Mismatch repair deficiency is not sufficient to elicit tumor immunogenicity

DNA mismatch repair deficiency (MMRd) is associated with a high tumor mutational burden (TMB) and sensitivity to immune checkpoint blockade (ICB) therapy. Nevertheless, most MMRd tumors do not durably respond to ICB and critical questions remain about immunosurveillance and TMB in these tumors. In the present study, we developed autochthonous mouse models of MMRd lung and colon cancer. Surprisingly, these models did not display increased T cell infiltration or ICB response, which we showed to be the result of substantial intratumor heterogeneity of mutations. Furthermore, we found that immunosurveillance shapes the clonal architecture but not the overall burden of neoantigens, and T cell responses against subclonal neoantigens are blunted. Finally, we showed that clonal, but not subclonal, neoantigen burden predicts ICB response in clinical trials of MMRd gastric and colorectal cancer. These results provide important context for understanding immune evasion in cancers with a high TMB and have major implications for therapies aimed at increasing TMB.

Abstract 2194: Rapid interrogation of colon cancer driver genes in vivo using split Cre and CRISPR-Cas9

Colorectal cancer (CRC) is the second leading cause of cancer-related deaths worldwide, with a five-year survival rate of only 63% with current treatment regimens. While genetically engineered mouse models (GEMMs) have contributed widely to our understanding of the underlying genetics and molecular mechanisms of the disease, major limitations exist. Most models of CRC lack flexibility to initiate focal adenocarcinomas with different genetic perturbations within the native microenvironment of the distal colon. Specifically, no autochthonous model of metastatic CRC compatible with in vivo CRISPR-Cas9 genome engineering has been described. Therefore, we developed a novel split Cre-recombinase system restricting activation of oncogenic KrasG12D and deletion of the tumor suppressor gene (TSG) Trp53 to Lgr5+ stem cells of the colon crypts. Importantly, these events are not only critical drivers of CRC progression and metastasis in mice and humans but can also lead to non-specific transformation of the surrounding colonic stroma. By expressing one half of Cre from the endogenous Lgr5 locus and other half via colonoscopy-guided submucosal injection of lentivirus, we restricted Cre-mediated recombination to enterocytes. Lentivirus was also engineered to express a single guide RNA (sgRNA) against Apc, facilitating tumor initiation via deletion of this critical CRC TSG in mice expressing Cas9. A second sgRNA was included to facilitate rapid interrogation of putative cancer driver genes. As proof-of-principle, we targeted Smad4, a critical suppressor of metastasis in CRC, and observed adenocarcinoma formation and liver metastases with complete recombination and editing of all targeted genes. To prioritize candidate TSGs for future in vivo interrogation, we applied MutSigCV to large human sequencing datasets and identified genes significantly co-mutated with APC and KRAS in CRC. Altogether, this faithful and tractable model of CRC can be used for rapid functional interrogation of TSGs and should accelerate downstream mechanistic and preclinical studies.

Citation Format: Daniel Zhang, Peter Westcott, Santiago Naranjo, Haley Hauck, William Rideout, Nate Sacks, Arjun Bhutkar, Justin Patten, Norihiro Goto, Joseph Sedlak, Tyler Jacks. Rapid interrogation of colon cancer driver genes in vivo using split Cre and CRISPR-Cas9 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2194.

Abstract P023: Mismatch repair deficiency is not sufficient to increase tumor immunogenicity

Deficient DNA mismatch repair (dMMR) in human cancer is associated with high tumor mutation burden (TMB), frameshift mutation-derived neoantigens, increased T cell infiltration, and remarkable responsiveness to immune checkpoint blockade (ICB) therapy. Nevertheless, about half of these tumors do not respond to ICB for unclear reasons. While tumor cell line transplant models of dMMR have helped solidify the importance of TMB in immune response, critical questions remain regarding the role of immune surveillance in the evolution of dMMR tumors induced in vivo. Here, we developed autochthonous mouse models of lung and colon cancer with highly efficient ablation of MMR genes via in vivo CRISPR/Cas9 targeting. Surprisingly, dMMR in these models did not result in increased immunogenicity or response to ICB, which we showed is driven by profound intratumoral heterogeneity. Studies in animals depleted of T cells further demonstrated that immune surveillance in dMMR tumors has no impact on TMB but shapes the clonal architecture of neoantigens. These results provide important context for understanding immune evasion in cancers with high TMB and have major implications for therapies aimed at increasing TMB.

