearance and cytokine induction in Staphylococcus aureus infected lungs.

RATIONALE: Staphylococcus aureus is a major pathogen complicating postsurgical care. OBJECTIVES: To test the effect of sterile laparotomy (LAP) on pulmonary clearance of S. aureus in a murine model. METHODS: Control and LAP mice were infected intranasally with 10(8) cfu of S. aureus. Microbial clearance, pulmonary leukocyte recruitment, and cytokine profiles were compared between the groups. Antibody neutralization or cytokine gene knockout mice were used to evaluate the role of cytokines. MEASUREMENTS AND MAIN RESULTS: Laparotomy resulted in a 10-fold increase in S. aureus lung colony-forming units on Days 2 and 3 postinfection. Both groups cleared the infection by Day 4. No defect in leukocyte recruitment into the lungs was observed in infected LAP animals; however, an increase in the number of Mac-3-positive cells and a significant decrease of cells with high surface expression of Fc-gammaR suggest suboptimal activation of leukocytes in the lungs of infected LAP animals. Infected LAP mice had decreased expression of interferon (IFN)-gamma and increased expression of mRNA for IL-13 in the lungs on Day 1 postinfection and decreased levels of IL-6, keratinocyte-derived chemokine (KC), and macrophage inflammatory protein-2 (MIP-2) in bronchoalveolar lavage at Day 2 postinfection. Neutralization of IFN-gamma mimicked the effect of LAP with impaired clearance on Day 2. CONCLUSIONS: Sterile LAP induced temporary deactivation of innate immune responses to pulmonary S. aureus challenge. Impaired microbial clearance was accompanied by altered cytokine expression and suboptimal activation of pulmonary leukocytes. Lack of early IFN-gamma induction in the infected lungs of LAP animals is a likely mechanism contributing to the observed phenotype.