Modeling the Repertoire of True Tumor-Specific MHC I Epitopes in a Human Tumor

DNA replication has a finite measurable error rate, net of repair, in all cells. Clonal proliferation of cancer cells leads therefore to accumulation of random mutations. A proportion of these mutational events can create new immunogenic epitopes that, if processed and presented by an MHC allele, may be recognized by the adaptive immune system. Here, we use probability theory to analyze the mutational and epitope composition of a tumor mass in successive division cycles and create a double Pölya model for calculating the number of truly tumor-specific MHC I epitopes in a human tumor. We deduce that depending upon tumor size, the degree of genomic instability and the degree of death within a tumor, human tumors have several tens to low hundreds of new, truly tumor-specific epitopes. Parenthetically, cancer stem cells, due to the asymmetry in their proliferative properties, shall harbor significantly fewer mutations, and therefore significantly fewer immunogenic epitopes. As the overwhelming majority of the mutations in cancer cells are unrelated to malignancy, the mutation-generated epitopes shall be specific for each individual tumor, and constitute the antigenic fingerprint of each tumor. These calculations highlight the benefits for personalization of immunotherapy of human cancer, and in view of the substantial pre-existing antigenic repertoire of tumors, emphasize the enormous potential of therapies that modulate the anti-cancer immune response by liberating it from inhibitory influences.     

Smoking, humoral immunity, and ulcerative colitis

Since ulcerative colitis predominantly affects non-smokers and ex-smokers we have examined the possibility that smoking modifies the humoral immune response to an antigenic challenge from the gut lumen. Gut lavage was used in healthy subjects and patients with ulcerative colitis, including both smokers and non-smokers. Antibodies in the intestinal fluid to Escherichia coli (five pooled serotypes), Candida albicans, gliadin, ovalbumin, and beta lactoglobulin were measured by ELISA to determine specific antibody concentrations of IgG, IgA, and IgM classes. Total IgG, IgA, and IgM were also measured in intestinal secretions and serum. In addition, circulating antibody concentrations of IgG, IgA, and IgM to three gut commensals - E coli (five pooled serotypes) C albicans, and Poroteus mirabilis were measured. There was a significant reduction in the IgA concentration in intestinal fluid of smokers with ulcerative colitis compared with healthy non-smoking controls. No other significant differences were found between the groups. Overall, these data are not consistent with the idea that smoking suppresses immune responses in the gut and suggest that the effect of smoking in colitis is mediated by another mechanism.     

A randomized double-blind placebo-controlled trial showing rifaximin to improve constipation by reducing methane production and accelerating colon transit: A pilot study

Objective

Gut microbe-derived methane may slow colon transit causing chronic constipation (CC). Effect of rifaximin on breath methane and slow-transit CC was evaluated.

Method

Bristol stool form, frequency, colon transit time (CTT), and breath methane were evaluated in 23 patients with CC (10 patients with constipation-predominant irritable bowel syndrome [IBS-C], 13 functional constipation, Rome III) and m-ethane production compared with 68 non-constipating IBS. Methane-producing CC (basal ≥?10 PPM and/or post-lactulose rise by >?10 PPM) was randomized (double-blind) to rifaximin (400-mg thrice/day, 2-weeks) or placebo. Stool forms, frequency, breath methane, and CTT were recorded afterward.

Results

CC patients tended to be methane producer more often (13/23 [56.5%] vs. 25/68 [36.5%], p?=?0.07) and had greater area under curve (AUC) for methane (2415 [435–23,580] vs. 1335 [0–6562.5], p?=?0.02) than non-constipating IBS. Methane producers (8/13 [61.5%]) and 5/10 (50%) non-producers had abnormal CTT (marker retention: 36-h, 53 [0–60] vs. 19 [8–56], p?=?0.06; 60-h, 16 [0–57] vs. 13 [3–56], p?=?0.877). Six and 7/13 methane producers were randomized to rifaximin and placebo, respectively. Rifaximin reduced AUC for methane more (6697.5 [1777.5–23,580] vs. 2617.5 [562.5–19,867.5], p?=?0.005) than placebo (3945 [2415–12,952.5] vs. 3720 [502.5–9210], p?=?0.118) at 1 month. CTT normalized in 4/6 (66.7%) on rifaximin (36-h retention, 54 [44–57] vs. 36 [23–60], p?=?0.05; 60-h, 45 [3–57] vs. 14 [11–51], p?=?0.09) but none on placebo (p?=?0.02) (36-h, 31 [0–60] vs. 25 [0–45], p?=?0.078; 60-h, 6 [0–54] vs. 12 [0–28], p?=?0.2). Weekly stool frequency (3 [1–9] and 7 [1–14], p?=?0.05) and forms improved with rifaximin than placebo.

Conclusion

Rifaximin improves CC by altering methane production and colon transit.

Trial registration

Clinical Trial Registry, India: REF/2012/01/003216

Open image in new window

? ?

     

Prospective Evaluation of Transseptal TMVR for Failed Surgical Bioprostheses: MITRAL Trial Valve-in-Valve Arm 1-Year Outcomes

ObjectivesThe aim of this study was to assess 1-year clinical outcomes among high-risk patients with failed surgical mitral bioprostheses who underwent transseptal mitral valve-in-valve (MViV) with the SAPIEN 3 aortic transcatheter heart valve (THV) in the MITRAL (Mitral Implantation of Transcatheter Valves) trial.BackgroundThe MITRAL trial is the first prospective study evaluating transseptal MViV with the SAPIEN 3 aortic THV in high-risk patients with failed surgical mitral bioprostheses.MethodsHigh-risk patients with symptomatic moderate to severe or severe mitral regurgitation (MR) or severe mitral stenosis due to failed surgical mitral bioprostheses were prospectively enrolled. The primary safety endpoint was technical success. The primary THV performance endpoint was absence of MR grade ≥2+ or mean mitral valve gradient ≥10 mm Hg (30 days and 1 year). Secondary endpoints included procedural success and all-cause mortality (30 days and 1 year).ResultsThirty patients were enrolled between July 2016 and October 2017 (median age 77.5 years [interquartile range (IQR): 70.3 to 82.8 years], 63.3% women, median Society of Thoracic Surgeons score 9.4% [IQR: 5.8% to 12.0%], 80% in New York Heart Association functional class III or IV). The technical success rate was 100%. The primary performance endpoint in survivors was achieved in 96.6% (28 of 29) at 30 days and 82.8% (24 of 29) at 1 year. Thirty-day all-cause mortality was 3.3% and was unchanged at 1 year. The only death was due to airway obstruction after swallowing several pills simultaneously 29 days post-MViV. At 1-year follow-up, 89.3% of patients were in New York Heart Association functional class I or II, the median mean mitral valve gradient was 6.6 mm Hg (interquartile range: 5.5 to 8.9 mm Hg), and all patients had MR grade ≤1+.ConclusionsTransseptal MViV in high-risk patients was associated with 100% technical success, low procedural complication rates, and very low mortality at 1 year. The vast majority of patients experienced significant symptom alleviation, and THV performance remained stable at 1 year.