Citation Format: Peter M. K. Westcott, Francesc M. Remolar, Olivia Smith, Haley Hauck, Nathan J. Sacks, Zackery A. Ely, Alex M. Jaeger, William M. Rideout, Arjun Bhutkar, Daniel Zhang, Mary C. Beytagh, Roderick T. Bronson, David A. Canner, Santiago Naranjo, Abbey Jin, J. J. Patten, Amanda M. Cruz, Isidro Cortes-Ciriano, Tyler Jacks. Mismatch repair deficiency is not sufficient to increase tumor immunogenicity [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P023.

Low neoantigen expression and poor T-cell priming underlie early immune escape in colorectal cancer

Immune evasion is a hallmark of cancer, and therapies that restore immune surveillance have proven highly effective in cancers with high tumor mutation burden (TMB) (e.g., those with microsatellite instability (MSI)). Whether low TMB cancers, which are largely refractory to immunotherapy, harbor potentially immunogenic neoantigens remains unclear. Here, we show that tumors from all patients with microsatellite stable (MSS) colorectal cancer (CRC) express clonal predicted neoantigens despite low TMB. Unexpectedly, these neoantigens are broadly expressed at lower levels compared to those in MSI CRC. Using a versatile platform for modulating neoantigen expression in CRC organoids and transplantation into the distal colon of mice, we show that low expression precludes productive cross priming and drives immediate T cell dysfunction. Strikingly, experimental or therapeutic rescue of priming rendered T cells capable of controlling tumors with low neoantigen expression. These findings underscore a critical role of neoantigen expression level in immune evasion and therapy response.

Abstract 2924: In vivo CRISPR/Cas9 models of microsatellite instable colon cancer reveal recurrent mutations in putative tumor supressor genes

Microsatellite instability is a hallmark of DNA mismatch repair (MMR)-deficient colorectal cancer (CRC), and is accompanied by genome-wide somatic hypermutation and enhanced immunogenicity. Clinical trials have demonstrated remarkable efficacy of immune checkpoint blockade (i.e. anti-PD-1) in treating MMR-deficient cancers, which is thought to be driven by an enhanced burden of mutation-derived tumor specific antigens (neoantigens). Despite these successes, tumor mutation burden is an imperfect clinical predictor of immunotherapy response, and major questions remain regarding the mechanistic role of neoantigens and other features of MMR-deficiency in the anti-tumor immune response. Notably, most genetically engineered mouse models (GEMMs) fail to recapitulate the mutation burden of their associated human cancer and lack prominent immune involvement, precluding careful study of these questions. To model microsatellite instability in colon cancer, we developed novel autochthonous GEMMs utilizing CRISPR/Cas9-based knockout of DNA MMR genes in the distal colon. Colonoscopy-guided submucosal injection was used to deliver lentivirus containing two single-guide RNAs (sgRNAs) against Apc (the initiating event in the majority of colon cancers) and MMR pathway genes (Msh2, Mlh1, Msh3, Msh6). Whole-exome sequencing of MMR-targeted colon tumors revealed a high mutation burden with signatures consistent with those found in MMR-deficient human cancer. In addition, sequencing revealed a number of recurrently mutated microsatellites, including those within putative tumor suppressor genes Asxl1, Acvr2a, and Acvr1b. To interrogate the functional relevance of these genes in MMR-deficient colon cancer, we developed a novel ex vivo organoid competition assay. Specifically, Apc null organoids expressing Cas9 were infected with lentivirus expressing the fluorophore mScarlet and sgRNAs targeting the putative tumor suppressor genes. Flow cytometry was used to longitudinally assess kinetics of the mScarlet positive fraction. Preliminary results suggest a selective advantage following deletion of Asxl1 and Acvr2a. Further assessment of tumorigenesis in vivo will be performed to confirm the role of these putative tumor suppressors. Altogether, these genetically manipulable systems can be used for rapid functional interrogation of tumor suppressor genes, facilitating downstream mechanistic studies and preclinical testing of therapies in these important subsets of CRC.

Citation Format: Daniel D. Zhang, Peter M. Westcott, Olivia Smith, Nate Sacks, Haley Hauck, Mary C. Beytagh, Abbey Jin, Tyler Jacks. In vivo CRISPR/Cas9 models of microsatellite instable colon cancer reveal recurrent mutations in putative tumor supressor genes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2924.

