The elderly are more susceptible to infectious diseases. Mortality and morbidity from infections increase sharply over the age of 65 years. At the same time, the efficacy of vaccinations in the elderly is decreased. The elderly also have an increased incidence of cancer and inflammatory diseases. All the above indicate an age-related dysregulation of the immune system. Evidence suggests that the change in the humoral immune response with age is a qualitative rather than a quantitative one, i.e. it is the affinity and specificity of the antibody that changes, rather than the quantity of antibody produced. There are a number of possible causes of this failure, one of which is a defect in the mechanism of hypermutation of immunoglobulin genes. We have studied individual clonal responses within germinal centres of spleen and Peyer's patches in young and old patient groups. Our results indicate that there is no difference in the actual mechanism of hypermutation with age. There are, however, differences that are due either to a change in selection processes or to a change in the founder cells available for activation.

Recently, modulation of immune checkpoints has risen to prominence as a means to treat a number of solid malignancies, given the durable response seen in many patients and improved side effect profile compared to conventional chemotherapeutic agents. Several classes of immune checkpoint modulators have been developed. Here, we review current monoclonal antibodies directed against immune checkpoints that are employed in practice today. We discuss the history, mechanism, indications, and clinical data for each class of therapies. Furthermore, we review the challenges to durable tumor responses that are seen in some patients and discuss possible interventions to circumvent these barriers.

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758 Background: Accurate disease monitoring in PBC is instrumental for optimal therapeutic decision-making. CA 19-9 is the most utilized biomarker, though it has limited sensitivity/specificity and cannot be used in CA 19-9 non-secretors (n-S). ctDNA is a potentially helpful monitoring aid and surrogate for PBC n-S. Serial ctDNA could identify emerging resistant driver mutations. Our study prospectively examined ctDNA in PBC patients receiving treatment and retrospectively correlated it with clinical response. Methods: We performed genomic testing of ctDNA from metastatic PBC patients’ plasma from 11/2016 to 08/2019. This included 77 patients, of those, 18 had >1 ctDNA measurement with 49 correlative data points in total. Demographics, serial CA 19-9 levels and imaging results were collected. ctDNA analysis by parallel sequencing of amplified target genes (74) using Guardant360 was obtained. We correlated imaging and CA 19-9 responses with molecular alterations in patients receiving systemic chemotherapy. Descriptive statistics and logistic regression of the data was performed. Results: Of those included, median age was 66 yo, 50% male, and 92% pancreatic ductal adenocarcinoma. Baseline ctDNA showed 103 mutations including TP53 12.6%, KRAS 9.7%, MET 6.8%, APC, ARID1A and NF1 4.8% each, and others < 3%. 44% of patients were n-S with 75% having both TP53 and KRAS mutations. APC, ARID1A, and NF1 were only present in n-S. 91% vs 90% KRAS and 84% vs 78% TP53 of n-S and secretors (S), respectively, had correlation between ctDNA levels and imaging response. S TP53 and KRAS mutations correlated to CA19-9 levels and scans in 78% and 70% responses. New TP53 subclonal variant mutations were the most common resistance mutations for all progressions (75%). A logistic regression model of imaging progression on change in CA19-9 secretion and TP53 or KRAS expression was not statistically significant. Conclusions: Baseline ctDNA level changes ( TP53 and KRAS) can potentially act as a biomarker of response in PBC, specifically in n-S. TP53 subclonal mutations were the most common resistant alterations at progression and can be explored as future targets. This is being explored in larger prospective trials.