DNA Repair Mechanisms, Protein Interactions and Therapeutic Targeting of the MRN Complex.

Repair of a DNA double-strand break relies upon a pathway of proteins to identify damage, regulate cell cycle checkpoints, and repair the damage. This process is initiated by a sensor protein complex, the MRN complex, comprised of three proteins-MRE11, RAD50, and NBS1. After a double-stranded break, the MRN complex recruits and activates ATM, in-turn activating other proteins such as BRCA1/2, ATR, CHEK1/2, PALB2 and RAD51. These proteins have been the focus of many studies for their individual roles in hereditary cancer syndromes and are included on several genetic testing panels. These panels have enabled us to acquire large amounts of genetic data, much of which remains a challenge to interpret due to the presence of variants of uncertain significance (VUS). While the primary aim of clinical testing is to accurately and confidently classify variants in order to inform medical management, the presence of VUSs has led to ambiguity in genetic counseling. Pathogenic variants within MRN complex genes have been implicated in breast, ovarian, prostate, colon cancers and gliomas; however, the hundreds of VUSs within MRE11, RAD50, and NBS1 precludes the application of these data in genetic guidance of carriers. In this review, we discuss the MRN complex's role in DNA double-strand break repair, its interactions with other cancer predisposing genes, the variants that can be found within the three MRN complex genes, and the MRN complex's potential as an anti-cancer therapeutic target.

A diversity outbred F1 mouse model identifies host-intrinsic genetic regulators of response to immune checkpoint inhibitors.

Immune checkpoint inhibitors (ICI) have improved outcomes for a variety of malignancies; however, many patients fail to benefit. While tumor-intrinsic mechanisms are likely involved in therapy resistance, it is unclear to what extent host genetic background influences response. To investigate this, we utilized the Diversity Outbred (DO) and Collaborative Cross (CC) mouse models. DO mice are an outbred stock generated by crossbreeding eight inbred founder strains, and CC mice are recombinant inbred mice generated from the same eight founders. We generated 207 DOB6F1 mice representing 48 DO dams and demonstrated that these mice reliably accept the C57BL/6-syngeneic B16F0 tumor and that host genetic background influences response to ICI. Genetic linkage analysis from 142 mice identified multiple regions including one within chromosome 13 that associated with therapeutic response. We utilized 6 CC strains bearing the positive (NZO) or negative (C57BL/6) driver genotype in this locus. We found that 2/3 of predicted responder CCB6F1 crosses show reproducible ICI response. The chromosome 13 locus contains the murine prolactin family, which is a known immunomodulating cytokine associated with various autoimmune disorders. To directly test whether prolactin influences ICI response rates, we implanted inbred C57BL/6 mice with subcutaneous slow-release prolactin pellets to induce mild hyperprolactinemia. Prolactin augmented ICI response against B16F0, with increased CD8 infiltration and 5/8 mice exhibiting slowed tumor growth relative to controls. This study highlights the role of host genetics in ICI response and supports the use of F1 crosses in the DO and CC mouse populations as powerful cancer immunotherapy models.

Paul Holland: contributions to transfusion medicine.

Paul Holland began his career in transfusion medicine in 1963 as an assistant to Dr. Paul Schmidt in the Blood Bank at the National Institutes of Health (NIH). He served at the NIH for 20 years and retired in 1983 with the rank of Captain in the Public Health Service. He subsequently became the Medical Director/CEO of the Sacramento Medical Foundation Blood Center, now Blood Source, a position he held for the next 21 years. Paul Holland has authored/co-authored 265 articles, chapters and monographs, mostly concerning issues relating to either viral hepatitis or HIV. In addition to his research career, Paul was a very active educator, having contributed importantly to the development of many current thought leaders in transfusion medicine. His distinguished career also included important administrative roles in national and international organizations relevant to transfusion medicine. He also was the recipient of many honors and awards which has won him wide-spread renown and the respect of his many colleagues.

The original blood group pioneers: the Hirszfelds.