Epigenomic State Transitions Characterize Tumor Progression in Mouse Lung Adenocarcinoma

Regulatory networks that maintain functional, differentiated cell states are often dysregulated in tumor development. Here, we use single-cell epigenomics to profile chromatin state transitions in a mouse model of lung adenocarcinoma (LUAD). We identify an epigenomic continuum representing loss of cellular identity and progression toward a metastatic state. We define co-accessible regulatory programs and infer key activating and repressive chromatin regulators of these cell states. Among these co-accessibility programs, we identify a pre-metastatic transition, characterized by activation of RUNX transcription factors, which mediates extracellular matrix remodeling to promote metastasis and is predictive of survival across human LUAD patients. Together, these results demonstrate the power of single-cell epigenomics to identify regulatory programs to uncover mechanisms and key biomarkers of tumor progression.

Iliofemoral Crossover Bypass in High-Risk Patients: Management and Results

Between 1982 and 1986, 65 high-risk patients underwent iliofemoral cross over bypass (COBP) for unilateral iliac occlusion or stenosis; 53.8% complained of rest pain, 27.6% showed beginning gangrene, and 13.8% were operated on because of acute iliac occlusion. The proximal anastomosis was placed on the external iliac artery in 76.9%, the distal anastomosis on the profound femoral artery in 89.2%. The authors usually used PTFE grafts placed in the retrorec tal-preperitoneal space.

Doppler index rose by 0.3, flow improvement averaged 3 mL/100 mg tis sue/min; no steal phenomenon was observed. Perioperative mortality was 7.6%, limb salvage rate was 93.4%. After a mean interval of 31.3 months, 31.6% had died, and 8 patients had had to undergo major amputations. Cumulative pat ency rate after one year was 81 %, after two years 71 %, and after three years 60%.

The authors conclude that COBP is a valid alternative to anatomic iliac re construction in high-risk patients with unilateral iliac artery occlusion or steno sis.

Low levels of air pollution induce changes of lung function in a panel of schoolchildren

In search of sensitive screening parameters for assessing acute effects of ambient air pollutants in young schoolchildren, the impact of 8-h average air pollution before lung function testing was investigated by oscillatory measurements of resistance and spirometry with flow-volume loops. At a central elementary school in Linz, the capital of Upper Austria, 163 children aged 7-10 yrs underwent repeated examinations at the same time of day during 1 school year, yielding a total of 11-12 lung function tests per child. Associations to mass concentrations of particulate matter and nitrogen dioxide (NO(2)) measured continuously at a nearby monitoring station were tested, applying the Generalised Estimating Equations model. Reductions per 10 microg.m(-3) (both for particles and for NO(2)) were in the magnitude of 1% for most lung function parameters. The most sensitive indicator for acute effects of combustion-related pollutants was a change in maximal expiratory flow in small airways. NO(2) at concentrations below current standards reduced (in the multipollutant model) the forced expiratory volume in one second by 1.01%, maximal instantaneous forced flow when 50% of the forced vital capacity remains to be exhaled (MEF(50%)) by 1.99% and MEF(25%) by 1.96%. Peripheral resistance increased by 1.03% per 10 microg.m(-3) of particulate matter with a 50% cut-off aerodynamic diameter of 2.5 mum (PM(2.5)). Resistance is less influenced by the child's cooperation and should be utilised more often in environmental epidemiology when screening for early signs of small airway dysfunction from urban air pollution, but cannot replace the measurement of MEF(50%) and MEF(25%). In the basic model, the reduction of these parameters per 10 microg.m(-3) was highest for NO(2), followed by PM(1), PM(2.5) and PM(10), while exposure to coarse dust (PM(10)-PM(2.5)) did not change end-expiratory flow significantly. All acute effects of urban air pollution found on the lung function of healthy pupils were evident at levels below current European limit values for nitrogen dioxide. Thus, planned reduction of nitrogen dioxide emission (Euro 5; vehicles that comply with the emission limits as defined in Directive 99/96/EC) of 20% in 2010 would seem to be insufficient.

Multiple endometrial stromal nodules with sparse cysts and glands in the lung--a nodular variation of endometriosis that may mimic metastases of sarcoma

We report an unusual case of a nodular variation of pulmonary endometriosis. To our knowledge, there is no previous report on a morphological investigation of this entity. The etiology of this rare condition is still a matter of discussion. The well-circumscribed nodular mass is composed of cells identical to, or closely resembling, those of endometrial stroma containing sparse cysts and glands. Immunohistochemically, the cells showed an extensive co-expression of cytokeratin AE1/AE3 and vimentin and were highly positive for progesterone receptor (PRICA) and estrogen receptor (ERICA). Cells lining the cysts and glands as a monolayer were reactive for Ber-Ep4, cytokeratin Pan and cytokeratin AE1/AE3 and negative to all other markers used including PRICA and ERICA. The differential diagnosis of this entity included fibrous tumor of the pleura and metastatic low-grade-endometrial-stromal-sarcoma. The morphological findings are correlated with immunohistochemical studies and results of cell image analysis. This study details the clinicopathological features of the nodular variation of pulmonary endometriosis.