Ludwik Hirszfeld, together with his wife Hanka, was the first to study the blood groups in large numbers of subjects (soldiers) during World War I at the Macedonian front. They found significant differences in the distribution of the ABO blood groups, that is, type A was more common in soldiers from North Central Europe, whereas type B was more common in those from Eastern Europe. Their data were later (in the 1920s and 1930s) misused by German nationalists to support the concept of Aryan supremacy. The Hirszfelds also discovered Salmonella paratyphi C, now known as Salmonella hirzfeldi. Their landmark studies drew others to this new field of seroanthropology, most notably Arthur Mourant, as well as Robin Race and Ruth Sanger, who wrote "Blood Groups in Man" detailing the antigenic differences among various peoples.

Sickle cell disease: two fatalities due to bone marrow emboli in patients with acute chest syndrome.

Acute chest syndrome (ACS) in patients with sickle cell disease (SCD) is a common complication contributing to death. ACS can present as sudden, unexpected death, and the medical history of SCD may not be immediately available for the medical examiner. Forensic implications for ACS are more likely to be encountered in patients with the HgbSC variant of SCD because the presence of a spleen may obscure recognition of SCD. Pathologists commonly observe small bone marrow emboli within the lung vasculature postmortem after trauma or vigorous cardiopulmonary resuscitation. Consequently, the finding of pulmonary marrow emboli in ACS may be dismissed as incidental and nonpathologic. Pulmonary marrow emboli cause ACS in patients with SCD, when there is parvoviral infection with marrow necrosis. Pulmonary marrow embolism in ACS has special significance in forensic pathology. Forensic pathologists investigate sudden, unexpected deaths during exertion, such as athletics, police pursuit, or military training. A causal relationship linking sickling hemoglobinopathy with physical exertion and sudden death has been reported. In the absence of a specific and timely medical history of SCD, and with a normal or enlarged spleen in patients with HgbSC, pathologists may wrongly dismiss bone marrow emboli as consequences of cardiopulmonary resuscitation, when those emboli might actually have been causative of fatal ACS.

Transfusion-related acute lung injury: a thrombotic thrombocytopenic purpura treatment-associated case report and concise review.

Blood products are frequently required immediately prior to, during, or just after an apheresis procedure. Transfusion-related acute lung injury (TRALI) is now the leading cause of transfusion-related mortality, surpassing ABO-incompatible hemolytic reactions. The reported incidence of TRALI varies but is estimated at 1 in 5,000 transfusions. The true incidence could be higher because of under-reporting and under-diagnosis. Plasma is the most frequently implicated blood product. While the pathogenesis of TRALI appears multifactorial, one contributing factor seems to be donor antibodies to cognate recipient neutrophil antigens. Biologically active neutrophil-priming substances may also play a role. New diagnostic criteria have recently been proposed to aid in the diagnosis of TRALI. We report a thrombotic thrombocytopenic purpura (TTP) treatment-associated case of TRALI and review the history, pathogenesis, diagnosis and management of this syndrome. Current risk reduction strategies are also discussed.

Arsine toxicity treated with red blood cell and plasma exchanges.

BACKGROUND: Acute toxicity due to inhalation of arsine gas (AsH(3)) has no known antidote. Exchange transfusion may be beneficial, and dialysis is often required because arsine may cause acute intravascular hemolysis and renal failure. A patient with arsine toxicity has recently been treated by both red blood cell exchange (RBC-E) and plasma exchange (PE) therapy and our experience is reported. CASE REPORT: A 46-year-old man was accidentally and unknowingly exposed to arsine gas while observing an industrial procedure. Within 6 hours he developed fatigue, nausea, vomiting, and tingling in his extremities and voided dark urine. He quickly developed renal failure secondary to acute arsine toxicity (arsenic level, 1250 microg/L). Laboratory findings were a hematocrit level of 24 percent; blood urea nitrogen and creatinine, 84 and 5.5 mg per dL, respectively; bilirubin, 9.1 mg per dL; indirect bilirubin, 6.8 mg per dL; haptoglobin, less than 6 (normal, 30-200); and lactic dehydrogenase, 10,413 units per L (normal, 265-580). An emergent 1-vol RBC-E transfusion by continuous-flow method revealed dramatic black, grossly hemolyzed plasma. After two additional RBC-E and two PE and daily hemodialysis, he completely recovered over the course of 1 month. CONCLUSION: Patients with arsine toxicity resulting in intravascular hemolysis should receive RBC-E as soon as possible. In addition, PE may be beneficial in removing the components of RBC lysis and further reducing arsenic levels.

Thrombotic thrombocytopenic purpura: yesterday, today, tomorrow.

Although much has been learned about the pathophysiologic process of thrombotic thrombocytopenic purpura (TTP), both diagnostically and therapeutically, since its initial description by Moschcowitz in 1924, its etiology and treatments remain, in many instances, problematic. Thrombotic thrombocytopenic purpura remains a rare entity whose etiology is usually unknown, but several drugs and infections have now been implicated in its development (i.e. Cyclosporine A, Mitomycin-C, Ticlopidine, Simvastatin, Lipitor, Plavix, FK 506, Rapamune (sirolimus), HIV). Although its treatment by plasma exchange has gained worldwide acceptance since the late 1970s, the optimal exchange media is not known, nor the volume and duration of exchange therapy, nor appropriate salvage therapy(ies). Without the benefit of randomized controlled trials, its treatment, to a large extent, remains not evidence-based but 'eminence-based', making the same mistakes with increasing confidence over an impressive number of years.

Drug-induced thrombotic thrombocytopenic purpura/hemolytic uremic syndrome: a concise review.

An extensive variety of drugs have been associated with thrombotic thrombocytopenic purpura and hemolytic uremic syndrome (TTP/HUS). Although a direct causal effect has usually not been proven, the cumulative evidence linking several drugs with TTP/HUS is strong. This paper reviews several categories of drugs including antineoplastics, immunotherapeutics and anti-platelet agents that have been reported to induce TTP/HUS. The pathogenesis of drug-induced TTP/HUS and the effectiveness of treatment regimens are also reviewed. A consensus on diagnostic criteria to accurately and consistently diagnose drug-induced TTP is needed.

Evidence-based medicine for apheresis: an ongoing challenge.

Although much has been learned about the pathophysiologic process of thrombotic thrombocytopenic purpura (TTP) since Moschcowitz's initial description in 1924, its etiology and treatments remain problematic. We treated our first patient with TTP by plasma exchange in 1975 and have now treated over 160 patients. We report our experience exchanging patients using FFP, solvent detergent (SD) and cryopoor plasma as the exchange media. Most patients experience allergic reactions, some severe, during the course of treatment. However, use of SD plasma virtually eliminates all allergic reactions. Splenectomy was a much more common treatment prior to plasma exchange, but can still be a useful treatment option for some refractory patients. Recombinant ADAMTS-13 can hopefully provide not only more useful diagnostic assays but also could provide specific and more efficacious treatment of patients with both acquired and familial forms of TTP.

What are appropriate initial and salvage therapies for patients with thrombotic thrombocyopenic purpura (TTP)?

Although much has been learned about the pathophysiologic process of thrombotic thrombocytopenic purpura (TTP), both diagnostically and therapeutically, since its initial description by Moschowitz in 1924, its etiology and treatments remain, in many instances, problematic. Thrombotic thrombocytopenic purpura remains a rare entity whose etiology is usually unknown, but several drugs and infections have now been implicated in its development. Although treatment by plasma exchange has gained worldwide acceptance, the optimal exchange media is not known, nor the volume and duration of exchange therapy, not appropriate salvage therapies. Without the benefit of randomized controlled trials, its treatment, to a large extent, remains not evidence-based but "eminence-based", making the same mistakes with increasing confidence over decades.