Revision of ambient air quality standards for PM?

Recent epidemiologic findings gave rise to new approaches in setting ambient air quality guidelines for particulate matter in various countries. Because of the complexity of this system defined by many parameters like size distribution, chemical composition, geometry, formation, hygroscopy, or concentration the toxicologic base for acute and chronic effects, especially in the low dose range, is not yet adequate for the formulation of air quality guidelines. Open questions as there is existence of a threshold, shape of the dose-response curve, causative models for the mechanisms and health effects outcome in connection with relatively low doses and groups at higher risks are still under discussion at an international level, thus making political decisions very difficult.

[Reduced lung function parameters after physical exertion in Austrian Alps in ozone concentrations below the legal warning limit]

The ambient ozone concentration has increased greatly over the past decades, which may lead to environmental health problems, especially during the summer. WHO guidelines recommend an 8 hour mean value of < or = 60 ppb ozone without health risk. The aim of the present study was to investigate if elevated zone concentrations at moderate altitudes in the Austrian Alps, characteristic of the situation in the summer months, influence pulmonary function after physical exercise. 24 male non-smokers (mean age 26.7 +/- 4 years) were investigated in the Tyrol (Pitztal) at a mean sea level of 2434 m. During a mountain-guide course lasting for 6 days the subjects were physically active all day long. Spirometry was performed in the morning and in the evening after 8 h of exercise. Ozone and PM10 concentrations were measured on site. The ozone 24 hour mean values ranged between 53 and 71 ppb. A mean decrease of 5.3% (p < 0.00001) was measured in forced vital capacity (FVC) and forced expiratory volume (FEV1) at t3,m in immediately after the highest ozone 24 hour mean value had been registered (71 ppb). A clinically relevant decrease of FVC and FEV1 > 10% was observed at t3,m in 35% of the subjects. However, a linear dependence of lung function changes on the ozone 8 hour mean values was demonstrable for all measuring points only in 10% of these subjects. In 90% of the subjects with a decrease of lung function parameters > 10%, this reduction was at least not monocausally linked to ozone.

Complicated pneumothorax: short- and long-term results of endoscopic fibrin pleurodesis

Complicated pneumothorax is defined as a recurrent or persistent air leak in the pleural interspace beyond 5 days despite adequate tube drainage. Up to now, this disorder could only be corrected by open thoracotomy. Endoscopic fibrin pleurodesis is shown to be a method that could obviate, in most cases, the need for thoracotomy. In the last 6 years, 138 of 153 patients presenting with complicated spontaneous pneumothorax were treated with this method. The fibrin sealant consists of 2 components: fibrinogen, factor XIII, and albumin dissolved in aprotinin (3,000 KIU/ml), and a thrombin calcium chloride solution, which is applied through the working channel of a thoracoscope and vaporized with nitrous oxide. In this observation period, 6 (4.4%) recurrences were observed, which were subsequently treated with thoracotomy; a second attempt at fibrin pleurodesis was not undertaken. In all cases, endoscopic sealing was followed by prompt reexpansion of the collapsed lung. Long-term follow-up was satisfactory, pulmonary function tests showed no signs of restrictive dysfunction, and pleural fibrosis was not observed on x-ray as reported in other modes of treatment. Following these results, it is concluded that this method is useful in cases of persistent, therapy-resistant, complicated spontaneous pneumothorax; its effects are durable and it has a low rate of recurrence. It produces a physiological healing process without damage to the pleura.

Parameters influencing carbon monoxide kinetics

Carbon monoxide exchange via the lungs can be satisfactorily described by mathematical models. More complex models allow consideration of various parameters influencing this process. Particularly for special situations like for high risk groups or for extreme environments such a model can be used successfully.

[Effect of serum factors on the intracellular killing of Trichophyton mentagrophytes microconidia by human polymorphonuclear leukocytes]

The rate of intracellular killing of T. mentagrophytes microconidia by polymorphonuclear leucocytes (PMNL) was investigated in 35 patients with anamnestic or actually present tinea infections under various conditions: in autologous serum, in serum of healthy controls, and in heat-inactivated serum. If the PMNL were incubated in serum from "immunologically experienced" persons, we found acceleration of the intracellular killing rate. Differences regarding killing rates were seen in the first hour of incubation (13 +/- 7.7% against 1 +/- 0.8%), becoming even more pronounced after heat-inactivation of the serum. Absorption of the patient's serum with T. mentagrophytes microconidia markedly reduced the rate of intracellular killing during the first hour of incubation, whereas microconidia pre-incubated in patients serum were readily killed even if a negative control serum was present.

Carbon monoxide uptake and the resulting carboxyhemoglobin in man

In order to calculate the carboxyhemoglobin concentration in human blood under various circumstances and for particular groups or individuals, the model proposed originally by Coburn and coworkers in a slightly revised form was tested. The relevant breathing parameters were measured as minute averages and used for computation of COHb time course. At the same time blood samples were taken and analysed for carboxyhemoglobin. For four different subjects, various breathing conditions and work rates the average deviation of experimental data from theoretical predictions is 7.4%. Some data are presented graphically. Excellent conformity of all the results indicate, that the model is suitable to show the influence of most physiological and breathing parameters on the dynamics of carbon monoxide uptake.

[Senear-Usher syndrome: acquired hemophilia caused by the occurrence of a factor VIII inhibitor]

A 25-year-old woman who had suffered from pemphigus for 2 years developed widespread, scalded skin-like lesions after stopping an immunosuppressive treatment. Histological and immunofluorescence studies confirmed the diagnosis of pemphigus erythematosus. Apart from IgG pemphigus antibodies, granular deposits for IgM at the dermoepidermal junction and circulating antinuclear IgM-antibodies could be detected. Despite of restarting an immunosuppressive regime, the patient developed severe hemophilia due to the occurrence of a factor VIII antiglobulin. Its possible immunopathologic basis is discussed.

[Candida infections in geriatrics-a current problem (author's transl)]

Investigations for candidiasis of the skin and mucous membranes were done in 191 probands over 65 years of age, of whon 187 were occupants of an old people's home and 4 were having in-patient treatment. In the homes being tested Candida infections of the skin and mucous membranes were very numerous (48% and 26% of those investigated) comparable with the epidemics of thrush in premature and newborn units in previous years. Even the localisation of candidiasis was remarkably similar to that in the newborn and infant age groups (Candida mycosis of the external ear and intercrural area, generalised skin candidiasis resembling Leiner's desquamating erythrodermia). The cause of cutaneous candidiasis in old age was in most cases faecal incontinence in chronically bedridden obese patients (intestinal colonisation with C. albicans). Diabetes mellitus, on the other hand, seems to play only a secondary role in the conditions of old people's homes.

Serological diagnosis of Candida albicans-balanitis and -balanoposthitis

The Candida hemagglutination test (Candida-HA-Test), the complement fixation, Candida immunofluorescent test (Candida-IF-Test) and the agglutination-test were performed in 34 patients suffering from genital candidosis and in 34 healthy controls. The results obtained were: Candida hemagglutination and complement fixation titers are raised to the same extent in patients suffering from Candida albicans-balanoposthitis when soluble polysaccharide antigens are used in both tests. The high titers indicate a great portion of mercaptoethanol susceptible antibodies in those subjects. When compared with controls, the hemagglutination titers are fourfold lower than those of the patients. There is a four-to-sixfold decrease of the hemagglutination titers performed after mercaptoethanol treatment of the sera in the patients. On the other hand, there is only a twofold decrease of hemagglutination titers in the controls. In chronically infected persons the hemagglutination titers are within the normal range or are raised insignificantly. There is only a twofold decrease in HA-titers after treatment of the sera with mercaptoethanol. On the other hand, the agglutination- and the Candida-IF-titers seem to be elevated as a rule in chronically infected. In those patients the gamma G- and the gamma A-titers are significantly raised, too. The results mentioned above are discussed with regard to their clinical significance.

[Fungus diagnostics in practice]

For the practising dermatologist the following examinations for the diagnosis of a fungus infection are recommended: unstained and stained preparations, as well as cultural differentiation of the causative organisms. In case of a first negative culture of a cutaneous mycosis histological examination is advised. The section should be stained by the PAS method. In all mycotic diseases of the skin, skin appendages and mucous membranes, which are resistant to therapy, an intracutaneous test with the specific antigen should be performed to examine the cellular immunity against the cultured organism.

[A rapid carboxyhemoglobin determination by means of non-dispersive ultra-red gas analysis (author's transl)]

A rapid and reliable method of carboxyhemoglobin determination is described. Hemoglobin-bound carbon monoxide is released chemically into a continuous nitrogen stream and transported to an infrared gas analyser. The total amount of released CO is determined electronically. 100% CO Hb values are obtained in the same way from diluted blood samples after flushing with pure CO in special saturation vessels. The method described yields results with a standard deviation of +/- 2.5%.